Hedgehog-Fox Heterotaxy Syndrome Links CCD, IM, CC

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Hedgehog-Fox Heterotaxy Syndrome Links Congenital Heart Disease, Intestinal Malrotation
and Choledochal Cysts
Abstract
We present in this article evidence suggesting that heterotaxy syndrome disorders of left-right
axis determination during early embryonic development link some forms of congenital cardiac
disease (CCD) to both intestinal malrotation (IM) and choledochal cysts (CC). Recent studies
indicate that 27.1% of patients with (IM) also had (CCD) and 30.7% of patients with CC likewise
had CCD. These data support a strong association among cardiac anomalies, intestinal
malrotation, and choledochal cysts that most often manifests in infancy, suggesting a potential
genetic link among these three maladies. Lastly, heterotaxy syndrome, which is randomization
of cardiac, pulmonary and gastrointestinal situs, is frequently associated with congenital heart
disease, specifically atrioventricular septal defects, and transposed great arteries. A likely
candidate are the Sonic Hedgehog (SHh) signaling regulated developmental processes. The
Forkhead box transcription factors FOXF1A and FOXF2 have been identified as SHh targets and
haploinsufficiency mutations in the forkhead box transcription factors FOXF1 and FOXF2. A
subset of these cases have been identified to be caused by mutations in ZIC3, CFC1, ACVR2B,
and LEFTYA, genes that regulate left-right asymmetry in the developing embryo.
Morphological errors related to Hh signaling and FOXF1 and FOXF2 transcription are common
to CCD, IM, and CC. The role of the forkhead transcription factors in CCD is well established.
Examples include compound haploinsufficiency in the FOXF1a and FOXF2 regulatory network
causing atrioventricular septal defects. Also FOXF1 was identified as a causative gene for
Alveolar capillary dysplasia with misalignment of pulmonary veins (ACDMPV). Recently, it was
shown that intestinal malrotation results from inactivating heterozygous mutations in FOXF1.
Studies also supports a strong genetic basis for CDD and show that CDD is not only genetically
heterogeneous but also non-monogenic, requiring mutations in more than one gene for the
disease to develop. Choledochal cysts and biliary atresia are sometimes found simultaneously,
a disorder termed biliary cystic malformations. In our study, the association between
choledochal cysts or biliary atresia and congenital cardiac anomalies was most robust in
infancy, supporting a unifying embryologic or genetic cause. Alagille syndrome, an autosomal
dominant, congenital syndromic paucity of the interlobular bile ducts which leads to cholestasis
in the first year of life, also includes branch pulmonary artery hypoplasia or stenosis as one if its
main features. Coupled with data from a recent study, which suggests a congenital link
between choledochal cysts, biliary atresia, and cardiac anomalies called Biliary Atresia
Structural Malformation (BASM) syndrome, these findings are suggestive of a potential
embryonic link between these disorders which could occur at the inductive signaling interface
between the hepatic diverticulum and cardiac mesoderm during embryogenesis. In addition,
patients with biliary atresia and situs abnormalities have been found to harbor mutations in the
left-right axis patterning genes CFC1 and ZIC3.
We suggest the syndrome described here be called Hedgehog-Fox Heterotaxy Syndrome. Since
the phenotypes of these defects can be highly variable, in particular the patients with a mild
phenotype, the diagnosis can be missed at birth and can be made very belatedly. We
recommend that all patients with heterotaxy, especially those with isomerism of the right atrial
appendages or asplenia syndrome, should have a study to evaluate for intestinal malrotation,
given the associated potential morbidity. When choledochal cysts are diagnosed it is important
to consider they may be syndromic and cardiac defects as well as intestinal malrotation should
be investigate prior to performing cyst surgery.
Here we also explore the possibility that defects in cholesterol biosynthesis is the early stages
of embryonic development are tied to the defects in Hh transcription. There is a direct
relationship between maternal and fetal plasma cholesterol concentrations early in gestation,
and low maternal cholesterol (Hypocholesterolemia) during early embryonic development
could play a role in compromise Hh signaling, thus leading to Hedgehog-Fox Heterotaxy
Syndrome.
The importance of maternal cholesterol as an exogenous cholesterol source for the growing
embryo was first reported in studies of Smith-Lemli-Opitz syndrome. Although most of the
fetus's cholesterol is synthesized by the fetus itself, there is now growing evidence that during
the first weeks of life, when most organs develop, the fetus largely depends on maternal
cholesterol as its cholesterol source. The maternal-fetal cholesterol transport mechanism, by
transporters in both the yolk sac and placenta, is becoming better understood. As the
prevalence of maternal diseases, such as diabetes, obesity, and the metabolic syndrome that
adversely affect maternal cholesterol levels, is now rapidly reaching epidemic proportions, we
urgently need to determine the impact of these maternal conditions on the developing human
fetus.
One can postulate that pathogenicity results from a lack of cholesterol or related sterols,
accumulation of toxic sterol intermediates above each enzyme block, abnormal feedback
regulation of earlier steps in the pathway, including synthesis of key isoprenoid compounds,
and/or abnormal signaling by hedgehog proteins that normally contain bound cholesterol. It is
attractive to postulate important roles for hedgehog proteins—sonic hedgehog, Indian
hedgehog and desert hedgehog—in disease pathogenesis. One or more of the hedgehog
proteins are involved in many of the developmental processes that are perturbed in these
disorders, including establishing a proper midline and left–right axis, proper differentiation of
the lung and gut, chondrocyte differentiation and hair follicle development. While 7DHC can
substitute for cholesterol in the auto-processing of and binding to hedgehog proteins, at
least in vitro (120), it is unlikely that earlier intermediates, such as methylsterols, can perform
these functions.
In the past 10 years, proven or suspected human disorders involving each step of post-squalene
cholesterol biosynthesis have been described. The frequency of the most common of these
disorders, Smith–Lemli–Opitz syndrome (SLOS), and the range of malformations associated with
them make cholesterol biosynthesis disorders the prototypic metabolic malformation
syndromes. Although their pathogenesis is not well understood, they underline the important
role(s) of cholesterol and its metabolic precursors in mammalian development.
Most of these data support the hypothesis that, during early fetal life, maternal cholesterol
could be the most important source of cholesterol for the growing embryo. Shortage of
maternal cholesterol may therefore result in congenital anomalies in the offspring. Obviously,
the numbers of human cases of the genetic defects described are low and are not conclusive. In
the near future next generation sequencing may help us to reveal more pathogenic mutations
in humans and their genotype-phenotype correlation.
Besides oxidative stress, we also believe that changes in plasma lipid composition during
maternal obesity and diabetes also contribute to the increased risk for fetal malformations,
because cholesterol, especially HDL cholesterol, might be of crucial importance during early
fetal life. A reduction in maternal-fetal HDL cholesterol transport in humans in the first
trimester of pregnancy could therefore act as a negative modifier of fetal development,
especially in those children that already have a genetic susceptibility for congenital anomalies
due to mutations in cholesterol related genes.
Because early intervention aimed at normalizing cholesterol levels could possibly prevent
congenital anomalies in offspring of those who already have a genetic susceptibility, further
study of the role played by maternal cholesterol in early fetal development is urgently required.
As an example, in utero treatment with an LXR agonist, as we previously suggested, has been
successfully applied in an animal model of SLOS and resulted in milder phenotypes.
Postnatal cholesterol supplementation is provided; however, it cannot correct developmental
malformations due to in utero cholesterol deficit. Increased transport of cholesterol from
maternal to fetal circulation might attenuate congenital malformations. The cholesterol
transporters Abca1, Abcg1, and Sr-b1 are present in placenta; however, their potential role in
placental transport remains undetermined. In mice, expression analyses showed that Abca1
and Abcg1 transcripts increased 2-3-fold between embryonic days 13.5 and 18.5 in placental
tissue; whereas, Sr-b1 expression decreased. To examine the functional role of Abca1, Abcg1
and Sr-b1 we measured the maternal-fetal transfer of (14)C-cholesterol in corresponding
mutant embryos. Disruption of either Abca1 or Sr-b1 decreased cholesterol transfer by
approximately 30%. In contrast, disruption of the Abcg1 had no effect. Treatment of pregnant
C57Bl/6 female mice with TO901317, an LXR-agonist, increased both Abca1 expression and
maternal-fetal cholesterol transfer to the fetus. In an SLOS mouse model (Dhcr7(-/-)), which is
incapable of de novo synthesis of cholesterol, in utero treatment with TO901317 resulted in
increased cholesterol content in Dhcr7(-/-) embryos. Our data support the hypothesis that
Abca1, and possibly Sr-b1, contributes to transport maternal cholesterol to the developing
fetus. Furthermore, we show, as a proof of principle, that modulating maternal-fetal cholesterol
transport has potential for in utero therapy.
In addition a recent study suggested that vitamin E can inhibit the peroxidation of 7-DHC in
human fibroblasts and in newborn SLOS mice exposed to vitamin E through the diet of their
pregnant mothers, leading to a reduction in the DHCEO concentrations in the brain and liver of
these mice (Korade et al., 2014). This suggests that antioxidants, particularly vitamin E, may
have a role in the treatment of SLOS and, by extension, cardiac anomalies, intestinal
malrotation, and choledochal cysts associated with Hedgehog-Fox Heterotaxy Syndrome.
Questions:
1.
2.
3.
4.
Are the types of cardiac defects similar for all these patients?
CCD - Malformation due to SHH defects cause of cardiac malformation?
Intestinal Malrotation - Malformation due to SHH defects cause of malrotation?
Choledochal Cysts (Cystic BA?) - Malformation due to SHH defects cause situs
ambiguous for incorrect formation, positioning of bile duct?
5. Cholesterol biosynthesis is required for proper function of HH transcription. Mother’s
cholesterol level? Hypocholesterolemia?
Studies that address above questions:
1. Are the types of cardiac defects similar for all these patients?
2. CCD - Malformation due to SHH defects cause of cardiac malformation?
Which cardiac defects were discovered in these patients? The heart defects that are associated
with Heterotaxy include: Alveolar Capillary Dysplasia with Misalignment of Pulmonary Veins,
dextocaria, atrioventricular septal defects (AVSDs), transposition of the great vessels, common
AV valve, total/partial anomalous pulmonary venous return (TAPVR/PAPVR), multiple sinus
nodes, endocardial cushion defect, coarctation of the aorta, pulmonary atresia, branch
pulmonary artery hypoplasia or stenosis, double outlet right ventricle, patent ductus arteriosus
(PDA), ventricular septal defect (VSD), and branch pulmonary artery hypoplasia or stenosis.
Genetics of Congenital Heart Defects
Alveolar Capillary Dysplasia with Misalignment of Pulmonary Veins
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4009999/
CONCLUSION
In aggregate, FOXF1 is a transcription factor involved in hedgehog-regulated developmental
processes. Disruptions or amplifications in FOXF1 cause severe human disorders. The
identification of FOXF1 as a causative gene for ACDMPV has enabled prenatal genetic testing
and estimation of recurrence risks for parents of infants with ACDMPV. Consistent with
previous empirical observations for mutations in some genes located on the X chromosome
[108, 109], recent mathematical analyses of the sexual dimorphisms of gametogenesis suggest
that new mutations that occur on the maternal allele are more likely to be recurrently
transmitted to offspring [110, 111]. Thus, given that all hitherto analyzed deletions of
the FOXF1 locus arose de novo on the maternal chromosome 16q24.1, the recurrence risk for
ACDMPV may potentially be elevated in comparison to that observed for other sporadic
diseases. Discerning the effects of FOXF1 over- and/or ectopic expression is of primary
importance for any future work toward FOXF1-based gene therapies for ACDMPV and other
disorders caused by FOXF1 abnormal dosage. Future studies will involve designing novel
therapeutic strategies to treat ACDMPV by manipulation of the epigenetic lncRNA regulation
of FOXF1, using antisense oligos (ASOs). Generation of novel mouse models with conditional
inactivation or overexpression of Foxf1 in different cell types will help elucidate molecular
mechanisms regulated by Foxf1 during embryonic development and various human diseases.
Due to phenotype similarities in haploinsufficient mice and humans, Foxf1+/- mouse line can be
used as a preclinical model to develop novel therapeutic strategies to treat ACDMPV.
Foxf Genes Integrate Tbx5 and Hedgehog Pathways in the Second Heart Field for Cardiac
Septation
http://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1004604
Abstract
The Second Heart Field (SHF) has been implicated in several forms of congenital heart disease
(CHD), including atrioventricular septal defects (AVSDs). Identifying the SHF gene regulatory
networks required for atrioventricular septation is therefore an essential goal for understanding
the molecular basis of AVSDs. We defined a SHF Hedgehog-dependent gene regulatory network
using whole genome transcriptional profiling and GLI-chromatin interaction studies. The
Forkhead box transcription factors Foxf1a and Foxf2 were identified as SHF Hedgehog targets.
Compound haploinsufficiency for Foxf1a and Foxf2 caused atrioventricular septal defects,
demonstrating the biological relevance of this regulatory network. We identified a Foxf1a cisregulatory element that bound the Hedgehog transcriptional regulators GLI1 and GLI3 and the
T-box transcription factor TBX5 in vivo. GLI1 and TBX5 synergistically activated transcription
from this cis-regulatory element in vitro. This enhancer drove reproducible expression in vivo in
the posterior SHF, the only region where Gli1 and Tbx5 expression overlaps. Our findings
implicate Foxf genes in atrioventricular septation, describe the molecular underpinnings of the
genetic interaction between Hedgehog signaling and Tbx5, and establish a molecular model for
the selection of the SHF gene regulatory network for cardiac septation.
Mutations in ZIC3 and ACVR2B are a common cause of heterotaxy and associated
cardiovascular anomalies
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3678527/
Heterotaxy syndrome is caused by left-right asymmetry disturbances and is associated with
abnormal lateralization of the abdominal and thoracic organs. The heart is frequently involved
and the severity of the abnormality usually determines the outcome.
Human Heterotaxy Syndrome
– From Molecular Genetics to Clinical Features, Management, and Prognosis –
https://www.jstage.jst.go.jp/article/circj/76/9/76_CJ-12-0957/_article
Consequently, Nodal in the left LPM upregulates a transcription factor, Pitx2. Pitx2 is a major
laterality gene and plays a direct and pivotal role in asymmetric organogenesis of the heart and
other visceral organs.57
Among the various kinds of CHD, heterotaxy syndrome is one of the most serious. This
syndrome occurs in approximately 1 to 5,000–7,000 of live births with CHD.6,7 Heterotaxy
syndrome is primarily induced by disorders of left-right axis determination during early
embryonic development. Recently, the molecular mechanisms of the left-right axis
determination have been extensively investigated in animal models including genetic
engineering of mice.8–11 Brie y, an initial break in symmetry occurs at the primitive node as a
leftward “nodal ow”, which is created by unidirectional rotation of nodal cell cilia. This ow
provokes asymmetry signals that are transmitted toward the left lateral plate mesoderm (LPM),
where down- stream left-side specific growth and transcription factors, Nodal, Lefty2, and
Pitx2c, are activated. As a result, Pitx2c and other undetermined factors regulate genetic
programs in the left side of the body and create asymmetric organ morphogenesis. Human
genetics have also revealed several genes that are responsible for left-right laterality and
heterotaxy syndrome, including ZIC3, NODAL, LEFTY2.
3. IM - Malformation due to SHH, FoxF1 defects cause of malrotation?
Congenital cardiovascular defects in children with intestinal malrotation
https://link.springer.com/article/10.1007/s00383-007-2086-4
Intestinal malrotation (IM) is refers to all abnormalities of intestinal position and attachment
and includes the concept of atypical malrotation or malrotation variant [1].
Discussion
This study addresses the co-existence of malrotation with different types of congenital
cardiovascular defects. We found 27.1% of all the patients registered in the last 25 years for IM
to have a major or minor CCVD.
Demographics
During a period of 25 years, 284 patients were diagnosed in our centre with IM. Ninety-three of
the 284 patients were identified with CCVD as well. Fifteen patients had persistent pulmonary
hypertension (PPHT), all but one with congenital diaphragmatic hernia. One patient had a
solitary pre-duodenal portal vein. The records of these 16 patients without structural CCVD
were excluded, leaving 77 patients with both IM and CCVD (27.1% of the total IM population in
the last 25 years) for further analysis. The gestational age range was 26–42 weeks with a
median of 39 weeks. Median birth weight was 2.86 kg (range 0.72–4.53). A female
predominance was seen with 47 girls (61%) and 30 boys (39%). Median follow-up period after
IM diagnosis was 2.8 years (range 0–24 years).
Review of genetic factors in intestinal malrotation
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2908440/
Intestinal malrotation is well covered in the surgical literature from the point of view of
operative management, but few reviews to date have attempted to provide a comprehensive
examination of the topic from the point of view of aetiology, in particular genetic aetiology.
Following a brief overview of molecular embryology of midgut rotation, we present in this
article instances of and case reports and case series of intestinal malrotation in which a genetic
aetiology is likely. Autosomal dominant, autosomal recessive, X-linked and chromosomal forms
of the disorder are represented. Most occur in syndromic form, that is to say, in association
with other malformations. In many instances, recognition of a specific syndrome is possible,
one of several examples discussed being the recently described association of intestinal
malrotation with alveolar capillary dysplasia, due to mutations in the forkhead box transcription
factor FOXF1. New advances in sequencing technology mean that the identification of the
genes mutated in these disorders is more accessible than ever, and paediatric surgeons are
encouraged to refer to their colleagues in clinical genetics where a genetic aetiology seems
likely.
The key event leading to formation of the dorsal mesentery is the division of the lateral plate
mesoderm into its somatic and splanchnic components, creating the coelom or body cavity, at
around weeks 3–4 of gestation (Fig. 1a–g). The forkhead box transcription factor Foxf1plays a
key role in this process. Division of the lateral plate mesoderm is disrupted in mice with
targeted knock-out of Foxf1 [6], with somatic and splanchnic layers either remaining fused
together, or with residual points of attachment leading to incomplete separation.
Recently, it was shown that intestinal malrotation results from inactivating heterozygous
mutations in the forkhead transcription factor FOXF1 [9]
Hedgehog signals regulate multiple aspects of gastrointestinal development.
Ramalho-Santos M1, Melton DA, McMahon AP.
Author information
https://www.ncbi.nlm.nih.gov/pubmed/10821773
Abstract
The gastrointestinal tract develops from the embryonic gut, which is composed of an
endodermally derived epithelium surrounded by cells of mesodermal origin. Cell signaling
between these two tissue layers appears to play a critical role in coordinating patterning and
organogenesis of the gut and its derivatives. We have assessed the function of Sonic hedgehog
and Indian hedgehog genes, which encode members of the Hedgehog family of cell signals.
Both are expressed in gut endoderm, whereas target genes are expressed in discrete layers in
the mesenchyme. It was unclear whether functional redundancy between the two genes would
preclude a genetic analysis of the roles of Hedgehog signaling in the mouse gut. We show here
that the mouse gut has both common and separate requirements for Sonic hedgehog and
Indian hedgehog. Both Sonic hedgehog and Indian hedgehog mutant mice show reduced
smooth muscle, gut malrotation and annular pancreas. Sonic hedgehog mutants display
intestinal transformation of the stomach, duodenal stenosis (obstruction), abnormal
innervation of the gut and imperforate anus. Indian hedgehog mutants show reduced epithelial
stem cell proliferation and differentiation, together with features typical of Hirschsprung's
disease (aganglionic colon). These results show that Hedgehog signals are essential for
organogenesis of the mammalian gastrointestinal tract and suggest that mutations in members
of this signaling pathway may be involved in human gastrointestinal malformations.
Hedgehog signaling in development and homeostasis of the gastrointestinal tract.
van den Brink GR1.
Author information
https://www.ncbi.nlm.nih.gov/pubmed/17928586
Abstract
The Hedgehog family of secreted morphogenetic proteins acts through a complex evolutionary
conserved signaling pathway to regulate patterning events during development and in the adult
organism. In this review I discuss the role of Hedgehog signaling in the development, postnatal
maintenance, and carcinogenesis of the gastrointestinal tract. Three mammalian hedgehog
genes, sonic hedgehog (Shh), indian hedgehog (Ihh), and desert hedgehog (Dhh) have been
identified. Shh and Ihh are important endodermal signals in the endodermal-mesodermal crosstalk that patterns the developing gut tube along different axes. Mutations in Shh, Ihh, and
downstream signaling molecules lead to a variety of gross malformations of the murine
gastrointestinal tract including esophageal atresia, tracheoesophageal fistula, annular pancreas,
midgut malrotation, and duodenal and anal atresia. These congenital malformations are also
found in varying constellations in humans, suggesting a possible role for defective Hedgehog
signaling in these patients. In the adult, Hedgehog signaling regulates homeostasis in several
endoderm-derived epithelia, for example, the stomach, intestine, and pancreas. Finally, growth
of carcinomas of the proximal gastrointestinal tract such as esophageal, gastric, biliary duct,
and pancreatic cancers may depend on Hedgehog signaling offering a potential avenue for
novel therapy for these aggressive cancers.
Intestinal malrotation in monozygotic twins; the asymptomatic twin should be screened: A
case report and review
http://www.sciencedirect.com/science/article/pii/S2213576614000104b
Martin and Shaw-Smith recently published a comprehensive review regarding the genetic
etiology of intestinal malrotation. In their review of the literature, they identified 18 separate
syndromic conditions with intestinal malrotation as one of the defining anomalies [14].
Moreover, researchers have begun to identify gene mutations associated with the failure of
normal midgut rotation. Heterozygous mutations in the forkhead transcription
factor FOXF1 lead to the development of intestinal malrotation in addition to lethal lung
abnormalities [15]. With a possible genetic etiology for intestinal malrotation, it would be
expected that monozygotic twins would have a higher concordance rate than would be
predicted by random association.
4. Choledochal Cysts (Cystic BA?) - Malformation due to SHH defects cause situs
ambiguous for incorrect formation, positioning of bile duct?
Associations Between Pediatric Choledochal Cysts, Biliary Atresia, and Congenital Cardiac
Anomalies
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3417077/pdf/nihms-370335.pdf
This constellation of findings has been termed BASM for Biliary Atresia Structural Malformation
syndrome. Although the genetic basis of this syndrome has not yet been clarified, patients with
biliary atresia and situs abnormalities have been found to harbor mutations in the left-right axis
patterning genes CFC1 and ZIC3.(8)
Choledochal cysts, interestingly, have also been associated with malrotation in clinical case
reports, but otherwise have not been linked to anomalies typical of BASM (with the exception
of the current report and cardiac anomalies).(12, 13) Furthermore, choledochal cysts and biliary
atresia are sometimes found simultaneously, a disorder termed biliary
cystic malformations.(14) In our study, the association between choledochal cysts or biliary
atresia and congenital cardiac anomalies was most robust in infancy, supporting a unifying
embryologic or genetic cause. Alagile syndrome, an autosomal dominant, congenital syndromic
paucity of the interlobular bile ducts which leads to cholestasis in the first year of life, also
includes branch pulmonary artery hypoplasia or stenosis as one if its main features.(15, 16)
Coupled with data from the current study, which suggests a congenital link between
choledochal cysts, biliary atresia, and cardiac anomalies, these findings are suggestive of a
potential embryonic link between these disorders, which could occur at the inductive signaling
interface between the hepatic diverticulum and cardiac mesoderm during embryogenesis.
Of 1,646 estimated discharges for patients with choledochal cysts, 506 (30.7%) were for
patients who also had congenital cardiac anomalies, compared to 2.6% in the general
hospitalized population.
Of 7.4 million hospital discharge records predicted by the 2009 HCUP KID database, 1646
hospitalizations were identified for patients with the diagnosis of choledochal cyst. Among
these choledochal cyst hospitalizations, 506 (30.7%) were also associated with the diagnosis of
a congenital cardiac anomaly, compared to 2.6% in the general hospitalized population.
These data support a strong association between choledochal cysts and cardiac anomalies that
most often manifests in infancy, suggesting a potential congenital link between these two
maladies. This association appears to be at least as strong as the link between biliary atresia
and cardiac anomalies, however, from this study, both choledochal cysts and biliary atresia
have a greater association with congenital cardiac anomalies than does the general hospitalized
population.
Genetic study of congenital bile-duct dilatation identifies de novo and inherited variants in
functionally related genes
https://bmcmedgenomics.biomedcentral.com/articles/10.1186/s12920-016-0236-z
Abstract
Background
Congenital dilatation of the bile-duct (CDD) is a rare, mostly sporadic, disorder that results in
bile retention with severe associated complications. CDD affects mainly Asians. To our
knowledge, no genetic study has ever been conducted.
Methods
We aim to identify genetic risk factors by a “trio-based” exome-sequencing approach, whereby
31 CDD probands and their unaffected parents were exome-sequenced. Seven-hundred
controls from the local population were used to detect gene-sets significantly enriched with
rare variants in CDD patients.
Results
Twenty-one predicted damaging de novo variants (DNVs; 4 protein truncating and 17 missense)
were identified in several evolutionarily constrained genes (p < 0.01). Six genes carrying DNVs
were associated with human developmental disorders involving epithelial, connective or bone
morphologies (PXDN, RTEL1, ANKRD11, MAP2K1, CYLD, ACAN) and four linked with cholangioand hepatocellular carcinomas (PIK3CA, TLN1 CYLD, MAP2K1). Importantly, CDD patients have
an excess of DNVs in cancer-related genes (p < 0.025). Thirteen genes were recurrently mutated
at different sites, forming compound heterozygotes or functionally related complexes within
patients.
Conclusions
Our data supports a strong genetic basis for CDD and show that CDD is not only genetically
heterogeneous but also non-monogenic, requiring mutations in more than one genes for the
disease to develop. The data is consistent with the rarity and sporadic presentation of CDD.
Thus, it would appear that carriers of TRIM28 or ZNF382 rare damaging variants might have a
higher risk of developing CDD. Replication of this finding in independent Chinese patients is
needed. Similar studies should be conducted in non-Asian CDD patients to assess whether
the TRIM28 association is population specific.
Hedgehog activity, epithelial-mesenchymal transitions, and biliary dysmorphogenesis in
biliary atresia.
Omenetti A1, Bass LM, Anders RA, Clemente MG, Francis H, Guy CD, McCall S, Choi SS, Alpini
G, Schwarz KB, Diehl AM, Whitington PF.
Author information
https://www.ncbi.nlm.nih.gov/pubmed/21480329
Abstract
Biliary atresia (BA) is notable for marked ductular reaction and rapid development of fibrosis.
Activation of the Hedgehog (Hh) pathway promotes the expansion of populations of immature
epithelial cells that coexpress mesenchymal markers and may be profibrogenic. We examined
the hypothesis that in BA excessive Hh activation impedes ductular morphogenesis and
enhances fibrogenesis by promoting accumulation of immature ductular cells with a
mesenchymal phenotype. Livers and remnant extrahepatic ducts from BA patients were
evaluated by quantitative reverse-transcription polymerase chain reaction (QRT-PCR) and
immunostaining for Hh ligands, target genes, and markers of mesenchymal cells or ductular
progenitors. Findings were compared to children with genetic cholestatic disease, age-matched
deceased donor controls, and adult controls. Ductular cells isolated from adult rats with and
without bile duct ligation were incubated with Hh ligand-enriched medium ± Hh-neutralizing
antibody to determine direct effects of Hh ligands on epithelial to mesenchymal transition
(EMT) marker expression. Livers from pediatric controls showed greater innate Hh activation
than adult controls. In children with BA, both intra- and extrahepatic ductular cells
demonstrated striking up-regulation of Hh ligand production and increased expression of Hh
target genes. Excessive accumulation of Hh-producing cells and Hh-responsive cells also
occurred in other infantile cholestatic diseases. Further analysis of the BA samples
demonstrated that immature ductular cells with a mesenchymal phenotype were Hhresponsive. Treating immature ductular cells with Hh ligand-enriched medium induced
mesenchymal genes; neutralizing Hh ligands inhibited this.
CONCLUSION:
BA is characterized by excessive Hh pathway activity, which stimulates biliary EMT and may
contribute to biliary dysmorphogenesis. Other cholestatic diseases show similar activation,
suggesting that this is a common response to cholestatic injury in infancy.
5. Cholesterol biosynthesis is required for proper function of HH transcription. Mother’s
cholesterol level?
Possible causes of low cholesterol and lipid profile anomalies:
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statins
hyperthyroidism, or an overactive thyroid gland
adrenal insufficiency
liver disease
malabsorption (inadequate absorption of nutrients from the intestines), such as in celiac
disease
malnutrition
abetalipoproteinemia - a rare genetic disease that causes cholesterol readings below 50 mg/dl.
It is found mostly in Jewishpopulations.[2]
hypobetalipoproteinemia - a genetic disease that causes cholesterol readings below
50 mg/dl[2]
manganese deficiency
Smith-Lemli-Opitz syndrome
Marfan syndrome
leukemias and other hematological diseases[3]
Fetal alcohol syndrome
Diabetes mellitus
Obesity
First trimester 3 to 13 weeks is critical period, left right rotation around 10 weeks.
(6 - 10 weeks) The midgut forms the primary intestinal loop, from which originates the distal
duodenum to the entrance of the bile duct. The loop continues to the junction of the proximal
two-thirds of the transverse colon with the distal third. At its apex, the primary loop remains
temporarily in open connection with the yolk sac through the vitelline duct. During the sixth
week, the loop grows so rapidly that it protrudes into the umbilical cord
(physiological herniation). In the 10th week, it returns into the abdominal cavity. While these
processes are occurring, the midgut loop rotates 270° counterclockwise. Common
abnormalities at this stage of development include remnants of the vitelline duct, failure of the
midgut to return to the abdominal cavity, malrotation, stenosis, and duplication of parts.[3]
(3 - 7 weeks) The heart tube continues stretching and by day 23, in a process
called morphogenesis, cardiac looping begins. The cephalic portion curves in a frontal clockwise
direction. The atrial portion starts moving in a cephalic ally and then moves to the left from its
original position. This curved shape approaches the heart and finishes its growth on day 28 (7
weeks). The conduit forms the atrial and ventricular junctions which connect the common
atrium and the common ventricle in the early embryo. The arterial bulb forms the trabecular
portion of the right ventricle. A cone will form the infundibula blood of both ventricles. The
arterial trunk and the roots will form the proximal portion of the aorta and the pulmonary
artery. The junction between the ventricle and the arterial bulb will be called the primary intraventricular hole. The tube is divided into cardiac regions along its craniocaudal axis: the
primitive ventricle, called primitive left ventricle, and the trabecular proximal arterial bulb,
called the primitive right ventricle.[9]
Septum formation of the atrioventricular canalEdit
At the end of the fourth week, two atrioventricular endocardial cushions appear. Initially the
atrioventricular canal gives access to the primitive left ventricle, and is separated from arterial
bulb by the edge of the ventricular bulb. In the fifth week, the posterior end terminates in the
center part of the upper endocardial cushion. Because of this, blood can access both the left
primitive ventricle and the right primitive ventricle. As the anterior and posterior pads project
inwardly, they merge to form a right and left atrioventricular orifice.
Cellular Cholesterol Directly Activates Smoothened in Hedgehog Signaling
http://www.sciencedirect.com/science/article/pii/S009286741631011X?_rdoc=1&_fmt=high&_
origin=gateway&_docanchor=&md5=b8429449ccfc9c30159a5f9aeaa92ffb
panelPengxiangHuang1DanielNedelcu1MiyakoWatanabe1CindyJao1YoungchangKim2JingLiu1Adri
anSalic13


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Sterol-induced conformational change in Smoothened triggers Hedgehog signaling
Cholesterol is the endogenous activator of Smoothened
Stimulation of Hedgehog pathway activates Smoothened through cholesterol
Summary
In vertebrates, sterols are necessary for Hedgehog signaling, a pathway critical
in embryogenesis and cancer. Sterols activate the membrane protein Smoothened by binding
its extracellular, cysteine-rich domain (CRD). Major unanswered questions concern the nature
of the endogenous, activating sterol and the mechanism by which it regulates Smoothened. We
report crystal structures of CRD complexed with sterols and alone, revealing that sterols induce
a dramatic conformational change of the binding site, which is sufficient for Smoothened
activation and is unique among CRD-containing receptors. We demonstrate that Hedgehog
signaling requires sterol binding to Smoothened and define key residues for sterol recognition
and activity. We also show that cholesterol itself binds and activates Smoothened.
Furthermore, the effect of oxysterols is abolished in Smoothened mutants that retain activation
by cholesterol and Hedgehog. We propose that the endogenous Smoothened activator is
cholesterol, not oxysterols, and that vertebrate Hedgehog signaling controls Smoothened by
regulating its access to cholesterol.
The Hedgehog (Hh) cell-cell signaling pathway controls key events in the development of most
animals. Insufficient Hh activity during embryogenesis causes birth defects such
as holoprosencephaly and brachydactyly, while hyperactive Hh signaling after birth is
implicated in many cancers (Ingham and McMahon, 2001; Lum and Beachy, 2004), including
basal cell carcinoma and medulloblastoma.
The sterol-sensing domain of Patched protein seems to control Smoothened activity through
Patched vesicular trafficking.
https://www.ncbi.nlm.nih.gov/pubmed/11369205
Martín V1, Carrillo G, Torroja C, Guerrero I.
Author information
Abstract
The Hedgehog (Hh) family of signaling molecules function as organizers in many morphogenetic
processes. Hh signaling requires cholesterol in both signal-generating and -receiving cells, and it
requires the tumor suppressor Patched (Ptc) in receiving cells in which it plays a negative role.
Ptc both blocks the Hh pathway and limits the spread of Hh. Sequence analysis suggests that it
has 12 transmembrane segments, 5 of which are homologous to a conserved region that has
been identified in several proteins involved in cholesterol homeostasis and has been designated
the sterol-sensing domain (SSD). In the present study, we show that a Ptc mutant with a single
amino acid substitution in the SSD induces target gene activation in a ligand-independent
manner. This mutant Ptc(SSD) protein shows dominant-negative activity in blocking Hh
signaling by preventing the downregulation of Smoothened (Smo), a positive effector of the Hh
pathway. Despite its dominant-negative activity, the mutant Ptc protein functioned like the
wild-type protein in sequestering and internalizing Hh. In addition, we show that Ptc(SSD)
preferentially accumulates in endosomes of the endocytic compartment. All these results
suggest a role of the SSD of Ptc in mediating the vesicular trafficking of Ptc to regulate Smo
activity.
The Role of Maternal-Fetal Cholesterol Transport in Early Fetal Life: Current Insights
https://academic.oup.com/biolreprod/article/88/1/24,%201-9/2514198
Abstract
The importance of maternal cholesterol as an exogenous cholesterol source for the growing
embryo was first reported in studies of Smith-Lemli-Opitz syndrome. Although most of the
fetus's cholesterol is synthesized by the fetus itself, there is now growing evidence that during
the first weeks of life, when most organs develop, the fetus largely depends on maternal
cholesterol as its cholesterol source. The maternal-fetal cholesterol transport mechanism, by
transporters in both the yolk sac and placenta, is becoming better understood. This minireview
summarizes current insights on maternal-fetal cholesterol transport based on in vitro and in
vivo studies. As the prevalence of maternal diseases, such as diabetes, obesity, and the
metabolic syndrome that adversely affect maternal cholesterol levels, is now rapidly reaching
epidemic proportions, we urgently need to determine the impact of these maternal conditions
on the developing human fetus.
Cholesterol is present in every cell of the human body. It helps maintaining the integrity of cell
membranes and plays an important role in cell signaling. Cholesterol is a precursor for all
steroid hormones and bile acids and also plays a crucial role in early fetal development: it
moderates the sonic hedgehog (SHH) proteins and important nuclear receptors such as
fetoprotein transcription factor and is therefore involved in the most fundamental signaling
pathways during embryonic development. SHH proteins play a role in migration and survival of
neural crest cells, a population of cells that highly contribute to the development of the brain,
limbs, lungs, heart and urogenital system [1, 2]. Fetoprotein transcription factor, also known as
NR5A2, can bind GATA elements, essential for the development of many organ systems, and is
also highly expressed in the neural crest cells [3, 4].
It is assumed that most of the fetus's cholesterol is synthesized by the fetus itself, mainly by the
fetal liver [5] although evidence is growing that during the first weeks of life, when most organs
are formed, the fetus depends largely on maternal cholesterol. Recent data show that the byproducts of endogenous fetal cholesterol synthesis in amniotic fluid, dihydrolanosterol,
lanosterol, and lathosterol are very low until the 19th week of pregnancy, after which their
levels increase strongly [6]. Together with relatively constant levels of total cholesterol in the
amniotic fluid and the presence of maternally derived cholesterol (measured as β-sitosterol)
during the same period, these data suggest that maternal cholesterol plays a crucial role in
providing the cholesterol for fetal development.
If the fetus is indeed dependent on a maternal supply of cholesterol during early pregnancy,
then diseases affecting maternal cholesterol levels may have an adverse effect on the
development and growth of the fetus. The aim of this review is to summarize current insights
on maternal-fetal cholesterol transport based on in vitro and in vivo studies, and to emphasize
the importance of maternal cholesterol in early human pregnancy. As the prevalence of
diseases that influence maternal cholesterol levels, like obesity and dyslipidemia (as part of the
metabolic syndrome) is reaching epidemic proportions, the impact of these maternal conditions
on the growing fetus needs to be determined.
Conclusions and Perspectives
In this minireview, we have attempted to summarize the basic mechanisms of maternal-fetal
cholesterol transport with emphasis on clinical consequences of their failure. Most of these
data support the hypothesis that, during early fetal life, maternal cholesterol could be the most
important source of cholesterol for the growing embryo. Shortage of maternal cholesterol may
therefore result in congenital anomalies in the offspring. Obviously, the numbers of human
cases of the genetic defects described are low and are not conclusive. In the near future next
generation sequencing may help us to reveal more pathogenic mutations in humans and their
genotype-phenotype correlation.
The Western world faces a large and increasing number of individuals with aberrant lipid
profiles related to our unhealthy life style. In Western countries, the prevalence of diseases that
influence cholesterol levels, such as diabetes mellitus (DM) and obesity, are increasing
dramatically among pregnant women. In the United Kingdom, for example, the prevalence of
maternal obesity has doubled over the last 20 years [79]. Both obesity and DM result in changes
in the mother's lipid profile, with plasma LDL cholesterol rising and HDL cholesterol falling [80].
Dyslipidemia in mothers with DM results in similar lipid profiles in the offspring[81]. Children of
women who have either obesity or DM do indeed appear to have an increased risk of
congenital anomalies [82–84].
Oxidative stress is one mechanism proposed to play a role in the cause of congenital anomalies
in the offspring of these women [85, 86]. The increase in oxidative stress in both obesity and
DM [87] has many adverse side effects including increased levels of oxysterols in blood which
are known to be toxic for cells [88–90]. In animals, it has already been shown that the increase
of oxysterols in SLOS contributes to the disease [91]. Furthermore, nuclear receptors in the
trophoblast recognize oxysterols as endogenous ligands [92, 93]. It is therefore possible that
they also cross the placenta to assert their effect on the development of the fetus, although
this has not yet been demonstrated.
Besides oxidative stress, we also believe that changes in plasma lipid composition during
maternal obesity and diabetes also contribute to the increased risk for fetal malformations,
because cholesterol, especially HDL cholesterol, might be of crucial importance during early
fetal life. A reduction in maternal-fetal HDL cholesterol transport in humans in the first
trimester of pregnancy could therefore act as a negative modifier of fetal development,
especially in those children that already have a genetic susceptibility for congenital anomalies
due to mutations in cholesterol related genes.
Because early intervention aimed at normalizing cholesterol levels could possibly prevent
congenital anomalies in offspring of those who already have a genetic susceptibility, further
study of the role played by maternal cholesterol in early fetal development is urgently required.
As an example, in utero treatment with an LXR agonist, as we previously suggested [39], has
been successfully applied in an animal model of SLOS and resulted in milder phenotypes [40].
In the long term, population studies of large numbers of women with dyslipidemia, including
information about their blood cholesterol levels and genetic lipid profiles and thorough
examination of the offspring, will be needed to elucidate whether maternal cholesterol is the
key factor relating DM and obesity to an increased prevalence of congenital malformations
in the offspring.
Deviant early pregnancy maternal triglyceride levels and increased risk of congenital
anomalies: a prospective community-based cohort study
http://onlinelibrary.wiley.com/store/10.1111/14710528.13393/asset/bjo13393.pdf;jsessionid=2D3A59424C5A0D92BC340236530A63AF.f03t02?v=
1&t=jbpfom83&s=387ba582ce9e2139281ffe5230060d2906c5014b.
Objective The maternal lipid profile could be of importance in congenital anomaly
development. This study therefore investigates whether the maternal lipid profile during early
pregnancy is associated with major nonsyndromic congenital anomalies (MNCA).
Conclusions Both low and high maternal TG levels during early pregnancy were associated with
an increased risk of MNCA in offspring. This suggests that an attempt should be made to
normalise TG levels before or during early pregnancy; however, replication of our results is
necessary before clinical practice recommendations can be made.
Design Prospective community-based cohort study. Setting Amsterdam Born Children and their
Development
(ABCD) study.
Population A cohort of 3074 pregnant women recruited in 2003– 2004 and their offspring.
Methods Non-fasting blood samples from pregnant women participating in the ABCD-study
(median 12.9 weeks of gestation) were analysed for triglycerides (TG), cholesterol (TC), free
fatty acids (FFA), apolipoprotein B (ApoB), and apolipoprotein A1 (ApoA) (n = 3074). The
perinatal outcome (MNCA) was obtained from the Youth Health Care Registration and two
questionnaires. Adjustment was made for ethnicity.
Fetal and Neonatal Cholesterol Metabolism
Woollett L, Heubi JE.
https://www.ncbi.nlm.nih.gov/books/NBK395580/
Excerpts.
The absence of cholesterol, they report, affects the secretion of Hh, its multimerisation and
also, intriguingly, Hh long-range signalling activity. For example, distant cell types in the dorsal
ectoderm, which require low Hh levels, are absent in Hh-N-expressing embryos, indicating that
the range of activity of Hh-N is limited.
Conversely, several direct and indirect lines of evidence suggest that cholesterol can be
transported from the maternal to fetal circulation. First, while there is no correlation between
maternal and newborn cholesterol concentrations in term or late preterm infants, there is a
direct relationship between maternal and fetal plasma cholesterol concentrations early in
gestation (58). Thus, cholesterol might be transported early in gestation but not late in
gestation. Interestingly, though there is not a direct correlation between maternal and fetal
cholesterol, some studies have shown a direct correlation between maternal cholesterol levels
and birthweight (59-61). Second, fetuses of mothers with higher plasma cholesterol levels have
increased intimal plaque (58). Third, there are significant amounts of plant sterols in the
newborn circulation, 40-50% of that found in the maternal circulation (30). As these sterols are
only obtained from the diet of the mother, they must cross the placental barrier. Fourth,
fetuses that are lacking the ability to synthesize cholesterol due to a defect in one of the
enzymes of cholesterol biosynthetic pathway, such as those with the Smith-Lemli-Opitz
syndrome, have measurable amounts of cholesterol in their body, even those with null-null
mutations (62, 63). Fifth, indirect evidence that maternal cholesterol is present in the fetal
circulation is that maternal plasma cholesterol levels increase during gestation, possibly to aid
in development of the fetus. In a normal pregnancy, plasma cholesterol levels increase 25-50%
by the third trimester (64-66). The increase could be driven by the increase in cholesterol
synthesis that occurs in late gestation in rodent as well as human mothers (67, 68), possibly as a
consequence of loss of cholesterol to the developing fetus or placenta or in anticipation of the
future need of cholesterol by the fetal unit. Finally, the proteins required for uptake, transport
and secretion, and efflux are present in tissues that separate the fetal and maternal circulations
and in the fetus.
Activation of Hh signaling induces the conversion of cholesterol to progesterone (P4) and
estradiol (E2) through up-regulating the expression of steroidogenic enzymes including P450
cholesterol side chain cleavage enzyme (P450scc), 3β-hydroxysteroid dehydrogenase type 1
(3β-HSD1), and aromatase. In the present study, by using both biochemical approaches and a
xenograft model, we have uncovered the important roles of Hh signaling in conversion of
cholesterol into steroids in human primary CTBs and trophoblast-like cell line. At the molecular
level, Hh induces the transcription of 3β-HSD1 and aromatase through Gli2, and P450scc via
Gli3, thereby increasing the conversion of cholesterol to P4 and E2 (Fig. 5J). Our results
therefore identify Hh as a critical signal in supporting the physiological function of cholesterol
metabolism. We demonstrated that systemic inhibition of Hh signaling reduced P4 and
E2 production and resulted in the attenuation of uterine response to P4 and E2, providing
further in vivoevidence of Hh signaling in the conversion of cholesterol into P4 and E2.
Thus, cholesterol modification is essential for the normal range of signaling. It also appears to
be necessary for appropriate modulation of signaling by the Shh receptor,
Post-translational protein modification plays an essential role in facilitating signal transduction
regulation of gene expression. Protein modification by phosphorylation, acetylation, or
methylation helps control the proper timing and sequence of events during embryogenesis;
therefore, it is not surprising that defective modifications of these proteins can be important
causes in the development of many types of congenital diseases. Accumulating evidence
illustrates the importance of post-translational lipid modifications for regulating protein
function. One example is the cholesterol and palmitoyl modification of Sonic hedgehog (Shh),
which guides this protein's biogenesis, cellular trafficking, and functionality.1
Shh is a highly conserved fetal morphogen that plays a central role in cell proliferation,
differentiation, and embryonic patterning by activating the Hedgehog (Hh) signal
pathway.2, 3 The 45 kDa Shh precursor protein undergoes modification by auto-processing,
followed by covalent linkage of cholesterol to the N-terminal proteolytic product.4 This mature,
cholesterol-modified protein (19 kDa) can be transported to the cell membrane for
secretion.5 Once secreted, the cholesterol-modified Shh ligand can initiate signal transduction
by binding to its receptor, Patched (Ptc). Upon binding, Ptc relieves the inhibition of the signal
transducer, Smoothened (Smo),6 which then activates Gli transcription factors by uncoupling
them from the negative regulator, Suppressor of Fused.7 Gli is subsequently translocated to the
nucleus and regulate expression of target genes including Ptc,8Gli19 itself and Nkx2.2.10
During embryogenesis, Shh is expressed specifically in Hensen's node, the floor plate of the
neural tube, the cardiac mesenchyme, the early gut endoderm, the posterior portion of the
limb buds, and throughout the notochord. As it is a morphogen, Shh also affects the
development of tissues that are distal to where it is produced. Shh is apparently a key inductive
signal for patterning of the ventral neural tube11, 12 the anterior–posterior limb axis,13 and the
ventral somites.14
To summarize this review, cholesterol is essential for normal growth and development. In the
fetus, most cholesterol is derived from de novo synthesis, with a second source of cholesterol
derived from the maternal circulation. The amount that is transported from the mother to the
fetus is currently unknown. Due to its critical role in development, sterol synthesis rates are
regulated less in the fetus and if synthesis is reduced due to genetic defects, abnormal
development often occurs. The neonate also requires cholesterol for continued growth and
development. The neonate obtains cholesterol from de novo synthesis as well as dietary
cholesterol, with breast milk being the largest contributor of exogenous cholesterol. Unlike the
fetus, sterol synthesis in neonates can be regulated.
To determine whether oxidized LDL enhances atherogenesis by promoting monocyte
recruitment into the vascular intima, we investigated whether LDL accumulation and oxidation
precede intimal accumulation of monocytes in human fetal aortas (from spontaneous abortions
and premature newborns who died within 12 h; fetal age 6.2+/-1.3 mo). For this purpose, a
systematic assessment of fatty streak formation was carried out in fetal aortas from
normocholesterolemic mothers (n = 22), hypercholesterolemic mothers (n = 33), and mothers
who were hypercholesterolemic only during pregnancy (n = 27). Fetal plasma cholesterol levels
showed a strong inverse correlation with fetal age (R = -0.88, P < 0.0001). In fetuses younger
than 6 mo, fetal plasma cholesterol levels correlated with maternal ones (R = 0.86, P = 0.001),
whereas in older fetuses no such correlation existed. Fetal aortas from hypercholesterolemic
mothers and mothers with temporary hypercholesterolemia contained significantly more and
larger lesions (758,651+/-87,449 and 451,255+/-37,448 micron2 per section, respectively;
mean+/-SD) than aortas from normocholesterolemic mothers (61,862+/-9,555 micron2; P <
0.00005). Serial sections of the arch, thoracic, and abdominal aortas were immunostained for
recognized markers of atherosclerosis: macrophages, apo B, and two different oxidationspecific epitopes (malondialdehyde- and 4-hydroxynonenal-lysine). Of the atherogenic sites
that showed positive immunostaining for at least one of these markers, 58.6% were established
lesions containing both macrophage/foam cells and oxidized LDL (OxLDL). 17.3% of all sites
contained only native LDL, and 13.3% contained only OxLDL without monocyte/ macrophages.
In contrast, only 4.3% of sites contained isolated monocytes in the absence of native or oxidized
LDL. In addition, 6.3% of sites contained LDL and macrophages but few oxidation-specific
epitopes. These results demonstrate that LDL oxidation and formation of fatty streaks occurs
already during fetal development, and that both phenomena are greatly enhanced by maternal
hypercholesterolemia. The fact that in very early lesions LDL and OxLDL are frequently found in
the absence of monocyte/macrophages, whereas the opposite is rare, suggests that intimal LDL
accumulation and oxidation contributes to monocyte recruitment in vivo.
One can postulate that pathogenicity results from a lack of cholesterol or related sterols,
accumulation of toxic sterol intermediates above each enzyme block, abnormal feedback
regulation of earlier steps in the pathway, including synthesis of key isoprenoid compounds,
and/or abnormal signaling by hedgehog proteins that normally contain bound cholesterol. It is
attractive to postulate important roles for hedgehog proteins—sonic hedgehog, Indian
hedgehog and desert hedgehog—in disease pathogenesis. One or more of the hedgehog
proteins are involved in many of the developmental processes that are perturbed in these
disorders, including establishing a proper midline and left–right axis, proper differentiation of
the lung and gut, chondrocyte differentiation and hair follicle development (14–16). While
7DHC can substitute for cholesterol in the auto-processing of and binding to hedgehog proteins,
at least in vitro (120), it is unlikely that earlier intermediates, such as methylsterols, can
perform these functions.
In the past 10 years, proven or suspected human disorders involving each step of post-squalene
cholesterol biosynthesis have been described. The frequency of the most common of these
disorders, Smith–Lemli–Opitz syndrome (SLOS), and the range of malformations associated with
them make cholesterol biosynthesis disorders the prototypic metabolic malformation
syndromes. Although their pathogenesis is not well understood, they underline the important
role(s) of cholesterol and its metabolic precursors in mammalian development.
Characterization of placental cholesterol transport: ABCA1 is a potential target for in utero
therapy of Smith-Lemli-Opitz syndrome.
https://www.ncbi.nlm.nih.gov/pubmed/18775956
Lindegaard ML1, Wassif CA, Vaisman B, Amar M, Wasmuth EV, Shamburek R, Nielsen
LB, Remaley AT, Porter FD.
Author information
Abstract
Patients with Smith-Lemli-Opitz syndrome (SLOS) are born with multiple congenital
abnormalities. Postnatal cholesterol supplementation is provided; however, it cannot correct
developmental malformations due to in utero cholesterol deficit. Increased transport of
cholesterol from maternal to fetal circulation might attenuate congenital malformations. The
cholesterol transporters Abca1, Abcg1, and Sr-b1 are present in placenta; however, their
potential role in placental transport remains undetermined. In mice, expression analyses
showed that Abca1 and Abcg1 transcripts increased 2-3-fold between embryonic days 13.5 and
18.5 in placental tissue; whereas, Sr-b1 expression decreased. To examine the functional role of
Abca1, Abcg1 and Sr-b1 we measured the maternal-fetal transfer of (14)C-cholesterol in
corresponding mutant embryos. Disruption of either Abca1 or Sr-b1 decreased cholesterol
transfer by approximately 30%. In contrast, disruption of the Abcg1 had no effect. Treatment of
pregnant C57Bl/6 female mice with TO901317, an LXR-agonist, increased both Abca1
expression and maternal-fetal cholesterol transfer to the fetus. In an SLOS mouse model
(Dhcr7(-/-)), which is incapable of de novo synthesis of cholesterol, in utero treatment with
TO901317 resulted in increased cholesterol content in Dhcr7(-/-) embryos. Our data support
the hypothesis that Abca1, and possibly Sr-b1, contributes to transport maternal cholesterol to
the developing fetus. Furthermore, we show, as a proof of principle, that modulating maternalfetal cholesterol transport has potential for in utero therapy of SLOS.
Example: Cholesterol - Fetal Alcohol Defects
https://spacedoc.com/articles/cholesterol-fetal-alcohol-defects
Maternal alcohol consumption causes Fetal Alcohol Spectrum Defects (FASD), an array of
developmental abnormalities that includes neurological, craniofacial, cardiac and limb
malformations, as well as mental and growth retardation. FASD is enormously detrimental to
afflicted individuals, to their families, and to society as a whole. Although there has been great
progress in delineating mechanisms contributing to alcohol-induced birth defects, there are still
many gaps that need filling. We have evidence that a post-translational modification defect
may be at the root of FASD, namely, ethanol-impairment of cholesterol esterification of a
potent fetal morphogen, Sonic hedgehog (Shh). Shh is a cholesterol-modified protein that is
produced in different regions of developing embryos at various stages of embryogenesis. It
regulates cell differentiation and proliferation of neural, cardiac, bone, blood, and endodermal
progenitors in early embryonic development. Knocking-down Hedgehog (Hh) signaling pathway
components causes a spectrum of developmental defects that resemble those that occur in
FASD. We note dose-dependent reductions in cholesterol esters, cholesterol-modified Shh, and
Hh pathway activity in zebrafish embryos that develop FASD following transient alcohol
exposure. These findings prompted our HYPOTHESIS that ethanol-inhibition of Shh ligand
modification by cholesterol, and the consequent decreases in Hh pathway activity during
embryogenesis, contribute to FASD pathogenesis. We will evaluate this hypothesis by two aims:
(1) To characterize the effects of ethanol on Hh signaling and the resulting pattern of
morphological defects throughout embryogenesis. (2) To determine whether inhibited
cholesterol modification of Shh is responsible for ethanol-induced developmental defects
defects. The results from this investigation may provide insight into a novel mechanism for
alcohol's teratogenic effects and he lead to new directions for the prevention, diagnosis and
treatment of Fetal Alcohol Spectrum Defects.
The same research group at Duke University that reported its concern about the association of
excess Parkinsonism cases with the taking of statin drugs has now reported a previously
unsuspected role of serum cholesterol levels in the condition of fetal alcohol syndrome.
U.S. medical researchers have found cholesterol supplementation prevents the fetal alcohol
spectrum of defects in alcohol-exposed zebra fish embryos.
The Duke University Medical Center study by Yin-Xiong Li and colleagues details the mechanism
and prevention of fetal alcohol defects and has implications for potential preventative prenatal
intervention.
Experts estimate approximately 100 babies are born daily suffering from alcohol related defects
that include abnormalities such as neurological, craniofacial, and cardiac malformations.
Using the zebra fish model, the researcher found alcohol interferes with embryonic
development by disrupting cholesterol-dependent activation of a critical signaling molecule,
called sonic hedgehog. They also showed cholesterol supplementation of the alcohol-exposed
embryos restored the functionality of the molecular pathway and prevented development of
such defects.
In addition, the authors report alcohol related defects in zebra fish resulted from minimal fetal
alcohol exposure, equivalent to a 120-pound woman drinking one 12-ounce bottle of beer. The
findings suggest even small amounts of alcohol might be unsafe for pregnant women and also
indicate cholesterol supplementation may be a potential means to prevent fetal alcohol
defects.
There is now an abundance of research data documenting the vital role of cholesterol in our
body. Although this study used Zebra fish as a model, at the cellular level of glycoprotein and
neuropeptide synthesis, the biochemical steps are the same. Even with a lowly worm we share
some 60% of our genes and Zebra fish are much higher on the evolutionary chain. The tiny, but
incredibly complex, factories common to all cells are known as the endoplasmic reticulum and
Golgi apparatus. The joining of peptide and amino acids is like the threading of popcorn on a
string with their sequence determining the final message.
Now we have evidence for an even greater role for cholesterol along with brain cognition and
substrate for our vital hormones. Can one imagine the effect of statins on this cholesterol
dependent mechanism? Thousands of women currently taking statins are in their childbearing
age ( although women are to avoid pregnancies while on statins, hundreds do get pregnant )
and social drinking being what it is...?
Cholesterol transport by the placenta: placental liver X receptor activity as a modulator of
fetal cholesterol metabolism?
https://www.ncbi.nlm.nih.gov/pubmed/17141866
Plösch T1, van Straten EM, Kuipers F.
Author information
Abstract
Cholesterol is an important sterol in mammals. Defects in cholesterol synthesis or intracellular
routing have devastating consequences already in utero: the Smith-Lemli-Opitz syndrome,
desmosterolosis and Niemann-Pick C1 disease provide examples of severe human inherited
diseases caused by mutations in cholesterol metabolism genes. On the other hand, elevated
plasma cholesterol concentrations are associated with the development of atherosclerosis
which represents a major health risk in Western societies. Moreover, several studies indicate
that development of atherosclerosis may already start during fetal life. Hence, a carefully
balanced regulation of cholesterol metabolism appears of critical importance for both the
development of the fetus and health of the adult. In the adult, the liver X receptor is a key
regulator of cholesterol metabolism. Its target genes regulate cellular cholesterol efflux and
thereby modulate whole-body cholesterol fluxes. LXR and several of its target genes have
recently been demonstrated to be expressed in the placenta, which would provide a means to
control delivery of maternal cholesterol to the fetus. Here we discuss the potential role of the
placenta in the regulation of fetal cholesterol homeostasis and strategies to influence maternalfetal cholesterol transfer.
Heterotaxy Terminology
The nomenclature, definition and classification of cardiac structures in the setting of
heterotaxy.
Cardiol Young. 2007 Sep;17 Suppl 2:1-28. doi: 10.1017/S1047951107001138.
Jacobs JP1, Anderson RH, Weinberg PM, Walters HL 3rd, Tchervenkov CI, Del Duca D, Franklin
RC, Aiello VD, Béland MJ, Colan SD, Gaynor JW, Krogmann ON, Kurosawa H, Maruszewski
B, Stellin G, Elliott M
https://www.ncbi.nlm.nih.gov/pubmed/18039396
Abstract
In this manuscript, we review the nomenclature, definition, and classification of heterotaxy,
also known as the heterotaxy syndrome, placing special emphasis on the philosophical
approach taken by both the Bostonian school of segmental notation developed from the
teachings of Van Praagh, and the European school of sequential segmental analysis. The
Nomenclature Working Group offers the following definition for the term "heterotaxy":
"Heterotaxy is synonymous with 'visceral heterotaxy' and 'heterotaxy syndrome'. Heterotaxy is
defined as an abnormality where the internal thoraco-abdominal organs demonstrate abnormal
arrangement across the left-right axis of the body. By convention, heterotaxy does not include
patients with either the expected usual or normal arrangement of the internal organs along the
left-right axis, also known as 'situs solitus', nor patients with complete mirror-imaged
arrangement of the internal organs along the left-right axis also known as 'situs inversus'."
"Situs ambiguus is defined as an abnormality in which there are components of situs solitus and
situs inversus in the same person. Situs ambiguus, therefore, can be considered to be present
when the thoracic and abdominal organs are positioned in such a way with respect to each
other as to be not clearly lateralised and thus have neither the usual, or normal, nor the mirrorimaged arrangements."The heterotaxy syndrome as thus defined is typically associated with
complex cardiovascular malformations. Proper description of the heart in patients with this
syndrome requires complete description of both the cardiac relations and the junctional
connections of the cardiac segments, with documentation of the arrangement of the atrial
appendages, the ventricular topology, the nature of the unions of the segments across the
atrioventricular and the ventriculoarterial junctions, the infundibular morphologies, and the
relationships of the arterial trunks in space. The position of the heart in the chest, and the
orientation of the cardiac apex, must also be described separately. Particular attention is
required for the venoatrial connections, since these are so often abnormal. The malformations
within the heart are then analysed and described separately as for any patient with suspected
congenital cardiac disease. The relationship and arrangement of the remaining thoracoabdominal organs, including the spleen, the lungs, and the intestines, also must be described
separately, because, although common patterns of association have been identified, there are
frequent exceptions to these common patterns. One of the clinically important implications of
heterotaxy syndrome is that splenic abnormalities are common. Investigation of any patient
with the cardiac findings associated with heterotaxy, therefore, should include analysis of
splenic morphology. The less than perfect association between the state of the spleen and the
form of heart disease implies that splenic morphology should be investigated in all forms of
heterotaxy, regardless of the type of cardiac disease. The splenic morphology should not be
used to stratify the form of disease within the heart, and the form of cardiac disease should not
be used to stratify the state of the spleen. Intestinal malrotation is another frequently
associated lesion that must be considered. Some advocate that all patients with heterotaxy,
especially those with isomerism of the right atrial appendages or asplenia syndrome, should
have a barium study to evaluate for intestinal malrotation, given the associated potential
morbidity. The cardiac anatomy and associated cardiac malformations, as well as the
relationship and arrangement of the remaining thoraco-abdominal organs, must be described
separately. It is only by utilizing this stepwise and logical progression of analysis that it becomes
possible to describe correctly, and to classify properly, patients with heterotaxy.
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