FINAL PROJECT – DRAFT #1
Introduction:
Long QT Syndrome (LQTS) is an inherited arrhythmia condition thought to
have a prevalence of approximately 1/2500. Classified as a channelopathy,
mutations in both cardiac potassium and sodium channels have been identified in a
majority of patients with LQTS. Patients with these rare genetic mutations are predisposed to fainting episodes, seizures, cardiac arrests and sudden death due to the
abnormal electrical conduction of heart tissue. Further, it has been estimated that
up to 15% of sudden unexpected death with no identifiable cause may due to LQTS.
It has been known that patients with LQTS are at particular risk of cardiac
events and arrhythmias during late pregnancy and the early post-partum period.
Recently, a study showed that up to 8% of intrauterine fetal deaths may be due to
genetic mutations associated with LQTS. There is fairly little evidence in the
literature to support a mechanism responsible for this increased maternal and fetal
risk of cardiac events during late pregnancy in LQTS patients. With the new
evidence showing up to 8% of intrauterine fetal deaths being associated with LQTS,
there is a high need for further research to help identify the mechanism at play, and
reduce the risk of sudden death during pregnancy.
Speculations amongst researchers have questioned whether progesterone, a
female reproductive hormone, may play a role at increasing risk of cardiac
arrhythmias during pregnancy. At least one study has shown progesterone may play
a role in the regulation of the HERG gene, which codes for a potassium ion channel,
partially responsible for controlling cardiac electrical conduction, and the QT
interval of the cardiac action potential (Wu et al, 2011). Further, progesterone is
known to increase during the third trimester of pregnancy, therefore fitting with the
increased risk of cardiac events and sudden death during this period.
In the past decade, the development of stem cell technology has rapidly
changed the face of drug testing in the electrophysiology field. It is now possible to
develop patient-specific cardiomyocytes from human induced pluripotent stem
cells. These cardiomyocyte-like cells harbor the same genetic variants present in
vivo, and provide an excellent new media for preforming expressivity and functional
studies to observe the impact of these genetic variants. Recently, a paper by Matsa,
et al showed the ability to create patient specific cardiomyocytes harboring LQTS
mutations, and using patch-clamp technology, researchers were able to demonstrate
the prolonged cardiac action potential associated with LQTS. Further, using
potassium channel blockers, they were able to both provoke arrhythmic events and
test the effectiveness of beta-blocker drug therapies in reducing invoked arrhythmic
events (Matsa et al, 2011).
In order to test the potential mechanism of potassium increasing cardiac
events and arrhythmias during pregnancy in LQTS patients, and the increased risk
of intrauterine fetal death, I propose a study to look at the effect of progesterone on
cardiomyocytes derived from human induced pluripotent stem cells taken from
LQTS gene-positive intrauterine fetal death victims and their surviving mothers.
METHODS: (Still under development!)
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Establish a biobank to store the cord blood from intrauterine fetal death
victims (such biobanks already exist, and are therefore ethically feasible)
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Run LQTS gene - panels on blood to identify gene positive victims
Cell-line #1: Following methods shown by Haase et al (2009), induced
human pluripotent stem cells from cord blood of LQTS gene positive victims
and differentiate into cardiomyocytes
Cell-line #2: Harvest fibroblast tissue from LQTS gene-positive surviving
mothers (as control), induce human pluripotent stem cells and differentiate
into cardiomyocytes following method proposed by Matsa et al for LQTS
drug evaluation
Cell-line #3: Differentiate cardiomyocytes from an established human
embryonic stem cell line to function as a gene-negative control
Using multi-electrode array and patch-clamp technology, observe the cardiac
action potential of induced cardiomyocytes
Treat both gene-positive cell lines and gene-negative control cardiomyocytes
with progesterone and observe effects by comparing length of cardiac action
potential to baseline (as well as observing any arrhythmic events).
Compare the length of cardiac action potential and number of arrhythmic
events between fetal derived and maternally derived cardiomyocytes
EXPECTED RESULTS:
 One would expect an increase in the length of the cardiac action potential in
all progesterone treated cells
 Cells harboring the LQTS mutations will likely have a longer cardiac action
potential and increased arrhythmic events compared to those who do not
harbor the mutation
 Considering the fact that the mutation was lethal in the case of intrauterine
fetal death patients but not gene-carrying mothers, one might expect to see a
difference in arrhythmic events between fetal and maternal cardiomyocytes.