OTOLOGY SEMINAR
The role of middle ear mucin in diseased ears
R3 楊宗霖
2002-01-02
Basic Concept
/ Mucins
- heavily glycosylated proteins
- high molecular weight and heterogeneous structure
-
in the mucociliary transport system of the middle ear and Eustachian tube
protects epithelium against invading microorganism
little is known under physiological and pathological condition
- expression of MUC5B, MUC5AC, MUC4, and MUC1 in the human E-tube
- only MUC5B mucin expression was noted in noninflamed middle ears
- middle ear and Eustachian tube expresses distinct mucin profiles
/ Normal mucociliary function
- mucin production and periciliary fluid homeostasis
- dysfunction: risk factor for otitis media.
- secreted antimicrobial molecules of the tubotympanum
lysozyme, lactoferrin, beta defensins, surfactant proteins A and D
- defects in the expression or regulation of these molecule
-> the major risk factor for otitis media.
/ Mucin genes
- expressed in a tissue- or epithelium-specific manner
- little known about mucin gene expression unique to the middle ear.
- MUC3 and MUC5AC mucin genes
dominantly expressed in rodent intestine and trachea
not detected in the rat middle ears
- middle ear MUC2 messenger RNA harvested by lavage
characterized by a single transcript
unlike its counterpart in intestine and airway characterized by polydispersity
/ MUC5B and MUC4 mucin genes
-
upregulated 4.2- and 6-fold, respectively,
in middle ears with COM or mucoid otitis media
an increase of MUC5B- and MUC4-producing cells in the middle ear mucosa.
-
electron microscopy of the secretions from COM
showed the presence of chainlike polymeric mucin.
-
MUC5B and MUC4 mucins are highly produced in diseased ear
form thick mucous effusion in the middle ear cavity
compromise the function of the middle ear.
Otitis media with effusion
/ Etiology of OME
- the primary event is inflammation of the middle ear mucosa
usually due to the presence of bacteria.
- This leads to the release of inflammatory mediators
-> secretion of a mucin-rich effusion by up-regulating mucin genes.
- Prolonged inflammatory response and poor mucociliary clearance
persistence of the middle ear fluid
/ Up-regulation of MUC5AC mRNA expression in OME
-
using RT-PCR & morphology of middle ear mucosa in rat
experimental OME induced after middle ear instillation of LPS
Normal middle ear mucosa: no expression of mucin genes
endotoxin upregulated the expression of MUC5AC mRNA between 12 h and
Day 7, maximal expression at Days 1 and 3
-
middle ears treated three times with LPS upregulated more MUC5AC mRNA
expression, by a factor of approximately 3.5
-
These suggest MUC5AC could be one of the major mucin genes in the middle
ear mucosa related to otitis media.
/ tumor necrosis factor (TNF)-alpha in OME
-
a proinflammatory cytokine in mucoid effusion
markedly increased Muc2 mucin mRNA expression in middle ear epithelium
in a time- and dose-dependent manner.
a marked increase in mucin glycoprotein in middle ear fluid.
-
Also, TNF-alpha demonstrated an autocrine and/or paracrine effect on the
expression of endogenous TNF-alpha gene in the middle ear
/ Haemophilus influenzae model
-
OME in children & COPD in adults
Mucin overproduction: a hallmark of OME & COPD
mucin genes are expressed in a tissue- or epithelium-specific manner
cause conductive hearing loss in OME & airway obstruction in COPD
-
H inf. strongly up-regulates MUC5AC mucin transcription
only after bacterial cell disruption
maximal up-regulation is induced by heat-stable bacterial cytoplasmic protein
surface membrane proteins induce only moderate MUC5AC transcription
-
Cytoplasmic molecules from lysed bacteria in the pathogenesis of infections
may explain why many patients still have persistent symptoms
such as middle ear effusion in OME after intensive antibiotic treatment
- Furthermore, activation of p38 MAP kinase
is required for H. influenza-induced MUC5AC transcription
Chronic otitis media
/ Genetic predisposition to COM
-
animal model with two different strains of rats
exposure of the middle ear to endotoxin
early extensive exudation
later goblet cell hyperplasia and mucin hypersecretion.
- animals were given transtympanic injection with gram-positive bacterial
- quantity of mucin exudate by enzyme-linked immunosorbent assay
- histological evaluation of the middle ear epithelial thickness
- significant difference in middle ear inflammation and effusion formation
- middle ear response to PG-PS may be genetically determined
- genetic predisposition may play a role in the pathogenesis of COM
/ MUC5B mucin gene in human middle ear with COM
-
middle ear mucosal specimens removed from patients with COM op
-
H&E staining revealed
pseudostratified epithelia in & cuboidal secretory epithelia
-
AB-PAS staining of epithelia
abundant secretory cells and glycoconjugates
-
In situ hybridization and immunohistochemistry
secretory cells of the middle ear mucosa with COM
expressed MUC5B mucin mRNA and its product MUC5B mucin.
-
The MUC5B mucin gene and its product
were identified in the middle ear secretory cells of patients with COM
-
Its expression was extensive in pseudostratified mucosal epithelia
and related to infiltration of inflammatory cells in the submucosa of the middle
ear cleft with COM
-
suggestive that inflammatory cell products are involved in the production of
MUC5B.
/ Nitric oxide mediates mucin secretion in otitis media
- a mechanisms that regulate mucin release in COM
- rats middle ear was injected transtympanically
after 7 days, the volume of effusion & the quantity of mucin
significantly greater in lipopolysaccharide-exposed ears than in controls
- By antimucin immunostaining
1. mucous cell hyperplasia in response to lipopolysaccharide
2. lipopolysaccharide-induced production of mucin and mucous cell hyperplasia
was inhibited in ears treated with lipopolysaccharide and L-NAME
- NO is a mediator in the pathway of mucin secretion in COM
REFERENCES
1. Clark JM, Brinson G, Newman MK et al. An animal model for the study of genetic
predisposition in the pathogenesis of middle ear inflammation.Laryngoscope.
2000;110:1511-5.
2. Kawano H, Paparella MM, Ho SB et al. Identification of MUC5B mucin gene in
human middle ear with chronic otitis media.Laryngoscope. 2000;110:668-73.
3. Lin J, Tsuprun V, Kawano H et al. Characterization of mucins in human middle ear
and Eustachian tube. Am J Physiol Lung Cell Mol Physiol. 2001;280:L1157-67.
4. Lim DJ, Chun YM, Lee HY et al. Cell biology of tubotympanum in relation to
pathogenesis of otitis media. Vaccine. 2000;19: S17-25
5. Kubba H, Pearson JP, Birchall JP. The aetiology of otitis media with effusion: a
review. Clin Otolaryngol. 2000;25:181-94.
6. Rose AS, Prazma J, Randell SH et al. Nitric oxide mediates mucin secretion in
endotoxin-induced otitis media with effusion.Otolaryngol Head Neck Surg.
1997;116:308-16.
7. Moyse E, Lyon M, Cordier G et al. Viral RNA in middle ear mucosa and exudates
in patients with chronic otitis media with effusion. Arch Otolaryngol Head Neck
Surg. 2000;126:1105-10.
8. Kim YT, Jung HH, Ko TO, Kim SJ. Up-regulation of MUC5AC mRNA expression
in endotoxin-induced otitis media. Acta Otolaryngol. 2001;121:364-70
9. Chen YP, Tong HH, James, Demaria TF. Detection of mucin gene expression in
normal rat middle ear mucosa by reverse transcriptase-polymerase chain reaction.
Acta Otolaryngol. 2001;121:45-51.
10. Lin J, Haruta A, Kawano H et al. Induction of mucin gene expression in middle
ear of rats by tumor necrosis factor-alpha: potential cause for mucoid otitis media. J
Infect Dis. 2000;182:882-7