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Ocular Surface Mucins

Friday, August 10, 2018


Mucins are glycoproteins expressed by epithelial tissues of mucosal surfaces. Mucins are classified as either secretory or membrane spanning, and the ocular epithelium contain both types. Since the mid-1990s, a large number of mucin (MUC) genes have been identified: MUC1, MUC2, MUC4, MUC5A, MUC5B, MUC7MUC13, MUC15, MUC16 and MUC17.


An ocular mucin structure /function discussion


Ocular mucins protect against bacterial adherence to the corneal epithelium, and alterations in mucus production promote bacterial adherence to the cornea. A deficiency in mucin production can ​affect ocular health.


Currently, the proposed sources of ocular mucin include the conjunctival goblet cells, conjunctival, corneal epithelial cells and lacrimal gland, as well as ocular surface wound healing growth factors (epidermal and transforming) that may stimulate goblet cell mucin secretion.


Origins and secretion of mucins


MUC1, MUC4 and MUC16 are membrane-spanning mucins with a hydrophobic amino acid segment that allows the mucin core protein to remain intimately associated with the ocular surface epithelial cells.


MUC2, MUC5A, MUC5B are secretory mucins that overlay the ocular surface and provide structure for lubrication as well as protection to the cells.


MUC7 is a smaller peptide-soluble secretory mucin that does not form a gel but provides mechanisms for efficiently mixing all the secretory mucins with the aqueous produced by the lacrimal gland.


MUC13, MUC15 and MUC17 have been proven to exist in human conjunctival epithelium from healthy donors. The exact function of these genes remains to be further elucidated.


​Membrane-Associated Mucins


Membrane-associated mucins (MAMs) on the ocular surface (MUC1, MUC4 and MUC6) project from microplicae found on the anterior surface of corneal and conjunctival epithelial cells.


​Mucins cover all wet-surfaced epithelia in the body. The mucins expressed on the ocular surface have vital functions in protecting sight. In order to provide a stable refractive surface through which light can be transmitted to the retina, the ocular surface must maintain important balances in hydration and lubrication as well as protection against pathogens and mechanical damage due to exposure to the environment.


Ellen Troyer, with Spencer Thornton, MD, David Amess and the Biosyntrx staff



PEARL

We strongly recommend that our readers with a passionate professional or personal interest in mucin biochemistry, ocular surface health and tear film dependent visual acuity, take the time to further research the role mucins play in full body mucosal tissue health, as well as eye health.









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