Functions of ocular surface mucins in health and disease

Purpose of review The purpose of the present review is to describe new concepts on the role of mucins in the protection of corneal and conjunctival epithelia and to identify alterations of mucins in ocular surface diseases. Recent findings New evidence indicates that gel-forming and cell surface-associated mucins contribute differently to the protection of the ocular surface against allergens, pathogens, extracellular molecules, abrasive stress, and drying. Summary Mucins are high-molecular weight glycoproteins characterized by their extensive O-glycosylation. Major mucins expressed by the ocular surface epithelia include cell surface-associated mucins MUC1, MUC4, MUC16, and the gel-forming mucin MUC5AC. Recent advances using functional assays have allowed the examination of their roles in the protection of corneal and conjunctival epithelia. Alterations in mucin and mucin O-glycan biosynthesis in ocular surface disorders, including allergy, nonautoimmune dry eye, autoimmune dry eye, and infection, are presented.