The mucus of the tear film is responsible for maintenance of fluid on the surface of the eye and for providing a microbe barrier to protect the eye from infection. Ocular surface diseases such as those of the dry eye type, vitamin A deficiency, ocular surface infections as well as allergic conjunctivits may involve mucus deficiency, disruption of the mucus layer, or discharge of large amounts of mucus. During the previous funding period, we demonstrated that three mucin genes are expressed by the ocular surface epithelium, two prevalent ones being the membrane- spanning mucin MUC4 and the goblet cell-specific mucin MUC5AC. We sequenced portions of MUC4 and developed probes, antibodies, and assay methods for both mucins that we now propose to use in four specific aims toward understanding aspects of the function and regulation of expression of these mucins on the ocular surface in normal and pathologic states.
Aim I : Characterize two aspects of the membrane-spanning mucin MUC4 on the ocular surface. A. determine whether the mucin remains associated with the apical membrane glycocalyx or whether its extracellular domain is shed into the tear film. b. Test candidate inducers of MUC4 gene expression, based on presence of putative transcription factor binding sites identified from sequencing the MUC4 regulatory region and on preliminary data indicating their potential role in its regulation.
Aim II : We hypothesize that conjunctival goblet cell differentiation is characterized by induction of expression of the MUC5AC gene and that such induction can be regulated by environmental stimuli as well as cellular effectors. We propose to: a. determine in a mouse model whether goblet cell differentiation/Muc5AC expression can be influenced by surface irritants, infections, or specific allergens; b. determine whether conjunctival goblet cell differentiation can be enhanced in vitro, based on demonstrated presence of regulatory elements in the promoter region of MUC5AC and on culture conditions known to affect gastrointestinal goblet cell differentiation.
Aim III : Determine if MUC5AC has specific affinities for MUC4 and the bactericidal proteins prevalent in the tear film, lysozyme, and secretory IgA.
Aim I V: Determine in a specific type of dry eye (Sjogren's syndrome), and in seasonal allergic conjunctivitis whether amounts of MUC4 and MUC5AC mRNA and protein differ from the normal population. We hypothesize that dry eye syndromes are characterized by loss of surface wetting due to reduced amounts of MUC5AC and MUC4 protein, whereas, allergic conjunctivitis is characterized by an increased amount of mucins to facilitate allergen removal.
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