SALIVARY MUCIN, SYNTHESIS, PROCESSING AND SECRETION

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Mucins from saliva are a class of glycoproteins whose bioactivities range from formation of protective coatings to aggregation and/or inactivation of specific strains of viruses and oral bacteria. The ultimate goal of this project is to provide a rationale for developing treatments to reverse losses of mucin from salivary glands and saliva such as observed to accompany aging in humans and mice. An understanding of the fundamental processes surrounding mucin synthesis and glycosylation is the key to revealing the origins of the aging-related losses and to development of appropriate treatment responses. The model systems that will be employed for this study of mucin production use the young adult mouse submandibular and sublingual glands. Both glands are included because each makes a unique mucin. These mucins appear to be analogous to the human salivary mucins, MG1 and MG2. In addition, the secretion of each mucin is regulated differently, providing the opportunity for evaluating the secretion and restitution of mucin that is elicited either primarily as a cholinergic or as a beta-adrenergic response. With these systems, transcription, compartmentalization and stability of mucin mRNAs will be measured. Apomucin synthesis and glycosylation will also be evaluated before and after secretion to provide a baseline for comparison of mucin recovery rates in young and aged mice. In preliminary studies, it has been shown that mucin production in both glands can be upregulated by a regimen of chronic hyperstimulation. This upregulation of mucin can also be accomplished in senescent mice leading to levels higher than in young mice. However, it is not known if this approach to reversing the aging effect is appropriate or the underlying cause of the aging-related loss. Thus, the later aspects of this project will focus on gaining a better understanding of which of the mucin production processes decline with aging and which processes are upregulated in response to hyperstimulation. To accomplish the above goals, molecular and immunological probes have been developed. These include cDNA clones for both mucins as well as antisera against both apomucins and their fully glycosylated counterparts. These will be used to quantitate the mucins and their mRNAs. A system for quantitating and sequencing both N- and O-linked oligosaccharides will also be employed. The submandibular and sublingual mucin cDNA clones and a cDNA clone for a salivary cell-specific protein, P2O, that shows sequence homology with mucins will also be used to probe the mouse genome for evidence of their relatedness and or possible gene polymorphism.