SALIVARY MUCIN SYNTHESIS, PROCESSING AND SECRETION

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A key purpose of this proposal is to standardize and describe in vivo the stimulus-secretion-synthesis cycle of a mouse submandibular gland mucin. This system is intended to provide insight into the control and synthesis processes which are responsible for the diurnal replenishment of exocrine proteins in the salivary glands. It is postulated that by clarifying the normal flow of events, it will be possible to begin to understand some forms of salivary gland dysfunction. Protocols are described for obtaining rates of synthesis and degradation of the mucin core protein at different stages of the cycle. Rates and sequence of mucin oligosaccharide assembly will also be ascertained. A strategy for identifying the mechanism for activation of the synthesis phase is described and possible coordination between translation and glycosylation processes will be tested. The final phase of this part of the project will be to examine the effects of different stimuli on the cycle. We will extend to senescent mice our recent study with young to mid-adult mice which indicated that mucin oligosaccharide composition was stabilized by chronic isoproterenol treatment. The intent of this phase of the study is to determine if the carbohydrate composition of mucin varies more in old mice than in young and if isoproterenol treatment can reduce this variation. The effects of chronic pilocarpine treatment will be tested in the same age groups. A study of the relationship of different secretagogues to mucin concentrations in saliva will be repeated and extended in a mouse population in which inherent variation has been reduced substantially. Steps have been taken to provide this population and additional approaches are under investigation. In the previous study, a greater than 60-fold range of mucin concentrations in saliva was observed following stimulation of secretion with the same dosage of pilocarpine in different animals of a regular laboratory population. We plan to compare effects of different dosages but do not predict success unless the inherent variation is reduced. Finally, we present evidence suggesting that mucin undergoes an oligosaccharide processing step at secretion. Two protocols will test this possibility. If processing is confirmed, we will determine which class of oligosaccharides is affected, how this impacts intracellular sialic acid and the mechanisms involved.