The function of salivary proteins and the regulation of their secretion by salivary glands

Abstract

Salivary glycoproteins give saliva its characteristic physical properties and enable it to form a thin film over hard and soft tissues in the mouth. Oral health and homeostasis are dependent upon the functions performed by the salivary film and most of these functions, including lubrication, barrier function and microbial interactions, are in turn dependent upon salivary proteins. Some salivary proteins appear to fulfil more than one function and some functions are performed by a number of different proteins. There are relatively great variations in amounts of different proteins present in salivas from different subjects. However, subjects with low levels of particular proteins do not appear to suffer terms of oral health and this may be due to functional compensation by other proteins. Salivary protein secretion by salivary glands is dependent upon stimuli mediated by sympathetic and parasympathetic nerves and both acinar and ductal cells make a contribution to protein secretion. In addition to the well-characterized storage granule exocytosis pathway of protein secretion, salivary cells can secrete proteins by vesi cular, non-storage granule pathways. These include direct secretion of newly synthesized proteins to saliva and to the glandular matrix and to circulation, and transcytosis of polymeric immunoglobulin A into saliva following secretion by glandular plasma cells. Recent data indicate that all ofthese pathways are subject to regulation by autonomic ner ves. Resynthesis of some salivary proteins following secretion also shows a dependency upon nerve-mediated stimuli. The distal intracellular mechanisms coupling stimulation to synthesis are uncertain although the proximal events appear to be similar to those coupling stimulation to exocytosis. The synthesis of some salivary proteins can be upregulated by cy-tokines released from inflammatory cells and this can lead to increased salivary levels of antimicrobial proteins including lactoferrin and immunoglobulin A. Biomedical Reviews 1998; 9: 3-15.