In Defense of the Oral Cavity: Structure, Biosynthesis, and Function of Salivary Mucins

Abstract

The oral environment, like other mucosal surfaces of the body, is coated by a slimy, viscoelastic coat termed mucus. This adherent layer, consisting predom­ inately of salivary glycoproteins, proteins, and lipids, forms ajelly-like blanket that represents the perimeter defense of the tissue/environmental interface (77). The unique physicochemical and rheological properties of the mucus coat are contributed largely by the heavily O-glycosylated mucin-glycoproteins (mu­ cins). Salivary mucins are synthesized by the mucus acinar cells of the paired submandibular (SMG) and sublingual (SLG) glands, as well as minor salivary glands distributed throughout the palatal and buccal mucosa. Serous acinar cells, such as those found in the human or rat parotid glands, do not contribute to the production of salivary mucins. Much of our current understanding of salivary mucin function has been derived by inference. Various subjective and objective functional losses have been catalogued in persons who lack the ability to produce adequate levels of saliva (4). Relevant findings include (a) the sensation of oral dryness, partic­ ularly among those subjects with compromised mucus gland function (26); (b) difficulty with swallowing; and (c) an increased susceptibility to dental cavity (caries) formation and the appearance of opportunistic yeast infections (thrush mouth). These findings have led to a generalized view that saliva functions to (a) hydrate and lubricate the oral structures; (b) facilitate the oral phase of