Multifunctional roles of growth factors or biologically active peptides in salivary glands and saliva

Abstract

Salivary glands secrete saliva which contains mucins, antimicrobial substances and growth factors. Since epidermal growth factor (EGF) and nerve growth factor (NGF) were demonstrated in murine submandibular glands (SMGs), several growth factors and biologically-active peptides have been studied in the human or other mammalian salivary glands and saliva. These growth factors may have a functional role in cell migration, proliferation and maturation within not only salivary glands but also other organs. In the SMGs of mice and rats, EGF, NGF and other known growth factors are usually synthesized in granular convoluted tubule cells (GCT). However, human SMGs are devoid of GCT cells, and growth factors in human salivary glands are usually produced in striated ducts. These findings suggest an evolutionary trace of ductal cells in mammals. The present review describes expression patterns of the following salivary gland growth factors: nerve growth factor (NGF); transforming growth factor α and β (TGF-α/β) bone morphogenetic protein (BMP); insulin-like growth factor (IGF); fibroblastic growth factor (FGF); and somatostatin, as well as their receptors. This review also discusses their cell biological roles in pathophysiological conditions.