Age-related changes in IGF-1 expression in submandibular glands of senescence-accelerated mice

Saliva is known to play important roles in such functions as swallowing, mastication, speech, and taste. Furthermore, salivary glands synthesize and secrete a number of growth factors involved in cell/tissue homeostasis. It has been demonstrated that IGF-1, which is structurally analogous to insulin, has been shown to be expressed in mouse submandibular glands, and that IGF-1 stimulates DNA synthesis, amino acid uptake, protein synthesis, and glucose transport in various cells. Diminished function of the salivary glands is thought to lead to increased dental caries and periodontal diseases, which are commonly associated with aging. However, very little is known regarding the effects of age on IGF-1 expression in submandibular glands. The senescence-accelerated mouse (SAM), an experimental murine model of accelerated aging, has been extensively used to examine the mechanisms responsible for aging. In the present study, IGF-1 production and mRNA levels in the submandibular glands of SAM-P1 mice were examined. IGF-1 levels were determined by radioimmunoassay and IGF-1 mRNA levels by semi-quantitative RT-PCR. We found that IGF-1 protein levels in homogenates and IGF-1 mRNA levels decreased with age in SAMP1 mice. These findings suggest that IGF-1 synthesis in submandibular glands decreases with aging, and this may result in lower levels of cellular proliferation, regeneration and wound healing in aged oral tissues. (J. Oral Sci. 46, 119-125, 2004)