Expression of insulin-like growth factor family in the rat olfactory epithelium

The goal of this study was to determine the cellular sites of insulin-like growth factor (IGF) family expression in the rat olfactory epithelium. By RT-PCR analysis, mRNAs of IGF-I, II, IGF-I receptor (IGF-IR), and IGF binding proteins (IGFBPs) 2, 3, 4, 5, and 6 were found to be expressed in the olfactory mucosa. Immunoreactivity for IGF-IR was restricted to a subset of olfactory receptor cells whose cell bodies were situated in the basal region of the olfactory epithelium. Intense IGF-I immunoreactivity was detected in the supporting cells, whereas IGF-II immunoreactivity was observed in the lamina propria, but not in the epithelium. Immunoreactivities for IGFBP-2, IGFBP-3, and IGFBP-6 were detected in olfactory receptor cells. In addition, axon bundles in the lamina propria displayed an intense reaction for IGFBP-6. IGFBP-4 immunoreactivity was restricted to the apex of the olfactory epithelium. Intense IGFBP-5 immunoreactivity was observed in Bowman's glands. These results suggest that IGF-I is secreted from supporting cells and affects its receptor- expressing olfactory cells. IGFBPs may modulate IGF-I activity via their production by Bowman's glands, olfactory cells, and supporting cells themselves.