Secretion of tenascin-C by cultured astrocytes: regulation of cell proliferation and process elongation.
Tenascin-C (TNC), an extracellular matrix glycoprotein, is involved in tissue morphogenesis like embryogenesis, wound healing or tumorigenesis. Quiescent astroglia in long-term primary cultures are known to show rapid morphological changes after subculture and serum deprivation/re-addition (SSDR). To elucidate roles of TNC in the morphogenetic processes of cultured astrocytes, we have revealed morphological changes in association with soluble TNC contents in the medium and expression of TNC mRNA, TNC, glial fibrillary acidic protein (GFAP) and integrin beta1, one of its cell surface receptors, in glial cells after SSDR. Soluble TNC in the medium rapidly increased in amount at 4 h when GFAP-positive cells expressed TNC mRNA, TNC and integrin beta1. Cellular proliferation and growth occurred in colonies expressing TNC mRNA, TNC and integrin beta1 during the first 24 h. During the next 24 h, process elongation and cell migration occurred in association with increased GFAP expression and re-elevation of soluble TNC in the medium. Cell bodies became flat and larger with increased GFAP and reduced TNC expression at 72 h, while cultures became confluent with reduced GFAP and TNC expression at 96 h after SSDR. Functional blocking with anti-TNC antibody reduced cell proliferation and induced morphological change from a process-bearing slender shape to a flat and wide shape presumably due to increased cell adhesion. These findings strongly support the idea that endogenous TNC produced and released by astrocytes in response to serum stimulation induces their proliferation and process elongation through a paracrine/autocrine mechanism.