Platelet‐derived growth factor and regulation of schwann cell proliferation in vivo

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Abstract
To examine the role of platelet-derived growth factor (PDGF) in the in vivo regulation of Schwann cell proliferation, steady-state levels of mRNAs encoding PDGF A and B chains, and PDGF α and β receptors were measured in immature and adult rat sciatic nerves and in cultured rat Schwann cells. PDGF B chain and PDGF β receptor mRNAs are present in immature rat sciatic nerves and to a lesser extent in adult rat nerves. Short-term cultures of neonatal rat Schwann cells express PDGF β receptor mRNA, but not PDGF B chain mRNA, and are stimulated to synthesize DNA by addition of PDGF BB to the medium. These data indicate that PDGF BB is a developmenttally regulated paracrine growth factor for rat Schwann cells. Very long-term cultures of rat Schwann cells, which have lost normal dependence on exogenous growth factors, express PDGF B chain mRNA as well as mRNAs encoding the PDGF α and β receptors, suggesting that, under these circumstances, PDGF BB also acts as an autocrine growth factor. PDGF A chain mRNA is present in both immature and adult rat sciatic nerves and is expressed by primary and secondary cultures of rat Schwann cells as well. However, because the abundance of PDGF α receptor mRNA is very low in rat Schwann cells, PDGF AA is not likely to be a significant autocrine growth factor for rat Schwann cells.