The promoting effects of bFGF and astrocyte extracellular matrix on process outgrowth by adult human oligodendrocytes are mediated by protein kinase C.

Process extension by oligodendrocytes (OLs) is a critical early step in myelin formation. We have previously reported that the basal- or phorbol ester-enhanced process outgrowth by adult human OLs is mediated by oligodendroglial protein kinase C (PKC). Recently, we demonstrated that astrocytes facilitated process outgrowth by adult human OLs through the interaction between astrocyte-derived basic fibroblast growth factor (bFGF) and astrocyte extracellular matrix (ECM). If PKC is central to the signal transduction cascade that leads to process formation by OLs, then the effects of bFGF and astrocyte ECM should also involve PKC. In the current study, we have addressed the involvement of PKC in the bFGF- and astrocyte ECM- enhanced process formation by adult human OLs by using a selective inhibitor of PKC, calphostin C. The results show that calphostin C dose-dependently reduced process extension elicited by bFGF and astrocyte ECM, at IC50 concentrations of 24.5 and 26.6 nM, respectively. At the concentrations of calphostin C that inhibited process extension by adult human OLs, necrosis (measured by lactate dehydrogenase release) and apoptosis (determined by using a fluorescent terminal deoxynucleotidyl transferase assay) of OLs did not occur. Finally, we demonstrate that another specific inhibitor of PKC, CGP 41251, also reduced process formation that is elicited by bFGF and astrocyte ECM. Thus, all process-extending agents for adult human OLs identified to date signal through PKC, further implicating PKC of OLs as being central to the production of process extension, an early event in myelinogenesis.