Protein kinase C and mouse sciatic nerve regeneration.

We have studied the role of protein kinase C (PKC) in peripheral nerve regeneration by using the cultured adult mouse sciatic nerve, which displays regrowth of sensory axons under serum-free conditions. By the use of immunohistochemistry we show that one of the isoforms of PKC, PKC beta, is present in the nerve cell bodies of normal nerves and is upregulated after injury. In spite of this, the specific PKC inhibitor chelerythrine at 5 microM, a concentration well above its IC50 value for PKC, failed to reduce the outgrowth distance of new axons. This was not due to impermeability of the drug, since the same concentration caused a clear reduction of the injury-induced proliferation of Schwann cells in the crush region. Likewise, HA-1004, an inhibitor of cyclic nucleotide-dependent protein kinases, also lacked effect on outgrowth when used on its own, even at very high concentrations (100 microM). In contrast, outgrowth was significantly reduced when 5 microM chelerythrine and 5 microM HA-1004 were used in combination. In conclusion, the present results suggest that PKC-activity is important but not indispensable for the regeneration process. Successful completion of the latter could be achieved by several, perhaps redundant, phosphorylation systems.