Regulation of Schwann cell proliferation in cultured segments of the adult rat sciatic nerve.

Schwann cell proliferation was studied in cultured segments of the rat sciatic nerve by measurement of [3H] thymidine incorporation or through bromodeoxyuridine-(BrdU)-labelling and immunocytochemistry. The aim was to delineate mechanisms involved in the injury-induced proliferative response of Schwann cells. Removal of extracellular Ca2+ by addition of EGTA to the culture medium suppressed [3H] thymidine incorporation as did the calmodulin inhibitor 48/80. The Ca2+ ionophore A23187 increased incorporation. Staurosporin, an inhibitor of protein kinase C (PKC), suppressed [3H] thymidine incorporation while phorbol-12-myristate-13-acetate (PMA) enhanced incorporation. Manipulation of the cAMP system showed that increased cAMP levels inhibited proliferation. Inhibition of protein kinase A by HA 1004 increased the incorporation of [3H] thymidine. Immunostaining for BrdU and glial specific markers together with morphological evaluation of myelin association showed that proliferation occurred in Schwann cells. The results are consistent with a model in which Schwann cell proliferation is enhanced by Ca2+ through activation of calmodulin-dependent and/or PKCdependent mechanisms. Inhibition is achieved through the cAMP system. Together, these results show that Schwann cells regulate proliferation differently in an integrated environment, e.g. the nerve structure, than in isolation as primary monocultures.