THROMBIN-INDUCED REVERSAL OF ASTROCYTE STELLATION IS MEDIATED BY ACTIVATION OF PROTEIN-KINASE-C BETA-1

Exogenous or endogenous injuries of the central nervous system trigger astrogliosis characterized by proliferation of astrocytes and changes in their morphology from stellate to flat polygonal. Astrocytes in cu lture are very sensitive to thrombin, a serine protease, which through its proteolytically activated receptor (PAR-1) induces proliferation and morphological changes comparable to astrogliosis. Evaluation of th e thrombin signal-transduction pathway in the reversal of astrocyte st ellation might help to understand astrogliosis. For this purpose, prim ary cultured murine cortical astrocytes were treated with H7, a protei n-kinase inhibitor, and thrombin, which resulted in an inhibition of s tellation reversal. Treatments with phorbol 12-myristate 13-acetate (P MA), a protein kinase C (PKC) activator, mimicked the action of thromb in. Subsequently, direct assay of astrocyte PKC activity after thrombi n or PMA treatment demonstrated involvement of PKC in thrombin signali ng associated with shape change. Western blotting showed that PKC isof orm beta-1 was involved in this pathway, while PKC alpha was only weak ly activated and PKC beta-2 was not activated by thrombin. PKC beta-1 translocation was also elicited by a thrombin-receptor active peptide (SFLLRN), demonstrating the involvement of PAR-1 in this process. PKC delta and epsilon were located constitutively in the membrane fraction in stellate astrocytes. Isoforms gamma, eta, theta, and zeta were abs ent from astrocytes. These results suggest that astrogliosis in vivo m ight be regulated by modulating the activity of thrombin, PAR-1, or sp ecific PKC isoforms.