Proliferation of rat astrocytes, but not of oligodendrocytes, is stimulated in vitro by protease inhibitors.

Various natural protease inhibitors stimulate the proliferation of rat astrocytes grown in primary culture in the absence of serum. They are inactive on the proliferation of oligodendrocytes. The mean level of stimulation of the astrocyte proliferation elicited by the protease inhibitors is higher when the cells are in the growth phase, at low cell density than when they are quiescent, at high cell density. Among the protease inhibitors tested three serum proteins, alpha 1-antitrypsin, alpha 2-macroglobulin and anti-thrombin III were the most active. The present results, taken together with our previous finding that thrombin and some other proteases also stimulate the proliferation of astroglial cells but not of oligodendroglial cells, suggest that proteases and protease inhibitors participate, through still unclear mechanisms, in the control of the proliferation of astrocytes, but not in that of oligodendrocytes, during brain ontogenesis.