Thrombin-induced activation of cultured rodent microglia

Microglia are the resident immune cells of the CNS. Upon brain damage, thes e cells are rapidly activated and function as tissue macrophages. The first steps in this activation still remain unclear, but it is widely believed t hat substances released from damaged brain tissue trigger this process. In this article, we describe the effects of the blood coagulation factor throm bin on cultured rodent microglial cells. Thrombin induced a transient Ca2increase in microglial cells, which persisted in Ca2+-free media. It was bl ocked by thapsigargin, indicating that thrombin caused a Ca2+ release from internal stores. Preincubation with pertussis toxin did not alter the throm bin-induced [Ca2+](i) signal, whereas it was blocked by hirudin, a blocker of thrombin's proteolytic activity. Incubation with thrombin led to the pro duction of nitric oxide and the release of the cytokines tumor necrosis fac tor-alpha, interleukin-6, interleukin-12, the chemokine KC, and the soluble tumor necrosis factor-alpha receptor II and had a significant proliferativ e effect. Our findings indicate that thrombin, a molecule that enters the b rain at sites of injury, rapidly triggered microglial activation.