Plasminogen-induced IL-1β and TNF-α production in microglia is regulated by reactive oxygen species

Microglia, major immune effector cells in the central nervous system, become activated during brain injury. In this study we showed that the blood component plasminogen/plasmin activates microglia. Plasminogen-induced IL-1β, TNF-α, and iNOS mRNA expression in primary cultured rat microglia and BV2 murine microglial cells. Plasmin caused a similar response. Serine protease inhibitors suppressed both plasminogen- and plasmin-induced IL-1β and TNF-α expression, indicating the importance of serine protease activity in plasminogen/plasmin activation of microglia. Reactive oxygen species (ROS) appeared to play an important role in plasminogen-induced microglial activation, with ROS being generated within 15 min of plasminogen treatment, and antioxidants (100 μM trolox and 10 mM NAC) reducing IL-1β and TNF-α expression in plasminogen-treated cells. Furthermore, plasminogen stimulated CREB and NF-κB DNA binding activity, and this activation was also reduced by trolox and NAC. These results suggest that plasminogen activates microglia via stimulation of ROS production.