tPA (tissue-type Plasminogen Activator) is a serine protease that is secreted by vascular endothelial cells, fibroblasts, neurons, microglia, and astrocytes. The partially active single chain can be further processed to full activity by Plasmin, Kallikrein 1, or Coagulation Factor Xa. Active tPA converts Plasminogen to Plasmin, a fibrinolytic protease, by hydrolyzing an Arg-Val peptide bond in Plasminogen. Unusually high levels of tPA activity can result in excessive bleeding, and low levels of tPA activity can result in thrombosis or embolism. tPA-mediated breakdown of the extracellular is also involved in promoting synaptic plasticity, neurite outgrowth, and synapse remodeling. Human tPA contains an N-terminal fibronectin type-1 domain, an epidermal growth factor-like domain, two kringle domains, and a serine protease catalytic domain.