Extracellular serine proteases play important roles in the central nervous system (CNS) by modifying extracellular environments. Prothrombin is expressed in the CNS and thrombin has been shown to have inhibitory function on neurite extension, however, its physiological function is not fully understood. Tissue plasminogen activators (tPA) has important function on neural plasticity in ocular dominance and long-term potentiation (LTP). tPA also has crucial function in the excitotoxic neuronal cell death through the activation of plasminogen. Beyond these proteases, several kallikrein family proteases including neuropsin and protease M are expressed in the CNS. Neuropsin is mainly expressed in the neurons of the limbic system and has important in the neural plasticity such as LTP and kindling. Following injury, neuropsin is induced in oligodendrocytes and may be related to demyelination. Protease M is constitutively expressed in oligodendrocytes and may have scavenging function. Other kallikrein family proteases are expressed in the CNS but their functions remained to be clarified.
