Tissue-type plasminogen activator rescues neurones from serum deprivation-induced apoptosis through a mechanism independent of its proteolytic activity.

Although the mechanism of action of tissue-type plasminogen activator (tPA) in excitotoxic necrosis is well documented, whether this serine protease can influence the apoptotic cascade remains a subject of debate. Here, we report that tPA protects cultured cortical neurones against apoptotic cell death induced by serum deprivation, an effect associated with a reduction of caspase-3 activation. Interestingly, blocking tPA proteolytic activity by either tPA stop or neuroserpin did not prevent this neuroprotection. Similarly, prevention of the interaction between tPA and its receptor low-density lipoprotein receptor-related protein (LRP) could not alter tPA anti-apoptotic activity. Interestingly, the survival-promoting effect of tPA was blocked by the phosphatidylinositol-3 (PI-3) kinase inhibitor, LY294002, but not by the mitogen-activated protein (MAP) kinase inhibitor, U0126. In conclusion, the present demonstration of an anti-apoptotic effect of tPA, independent of its enzymatic activity, reveals an additional level of complexity in our understanding of this critical mediator of brain physiology and pathology.