Thrombolysis by PLAT/tPA increases serum free IGF1 leading to a decrease of deleterious autophagy following brain ischemia.

ABSTRACT

Cerebral ischemia is a pathology involving a cascade of cellular mechanisms, leading to the deregulation of proteostasis, including macroautophagy/autophagy, and finally to neuronal death. If it is now accepted that cerebral ischemia induces autophagy, the effect of thrombolysis/energy recovery on proteostasis remains unknown. Here, we investigated the effect of thrombolysis by PLAT/tPA (plasminogen activator, tissue) on autophagy and neuronal death. In two in vitro models of hypoxia reperfusion and an in vivo model of thromboembolic stroke with thrombolysis by PLAT/tPA, we found that ischemia enhances neuronal deleterious autophagy. Interestingly, PLAT/tPA decreases autophagy to mediate neuroprotection by modulating the PI3K-AKT-MTOR pathways both in vitro and in vivo. We identified IGF1R (insulin-like growth factor I receptor; a tyrosine kinase receptor) as the effective receptor and showed in vitro, in vivo and in human stroke patients and that PLAT/tPA is able to degrade IGFBP3 (insulin-like growth factor binding protein 3) to increase IGF1 (insulin-like growth factor 1) bioavailability and thus IGF1R activation.Abbreviations AKT/protein kinase B thymoma viral proto-oncogene 1; EGFR epidermal growth factor receptor; Hx hypoxia; IGF1 insulin-like growth factor 1; IGF1R insulin-like growth factor I receptor; IGFBP3 insulin-like growth factor binding protein 3; Ka Kainate; MAP1LC3/LC3 microtubule-associated protein 1 light chain 3; MAPK/ERK mitogen-activated protein kinase; MTOR mechanistic target of rapamycin kinase; MTORC1 MTOR complex 1; OGD oxygen and glucose deprivation; OGDreox oxygen and glucose deprivation + reoxygentation; PepA pepstatin A1; PI3K phosphoinositide 3-kinase; PLAT/tPA plasminogen activator, tissue; PPP picropodophyllin; SCH77 SCH772984; ULK1 unc-51 like kinase 1; Wort wortmannin.