PTP1B inhibitor alleviates deleterious microglial activation and neuronal injury after ischemic stroke by modulating ER stress-autophagy axis via PERK signaling in microglia
: Cerebral ischemia/reperfusion (IR) after ischemic stroke causes microglial activation which lead to neuronal injury. Protein tyrosine phosphatase 1B (PTP1B) emerges to be a positive regulator of neuroinflammation, yet the effect of its inhibition on microglial activation as well as cerebral IR injury is largely unknown. Here we explored whether PTP1B inhibitor sc-222227 attenuates microglial activation and mitigates neuronal injury after cerebral IR injury. Methods : Cerebral IR injury rat
... al IR injury rat model was induced by transient middle cerebral artery occlusion (MCAO) and reperfusion. PTP1B inhibitor sc-222227 was administered intracerebroventricularly 0.5 h before IR injury. Neurological deficits, infarct volume and brain water content were examined. In vitro IR injury model were established by oxygen glucose deprivation/reoxygenation (OGD/R) in rat primary microglia. PTP1B protein level, microglial activation, neuroinflammation, endoplasmic reticulum (ER) stress, autophagy and neuronal apoptosis were detected in vivo and/or in vitro using western blot, immunohistochemistry, immunofluorescence, ELISA and real-time PCR assay. Protein interaction were assessed by proximity ligation assay. Results : PTP1B expression were significantly increased after cerebral IR injury in vivo, and the enhancement was most prominent in microglia. PTP1B inhibitor reduced IR-induced microglial activation both in vitro and in vivo, and further attenuated IR-induced microglial ER stress and autophagy in rat. In vitro experiment showed PTP1B inhibitor mitigated OGD/R-induced microglial activation through inhibiting ER stress-dependent autophagy, whose effect was partly abolished by PERK activator CCT020312. The protein interaction between PTP1B and phosphorylated PERK were significantly increase in response to OGD/R in primary microglia. Finally, PTP1B inhibitor reduced neuronal apoptosis and improved neurologic function after cerebral IR injury in rat. Conclusions : PTP1B inhibitor ameliorated neuronal injury and neurologic deficits following cerebral IR injury via attenuating deleterious microglial activation and subsequent neuroinflammation through modulating ER stress-autophagy axis in microglia. Treatment targeting microglial PTP1B might be a potential therapeutic strategy for ischemic stroke treatment. Background 4 Ischemic stroke is a world-wide neurological disorder causing severe mortality and morbidity [1, 2]. While restoring cerebral bleed supply by vessel recanalization is the current treatment for ischemic stroke, the reperfusion process can induce inflammation and is a major cause of neuronal injury and unfavorable prognosis [3, 4]. Microglia, as the major resident immune cells of the central nervous system, play important role in mediating inflammatory response and brain injury upon diverse insults. After ischemic stroke, microglia become activated and release multipole proinflammatory cytokines which further result in deleterious and neurotoxic consequences . While reducing microglial activation and inhibit neuroinflammatory response is considered to be a promising therapeutic strategy for ischemic stroke, the underlining mechanisms of microglial activation after ischemic stroke is far from clear. Protein tyrosine phosphatase 1B (PTP1B) is a member of protein tyrosine phosphatase family which recently attracted much attention as a regulator of a variety of processes within the central nervous system. In addition to early findings of PTP1B's roles in mediating insulin signaling to regulate energy expenditure and adiposity [8, 9] , recent studies further revealed that PTP1B is highly expressed in microglia and is a positive regulator of neuroinflammation  . However, the roles of PTP1B in both ischemic stroke and microglia are still unclear, and based on current evidences it is possible that inhibition of PTP1B after ischemic stroke may exert neuroprotective effects by reducing neuroinflammation. Endoplasmic reticulum (ER) stress has been demonstrated to be involved in the neuronal injury after ischemia/reperfusion (IR) injury, and inhibition of ER stress effectively protected neuronal injury after ischemic stroke    . Several studies have also demonstrated the role of PTP1B in positively regulating ER stress, and inhibition of PTP1B significantly alleviated ER stress-induced neurotoxicity [15, 16] . Moreover, recent researches revealed that ER stress is involved in the microglial activation process which causes neuroinflammation [17, 18]. Autophagy is a lysosome-mediated self-degradation process which eliminates damaged or aged proteins and organelles and is recognized as an important element of innate immune response  . Newly emerged evidences showed complicated roles of autophagy to be both neuroprotective or 5 destructive in neuronal cell death , and various factors has been found to be involved in modulating autophagy. Studies have revealed the role of ER stress as an upstream trigger for autophagy induction , and recent researches further showed that ER stress-autophagy axis is involved in the acute neuronal injury caused by ischemic stroke-induced neuroinflammation and particularly, the microglial ER stress-autophagy axis was found to plays critical role in regulating microglial activation and subsequent neuroinflammation in response to external cocaine stimulation . The exact role of PTP1B in the ER stress and autophagy remained elusive, yet a recent study showed protective effects of PTP1B deletion for myocardial injury by obliterating ER stress through regulation of autophagy, indicating a potential involvement of PTP1B in the ER stress-autophagy axis. Based on these findings, in the present study we investigated whether pharmacological inhibition of PTP1B might be able to modulate microglial ER stress-autophagy axis, and we explore the effect of PTP1B inhibition against cerebral ischemia /reperfusion (IR) injury.