Catalytically inactive RIP1 and RIP3 deficiency protect against acute ischemic stroke by inhibiting necroptosis and neuroinflammation

Necroptosis, which is mediated by RIP1/RIP3/MLKL (receptor-interacting protein kinase 1/receptor-interacting protein kinase 3/mixed lineage kinase domain-like protein) signaling, is a critical process in the development of acute ischemic stroke. However, it is unclear precisely how necroptosis promotes the pathogenesis of acute ischemic stroke. In this experimental study in mice, we investigated how necroptosis loss-of-function mice, RIP1 kinase-dead mice, RIP3-deficiency mice, and MLKL-deficiency mice could be protected against cerebral injury after acute ischemic stroke. Insoluble RIP1, RIP3, and MLKL were all detected in the infarct area of the study mice, indicating activation of necroptosis. Two types of RIP1 kinase-dead mutant mice (Rip1(K45A/K45A) or Rip1(Δ/Δ)) were used to show that catalytically-inactive RIP1 can decrease the infarct volume and improve neurological function after MCAO/R (middle cerebral artery occlusion/reperfusion). Both Rip3(−/−) mice and Mlkl(−/−) mice were protected against acute ischemic stroke. In addition, necroptosis loss-of-function mice showed less inflammatory responses in the infarct area. Therefore, necroptosis and its accompanying inflammatory response can lead to acute injury following ischemia stroke. Our study provides new insight into the pathogenetic mechanisms of acute ischemic stroke, and suggests potential therapeutic targets for neuroprotection.