Deletion of Bak1 alleviates microglial necroptosis and neuroinflammation after experimental subarachnoid hemorrhage.

Microglial necroptosis exacerbates neurodegenerative diseases, central nervous system (CNS) injury and demonstrates a pro-inflammatory process, but its contribution to subarachnoid hemorrhage (SAH) is poorly characterized. BCL-2 homologous antagonist-killer protein (Bak1), a critical regulatory molecule of endogenous apoptosis, can be involved in the pathological process of necroptosis by regulating mitochondrial permeability. In this study, we revealed microglia undergo necroptosis after SAH in vivo and vitro. Western blot revealed that Bak1 was elevated at 24h after SAH. Knocked-down of Bak1 by adeno-associated virus attenuates microglial necroptosis, alleviates neuroinflammation, and improves neurological function after SAH in mice. Furthermore, oxyhemoglobin (10μM) induced necroptosis in BV2 microglia, increasing Bak1 expression and mediating pro-inflammatory phenotype transformation, exacerbating oxidative stress and neuroinflammation. Abrogating BV2 Bak1 could reduce necroptosis by downregulating the expression of phosphorylated pseudokinase mixed lineage kinase domain-like protein (p-MLKL), then downregulating pro-inflammatory phenotype gene expression. RNA-Seq showed that disrupting BV2 Bak1 downregulates multiple immune and inflammatory pathways and ameliorates cell injury by elevating Thrombospondin 1 (THBS1) expression. In summary, we identified a critical regulatory role for Bak1 in microglial necroptosis and neuroinflammation after SAH. Bak1 is expected to be a potential target for the treatment strategy of SAH.