PHLDA1 Blockade Alleviates Cerebral Ischemia/Reperfusion Injury by Affecting Microglial M1/M2 Polarization and NLRP3 Inflammasome Activation

Cerebral ischemia/reperfusion injury is the main cause of neurological deficit following stroke. Pleckstrin homology-like domain, family A, member 1 (PHLDA1) is increasingly recognized as a critical determinant in immunological regulation and cell apoptosis, but its role in neuroinflammation during cerebral ischemia/reperfusion injury remains to be elucidated. In this study, middle cerebral artery occlusion/reperfusion (MCAO/R) in C57BL/6 mice and oxygen-glucose deprivation/reoxygenation (OGD/R) in BV-2 cells were used as models in vivo and in vitro, respectively. MACO/R mice and OGD/R cells were treated with scramble or PHLDA1 small interfering RNAs (siRNAs) to achieve the goal of PHLDA1 knockdown. The results showed that the expression of PHLDA1 was significantly increased in MCAO/R mice and OGD/R cells compared to their normal controls, respectively. Mice treated with PHLDA1 siRNA exhibited a lower degree of infarct volume and brain water content compared to the NC siRNA-treated mice. Notably, PHLDA1 knockdown switched the M1 pro-inflammatory phenotype to the M2 anti-inflammatory phenotype by decreasing the expression of M1 markers (i.e., CD16, TNF-α, IL-6 and IFN-γ, and iNOS) and elevating the expression of M2 markers (i.e., CD206, IL-4, IL-10, and Arg-1). Moreover, PHLDA1 knockdown suppressed the NLRP3 inflammasome activation by reducing NLRP3, ASC, cleaved caspase 1 and cleaved IL-1β expression. In summary, these results suggest that PHLDA1 blockade effectively alleviates the ischemia/reperfusion-induced cerebral injury by switching microglial M1/M2 polarization and inhibiting NLRP3 inflammasome activation. Targeting PHLDA1 could be considered as a novel strategy in the treatment against post-ischemic brain injury.