Microglial Ring1 enhances post-phagocytic myelin debris processing: Attenuation of cognitive dysfunction after hemorrhagic shock and reperfusion.

Cerebral ischemia-reperfusion induces myelin injury, resulting in cognitive impairment. Efficient clearance of myelin debris is important for neural repair. The E3 ubiquitin ligase Ring1 (RING finger protein 1) participates in ubiquitin signaling and gene expression regulation, However, whether Ring1 ameliorates cerebral ischemia-reperfusion injury-induced cognitive impairment by promoting microglial post-phagocytic myelin debris processing remains unknown. In this study, we employed a hemorrhagic shock and reperfusion model, a hippocampal myelin debris injection model, and an in vitro microglia-myelin debris co-culture model to simulate cerebral ischemia-reperfusion injury, and combined these models with proteomic and transcriptomic analyses and Ring1 gain- and loss-of-function approaches. Hemorrhagic shock and reperfusion induced hippocampal myelin injury and cognitive dysfunction, while hippocampal administration of myelin debris further impaired cognition. Transcriptomic analysis identified Ring1 as a candidate regulator associated with postphagocytic myelin debris processing. Ring1 overexpression alleviated cognitive deficits and hippocampal myelin injury and restored mitochondrial DNA-encoded gene expression and adenosine triphosphate levels after hemorrhagic shock and reperfusion. In contrast, Ring1 knockdown in the microglia-myelin debris co-culture model reduced mitochondrial DNAencoded gene expression and adenosine triphosphate levels and delayed post-phagocytic myelin debris processing. Mechanistically, Ring1 interacted with mitochondrial transcription factor B2, with K27-linked ubiquitin signals detected in Ring1- and mitochondrial transcription factor B2-containing immunocomplexes. Ring1 depletion reduced mitochondrial transcription factor B2-associated K27-linked ubiquitin signaling, mitochondrial DNA-encoded gene expression, adenosine triphosphate levels, and post-phagocytic myelin debris processing. Collectively, our findings suggest that Ring1 attenuates hemorrhagic shock and reperfusion-related cognitive impairment by promoting microglial post-phagocytic myelin debris processing through mitochondrial transcription factor B2-associated K27-linked ubiquitin signaling and mitochondrial regulation.