USP7 promotes PINK1/Parkin-dependent mitophagy to ameliorate cerebral ischemia-reperfusion injury by deubiquitinating and stabilizing SIRT1.

BACKGROUND

Cerebral ischemia-reperfusion (CI/R) injury, a major complication of ischemic stroke, is characterized by mitochondrial dysfunction and neuronal apoptosis, and understanding its underlying molecular mechanisms is essential for the development of effective therapeutic strategies. This study aimed to investigate the role of ubiquitin-specific protease 7 (USP7) in CI/R injury and elucidate its regulatory mechanisms.

METHODS

A rat model of middle cerebral artery occlusion/reperfusion (MCAO/R) and an in vitro neuronal model subjected to oxygen-glucose deprivation/reperfusion (OGD/R) were used to mimic CI/R injury. USP7 was overexpressed or knocked down, with or without co-treatment, using the autophagy inhibitor 3-methyladenine (3-MA). Neurological function was evaluated using standardized scoring systems, and cerebral infarct volume was quantified by TTC staining. Histopathological changes in the cortex and hippocampus were assessed using hematoxylin-eosin (HE) and Nissl staining. Neuronal viability and apoptosis were measured by CCK-8 assay, TUNEL staining, and flow cytometry. To assess cellular metabolism and oxidative stress, ATP and LDH levels, along with antioxidant markers (including SOD, GSH, and GSH-Px), were analyzed using commercial biochemical kits. Mitochondrial morphology and autophagosome formation were visualized using transmission electron microscopy. Gene and protein expression levels were quantified by qRT-PCR and Western blotting, respectively. Immunofluorescence microscopy was performed to evaluate the subcellular localization of target proteins and co-localization with mitochondrial membrane markers. Lastly, protein-protein interactions and ubiquitination modification were analyzed by co-immunoprecipitation assays.

RESULTS

USP7 overexpression significantly alleviated neurological deficits, reduced infarct volume, attenuated histological damage, and decreased neuronal apoptosis in the MCAO/R model. Similarly, in the OGD/R model, USP7 overexpression markedly enhanced neuronal viability, suppressed apoptosis, restored ATP production, improved antioxidant capacity (as evidenced by increased levels of SOD, GSH, and GSH-Px), and reduced LDH release. Mechanistically, USP7 stabilized SIRT1 protein expression through deubiquitination, which in turn activated the PINK1/Parkin pathway and enhanced mitophagy. This activation was demonstrated by an increased LC3II/LC3I ratio, elevated ATG5 expression, enhanced co-localization of Tomm20 and Parkin, and increased autophagosome formation. Moreover, these protective effects were abolished when either 3-MA treatment was applied or SIRT1/PINK1 expression was knocked down.

CONCLUSION

USP7 mitigates CI/R injury by promoting PINK1/Parkin-dependent mitophagy through SIRT1 deubiquitination and stabilization, suggesting USP7 as a potential therapeutic target for ischemic stroke.