SOD1 regulates CXCR4 transcription in cortical neurons for establishment of cerebral ischemic tolerance

INTRODUCTION: Understanding of cerebral ischemic tolerance could provide important insight into viable neuroprotective strategies against ischemic stroke. OBJECTIVES: To elucidate the function of superoxide dismutase 1 (SOD1) in cellular tolerance to ischemia and its underlying molecular mechanism. METHODS: Two-vessel occlusion of the carotid arteries and oxygen-glucose deprivation were used for modelling global ischemic preconditioning (IPC) and in vitro ischemic preconditioning models, respectively. Cleavage-Under-Targets-And-Tagmentation (CUT&Tag)-sequencing analysis was performed for mapping SOD1-whole genome-binding sites in cultured cortical neurons in the in vitro ischemic tolerance model. Cell fractionation and immunofluorescent staining were used for analyzing the subcellular localization of SOD1 in tissue and cultured neuronal cells. RESULTS: Here, we showed that cortex, striatum and thalamus, but not hippocampus, exhibited ischemic tolerance phenotypes after global IPC. Intriguingly, we found that SOD1 was accumulated in the cellular nucleus after IPC. Notably, cortex was the most responsive brain region in terms of neuronal SOD1 nuclear translocation in response to IPC. We further confirmed these observations in the cultured cortical neurons in the in vitro ischemic tolerance model. CUT&Tag-sequencing analysis revealed that SOD1 bound to promoter regions in cortical neurons, and its binding was significantly altered after IPC stimulus. Notably, SOD1 was most prominently accumulated at the gene promoter of CXCR4 after IPC, which was correlated with transcriptional activation of CXCR4. Furthermore, we found that upregulation of CXCR4 expression was accompanied by modulation of gene expression resulting in anti-apoptosis. Moreover, we showed that pharmacological manipulation of CXCR4 activity could regulate cell viability through STAT3 in cortical neurons. Finally, we found that SOD1 was required for CXCR4-STAT3-mediated apoptosis in the IPC-induced ischemic tolerance. CONCLUSION: Therefore, these results demonstrate a non-canonical transcription-regulatory function of SOD1 which regulates CXCR4-STAT3 pathway to confer ischemic tolerance in cortical neurons.