Smurf2-Mediated Ubiquitination of FOXO4 Regulates Oxygen-glucose Deprivation/Reperfusion-induced Pyroptosis of Cortical Neurons

BACKGROUND: Smad ubiquitination regulatory factor 2 (Smurf2) has been observed to alleviate ischemia-reperfusion injury. This study sought to explore the molecular mechanism of Smurf2-mediated forkhead box O4 (FOXO4) ubiquitination in oxygen-glucose deprivation/ reperfusion (OGD/R)-induced pyroptosis of cortical neurons. METHODS: Human cortical neurons (HCN-2) were subjected to OGD/R to establish a cell model of cerebral stroke. Smurf2, FOXO4, and doublecortin domain containing 2 (DCDC2) expressions were determined by RT-qPCR and Western blot. LDH release, pyroptosis-related proteins NLRP3, GSDMD-N, and cleaved-caspase-3, as well as inflammatory factors IL-1β and IL-18, were assessed by LDH assay kit, Western blot, and ELISA. The ubiquitination level of FOXO4 was determined by ubiquitination assay. The bindings of Smurf2 to FOXO4 and FOXO4 to DCDC2 were testified by Co-IP, ChIP, and dual-luciferase assays. Rescue experiments were designed to validate the role of FOXO4/DCDC2 in the pyroptosis of HCN-2 cells. RESULTS: Smurf2 was weakly expressed, while FOXO4 and DCDC2 were prominently expressed in OGD/R-treated HCN-2 cells. Smurf2 overexpression promoted LDH release, reduced NLRP3, GSDMD-N, and cleaved-caspase-3 proteins, and decreased IL-1β and IL-18 concentrations. Sumrf2 improved the ubiquitination level of FOXO4 to downregulate its protein level. FOXO4 is bound to the DCDC2 promoter to facilitate its transcription. Overexpression of FOXO4 or DCDC2 reversed the inhibition of Smurf2 overexpression on pyroptosis of OGD/Rtreated HCN-2 cells. CONCLUSION: Smurf2 overexpression facilitated the ubiquitination of FOXO4 to reduce its protein level, thereby suppressing DCDC2 transcription and restricting OGD/R-induced pyroptosis of cortical neurons.