TNFR2 Stimulation Promotes Mitochondrial Fusion Via Stat3/NF-kB-dependent OPA1 Expression

Background:The mechanisms underlying the protective roles of TNFR2 activation remain largely unknown for cardiomyocytes.Methods and results:Freshly isolated neonatal mouse cardiomyocytes(NMCMs)were treated with shRNA targeting TNFR1 followed by TNFa therapy,allowing for studying the effects of TNFR2 activation.These TNFR2 activated NMCMs exhibited an increased mitochondrial fusion process,which was evidenced by increased mitochondrial size and circularity index and decreased mitochondrial number per unit of area.These changes were associated mitochondrial membrane potential,intracellular ATP levels and oxygen consumption capacity.Importantly,increased OPA1 protein level induced by TNFR2 activation was responsible for this enhanced mitochondrial function,which could be attenuated by using siRNA targeting OPA1.In addition,we showed that both Stat3 and RelA bind to the promoter region of OPA1,and their interactions synergistically upregulated OPA1 expression at transcriptional levels.Moreover,the acetylation status of Stat3,specifically at lysine 370 or lysine 383,plays key roles in its interaction with RelA for a supercomplex formation.We also provided evidence that p300 modulated the Stat3 acetylation state,which has been tested in HEL293T cells and recapitulated in NMCMs.And this p300 mediated Stat3/RelA interaction was indispensible for upregulated OP1 expression.Finally,the beneficial effect of TNFR2 activation on enhanced OPA1 expression was validated in an in vivo transverse aortic constriction model where TNFR1 knock out mice showed much improved outcome compared with TNFR1 and TNFR2 double knock out mice.Conclusion:TFR2 activation confers protection for cardiomyocytes against stress via upregulating OPA expression for which p300 mediated acetylation of Stat3 facilitated its interaction with RelA to activate the transcriptional activity of OPA1,leading to improved mitochondrial morphology and function.