CircTLK1 Modulates Sepsis-Induced Cardiomyocyte Apoptosis via Enhancing PARP1/HMGB1 Axis-Mediated Mitochondrial DNA Oxidative Damage by Sponging miR-17-5p

Background: Septic cardiomyopathy is a primary complication of sepsis with higher mortality rate, but specific therapy for it remains limited. This study evaluated the role and novel mechanisms of circTLK1 in septic cardiomyopathy. Methods: Lipopolysaccharide (LPS)-challenged HCM cells and cecal ligation and puncture (CLP)-treated rats were used as in vitro and in vivo models of septic cardiomyopathy. Cell viability and apoptosis were detected by CCK8, TUNEL and flow cytometry. LDH, CK, SOD, MDA, ATP, 8-OHdG and NAD+/NADH ratio were evaluated using commercial kits. qRT-PCR and western blotting were performed for determining mRNA and protein levels. MitoSOX Red staining, JC-1 staining, and immunofluorescent staining were used for detecting ROS level, mitochondrial membrane potential, and cytochrome C distribution, respectively. Mitochondrial DNA (mtDNA) copy number and transcription were assessed by quantitative PCR. The effect of PARP1 on HMGB1 acetylation was detected by co-immunoprecipitation. The interaction between circTLK1/PARP1 and miR-17-5p was verified by dual luciferase assay and RNA immunoprecipitation. Results: CircTLK1, PARP1 and HMGB1 were up-regulated in HCM cells and myocardial tissues induced by sepsis. Inhibition of circTLK1 restrained LPS-induced PARP1 and HMGB1 expression. Moreover, suppression of circTLK1 repressed sepsis-induced mtDNA oxidative damage, mitochondrial dysfunction and consequent cardiomyocyte apoptosis by inhibiting PARP1/HMGB1 axis in vitro and in vivo. In addition, circTLK1 enhanced PARP1 expression via sponging miR-17-5p. Inhibition of miR-17-5 abolished the protection of circTLK1 silencing against oxidative mtDNA damage-mediated cardiomyocyte apoptosis. Conclusion: CircTLK1 sponged miR-17-5p to promote mtDNA oxidative damage, mitochondrial dysfunction, and cardiomyocyte apoptosis via activating PARP1/HMGB1 axis. Funding Statement: This work was supported by the grants from the National Natural Sciences Foundation of China (81671969), Key Laboratory of Emergency Medicine for Children, and Ministry of Science and Technology of Hunan Province (2018TP1028). Declaration of Interests: The authors declare that they have no conflict of interest. Ethics Approval Statement: All experiments performed were approved by the Animal Care and Use Committee of Hunan Children’s Hospital.