Low Post‐ischemic Recovery of SIRT3 Deficient Mouse Heart is Not Associated with Oxidative Damage of Mitochondrial Proteins and Genome

Background Sirtuins are NAD + ‐dependent deacetylases that regulate cell metabolism through protein acetylation/deacetylation. Among mitochondrial isoforms (SIRT3–5), SIRT3 is the major deacetylase. Recent studies demonstrated that SIRT3 can affect the activity of cyclophilin D (CyP‐D), a key regulator of the mitochondrial permeability transition pore (mPTP). mPTP opening occurs in response to oxidative stress due to increased mitochondrial Ca 2+ , Pi, and ROS, and initiates mitochondria‐mediated cell death. Hyperacetylation of CyP‐D due to downregulation of SIRT3 could lead to an increase in mPTP formation. Here, we elucidated the possible role of mitochondrial oxidative stress in cardiac dysfunction induced by ischemia‐reperfusion (IR) in SIRT3 knockout (SIRT3 −/− ) mice. Methods Male wild type (WT) and SIRT3 −/− mice hearts were subjected to IR by the Langendorff‐mode perfusion in the presence or absence of the mPTP inhibitor, sanglifehrin A (SfA). Results Hearts of SIRT3 −/− mice exhibited significantly (P<0.001) less recovery of cardiac function at the end of reperfusion when compared to WT mice. SfA had no protective effects on post‐ischemic recovery of WT and SIRT3 −/− hearts. However, activity of lactate dehydrogenase, a marker for tissue damage, in the cardiac effluent was significantly (P<0.004) higher in SIRT3 −/− mice compared to WT counterparts, and this effect was prevented by SfA during the first ten minutes of reperfusion. In addition, mitochondria from SIRT3 −/− hearts exhibited high basal swelling (P<0.046), and Ca 2+ ‐induced swelling was prevented by SfA in vitro in mitochondria from both WT and SIRT3 −/− hearts. Ca 2+ ‐stimulated hydrogen peroxide production was significantly (P<0.0003) higher in SIRT3 −/− mitochondria but this effect was lost (P<0.005) in SIRT3 −/− mitochondria from hearts perfused with SfA. Notably, carbonylation of mitochondrial proteins was not affected in SIRT3 −/− liver. Mitochondria of SIRT3 −/− liver showed increased acetylation of proteins (P<0.001), despite increased SIRT4 (P<0.0073) levels. Mitochondrial SOD (SOD2) expression in liver mitochondria of SIRT3 −/− mice was higher (P<0.041) than that of WT. The protein level of the base excision repair enzyme, OGG‐1 that effectively removes DNA damage induced by oxidative stress was significantly (P< 0.01) increased in SIRT3 −/− liver mitochondria and the integrity of mitochondrial DNA was not affected. Conclusion SIRT3 deficiency exacerbates cardiac dysfunction during post‐ischemic recovery, and increases mPTP and ROS generation without oxidative damage to mitochondrial proteins and DNA. Absence of SIRT3 leads to upregulation of mitochondrial SIRT4, SOD2, and OGG‐1 suggesting the development of a compensatory response in SIRT3 −/− mice in order to preserve mitochondrial integrity. Support or Funding Information SC1HL118669 NHLBI NIH, and R25‐GM061838 MBRS‐RISE NIH Grants