Abstract
Aim: Sirtuins are NAD+-dependent deacetylases that regulate cell metabolism through protein acetylation/deacetylation, and SIRT3 is the major deacetylase among mitochondrial isoforms. Here, we elucidated the possible role of acetylation of cyclophilin D, a key regulator of the mitochondrial permeability transition pore (mPTP), in mitochondria-mediated cardiac dysfunction induced by ischemia-reperfusion (IR) in wild type (WT) and SIRT3 knockout (SIRT3-/-) mice.Materials and Methods: Isolated and Langendorff-mode perfused hearts of WT and SIRT3-/- mice were subjected to 25-min global ischemia followed by 60-min of reperfusion in the presence or absence of the mPTP inhibitor, sanglifehrin A (SfA).Results: Analysis of mitochondrial sirtuins demonstrated that SIRT3 deficiency upregulated SIRT4 with no effect on SIRT5 expression. Hearts of SIRT3-/- mice exhibited significantly less recovery of cardiac function at the end of IR compared to WT mice. Intact (non-perfused) SIRT3-/- hearts exhibited an increased rate of Ca2+-induced swelling in mitochondria as an indicator of mPTP opening. However, there was no difference in mPTP opening and cyclophilin D acetylation between WT and SIRT3-/- hearts subjected to IR injury. Ca2+-stimulated H2O2 production was significantly higher in SIRT3-/- mitochondria that was prevented by SfA. Superoxide dismutase activity was lower in SIRT3-/- heart mitochondria subjected to IR which correlated with an increase in protein carbonylation. However, mitochondrial DNA integrity was not affected in SIRT3-/- hearts after IR.Conclusion: SIRT3 deficiency exacerbates cardiac dysfunction during post-ischemic recovery, and increases mPTP opening and ROS generation without oxidative damage to mitochondrial proteins and DNA.
Highlights
Amongst all post-translational modifications, acetylation is thought to be the most common and important for mitochondrial proteins
Hearts isolated from wild type (WT) and SIRT3−/− mice were evaluated in the following six groups: (1) WT, WT hearts; (2) S3 SIRT3−/−; WT-IR, WT hearts subjected to IR; WT-IS, WT hearts subjected to IR in the presence of 0.2 μM sanglifehrin A (SfA); S3-IR, SIRT3−/− hearts subjected to IR; S3-IS, SIRT3−/− hearts subjected to IR in the presence of 0.2 μM SfA
In order to assess the effects of SIRT3 ablation on cardiac function, hearts of WT and SIRT3−/− mice were subjected to ex vivo IR in the presence and absence of the mitochondrial permeability transition pore (mPTP) inhibitor, SfA
Summary
Amongst all post-translational modifications, acetylation is thought to be the most common and important for mitochondrial proteins. Over 60% of mitochondrial proteins contain acetylation sites and most of them are involved in energy metabolism (Baeza et al, 2016). At least in the mitochondria, has an inhibitory role, and an acetylated mitochondrial proteome would result in inhibition of mitochondrial metabolism and ATP synthesis. Acetylation/deacetylation of mitochondrial proteins is regulated by sirtuins. Sirtuins are NAD+-dependent deacetylases that play an essential role in cell metabolism as energy and redox sensors (Kim et al, 2006). SIRT3 is the major mitochondrial deacetylase (Lombard et al, 2007) that deacetylates and stimulates the activity of metabolic enzymes involved in fatty acid oxidation (Hirschey et al, 2010; Bharathi et al, 2013), glucose oxidation (Ozden et al, 2014), tricarboxylic acid cycle (Yu et al, 2012), and electron transfer chain (ETC) complexes (Vassilopoulos et al, 2014). The contribution of protein acetylation to coronary heart diseases such as IR has not been elucidated
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