Brief left ventricular pressure overload reduces myocardial apoptosis

Hypertrophic preconditioning attenuates myocardial ischemia/reperfusion injury through the deacetylation of isocitrate dehydrogenase 2

To test the hypothesis that transient nonischemic stimulation of hypertrophy would render the heart resistant to subsequent ischemic stress, short-term transverse aortic constriction (TAC) was performed in mice and then withdrawn for several days by aortic debanding, followed by subsequent myocardial exposure to ischemia/reperfusion (I/R). Following I/R injury, the myocardial infarct size and apoptosis were markedly reduced, and contractile function was significantly improved in the TAC preconditioning group compared with the control group. Mechanistically, hypertrophic preconditioning remarkably alleviated I/R-induced oxidative stress, as evidenced by the increased reduced nicotinamide adenine dinucleotide phosphate (NADPH)/nicotinamide adenine dinucleotide phosphate (NADP) ratio, increase in the reduced glutathione (GSH)/oxidized glutathione (GSSH) ratio, and reduced mitochondrial reactive oxygen species (ROS) production. Moreover, TAC preconditioning inhibited caspase-3 activation and mitigated the mitochondrial impairment by deacetylating isocitrate dehydrogenase 2 (IDH2) via a sirtuin 3 (SIRT3)-dependent mechanism. In addition, the expression of a genetic deacetylation mimetic IDH2 mutant (IDH2 K413R) in cardiomyocytes, which increased IDH2 enzymatic activity and decreased mitochondrial ROS production, and ameliorated I/R injury, whereas the expression of a genetic acetylation mimetic (IDH2 K413Q) in cardiomyocytes abolished these protective effects of hypertrophic preconditioning. Furthermore, both the activity and expression of the SIRT3 protein were markedly increased in preconditioned mice exposed to I/R. Treatment with an adenovirus encoding SIRT3 partially emulated the actions of hypertrophic preconditioning, whereas genetic ablation of SIRT3 in mice blocked the cardioprotective effects of hypertrophic preconditioning. The present study identifies hypertrophic preconditioning as a novel endogenous self-defensive and cardioprotective strategy for cardiac I/R injury that induces IDH2 deacetylation through a SIRT3-dependent mechanism. A therapeutic strategy targeting IDH2 may be a promising treatment for cardiac ischemic injury.

Hypertrophic Preconditioning Attenuates Myocardial Ischaemia-Reperfusion Injury by Modulating SIRT3-SOD2-mROS-Dependent Autophagy

Background

Ischaemic preconditioning elicited by brief periods of coronary occlusion and reperfusion protects the heart from a subsequent prolonged ischaemic insult. Here, we test the hypothesis that short‐term non‐ischaemic stimulation of hypertrophy renders the heart resistant to subsequent ischaemic injury.

Methods and Results

Transient transverse aortic constriction (TAC) was performed for 3 days in mice and then withdrawn for 4 days by aortic debanding, followed by subsequent exposure to myocardial ischaemia‐reperfusion (I/R) injury. Following I/R injury, myocardial infarct size and apoptosis were significantly decreased, and cardiac dysfunction was markedly improved in the TAC preconditioning group compared with the control group. Mechanistically, TAC preconditioning markedly suppressed I/R‐induced autophagy and preserved autophagic flux by deacetylating SOD2 via a SIRT3‐dependent mechanism. Moreover, treatment with an adenovirus encoding SIRT3 partially mimicked the effects of hypertrophic preconditioning, whereas genetic ablation of SIRT3 in mice blocked the cardioprotective effects of hypertrophic preconditioning. Furthermore, in vivo lentiviral‐mediated knockdown of Beclin 1 in the myocardium ameliorated the I/R‐induced impairment of autophagic flux and was associated with a reduction in cell death, whereas treatment with a lentivirus encoding Beclin 1 abolished the cardioprotective effect of TAC preconditioning.

Conclusions

The present study identifies TAC preconditioning as a novel strategy for induction of an endogenous self‐defensive and cardioprotective mechanism against cardiac injury. Specifically, TAC preconditioning reduced myocardial autophagic cell death in a SIRT3/SOD2 pathway‐dependent manner.

Hypertrophic preconditioning cardioprotection after myocardial ischaemia/reperfusion injury involves ALDH2-dependent metabolism modulation

Brief episodes of ischaemia and reperfusion render the heart resistant to subsequent prolonged ischaemic insult, termed ischaemic preconditioning. Here, we hypothesized that transient non-ischaemic stress by hypertrophic stimulation would induce endogenous cardioprotective signalling and enhance cardiac resistance to subsequent ischaemic damage. Transient transverse aortic constriction (TAC) or Ang-Ⅱ treatment was performed for 3-7 days in male mice and then withdrawn for several days by either aortic debanding or discontinuing Ang-Ⅱ treatment, followed by subsequent exposure to regional myocardial ischaemia by in situ coronary artery ligation. Following ischaemia/reperfusion (I/R) injury, myocardial infarct size and apoptosis were markedly reduced and contractile function was significantly improved in the TAC preconditioning group compared with that in the control group. Similar results were observed in mice receiving Ang-Ⅱ infusion. Mechanistically, TAC preconditioning enhanced ALDH2 activity, promoted AMPK activation and improved mitochondrial energy metabolism by increasing myocardial OXPHOS complex expression, elevating the mitochondrial ATP content and improving viable myocardium glucose uptake. Moreover, TAC preconditioning significantly mitigated I/R-induced myocardial iNOS/gp91^phox activation, inhibited endoplasmic reticulum stress and ameliorated mitochondrial impairment. Using a pharmacological approach to inhibit AMPK signalling in the presence or absence of preconditioning, we demonstrated AMPK-dependent protective mechanisms of TAC preconditioning against I/R injury. Furthermore, treatment with adenovirus-encoded ALDH2 partially emulated the actions of hypertrophic preconditioning, as evidenced by improved mitochondrial metabolism, inhibited oxidative stress-induced mitochondrial damage and attenuated cell death through an AMPK-dependent mechanism, whereas genetic ablation of ALDH2 abrogated the aforementioned actions of TAC preconditioning. The present study demonstrates that preconditioning with hypertrophic stress protects the heart from I/R injury via mechanisms that improve mitochondrial metabolism, reduce oxidative/nitrative stress and inhibit apoptosis. ALDH2 is obligatorily required for the development of cardiac hypertrophic preconditioning and acts as the mediator of this process.

NLRX1 attenuates apoptosis and inflammatory responses in myocardial ischemia by inhibiting MAVS-dependent NLRP3 inflammasome activation

Increasing evidence suggests that inflammation and apoptosis are involved in the development of acute myocardial ischemia (AMI). Nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) have recently been identified as key mediators of inflammatory responses. The aim of this study was to explore the specific role and the underlying regulatory mechanism of NLRX1 in myocardial ischemic injury. The results show that NLRX1, located in mitochondria, was significantly down-regulated in AMI tissues and hypoxia-induced H9c2 cells. Overexpression of NLRX1 markedly decreased the levels of lactate dehydrogenase (LDH), creatine kinase-MB (CK-MB) and cardiac troponin-I (cTn-I), down-regulated the production of IL-1β，IL-18 and IL-6, and reduced apoptosis induced by hypoxia. Conversely, depletion of NLRX1 with small interfering RNA (siRNA) aggravated hypoxia-induced ischemic injury. We then demonstrated that NLRX1 was associated with the mitochondrial antiviral signaling protein (MAVS) and regulated MAVS-dependent NLRP3 inflammasome activation. NLRX1 overexpression significantly inhibited hypoxia-induced up-regulation of MAVS, NLRP3 and Caspase-1 expression. Additionally, the negative effects of NLRX1 overexpression on hypoxia-induced inflammatory factor production and apoptosis were neutralized by MAVS or NLRP3 overexpression. Taken together, these findings suggest that NLRX1 may function as a cardiac-protective molecule in myocardial ischemic injury by repressing inflammation and apoptosis; the biological effects appear to be mediated by the inhibition of MAVS-dependent NLRP3 inflammasome activation.

Baicalein Reduces Liver Injury Induced by Myocardial Ischemia and Reperfusion

Baicalein is a component of the root of Scutellaria baicalensis Georgi, which has traditionally been used to treat liver disease in China. In the present study, we investigated baicalein' ability to reduce the liver injury induced by myocardial ischemia and reperfusion (I/R). Myocardial I/R was induced in this experiment by a 40[Formula: see text]min occlusion of the left anterior descending coronary artery and a 3[Formula: see text]h reperfusion in rats. The induced myocardial I/R significantly increased the serum levels of aspartate transaminase (AST) and alanine transaminase (ALT), indicating the presence of liver injury. Hepatic apoptosis was significantly increased. The serum levels of tumor necrosis factor-[Formula: see text] (TNF-[Formula: see text]), interleukin-1[Formula: see text] (IL-1[Formula: see text]), and interleukin-6 (IL-6) were significantly elevated, as was the TNF-[Formula: see text] level in the liver. Intravenous pretreatment with baicalein (3, 10, or 30[Formula: see text]mg/kg) 10[Formula: see text]min before myocardial I/R significantly reduced the serum level increase of AST and ALT, apoptosis in the liver, and the elevation of TNF-[Formula: see text], IL-1[Formula: see text], and IL-6 levels. Moreover, baicalein increased Bcl-2 and decreased Bax in the liver. Phosphorylation of the prosurvival kinases, including Akt and extracellular signal-regulated kinases 1 and 2 (ERK1/2), was also increased. In conclusion, we found that baicalein can reduce the liver injury induced by myocardial I/R. The underlying mechanisms are likely related to the inhibition of the extrinsic and intrinsic apoptotic pathways, possibly via the inhibition of TNF-[Formula: see text] production, the modulation of Bcl-2 and Bax, and the activation of Akt and ERK1/2. Our findings may provide a rationale for the application of baicalein or traditional Chinese medicine containing large amounts of baicalein to prevent liver injury in acute myocardial infarction and cardiac surgery.