Dataset Information

Melatonin as a therapy in cardiac ischemia-reperfusion injury: Potential mechanisms by which MT2 activation mediates cardioprotection.

ABSTRACT:

Introduction

Previous studies reported the beneficial effects of pretreatment with melatonin on the heart during cardiac ischemia/reperfusion (I/R) injury. However, the effects of melatonin given after cardiac ischemia, as well as its comparative temporal effects are unknown. These include pretreatment, during ischemia, and at the onset of reperfusion. Also, the association between melatonin receptors and cardiac arrhythmias, mitochondrial function and dynamics, autophagy, and mitophagy during cardiac I/R have not been investigated.

Objectives

We tested two major hypotheses in this study. Firstly, the temporal effect of melatonin administration exerts different cardioprotective efficacy during cardiac I/R. Secondly, melatonin provides cardioprotective effects via MT2 activation, leading to improvement in cardiac mitochondrial function and dynamics, reduced excessive mitophagy and autophagy, and decreased cardiac arrhythmias, resulting in improved LV function.

Methods

Male rats were subjected to cardiac I/R, and divided into 4 intervention groups: vehicle, pretreatment with melatonin, melatonin given during ischemia, and melatonin given at the onset of reperfusion. In addition, either a non-specific melatonin receptor (MT) blocker or specific MT2 blocker was given to rats.

Results

Treatment with melatonin at all time points alleviated cardiac I/R injury to a similar extent, quantified by reduction in infarct size, arrhythmia score, LV dysfunction, cardiac mitochondrial dysfunction, imbalance of mitochondrial dynamics, excessive mitophagy, and a decreased Bax/Bcl2 ratio. In H9C2 cells, melatonin increased %cell viability by reducing mitochondrial dynamic imbalance and a decrease in Bax protein expression. The cardioprotective effects of melatonin were dependent on MT2 activation.

Conclusion

Melatonin given before or after ischemia exerted equal levels of cardioprotection on the heart with I/R injury, and its beneficial effects on cardiac arrhythmias, cardiac mitochondrial function and dynamics were dependent upon the activation of MT2.

SUBMITTER: Singhanat K

PROVIDER: S-EPMC8020169 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:Little is known about the role of the neuropeptide somatostatin (SST) in myocardial ischemia/reperfusion injury and cardioprotection. Here, we investigated the direct cardiocytoprotective effect of SST on ischemia/reperfusion injury in cardiomyocyte cultures, as well as the expression of SST and its receptors in pig and human heart tissues. SST induced a bell-shaped, concentration-dependent cardiocytoprotection in both adult rat primary cardiomyocytes and H9C2 cells subjected to simulated ischemia/reperfusion injury. Furthermore, in a translational porcine closed-chest acute myocardial infarction model, ischemic preconditioning increased plasma SST-like immunoreactivity. Interestingly, SST expression was detectable at the protein, but not at the mRNA level in the pig left ventricles. SSTR1 and SSTR2, but not the other SST receptors, were detectable at the mRNA level by PCR and sequencing in the pig left ventricle. Moreover, remote ischemic conditioning upregulated SSTR1 mRNA. Similarly, SST expression was also detectable in healthy human interventricular septum samples at the protein level. Furthermore, SST-like immunoreactivity decreased in interventricular septum samples of patients with ischemic cardiomyopathy. SSTR1, SSTR2, and SSTR5 but not SST and the other SST receptors were detectable at the mRNA level by sequencing in healthy human left ventricles. In addition, in healthy human left ventricle samples, SSTR1 and SSTR2 mRNAs were expressed especially in vascular endothelial and some other cell types as detected by RNA Scope® in situ hybridization. This is the first demonstration that SST exerts a direct cardiocytoprotective effect against simulated ischemia/reperfusion injury. Moreover, SST is expressed in the heart tissue at the peptide level; however, it is likely to be of sensory neural origin since its mRNA is not detectable. SSTR1 and SSTR2 might be involved in the cardioprotective action of SST, but other mechanisms cannot be excluded.

Project description:Reperfusion injury after extended ischemia accounts for approximately 50% of myocardial infarct size, and there is no standard therapy. HDAC inhibition reduces infarct size and enhances cardiomyocyte autophagy and PGC1α-mediated mitochondrial biogenesis when administered at the time of reperfusion. Furthermore, a specific autophagy-inducing peptide, Tat-Beclin 1 (TB), reduces infarct size when administered at the time of reperfusion. However, since SAHA affects multiple pathways in addition to inducing autophagy, whether autophagic flux induced by TB maintains mitochondrial homeostasis during ischemia/reperfusion (I/R) injury is unknown. We tested whether the augmentation of autophagic flux by TB has cardioprotection by preserving mitochondrial homeostasis both in vitro and in vivo. Wild-type mice were randomized into two groups: Tat-Scrambled (TS) peptide as the control and TB as the experimental group. Mice were subjected to I/R surgery (45 min coronary ligation, 24 h reperfusion). Autophagic flux, mitochondrial DNA (mtDNA), mitochondrial morphology, and mitochondrial dynamic genes were assayed. Cultured neonatal rat ventricular myocytes (NRVMs) were treated with a simulated I/R injury to verify cardiomyocyte specificity. The essential autophagy gene, ATG7, conditional cardiomyocyte-specific knockout (ATG7 cKO) mice, and isolated adult mouse ventricular myocytes (AMVMs) were used to evaluate the dependency of autophagy in adult cardiomyocytes. In NRVMs subjected to I/R, TB increased autophagic flux, mtDNA content, mitochondrial function, reduced reactive oxygen species (ROS), and mtDNA damage. Similarly, in the infarct border zone of the mouse heart, TB induced autophagy, increased mitochondrial size and mtDNA content, and promoted the expression of PGC1α and mitochondrial dynamic genes. Conversely, loss of ATG7 in AMVMs and in the myocardium of ATG7 cKO mice abolished the beneficial effects of TB on mitochondrial homeostasis. Thus, autophagic flux is a sufficient and essential process to mitigate myocardial reperfusion injury by maintaining mitochondrial homeostasis and partly by inducing PGC1α-mediated mitochondrial biogenesis.