ALKBH5 ALLEVIATES HYPOXIA POSTCONDITIONING INJURY IN d -GALACTOSE-INDUCED SENESCENT CARDIOMYOCYTES BY REGULATING STAT3

SIRT3 MEDIATES THE CARDIOPROTECTIVE EFFECT OF THERAPEUTIC HYPOTHERMIA AFTER CARDIAC ARREST AND RESUSCITATION BY RESTORING AUTOPHAGIC FLUX VIA THE PI3K/AKT/MTOR PATHWAY

ABSTRACT

Background : Postresuscitation cardiac dysfunction is a significant contributor to early death following cardiopulmonary resuscitation (CPR). Therapeutic hypothermia (TH) mitigates myocardial dysfunction due to cardiac arrest (CA); however, the underlying mechanism remains unclear. Sirtuin 3 (Sirt3) was found to affect autophagic activity in recent research, motivating us to investigate its role in the cardioprotective effects of TH in the treatment of CA. Methods : Sprague-Dawley rats were used to establish an in vivo CA/CPR model and treated with a selective Sirt3 inhibitor or vehicle. Survival rate, myocardial function, autophagic flux, and Sirt3 expression and activity were evaluated. H9C2 cells were subjected to oxygen-glucose deprivation/reoxygenation (OGD/R) injury in vitro . The cells were transfected with Sirt3-siRNA and treated with the autophagy inhibitor chloroquine or the PI3K inhibitor LY294002, and cell viability and autophagic flux were assessed. Results : Rats exhibited decreased survival and impaired cardiac function after CA/CPR, which were alleviated by TH. Mechanistically, TH restored Sirt3 expression and autophagic flux, which were impaired by CA/CPR. Sirt3 inactivation diminished the capacity of TH to restore autophagic flux and partially abolished the improvements in myocardial function and survival. An in vitro study further showed that TH-induced restoration of disrupted autophagic flux by OGD/R was attenuated by pretreatment with Sirt3-siRNA, and this attenuation was partially rescued by the inhibition of PI3K/Akt/mTOR signaling cascades. Conclusions : Sirt3 mediates the cardioprotective effect of TH by restoring autophagic flux via the PI3K/Akt/mTOR pathway. These findings suggest the potential of Sirt3 as a therapeutic target for CA.

Epitranscriptomic regulation in fasting hearts: implications for cardiac health

Cardiac tolerance to ischaemia can be increased by dietary interventions such as fasting, which is associated with significant changes in myocardial gene expression. Among the possible mechanisms of how gene expression may be altered are epigenetic modifications of RNA - epitranscriptomics. N6-methyladenosine (m6A) and N6,2'-O-dimethyladenosine (m6Am) are two of the most prevalent modifications in mRNA. These methylations are reversible and regulated by proteins called writers, erasers, readers, and m6A-repelled proteins. We analysed 33 of these epitranscriptomic regulators in rat hearts after cardioprotective 3-day fasting using RT-qPCR, Western blot, and targeted proteomic analysis. We found that the most of these regulators were changed on mRNA or protein levels in fasting hearts, including up-regulation of both demethylases - FTO and ALKBH5. In accordance, decreased methylation (m6A+m6Am) levels were detected in cardiac total RNA after fasting. We also identified altered methylation levels in Nox4 and Hdac1 transcripts, both of which play a role in the cytoprotective action of ketone bodies produced during fasting. Furthermore, we investigated the impact of inhibiting demethylases ALKBH5 and FTO in adult rat primary cardiomyocytes (AVCMs). Our findings indicate that inhibiting these demethylases reduced the hypoxic tolerance of AVCMs isolated from fasting rats. This study showed that the complex epitranscriptomic machinery around m6A and m6Am modifications is regulated in the fasting hearts and might play an important role in cardiac adaptation to fasting, a well-known cardioprotective intervention.

DEXMEDETOMIDINE AMELIORATES ACUTE BRAIN INJURY INDUCED BY MYOCARDIAL ISCHEMIA-REPERFUSION VIA UPREGULATING THE HIF-1 PATHWAY

ABSTRACT

Objective: Neurological complications after myocardial ischemia/reperfusion (IR) injury remain high and seriously burden patients and their families. Dexmedetomidine (Dex), an α 2 agonist, is endowed with analgesic-sedative and anti-inflammatory effects. Therefore, our study aims to explore the mechanism and effect of Dex on brain damage after myocardial IR injury. Methods C57BL/6 mice were randomly divided into sham, IR, and IR + Dex groups, and myocardial IR models were established. The impact of Dex on brain injury elicited by myocardial IR was assessed via ELISA for inflammatory factors in serum and brain; Evans blue for blood-brain barrier permeability; hematoxylin-eosin staining for pathological injury in brain; immunofluorescence for microglia activation in brain; Morris water maze for cognitive dysfunction; western blot for the expression level of HIF-1α, occludin, cleaved caspase-3, NF-κB p65, and p-NF-κB p65 in the brain. In addition, HIF-1α knockout mice were used to verify whether the neuroprotective function of Dex is associated with the HIF-1 pathway. Results: Dex was capable of reducing myocardial IR-induced brain damage including inflammatory factor secretion, blood-brain barrier disruption, neuronal edema, microglial activation, and acute cognitive dysfunction. However, the protective role of Dex was attenuated in HIF-1α knockout mice. Conclusion: Dex protects against myocardial IR-induced brain injury, and the neuroprotection of Dex is at least partially dependent on the activation of the HIF-1 pathway.