Anti-apoptotic effects of myocardin-related transcription factor-A on rat cardiomyocytes following hypoxia-induced injury

Myocardin-related transcription factor A, regulated by serum response factor, contributes to diabetic cardiomyopathy in mice

AIMS

Diabetic cardiomyopathy is a significant contributor to the global pandemic of heart failure. In the present study we investigated the involvement of myocardin-related transcription factor A (MRTF-A), a transcriptional regulator, in this process.

MATERIALS AND METHODS

Diabetic cardiomyopathy was induced in mice by feeding with a high-fat diet (HFD) or streptozotocin (STZ) injection.

KEY FINDINGS

We report that MRTF-A was up-regulated in the hearts of mice with diabetic cardiomyopathy. MRTF-A expression was also up-regulated by treatment with palmitate in cultured cardiomyocytes in vitro. Mechanistically, serum response factor (SRF) bound to the MRTF-A gene promoter and activated MRTF-A transcription in response to pro-diabetic stimuli. Knockdown of SRF abrogated MRTF-A induction in cardiomyocytes treated with palmitate. When cardiomyocytes conditional MRTF-A knockout mice (MRTF-A CKO) and wild type (WT) mice were placed on an HFD to induce diabetic cardiomyopathy, it was found that the CKO mice and the WT mice displayed comparable metabolic parameters including body weight, blood insulin concentration, blood cholesterol concentration, and glucose tolerance. However, both systolic and diastolic cardiac function were exacerbated by MRTF-A deletion in the heart.

SIGNIFICANCE

These data suggest that MRTF-A up-regulation might serve as an important compensatory mechanism to safeguard the deterioration of cardiac function during diabetic cardiomyopathy.

MRTF-A alleviates myocardial ischemia reperfusion injury by inhibiting the inflammatory response and inducing autophagy

Myocardin-related transcription factor A (MRTF-A) has an inhibitory effect on myocardial infarction; however, the mechanism is not clear. This study reveals the mechanism by which MRTF-A regulates autophagy to alleviate myocardial infarct-mediated inflammation, and the effect of silent information regulator 1 (SIRT1) on the myocardial protective effect of MRTF-A was also verified. MRTF-A significantly decreased cardiac damage induced by myocardial ischemia. In addition, MRTF-A decreased NLRP3 inflammasome activity, and significantly increased the expression of autophagy protein in myocardial ischemia tissue. Lipopolysaccharide (LPS) and 3-methyladenine (3-MA) eliminated the protective effects of MRTF-A. Furthermore, simultaneous overexpression of MRTF-A and SIRT1 effectively reduced the injury caused by myocardial ischemia; this was associated with downregulation of inflammatory factor proteins and when upregulation of autophagy-related proteins. Inhibition of SIRT1 activity partially suppressed these MRTF-A-induced cardioprotective effects. SIRT1 has a synergistic effect with MRTF-A to inhibit myocardial ischemia injury through reducing the inflammation response and inducing autophagy.

Oxygen Delivery Approaches to Augment Cell Survival After Myocardial Infarction: Progress and Challenges

Myocardial infarction (MI), triggered by blockage of a coronary artery, remains the most common cause of death worldwide. After MI, the capability of providing sufficient blood and oxygen significantly decreases in the heart. This event leads to depletion of oxygen from cardiac tissue and consequently leads to massive cardiac cell death due to hypoxemia. Over the past few decades, many studies have been carried out to discover acceptable approaches to treat MI. However, very few have addressed the crucial role of efficient oxygen delivery to the injured heart. Thus, various strategies were developed to increase the delivery of oxygen to cardiac tissue and improve its function. Here, we have given an overall discussion of the oxygen delivery mechanisms and how the current technologies are employed to treat patients suffering from MI, including a comprehensive view on three major technical approaches such as oxygen therapy, hemoglobin-based oxygen carriers (HBOCs), and oxygen-releasing biomaterials (ORBs). Although oxygen therapy and HBOCs have shown promising results in several animal and clinical studies, they still have a few drawbacks which limit their effectiveness. More recent studies have investigated the efficacy of ORBs which may play a key role in the future of oxygenation of cardiac tissue. In addition, a summary of conducted studies under each approach and the remaining challenges of these methods are discussed.

An ultrasound activated oxygen generation nanosystem specifically alleviates myocardial hypoxemia and promotes cell survival following acute myocardial infarction

Hypoxemia after acute myocardial infarction (AMI) causes severe damage to cardiac cells and induces cardiac dysfunction. Protection of cardiac cells and reconstruction of cardiac functions by re-introducing oxygen into the infarcted myocardium represents an efficient approach for the treatment of AMI. However, the established methods for oxygen supplementation mainly focus on systemic oxygen delivery, which always results in inevitable oxidative stress on normal tissues. In this work, an ultrasound (US) activated oxygen generation nanosystem has been developed, which specifically releases oxygen in the infarcted myocardium and alleviates the hypoxemic myocardial microenvironment to protect cardiac cells after AMI. The nanosystem was constructed through the formation of calcium peroxide in the mesopores of biocompatible mesoporous silica nanoplatforms, followed by the assembly of the thermosensitive material heneicosane and polyethyleneglycol. The mild hyperthermia induced by US irradiation triggered the phase change of heneicosane, thus achieving US responsive diffusion of water and release of oxygen. The US-activated oxygen release significantly alleviated the hypoxia and facilitated the mitigation of oxidative stress after AMI. Consequently, the survival of cardiac cells under hypoxic conditions was substantially improved and the damage in the infarcted myocardial tissue was minimized. This US-activated oxygen generation nanosystem may provide an efficient modality for the treatment of AMI.

MRTF-A promotes angiotensin II-induced inflammatory response and aortic dissection in mice

Aortic dissection (AD) is a major cause of acute aortic syndrome with high mortality due to the destruction of aortic walls. Although recent studies indicate the critical role of inflammation in the disease mechanism of AD, it is unclear how inflammatory response is initiated. Here, we demonstrate that myocardin-related transcription factor A (MRTF-A), a signal transducer of humoral and mechanical stress, plays an important role in pathogenesis of AD in a mouse model. A mouse model of AD was created by continuous infusion of angiotensin II (AngII) that induced MRTF-A expression and caused AD in 4 days. Systemic deletion of Mrtfa gene resulted in a marked suppression of AD development. Transcriptome and gene annotation enrichment analyses revealed that AngII infusion for 1 day caused pro-inflammatory and pro-apoptotic responses before AD development, which were suppressed by Mrtfa deletion. AngII infusion for 1 day induced pro-inflammatory response, as demonstrated by expressions of Il6, Tnf, and Ccl2, and apoptosis of aortic wall cells, as detected by TUNEL staining, in an MRTF-A-dependent manner. Pharmacological inhibition of MRTF-A by CCG-203971 during AngII infusion partially suppressed AD phenotype, indicating that acute suppression of MRTF-A is effective in preventing the aortic wall destruction. These results indicate that MRTF-A transduces the stress of AngII challenge to the pro-inflammatory and pro-apoptotic responses, ultimately leading to AD development. Intervening this pathway may represent a potential therapeutic strategy.