Metformin as a modulator of myocardial fibrosis postmyocardial infarction via regulation of cardiomyocyte-fibroblast crosstalk

Senescent cardiac fibroblasts: A key role in cardiac fibrosis

Cardiac fibroblasts are a cell population that controls the homeostasis of the extracellular matrix and orchestrates a damage response to maintain cardiac architecture and performance. Due to these functions, fibroblasts play a central role in cardiac fibrosis development, and there are large differences in matrix protein secretion profiles between fibroblasts from aged versus young animals. Senescence is a multifactorial and complex process that has been associated with inflammatory and fibrotic responses. After damage, transient cellular senescence is usually beneficial, as these cells promote tissue repair. However, the persistent presence of senescent cells within a tissue is linked with fibrosis development and organ dysfunction, leading to aging-related diseases such as cardiovascular pathologies. In the heart, early cardiac fibroblast senescence after myocardial infarction seems to be protective to avoid excessive fibrosis; however, in non-infarcted models of cardiac fibrosis, cardiac fibroblast senescence has been shown to be deleterious. Today, two new classes of drugs, termed senolytics and senostatics, which eliminate senescent cells or modify senescence-associated secretory phenotype, respectively, arise as novel therapeutical strategies to treat aging-related pathologies. However, further studies will be needed to evaluate the extent of the utility of senotherapeutic drugs in cardiac diseases, in which pathological context and temporality of the intervention must be considered.

AMPK/mTOR-mediated therapeutic effect of metformin on myocardial ischaemia reperfusion injury in diabetic rat

BACKGROUND

The autophagy associated signalling pathways such as AMPK/mTOR previously were suggested to play a crucial role in protecting from ischaemia-reperfusion injury (IRI). The objective of this study was to evaluate the effect of metformin (DMBG) on autophagy during myocardial IRI with diabetes mellitus (DM).

METHODS

The DM rat model was established using streptozocin, and further induced ischaemia model via transitory ligation of the left anterior coronary artery and following reperfusion. The model rats were treated with 400 mg/kg/day DMBG for 1 week. Autophagosomes were investigated using transmission electron microscopy. Autophagy-associated signalling pathways were detected by western blot.

RESULTS

The myocardial infarct size was shown to significantly increase in the DM rats exposed to IRI compared to negative control, but decrease in DMBG treated. The mature autophagosomes were elevated in infarction and marginal zones of DM + IRI + DMBG compared to DM + IRI. Furthermore, the increasing protein levels of LC3-II, BECLIN 1, autophagy related 5 (ATG5) and AMP-activated protein kinase suggested activated autophagy-associated intracellular signalling AMPK and mTOR pathways upon DMBG treated.

CONCLUSIONS

Taken together, the outcomes determinate a novel mechanism that DMBG could activate autophagy process to provide a cardio-protective effect against DM induced myocardial IRI.

Protective effects of metformin against myocardial ischemia‑reperfusion injury via AMPK‑dependent suppression of NOX4

Numerous studies have demonstrated that metformin can reduce the incidence of myocardial infarction and improve the prognosis of patients. However, its specific mechanism has not been determined. Using a rat model of myocardial ischemia-reperfusion injury (MIRI), it was observed that metformin significantly reduced infarct size, and decreased the levels of plasma lactate dehydrogenase and creatine kinase-MB form. A TTC-Evans blue staining was used to detect the infarct size and MTT assay was used to evaluate the cell viability. TUNEL assay was performed to evaluate apoptosis. Furthermore, 4-hydroxynonenal was detected by immunohistochemical staining. mRNA expression levels were detected by reverse transcription-quantitative PCR; protein expression levels were detected by immunoblotting. When treated with metformin, the number of TUNEL-positive cells was significantly decreased. Reduced 4HNE immunoreactivity was observed in metformin-treated rats as determined via immunohistochemistry. Furthermore, NADPH oxidase 4 (NOX4) was downregulated by metformin at both the mRNA and protein levels, and adenosine 5′-monophosphate-activated protein kinase (AMPK) phosphorylation was increased by metformin. In a primary myocardial hypoxia-reoxygenation cell model, metformin increased the viability of cardiomyocytes and reduced the content of malondialdehyde. It was also found that metformin upregulated the phosphorylation of AMPK and decreased the expression of NOX4. Furthermore, pre-treatment with AMPK inhibitor compound-C could block the effect of metformin, indicated by increased NOX4 compared with metformin treatment alone. These results suggested that metformin was capable of reducing the oxidative stress injury induced by MIRI. In conclusion, the present study indicated that metformin activated AMPK to inhibit the expression of NOX4, leading to a decrease in myocardial oxidative damage and apoptosis, thus alleviating reperfusion injury.