Altered biogenesis of microRNA-1 is associated with cardiac dysfunction in aging of spontaneously hypertensive rats

Hypertension Induces Pro-arrhythmic Cardiac Connexome Disorders: Protective Effects of Treatment

Prolonged population aging and unhealthy lifestyles contribute to the progressive prevalence of arterial hypertension. This is accompanied by low-grade inflammation and over time results in heart dysfunction and failure. Hypertension-induced myocardial structural and ion channel remodeling facilitates the development of both atrial and ventricular fibrillation, and these increase the risk of stroke and sudden death. Herein, we elucidate hypertension-induced impairment of "connexome" cardiomyocyte junctions. This complex ensures cell-to-cell adhesion and coupling for electrical and molecular signal propagation. Connexome dysfunction can be a key factor in promoting the occurrence of both cardiac arrhythmias and heart failure. However, the available literature indicates that arterial hypertension treatment can hamper myocardial structural remodeling, hypertrophy and/or fibrosis, and preserve connexome function. This suggests the pleiotropic effects of antihypertensive agents, including anti-inflammatory. Therefore, further research is required to identify specific molecular targets and pathways that will protect connexomes, and it is also necessary to develop new approaches to maintain heart function in patients suffering from primary or pulmonary arterial hypertension.

Cardiac dysfunction in spontaneously hypertensive old rats is associated with a significant decrease of SUR2 expression

ATP-sensitive potassium (K_ATP) channels are participants of mechanisms of pathological myocardial remodeling containment. The aim of our work was to find the association of changes in the expression of Kir6.1, Kir6.2, SUR1, and SUR2 subunits of K_ATP channels with changes in heart function and structure during aging under conditions of the constant increase of vascular pressure. The experiments were carried out on young and old spontaneously hypertensive rats (SHR) and Wistar rats. The expression levels of K_ATP channels subunits were determined using reverse transcription and quantitative PCR. It is shown that the mRNA expression level of Kir6.1 in young SHR rats is significantly lower (6.3-fold, p = 0.035) than that of young Wistar rats that may be one of the causes of arterial hypertension in SHR. At the same time, mRNA expression of both Kir6.1 and Kir6.2 in old SHR rats was significantly higher (6.8-fold, p = 0.003, and 5.9-fold, p = 0.006, respectively) than in young hypertensive animals. In both groups of old animals, SUR2 expression was significantly reduced compared to young animals, in Wistar rats at 3.87-fold (p = 0.028) and in SHR rats at 48.2-fold (p = 0.033). Changes in SUR1 expression were not significant. Thus, significant changes in the cardiovascular system, including impaired function and structure of the heart in old SHR rats, were associated with a significant decrease in SUR2 expression that may be one of the mechanisms of heart failure decompensation. Therefore, it can be assumed that increased expression of SUR2 may be one of the protective mechanisms against pathological myocardial remodeling.

Inhibiting miR‑1 attenuates pulmonary arterial hypertension in rats

MicroRNAs (miRs) are reported to serve key roles in pulmonary arterial hypertension (PAH). miR-1 has been found in cardiovascular diseases. The present study aimed to determine whether the knockdown of miR-1 could inhibit right ventricle (RV) remodeling and thereby control PAH in model rats. PAH model rats were established by exposing rats to hypoxia, while cardiac fibroblasts (CFs) obtained from PAH model rats were treated with hypoxia to establish an in vitro model, and RV remodeling was evaluated by Masson staining and the levels of collagen I, collagen III, α-smooth muscle actin (α-SMA) and connective tissue growth factor (CTGF) evaluated by western blotting or reverse transcription-quantitative PCR. The results revealed that the expression levels of miR-1 were upregulated in the RV of PAH model rats induced with hypoxia and in the CFs treated with hypoxia. The mean pulmonary arterial pressure, RV systolic pressure, RV/(left ventricle + interventricular septum) and RV/tibia length were increased in PAH rats; however, the increases in all parameters were subsequently reversed by transfection with a miR-1 antagomiR in PAH model rats. The transfection with the miR-1 antagomiR inhibited the development of RV fibrosis and downregulated the mRNA expression levels of collagen I, collagen III, α-SMA and CTGF in the RV tissue of PAH model rats. The upregulation of collagen I, collagen III, α-SMA and CTGF expression levels in hypoxia-treated CFs was also subsequently reversed by miR-1 antagomiR transfection. The expression levels of collagen I, collagen III, α-SMA and CTGF were also upregulated in the CFs obtained from PAH model rats, and these increases were attenuated by miR-1 antagomiR transfection. The expression levels of phosphorylated (p)-PI3K and p-AKT were also upregulated in hypoxia-treated CFs, and these increases were also inhibited by transfection with miR-1 antagomiR. In conclusion, these results indicated that inhibiting miR-1 may attenuate RV hypertrophy and fibrosis in PAH model rats, a mechanism that may involve the PI3K/AKT signaling pathway.

MicroRNA-26a Protects the Heart Against Hypertension-Induced Myocardial Fibrosis

Background Hypertensive myocardial fibrosis (MF) is characterized by excessive deposition of extracellular matrix and cardiac fibroblast proliferation, which can lead to heart failure, malignant arrhythmia, and sudden death. In recent years, with the deepening of research, microRNAs have been found to have an important role in blood pressure control and maintaining normal ventricular structure and function. Methods and Results In this study, we first documented the downregulation of microRNA-26a (miR-26a) in the plasma and myocardium of spontaneously hypertensive rats; more importantly, miR-26a-deficient mice showed MF, whereas overexpression of miR-26a significantly prevented elevated blood pressure and inhibited MF in vivo and angiotensin II-induced fibrogenesis in cardiac fibroblasts by directly targeting connective tissue growth factor and Smad4. miR-26a inhibited cardiac fibroblast proliferation by the enhancer of zeste homolog 2/p21 pathway. Conclusions Our study identified a novel role for miR-26a in blood pressure control and hypertensive MF and provides a possible treatment strategy for miR-26a to alleviate and reverse hypertensive MF.