[miR-34a targets MTUS1 to regulate cardiac fibrosis in rats]

Cardiac fibrosis is a common pathological feature during the progression of various cardiovascular diseases and is characterized by excessive deposition of extracellular matrix (ECM) in the myocardial interstitium, accompanied by alterations in cardiac structure and function. MicroRNAs (miRNAs) play important roles in the regulation of cardiac fibrosis. Previous studies have suggested that miR-34a is involved in fibrotic processes; however, its in vivo effects on cardiac fibrosis and cardiac function, as well as its relationship with mitochondrial tumor suppressor 1 (MTUS1), remain unclear. This study aimed to investigate the effects of miR-34a targeting MTUS1 on cardiac fibrosis and cardiac function in rats through in vivo intervention.

Healthy adult male Sprague-Dawley (SD) rats were used to establish a myocardial fibrosis model by subcutaneous injection of isoproterenol (ISO) at a dose of 10 mg/(kg·d) for 14 consecutive days (model group), while the control group received equal volumes of normal saline. Transthoracic echocardiography (TTE) was performed to evaluate cardiac structural and functional changes. Left ventricular tissues were collected and paraffin sections were prepared. Hematoxylin-eosin (HE) staining was used to observe histological changes in myocardial tissue, and Masson staining was used to assess collagen deposition. Real-time polymerase chain reaction (real-time PCR) and Western blotting were performed to detect the expression levels of miR-34a, MTUS1, and fibrosis-related proteins including α-smooth muscle actin (α-SMA) and collagen I. Bioinformatics analysis was used to predict potential binding sites between miR-34a and MTUS1. A dual-luciferase reporter assay was performed to verify the targeting relationship between miR-34a and MTUS1. Furthermore, adeno-associated virus (AAV) was used in vivo to downregulate the expression of miR-34a and MTUS1, and the effects on cardiac function and myocardial fibrosis were evaluated.

ISO-treated rats exhibited pronounced myocardial fibrotic changes. HE staining revealed disorganized myocardial fibers and widened interstitial spaces, and Masson staining demonstrated increased collagen deposition. TTE analysis showed that left ventricular ejection fraction was reduced in the model group compared with the control group (P<0.05). Compared with control rats, ISO-treated rats showed increased miR-34a expression and decreased MTUS1 expression in myocardial tissues, accompanied by elevated protein levels of α-SMA and collagen I (all P<0.05). Dual-luciferase reporter assays demonstrated that miR-34a directly bound to the 3' untranslated region of MTUS1 and suppressed its expression. AAV-mediated downregulation of miR-34a attenuated myocardial fibrosis, reduced collagen deposition, and improved cardiac functional parameters compared with the model group; these effects were correspondingly altered when MTUS1 expression was concurrently modulated.

In an ISO-induced rat model of cardiac fibrosis, miR-34a participates in the regulation of myocardial fibrosis and cardiac functional alterations by targeting MTUS1. The in vivo AAV intervention results suggest that the miR-34a-MTUS1 regulatory axis is associated with the progression of cardiac fibrosis.