The effect of aerobic exercise on MMP-2 / miR-21 signaling pathway of cardiac fibrosis in elderly rats

Background :The concept of survival has changed since the twentieth century to guarantee quality of life in the twenty-first century (1). Aging is associated with a certain degree of interstitial fibrosis, which progresses to heart failure. Therefore, finding new and practical methods is an important and necessary help to reduce heart tissue fibrosis in the elderly (2). Providing mechanisms by which exercise can benefit the cardiovascular system may provide a picture of a healthy heart, and this process provides new ways to prevent and treat heart disease.  The most common heart disease associated with aging is diastolic dysfunction and is referred to as heart failure along with the maintenance of the injection fraction. Heart failure increases stiffness and myocardial fibrosis and is associated with poor endothelial function. Fibrosis is a complex reactive tissue that occurs due to excessive accumulation of compounds, especially collagen, and is one of the biological causes of changes in the heart. The findings show that fibrosis occurs in the hearts of older mice and humans (3). In mammals, the structure of the extracellular matrix (ECM) of the heart is 85% collagen and 11% collagen. The ability to make ECM compounds depends on its cell type. For example, fibroblasts and smooth muscle cells make type I and collagen, while myocytes and endothelial cells make type I collagen. Changes in ECM protein profiles can affect heart function and shape (4). MicroRNAs (miRNAs) are small, non-coding RNAs of 18 to 25 nucleotides that regulate gene expression at the post-transcriptional level in physiological and pathological conditions (5).miR-21 is overexpressed during fibrosis and can regulate the fibrogenic process in different organs and tissues from different pathways. MiR-21 has been shown to directly target phosphate and tensin homologue (PTEN) and It can regulate the fibrosis process from the phosphoinositide 3-kinase / AKT pathway by targeting PTEN (6). Matrix metalloproteins (MMPs) are zinc-dependent endonucleases (Zn) that are capable of degrading various extracellular matrix (ECM) compounds and are made and stored in the form of pre-enzymes. MMP-2- Collagenase A is a 72 kDa protein whose gene is located on chromosome 16 in humans and arm 12.2 q and in mice on chromosome 8. Kwak showed 12 weeks of training significantly reduced age-induced intercellular space collagen in mice (2). Eight weeks of regular swimming in male diabetic rats significantly reduced TGF-β and normalized cardiac MMP-2. miR-21has multiple functions related to exercise and heart disease and Significantly, miR-21 is highly dependent on the target genes it regulates (7). Materials and Methods: : The present study is an experimental and basic study with a post-test design with a control group. All stages of the research were carried out in accordance with the ethical principles of working with laboratory animals approved by Shahid Beheshti University of Medical Sciences in accordance with the 2006 Helsinki Protocol.  In this experimental study, 18 Wistar rats with age (24 months) and mean weight (537±5 g) were randomly divided into control (n = 9) and aerobic exercise (n = 9) groups. After getting acquainted with the environment and training method, the training group performed their program on a treadmill with a constant slope of zero degrees and a constant speed of 12 meters per minute for eight weeks and 5 days a week. Training time increased from 10 minutes in the first week to 52 minutes in the eighth week. The control group did not perform any exercises during this period. At the end of every session warm up were performed. Research variables were measured by RT-PCR. To make the cDNA pattern, miRNA-21 MMP-2 Takara Master Mix Kit was used and the instructions were followed. Independent t-test was used to measure and analyze the data and a significance level of p <0.05 was considered (8; 9).  Results: The results of data analysis using independent t for ventricular collagen percentage showed that there was a significant difference between the control and exercise groups (P = 0.001, t = 506.5), data analysis using independent t for expression of miR-21 gene showed that there is a significant difference between the control and exercise groups (P = 0.006, t = 131.3) and data analysis using independent t for MMP-2 gene showed that there is a significant difference between the control and exercise groups (P = 0.027, t = 441.2). Conclusion: Sub-maximal intensity aerobic exercise significantly increased miR-21 followed by downstream suppression of MMP-2 and decreased collagen deposition in the left ventricle of healthy elderly mice Collagen is known as one of the markers of fibrosis and physical activity can reduce its deposition and formation (2). Suppress collagen production is a way to reduce the expression of the MMP-2 gene by the PTEN pathway. It should be noted that the signal pathways for fibrosis are interconnected, for example, the PI3K pathway positively regulates Smad3 transcription and increases collagen production (10). These pathways affect the production of miR-21 and, in contrast to miR-21, regulate these pathways by targeting target proteins. In other words, miR-21 plays a key role in this network. Many of these proteins have an inhibitory role on metalloproteins: MMP-2 destroys the extracellular matrix and suppresses the PTEN pathway in cardiac fibroblasts (6). The results showed that aerobic exercise significantly increased miR-21 gene expression and significantly decreased intercellular collagen expression and MMP-2 gene expression. It seems that aerobic exercise with increased miR-21 decreased the expression of MMP-2 and the amount of collagen deposition in the intercellular space.