The role of microRNAs in phenotypic changes of skeletal muscle of obese Zucker rats submitted to aerobic training

Abstract

Obesity is a chronic disease characterized by body fat excess and is a predisposing factor to other diseases such as diabetes, hypertension, dyslipidemia and some cancer types. The epidemic proportions of obesity has increased dramatically over the years and today it is considered a worldwide public health problem. It is also a risk factor for pathological morphological changes in skeletal muscle. Among all this factors, we can highlight the capillary rarefaction, which often occurs in vascular disease as a result from inflammation and altered lipid profile. Furthermore, obesity changes intramuscular components related to lipid and protein content. Although the obesity is not easily healed, physical training has been shown to be an important nonpharmacological disease control treatment, as it helps by contributing to fat mass decrease and lean mass increase. The literature suggests that physical exercise can cause skeletal muscle phenotype changes among them, we mentioned: changes in capillary density, fiber diameter, content of intramuscular fat and collagen. However, there are few studies that bind obese patients morphological muscle characteristics and physical training changes. Recently, our research group conducted a study in order to determine the morphological changes that occur in skeletal muscle of obese rats submitted to aerobic exercise. Between the results, obese sedentary rats showed muscle fibers cross-sectional area, intramuscular fat content and capillary rarefaction has decreased when compared with obese trained rats. Furthermore, physical training was able to partially reverse these conditions. Although, researches about skeletal muscle morphological profile changes has presented interesting and important results, this research field still remains unclear and it is important to investigate how aerobic training facts some factors. Recently a new class of molecules known as microRNAs has been investigated. These molecules were associated with some physiologic and pathologic process. MicroRNAs are small RNAs that do not encode proteins, which bind with complementary RNAs and blocks partially or totally ribosomes translation. There are several families of microRNAs and each one has several targets. The literature indicates that microRNAs control the expression of many genes in different tissues. Also, in known that exercise has an important role regulating the expression of certain microRNAs, for example, microRNA -16 is considered as an inhibitor of angiogenic factor. A study by Fernandes et al, 2012 showed that there is a decrease in the expression of this microRNA in hypertensive rats submitted to aerobic exercise training, thus enabling the highest expression of angiogenic factors inhibited by high blood pressure in spontaneously hypertensive rats. Thus, the aim of this study is to determine the involvement of miRNAs in the morphological changes that occur in skeletal muscle of obeses Zucker rats. And specifically the expression of microRNA- 126 and microRNA -16, which have validated targets closely associated with angiogenic process, and microRNA -133 which is related to the AKT pathway, a proven marker of skeletal muscle hypertrophy. (AU)