Molecular mechanisms associated to palmitate induced atrophy in C2C12 cells

Abstract

Obesity is a multifactorial and complex disease that is defined as excess fat in the body. Besides the expansion of adipose tissue, occurs ectopic fat accumulation in non-adipose tissue such as skeletal muscle, leading to insulin resistance in this tissue. Insulin resistance is characterized by impaired insulin action on adipocyte lipolysis, suppression of endogenous glucose production and skeletal muscle glucose uptake, resulting in the onset of type 2 diabetes mellitus (T2DM). In patients with type 1 diabetes mellitus (DM1) with inadequate glycemic control and in elderly patients with DM2 is observed a progressive loss of skeletal muscle, the reduction of muscle mass is most likely due to the fact that insulin act promoting protein synthesis. The development of skeletal muscle is controlled by myogenic regulatory factors such as Murf4, Myf5 and MyoD, and the IGF1/PI3K/AKT/MTOR is the main signaling pathway involved in skeletal differentiation and growth. Furthermore, myogenesis is also controlled by microRNAs (miRNAs), a class of small non-coding RNAs that negatively regulates the expression of genes encoding proteins. They are involved in processes such as proliferation and muscle differentiation, regeneration and hypertrophy, and as regards myogenesis, the miomiRs act by controlling the signaling pathway IGF1 / PI3K / AKT / mTOR, thus, we believe that microRNAs may be involved with muscle mass loss associated with diabetes. Palmitic acid, a saturated fatty acid, induces insulin resistance by inhibiting the phosphorylation of AKT and inducing the synthesis of lipid metabolites such as diacylglycerol (DAG) and ceramides, which presents negative effects on insulin signaling pathway. Using C2C12 cells, we propose to evaluate the mechanism by which palmitate induces skeletal muscle cells atrophy. Specifically, the effect of palmitate in proliferation of myoblasts and myotubes will be evaluated by flow cytometry. Next, in differentiating myotubes (0, 1, 3 and 5 days) we will measure myogenic markers ((MyoG, MyoD, Pax7, MHC) and the expression of myomiRs, miR-1a, miR-133a/b, miR-206 and miR-23a. After 5 days in differentiation media, we will quantify the effect of palmitate in protein synthesis and degradation, as well as, protein involved in IGF1/AKT/MTOR pathway. Our results may clarify the mechanisms involved in obesity-induced atrophy. (AU)