IMPROVED RESISTANCE TO EXERCISE IN MICE TREATED WITH METFORMIN

Skeletal muscle insulin resistance is a key development in diabetes pathogenesis and induces functional, metabolic and structural changes leading to muscle weakness and muscle atrophy. Metformin (MET) belongs to biguanides and is a first-line anti-diabetic therapy exhibiting potent antihyperglycemic and insulin-sensitizing properties. Its ability to regulate blood glucose has largely been attributed to a suppression of hepatic gluconeogenesis and increased glucose uptake in peripheral tissues such as skeletal muscle. The mechanism underpinning its action in skeletal muscle still remains unclear, although a number of studies have suggested that MET may act to stimulate glucose uptake independently of insulin or may potentiate insulin-stimulated glucose uptake, possibly via effects on insulin binding or proximal components of the insulin signaling cascade. Skeletal muscle differentiation is a process in which proliferative myoblasts break free from the cell cycle and fuse to form multinucleated myotubes. These events are orchestrated by early Myogenic Regulator Factors (MRFs: MyoD, Myf-5, myogenin and Myf-6) and late myogenic protein MyHC (Myosin Heavy Chain), through p38 MAP kinase/ERK pathway modulation. Our previous data suggested that MET induces ERK pathway activation and MyHC synthesis in vitro muscle model (C2C12). Aim of this work is to confirm in C2C12 in vitro model and to study in vivo, in a rodent model, the action of MET during myogenesis process and in hypertrophy genesis. We studied muscle proteosynthesis and morphological features in the late differentiation. After 72h of differentiation, cells were treated with 400 μM MET for 4, 8 and 24 hours. We used a positive control with 0.1 nM insulin added to medium and a negative control in which MET and insulin were not added. MRFs protein expression levels and morphological characteristics were evaluated by Western Blot and Immunofluorescence. To test those results in vivo, we investigated the action of MET on exercise performance in adult C57BL6 mice through an endurance performance treadmill running test. Mice were injected intra abdominally with MET (250 mg/kg) and the control mice with 0.9% saline for 30 days. During late differentiation, MRFs, cytoskeletal and muscle marker protein expression levels were higher in cells treated with MET in respect to control. Furthermore, MET treatment is able to increase cell mass and fusion competence indicating that MET may regulate myogenesis progression and hypertrophy genesis. Endurance performance treadmill running test, made at the beginning and at the end of this study, revealed that MET treated mice exhibit an enhanced performance respect to the control mice. Statistical evaluation was performed using an umpaired t-test. Data are presented as means ± SD. Results were considered statistically significant if p≤0.05. Data shown the role of MET in myogenesis promotion and in neo-formed myotubes hypertrophy induction. Our findings revealed a novel therapeutic indication of MET for muscle hypotrophy conditions in chronic muscle impairment (diabetic sarcopenia and cachexia) and a new potential role as integrator in exercise performance