The primary antibodies against p-Akt (Ser473), Akt, p-Smad2, p-Smad3, PPARγ, p-ACC1 and PGC1-α were from Cell Signaling Technology (Beverly, MA). Antibodies against F4/80, CD68, Fndc5 and UCP-1 were from Abcam (Cambridge, MA). ELISA kits for measuring irisin, IL-6 or adiponectin were from BioVision (Milpitas, CA), eBioscience (San Diego, CA) or R&D Systems (Minneapolis, MN) respectively. The recombinant proteins, irisin or myostatin were obtained from Enzo life Sciences (Farmingdale, NY) or R&D systems. The anti-myostatin peptibody (peptibody) was from Atara Biotherapeutics (Westlake Village, CA) (21 (link);22 (link)). Serum insulin concentration was measured using the Rat/Mouse Insulin ELISA kit (Millipore, Billerica, MA). Serum free fatty acid levels were measured using the NEFA C kit from Wako (Richmond, VA).