Myostatin is an important regulator of muscle mass that contributes to the loss of muscle mass in a number of chronic diseases. Myostatin is known to activate the expression of components of the ubiquitin-proteosomal pathway but its effect on the autophagic pathway is not known. We therefore analysed the effect of myostatin and TGF-beta on autophagy in C2C12 cells by determining the effect of these proteins on LC3 processing, autophagosome formation and autophagy gene expression. Both myostatin and TGF-beta increased LC3II expression and turnover as well as autophagosome formation (marked by the formation of puncta in LC3-GFP transfected cells). Myostatin also significantly increased the expression of ATG-4B and ULK-2 mRNA while TGF-beta caused a trend towards an increase in these genes. We conclude that myostatin and TGF-beta increase autophagy in skeletal muscle cells. (C) 2011 Elsevier Inc. All rights reserved.