Myostatin is a TGFβ family ligand that reduces muscle mass. In cancer cells, TGFβ signalling is increased by the protein FHL1. Consequently, FHL1 may promote signalling by myostatin. We therefore tested the ability of FHL1 to regulate myostatin function. FHL1 increased the myostatin activity on a SMAD reporter and increased myostatin dependent myotube wasting. In mice, independent expression of myostatin reduced fibre diameter whereas FHL1 increased fibre diameter, both consistent with previously identified effects of these proteins. However, co-expression of FHL1 and myostatin reduced fibre diameter to a greater extent than myostatin alone. Together, these data suggest that the expression of FHL1 may exacerbate muscle wasting under the appropriate conditions.
Abbreviations

FHL1, four and a half LIM domain protein 1; COPD, chronic obstructive pulmonary disease; TGF-β, transforming growth factor beta; MHC, myosin heavy chain; GDF-15, growth and differentiation factor 15; PAI-1, plasminogen activator inhibitor 1; TA, tibialis anterior; VEGF-C, vascular endothelial growth factor C