Location matters – how the cytoskeletal protein Leiomodin 1 controls myogenic differentiation by modulating Sirtuin 1 localization. Location matters – how the cytoskeletal protein Leiomodin 1 controls myogenic differentiation by modulating Sirtuin 1 localization

During myogenic differentiation the architecture and proteome of muscle stem cells undergo extensive remodelling. These processes are only partially understood and display impairments in age and disease. Using mass spectrometry to analyse protein dynamics during myogenic differentiation, we identified the actin nucleator Leiomodin 1 (LMOD1) increasing in abundance in early phases of myogenic differentiation. Knockdown of LMOD1 in primary myoblasts severely affected myogenic differentiation and fusion of myotubes, while overexpression had the opposite effect. Mechanistically, we show that LMOD1 interacts with Sirtuin1 (SIRT1) and that both follow similar changes in nuclear/cytoplasmic localization during differentiation. We demonstrate that LMOD1 influences SIRT1 localization and the expression of a subset of its target genes. Consistently, depletion or pharmacological inhibition of SIRT1 partially rescues the effects of LMOD1 knockdown. Our work identifies a novel regulator of myogenic differentiation that might be a potential target to improve muscle regeneration in aging and disease. Overall design: To identify downstream effectors that could explain the observed rescue effect after siLmod1/siSirt1 double knockdown, an RNA-Seq experiment was conducted. Therefore, siRNA against Lmod1 and Sirt1 was performed in 5 different primary myoblast cell lines, and primary myoblasts were differentiated for one day. Differential gene expression analysis of RNASeq Data was used to understand the early transcriptional changes in the myogenic program under the different knockdown conditions (siSirt1 vs siCtrl and siLmod1 vs siCtrl).