Overexpression of Striated Muscle Activator of Rho Signaling (STARS) Increases C2C12 Skeletal Muscle Cell Differentiation.

Paul A Della Gatta,Malcom J Mcconville,Joachim Kloehn,Greg M Kowalski,Séverine Lamon,Marita A Wallace,Bilal Ahmad Mir,Aaron P Russell

doi:10.3389/fphys.2016.00007

Paul A Della Gatta, Malcom J Mcconville + Show 6 more

Open Access

https://doi.org/10.3389/fphys.2016.00007

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Abstract

Background: Skeletal muscle growth and regeneration depend on the activation of satellite cells, which leads to myocyte proliferation, differentiation and fusion with existing muscle fibers. Skeletal muscle cell proliferation and differentiation are tightly coordinated by a continuum of molecular signaling pathways. The striated muscle activator of Rho signaling (STARS) is an actin binding protein that regulates the transcription of genes involved in muscle cell growth, structure and function via the stimulation of actin polymerization and activation of serum-response factor (SRF) signaling. STARS mediates cell proliferation in smooth and cardiac muscle models; however, whether STARS overexpression enhances cell proliferation and differentiation has not been investigated in skeletal muscle cells.Results: We demonstrate for the first time that STARS overexpression enhances differentiation but not proliferation in C2C12 mouse skeletal muscle cells. Increased differentiation was associated with an increase in the gene levels of the myogenic differentiation markers Ckm, Ckmt2 and Myh4, the differentiation factor Igf2 and the myogenic regulatory factors (MRFs) Myf5 and Myf6. Exposing C2C12 cells to CCG-1423, a pharmacological inhibitor of SRF preventing the nuclear translocation of its co-factor MRTF-A, had no effect on myotube differentiation rate, suggesting that STARS regulates differentiation via a MRTF-A independent mechanism.Conclusion: These findings position STARS as an important regulator of skeletal muscle growth and regeneration.

Highlights

Pre- and post- natal skeletal muscle development and regeneration of mature adult skeletal muscle require the coordinated control of myocyte proliferation and differentiation (Buckingham et al, 2003; Bentzinger et al, 2012)
Stars mRNA expression increased by 1.5-fold in confluent myoblasts when compared to sub-confluent myoblasts (p < 0.001; Figure 1A); there was no significant increase in striated muscle activator of Rho signaling (STARS) protein expression during myoblast proliferation (Figure 1B)
Stars mRNA levels gradually increased during myotube differentiation to reach a 80-fold increase by differentiation day 5 when compared to proliferating myoblasts (Figure 1C)

Summary

Introduction

Pre- and post- natal skeletal muscle development and regeneration of mature adult skeletal muscle require the coordinated control of myocyte proliferation and differentiation (Buckingham et al, 2003; Bentzinger et al, 2012). Each stage of muscle cell development and maturation is precisely regulated by the basic helix-loop-helix (bHLH) E-box binding protein family of myogenic regulatory factors (MRFs; Zhang et al, 1995; Kablar et al, 1997; Perry and Rudnick, 2000; Yokoyama and Asahara, 2011). The striated muscle activator of Rho signaling (STARS) is an actin binding protein that regulates the transcription of genes involved in muscle cell growth, structure and function via the stimulation of actin polymerization and activation of serum-response factor (SRF) signaling. STARS mediates cell proliferation in smooth and cardiac muscle models; whether STARS overexpression enhances cell proliferation and differentiation has not been investigated in skeletal muscle cells

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