The LINC complex modulates satellite cell response to injury via cell cycle regulation

Louise Moyle (1), Olivia McKee-Muir (2), Aaryn Montgomery-Song (1), Sabrina Cancelliere (1), Penney Gilbert (1, 2)

(1) Institute of Biomaterials and Biomedical Engineering, University of Toronto

(2) Department of Biochemistry, University of Toronto

A fundamental goal in muscle stem cell (MuSC) biology is to understand how a combination of physical and chemical cues results in the transition from quiescence to activation. The Linker of Nucleoskeleton and Cytoskeleton (LINC) complex is a physical bridge between cytoskeletal networks and the nuclear envelope which acts as an intracellular force conductor. Nesprins bind to cytoplasmic f-actin and to SUN proteins, which in turn bind to Lamin A/C and Emerin of the nuclear lamina, and subsequently to chromatin. This provides a mechanism by which physical cues arising from the MuSC niche could lead to transcriptional changes that result in MuSC activation. Whilst the LINC complex has been shown to regulate myonuclear position and sarcomere assembly, a role in MuSC activation is currently unexplored. Discerning this is particularly relevant as mutations in LINC complex proteins cause Emery-Dreifuss muscular dystrophy (EDMD), a progressive muscle wasting disorder. To address this, we have performed a thorough assessment of the LINC-complex associated proteins during MuSC regeneration, and show that some components of the LINC complex are expressed in quiescent MuSCs, whilst others rapidly increase upon activation. LINC complex proteins were disrupted in MuSCs using siRNA and dominant-negative (DN) constructs and cell cycle dynamics and transcriptional assessed. Finally, Pax7tm2.1(CRE/ERT2):Tg(CMV-LacZ/eGFP-KASH2) mice expressing DN-Nesprin2 in MuSCs were subjected to rounds of myotoxic injury to assess how LINC disruption affects myogenic regeneration within the native niche. These results extend our understanding of how MuSCs respond to physical cues and give insight into the pathogenesis of EDMD.