Thrombospondin expression in myofibers stabilizes muscle membranes.

Davy Vanhoutte,Michelle A Sargent,Hong Yi,Andoria Tjondrokoesoemo,Jennifer Q Kwong,Elizabeth M Mcnally,Onur Kanisicak,Tobias G Schips,Jeffery D Molkentin,Jennifer Davis,Talila Volk,Quan Q Gao,Matthew J Brody,Joseph E Rabinowitz

doi:10.7554/elife.17589

Abstract

Skeletal muscle is highly sensitive to mutations in genes that participate in membrane stability and cellular attachment, which often leads to muscular dystrophy. Here we show that Thrombospondin-4 (Thbs4) regulates skeletal muscle integrity and its susceptibility to muscular dystrophy through organization of membrane attachment complexes. Loss of the Thbs4 gene causes spontaneous dystrophic changes with aging and accelerates disease in 2 mouse models of muscular dystrophy, while overexpression of mouse Thbs4 is protective and mitigates dystrophic disease. In the myofiber, Thbs4 selectively enhances vesicular trafficking of dystrophin-glycoprotein and integrin attachment complexes to stabilize the sarcolemma. In agreement, muscle-specific overexpression of Drosophila Tsp or mouse Thbs4 rescues a Drosophila model of muscular dystrophy with augmented membrane residence of βPS integrin. This functional conservation emphasizes the fundamental importance of Thbs' as regulators of cellular attachment and membrane stability and identifies Thbs4 as a potential therapeutic target for muscular dystrophy.

Highlights

Muscle degenerative diseases such as muscular dystrophy (MD) are most commonly caused by mutations in genes that are part of the dystrophin-glycoprotein (DGC) complex or the integrin complex of proteins (Grounds et al, 2005; McNally and Pytel, 2007)
In agreement with previous findings, Thbs4 RNA is induced in muscle biopsies from human patients with Becker MD, Duchenne MD, and limb-girdle MD (LGMD) (Figure 1A; Figure 1—figure supplement 1A) (Chen et al, 2000)
Tissue Immunofluorescent analysis revealed that Thbs4 protein was undetectable in uninjured skeletal muscle while the transgene produced abundant expression that co-localized with calreticulin to a vesicular network on the periphery of the myofibers of paraffin-embedded quadriceps and was clearly inside of collagen I staining that marks the extracellular matrix (ECM) of cryo-embedded quadriceps (Figure 1E)

Summary

Introduction

Muscle degenerative diseases such as muscular dystrophy (MD) are most commonly caused by mutations in genes that are part of the dystrophin-glycoprotein (DGC) complex or the integrin complex of proteins (Grounds et al, 2005; McNally and Pytel, 2007). Proper post-translational processing and trafficking of these complexes to the sarcolemma are essential to form a molecular attachment network between the myofilament proteins within the myofibers and the basal lamina and extracellular matrix (ECM) outside the cell (Goddeeris et al, 2013; Liu et al, 2012; Xu et al, 2009) This attachment network provides critical structural support to the plasma membrane (sarcolemma) to withstand contractile forces (Burr and Molkentin, 2015; Grounds et al, 2005; Gumerson and Michele, 2011; Lapidos et al, 2004).

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Conclusion