Alpha sarcoglycan is required for FGF-dependent myogenic progenitor cell proliferation in vitro and in vivo

Abstract

SUMMARYMice deficient in -sarcoglycan (Sgca-null mice) develop progressive muscular dystrophy and serve as a model for human limb girdle muscular dystrophy type 2D. Sgca-null mice suffer a more severe myopathy than that of mdx mice, the model for Duchenne muscular dystrophy. This is the opposite of what is observed in humans and the reason for this is unknown. In an attempt to understand the cellular basis of this severe muscular dystrophy, we isolated clonal populations of myogenic progenitor cells (MPCs), the resident postnatal muscle progenitors of dystrophic and wild-type mice. MPCs from Sgca-null mice generated much smaller clones than MPCs from wild-type or mdx dystrophic mice. Impaired proliferation of Sgca-null myogenic precursors was confirmed by single fiber analysis and this difference correlated with Sgca expression during MPC proliferation. In the absence of dystrophin and associated proteins, which are only expressed after differentiation, SGCA complexes with and stabilizes FGFR1. Deficiency of Sgca leads to an absence of FGFR1 expression at the membrane and impaired MPC proliferation in response to bFGF. The low proliferation rate of Sgca-null MPCs was rescued by transduction with Sgca-expressing lentiviral vectors. When transplanted into dystrophic muscle, Sgca-null MPCs exhibited reduced engraftment. The reduced proliferative ability of Sgca-null MPCs explains, at least in part, the severity of this muscular dystrophy and also why wild-type donor progenitor cells engraft efficiently and consequently ameliorate disease.

CD82 Is a Marker for Prospective Isolation of Human Muscle Satellite Cells and Is Linked to Muscular Dystrophies

“…We hypothesized that if CD82 is associated with dystrophin or a member of the DAPC, its expression might be decreased in diseased muscle. A candidate DAPC-interacting protein could be α-sarcoglycan, since its expression is reduced in DMD muscle cells compared to normal ones (Cassano et al, 2011) as a result of instability of the entire DAPC complex when dystrophin is mutated (Ervasti et al, 1990). CD82 and α7-ITG protein pulldowns were analyzed by western blot using anti-α-sarcoglycan (Figure 4C) and confirmed that α-sarcoglycan co-immunoprecipitated with CD82 and α7-ITG.…”

The Dystrophin Complex: Structure, Function, and Implications for Therapy

“…Hence α-sarcoglycan may act to protect muscle fibers from tissue injury caused by exercise or muscle degeneration by reducing extracellular ATP levels. Before muscle cell differentiation, α-sarcoglycan plays a role in regulating proliferation ability of the myogenic progenitor cells by binding to and stabilizing fibroblast growth factor receptor 1 (FGFR1) (37). α-sarcoglycan deficient myogenic progenitor cells lost FGFR1 at the plasma membrane and had impaired proliferation in response to basic fibroblast growth factor.…”

Human artificial chromosomes for Duchenne muscular dystrophy and beyond: challenges and hopes

“…Moreover, after years of assiduous research, gene therapy is now delivering excellent clinical results (Aiuti et al 2009;Gaspar et al 2011;Biffi et al 2013). However, specific hurdles slowing down major progress in DMD gene therapy are as follows: (1) dystrophin is the largest human gene (2.4 Mb) with a complex transcriptional regulation (Muntoni et al 2003); (2) even dystrophin full complementary DNA (cDNA) (14 kb) cannot be accommodated inside conventional vectors that allow stable gene expression in dividing and non-dividing cells; (3) the main tissue affected in DMD is skeletal muscle, which is also the most abundant tissue of the human body, and this means that the transgene needs to target a reasonable high number of nuclei to provide some efficacy; (4) increasing evidence shows exhaustion or dysfunction of dystrophic stem/progenitor cells, necessary for ex vivo gene therapy (Blau et al 1983;Cohn et al 2002;Sacco et al 2010;Cassano et al 2011;Kudryashova et al 2012;Tedesco et al 2012); and (5) the brain and heart are also affected in DMD, and this together with the widespread distribution of skeletal muscle poses additional hurdles for the delivery of the transgene.…”