Dystrophin regulates polarity and self-renewal of muscle stem cells

The study, published in Nature Medicine on November 16, 2015, is the first to show that Duchenne muscular dystrophy directly affects muscle stem cells.

For nearly 20 years, we’ve thought that the muscle weakness observed in patients with Duchenne muscular dystrophy is primarily due to problems in their muscle fibres, but our research shows that it is also due to intrinsic defects in the function of their muscle stem cells. This completely changes our understanding of Duchenne muscular dystrophy and could eventually lead to far more effective treatments.

Wnt/β-catenin induces follistatin to regulate myogenic differentiation of satellite cells

Adult skeletal muscle regeneration is a highly orchestrated process involving the activation and proliferation of satellite cells, an adult skeletal muscle stem cell. Activated satellite cells generate a transient amplifying progenitor pool of myoblasts that commit to differentiation and fuse into multinucleated myotubes. During regeneration, canonical Wnt signalling is activated and has been implicated in regulating myogenic lineage progression and terminal differentiation. We identified a novel mechanism by which myogenin mediates the canonical Wnt/β-catenin-dependent activation of follistatin and induction of the myogenic differentiation process.

New Endocrinology paper finds Periostin induces Pancreatic Regeneration.

Diabetes occurs when the body fails to properly regulate the level of sugar in the blood, either because the pancreas does not produce enough insulin, or because the body does not respond properly to insulin. Research in our lab shows that a protein called Periostin (Postn) plays a crucial role in pancreas regeneration, and injection of the recombinant protein can stimulate pancreas regeneration and improve blood sugar regulation in the mouse.

Inhibition of JAK-STAT signaling stimulates adult satellite cell function.

Diminished regenerative capacity of skeletal muscle occurs during adulthood. We identified a reduction in the intrinsic capacity of mouse adult satellite cells to contribute to muscle regeneration and repopulation of the niche.

Wnt7a stimulates myogenic stem cell motility and engraftment resulting in improved muscle strength.

Wnt7a/Fzd7 signaling stimulates skeletal muscle growth and repair by inducing the symmetric expansion of satellite stem cells through the planar cell polarity pathway and by activating the Akt/mTOR growth pathway in muscle fibers. Here we describe a third level of activity where Wnt7a/Fzd7 increases the polarity and directional migration of mouse satellite cells and human myogenic progenitors through activation of Dvl2 and the small GTPase Rac1.

A truncated Wnt7a retains full biological activity in skeletal muscle.

Wnt signaling has essential roles during embryonic development and tissue homoeostasis. Wnt proteins are post-translationally modified and the attachment of a palmitate moiety at two conserved residues is believed to be a prerequisite for the secretion and function of Wnt proteins. Here we demonstrate that a mammalian Wnt protein can be fully functional without palmitoylation.

Pax7 is critical for the normal function of satellite cells in adult skeletal muscle.

Extensive analyses of mice carrying null mutations in paired box 7 (Pax7) have confirmed the progressive loss of the satellite cell lineage in skeletal muscle, resulting in severe muscle atrophy and death. A recent study using floxed alleles and tamoxifen-induced inactivation concluded that after 3 wk of age, Pax7 was entirely dispensable for satellite cell function. Here, we demonstrate that Pax7 is an absolute requirement for satellite cell function in adult skeletal muscle.

MicroRNA-133 Controls Brown Adipose Determination in Skeletal Muscle Satellite Cells by Targeting Prdm16

Brown adipose tissue (BAT) is an energy-dispensing thermogenic tissue that plays an important role in balancing energy metabolism. Lineage-tracing experiments indicate that brown adipocytes are derived from myogenic progenitors during embryonic development. However, adult skeletal muscle stem cells (satellite cells) have long been considered uniformly determined toward the myogenic lineage.

Fibronectin regulates Wnt7a signaling and satellite cell expansion

The influence of the extracellular matrix (ECM) within the stem cell niche remains poorly understood. We found that Syndecan-4 (Sdc4) and Frizzled-7 (Fzd7) form a coreceptor complex in satellite cells and that binding of the ECM glycoprotein Fibronectin (FN) to Sdc4 stimulates the ability of Wnt7a to induce the symmetric expansion of satellite stem cells.

Carm1 Regulates Pax7 Transcriptional Activity through MLL1/2 Recruitment during Asymmetric Satellite Stem Cell Divisions.

In skeletal muscle, asymmetrically dividing satellite stem cells give rise to committed satellite cells that transcribe the myogenic determination factor Myf5, a Pax7-target gene. We identified the arginine methyltransferase Carm1 as a Pax7 interacting protein and found that Carm1 specifically methylates multiple arginines in the N terminus of Pax7.