Muscle regeneration is an intricate process involving multiple factors that spatially and temporally dictate the activation, proliferation, migration, and differentiation of skeletal muscle stem cells known as satellite cells (SC) and the fusion of nascent myoblasts (differentiated SC). Understanding the regulatory factors participating in each individual stage of muscle regeneration would therefore open new venues for designing better treatments for muscle related diseases such as muscular dystrophy and atrophy. Our previous study has shown that loss of heparan sulfate-6-O-endosulfatases (Sulfs) leads to a delay in muscle regeneration and a transient increase in SC population, and such phenotypes may be caused by Sulf-mediated repression of FGF2 signaling during SC differentiation. Whether Sulfs play additional roles during skeletal muscle regeneration is unknown. Here preliminary studies show that Sulfs repress the noncanonical Wnt signaling pathway during muscle regeneration and in satellite cell cultures. Since noncanonical Wnt signaling is shown to promote SC expansion by driving the symmetric cell division, we hypothesize that Sulfs regulate the noncanonical Wnt signaling to affect SC population during muscle regeneration. Results of our studies are expected to provide matrix-dependent mechanisms that regulate myogenesis and SC preservation during skeletal muscle regeneration and degenerative diseases. These findings may provide basis for future application of heparan sulfate (HS) and HS-derivatives in stem cell engineering and treatment of muscular degenerative diseases. To investigate such hypothesis, we will utilize a combination of in vitro cell model (single myofibers) and animal models of regeneration by injury and by muscular dystrophy in mice having Sulfs specifically inactivated in the satellite cells Pax7Sulf-DN (Pax7-Cre:ER/Rosa26;eYFP/Sulf1/2flox) and Pax7Sulf-DN;mdx, respectively. We will also utilize lentivirus expressing the dominant negative Sulf2 to acutely inactivate Sulfs.
The following studies will be conducted to investigate the regulatory roles of Sulfs on satellite cell expansion and the mechanisms underlying Sulf regulation on the noncanonical Wnt signaling pathway. Information derived from this study would open new venues for designing better treatments for muscle related diseases such as muscular dystrophy and atrophy.
