Sulfs are regulators of growth factor signaling for satellite cell differentiation and muscle regeneration.

Heparan sulfate proteoglycans (HSPGs) are required during muscle regeneration for regulating extracellular signaling pathways. HSPGs interact with growth factors and receptors through heparan sulfate (HS) chains. However, the regulatory mechanisms that control HS sulfation to affect the growth factor-dependent proliferation and differentiation of satellite cells are yet unknown. Here we report the essential functions of extracellular HS 6-O-endosulfatases (Sulfs) during muscle regeneration. We show that quiescent and activated satellite cells differentially express mouse Sulf1 (MSulf1) and MSulf2. MSulfs are not required for the formation of skeletal muscles and satellite cells, but they have redundant, essential roles to promote muscle regeneration, as MSulf double mutant mice exhibit delayed myogenic differentiation and prolonged Pax7 expression after cardiotoxin-induced skeletal muscle injury, while single MSulf knockouts regenerate normally. HS structural analysis demonstrates that Sulfs are regulatory HS-modifying enzymes that control HS 6-O-desulfation of activated satellite cells. Mechanistically, we show that MSulfs repress FGF2 signaling in activated satellite cells, leading us to propose that MSulfs are growth factor signaling sensors to control the proliferation to differentiation switch of satellite cells to initiate differentiation during regeneration. Our results establish Sulfs as essential regulators of HS-dependent growth factor signaling in the adult muscle stem cell niche.