Arylsulfatase L is a Golgi chondroitin sulfatase regulating skeletal development

: Sulfatases are a family of enzymes that hydrolyze sulfate esters from various substrates. Defects, in sulfatase activity, are associated with various human diseases due to the accumulation of sulfated substrates. Deficiency in ARSL, a Golgi sulfatase, is associated with X-linked recessive chondrodysplasia punctata (CDPX), a disorder characterized by defects in cartilage and bone development. However, until now, ARSL function has remained unknown. In this study, we demonstrate that ARSL promotes 4-O-desulfation of Chondroitin Sulfate (CS) during proteoglycan biosynthesis. Chondrocytes lacking ARSL exhibit hypersulfated CS and altered responses to TGF-β stimulation. Loss of function of ARSL orthologous in medaka fish (Ol-Arsd) results in hyper-4-O-sulfated CS, skeletal malformations, and craniofacial defects that partly resemble the human CDPX phenotype. Our findings uncover a previously unrecognized step in glycosaminoglycan (GAG) maturation-Golgi-based desulfation-and reveal a new layer of regulatory control in skeletal development.