Abstract
Heparan sulfate (HS) is a linear carbohydrate composed of polymerized uronate-glucosamine disaccharide units that decorates cell surface and secreted glycoproteins in the extracellular matrix. In mammals HS is subjected to differential sulfation by fifteen different heparan sulfotransferase (HST) enzymes of which Hs2st uniquely catalyzes the sulfation of the 2-O position of the uronate in HS. HS sulfation is postulated to be important for regulation of signaling pathways by facilitating the interaction of HS with signaling proteins including those of the Fibroblast Growth Factor (Fgf) family which signal through phosphorylation of extracellular signal-regulated kinases Erk1/2. In the developing mouse telencephalon Fgf2 signaling regulates proliferation and neurogenesis. Loss of Hs2st function phenocopies the thinned cerebral cortex of mutant mice in which Fgf2 or Erk1/2 function are abrogated, suggesting the hypothesis that 2-O-sulfated HS structures play a specific role in Fgf2/Erk signaling pathway in this context in vivo. This study investigated the molecular role of 2-O sulfation in Fgf2/Erk signaling in the developing telencephalic midline midway through mouse embryogenesis at E12.5. We examined the expression of Hs2st, Fgf2, and Erk1/2 activity in wild-type and Hs2st-/- mice. We found that Hs2st is expressed at high levels at the midline correlating with high levels of Erk1/2 activation and Erk1/2 activation was drastically reduced in the Hs2st-/- mutant at the rostral telencephalic midline. We also found that 2-O sulfation is specifically required for the binding of Fgf2 protein to Fgfr1, its major cell-surface receptor at the rostral telencephalic midline. We conclude that 2-O sulfated HS structures generated by Hs2st are needed to form productive signaling complexes between HS, Fgf2 and Fgfr1 that activate Erk1/2 at the midline. Overall, our data suggest the interesting possibility that differential expression of Hs2st targets the rostral telencephalic midline for high levels of Erk signaling by increasing the sensitivity of cells to an Fgf2 signal that is rather more widespread.
Highlights
Heparan sulfate proteoglycans (HSPGs) are cell surface and secreted molecules expressed by all animal cells
heparan sulfate (HS) in Hs2st-/- embryos lacks 2-O HS sulfation and is unable to form a ternary structure with Fgf2 and Fgfr1 leading to the dramatic decrease in the cells’ ability to activate Erk1/2 (Fig 5B)
While some of these findings could be predicted from previous crystallography studies [9,10,33] and in vitro studies [6,7,14,16], to the best of our knowledge, this is the first time that 2-O HS sulfation has been demonstrated to be critical in vivo for regulating Erk signaling and the formation of HS:Fgf2:Fgfr1 complexes in neural tissue
Summary
Heparan sulfate proteoglycans (HSPGs) are cell surface and secreted molecules expressed by all animal cells. HS is differentially sulfated by specific 2-O, 3-O, 6-O and N- sulfotransferases and 6-O desulfated by sulfatases giving rise to a potentially enormous variety of HS structures This variety is key in HS’s biological role according to the HS “sugar code” hypothesis which states that different HS structures differentially instruct signaling pathways during biological processes including brain development [1,2,3,4,5]. 2-O HS sulfation catalyzed by Hs2st could be regulating Fgf2/Erk signaling in vivo by regulating the levels of the Fgf ligand and/or the ability of Fgf to bind to its receptors on the surface of target cells
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
