Heparan sulfate 2-O-sulfotransferase is required for triglyceride-rich lipoprotein clearance.

Hepatic clearance of triglyceride-rich lipoproteins depends on heparan sulfate and low density lipoprotein receptors expressed on the basal membrane of hepatocytes. Binding and uptake of the lipoproteins by way of heparan sulfate depends on the degree of sulfation of the chains based on accumulation of plasma triglycerides and delayed clearance of triglyceride-rich lipoproteins in mice bearing a hepatocyte-specific alteration of N-acetylglucosamine (GlcNAc) N-deacetylase-N-sulfotransferase 1 (Ndst1) (MacArthur, J. M., Bishop, J. R., Stanford, K. I., Wang, L., Bensadoun, A., Witztum, J. L., and Esko, J. D. (2007) J. Clin. Invest. 117, 153-164). Inactivation of Ndst1 led to decreased overall sulfation of heparan sulfate due to coupling of uronyl 2-O-sulfation and glucosaminyl 6-O-sulfation to initial N-deacetylation and N-sulfation of GlcNAc residues. To determine whether lipoprotein clearance depends on 2-O-and 6-O-sulfation, we evaluated plasma triglyceride levels in mice containing loxP-flanked conditional alleles of uronyl 2-O-sulfotransferase (Hs2st(f/f)) and glucosaminyl 6-O-sulfotransferase-1 (Hs6st1(f/f)) and the bacterial Cre recombinase expressed in hepatocytes from the rat albumin (Alb) promoter. We show that Hs2st(f/f)AlbCre(+) mice accumulated plasma triglycerides and exhibited delayed clearance of intestinally derived chylomicrons and injected human very low density lipoproteins to the same extent as observed in Ndst1(f/f)AlbCre(+) mice. In contrast, Hs6st1(f/f)AlbCre(+) mice did not exhibit any changes in plasma triglycerides. Chemically modified heparins lacking N-sulfate and 2-O-sulfate groups did not block very low density lipoprotein binding and uptake in isolated hepatocytes, whereas heparin lacking 6-O-sulfate groups was as active as unaltered heparin. Our findings show that plasma lipoprotein clearance depends on specific subclasses of sulfate groups and not on overall charge of the chains.

Cerebral hypoplasia and craniofacial defects in mice lacking heparan sulfate Ndst1 gene function.

Mutant mice bearing a targeted disruption of the heparan sulfate (HS) modifying enzyme GlcNAc N-deacetylase/N-sulfotransferase 1 (Ndst1) exhibit severe developmental defects of the forebrain and forebrain-derived structures, including cerebral hypoplasia, lack of olfactory bulbs, eye defects and axon guidance errors. Neural crest-derived facial structures are also severely affected. We show that properly synthesized heparan sulfate is required for the normal development of the brain and face, and that Ndst1 is a modifier of heparan sulfate-dependent growth factor/morphogen signalling in those tissues. Among the multiple heparan sulfate-binding factors potentially affected in Ndst1 mutant embryos, the facial phenotypes are consistent with impaired sonic hedgehog (Shh) and fibroblast growth factor (Fgf) interaction with mutant heparan sulfate. Most importantly, the data suggest the possibility that defects in heparan sulfate synthesis could give rise to or contribute to a number of developmental brain and facial defects in humans.