Elsevier

Matrix Biology

Volume 35, April 2014, Pages 18-24
Matrix Biology

EXTL2 controls liver regeneration and aortic calcification through xylose kinase-dependent regulation of glycosaminoglycan biosynthesis

https://doi.org/10.1016/j.matbio.2013.10.010Get rights and content
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Highlights

  • The role of EXTL2 in glycosaminoglycan (GAG) biosynthesis was proposed.

  • Production of GAGs was higher in EXTL2-knockout mice than in wild-type mice.

  • Liver regeneration was impaired in EXTL2-knockout mice.

  • Matrix mineralization in vascular smooth muscle cells of EXTL2-knockout mice was enhanced.

  • Lack of EXTL2 causes structural changes of GAGs associated with pathological processes.

Abstract

The gene products of two members of the EXT gene family, EXT1 and EXT2, function together as a polymerase in the biosynthesis of heparan sulfate. EXTL2, one of the three EXT-like genes in the human genome that are homologous to EXT1 and EXT2, encodes an N-acetylhexosaminyltransferase. However, both the role of EXTL2 in glycosaminoglycan (GAG) biosynthesis and the biological significance of EXTL2 remain unclear. Interestingly, EXTL2 can transfer a GlcNAc residue to the tetrasaccharide linkage region when this region is phosphorylated by a xylose kinase 1 (FAM20B) and thereby terminate chain elongation. Production of GAGs was significantly higher in EXTL2-knockout mice than in wild-type mice. EXTL2-knockout mice are viable and apparently healthy during development and after birth. Therefore, EXTL2-knockout mice were analyzed following the experimental induction of two separate pathological conditions. Carbon tetrachloride (CCl4) was used to induce liver failure, and 5/6th nephrectomy in combination with a high-phosphate diet was used to induce chronic kidney disease (CKD). Under conditions of CCl4-induced liver failure, hepatocyte proliferation following CCl4 treatment was lower in EXTL2-knockout mice than in wild-type mice; consequently, liver regeneration was impaired in EXTL2-knockout mice. This reduction in hepatocyte proliferation resulted partially because EXTL2-knockout mice experienced less hepatocyte-growth-factor-mediated signaling than did wild-type mice. Under conditions of induced CKD, matrix mineralization in vascular smooth muscle cells (VSMCs) in aortic rings of EXTL2-knockout mice was enhanced relative to that in wild-type mice. Altered biosynthesis of GAGs in EXTL2-knockout mice affected bone-morphogenetic-protein signaling, and consequently enhanced the differentiation of VSMCs into osteoblasts. Taken together, these results indicated that the EXTL2-dependent mechanism that regulates GAG biosynthesis is important for the maintenance of tissue homeostasis under pathological conditions, that is, lack of EXTL2 causes GAG overproduction and structural changes of GAGs associated with pathological processes.

Keywords

Proteoglycans
Heparan sulfate (HS)
Chondroitin sulfate (CS)
Exostosin (EXT) gene family
Liver regeneration
Aortic calcification

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