Mutations in B3GALNT2 Cause Congenital Muscular Dystrophy and Hypoglycosylation of α-Dystroglycan
Mutations in B3GALNT2 Cause Congenital Muscular Dystrophy and Hypoglycosylation of α-Dystroglycan
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DOI：
10.1016/j.ajhg.2013.01.016
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发表时间：
2013-03-07
影响因子：
9.8
通讯作者：
Muntoni, Francesco
中科院分区：
文献类型：
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作者：
Stevens, Elizabeth;Carss, Keren J.;Muntoni, Francesco
几种已知或推定的糖基转移酶的突变导致α-肌营养不良蛋白聚糖（α-DG）的糖基化缺陷，α-DG是肌营养不良蛋白糖蛋白复合物的组成部分。低糖基化降低了α-DG结合层粘连蛋白和其他细胞外基质配体的能力，并且是称为肌营养不良聚糖病的遗传性肌营养不良亚群的发病机制的原因。通过外显子组和桑格测序，我们确定了两个人患有β-1，3-N-乙酰氨基半乳糖转移酶2（B3 GALNT 2）突变的肌营养不良症。B3 GALNT 2将β-1，3键中的N-乙酰基半乳糖胺（GalNAc）转移至N-乙酰基葡糖胺（GlcNAc）。随后对一组单独的个体进行的研究在另外4例病例中发现了隐性突变，这些病例均受结构性脑受累的肌营养不良症的影响。我们通过流式细胞术、免疫印迹和免疫细胞化学显示，这些个体的成纤维细胞和肌肉（可用时）中的功能性肌营养不良蛋白聚糖糖基化减少。B3 GALNT 2定位于内质网，并且这种定位受到鉴定的一些错义突变的干扰。此外，斑马鱼中b3 galnt 2的敲除重现了人类先天性肌营养不良症的表型，表现为运动能力降低、大脑异常和肌纤维紊乱，并有肌间隔和肌膜损伤的证据。在b3 galnt 2基因敲低的斑马鱼胚胎中，功能性肌营养不良蛋白聚糖糖基化也减少。总之，这些结果证明了B3 GALNT 2在α-DG糖基化中的作用，并表明B3 GALNT 2突变可引起肌肉和大脑受累的肌营养不良症。
Mutations in several known or putative glycosyltransferases cause glycosylation defects in alpha-dystroglycan (alpha-DG), an integral component of the dystrophin glycoprotein complex. The hypoglycosylation reduces the ability of alpha-DG to bind laminin and other extracellular matrix ligands and is responsible for the pathogenesis of an inherited subset of muscular dystrophies known as the dystroglycanopathies. By exome and Sanger sequencing we identified two individuals affected by a dystroglycanopathy with mutations in beta-1,3-N-acetylgalactosaminyltransferase 2 (B3GALNT2). B3GALNT2 transfers N-acetyl galactosamine (GalNAc) in a beta-1,3 linkage to N-acetyl glucosamine (GlcNAc). A subsequent study of a separate cohort of individuals identified recessive mutations in four additional cases that were all affected by dystroglycanopathy with structural brain involvement. We show that functional dystroglycan glycosylation was reduced in the fibroblasts and muscle (when available) of these individuals via flow cytometry, immunoblotting, and immunocytochemistry. B3GALNT2 localized to the endoplasmic reticulum, and this localization was perturbed by some of the missense mutations identified. Moreover, knockdown of b3galnt2 in zebrafish recapitulated the human congenital muscular dystrophy phenotype with reduced motility, brain abnormalities, and disordered muscle fibers with evidence of damage to both the myosepta and the sarcolemma. Functional dystroglycan glycosylation was also reduced in the b3galnt2 knockdown zebralish embryos. Together these results demonstrate a role for B3GALNT2 in the glycosylation of alpha-DG and show that B3GALNT2 mutations can cause dystroglycanopathy with muscle and brain involvement.