Yoon Jung Hae, Chandrasekharan Kumaran, Xu Rui, Glass Matthew, Singhal Neha, Martin Paul T
Center for Gene Therapy, The Research Institute at Nationwide Children's Hospital, Department of Pediatrics, Ohio State University College of Medicine, 700 Children's Drive, Columbus, OH 43205, USA.
Mol Cell Neurosci. 2009 Aug;41(4):448-63. doi: 10.1016/j.mcn.2009.04.013. Epub 2009 May 12.
The CT carbohydrate, Neu5Ac/Neu5Gcalpha2,3[GalNAcbeta1,4]Galbeta1,4GlcNAcbeta-, is specifically expressed at the neuromuscular junction in skeletal myofibers of adult vertebrates. When Galgt2, the glycosyltransferase that creates the synaptic beta1,4GalNAc portion of this glycan, is overexpressed in extrasynaptic regions of the myofiber membrane, alpha dystroglycan becomes glycosylated with the CT carbohydrate and this coincides with the ectopic expression of synaptic dystroglycan-binding proteins, including laminin alpha4, laminin alpha5, and utrophin. Here we show that both synaptic and extrasynaptic forms of laminin and agrin have increased binding to the CT carbohydrate compared to sialyl-N-acetyllactosamine, its extrasynaptically expressed precursor. Muscle laminins also show increased binding to CT-glycosylated muscle alpha dystroglycan relative to its non-CT-containing glycoforms. Overexpression of Galgt2 in transgenic mouse skeletal muscle increased the mRNA expression of extracellular matrix (ECM) genes, including agrin and laminin alpha5, as well as utrophin, integrin alpha7, and neuregulin. Increased expression of ECM proteins in Galgt2 transgenic skeletal muscles was partially dependent on utrophin, but utrophin was not required for Galgt2-induced changes in muscle growth or neuromuscular development. These experiments demonstrate that overexpression of a synaptic carbohydrate can increase both ECM binding to alpha dystroglycan and ECM expression in skeletal muscle, and they suggest a mechanism by which Galgt2 overexpression may inhibit muscular dystrophy and affect neuromuscular development.
CT碳水化合物，即Neu5Ac/Neu5Gcalpha2,3[GalNAcbeta1,4]Galbeta1,4GlcNAcbeta-，在成年脊椎动物骨骼肌纤维的神经肌肉接头处特异性表达。当Galgt2（即产生这种聚糖突触β1,4GalNAc部分的糖基转移酶）在肌纤维膜的突触外区域过表达时，α- dystroglycan会被CT碳水化合物糖基化，这与包括层粘连蛋白α4、层粘连蛋白α5和抗肌萎缩蛋白在内的突触性dystroglycan结合蛋白的异位表达相吻合。在这里，我们表明，与唾液酸-N-乙酰乳糖胺（其突触外表达的前体）相比，层粘连蛋白和聚集蛋白的突触和突触外形式与CT碳水化合物的结合均增加。相对于不含CT的糖型，肌肉层粘连蛋白与CT糖基化的肌肉α- dystroglycan的结合也增加。Galgt2在转基因小鼠骨骼肌中的过表达增加了细胞外基质（ECM）基因的mRNA表达，包括聚集蛋白和层粘连蛋白α5，以及抗肌萎缩蛋白、整合素α7和神经调节蛋白。Galgt2转基因骨骼肌中ECM蛋白表达的增加部分依赖于抗肌萎缩蛋白，但Galgt2诱导的肌肉生长或神经肌肉发育变化并不需要抗肌萎缩蛋白。这些实验表明，突触碳水化合物的过表达可以增加ECM与α- dystroglycan的结合以及骨骼肌中ECM的表达，并且它们提示了Galgt2过表达可能抑制肌肉营养不良并影响神经肌肉发育的一种机制。
