Shields D C, Banik N L
Department of Neurology, Medical University of South Carolina, 171 Ashley Avenue, Charleston, S.C., 29425, USA.
Exp Eye Res. 1998 Oct;67(4):403-10. doi: 10.1006/exer.1998.0537.
Since myelin proteins are degraded in autoimmune demyelinating diseases such as optic neuritis, proteinases are believed to participate in myelinolysis. Calpain (calcium activated neutral proteinase) degrades myelin proteins at physiological pH and is found in glial and inflammatory cells involved in demyelination. To examine the putative role of calpain in myelinolysis, the activity and expression (translational and transcriptional) of this enzyme and endogenous inhibitor, calpastatin were examined in optic nerves of Lewis rats with experimental allergic encephalomyelitis (EAE), an animal model of optic neuritis. Calpain activity was examined via Western blotting by measuring the extent of myelin protein degradation and calpain-specific fodrin proteolysis in optic nerves from controls versus rats with experimental optic neuritis. RT-PCR studies demonstrated no significant change in millicalpain, microcalpain, or calpastatin expression at the mRNA level in optic nerves from animals with experimental optic neuritis compared to controls. However, myelin associated glycoprotein (MAG) levels were decreased by 25.5% while calpain translational expression and calpain-autolyzed fodrin levels were increased by 72.1% and 462.8% respectively, in experimental optic neuritis compared to controls. Translational expression of calpastatin isoforms (80, 68 and 55 KD) was not significantly different in rats with experimental optic neuritis compared to controls. Thus, increased activity and translational expression of calpain in experimental optic neuritis suggests this proteinase may participate in the degradation of myelin and cytoskeletal proteins in demyelinating diseases such as optic neuritis.
由于髓磷脂蛋白在自身免疫性脱髓鞘疾病（如视神经炎）中会发生降解，因此蛋白酶被认为参与了髓鞘溶解过程。钙蛋白酶（钙激活中性蛋白酶）在生理pH值下可降解髓磷脂蛋白，且存在于参与脱髓鞘过程的神经胶质细胞和炎症细胞中。为了研究钙蛋白酶在髓鞘溶解中的假定作用，我们检测了实验性变应性脑脊髓炎（EAE，一种视神经炎动物模型）Lewis大鼠视神经中该酶及其内源性抑制剂钙蛋白酶抑制蛋白的活性和表达（翻译水平和转录水平）。通过蛋白质印迹法，测量对照大鼠与实验性视神经炎大鼠视神经中髓磷脂蛋白降解程度以及钙蛋白酶特异性的血影蛋白水解程度，以此检测钙蛋白酶活性。逆转录聚合酶链反应（RT-PCR）研究表明，与对照组相比，实验性视神经炎动物视神经中毫微钙蛋白酶、微钙蛋白酶或钙蛋白酶抑制蛋白在mRNA水平上的表达没有显著变化。然而，与对照组相比，实验性视神经炎中髓鞘相关糖蛋白（MAG）水平降低了25.5%，而钙蛋白酶的翻译表达以及钙蛋白酶自溶的血影蛋白水平分别增加了72.1%和462.8%。与对照组相比，实验性视神经炎大鼠中钙蛋白酶抑制蛋白亚型（80、68和55千道尔顿）的翻译表达没有显著差异。因此，实验性视神经炎中钙蛋白酶活性和翻译表达的增加表明，这种蛋白酶可能参与了视神经炎等脱髓鞘疾病中髓磷脂和细胞骨架蛋白的降解。
