Hyposialylation of neprilysin possibly affects its expression and enzymatic activity in hereditary inclusion-body myopathy muscle
Hyposialylation of neprilysin possibly affects its expression and enzymatic activity in hereditary inclusion-body myopathy muscle
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DOI：
10.1111/j.1471-4159.2007.05208.x
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发表时间：
2008-05-01
影响因子：
4.7
通讯作者：
Mirabella, Massimiliano
中科院分区：
文献类型：
--
作者：
Broccolini, Aldobrando;Gidaro, Teresa;Mirabella, Massimiliano
常染色体隐性遗传性包涵体肌病（h-IBM）是由UDP-N-乙酰葡糖胺2-差向异构酶/N-乙酰甘露糖胺激酶基因（唾液酸代谢途径中的限速酶）突变引起的。之前的研究已经证明h-IBM中糖蛋白的唾液酸化异常。h-IBM肌肉显示蛋白质的异常积累，包括淀粉样蛋白β（A β）。Neprilysin（NEP）是一种切割A β的金属肽酶，其特征在于存在几个N-糖基化位点，并且这些糖部分的变化影响其稳定性和酶活性。在本研究中，我们发现，NEP是hyposialylated和它的表达和酶活性降低在所有的h-IBM肌肉分析。在体外培养的肌管中，用霍乱弧菌神经氨酸酶去除唾液酸导致NEP表达减少。这最有可能是因为翻译后修饰，包括蛋白质的异常唾液酸化，导致其稳定性降低。此外，用霍乱弧菌神经氨酸酶治疗与A β的免疫反应性增加相关，主要以肌管内不同细胞质病灶的形式。我们假设，在h-IBM肌肉，hyposialylated NEP有阻碍细胞A β清除系统的作用，从而有助于其异常积累在脆弱的纤维，并可能促进肌肉变性。
Autosomal recessive hereditary inclusion-body myopathy (h-IBM) is caused by mutations of the UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase gene, a rate-limiting enzyme in the sialic acid metabolic pathway. Previous studies have demonstrated an abnormal sialylation of glycoproteins in h-IBM. h-IBM muscle shows the abnormal accumulation of proteins including amyloid-beta (A beta). Neprilysin (NEP), a metallopeptidase that cleaves A beta, is characterized by the presence of several N-glycosylation sites, and changes in these sugar moieties affect its stability and enzymatic activity. In the present study, we found that NEP is hyposialylated and its expression and enzymatic activity reduced in all h-IBM muscles analyzed. In vitro, the experimental removal of sialic acid by Vibrio Cholerae neuraminidase in cultured myotubes resulted in reduced expression of NEP. This was most likely because of a post-translational modification consisting in an abnormal sialylation of the protein that leads to its reduced stability. Moreover, treatment with Vibrio Cholerae neuraminidase was associated with an increased immunoreactivity for A beta mainly in the form of distinct cytoplasmic foci within myotubes. We hypothesize that, in h-IBM muscle, hyposialylated NEP has a role in hampering the cellular A beta clearing system, thus contributing to its abnormal accumulation within vulnerable fibers and possibly promoting muscle degeneration.