Mastronardi Fabrizio G, Wood D Denise, Mei Jiang, Raijmakers Reinout, Tseveleki Vivian, Dosch Hans-Michael, Probert Lesley, Casaccia-Bonnefil Patrizia, Moscarello Mario A
Department of Structural Biology and Biochemistry, The Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.
J Neurosci. 2006 Nov 1;26(44):11387-96. doi: 10.1523/JNEUROSCI.3349-06.2006.
Modification of arginine residues by citrullination is catalyzed by peptidylarginine deiminases (PADs), of which five are known, generating irreversible protein structural modifications. We have shown previously that enhanced citrullination of myelin basic protein contributed to destabilization of the myelin membrane in the CNS of multiple sclerosis (MS) patients. We now report increased citrullination of nucleosomal histones by PAD4 in normal-appearing white matter (NAWM) of MS patients and in animal models of demyelination. Histone citrullination was attributable to increased levels and activity of nuclear PAD4. PAD4 translocation into the nucleus was attributable to elevated tumor necrosis factor-alpha (TNF-alpha) protein. The elevated TNF-alpha in MS NAWM was not associated with CD3+ or CD8+ lymphocytes, nor was it associated with CD68+ microglia/macrophages. GFAP, a measure of astrocytosis, was the only cytological marker that was consistently elevated in the MS NAWM, suggesting that TNF-alpha may have been derived from astrocytes. In cell cultures of mouse and human oligodendroglial cell lines, PAD4 was predominantly cytosolic but TNF-alpha treatment induced its nuclear translocation. To address the involvement of TNF-alpha in targeting PAD4 to the nucleus, we found that transgenic mice overexpressing TNF-alpha also had increased levels of citrullinated histones and elevated nuclear PAD4 before demyelination. In conclusion, high citrullination of histones consequent to PAD4 nuclear translocation is part of the process that leads to irreversible changes in oligodendrocytes and may contribute to apoptosis of oligodendrocytes in MS.
瓜氨酸化对精氨酸残基的修饰由肽基精氨酸脱亚氨酶（PADs）催化，已知有五种此类酶，它们会产生不可逆的蛋白质结构修饰。我们之前已经表明，髓鞘碱性蛋白瓜氨酸化增强会导致多发性硬化症（MS）患者中枢神经系统中髓鞘膜的不稳定。我们现在报告，在MS患者外观正常的白质（NAWM）以及脱髓鞘动物模型中，PAD4会使核小体组蛋白的瓜氨酸化增加。组蛋白瓜氨酸化归因于核内PAD4水平和活性的增加。PAD4易位至细胞核归因于肿瘤坏死因子-α（TNF-α）蛋白水平升高。MS患者NAWM中升高的TNF-α与CD3⁺或CD8⁺淋巴细胞无关，也与CD68⁺小胶质细胞/巨噬细胞无关。胶质纤维酸性蛋白（GFAP）是星形细胞增生的一个指标，是MS患者NAWM中唯一持续升高的细胞学标志物，这表明TNF-α可能来源于星形胶质细胞。在小鼠和人类少突胶质细胞系的细胞培养中，PAD4主要位于胞质，但TNF-α处理会诱导其核易位。为了研究TNF-α在将PAD4靶向细胞核中的作用，我们发现过表达TNF-α的转基因小鼠在脱髓鞘之前也有瓜氨酸化组蛋白水平升高和核内PAD4升高的情况。总之，PAD4核易位导致的组蛋白高度瓜氨酸化是导致少突胶质细胞发生不可逆变化过程的一部分，可能促成MS中少突胶质细胞的凋亡。
