Molecular pathological analysis of citrullinated proteins in the brain from neurodegenerative disorder patients.

瓜氨酸化蛋白是翻译后过程的产物，其中当被肽基精氨酸脱亚胺酶（PAD）以钙离子依赖性方式催化时，精氨酸残基经历修饰成瓜氨酸残基。酶促瓜氨酸消除天然蛋白质分子的正电荷，不可避免地导致其结构和功能的显著改变。在哺乳动物组织中，PAD被发现为五种不同的同种型（即，1- 4，6型）。PAD 2主要表达于大鼠大脑，在神经退行性变的早期被激活。为了阐明瓜氨酸在神经元变性中的作用，我们检测了瓜氨酸化蛋白是否在阿尔茨海默病（AD）、帕金森病和亨廷顿舞蹈病中产生。1.组织化学分析显示，在海马各处都检测到瓜氨酸化蛋白。然而，在正常海马中未检测到瓜氨酸化蛋白。在AD和正常脑中，PAD 2免疫反应也在整个海马中检测到。双重免疫荧光染色显示瓜氨酸蛋白和PAD 2阳性细胞与GFAP阳性细胞有很好的一致性，但并非所有GFAP阳性细胞都是PAD 2阳性细胞。由于胶质纤维酸性蛋白是星形胶质细胞特异性标志蛋白，因此PAD 2主要分布于星形胶质细胞。2. Western blot检测AD海马组织中存在不同分子量的瓜氨酸化蛋白，而正常脑组织中无瓜氨酸化蛋白。其中两种瓜氨酸化蛋白被鉴定为波形蛋白（vimentin）和胶质细胞酸性蛋白（GFAP），因此，AD海马中存在瓜氨酸化蛋白的异常积累和PAD 2的异常激活。提示PAD在AD的发生、发展中起重要作用，瓜氨酸化蛋白可能成为神经退行性疾病的一个有用的标志物。

Citrullinated proteins are the products of a post-translational process in which arginine residues undergo modification into citrulline residues when catalyzed by peptidylarginine deiminases(PADs) in a calcium ion-dependent manner. Enzymatic citrullination abolishes positive charges of native protein molecules, inevitably causing significant alterations in their structure and functions. In mammalian tissues, PADs are found as five different isoforms (i.e, types 1-4,6). PAD2 expressed mainly in the rat cerebrum became activated early in the neurodegenerative process. To elucidate the involvement of the citrullination in neuronal degeneration, we examined whether citrullinated proteins are produced in Alzheimer's disease(AD), Parkinson's disease, and Huntington chorea.1.Histochemical analysis revealed that citrullinated proteins were detected all over the hippocampus. However, no citrullinated proteins were detected in the normal hippocampus. PAD2 immunoreactivity was also detected all over the hippocampus both in the AD and the normal brain. Double immunofluorescence staining revealed that citrullinated protein- and PAD2-positive cells were well-coinddenced with GFAP-positive cells, but not all GFAP-positive cells were PAD2-positive cells. As GFAP is a astrocyte-spedfic marker protein, PAD2 is distributed mainly in astrocytes.2.Citrullinated proteins with various molecular weight were detected in AD hippocampus by Western blot analysis, but not in normal brain. Two of the citrullinated proteins were identified as a vimentin and a glial fibrillary acidic protein(GFAP).Thus, abnormal accumulation of citrullinated proteins and abnormal activation of PAD2 is occurring in AD hippocampus. These results strongly suggested that PAD has an important role in the onset and progression of AD and citrullinated proteins may became a possible useful marker for human neurodegenerative disease.