Critical role of KLK6 in the pathogenesis of Multiple Sclerosis

多发性硬化症（MS）是一种中枢神经系统（CNS）的炎症性脱髓鞘疾病。它会导致神经损伤。其中一种动物模型是髓鞘少突胶质细胞糖蛋白（MOG）诱导的实验性自身免疫性脑脊髓炎（EAE），其特征是中枢神经系统瘫痪和免疫细胞浸润。我们之前报道过一种丝氨酸蛋白酶，Kallikrein 6 (KLK6)，是由中枢神经系统中完全成熟的少突胶质细胞产生的，并且在脊髓损伤和EAE后，KLK6在少突胶质细胞中上调。然而，KLK6在MS发病机制中的作用尚不完全清楚。在这里，我们报道KLK6通过血脑屏障破坏参与了EAE的发病。为了研究KLK6在脱髓鞘中的作用，我们检测了KLK6对KLK6敲除（KO）小鼠EAE发病的影响。与野生型小鼠相比，KLK6 KO小鼠表现出EAE进展的改变，其特征是延迟发作和临床症状进展。luxol快速蓝的组织学研究也显示EAE患者脊髓内浸润炎性细胞数量减少，提示缺乏KLK6可抑制外周炎性细胞向中枢神经系统的浸润。接下来，我们通过evans蓝染料注射检测了KLK6对血脑屏障通透性的影响。与野生型小鼠相比，KLK6 KO小鼠明显抑制血脑屏障通透性。最后我们发现EAE对KLK6 KO小鼠的基质金属蛋白酶-9的激活有抑制作用。这些结果表明，KLK6在EAE的发病机制中起着至关重要的作用。

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS). It results in neurological impairments. One of animal model is myelin oligodendrocyte glycoprotein (MOG)- induced experimental autoimmune encephalomyelitis (EAE), which is characterized by paralysis and immune cell infiltration in the CNS. We have previously reported that a serine protease, Kallikrein 6 (KLK6), is produced by exclusively mature oligodendrocytes in the CNS, and that KLK6 is up-regulated in oligodendrocytes after spinal cord injury and EAE. However, the function of KLK6 in the pathogenesis of MS has not been fully understood.Here we report that KLK6 is involved in onset of EAE via BBB breakdown. To investigate the role of KLK6 in demyelination, we examined the effect of KLK6 on onset of EAE in KLK6 knock out (KO) mice. KLK6 KO mice exhibited an altered EAE progression characterized by delayed onset and progression of clinical symptoms as compared to wild-type mice. Histological study with luxol fast blue also revealed a decreased number of infiltrating inflammatory cells in spinal cord with EAE, suggesting that absence of KLK6 suppressed infiltration of peripheral inflammatory cells into the CNS with EAE. We next examined the effect of KLK6 on BBB permeability by evans blue dye injection. KLK6 KO mice showed much suppression of BBB permeability compared to wild-type mice. Finally we found that activation of Matrix metalloprotease-9 was inhibited in KLK6 KO mice with EAE. These results suggest that KLK6 play a crucial role of the pathogenesis of EAE.