Katsuki Hiroshi, Okawara Mitsugi, Shibata Haruki, Kume Toshiaki, Akaike Akinori
Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto, Japan.
J Neurochem. 2006 Jun;97(5):1232-42. doi: 10.1111/j.1471-4159.2006.03752.x. Epub 2006 Apr 21.
Activated microglia are considered to play important roles in degenerative processes of midbrain dopaminergic neurons. Here we examined mechanisms of neurotoxicity of thrombin, a protease known to trigger microglial activation, in organotypic midbrain slice cultures. Thrombin induced a progressive decline in the number of dopaminergic neurons, an increase in nitric oxide (NO) production, and whole tissue injury indicated by lactate dehydrogenase release and propidium iodide uptake. Microglia expressed inducible NO synthase (iNOS) in response to thrombin, and inhibition of iNOS rescued dopaminergic neurons without affecting whole tissue injury. Inhibitors of mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK), p38 MAPK and c-Jun N-terminal kinase (JNK) attenuated thrombin-induced iNOS induction and dopaminergic cell death. Whole tissue injury was also attenuated by inhibition of ERK and p38 MAPK. Moreover, depletion of resident microglia from midbrain slices abrogated thrombin-induced NO production and dopaminergic cell death, but did not inhibit tissue injury. Finally, antioxidative drugs prevented thrombin-induced dopaminergic cell death without affecting whole tissue injury. Hence, NO production resulting from MAPK-dependent microglial iNOS induction is a crucial event in thrombin-induced dopaminergic neurodegeneration, whereas damage of other midbrain cells is MAPK-dependent but is NO-independent.
活化的小胶质细胞被认为在中脑多巴胺能神经元的退行性变过程中起重要作用。在此，我们在器官型中脑切片培养物中研究了凝血酶（一种已知可触发小胶质细胞活化的蛋白酶）的神经毒性机制。凝血酶导致多巴胺能神经元数量逐渐减少、一氧化氮（NO）生成增加，以及乳酸脱氢酶释放和碘化丙啶摄取所表明的全组织损伤。小胶质细胞响应凝血酶表达诱导型一氧化氮合酶（iNOS），抑制iNOS可挽救多巴胺能神经元，而不影响全组织损伤。丝裂原活化蛋白激酶（MAPK）抑制剂，如细胞外信号调节激酶（ERK）、p38 MAPK和c-Jun氨基末端激酶（JNK），可减弱凝血酶诱导的iNOS诱导和多巴胺能细胞死亡。抑制ERK和p38 MAPK也可减轻全组织损伤。此外，从中脑切片中去除常驻小胶质细胞可消除凝血酶诱导的NO生成和多巴胺能细胞死亡，但不抑制组织损伤。最后，抗氧化药物可预防凝血酶诱导的多巴胺能细胞死亡，而不影响全组织损伤。因此，MAPK依赖的小胶质细胞iNOS诱导产生的NO生成是凝血酶诱导的多巴胺能神经退行性变中的关键事件，而其他中脑细胞的损伤是MAPK依赖的，但不依赖于NO。
