Ohkawa Toshika, Satake Shin'Ichiro, Yokoi Norihiko, Miyazaki Yu, Ohshita Tomohiko, Sobue Gen, Takashima Hiroshi, Watanabe Osamu, Fukata Yuko, Fukata Masaki
Division of Membrane Physiology, Department of Cell Physiology, and Department of Physiological Sciences, School of Life Science, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8787, Japan;
Division of Neural Signaling, Department of Information Physiology, National Institute for Physiological Sciences, National Institutes of Natural Sciences; and Department of Physiological Sciences, School of Life Science, The Graduate University for Advanced Studies (SOKENDAI), Okazaki 444-8787, Japan;
J Neurosci. 2014 Jun 11;34(24):8151-63. doi: 10.1523/JNEUROSCI.4415-13.2014.
Autoimmune forms of encephalitis have been associated with autoantibodies against synaptic cell surface antigens such as NMDA- and AMPA-type glutamate receptors, GABA(B) receptor, and LGI1. However, it remains unclear how many synaptic autoantigens are yet to be defined. Using immunoproteomics, we identified autoantibodies against the GABA(A) receptor in human sera from two patients diagnosed with encephalitis who presented with cognitive impairment and multifocal brain MRI abnormalities. Both patients had antibodies directed against the extracellular epitope of the β3 subunit of the GABA(A) receptor. The β3-subunit-containing GABA(A) receptor was a major target of the patients' serum antibodies in rat hippocampal neurons because the serum reactivity to the neuronal surface was greatly decreased by 80% when the β3 subunit was knocked down. Our developed multiplex ELISA testing showed that both patients had similar levels of GABA(A) receptor antibodies, one patient also had a low level of LGI1 antibodies, and the other also had CASPR2 antibodies. Application of the patients' serum at the time of symptom presentation of encephalitis to rat hippocampal neuron cultures specifically decreased both synaptic and surface GABA(A) receptors. Furthermore, treatment of neurons with the patients' serum selectively reduced miniature IPSC amplitude and frequency without affecting miniature EPSCs. These results strongly suggest that the patients' GABA(A) receptor antibodies play a central role in the patients' symptoms. Therefore, this study establishes anti-GABA(A) receptor encephalitis and expands the pathogenic roles of GABA(A) receptor autoantibodies.
自身免疫性脑炎与针对突触细胞表面抗原的自身抗体有关，如N-甲基-D-天冬氨酸（NMDA）型和α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）型谷氨酸受体、γ-氨基丁酸B（GABA(B)）受体和富含亮氨酸的胶质瘤失活蛋白1（LGI1）。然而，仍不清楚还有多少突触自身抗原有待确定。我们利用免疫蛋白质组学，在两名被诊断为脑炎且伴有认知障碍和多灶性脑磁共振成像（MRI）异常的患者的血清中，鉴定出了针对GABA(A)受体的自身抗体。两名患者均有针对GABA(A)受体β3亚基细胞外表位的抗体。在大鼠海马神经元中，含β3亚基的GABA(A)受体是患者血清抗体的主要靶点，因为当β3亚基被敲低时，血清对神经元表面的反应性大幅降低了80%。我们开发的多重酶联免疫吸附测定（ELISA）检测显示，两名患者的GABA(A)受体抗体水平相似，一名患者还存在低水平的LGI1抗体，另一名患者还存在接触蛋白相关蛋白2（CASPR2）抗体。在脑炎症状出现时，将患者血清应用于大鼠海马神经元培养物，特异性地降低了突触型和表面型GABA(A)受体。此外，用患者血清处理神经元可选择性降低微小抑制性突触后电流（mIPSC）的幅度和频率，而不影响微小兴奋性突触后电流（mEPSC）。这些结果强烈表明，患者的GABA(A)受体抗体在患者症状中起核心作用。因此，本研究确立了抗GABA(A)受体脑炎，并扩展了GABA(A)受体自身抗体的致病作用。
