From the Carl-Ludwig-Institute of Physiology (A.R.-J., F.G., T.K., S.M., S.H.), Faculty of Medicine, Leipzig University; Section Translational Neuroimmunology (J.S., C.G.), Department of Neurology, Jena University Hospital; Department of Biotechnology and Biophysics (S.S., C.W., M.S.), University of Würzburg, Biocenter, Germany; Institute of Science and Technology Austria (ISTA) (J.M., R.S.), Klosterneuburg, Austria; Oxford Autoimmune Neurology Group (S.R.I.), Nuffield Department of Clinical Neurosciences, University of Oxford, ; Department of Neurology (S.R.I.), John Radcliffe Hospital, Oxford University Hospitals, United Kingdom; and Departments of Neurology and Neurosciences (S.R.I.), Mayo Clinic Jacksonville, FL.
Neurol Neuroimmunol Neuroinflamm. 2024 Sep;11(5):e200284. doi: 10.1212/NXI.0000000000200284. Epub 2024 Aug 14.
Autoantibodies against the protein leucine-rich glioma inactivated 1 (LGI1) cause the most common subtype of autoimmune encephalitis with predominant involvement of the limbic system, associated with seizures and memory deficits. LGI1 and its receptor ADAM22 are part of a transsynaptic protein complex that includes several proteins involved in presynaptic neurotransmitter release and postsynaptic glutamate sensing. Autoantibodies against LGI1 increase excitatory synaptic strength, but studies that genetically disrupt the LGI1-ADAM22 complex report a reduction in postsynaptic glutamate receptor-mediated responses. Thus, the mechanisms underlying the increased synaptic strength induced by LGI1 autoantibodies remain elusive, and the contributions of presynaptic molecules to the LGI1-transsynaptic complex remain unclear. We therefore investigated the presynaptic mechanisms that mediate autoantibody-induced synaptic strengthening.
We studied the effects of patient-derived purified polyclonal LGI1 autoantibodies on synaptic structure and function by combining direct patch-clamp recordings from presynaptic boutons and somata of hippocampal neurons with super-resolution light and electron microscopy of hippocampal cultures and brain slices. We also identified the protein domain mediating the presynaptic effect using domain-specific patient-derived monoclonal antibodies.
LGI1 autoantibodies dose-dependently increased short-term depression during high-frequency transmission, consistent with increased release probability. The increased neurotransmission was not related to presynaptic calcium channels because presynaptic Ca2.1 channel density, calcium current amplitude, and calcium channel gating were unaffected by LGI1 autoantibodies. By contrast, application of LGI1 autoantibodies homogeneously reduced K1.1 and K1.2 channel density on the surface of presynaptic boutons. Direct presynaptic patch-clamp recordings revealed that LGI1 autoantibodies cause a pronounced broadening of the presynaptic action potential. Domain-specific effects of LGI1 autoantibodies were analyzed at the neuronal soma. Somatic action potential broadening was induced by polyclonal LGI1 autoantibodies and patient-derived monoclonal autoantibodies targeting the epitempin domain, but not the leucin-rich repeat domain.
Our results indicate that LGI1 autoantibodies reduce the density of both K1.1 and K1.2 on presynaptic boutons, without actions on calcium channel density or function, thereby broadening the presynaptic action potential and increasing neurotransmitter release. This study provides a molecular explanation for the neuronal hyperactivity observed in patients with LGI1 autoantibodies.
针对富含亮氨酸胶质瘤失活 1 蛋白（LGI1）的自身抗体导致以边缘系统为主受累的最常见自身免疫性脑炎亚型，伴发癫痫发作和记忆缺陷。LGI1 及其受体 ADAM22 是一个包含多个参与突触前神经递质释放和突触后谷氨酸感应的蛋白的突触间蛋白复合物的一部分。针对 LGI1 的自身抗体增加了兴奋性突触强度，但遗传破坏 LGI1-ADAM22 复合物的研究报告称，突触后谷氨酸受体介导的反应减少。因此，LGI1 自身抗体诱导的突触强度增加的机制仍不清楚，LGI1 突触间复合物中突触前分子的作用仍不清楚。因此，我们研究了介导自身抗体诱导的突触强化的突触前机制。
我们通过将海马神经元的突触前小泡和胞体的直接膜片钳记录与海马培养物和脑片的超分辨率光和电子显微镜相结合，研究了患者来源的纯化多克隆 LGI1 自身抗体对突触结构和功能的影响。我们还使用针对特定蛋白域的患者来源的单克隆自身抗体来鉴定介导突触前效应的蛋白域。
LGI1 自身抗体剂量依赖性地增加了高频传递时的短期抑郁，这与释放概率增加一致。增加的神经传递与突触前钙通道无关，因为 LGI1 自身抗体不影响突触前 Ca2.1 通道密度、钙电流幅度和钙通道门控。相比之下，LGI1 自身抗体的应用均匀地降低了突触前小泡表面的 K1.1 和 K1.2 通道密度。直接突触前膜片钳记录显示，LGI1 自身抗体导致突触前动作电位明显增宽。在神经元胞体上分析了 LGI1 自身抗体的特定蛋白域效应。多克隆 LGI1 自身抗体和针对 epitempin 结构域的患者来源的单克隆自身抗体诱导了胞体动作电位的增宽，但针对富含亮氨酸重复结构域的自身抗体则没有。
我们的结果表明，LGI1 自身抗体降低了突触前小泡上的 K1.1 和 K1.2 的密度，而不影响钙通道密度或功能，从而增宽了突触前动作电位并增加了神经递质释放。这项研究为 LGI1 自身抗体患者中观察到的神经元过度活跃提供了分子解释。
