Biology subjects

Kirmann, T.

Publications and source records attributed to Kirmann, T..

3 recordsLinked to original sources

bioRxiv2023

Peripherally derived LGI1-reactive monoclonal antibodies cause epileptic seizures in vivo

One striking clinical hallmark in patients with autoantibodies to leucine-rich glioma inactivated 1 (LGI1) is the very frequent focal seizure semiologies, including faciobrachial dystonic seizures (FBDS), in addition to the amnesia. Polyclonal serum IgGs have successfully modelled the cognitive changes in vivo but not seizures. Hence, it remains unclear whether LGI1-autoantibodies are sufficient to cause seizures. We tested this with the molecularly precise monoclonal antibodies directed against LGI1 (LGI1-mAbs), derived from patient circulating B cells. These were directed towards both major domains of LGI1, LRR (n=5) and EPTP (n=5) and infused intracerebroventricularly over 7 days into juvenile male Wistar rats using osmotic pumps. Continuous wireless EEG was recorded from a depth electrode placed in hippocampal CA3 plus behavioural tests for memory and hyperexcitability were performed. Following infusion completion (Day 9), post-mortem brain slices were studied using electrophysiology and immunostaining. By comparison to control-mAb injected rats (n=6), video-EEG analysis over 9 days revealed convulsive and non-convulsive seizure activity in rats infused with LGI1-mAbs, with a significant number of ictal events (245{+/-}83 vs. 7.8{+/-}7.8 in controls; p=0.002). Memory was not impaired in the novel object recognition test. Local field potential recordings from postmortem brain slices showed spontaneous ictal-like spike activity in the CA3 region (p=0.03). The LGI1-mAbs bound most strongly in the hippocampal CA3 region and induced a significant reduction in Kv1.1 cluster number in this subfield (6 controls; 7 LGI1-mAbs; p=0.01) Peripherally-derived human LGI1-mAbs infused into rodent CSF provide strong evidence of direct in vivo epileptogenesis with molecular correlations. These findings fulfill criteria for LGI1-antibodies in seizure causation.

neuroscience↗

bioRxiv2023

LGI1 autoantibodies enhance synaptic transmission by presynaptic Kv1 loss and increased action potential broadening

Background and ObjectivesAutoantibodies against the neuronally secreted protein leucine-rich glioma inactivated 1 (LGI1) cause the most common subtype of autoimmune limbic encephalitis 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. MethodsWe 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 acute brain slices. We also identified the protein domain mediating the presynaptic effect using domain-specific patient-derived monoclonal antibodies. ResultsLGI1 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, as presynaptic Cav2.1 channel density, calcium current amplitude, and calcium channel gating were unaffected by LGI1 autoantibodies. In contrast, application of LGI1 autoantibodies homogeneously reduced Kv1.1 and Kv1.2 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 analysed at the soma, where polyclonal LGI1 autoantibodies and patient-derived monoclonal autoantibodies targeting the Epitempin-domain but not the Leucin rich repeat-domain induced action potential broadening. DiscussionOur results indicate that LGI1 autoantibodies do not affect calcium channel density or function, but reduce the density of both Kv1.1 and Kv1.2 on presynaptic boutons, thereby broadening the presynaptic action potential and increasing neurotransmitter release. This study provides a molecular explanation for the neuronal hyperactivity induced by LGI1 autoantibodies.

neuroscience↗

bioRxiv2022

NMDA-receptor-Fc-fusion constructs neutralize anti- NMDA receptor antibodies

N-methyl-D-aspartate receptor (NMDAR) encephalitis is the most common subtype of autoimmune encephalitis characterized by a complex neuropsychiatric syndrome ranging from memory impairment and psychosis to coma. Patients develop an intrathecal immune response against NMDARs with antibodies that presumably bind to the amino-terminal domain (ATD) of the GluN1 subunit. The therapeutic response to immunotherapy is often delayed and does not directly interfere with intrathecal synthesis of pathogenic antibodies. Therefore, new therapeutic approaches for fast neutralization of NMDAR antibodies are needed. Here, we developed fusion constructs consisting of the Fc part of immunoglobulin G and the ATDs of either GluN1 or GluN2B or both, GluN1 and GluN2B, subunits. Surprisingly, both subunits were required to generate high-affinity epitopes. The construct with both subunits efficiently prevented NMDAR binding of patient-derived monoclonal antibodies and of patient cerebrospinal fluid containing high-titer NMDAR antibodies. Furthermore, it inhibited the internalization of NMDARs in rodent dissociated neurons and human induced pluripotent stem cells (iPSC)-derived neurons. Finally, the construct stabilized NMDAR currents recorded in rodent neurons. Our results demonstrate that both GluN1 and GluN2B subunits contribute to the main immunogenic region of the NMDAR and provide a promising strategy for fast and specific treatment of NMDAR encephalitis, which can complement immunotherapy.

neuroscience↗