An Epitope-Specific LGI1-Autoantibody Enhances Neuronal Excitability by Modulating Kv1.1 Channel

Abstract

Leucine-rich Glioma-Inactivated protein 1 (LGI1) is expressed in the central nervous system and its genetic loss of function is associated with epileptic disorders. Additionally, patients with LGI1-directed autoantibodies have frequent focal seizures as a key feature of their disease. LGI1 is composed of a Leucine-Rich Repeat (LRR) and an Epitempin (EPTP) domain. These domains are reported to interact with different members of the transsynaptic complex formed by LGI1 at excitatory synapses, including presynaptic Kv1 potassium channels. Patient-derived recombinant monoclonal antibodies (mAbs) are ideal reagents to study whether domain-specific LGI1-autoantibodies induce epileptiform activities in neurons and their downstream mechanisms. We measured the intrinsic excitability of CA3 pyramidal neurons in organotypic cultures from rat hippocampus treated with either an LRR- or an EPTP-reactive patient-derived mAb, or with IgG from control patients. We found an increase in intrinsic excitability correlated with a reduction of the sensitivity to a selective Kv1.1-channel blocker in neurons treated with the LRR mAb, but not in neurons treated with the EPTP mAb. Our findings suggest LRR mAbs are able to modulate neuronal excitability that could account for epileptiform activity observed in patients.

Comparative Effects of Domain-Specific Human Monoclonal Antibodies Against LGI1 on Neuronal Excitability

“…Previous studies showed simultaneous occurrence of both epitope-specific LGI1 antibodies in patients with LGI1 encephalitis with an increased ratio of LRR-specific IgG. 20 From our data and other reports investigating epitope-specific effects of LGI1 mAbs, 15 , 21 , 42 LRR-specific IgG might be more effective in inducing hyperexcitability and possibly leading to seizure initiation. However, larger patient cohorts need to be investigated to evaluate the relative contribution of epitope-specific IgG antibodies for disease symptom development.…”

“…These results obtained in primary neurons corroborate observations obtained in rat hippocampal slice cultures using similar patient-derived mAbs against LRR and EPTP, which have been attributed to reduced K v 1 channel–mediated I D current. 42 This has been substantiated here and in slice cultures 20 by reduced slope of ramp-like depolarization of subthreshold response at prerheobase current step injection (see also Refs. 20 , 29 , 30 for using this measure) and in recent studies by diminished effects of the K v 1.1-specific channel blocker dendrotoxin K. 20 , 42 This view is also supported by LRR-specific antibodies that may prevent the interaction of LGI1 to the K v β subunits, resulting in the transformation of slowly inactivating D-type currents into rapidly inactivating A-type currents, as shown in an in vitro model.…”

“… 42 This has been substantiated here and in slice cultures 20 by reduced slope of ramp-like depolarization of subthreshold response at prerheobase current step injection (see also Refs. 20 , 29 , 30 for using this measure) and in recent studies by diminished effects of the K v 1.1-specific channel blocker dendrotoxin K. 20 , 42 This view is also supported by LRR-specific antibodies that may prevent the interaction of LGI1 to the K v β subunits, resulting in the transformation of slowly inactivating D-type currents into rapidly inactivating A-type currents, as shown in an in vitro model. 36 This hypothesis would support our observations in the significantly reduced K v 1.1-dependent depolarization ramp and the underlying conductance G D , as shown in the computational model ( Figure 2D , Figure 3, A and B ).…”

“…Our findings are corroborated by other recent or parallel studies investigating different LRR and EPTP-specific mAbs that also describe a more pronounced effect of LRR-in comparison to EPTP-specific mAbs leading to increased neuronal excitability. 20 , 42 In addition to understand antibody-induced pathology at the AIS, it will be another important goal for further studies to address the role of epitope-specific antibodies in the dysfunction and disassembly of the macromolecular complex of LGI1, ADAM22/23, K v 1 channels, and AMPA receptors at the synapse. 16 , 20 …”

Rescue of normal excitability in LGI1-deficient epileptic neurons

“…Slices cultures were prepared as described previously (Debanne et al, 2008; Extrémet et al, 2022). Young Lgi1 KO mice (P7–P10) were killed by decapitation, the brain was removed, and each hippocampus dissected.…”