Oligodendrocyte-derived LGI3 and its receptor ADAM23 organize juxtaparanodal Kv1 channel clustering for short-term synaptic plasticity

Neurodevelopmental disorders, such as intellectual disability (ID), epilepsy, and autism, involve altered synaptic transmission and plasticity. Functional characterization of their associated genes is vital for understanding physio-pathological brain functions. LGI3 is a recently recognized ID-associated gene encoding a secretory protein related to an epilepsy-gene product, LGI1. Here, we find that LGI3 is uniquely secreted from oligodendrocytes in the brain and enriched at juxtaparanodes of myelinated axons, forming nanoscale subclusters. Proteomic analysis using epitope-tagged Lgi3 knockin mice shows that LGI3 uses ADAM23 as a receptor and selectively co-assembles with Kv1 channels. A lack of Lgi3 in mice disrupts juxtaparanodal clustering of ADAM23 and Kv1 channels and suppresses Kv1-channel-mediated short-term synaptic plasticity. Collectively, this study identifies an extracellular organizer of juxtaparanodal Kv1 channel clustering for finely tuned synaptic transmission. Given the defective secretion of the LGI3 missense variant, we propose a molecular pathway, the juxtaparanodal LGI3-ADAM23-Kv1 channel, for understanding neurodevelopmental disorders.

A reverse genetics and genomics approach to gene paralog function and disease: Myokymia and the juxtaparanode

The leucine-rich glioma-inactivated (LGI) family consists of four highly conserved paralogous genes, LGI1-4, that are highly expressed in mammalian central and/or peripheral nervous systems. LGI1 antibodies are detected in subjects with autoimmune limbic encephalitis and peripheral nerve hyperexcitability syndromes (PNHSs) such as Isaacs and Morvan syndromes. Pathogenic variations of LGI1 and LGI4 are associated with neurological disorders as disease traits including familial temporal lobe epilepsy and neurogenic arthrogryposis multiplex congenita 1 with myelin defects, respectively. No human disease has been reported associated with either LGI2 or LGI3. We implemented exome sequencing and family-based genomics to identify individuals with deleterious variants in LGI3 and utilized GeneMatcher to connect practitioners and researchers worldwide to investigate the clinical and electrophysiological phenotype in affected subjects. We also generated Lgi3-null mice and performed peripheral nerve dissection and immunohistochemistry to examine the juxtaparanode LGI3 microarchitecture. As a result, we identified 16 individuals from eight unrelated families with loss-of-function (LoF) bi-allelic variants in LGI3. Deep phenotypic characterization showed LGI3 LoF causes a potentially clinically recognizable PNHS trait characterized by global developmental delay, intellectual disability, distal deformities with diminished reflexes, visible facial myokymia, and distinctive electromyographic features suggestive of motor nerve instability. Lgi3-null mice showed reduced and mis-localized Kv1 channel complexes in myelinated peripheral axons. Our data demonstrate bi-allelic LoF variants in LGI3 cause a clinically distinguishable disease trait of PNHS, most likely caused by disturbed Kv1 channel distribution in the absence of LGI3.

LGI3 is secreted and binds to ADAM22 via TRIF-dependent NF-κB pathway in response to LPS in human keratinocytes

Recently, we reported that HaCaT human keratinocytes secreted leucine-rich repeat LGI family member 3 (LGI3) protein after exposure to ultraviolet B (UVB) irradiation. In the present study, we aimed to determine whether LGI3 is also released in response to stimulation by lipopolysaccharides (LPS), membrane components of gram-negative bacteria. Our results showed that LGI3 was indeed secreted by LPS-stimulated HaCaT cells. We also found that LPS potently stimulated the induction of cycloxygenase-2 (COX-2), which is involved in the inflammatory response. In addition, LPS-induced LGI3 secretion and COX-2 expression were blocked by NS-398, a selective COX-2 inhibitor. Moreover, LPS activated nuclear factor-κB (NF-κB) via a TRIF-dependent pathway, and activated NF-κB led to LGI3 production in HaCaT cells. For the first time, we predicted the LGI3 promoter sequence and demonstrated that NF-κB bound to the LGI3 gene promoter region. LPS treatment also increased the expression of a disintegrin and metalloproteinase domain-containing protein 22 (ADAM22), a candidate LGI3 receptor. Furthermore, co-immunoprecipitation, flow cytometry, and immunocytochemistry revealed that LGI3 associated with ADAM22 in LPS-treated keratinocytes. Thus, ADAM22 may be an LGI3 receptor in human keratinocytes. Taken together, these data suggest that the TRIF-dependent pathway is a novel regulator of LGI3 secretion in response to LPS stimulation in HaCaT cells and that keratinocyte-derived LGI3 interacts with ADAM22 and mediates LPS-induced inflammation.

Leucine-rich glioma inactivated 3: integrative analyses support its prognostic role in glioma

Background

Leucine-rich glioma inactivated 3 (LGI3) is a secreted protein member of LGI family. We previously reported that LGI3 was expressed in brain, adipose tissues and skin, where it played roles as a multifunctional cytokine. We postulated that LGI3 may be involved in cytokine network in cancers.

Aim

This study aimed to analyze differentially expressed genes in glioma tissues and glioma cohort data to investigate the prognostic role of LGI3 and its receptors.

Materials and methods

Expression microarray data from Gene Expression Omnibus and glioma cohort data were analyzed using bioinformatic tools for statistical analysis, protein–protein interactions, functional enrichment and pathway analyses and prognostic association analysis.

Results

We found that LGI3 and its receptors, ADAM22 and ADAM23, were significantly downregulated in glioma tissues. Eleven upregulated genes and two downregulated genes in glioma tissues were found to be the previously reported LGI3-regulated genes. Protein–protein interaction network analysis showed that 85% of the LGI3-regulated and glioma-altered genes formed a cluster of interaction network. Functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed the association of these genes with hypoxia responses, p53 and Akt signaling and various cancer-related pathways including glioma. Analysis of expression microarray data of glioma cohorts demonstrated that low expression levels of LGI3, ADAM22 and ADAM23 were significantly associated with poor prognosis of glioma.

Conclusion

These results propose that LGI3 and its receptors may play a prognostic role in glioma.

Leucine-rich glioma inactivated 3 and tumor necrosis factor-α regulate mutually through NF-κB

Leucine-rich glioma inactivated 3 (LGI3) is a secreted protein member of LGI family. We previously reported that LGI3 increased in obese adipose tissues and suppressed adipogenesis through its receptor, ADAM23. We proposed that LGI3 may be a pro-inflammatory adipokine secreted predominantly by preadipocytes and macrophages. In this study, we showed that LGI3 and tumor necrosis factor-α (TNF-α) upregulated each other in 3T3-L1 cells. Treatment of 3T3-L1 preadipocytes with LGI3 protein increased TNF-α mRNA and protein. LGI3 treatment led to NF-κB activation and binding to an NF-κB binding site (-523 to -514) in TNF-α promoter. TNF-α treatment increased mRNA and protein expression of LGI3 and ADAM23. TNF-α increased NF-κB binding to a predicted binding site (-40 to -31) in LGI3 promoter. High fat diet-fed mice showed that LGI3 and TNF-α were increased and colocalized in adipose tissue inflammation. Taken together, these results suggested that mutual upregulation of LGI3 and TNF-α may play a role in adipose tissue inflammation in obesity.

Leucine-rich glioma inactivated 3 is a melanogenic cytokine in human skin

Recently, we demonstrated that leucine-rich glioma inactivated 3 (LGI3) is expressed in human skin. However, the effects of LGI3 on melanocytes remain unknown. The present study demonstrated that LGI3 can serve to stimulate melanogenesis without affecting cell viability. To determine the effects of LGI3 on melanin synthesis, normal human melanocytes and Mel-Ab cells were treated with recombinant LGI3 and melanin content was measured. Our results showed that LGI3 promoted melanin synthesis in both cell types. Moreover, upregulation of microphthalmia-associated transcription factor (MITF) and tyrosinase was observed at both the mRNA and protein levels via RT-PCR and Western blotting, respectively. Furthermore, immunohistochemical staining showed that the expression of LGI3 increased in the basal layer of melasma skin samples, whereas it decreased slightly in vitiligo samples. These results suggest that LGI3 may play a role as a melanogenic cytokine in human skin.