LGI1-ADAM22-MAGUK configures transsynaptic nanoalignment for synaptic transmission and epilepsy prevention.

Physiological functioning and homeostasis of the brain rely on finely tuned synaptic transmission, which involves nanoscale alignment between presynaptic neurotransmitter-release machinery and postsynaptic receptors. However, the molecular identity and physiological significance of transsynaptic nanoalignment remain incompletely understood. Here, we report that epilepsy gene products, a secreted protein LGI1 and its receptor ADAM22, govern transsynaptic nanoalignment to prevent epilepsy. We found that LGI1-ADAM22 instructs PSD-95 family membrane-associated guanylate kinases (MAGUKs) to organize transsynaptic protein networks, including NMDA/AMPA receptors, Kv1 channels, and LRRTM4-Neurexin adhesion molecules. Adam22ΔC5/ΔC5 knock-in mice devoid of the ADAM22-MAGUK interaction display lethal epilepsy of hippocampal origin, representing the mouse model for ADAM22-related epileptic encephalopathy. This model shows less-condensed PSD-95 nanodomains, disordered transsynaptic nanoalignment, and decreased excitatory synaptic transmission in the hippocampus. Strikingly, without ADAM22 binding, PSD-95 cannot potentiate AMPA receptor-mediated synaptic transmission. Furthermore, forced coexpression of ADAM22 and PSD-95 reconstitutes nano-condensates in nonneuronal cells. Collectively, this study reveals LGI1-ADAM22-MAGUK as an essential component of transsynaptic nanoarchitecture for precise synaptic transmission and epilepsy prevention.

Biallelic ADAM22 pathogenic variants cause progressive encephalopathy and infantile-onset refractory epilepsy.

Pathogenic variants in A Disintegrin And Metalloproteinase (ADAM) 22, the postsynaptic cell membrane receptor for the glycoprotein leucine-rich repeat glioma-inactivated protein 1 (LGI1), have been recently associated with recessive developmental and epileptic encephalopathy. However, so far, only two affected individuals have been described and many features of this disorder are unknown. We refine the phenotype and report 19 additional individuals harbouring compound heterozygous or homozygous inactivating ADAM22 variants, of whom 18 had clinical data available. Additionally, we provide follow-up data from two previously reported cases. All affected individuals exhibited infantile-onset, treatment-resistant epilepsy. Additional clinical features included moderate to profound global developmental delay/intellectual disability (20/20), hypotonia (12/20) and delayed motor development (19/20). Brain MRI findings included cerebral atrophy (13/20), supported by post-mortem histological examination in patient-derived brain tissue, cerebellar vermis atrophy (5/20), and callosal hypoplasia (4/20). Functional studies in transfected cell lines confirmed the deleteriousness of all identified variants and indicated at least three distinct pathological mechanisms: (i) defective cell membrane expression; (ii) impaired LGI1-binding; and/or (iii) impaired interaction with the postsynaptic density protein PSD-95. We reveal novel clinical and molecular hallmarks of ADAM22 deficiency and provide knowledge that might inform clinical management and early diagnostics.

Characterizing the molecular etiology of arthrogryposis multiplex congenita in patients with LGI4 mutations.

Disruption of axon-glia interactions in the peripheral nervous system has emerged as a major cause of arthrogryposis multiplex congenita (AMC), a condition characterized by multiple congenital postural abnormalities involving the major joints. Several genes crucially important to the biology of Schwann cells have now been implicated with AMC. One such gene is LGI4 which encodes a secreted glycoprotein. LGI4 is expressed and secreted by Schwann cells and binds its receptor ADAM22 on the axonal membrane to drive myelination. Homozygous mutations in LGI4 or ADAM22 results in severe congenital hypomyelination and joint contractures in mice. Recently bi-allelic LGI4 loss of function mutations has been described in three unrelated families with severe AMC. Two individuals in a fourth, non-consanguineous family were found to be compound heterozygous for two LGI4 missense mutations. It is not known how these missense mutations affect the biology of LGI4. Here we investigated whether these missense mutations affected the secretion of the protein, its ADAM22 binding capacity, or its myelination-promoting function. We demonstrate that the mutations largely affect the progression of the mutant protein through the endomembrane system resulting in severely reduced expression. Importantly, binding to ADAM22 and myelination-promoting activity appear largely unaffected, suggesting that treatment with chemical chaperones to improve secretion of the mutant proteins might prove beneficial.

Insights into the mechanisms of epilepsy from structural biology of LGI1-ADAM22.

Epilepsy is one of the most common brain disorders, which can be caused by abnormal synaptic transmissions. Many epilepsy-related mutations have been identified in synaptic ion channels, which are main targets for current antiepileptic drugs. One of the novel potential targets for therapy of epilepsy is a class of non-ion channel-type epilepsy-related proteins. The leucine-rich repeat glioma-inactivated protein 1 (LGI1) is a neuronal secreted protein, and has been extensively studied as a product of a causative gene for autosomal dominant lateral temporal lobe epilepsy (ADLTE; also known as autosomal dominant partial epilepsy with auditory features [ADPEAF]). At least 43 mutations of LGI1 have been found in ADLTE families. Additionally, autoantibodies against LGI1 in limbic encephalitis are associated with amnesia, seizures, and cognitive dysfunction. Although the relationship of LGI1 with synaptic transmission and synaptic disorders has been studied genetically, biochemically, and clinically, the structural mechanism of LGI1 remained largely unknown until recently. In this review, we introduce insights into pathogenic mechanisms of LGI1 from recent structural studies on LGI1 and its receptor, ADAM22. We also discuss the mechanism for pathogenesis of autoantibodies against LGI1, and the potential of chemical correctors as novel drugs for epilepsy, with structural aspects of LGI1-ADAM22.

Loss-of-Function Mutations in LGI4, a Secreted Ligand Involved in Schwann Cell Myelination, Are Responsible for Arthrogryposis Multiplex Congenita.

Arthrogryposis multiplex congenita (AMC) is a developmental condition characterized by multiple joint contractures resulting from reduced or absent fetal movements. Through genetic mapping of disease loci and whole-exome sequencing in four unrelated multiplex families presenting with severe AMC, we identified biallelic loss-of-function mutations in LGI4 (leucine-rich glioma-inactivated 4). LGI4 is a ligand secreted by Schwann cells that regulates peripheral nerve myelination via its cognate receptor ADAM22 expressed by neurons. Immunolabeling experiments and transmission electron microscopy of the sciatic nerve from one of the affected individuals revealed a lack of myelin. Functional tests using affected individual-derived iPSCs showed that these germline mutations caused aberrant splicing of the endogenous LGI4 transcript and in a cell-based assay impaired the secretion of truncated LGI4 protein. This is consistent with previous studies reporting arthrogryposis in Lgi4-deficient mice due to peripheral hypomyelination. This study adds to the recent reports implicating defective axoglial function as a key cause of AMC.

ADAM22/LGI1 complex as a new actionable target for breast cancer brain metastasis.

BACKGROUND: Metastatic breast cancer is a major cause of cancer-related deaths in woman. Brain metastasis is a common and devastating site of relapse for several breast cancer molecular subtypes, including oestrogen receptor-positive disease, with life expectancy of less than a year. While efforts have been devoted to developing therapeutics for extra-cranial metastasis, drug penetration of blood-brain barrier (BBB) remains a major clinical challenge. Defining molecular alterations in breast cancer brain metastasis enables the identification of novel actionable targets. METHODS: Global transcriptomic analysis of matched primary and metastatic patient tumours (n = 35 patients, 70 tumour samples) identified a putative new actionable target for advanced breast cancer which was further validated in vivo and in breast cancer patient tumour tissue (n = 843 patients). A peptide mimetic of the target's natural ligand was designed in silico and its efficacy assessed in in vitro, ex vivo and in vivo models of breast cancer metastasis. RESULTS: Bioinformatic analysis of over-represented pathways in metastatic breast cancer identified ADAM22 as a top ranked member of the ECM-related druggable genome specific to brain metastases. ADAM22 was validated as an actionable target in in vitro, ex vivo and in patient tumour tissue (n = 843 patients). A peptide mimetic of the ADAM22 ligand LGI1, LGI1MIM, was designed in silico. The efficacy of LGI1MIM and its ability to penetrate the BBB were assessed in vitro, ex vivo and in brain metastasis BBB 3D biometric biohybrid models, respectively. Treatment with LGI1MIM in vivo inhibited disease progression, in particular the development of brain metastasis. CONCLUSION: ADAM22 expression in advanced breast cancer supports development of breast cancer brain metastasis. Targeting ADAM22 with a peptide mimetic LGI1MIM represents a new therapeutic option to treat metastatic brain disease.

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.

miR-221-3p inhibits oxidized low-density lipoprotein induced oxidative stress and apoptosis via targeting a disintegrin and metalloprotease-22.

Oxidized low-density lipoprotein (ox-LDL)-induced oxidative stress and apoptosis are considered as a critical contributor to atherosclerosis. MicroRNAs (miRNAs) have been reported versatile functions in all biological processes via directly suppressing target messenger RNA at a posttranscriptional level. Although miRNA-221 has been implied to be involved in the regulation of atherosclerosis, the underlying mechanism remains unclear. Here, we showed that ox-LDL treatment remarkably suppressed the expression of miR-221-3p in a concentration-dependent and time-dependent manner. Transfection of miR-221-3p mimic significantly reduced the foam cell formation and expression of lipid biomarkers, while transfection of the miR-221-3p inhibitor showed completely opposite effects. Moreover, miR-221-3p was also found to inhibit the process of cell apoptosis in macrophages. A disintegrin and metalloprotease-22 (ADAM22) is predicted as a direct target of miR-221-3p, and silencing AMAM22 resulted in a reduced foam cell formation and cell apoptosis. Furthermore, silencing AMAM22 restored the stimulatory effect of the miR-221-3p inhibitor in ox-LDL-induced foam cell formation and apoptosis. These findings suggest that miR-221-3p inhibits ox-LDL and apoptosis via directly targeting ADAM22.

miR-449a Suppresses Tamoxifen Resistance in Human Breast Cancer Cells by Targeting ADAM22.

BACKGROUND/AIMS: Most of estrogen receptor positive breast cancer patients respond well initially to endocrine therapies, but often develop resistance during treatment with selective estrogen receptor modulators (SERMs) such as tamoxifen. Altered expression and functions of microRNAs (miRNAs) have been reportedly associated with tamoxifen resistance. Thus, it is necessary to further elucidate the function and mechanism of miRNAs in tamoxifen resistance. METHODS: Tamoxifen sensitivity was validated by using Cell Counting Kit-8 in tamoxifen-sensitive breast cancer cells (MCF-7, T47D) and tamoxifen-resistant cells (MCF-7/TAM, T47D/ TAM). Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect the expression level of miR-449a in tamoxifen-sensitive/-resistant cells and patient serums. Dual-luciferase assay was used to identify the binding of miR-449a and predicted gene ADAM22. The expression level of ADAM22 was determined by qRT-PCR and western blotting in miR-449a +/- breast cancer cells. Subsequently, rescue experiments were carried out to identify the function of ADAM22 in miR-449a-reduced tamoxifen resistance. Finally, Gene ontology (GO) and Protein-protein interaction analyses were performed to evaluate the potential mechanisms of ADAM22 in regulating tamoxifen resistance. RESULTS: MiR-449a levels were downregulated significantly in tamoxifen-resistant breast cancer cells when compared with their parental cells, as well as in clinical breast cancer serum samples. Overexpression of miR-449a re-sensitized the tamoxifen-resistant breast cancer cells, while inhibition of miR-449a conferred tamoxifen resistance in parental cells. Luciferase assay identified ADAM22 as a direct target gene of miR-449a. Additionally, silencing of ADAM22 could reverse tamoxifen resistance induced by miR-449a inhibition in ER-positive breast cancer cells. GO analysis results showed ADAM22 was mainly enriched in the biological processes of cell adhesion, cell differentiation, gliogenesis and so on. Protein-protein interaction analyses appeared that ADAM22 might regulate tamoxifen resistance through PPARG, LGI1, KRAS and LYN. CONCLUSION: Decreased miR-449a causes the upregulation of ADAM22, which induces tamoxifen resistance of breast cancer cells. These results suggest that miR-449a, functioning by targeting ADAM22, contributes to the mechanisms underlying breast cancer endocrine resistance, which may provide a potential therapeutic strategy in ER-positive breast cancers.

The LGI1-ADAM22 protein complex directs synapse maturation through regulation of PSD-95 function.

Synapse development is coordinated by a number of transmembrane and secreted proteins that come together to form synaptic organizing complexes. Whereas a variety of synaptogenic proteins have been characterized, much less is understood about the molecular networks that support the maintenance and functional maturation of nascent synapses. Here, we demonstrate that leucine-rich, glioma-inactivated protein 1 (LGI1), a secreted protein previously shown to modulate synaptic AMPA receptors, is a paracrine signal released from pre- and postsynaptic neurons that acts specifically through a disintegrin and metalloproteinase protein 22 (ADAM22) to set postsynaptic strength. We go on to describe a novel role for ADAM22 in maintaining excitatory synapses through PSD-95/Dlg1/zo-1 (PDZ) domain interactions. Finally, we show that in the absence of LGI1, the mature synapse scaffolding protein PSD-95, but not the immature synapse scaffolding protein SAP102, is unable to modulate synaptic transmission. These results indicate that LGI1 and ADAM22 form an essential synaptic organizing complex that coordinates the maturation of excitatory synapses by regulating the functional incorporation of PSD-95.

A disintegrin and metalloproteinase 22 activates integrin ß1 through its disintegrin domain to promote the progression of pituitary adenoma.

BACKGROUND: Approximately 35% of pituitary adenoma (PA) display an aggressive profile, resulting in low surgical total resection rates, high recurrence rates, and worse prognosis. However, the molecular mechanism of PA invasion remains poorly understood. Although "a disintegrin and metalloproteinases" (ADAMs) are associated with the progression of many tumors, there are no reports on ADAM22 in PA. METHODS: PA transcriptomics databases and clinical specimens were used to analyze the expression of ADAM22. PA cell lines overexpressing wild-type ADAM22, the point mutation ADAM22, the mutated ADAM22 without disintegrin domain, and knocking down ADAM22 were generated. Cell proliferation/invasion assays, flow cytometry, immunohistochemistry, immunofluorescence, co-immunoprecipitation, mass spectrometry, Reverse transcription-quantitative real-time PCR, phos-tag SDS-PAGE, and Western blot were performed for function and mechanism research. Nude mice xenograft models and rat prolactinoma orthotopic models were used to validate in vitro findings. RESULTS: ADAM22 was significantly overexpressed in PA and could promote the proliferation, migration, and invasion of PA cells. ADAM22 interacted with integrin ß1 (ITGB1) and activated FAK/PI3K and FAK/ERK signaling pathways through its disintegrin domain to promote PA progression. ADAM22 was phosphorylated by PKA and recruited 14-3-3, thereby delaying its degradation. ITGB1-targeted inhibitor (anti-itgb1) exerted antitumor effects and synergistic effects in combination with somatostatin analogs or dopamine agonists in treating PA. CONCLUSIONS: ADAM22 was upregulated in PA and was able to promote PA proliferation, migration, and invasion by activating ITGB1 signaling. PKA may regulate the degradation of ADAM22 through post-transcriptional modification levels. ITGB1 may be a potential therapeutic target for PA.

Exploring the Potential Role of ADAM 17 and ADAM 22 in the Etiology of Autism Spectrum Disorders.

BACKGROUND: Autism spectrum disorder (ASD) encompasses a group of disorders characterized by difficulties with social interaction and repetitive behavior. The condition is supposed to originate from early shifts in brain development, while the underlying processes are unknown. Moreover, a considerable number of patients with ASD experience digestive difficulties. Metalloproteases (ADAMs) are a class of enzymes capable of cleaving membrane-bound proteins. Members of this family, ADAM17 and ADAM22, have the ability to cleave proteins like the pro-inflammatory cytokine TNF-ά and glutamate synaptic molecules, which are both engaged in neuro-inflammation and glutamate excitotoxicity as crucial etiological mechanisms in ASD. ADAM17 and ADAM22 may also have a role in ASD microbiota-gut-brain axis connections by regulating immunological and inflammatory responses in the intestinal tract. SUBJECTS AND METHODS: Using ELISA kits, the plasma levels of ADAM17 and ADAM22 were compared in 40 children with ASD and 40 typically developing children. All of the autistic participants' childhood autism rating scores (CARS), social responsiveness scales (SRS), and short sensory profiles (SSP) were evaluated as indicators of ASD severity. RESULTS: Our results showed that plasma levels of ADAM17 were significantly lower in ASD children than in control children, while ADAM22 demonstrated non-significantly lower levels. Our data also indicate that while ADAM17 correlates significantly with age, ADAM22 correlates significantly with CARS as a marker of ASD severity. CONCLUSIONS: Our interpreted data showed that alteration in ADAM17 and ADAM22 might be associated with glutamate excitotoxicity, neuroinflammation, and altered gut microbiota as etiological mechanisms of ASD and could be an indicator of the severity of the disorder.

ADAM22 ethnic-specific variant reducing binding of membrane-associated guanylate kinases causes focal epilepsy and behavioural disorder.

Pathogenic variants of ADAM22 affecting either its biosynthesis and/or its interactions with either LGI1 and/or PSD-95 have been recently identified in individuals with developmental and epileptic encephalopathy. Here, we describe a girl with seizures, delayed psychomotor development, and behavioural disorder, carrying a homozygous variant in ADAM22 (NM_021723.5:c.2714C > T). The variant has a surprisingly high frequency in the Roma population of the Czech and Slovak Republic, with 11 of 213 (∼5.2%) healthy Roma individuals identified as heterozygous carriers. Structural in silico characterization revealed that the genetic variant encodes the missense variant p.S905F, which localizes to the PDZ-binding motif of ADAM22. Studies in transiently transfected mammalian cells revealed that the variant has no effect on biosynthesis and stability of ADAM22. Rather, protein-protein interaction studies showed that the p.S905F variant specifically impairs ADAM22 binding to PSD-95 and other proteins from a family of membrane-associated guanylate kinases, while it has only minor effect on ADAM22-LGI1 interaction. Our study indicates that a significant proportion of epilepsy in patients of Roma ancestry may be caused by homozygous c.2714C > T variants in ADAM22. The study of this ADAM22 variant highlights a novel pathogenic mechanism of ADAM22 dysfunction and reconfirms an essential role of interaction of ADAM22 with membrane-associated guanylate kinases in seizure protection in humans.

An Unusual Case of LGI1 (Leucine-Rich Glioma-Inactivated Protein 1) Limbic Encephalitis With Anti-acetylcholine Receptor and Anti-striational Autoantibodies.

Autoimmune encephalitis (AE) results from immune-mediated damage to the central nervous system (CNS) with varying clinical manifestations depending on autoimmune antibodies present and the antigens they target. Leucine-rich glioma-inactivated protein 1 (LGI1) has been recognized as one of the leading causes of limbic encephalitis (LE), presenting with seizures, memory loss, and faciobrachial dystonic seizures. A better understanding of the unique presentations of these AE allows for quick and effective diagnosis and treatment. We are presenting a very unusual case of LGI1 autoimmune LE with two additional autoantibodies, anti-acetylcholine receptor (AChR) and anti-striational, in a patient with an underlying thymoma. We will discuss the pathophysiology and common clinical presentation of anti-LGI1 autoimmune LE.

Trans-synaptic LGI1-ADAM22-MAGUK in AMPA and NMDA receptor regulation.

Exquisitely-regulated synaptic transmission and plasticity underlie higher brain functions such as learning and memory. PSD-95, a member of the MAGUK family, scaffolds an array of postsynaptic proteins including AMPA and NMDA receptors, and plays essential roles in excitatory synaptic transmission and postsynaptic organization. Epilepsy-related secreted protein LGI1 and its receptor ADAM22 represent major constituent elements of the PSD-95-containing synaptic protein complex in the brain. Recent studies begin to reveal a trans-synaptic configuration of the LGI1-ADAM22 complex and its pivotal role in AMPA and NMDA receptor-mediated synaptic transmission through regulating MAGUKs. Especially interesting is that without the association with LGI1-ADAM22, PSD-95 cannot potentiate AMPA receptor-mediated synaptic transmission. Here, we review roles of LGI1-ADAM22 in synaptic function, and discuss its modes of action on the MAGUK regulation: as (i) a trans-synaptic hub, (ii) an extracellular scaffold, and (iii) an allosteric activator. We also highlight patho-physiological roles of the LGI1-ADAM22-MAGUK linkage in synaptic disorders such as epilepsy and autoimmune limbic encephalitis.

14-3-3 proteins stabilize LGI1-ADAM22 levels to regulate seizure thresholds in mice.

What percentage of the protein function is required to prevent disease symptoms is a fundamental question in genetic disorders. Decreased transsynaptic LGI1-ADAM22 protein complexes, because of their mutations or autoantibodies, cause epilepsy and amnesia. However, it remains unclear how LGI1-ADAM22 levels are regulated and how much LGI1-ADAM22 function is required. Here, by genetic and structural analysis, we demonstrate that quantitative dual phosphorylation of ADAM22 by protein kinase A (PKA) mediates high-affinity binding of ADAM22 to dimerized 14-3-3. This interaction protects LGI1-ADAM22 from endocytosis-dependent degradation. Accordingly, forskolin-induced PKA activation increases ADAM22 levels. Leveraging a series of ADAM22 and LGI1 hypomorphic mice, we find that ∼50% of LGI1 and ∼10% of ADAM22 levels are sufficient to prevent lethal epilepsy. Furthermore, ADAM22 function is required in excitatory and inhibitory neurons. These results suggest strategies to increase LGI1-ADAM22 complexes over the required levels by targeting PKA or 14-3-3 for epilepsy treatment.

ADAM23 is a negative regulator of Kv1.1/Kv1.4 potassium currents.

Background ADAM22 and ADAM23 are transmembrane proteins that bind the secreted synaptic protein LGI1 and associate with Kv1.1/Kv1.4 potassium channels. However, the roles of these proteins in regulated voltage-gated potassium currents are poorly understood. Methods Cultured cells were transfected to express ADAM22, ADAM23, and Kv1.1/Kv1.4. Voltage-gated potassium currents were measured by whole-cell patch-clamp. Immunostaining Kv1.1 with fluorescent antibodies and fluorescently tagged Kv1.1 subunits was used to measure the effects of ADAM proteins on cell-surface and total expression of Kv1.1 channels. LGI1-conditioned media was added to assess the effect on LGI1 on Kv1.1 currents. Results Cells transfected with Kv1.1/Kv1.4 showed voltage-gated potassium currents (Kv1.1 currents). ADAM23 was a powerful negative regulator of Kv1.1 currents and caused decreased surface expression of Kv1.1 subunits. This decrease in current was not mediated by clathrin-dependent endocytosis. LGI1-conditioned media did not affect the negative regulation of Kv1.1 currents by ADAM23. ADAM22 had no significant effect on Kv1.1 currents by itself, but in the presence of LGI1-conditioned media markedly potentiated Kv1.1 currents without changing channel activation kinetics. Conclusions ADAM22 and ADAM23 have opposite effects on Kv1.1 currents. The relative expression of these proteins, and the availability of LGI1 may shape the expression of Kv1.1 currents in different neuronal membrane domains.

A disintegrin and metalloprotease 22 accelerates neointima formation by activating ERK signaling.

BACKGROUND AND AIMS: Despite the advantage of arterial expansion for life-threatening vascular pathologies, the occurrence of neointima formation remains a prominent complication, with the underlying mechanisms largely unknown. A disintegrin and metalloprotease 22 (ADAM22) belongs to the family of ADAMs that possesses various biological capacities regulating vascular physiopathology. However, little is known about ADAM22 in vascular smooth muscle cell (VSMC)-mediated neointima formation. Here, we aimed to evaluate the potential functional regulation of ADAM22 in neointima formation and to further explore the underlying mechanisms. METHODS: In our study, platelet-derived growth factor-BB (PDGF-BB)-induced VSMC proliferation was examined using a 5-bromo-2'-deoxyuridine (BrdU) incorporation assay and a cell counting kit-8 (CCK8) assay, while VSMC migration was detected using a modified Boyden chamber method and a scratch-wound assay. The functional role of ADAM22 in neointima formation was evaluated based on a left carotid artery wire injury model in mice at 14 and 28 days. RESULTS: ADAM22 was significantly up-regulated in both PDGF-BB-challenged VSMCs and restenotic arteries of mice. When ADAM22 was overexpressed in VSMCs, cell proliferation, migration and phenotypic switching were simultaneously aggravated, whereas the opposite was observed when ADAM22 was knocked down in vitro. In ADAM22 heterozygote mice, wire-injury induced neointima formation was significantly ameliorated compared to wild-type control mice. Mechanistically, significantly up-regulated ERK phosphorylation is closely involved in the regulatory effects of ADAM22 in neointima formation. Interestingly, an ERK inhibitor largely reversed the aggravated VSMCs migration, proliferation and phenotypic switching induced by ADAM22 overexpression. CONCLUSIONS: Our results indicate that ADAM22 accelerates neointima formation by enhancing VSMC migration, proliferation and phenotypic switching via promoting ERK phosphorylation. Suppressing ADAM22 expression may be an effective strategy for ameliorating neointima formation.

The LGI1-ADAM22 protein complex in synaptic transmission and synaptic disorders.

Physiological functioning of the brain requires fine-tuned synaptic transmission, and its dysfunction causes various brain disorders such as autism, dementia, and epilepsy. It is therefore extremely important to identify and characterize key regulators of synaptic function. In particular, disease-related synaptic proteins, such as autism-related neurexin-neuroligin and psychiatric disorder-related NMDA receptor, have attracted considerable attention. Recent basic and clinical research has highlighted critical roles of a ligand-receptor complex, LGI1-ADAM22, in synaptic transmission and brain function, as mutations in the LGI1 gene cause autosomal dominant lateral temporal lobe epilepsy and autoantibodies to LGI1 cause limbic encephalitis which is characterized by memory loss and seizures. Here, we will review our current knowledge about LGI1 and ADAM22, and discuss their patho-physiological roles in synaptic transmission and synaptic disorders.

LGI1: from zebrafish to human epilepsy.

Mutations in the LGI1 gene predispose to autosomal dominant lateral temporal lobe epilepsy, a rare hereditary form with incomplete penetrance and associated with acoustic auras. LGI1 is not a structural component of an ion channel like most epilepsy-related genes, but is a secreted protein. Mutant null mice exhibit early-onset seizures, and electrophysiological analysis shows abnormal synaptic transmission. LGI1 binds to ADAM23 on the presynaptic membrane and ADAM22 on the postsynaptic membrane, further implicating it in regulating the strength of synaptic transmission. Patients with limbic encephalitis show autoantibodies against LGI1 and develop seizures, supporting a role for LGI1 in synapse transmission in the post developmental brain. LGI1, however, also seems to be involved in aspects of neurite development and dendritic pruning, suggesting an additional role in corticogenesis. LGI1 is also involved in cell movement and suppression of dendritic outgrowth in in vitro systems, possibly involving actin cytoskeleton dynamics. Expression patterns in embryonic development correspond to areas of neuronal migration. Loss of LGI1 expression also impacts on myelination of the central and peripheral nervous systems. In zebrafish embryos, knockdown of lgi1a leads to a seizure-like behavior and abnormal brain development, providing a system to study its role in early embryogenesis. Despite being implicated in a role in both synapse transmission and neuronal development, how LGI1 predisposes to epilepsy is still largely unknown. It appears, however, that LGI1 may function differently in a cell context-specific manner, implying a complex involvement in brain development and function that remains to be defined.