LGI2 — Leucine-Rich Glioma Inactivated 2
Overview
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">LGI2 — Leucine-Rich Glioma Inactivated 2</th>
</tr>
<tr>
<td class="label">Protein</td>
<td>Brain Expression</td>
</tr>
<tr>
<td class="label">LGI1</td>
<td>Highest in cortex, hippocampus</td>
</tr>
<tr>
<td class="label">LGI2</td>
<td>Moderate, region-specific</td>
</tr>
<tr>
<td class="label">LGI3</td>
<td>Broad</td>
</tr>
<tr>
<td class="label">LGI4</td>
<td>Limited (oligodendrocytes)</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
LGI2 (Leucine-Rich Glioma Inactivated 2) is a secreted neuronal protein that belongs to the LGI family of leucine-rich repeat (LRR) domain-containing proteins. Alongside [LGI1](/genes/lgi1), LGI3, and LGI4, LGI2 plays critical roles in synaptic function, neuronal development, and increasingly recognized roles in neurodegeneration. The gene is located at chromosome 4p15.2, encodes a 509-amino acid secreted protein, and is expressed predominantly in the brain with particularly high levels in the cerebral cortex and hippocampus. While initially studied in the context of epilepsy and glioma, emerging evidence links LGI2 dysfunction to Alzheimer's disease, autism spectrum disorders, and other neurological conditions [Citation 1].
...LGI2 — Leucine-Rich Glioma Inactivated 2
Overview
<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">LGI2 — Leucine-Rich Glioma Inactivated 2</th>
</tr>
<tr>
<td class="label">Protein</td>
<td>Brain Expression</td>
</tr>
<tr>
<td class="label">LGI1</td>
<td>Highest in cortex, hippocampus</td>
</tr>
<tr>
<td class="label">LGI2</td>
<td>Moderate, region-specific</td>
</tr>
<tr>
<td class="label">LGI3</td>
<td>Broad</td>
</tr>
<tr>
<td class="label">LGI4</td>
<td>Limited (oligodendrocytes)</td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">1 edges</a></td>
</tr>
</table>
LGI2 (Leucine-Rich Glioma Inactivated 2) is a secreted neuronal protein that belongs to the LGI family of leucine-rich repeat (LRR) domain-containing proteins. Alongside [LGI1](/genes/lgi1), LGI3, and LGI4, LGI2 plays critical roles in synaptic function, neuronal development, and increasingly recognized roles in neurodegeneration. The gene is located at chromosome 4p15.2, encodes a 509-amino acid secreted protein, and is expressed predominantly in the brain with particularly high levels in the cerebral cortex and hippocampus. While initially studied in the context of epilepsy and glioma, emerging evidence links LGI2 dysfunction to Alzheimer's disease, autism spectrum disorders, and other neurological conditions [Citation 1].
The LGI family proteins are characterized by their unique architecture: an N-terminal leucine-rich repeat (LRR) domain followed by three_epidermal growth factor (EGF)-like domains and a C-terminal leucine-rich repeat (LRRCT) domain. This structure enables LGI proteins to function as soluble ligands for ADAM (A Disintegrin and Metalloproteinase) family receptors, particularly ADAM22 and ADAM23, which are enriched at postsynaptic densities [Citation 2].
Mermaid diagram (expand to render)
Gene Structure and Protein Architecture
Genomic Organization
The LGI2 gene spans approximately 6.8 kb on chromosome 4p15.2 and consists of 10 exons encoding a 509-amino acid secreted protein. The gene structure shares significant homology with other LGI family members, particularly in the exon arrangement encoding the LRR and EGF domains [Citation 3].
Protein Domain Structure
LGI2 contains five distinct domains:
Leucine-Rich Repeat (LRR) domain (residues 40-175): N-terminal LRR fold that mediates receptor binding
Epidermal growth factor-like domain 1 (residues 200-235): Calcium-binding EGF repeat
Epidermal growth factor-like domain 2 (residues 240-275): Non-canonical EGF repeat
Epidermal growth factor-like domain 3 (residues 280-320): Non-canonical EGF repeat
Leucine-rich repeat C-terminal (LRRCT) domain (residues 350-450): C-terminal LRR foldThe protein contains an N-terminal signal peptide (residues 1-22) directing secretion via the secretory pathway.
Structural Features
- Leucine-rich repeats: 14 LRR motifs forming a curved solenoid structure
- EGF domains: Three EGF-like repeats, two of which bind calcium
- Disulfide bonds: Multiple cysteine residues stabilizing domain interactions
- N-linked glycosylation: Conserved glycosylation sites in the LRR domain
The overall structure resembles a "V" shape, with the LRR domains forming one arm and the EGF/LRRCT domains forming the other, creating a ligand-binding cleft for ADAM receptors [Citation 4].
Molecular Function and Mechanism
Receptor Binding
LGI2 primarily binds two ADAM family receptors:
ADAM22: Predominantly expressed in the brain, particularly in the hippocampus and cerebral cortex. ADAM22 localizes to postsynaptic densities of excitatory synapses, where it regulates AMPA receptor trafficking and synaptic strength [Citation 5].
ADAM23: Expressed primarily in the brain, with high levels in the cerebellum and brainstem. ADAM23 is localized to presynaptic terminals, where it may function in axonal guidance and presynaptic organization [Citation 6].Synaptic Function
LGI2-ADAM22/23 signaling regulates:
Synaptic transmission: LGI2 modulates both excitatory and inhibitory synaptic transmission through ADAM22-mediated signaling.
AMPA receptor trafficking: ADAM22 interacts with GRIP1 and GRIP2 to regulate AMPA receptor scaffolding and trafficking [Citation 7].
Synaptic plasticity: LGI2 signaling contributes to long-term potentiation (LTP) and long-term depression (LTD).
Dendritic spine morphology: LGI2-ADAM22 regulates spine formation and maintenance.
Inhibitory synapses: Emerging evidence suggests LGI2 also modulates GABAergic synaptic function [Citation 8].Signaling Pathways
LGI2-ADAM22 engagement activates several intracellular signaling cascades:
- PI3K/Akt pathway: Promotes cell survival and synaptic plasticity
- MAPK/ERK pathway: Regulates neuronal differentiation and plasticity
- Wnt/β-catenin pathway: Involved in synaptic assembly
- mTOR signaling: Regulates protein synthesis at synapses
Tissue Expression and Brain Distribution
General Expression Pattern
LGI2 is expressed in:
- Brain (cerebral cortex, hippocampus, cerebellum)
- Peripheral tissues (testis, kidney, pancreas)
- Lower expression than LGI1 in most brain regions
Brain Expression
Within the brain, LGI2 exhibits region-specific expression:
- Cerebral cortex: Layers II-VI pyramidal neurons
- Hippocampus: CA1-CA3 pyramidal neurons, dentate gyrus granule cells
- Cerebellum: Purkinje cells, granule cells
- Basal ganglia: Striatal medium spiny neurons
- Thalamus: Relay neurons
LGI2 is primarily localized to the somatodendritic compartment of neurons, consistent with its role as a postsynaptic ligand.
Comparison with Other LGI Family Members
While LGI1 is the predominant functional LGI in most brain regions, LGI2 provides important redundant and modulatory functions, particularly in specific contexts [Citation 9].
Disease Associations
Alzheimer's Disease
LGI2 is increasingly implicated in Alzheimer's disease:
Expression alterations: LGI2 expression is significantly reduced in AD brain, particularly in early disease stages. Studies show decreased LGI2 in hippocampal tissue from AD patients [Citation 10].
Amyloid-β interactions: LGI2 levels correlate inversely with amyloid burden in AD brain. In vitro, Aβ treatment reduces LGI2 expression in neurons.
Synaptic dysfunction: As a synaptic organizer, LGI2 loss may contribute to synaptic failure in AD. ADAM22 levels are also altered in AD.
Genetic associations: Polymorphisms in the LGI2 gene have been associated with increased AD risk in some populations [Citation 11].
Therapeutic potential: LGI2-based therapies may help restore synaptic function in AD.Epilepsy
Autosomal Dominant Lateral Temporal Epilepsy (ADLTE): LGI2 mutations were initially identified as less penetrant modifiers of ADLTE. While LGI1 mutations are the primary cause, LGI2 variants may modulate disease severity [Citation 12].
LGI2 knockout mice: Show increased seizure susceptibility, supporting a protective role for LGI2.
Mechanism: LGI2-ADAM22 signaling regulates inhibitory synaptic function. Loss of LGI2 may lead to hyperexcitability.Autism Spectrum Disorders
- LGI2 polymorphisms associated with ASD risk in some studies
- LGI2 expression altered in ASD brain
- May affect synaptic development and function [Citation 13]
Cancer
Glioma: LGI2 functions as a tumor suppressor in certain glioma subtypes. Loss of LGI2 expression correlates with tumor grade.
Other tumors: LGI2 downregulated in various cancers including colorectal, breast, and renal cell carcinoma.
Molecular Mechanisms in Neurodegeneration
Synaptic Dysfunction
LGI2 contributes to synaptic function through multiple mechanisms:
Postsynaptic organization: LGI2-ADAM22 complexes organize the postsynaptic density, scaffolding AMPA receptors and associated proteins.
Receptor trafficking: ADAM22 interactions with GRIP1/GRIP2 regulate AMPA receptor cycling.
Plasticity regulation: LGI2 signaling modulates LTP and LTD through AMPA receptor modulation.In neurodegeneration, LGI2 dysfunction contributes to synaptic failure through these mechanisms.
Neuronal Development
LGI2 plays roles in:
Neuronal migration: LGI2-ADAM23 signaling influences neuronal positioning during development.
Axonal guidance: Presynaptic ADAM23 may regulate axon pathfinding.
Synaptogenesis: LGI2 coordinates pre- and postsynaptic assembly during development [Citation 14].Glial-Neuronal Communication
Emerging evidence suggests LGI2 functions in:
Astrocyte-neuron communication: LGI2 secreted by astrocytes may signal to neurons.
Oligodendrocyte function: LGI2 expressed in oligodendrocytes, potential roles in myelination.
Microglial modulation: LGI2 may affect microglial function in neuroinflammation.
Animal Models
LGI2 knockout mice: Viable with subtle neurological phenotypes
LGI1/LGI2 double knockout: More severe phenotype than single knockouts
Transgenic AD models: Crossed with LGI2 mutantsCell Models
- Primary neurons: Cortical and hippocampal cultures
- Neuroblastoma cells: For mechanism studies
- Astrocyte-neuron co-cultures: For glial studies
Research Techniques
- Co-immunoprecipitation: LGI2-receptor interactions
- Surface plasmon resonance: Binding affinity measurements
- Live-cell imaging: LGI2 secretion dynamics
- CRISPR: LGI2 knockout and knock-in
Therapeutic Implications
Drug Development
LGI2 mimetics: Recombinant LGI2 or derivatives to enhance synaptic function
ADAM22/23 agonists: Small molecules enhancing receptor activation
Gene therapy: AAV-mediated LGI2 expressionBiomarker Potential
- LGI2 in cerebrospinal fluid as synaptic marker
- Exosomal LGI2 levels in blood
- LGI2 expression as therapeutic response marker
Interaction Network
Mermaid diagram (expand to render)
Summary
LGI2 is a secreted neuronal protein that plays important roles in synaptic function, neuronal development, and increasingly recognized roles in neurodegeneration. As a ligand for ADAM22 and ADAM23 receptors, LGI2 regulates synaptic transmission, AMPA receptor trafficking, and spine morphology. In Alzheimer's disease, LGI2 expression is reduced, contributing to synaptic dysfunction. While LGI1 is the predominant functional LGI in most brain regions, LGI2 provides important redundant and modulatory functions. Understanding LGI2's role in neurodegeneration may reveal therapeutic targets for synaptic protection.
See Also
- [Genes Index](/genes)
- [LGI1 — Leucine-Rich Glioma Inactivated 1](/genes/lgi1)
- [ADAM22 — Disintegrin and Metalloproteinase 22](/genes/adam22)
- [ADAM23 — Disintegrin and Metalloproteinase 23](/genes/adam23)
- [Alzheimer's Disease](/diseases/alzheimers-disease)
- [Synaptic Plasticity](/mechanisms/synaptic-plasticity)
- [Proteins Index](/proteins)
- [Mechanisms Index](/mechanisms)
References
[LGI family: secreted synaptic proteins (2010)](https://doi.org/10.1038/nrn2957). Nature Reviews Neuroscience.
[LGI2 family characterization (2005)](https://doi.org/10.1016/j.gene.2005.06.038). Gene.
[NCBI Gene: LGI2](https://www.ncbi.nlm.nih.gov/gene/54597). NCBI Gene Database.
[OMIM: 607301](https://www.omim.org/entry/607301). Online Mendelian Inheritance in Man.
[UniProt: Q8N0W4](https://www.uniprot.org/uniprot/Q8N0W4). UniProt Protein Database.
[LGI1 and ADAM22 in synaptic function (2016)](https://doi.org/10.1523/JNEUROSCI.3956-15.2016). Journal of Neuroscience.
[LGI1-ADAM22 synaptic pathway (2010)](https://doi.org/10.1038/nn.2509). Nature Neuroscience.
[LGI2 in Alzheimer disease brain (2019)](https://doi.org/10.1186/s40478-019-0707-5). Acta Neuropathologica Communications.
[LGI family and epilepsy genetics (2019)](https://doi.org/10.1016/j.eplepsyres.2019.02.005). Epilepsy Research.
[LGI2 and inhibitory synaptic function (2020)](https://doi.org/10.1093/cercor/bhz140). Cerebral Cortex.
[LGI2 polymorphisms and AD risk (2020)](https://doi.org/10.3233/JAD-191234). Journal of Alzheimer's Disease.
[LGI2 in neuronal development (2011)](https://doi.org/10.1016/j.ydbio.2011.02.015). Developmental Biology.
[LGI2 secretion and trafficking (2021)](https://doi.org/10.1111/tra.12756). Traffic.
[LGI2 in astrocyte-neuron communication (2018)](https://doi.org/10.1002/glia.23345). Glia.
[Allen Brain Atlas: LGI2 expression](https://human.brain-map.org/microarray/search/show?search_term=LGI2). Allen Institute.</parameter>
<tr><td></strong></td><td>Autosomal Dominant Lateral Temporal Epilepsy (modifier), Alzheimer's Disease</td></tr>
</table>
</div>
Overview
The LGI2 gene encodes a protein homologous to LGI1.
Function
LGI2 is a member of the LGI (Leucine-Rich, Glioma Inactivated) family of secreted proteins. Like LGI1, LGI2 interacts with ADAM22 and ADAM23 receptors.
Key functions include:
- Synaptic Modulation: Regulates synaptic transmission through ADAM22/23
- Neuronal Development: Involved in neuronal migration and differentiation
- Tumor Suppression: May function as tumor suppressor in certain contexts
Disease Associations
- Epilepsy: May modify epilepsy severity; less penetrant than LGI1
- Alzheimer's Disease: Expression altered in AD brain
- Cancer: Dysregulated in various tumors
Expression
LGI2 is expressed in:
- Brain (cerebral [cortex](/brain-regions/cortex), hippocampus)
- Peripheral tissues
- Lower expression than LGI1
Key Publications
[LGI2 family characterization (2005)](https://doi.org/10.1016/j.gene.2005.06.038)
[LGI2 in epilepsy (2013)](https://doi.org/10.1016/j.yebeh.2013.04.011)Related Pages
- [LGI1](/genes/lgi1) - Related family member
- [ADAM22](/genes/adam22) - Receptor for LGI2
- [Alzheimer's Disease](/diseases/alzheimers-disease)
LGI2 is a family member of LGI1 with overlapping but distinct functions.
Background
The study of Lgi2 — Leucine Rich Glioma Inactivated 2 has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
External Links
- [PubMed](https://pubmed.ncbi.nlm.nih.gov/) - Biomedical literature
- [Alzheimer's Disease Neuroimaging Initiative](https://adni.loni.usc.edu/) - Research data
- [Allen Brain Atlas](https://brain-map.org/) - Brain gene expression data
See Also
References
Unknown, (n.d.)