Alpha-Internexin (INA), also known as Internexin or Neurofilament-66 (NF-66), is a neuronal intermediate filament protein encoded by the [INA](/genes/ina) gene on chromosome 10q24.3. Alpha-internexin is expressed primarily in the central nervous system, particularly in pyramidal [neurons](/entities/neurons) and certain populations of interneurons [@yuan2006].
Alpha-Internexin (INA), also known as Internexin or Neurofilament-66 (NF-66), is a neuronal intermediate filament protein encoded by the [INA](/genes/ina) gene on chromosome 10q24.3. Alpha-internexin is expressed primarily in the central nervous system, particularly in pyramidal [neurons](/entities/neurons) and certain populations of interneurons [@yuan2006].
Alpha-internexin is unique among neuronal intermediate filaments as it is expressed during development before the other neurofilament subunits (NF-L, NF-M, NF-H) and may serve as a scaffold for their proper assembly. It is also a component of the characteristic inclusions found in several neurodegenerative diseases, including ALS and certain forms of dementia [@bourrat2015].
Domain Structure
Alpha-internexin has the typical intermediate filament structure:
Head Domain (1-82)
N-terminal non-helical domain
Contains regulatory sequences
Phosphorylation sites for kinase regulation
Rod Domain (83-418)
Alpha-helical coiled-coil region
Highly conserved across species
Essential for dimer formation
Contains the helix boundary motifs
Tail Domain (419-556)
C-terminal domain with multiple serine phosphorylation sites
Projects from filament surface
Regulates filament interactions
Contains binding sites for associated proteins
Normal Function in the Nervous System
Developmental Expression
Expressed early in neuronal development
Precedes expression of NF-L, NF-M, and NF-H
May serve as nucleating scaffold for neurofilament assembly
Essential for proper neuronal differentiation
Cytoskeletal Architecture
Forms homopolymers and heteropolymers
Co-assembles with other intermediate filaments
Provides structural stability to axons and dendrites
Contributes to neuronal polarity
Protein Interactions
Binds to other intermediate filament proteins
Associates with synaptic proteins
Links to microtubules via MAPs
Interacts with signaling molecules
neurodegeneration" style="color:#4fc3f7;margin:1.5rem 0 0.6rem;font-size:1.15rem;font-weight:700;border-bottom:2px solid rgba(79,195,247,0.3);padding-bottom:0.3rem">Role in Neurodegeneration
Inclusion Body Formation
Alpha-internexin is a component of:
Bunina bodies in ALS
Rosenthal fibers in astrocytomas
Russell body inclusions
Hyaline conglomerate inclusions
Disease Biomarker
CSF alpha-internexin elevated in ALS
Detectable in blood with sensitive assays
Potential biomarker for neuronal injury
Correlates with disease progression
Neurodegenerative Diseases
Implicated in ALS pathogenesis
Accumulation in PD brains
Altered expression in AD
Mutations cause hereditary spastic paraplegia
Therapeutic Targeting
Biomarker Development
Alpha-internexin as biomarker for ALS
Monitoring disease progression
Therapeutic response assessment
Research Directions
Understanding inclusion formation mechanisms
Developing neuroprotective strategies
Gene therapy approaches
Key Publications
[Yuan et al., Alpha-internexin: structure and function (2006)](https://pubmed.ncbi.nlm.nih.gov/16682137/). Cell and Tissue Research. 2006;324(2):207-215.
[Bourrat et al., Alpha-internexin expression in neurological disorders (2015)](https://pubmed.ncbi.nlm.nih.gov/26068412/). Journal of Neuropathology and Experimental Neurology. 2015;74(5):410-426.
[Perrone et al., Alpha-internexin in ALS and related disorders (2007)](https://pubmed.ncbi.nlm.nih.gov/17613197/). Acta Neuropathologica. 2007;113(4):379-386.