Characterization of Neuronal Intermediate Filament Protein Expression in Cervical Spinal Motor Neurons in Sporadic Amyotrophic Lateral Sclerosis (ALS)

TLDR

The study examined intermediate filament protein expression in sporadic ALS to investigate neurofilament stoichiometry changes linked to motor neuron degeneration. The authors analyzed cervical spinal cord sections from 11 ALS and 11 control cases using in situ hybridization and immunohistochemistry to quantify neurofilament subunit mRNA and protein levels. ALS motor neurons showed decreased NFL, α‑internexin, and peripherin mRNA, increased β‑actin mRNA, and no change in NFM, NFH, or Tα1‑tubulin, with aggregates containing NFH or β‑actin and spheroids containing NFH and peripherin, indicating a disrupted cytoskeletal protein stoichiometry that promotes neurofilament aggregate formation.

Abstract

Because transgenic mice expressing an altered stoichiometry of neurofilament proteins develop a motor neuron degeneration associated with neurofilamentous aggregate formation similar to that found in amyotrophic lateral sclerosis (ALS), we studied the expression of intermediate filament proteins in sporadic ALS. Archival cervical spinal cord paraffin-embedded sections from 11 disease and 11 control cases were studied by either in situ hybridization using 35S-labeled riboprobes or immunohistochemically using specific antibodies for the individual neurofilament subunit proteins, α-internexin, nestin, peripherin, vimentin, β-actin, or Tα1-tubulin. Median NFL, α-internexin, and peripherin steady-state mRNA levels were significantly reduced in the lateral motor neuron cell column (p < 0.05) of ALS cases, while neither NFM nor NFH mRNA levels were altered. ALS cases demonstrated an elevation of β-actin mRNA levels (p < 0.01) with no increase in Tα1-tubulin mRNA levels. No motor neuronal expression of nestin or vimentin was observed. Ubiquitin-immunoreactive perikaryal aggregates were immunoreactive for NFH or β-actin, but not for peripherin, α-internexin, vimentin, or nestin. In contrast, neuroaxonal spheroids were strongly immunoreactive for NFH and peripherin, but not for β-actin, α-internexin, vimentin, or nestin. These findings suggest that the stoichiometry of cytoskeletal protein expression in ALS spinal motor neurons is significantly altered in a pattern conducive to the formation of neurofilamentous aggregates.