Phenotypic Profiling of SOD1-G93A Mice: Integrating Sciatic Nerve Histopathology with Systemic Chemokine Dynamics During ALS Progression.

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder characterized by the progressive loss of motor neurons, leading to muscle atrophy and fatal respiratory failure. While neuroinflammation is a hallmark of ALS, the temporal and spatial relationship between systemic inflammation and peripheral nerve degeneration remains poorly understood. In the present study, the transgenic SOD1-G93A mouse model was employed to conduct a longitudinal analysis of amyotrophic lateral sclerosis (ALS) progression. We integrated morphometric and ultrastructural examinations of the sciatic nerve with immunofluorescent profiling of the spinal cord (GFAP, IBA1, NG2). In addition, cytokine and chemokine dynamics were analyzed using 33-plex multiplex assay in the serum at various stages of the disease. Histological analysis revealed a progressive decline in myelin fiber density within the sciatic nerve and axonal death. As the disease progressed, Schwann cells exhibited morphological features consistent with a pro-fibrotic shift, as suggested by collagen accumulation observed on TEM. However, direct confirmation of a fibrotic phenotype requires additional markers (e.g., Col I/III, α-SMA, TGF-β) and was not assessed in this study. Significant motor neuron loss and robust glial activation were demonstrated in the spinal cord. Blood plasma analysis identified a coordinated systemic up-regulation of MCP-3, Eotaxin, CTACK, and TECK. There was lack of inflammatory cell infiltration in the peripheral nerve tissues. Our results indicate that ALS-associated peripheral nerve degeneration in the SOD1-G93A mice model is primarily a degenerative process characterized by early demyelination and without leukocyte infiltration. However, increased levels of MCP-3, Eotaxin, CTACK, and TECK are associated with disease progression and may reflect ongoing central neuroinflammation. While these changes are temporally consistent with blood-spinal cord barrier dysfunction reported in SOD1 mice, direct assessment of barrier integrity was not performed in this study. These data highlight the potential of blood chemokines as step biomarkers and highlight the compartmental nature of inflammation in ALS, where systemic immune changes do not necessarily equate to local inflammation in the peripheral nerve.