Elucidation of relevant neuroinflammation mechanisms using gene expression profiling in skin fibroblast of amyotrophic lateral sclerosis

Abstract

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by loss of motoneurons. Its pathological mechanisms are not yet clear. Recent reports have highlighted that the inflammatory response occurring within the central nervous system contributes to pathogenesis of ALS. I aimed to investigate disease-specific gene expression associated with neuroinflammation in ALS using gene expression profiling. To this end, I collected fibroblasts from three patients with sporadic ALS (sALS) and three normal control subjects and conducted transcriptome analysis to obtain their gene expression profiles. Using DAVID software, KEGG pathway analysis was carried out, and 15 pathways were found to be upregulated in patients with sALS compared to controls. Of these 15 pathways, the toll-like receptor (TLR) and NOD-like receptor (NLR) signaling pathways are related to immune response. Eleven genes related to TLR and NLR signaling pathways identified to be overexpressed in sALS were selected for validation using RT-PCR; six genes including CD14, toll-interacting protein (TOLLIP), mitogen-activated protein kinase 9 (MAPK9), interleukin-1 beta (IL-1β), interleukin-8 (IL-8), and CXCL1 were confirmed to be significantly overexpressed in the fibroblasts of patients with sALS. Using western blotting, TOLLIP, MAPK9, IL-1β, IL-8, and chemokine ligand 1 (CXCL1) were finally validated as differentially expressed genes in sALS. CD 14 was validated using quantitative RT-PCR. Furthermore, TOLLIP expression was found to be related to cellular aging as judged by its expression through number of passages. In passage 4, TOLLIP was overexpressed in patients with sALS than in control subjects; however, its expression decreased with additional passages. In passage 12, it was underexpressed in patients with sALS than in controls. In conclusion, transcriptional profiling of genes and identification of pathways revealed that the TLR and NLR signaling pathways are involved in sALS-associated pathological innate immunity and neuroinflammation. I suggest that CD14, TOLLIP, MAPK9, IL-1β, IL-8, and CXCL1 are related to sALS-specific immune responses and the possibility that functional change of TOLLIP is associated with progression of sALS.