Integrative genomics and functional immunology reveal Clostridia species as modulators of neuroinflammation in amyotrophic lateral sclerosis.

Objective: This multiomics study investigated causal relationships between the gut microbiota (GM), immune dysregulation, and amyotrophic lateral sclerosis (ALS) pathogenesis using Mendelian randomization (MR) with experimental validation.

Materials: Analyses incorporated genome-wide data from 87,347 participants (GM: n = 7738; ALS: 20,806 patients, 59,804 controls; immune phenotypes: n = 3757), transcriptomic data from 71 subjects (56 ALS patients, 15 controls), and experimental validation in matched cohorts (n = 6 subjects per group).

Methods: Two-sample bidirectional MR and mediation analysis were used to evaluate associations. Experimental validation employed flow cytometry for myeloid-derived suppressor cell quantification, enzyme-linked immunosorbent assay for cytokines, and real-time polymerase chain reaction for bacterial validation. Statistical analyses included inverse variance weighted methods with Cohen's d calculations.

Results: Sixteen bacterial taxa, including p_Firmicutes.c_Clostridia, displayed protective associations with the risk of ALS, whereas sixteen showed harmful associations. Mediation analysis suggested that p_Firmicutes.c_Clostridia may confer protection through CD33+HLA-DR-myeloid-derived suppressor cell upregulation (23.8% mediation effect). Experimental validation confirmed fewer myeloid-derived suppressor cells in ALS patients (4.0 ± 0.8% vs. 7.5 ± 1.0%, p < 0.001, Cohen's d = 1.4) and lower levels of anti-inflammatory cytokines (TGF-β1: Cohen's d = 1.8, p < 0.001).

Conclusions: These findings support causal associations between gut microbial taxa and the ALS risk, which are mediated through immunoregulatory mechanisms, highlighting therapeutic targets within the gut‒immune‒brain axis.