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.