Uncovering metabolite-immune interactions in the pathogenesis of psoriatic arthritis: A 2-sample Mendelian randomization study.
PsA is a chronic inflammatory joint condition associated with psoriasis, and its underlying mechanisms are not fully elucidated. Serum metabolites, as direct reflections of metabolic status, may influence disease progression by regulating immune cell function; however, the causal relationships and specific pathways require further investigation. The present investigation utilized a 2-sample bidirectional MR methodology, leveraging extensive pooled GWAS data to thoroughly evaluate the causal relationships between 1440 serum metabolites and PsA. Additionally, mediation MR analysis was performed to explore the possible mediating effects of 731 immune cell characteristics. In the primary analysis, inverse-variance weighted was employed, and this was further supported by various sensitivity analyses to confirm the reliability of the findings. The genetic method to infer causality analysis revealed significant positive causal associations between 10 serum metabolites and PsA risk, with quinolinate levels demonstrating the most significant correlation (OR = 1.56, 95% CI: 1.26-1.93); while 4 metabolites (e.g., citrate levels, OR = 0.74, 95% CI: 0.61-0.89) exhibited protective effects. Regarding immune cells, 6 cellular features (e.g., CD20 on B cells) were positively correlated with disease risk, whereas 5 features (primarily HLA-DR expression on monocyte subsets) showed negative correlations. Mediation analysis identified 3 significant pathways,the percentage of the effect explained by the mediator: N6,N6,N6-trimethyllysine levels mediated via B cells (CD20 on IgD+ CD38br), with a proportion of 33.2%; 1-stearoyl-2-docosahexaenoyl-GPE (18:0/22:6) levels mediated through monocytes (HLA-DR on CD14- CD16-) with a 32.0% proportion; the unknown metabolite X-24736 also mediated 42.1% of the protective effect via the same monocyte phenotype. This study revealed that elevated amino acid-related metabolites and glycerophospholipids significantly increase PsA risk through immune cell effects. These are closely associated with PsA pathogenesis and may serve as potential biomarkers. The novel findings underscore metabolic-immune interactions as targets for biomarkers and therapies in PsA, advancing personalized medicine.