Unraveling new therapeutic targets in ankylosing spondylitis: Multi-omics Mendelian randomization on immune cells, metabolites, and inflammation proteins

This study aims to identify novel immunological, metabolic, and inflammatory determinants of ankylosing spondylitis (AS) using Mendelian randomization (MR), offering new insights into its pathogenesis and potential therapeutic interventions. Employing a bidirectional, secondary validation two-sample MR, this study investigated causal associations among 1400 serum metabolites, 731 immune cell traits, and 91 circulating inflammatory proteins with AS. Instrumental variables were identified using PLINK for minimal linkage disequilibrium, applying strict significance thresholds. Various MR methodologies, including inverse variance weighted, weighted median, and MR Egger, were applied to validate causal links. Sensitivity analyses, incorporating heterogeneity and pleiotropy tests, were performed to evaluate the robustness of the results. The false discovery rate correction was applied to adjust for multiple comparisons, while the MR Steiger directionality test and bidirectional MR analysis validated the causation direction. Secondary validation with data from diverse sources was undertaken to confirm the reliability of the findings. After false discovery rate correction, associations were identified between AS etiology and 9 immune cell traits, 2 serum metabolites, and 2 inflammatory proteins. Notably, the presence of CX3CR1 on monocytes and the absolute count of CD62L- CD86+ myeloid dendritic cells (DCs) were associated with an increased risk of AS. In contrast, expression of HLA DR on DCs, including myeloid and plasmacytoid DCs, and on CD14- CD16- monocytes, along with CD64 expression across various monocyte subsets (monocytes, CD14+ CD16+, and CD14+ CD16-), correlated with a decreased risk of AS development. Serum metabolites, specifically levels of hexadecanedioate and Bilirubin (E, Z or Z, E), were also linked to a reduced risk of AS. Regarding inflammatory factors, interleukin-6 levels were inversely associated with AS morbidity, whereas TNF-beta levels were positively correlated with higher AS morbidity. Neither bidirectional MR nor MR Steiger tests provided evidence supporting reverse causation. This study sheds light on the complex interactions between immune cells traits, metabolites, and inflammatory proteins in AS, offering new insights into its pathophysiology. The findings underscore the importance of the immune-metabolic-inflammation network in AS, suggesting novel biomarkers for diagnosis and targets for therapy.