Multi-Omics Evidence Linking Depression to MASLD Risk via Inflammatory Immune Signaling

<b>Background</b>: Depression and Metabolic Dysfunction-Associated Steatotic Fatty Liver Disease (MASLD) are common chronic diseases, respectively. However, the causal and molecular links between them remain unclear. In order to explore whether depression contributes to an increased risk of MASLD and whether inflammation mediates this effect, we integrated multi-level evidence from the epidemiology of the National Health and Nutrition Examination Survey (NHANES), the genetics of GWAS, the transcriptomes of GEO, and single-cell RNA sequencing datasets. <b>Methods</b>: A multi-level integrative analysis strategy was used to validate this pathway. First, a cross-sectional epidemiological analysis based on NHANES data was used to reveal the association between depression and MASLD, and to explore the mediating role of inflammation and liver injury markers. Secondly, a two-sample Mendelian randomization analysis was used to infer the causal direction of depression and MASLD, and to verify the mediating effect of systemic inflammation and liver injury indicators at the genetic level. Then, the transcriptome co-expression network analysis and machine learning were used to screen the common hub genes connecting the two diseases. Finally, single-cell transcriptome data were used to characterize the dynamic expression of potential key genes during disease progression at cellular resolution. <b>Results</b>: Depression significantly increased the risk of MASLD, especially in women (OR = 1.39, 95%CI [1.17-1.65]). Parallel mediation analysis showed that high-sensitivity C-reactive protein (hs-CRP) (<i>p</i> < 0.001), γ-glutamyltransferase (GGT) (<i>p</i> < 0.001), and alkaline phosphatase (ALP) (<i>p</i> < 0.001) mediated this relationship. Mendelian randomization analysis confirmed the unidirectional causal effect of depression on MASLD, and there was no reverse association (β = 0.483, SE = 0.146, <i>p</i> = 0.001). Weighted gene co-expression network analysis and machine learning identified <i>CD40LG</i> as a potential molecular bridge between depression-associated immune modules and MASLD. In addition, single-cell data analysis revealed a stage-specific trend of <i>CD40LG</i> expression in <i>CD4</i>⁺ T cells during MASLD progression, while its receptor <i>CD40</i> was also activated in B cells. In the female sample, <i>CD40LG</i> maintained an upward trend. However, the stability of this result is limited by the limited sample size. <b>Conclusions</b>: This study provides converging multi-omics evidence that depression plays a causal role in MASLD through inflammation-mediated immune signaling. The <i>CD40LG</i>-<i>CD40</i> axis has emerged as an immune mechanism that transposes depression into the pathogenesis of MASLD, providing a potential target for the intervention of gender-specific metabolic liver disease.