Abstract
Mendelian randomization (MR) was employed to investigate the causal relationships between immune cell phenotypes, hyperthyroidism (HD), and potential metabolic mediators. In this study, we acquired 731 immune cell phenotypes from genome-wide association studies (GWAS) (n = 18,622), HD data from the research by Handan Melike Dönertaş et al. (3,731 cases, 480,867 controls), and aggregated statistics of 1,400 blood metabolites from UK Biobank (n = 115,078). Bidirectional MR analysis was performed to explore the causal relationships between the immune cell phenotypes and HD, and two-sample and multi-variable MR were conducted to identify the potential plasma metabolites mediating in HD. In addition, sensitivity analyses were used to evaluate robustness, heterogeneity, and horizontal pleiotropy of results. Single-cell transcriptome-based exploration of potential key molecule and mechanism by which plasma metabolites regulated the immune cell differentiation in HD pathogenesis. Co-localization analysis was using single-cell eQTL (sc-eQTL) data with key molecule to probe genetically shared effects. Two-sample MRshowed that CD25 on naive-mature B cell, CD8 + NKT cell, and thymol sulfate level were found to have causal relationships with HD (P < 0.008). The causal relationship between thymol sulfate and HD were further validated in an independent cohort using the inverse-variance weighted (IVW). In addition, CD25 on naive-mature B cells and CD8 + NKT cells were both negatively correlated with thymol sulfate (P < 0.05). The results remained significant after MR-Egger and MR-PRESSO correction for horizontal pleiotropy and heterogeneity (P > 0.05). Multi-variable MR results showed that CD25 on naive-mature B cell and CD8 + NKT cell mediated 8.67% and 10.4% of the associations between thymol sulfate and HD, respectively. Moreover, thymol sulfate mediated the evolution of CD8 + NKT cells in the immune microenvironment, identifying PTPRC, PTK2B, KDM5A and TIGIT as the key participating molecules. Co-localization analysis showed that the key molecules had significant genetic sharing effects with CD8 + NKT cells (PPH4 > 0.75, R(2) > 0.8, P < 0.05), with PTK2B having the broadest sharing interval. Current MR study provides evidence supporting causal relationships between several specific immune cell phenotypes and HD, as well as potential mediating metabolites. Thymol sulfate may increases the risk of HD pathogenesis by mediating the evolution of PTK2B genetic variants inducing CD8 + NKT cells in the progression of the immune microenvironment.