Novel genetic insights into causal effects of potential metformin targets and immune mediation on sepsis

Sepsis remains a major global clinical challenge with limited therapies. Metformin shows promising therapeutic potential, likely through immune modulation, yet mechanistic evidence remains scarce. Hence, our study aimed to investigate the causal effect of metformin on sepsis and explore the role of immune function in mediating this effect. We first assessed metformin’s causal effect on sepsis using two-sample Mendelian randomization (MR), then employed two-step MR to evaluate immune mediation of this effect. MR-Egger regression was conducted to detect pleiotropy and heterogeneity. Database-based single-cell RNA-seq analysis and sepsis mouse model further validated the MR findings. Two-sample MR indicated that metformin use, via PRKAB1 activation, was associated with a reduced risk of sepsis (OR = 0.9743, 95% CI: 0.9538–0.9951, P = 0.0160). Mediation analysis showed that 10 specific immune cell subsets, including CD39 + CD4+%T cell, CD39 + CD4+AC, CD39 + secreting Treg AC, CD14 + CD16+ monocyte AC, CD86 on myeloid DC, CD14 + CD16+ monocyte% monocyte, CD127 on CD28 + CD4+, CD3-lymphocyte %leukocyte, CD127 on T cell and CD127 on CD45RA-CD4 not Treg mediated metformin’s protective effects. Single-cell RNA-seq analysis revealed reduced T cells and monocytes during sepsis, consistent with MR results that identified elevated T cells and monocytes as major protective factors. PRKAB1 and its homologous genes were highly expressed in the mediation-linked immune cells. In septic mice, metformin attenuated lung injury and inflammatory infiltration, concurrently upregulating PRKAB1 expression significantly. mIHC and IHC assays confirmed metformin pretreatment reversed sepsis-induced CD86 elevation and depletion of CD39, CD4 and CD14. Our findings implied that metformin might contribute to sepsis protection, potentially involving PRKAB1-mediated modulation of CD39, CD4, CD14 and CD86. These observations could provide clues for developing targeted therapeutic strategies combining metformin with immune modulation for sepsis.