Plasma apolipoprotein E levels and sepsis risk based on multi-center cohorts and multi-omics validation

Background Sepsis remains a leading cause of mortality in critical care, with limited reliable biomarkers that reflect upstream pathophysiology and enable early risk stratification. Apolipoprotein E (ApoE), a lipid transporter with immune-regulatory functions, has shown inconsistent associations with sepsis outcomes. Its causal and clinically actionable role in sepsis risk requires clarification. Materials and Methods We employed a multi-layered strategy integrating Mendelian randomization, colocalization, and phenome-wide association studies across five large proteogenomic cohorts (>500,000 individuals) to identify plasma proteins causally linked to sepsis. ApoE emerged as a top candidate and was validated in a clinical cohort of 291 ICU patients and in murine sepsis models. We assessed the relationship between ApoE levels and sepsis risk using logistic regression, restricted cubic spline models, and survival analyses, and explored underlying mechanisms via cytokine profiling, histopathology, and transcriptomics. Results ApoE was causally associated with sepsis risk in multiple independent datasets, supported by strong genetic colocalization (posterior probability for shared causal variant PP.H4 > 0.80). In ICU patients, both low (adjusted OR 12.74, 95% CI 5.72–28.36) and high ApoE levels (adjusted OR 4.54, 95% CI 2.25–9.16) were independently associated with increased sepsis risk compared to medium levels, forming a significant U-shaped pattern (P_nonlinear < 0.001). This biphasic risk was mirrored in murine models, where both hypo- and hyper-expression of ApoE aggravated systemic inflammation, organ injury, and mortality. LDL cholesterol mediated only ~ 20% of the ApoE–sepsis association, indicating lipid-independent mechanisms. Conclusion Plasma ApoE functions as a biphasic, dose-sensitive modulator of host response to sepsis. Both deficiency and excess disturb immune homeostasis and increase susceptibility, underscoring the need for precision-guided ApoE modulation in sepsis management. These findings provide a mechanistically grounded biomarker candidate and highlight new avenues for personalized therapy. Prospective trials are warranted to evaluate ApoE-targeted strategies in sepsis care.