# Protective impact of circulating ω-3 PUFAs on sepsis susceptibility through PCSK9 variant: evidence from Mendelian randomization and animal experiments

## TL;DR

This study shows that higher levels of ω-3 PUFAs and a PCSK9 gene variant may protect against sepsis, supported by human data and mouse experiments.

## Contribution

The study identifies a PCSK9 gene variant as a mediator of ω-3 PUFAs' protective effect against sepsis, validated through Mendelian randomization and animal models.

## Key findings

- ω-3 PUFAs and total PUFAs are associated with reduced sepsis risk in Mendelian randomization analysis.
- The PCSK9 variant rs11591147 may mediate the protective effect of PUFAs against sepsis.
- In mice, ω-3 PUFAs and PCSK9 inhibitors reduced sepsis mortality and organ damage.

## Abstract

Polyunsaturated fatty acids (PUFAs), particularly ω-3 PUFAs, can improve sepsis prognosis. However, the relationship between the pre-infection levels of PUFAs and sepsis risk remains unclear.

We conducted a two-sample Mendelian randomization (MR) analysis using UK Biobank data to explore the causal association between circulating unsaturated fatty acids (UFAs) and sepsis susceptibility, complemented by a sepsis mouse model (cecal ligation and puncture, CLP) for validation.

MR analysis revealed that ω-3 PUFAs (OR: 0.912, p = 0.005), ω-6 PUFAs (OR: 0.914, p = 0.036), total PUFAs (OR: 0.894, p = 0.003), and the PUFAs/MUFAs (monounsaturated fatty acids) ratio (OR: 0.927, p = 0.042) correlated with a reduced risk of sepsis, while the ω-6/ω-3 ratio increased susceptibility and mortality rates (OR: 1.084, p = 0.018). Sensitivity analyses showed no heterogeneity or horizontal pleiotropy, indicating robust findings. Ten single nucleotide polymorphisms (SNPs) were linked to both ω-3 and ω-6 PUFAs. Among which rs11591147 in the PCSK9 gene (a loss-of-function variant) may mediate the protective effect of PUFAs against sepsis. Mouse experiments showed that ω-3 PUFAs or/and the PCSK9 monoclonal antibody (evolocumab), reduced 7-day mortality (26.7, 40.0, and 53.3%, respectively) and multi-organ damage in CLP mice.

In patients with PCSK9 mutations, elevated plasma ω-3 PUFAs may reduce susceptibility to sepsis. Therefore, early detection of PUFA levels and PCSK9 genotypes, along with the targeted nutritional supplements, may help reduce sepsis risk in susceptible populations.

Overview of the study design. (A) Two-sample Mendelian randomization analysis was conducted to investigate the causal association between circulating UFAs (including ω-3 PUFAs, ω-6 PUFAs, total PUFAs, total MUFAs, ω-6/ω-3 ratio, and PUFAs/MUFAs ratio) and susceptibility to sepsis. (B) Among the 10 SNPs that mediate the occurrence of sepsis and are associated with both ω-3 and ω-6 PUFAs, rs11591147 in the PCSK9 gene is included. (C) CLP mouse experiments demonstrated that both ω-3 PUFAs and the PCSK9 monoclonal antibody, when administered individually or in combination, can significantly reduce mortality and multi-organ damage in sepsis. Partial illustrations were generated using BioRender.com. A valid publication license has been acquired.Flowchart depicting two-sample Mendelian randomization analysis and animal experiments. Panel A shows the selection of instrumental variables and the analysis process, illustrating three assumptions related to exposure (UFAs) and outcome (sepsis). Confounding factors are outlined. Panel B displays a Venn diagram of SNPs in sepsis patients (ieu-b-4980), highlighting intersections with PCSK9. Panel C depicts a CLP sepsis animal model with treatments including omega-3 and Evolocumab, with a diagram of the experimental procedure.

Overview of the study design. (A) Two-sample Mendelian randomization analysis was conducted to investigate the causal association between circulating UFAs (including ω-3 PUFAs, ω-6 PUFAs, total PUFAs, total MUFAs, ω-6/ω-3 ratio, and PUFAs/MUFAs ratio) and susceptibility to sepsis. (B) Among the 10 SNPs that mediate the occurrence of sepsis and are associated with both ω-3 and ω-6 PUFAs, rs11591147 in the PCSK9 gene is included. (C) CLP mouse experiments demonstrated that both ω-3 PUFAs and the PCSK9 monoclonal antibody, when administered individually or in combination, can significantly reduce mortality and multi-organ damage in sepsis. Partial illustrations were generated using BioRender.com. A valid publication license has been acquired.