# Aging-caused the changes of the gut microbiota drive intestinal barrier dysfunction and increase sepsis susceptibility

## TL;DR

Aging changes gut bacteria, which worsens intestinal barriers and increases sepsis risk through histamine production.

## Contribution

Identifies Klebsiella aerogenes and histamine as key drivers of sepsis susceptibility in aging via impaired gut barrier function.

## Key findings

- Aged septic hosts show increased Klebsiella aerogenes abundance linked to higher histamine production.
- Histamine impairs intestinal barrier function by inhibiting Nlrp6 and autophagy in sepsis.
- Modulating histamine or overexpressing Nlrp6 reduces inflammation in aged septic mice.

## Abstract

Physiological and pathological changes associated with aging contribute to deteriorating disease prognosis in sepsis. However, the mechanisms by which these disturbances exacerbate inflammation remain underexplored. In this study, fecal samples were collected from aged and young septic patients and mice and subsequently transplanted into young pseudo-germ-free mice via fecal microbiota transplantation. Fecal, colon tissue, and blood samples were collected to be used 16S rDNA sequencing to characterize the gut microbiota, histopathological examination, enzyme-linked immunosorbent assay and FITC-dextran intestinal permeability assay to assess gut injury and gut barrier function. Additionally, nontargeted and targeted metabolomics were used to identify differential metabolites in the feces of aged and young septic mice. To further validate the roles of specific bacterial strains and their metabolites in sepsis, genetically engineered bacteria were used in both in vivo and in vitro experiments. The results showed that an increased abundance of Klebsiella aerogenes (K. aero) in aged hosts, which led to elevated histamine (HA) production and exacerbated intestinal barrier dysfunction. Importantly, K. aero strains carrying a histidine decarboxylase gene variant were identified as major HA producers. Mechanistically, HA was shown to drive intestinal barrier dysfunction by inhibiting Nlrp6 expression and its subsequent binding to LC3, thereby impairing autophagy. Treatments that modulated HA levels or overexpressed Nlrp6 ameliorated inflammation in septic mice. These findings suggest that targeting the HA-Nlrp6-LC3 axis could offer a novel therapeutic approach for managing sepsis, particularly in aged populations.