Gut microbiota-dependent protection by Lactobacillus reuteri against renal injury in brain-dead rats

Donation-after-brain-death (DBD) serves as a major source of kidney transplant donors, and brain death (BD) induces systemic inflammation and gut barrier disruption, leading to renal injury and compromised organ quality. While Lactobacillus reuteri (L. reuteri) demonstrates anti-inflammatory and immunomodulatory properties that maintain gut microbiota homeostasis. However, its role in protecting organs against BD-associated injury remains unclear. This study investigated BD-induced renal injury mechanisms linked to gut-kidney axis dysregulation and evaluated L. reuteri's protective effects through microbiota-immune interactions. BD triggered intestinal barrier dysfunction, elevating gut permeability and promoting translocation of endotoxin lipopolysaccharide (LPS) to kidneys, which activated the TLR4/MyD88/NF-κB pathway, driving proinflammatory cytokine release, neutrophil infiltration, and renal dysfunction. L. reuteri pretreatment attenuated these effects by remodeling gut microbiota-reducing Proteobacteria while enriching Bacteroidota-and enhancing tight junction integrity, thereby suppressing pro-inflammatory LPS leakage and accumulation to renal tubule. Mechanistically, the increase in Bacteroidota abundance correlated with the downregulation of renal TLR4/NF-κB signaling, a pattern that is hypothesized to be explained by putative competitive inhibition by LPS derived from Bacteroidota. Concurrently, L. reuteri induced the upregulation of CD25⁺ immune cell expression in ileal glands and promoted CXCL2 production in renal and intestinal tissues, which is associated with the establishment of a gut-kidney immune homeostasis network. L. reuteri mitigates BD-induced renal injury through dual mechanisms-structural modulation of microbiota-derived LPS and intestinal immune remodeling-providing a novel microbiota-targeted adjunctive strategy to enhance donor organ viability in transplantation medicine.