Activation of aryl hydrocarbon receptor signaling by indole-3-lactic acid from Bacillus velezensis DS2 reinforces gut mucosal immunity and attenuates inflammaging in aged mice

BACKGROUND: Aging is characterized by progressive immunosenescence and inflammaging, in which impaired gut barrier and dysregulated mucosal immunity exacerbate systemic senescence. While probiotics modulate gut health, their role in mitigating age-related immune dysfunction via specific microbial metabolites remains unclear. This study aims to investigate the effects of Bacillus velezensis DS2, a novel probiotic, in alleviating inflammaging, with a focus on tryptophan-metabolic signaling and immune regulation. RESULTS: In senescent endothelial cells, DS2-sourced indole-3-lactic acid (ILA) activated aryl hydrocarbon receptor (AhR) signaling. This activation reduced the expression of senescence markers (p16, γ-H2A.X) and decreased the levels of pro-inflammatory molecules (ICAM-1, VCAM-1). In aged mice, DS2 supplementation increased the abundance of beneficial bacteria, including Lactobacillus and Ligilactobacillus. DS2 administration also elevated plasma ILA and IL-22 levels, and reduced intestinal permeability. This was evidenced by the expansion of IL-22-producing type 3 innate lymphoid cells (ILC3s) and activation of the AhR-IL-22 axis. Consequently, DS2 enhanced intestinal barrier integrity and mitigated systemic inflammation (TNF-α, IL-6). Exogenous ILA was sufficient to recapitulate these benefits by potentiating gut mucosal immunity and attenuating inflammaging, as all these effects were abolished by the AhR antagonist CH223191. CONCLUSIONS: We demonstrate that DS2 mitigates inflammaging by producing ILA, which acts as a key metabolite to activate the AhR-IL-22-ILC3 axis. Our findings highlight the potential of targeting the gut-immune axis with specific probiotics as a novel strategy against age-related immune decline.