Lactobacillus gasseri suppresses methionine-driven epigenetic programming of trained immunity-like priming to attenuate metabolic dysfunction.

Trained immunity-like epigenetic priming contributes to persistent metabolic inflammation in type 2 diabetes mellitus (T2DM), but the upstream metabolic and microbiota-dependent regulatory mechanisms remain unclear. Here, we performed an exploratory study to examine whether Lactobacillus gasseri (Lact. gasseri) attenuates metabolic dysfunction by suppressing methionine-dependent epigenetic priming of innate immune cells, and to characterize how metformin regulates Lact. gasseri colonisation in the intestine. A diabetes-prone mouse model was established using high-fat diet (HFD) and low-dose streptozotocin (STZ); a standard-chow plus STZ group was included to control for the direct β-cell toxicity of STZ. Metabolic phenotypes, histopathology, inflammatory responses, and intestinal barrier function were assessed. Bone marrow-derived macrophages (BMDMs) were rested ex vivo for 4 days in the absence of any in vivo stimulus and then subjected to an unrelated secondary LPS/IFN-γ challenge in order to evaluate primed responsiveness, and methionine-one‑carbon metabolism, H3K4me3, and cytokine expression were analysed by RT-qPCR, western blotting, ELISA and ChIP-qPCR. Lact. gasseri significantly reduced diabetes incidence and improved glucose tolerance and insulin sensitivity, ameliorated dyslipidaemia and pancreatic injury in HFD/STZ-treated mice. Mechanistically, Lact. gasseri was associated with reduced methionine availability and with lower absolute abundance of systemic and bone marrow methyl donors, accompanied by decreased H3K4me3 at the Il-1β promoter and attenuated IL-1β-mediated trained immunity-like priming. Methionine restriction in macrophages recapitulated these effects, whereas methionine replenishment restored histone methylation and IL-1β maturation, supporting a metabolic-epigenetic axis while not excluding contributions from other nutrient-sensitive pathways. Notably, metformin enhanced intestinal colonisation of Lact. gasseri without directly promoting bacterial growth in vitro, an effect accompanied by improved mucus barrier integrity and concordant upregulation of P53 and MUC2. Because no combined Lact. gasseri plus metformin arm was included in vivo, metabolic synergy was not tested in this study. Together, these exploratory findings describe a candidate microbiota-linked mechanism in which Lact. gasseri constrains methionine-dependent epigenetic priming of innate immune cells, connecting intestinal nutrient availability to systemic inflammatory memory and providing a rationale-rather than proof-for probiotic-drug combination strategies in T2DM.