Résumé : Background and aims: An altered gut bacterial composition is associatedwith the pathogenesis of type 1 diabetes (T1D) and short-chain fatty acids(SCFA) are known play a pivotal role in maintaining gut homeostasis. Aspecial diet based on high-amylose maize-resistant starch modified withacetate and butyrate metabolites (HAMSAB) provided protection fromautoimmune diabetes in the NOD mouse model. We recently tested theHAMSAB diet in patients with established T1D showing improvement inglucose control. Based on these findings, we studied the molecular mechanisms and effects of SCFA in pre-diabetic pancreatic islets.Materials and methods: EndoC-βH1 and INS-1E β-cell lines weretreated with acetate (250μM), butyrate (10μM) and/or IFN-γ (1,000U/mL) + IL-1β (50U/mL). The cell viability was analyzed using SYTOX™Green Nucleic Acid Stain assay. five-week-old female NOD mice werefed with HAMSAB or HAMS control diet for five consecutive weeks.The pancreata were harvested, islets isolated using collagenase, anddispersed into single cells by trypsin. Single-cell RNA (scRNA)-sequencing was performed with 10x Chromium. The raw counts were analyzedusing RStudio with the Seurat package. The cells were filtered based onRNA features, counts, and mitochondrial percentage and annotated bytheir principal component analysis using UMAP.Results: Physiological concentrations of acetate and/or butyrate showedminimal effects on pro-inflammatory cytokine-induced cell death inEndoC-βH1 and INS-1E β-cell lines, suggesting that improved β-cellfunction is not due to SCFA-induced β-cell survival. To study the effectof the gut metabolites in the endocrine cells, we performed scRNA-seq inpancreatic islets isolated from pre-diabetic NOD mice fed HAMSAB orHAMS diets for five weeks. scRNA-seq analysis mapped the geneexpression profiles of 4,301 and 4,113 individual islet cells fromHAMSAB or HAMS fed mice, respectively. Cells were annotated into12 clusters: 5 immune and 7 pancreatic endocrine cell types. The scRNAseq dataset indicated that T-cells, B-cells, macrophages, and dendritic cellsubsets infiltrated the islets of Langerhans from both HAMSAB andHAMS-fed mice. Interestingly, HAMSAB reduced the number ofCD8+ cytotoxic cells, in line with previously described tolerogeniceffects. Moreover, subclustering and differential gene expression analysisindicated that HAMSAB enhances β-cell function and decreases theirstress response. In addition, the HAMSAB preserved the identity of endocrine cells evaluated by decreased dedifferentiated poly-hormonal (Ins+Gluc, Ins+Sst) cells expressing endocrine progenitor genes (MafA, Nfix)in mice fed this diet.Conclusion: The HAMSAB diet prevents diabetes development in NODmice, at least in part, by enhancing β-cell function and preserving cellidentity of endocrine cells under inflammatory-mediated autoimmunestress.