Gut Microbiota-Tryptophan Metabolism-GLP-1 Axis Participates in ß-Cell Regeneration Induced by Dapagliflozin.

Sodium-glucose cotransporter 2 inhibitors, efficacious antidiabetic agents that have cardiovascular and renal benefits, can promote pancreatic ß-cell regeneration in type 2 diabetic mice. However, the underlying mechanism remains unclear. In this study, we aimed to use multiomics to identify the mediators involved in ß-cell regeneration induced by dapagliflozin. We showed that dapagliflozin lowered blood glucose level, upregulated plasma insulin level, and increased islet area in db/db mice. Dapagliflozin reshaped gut microbiota and modulated microbiotic and plasmatic metabolites related to tryptophan metabolism, especially l-tryptophan, in the diabetic mice. Notably, l-tryptophan upregulated the mRNA level of glucagon-like peptide 1 (GLP-1) production-related gene (Gcg and Pcsk1) expression and promoted GLP-1 secretion in cultured mouse intestinal L cells, and it increased the supernatant insulin level in primary human islets, which was eliminated by GPR142 antagonist. Transplant of fecal microbiota from dapagliflozin-treated mice, supplementation of l-tryptophan, or treatment with dapagliflozin upregulated l-tryptophan, GLP-1, and insulin or C-peptide levels and promoted ß-cell regeneration in db/db mice. Addition of exendin 9-39, a GLP-1 receptor (GLP-1R) antagonist, or pancreatic Glp1r knockout diminished these beneficial effects. In summary, treatment with dapagliflozin in type 2 diabetic mice promotes ß-cell regeneration by upregulating GLP-1 production, which is mediated via gut microbiota and tryptophan metabolism.

Glucagon Acting at the GLP-1 Receptor Contributes to ß-Cell Regeneration Induced by Glucagon Receptor Antagonism in Diabetic Mice.

Dysfunction of glucagon-secreting α-cells participates in the progression of diabetes, and glucagon receptor (GCGR) antagonism is regarded as a novel strategy for diabetes therapy. GCGR antagonism upregulates glucagon and glucagon-like peptide 1 (GLP-1) secretion and, notably, promotes ß-cell regeneration in diabetic mice. Here, we aimed to clarify the role of GLP-1 receptor (GLP-1R) activated by glucagon and/or GLP-1 in the GCGR antagonism-induced ß-cell regeneration. We showed that in db/db mice and type 1 diabetic wild-type or Flox/cre mice, GCGR monoclonal antibody (mAb) improved glucose control, upregulated plasma insulin level, and increased ß-cell area. Notably, blockage of systemic or pancreatic GLP-1R signaling by exendin 9-39 (Ex9) or Glp1r knockout diminished the above effects of GCGR mAb. Furthermore, glucagon-neutralizing antibody (nAb), which prevents activation of GLP-1R by glucagon, also attenuated the GCGR mAb-induced insulinotropic effect and ß-cell regeneration. In cultured primary mouse islets isolated from normal mice and db/db mice, GCGR mAb action to increase insulin release and to upregulate ß-cell-specific marker expression was reduced by a glucagon nAb, by the GLP-1R antagonist Ex9, or by a pancreas-specific Glp1r knockout. These findings suggest that activation of GLP-1R by glucagon participates in ß-cell regeneration induced by GCGR antagonism in diabetic mice. ARTICLE HIGHLIGHTS: Glucagon receptor (GCGR) antagonism promotes ß-cell regeneration in type 1 and type 2 diabetic mice and in euglycemic nonhuman primates. Glucagon and glucagon-like peptide 1 (GLP-1) can activate the GLP-1 receptor (GLP-1R), and their levels are upregulated following GCGR antagonism. We investigated whether GLP-1R activated by glucagon and/or GLP-1 contributed to ß-cell regeneration induced by GCGR antagonism. We found that blockage of glucagon-GLP-1R signaling attenuated the GCGR monoclonal antibody-induced insulinotropic effect and ß-cell regeneration in diabetic mice. Our study reveals a novel mechanism of ß-cell regeneration and uncovers the communication between α-cells and ß-cells in regulating ß-cell mass.

Dapagliflozin improves pancreatic islet function by attenuating microvascular endothelial dysfunction in type 2 diabetes.

AIMS: Sodium-glucose co-transporter 2 inhibitors, including dapagliflozin, improve ß cell function in type 2 diabetic individuals. Whether dapagliflozin can protect islet microvascular endothelial cells (IMECs) and thus contribute to the improvement of ß cell function remains unknown. MATERIALS AND METHODS: The db/db mice were treated with dapagliflozin or vehicle for 6 weeks. ß cell function, islet capillaries and the levels of inflammatory chemokines in IMECs were detected. The mouse IMEC cell line MS-1 cells were incubated with palmitate and/or dapagliflozin for 24 h. Angiogenesis and inflammatory chemokine levels were evaluated, and the involved signalling pathways were analysed. The mouse ß cell line MIN6 cells, in the presence or absence of co-culture with MS-1 cells, were treated with palmitate and/or dapagliflozin for 24 h. The expression of ß cell specific markers and insulin secretion in MIN6 cells were determined. RESULTS: Dapagliflozin significantly improved ß cell function, increased islet capillaries and decreased the levels of inflammatory chemokines of IMECs in db/db mice. In the palmitate-treated MS-1 cells, angiogenesis was enhanced and the levels of inflammatory chemokines were downregulated by dapagliflozin. Either a PI3K inhibitor or mTOR inhibitor eliminated the dapagliflozin-mediated effects. Importantly, dapagliflozin attenuated the palmitate-induced downregulation of ß cell function-related gene expression and insulin secretion in MIN6 cells co-cultured with MS-1 cells but not in those on mono-culture. CONCLUSIONS: Dapagliflozin restores islet vascularisation and attenuates the inflammation of IMECs in type 2 diabetic mice. The dapagliflozin-induced improvement of ß cell function is at least partially accounted for by its beneficial effects on IMECs in a PI3K/Akt-mTOR-dependent manner.

γ-aminobutyric acid modulates α-cell hyperplasia but not ß-cell regeneration induced by glucagon receptor antagonism in type 1 diabetic mice.

AIMS: To investigate whether treatment with γ-aminobutyric acid (GABA) alone or in combination with glucagon receptor (GCGR) monoclonal antibody (mAb) exerted beneficial effects on ß-cell mass and α-cell mass, and to explore the origins of the regenerated ß-cells in mice with type 1 diabetes (T1D). METHODS: Streptozotocin (STZ)-induced T1D mice were treated with intraperitoneal injection of GABA (250 µg/kg per day) and/or REMD 2.59 (a GCGR mAb, 5 mg/kg per week), or IgG dissolved in PBS for 8 weeks. Plasma hormone levels and islet cell morphology were evaluated by ELISA and immunofluorescence, respectively. The origins of the regenerated ß-cells were analyzed by double-immunostaining, α-cell lineage-tracing and BrdU-tracing studies. RESULTS: After the 8-week treatment, GABA or GCGR mAb alone or in combination ameliorated hyperglycemia in STZ-induced T1D mice. GCGR mAb upregulated plasma insulin level and increased ß-cell mass, and GABA appeared to have similar effects in T1D mice. However, combination treatment did not reveal any additive or synergistic effect. Interestingly, the GCGR mAb-induced increment of plasma glucagon level and α-cell mass was attenuated by the combined treatment of GABA. In addition, duct-derived ß-cell neogenesis and α-to-ß cell conversion but not ß-cell proliferation contributed to the increased ß-cell mass in T1D mice. CONCLUSION: These results suggested that GABA attenuated α-cell hyperplasia but did not potentiates ß-cell regeneration induced by GCGR mAb in T1D mice. Our findings provide novel insights into a combination treatment strategy for ß-cell regeneration in T1D.