Alba Rodríguez Blanco

• Diabetes mellitus (DM) remains a burden affecting hundreds of millions of people worldwide with increasing prevalence. Achieving a genuine cure for type I diabetes mellitus (T1DM) relies on regenerating functional β-cell mass. The renin-angiotensin system (RAS), traditionally known for regulating blood pressure, also plays a crucial role in metabolic regulation and diabetic complications. The classical pathway contributes to metabolic issues, such as insulin resistance, while the alternative pathway provides protective effects. Angiotensin (Ang)-(1-7), a key peptide of the alternative pathway of the RAS, exhibits regenerative properties and is linked to beneficial effects on glucose homeostasis and β-cell function, making it a promising therapeutic strategy for DM. This study investigates the impact of Ang-(1-7) and its receptors, Mas and MrgD, on restoring glucose homeostasis by stimulating β-cell proliferation and differentiation. Wild-type normoglycemic mice received varying doses of Ang-(1-7) via an osmotic pump for 14 days to examine its effects on pancreatic islets and β-cell mass. Ang-(1-7) was also applied to wild-type and Mas and/or MrgD KO mice by osmotic pumps for 14 days to characterize its impact on insulin and glucose tolerance and identify the receptor mediating this action. Due to their role in glucose metabolism, the effect of Ang-(1-7) on insulin-induced phosphorylation of insulin receptor (IR), IR substrate-1 (IRS-1), and Akt was examined in WT and KO skeletal muscle cells. Isolated islets from WT and KO mice were stimulated with Ang-(1-7) to determine its effect on the transcription of key genes for β-cell identity, function, and maturation. Ang-(1-7) was administered to Streptozotocin (STZ)-induced diabetic mice to evaluate its therapeutic potential under pathophysiological conditions. The results showed that exogenous administration of Ang-(1-7) at 400 µg/kg/day significantly increased β-cell mass and insulin content in normoglycemic mice compared to lower or higher doses. Administering Ang-(1-7) had only marginal effects on glucose tolerance in wild-type mice but still led to improved insulin secretion in response to glucose in vivo. Ang-(1-7) improved insulin-induced phosphorylation of IRS-1 and Akt in primary skeletal muscle cells through the Mas receptor, highlighting the role of the Ang-(1-7)/Mas axis in glycemic control. Furthermore, Ang-(1-7)/MrgD axis was shown to upregulate essential genes for pancreatic β-cell function (Ins2), β-cell identity (PDX1, Nkx6.1), and β-cell maturation (TCIRG1, Fltp, Ucn3, and MafA). Ang-(1-7) also upregulates progenitor stem cell genes (Ngn3 and CD133) through the MrgD receptor, while it downregulates CD133 via the Mas receptor in the islets. Ultimately, administering Ang-(1-7) failed to repair STZ-induced damage to pancreatic β-cells or to restore insulin production ability within a 14-day treatment time. Despite this, Ang-(1-7) administration delayed the rise of blood glucose levels in STZ-induced diabetic mice. In conclusion, this thesis presents new evidence underlining the therapeutic potential of Ang-(1-7) and its mechanistic pathways, through Mas and MrgD receptors, emphasizing its importance as a promoter of β-cell proliferation and differentiation, thereby potentially addressing the deficit of β-cell mass in T1DM.