14-OR: Harmine and Exenatide Combination Increases Human ß-Cell Survival

GLP1R agonists such as Exendin-4 (E) together with DYRK1A inhibitors such as Harmine (H) significantly increase human β-cell replication in vitro and in vivo. Importantly, 3-month treatment with H+E combination markedly increases human beta cell mass (∼7-fold) in islets transplanted in immunosuppressed mice, beyond the increase induced by proliferation. Therefore, we addressed whether H+E also enhances β-cell survival and that contributes to the increased human β-cell mass expansion in vivo. Treatment with H+E significantly decreased β-cell apoptosis in dispersed primary human islet cells treated in vitro with either thapsigargin (ER stress) , cytokines (inflammation) and H₂O₂ (ROS) , while the drugs alone or vehicle (V) did not induce such effect. Importantly, H+E treatment for 7 days significantly reduced β-cell apoptosis in human islet grafts transplanted in immunosuppressed mice assessed by insulin and TUNEL staining. Human β-cell mass analysis of these grafts by iDISCO+ revealed a significant ∼50% increase in H+E-treated mice compared with mice treated with drugs alone or V. Human α-cell mass was unchanged. To address the signaling pathways modulated by H+E after 7-day treatment, we performed RNA-seq analysis of these human islet grafts. We identified 29 differentially expressed human genes (> 2-fold, p<0.05) in H+E-treated human islet grafts. GSEA analysis revealed cell adhesion, survival, vascularization and secretion as the main pathways induced by H+E. Among the upregulated genes, VGF (VGF Nerve Growth Factor Inducible) is known to regulate insulin secretion and β-cell survival. We found that H+E treatment of human islets in vitro increases 2-to-3-fold VGF mRNA and secretion. We are now determining VGF involvement in H+E-induced human β-cell survival.

In conclusion, we have uncovered a novel prosurvival function of H+E in human β-cells with the potential implication of VGF in these effects. These studies can lead to the discovery of future β-cell protection and regeneration therapies for diabetes.