VMAT2 identified as a regulator of late-stage ß-cell differentiation.

Cell replacement therapy for diabetes mellitus requires cost-effective generation of high-quality, insulin-producing, pancreatic ß cells from pluripotent stem cells. Development of this technique has been hampered by a lack of knowledge of the molecular mechanisms underlying ß-cell differentiation. The present study identified reserpine and tetrabenazine (TBZ), both vesicular monoamine transporter 2 (VMAT2) inhibitors, as promoters of late-stage differentiation of Pdx1-positive pancreatic progenitor cells into Neurog3 (referred to henceforth as Ngn3)-positive endocrine precursors. VMAT2-controlled monoamines, such as dopamine, histamine and serotonin, negatively regulated ß-cell differentiation. Reserpine or TBZ acted additively with dibutyryl adenosine 3',5'-cyclic AMP, a cell-permeable cAMP analog, to potentiate differentiation of embryonic stem (ES) cells into ß cells that exhibited glucose-stimulated insulin secretion. When ES cell-derived ß cells were transplanted into AKITA diabetic mice, the cells reversed hyperglycemia. Our protocol provides a basis for the understanding of ß-cell differentiation and its application to a cost-effective production of functional ß cells for cell therapy.

Recovery from diabetes in neonatal mice after a low-dose streptozotocin treatment.

Administration of streptozotocin (STZ) induces destruction of ß-cells and is widely used as an experimental animal model of type I diabetes. In neonatal rat, after low-doses of STZ-mediated destruction of ß-cells, ß-cells regeneration occurs and reversal of hyperglycemia was observed. However, in neonatal mice, ß-cell regeneration seems to occur much slowly compared to that observed in the rat. Here, we described the time dependent quantitative changes in ß-cell mass during a spontaneous slow recovery of diabetes induced in a low-dose STZ mice model. We then investigated the underlying mechanisms and analyzed the cell source for the recovery of ß-cells. We showed here that postnatal day 7 (P7) female mice treated with 50 mg/kg STZ underwent the destruction of a large proportion of ß-cells and developed hyperglycemia. The blood glucose increased gradually and reached a peak level at 500 mg/dl on day 35-50. This was followed by a spontaneous regeneration of ß-cells. A reversal of non-fasting blood glucose to the control value was observed within 150 days. However, the mice still showed impaired glucose tolerance on day 150 and day 220, although a significant improvement was observed on day 150. Quantification of the ß-cell mass revealed that the ß-cell mass increased significantly between day 100 and day 150. On day 150 and day 220, the ß-cell mass was approximately 23% and 48.5% of the control, respectively. Of the insulin-positive cells, 10% turned out to be PCNA-positive proliferating cells. Our results demonstrated that, ß-cell duplication is one of the cell sources for ß-cell regeneration.

Dopamine D2 Receptor-Mediated Regulation of Pancreatic ß Cell Mass.

Understanding the molecular mechanisms that regulate ß cell mass and proliferation is important for the treatment of diabetes. Here, we identified domperidone (DPD), a dopamine D2 receptor (DRD2) antagonist that enhances ß cell mass. Over time, islet ß cell loss occurs in dissociation cultures, and this was inhibited by DPD. DPD increased proliferation and decreased apoptosis of ß cells through increasing intracellular cAMP. DPD prevented ß cell dedifferentiation, which together highly contributed to the increased ß cell mass. DRD2 knockdown phenocopied the effects of domperidone and increased the number of ß cells. Drd2 overexpression sensitized the dopamine responsiveness of ß cells and increased apoptosis. Further analysis revealed that the adenosine agonist 5'-N-ethylcarboxamidoadenosine, a previously identified promoter of ß cell proliferation, acted with DPD to increase the number of ß cells. In humans, dopamine also modulates ß cell mass through DRD2 and exerts an inhibitory effect on adenosine signaling.