Also, monitoring PDX-1 expression at different stages of the treatment period may answer whether or not these ductal cells are contributing to islet neogenesis. It is well known that b-cell replication strictly declines with age in mice and in humans. This phenomenon might be due to down regulation of key transcription factors and kinases implicated in b-cell mitosis. In our studies, the mice were,10 weeks old after diabetes induction and the mice were treated for 7 weeks. These mice were not aged mice, hence the replicative pool of cells would be considered abundant. Interestingly, the rate of b-cell replication in the pancreas of STZ-induced diabetic mice treated with PSN632408 was lower than the rate of b-cell replication in islet grafts in STZ-induced diabetic mice treated with PSN632408 in our earlier study. We do not know why PSN632408 could stimulate more b-cell replication in intact islet grafts. One possibility is that STZ demolished a lot of b-cells in the pancreas that have the capability to replicate. Another possible reason is that b-cells in intact islet grafts replicate more in a high glucose milieu, since almost all recipient mice had blood glucose levels.600 mg/dL before islet transplantation. Further studies are needed to determine whether b-cell replication is from self-renewal of mature b cells or from replication of specialized progenitors and whether different glucose Cycloheximide company levels affect b-cell replication in mice treated with PSN632408 and sitagliptin. In addition to b cells, we found a more than 2-fold increase in replication of a-cells when mice were treated with PSN632408 or sitagliptin alone, and more than a 5-fold increase when treated with combination therapys; however, a-cell mass was not measured. Alpha-cell replication and elevated Epoxomicin Proteasome inhibitor glucagon levels may aid in the formation of new b-cells, since pancreatic glucagon is required for b-cell formation and differentiation. Also, the composition of a-cells increases in pancreatic islets of diabetic human patients and of animal models. Interestingly, acells can be converted into b-cells under conditions of extreme damage to b-cells. Therefore, we cannot rule out the possibility that DPP-IV inhibitors or GPR119 agonists might play a role in a- tob-cell differentiation. There is some evidence for contribution of acinar cells in islet b-cell formation by transdifferentiation under specific conditions ; however, we did not find any increase in exocrine cell replication in any treatment group. To the best of our knowledge, this is the first 
study demonstrating the effects of a GPR119 agonist along with a DPP-IV inhibitor on b-cell regeneration via both replication and neogenesis in a diabetic mouse model. Besides b-cell regeneration, other factors including prevention of b-cell apoptosis may have also contributed to the increase of b-cell mass. Pancreatic b-cell mass was remarkably improved by combination therapy, which offers a novel therapeutic strategy for treating diabetic patients with a low b-cell mass. As there are clear discrepancies between rodent and human b-cell regeneration capacity, our future studies are aimed at evaluating the potential of these drug combinations on human islet regeneration by transplanting human islets from young and aged donors into immunodeficient mouse models. In addition, it will be interesting to further investigate the effect of combining a GPR119 agonist with a DPPIV inhibitor on reversing autoimmune diabetes.