Because type 1 and type 2 diabetes are characterized by loss of β-cells, β-cell regeneration has garnered great interest as an approach to diabetes therapy. Here, we developed a new model of β-cell regeneration, combining pancreatic duct ligation (PDL) with elimination of pre-existing β-cells with alloxan. In this model, in which virtually all β-cells observed are neogenic, large numbers of β-cells were generated within 2 weeks. Strikingly, the neogenic β-cells arose primarily from α-cells. α-cell proliferation was prominent following PDL plus alloxan, providing a large pool of precursors, but we found that β-cells could form from α-cells by direct conversion with or without intervening cell division. Thus, classical asymmetric division was not a required feature of the process of α- to β-cell conversion. Intermediate cells coexpressing α-cell- and β-cell-specific markers appeared within the first week following PDL plus alloxan, declining gradually in number by 2 weeks as β-cells with a mature phenotype, as defined by lack of glucagon and expression of MafA, became predominant. In summary, these data revealed a novel function of α-cells as β-cell progenitors. The high efficiency and rapidity of this process make it attractive for performing the studies required to gain the mechanistic understanding of the process of α- to β-cell conversion that will be required for eventual clinical translation as a therapy for diabetes.

The introduction of simian virus 40 large T antigen (SVLT) into human primary cells enables them to proliferate beyond their normal replicative life span. In most cases, this temporary escape from senescence eventually ends in a second proliferative block known as “crisis,” during which the cells cease growing or die. Rare immortalization events in which cells escape crisis are frequently correlated with the presence of telomerase activity. We tested the hypothesis that telomerase activation is the critical step in the immortalization process by studying the effects of telomerase activity in two mortal SVLT-Ras^val12-transformed human pancreatic cell lines, TRM-6 and βlox5. The telomerase catalytic subunit, hTRT, was introduced into late-passage cells via retroviral gene transfer. Telomerase activity was successfully induced in infected cells, as demonstrated by a telomerase repeat amplification protocol assay. In each of nine independent infections, telomerase-positive cells formed rapidly dividing cell lines while control cells entered crisis. Telomere lengths initially increased, but telomeres were then maintained at their new lengths for at least 20 population doublings. These results demonstrate that telomerase activity is sufficient to enable transformed cells to escape crisis and that telomere elongation in these cells occurs in a tightly regulated manner.