Pancreatic ß-cell neogenesis by direct conversion from mature α-cells.

Because type 1 and type 2 diabetes are characterized by loss of ß-cells, ß-cell regeneration has garnered great interest as an approach to diabetes therapy. Here, we developed a new model of ß-cell regeneration, combining pancreatic duct ligation (PDL) with elimination of pre-existing ß-cells with alloxan. In this model, in which virtually all ß-cells observed are neogenic, large numbers of ß-cells were generated within 2 weeks. Strikingly, the neogenic ß-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 ß-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 ß-cell conversion. Intermediate cells coexpressing α-cell- and ß-cell-specific markers appeared within the first week following PDL plus alloxan, declining gradually in number by 2 weeks as ß-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 ß-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 ß-cell conversion that will be required for eventual clinical translation as a therapy for diabetes.

Safety and effectiveness of rosiglitazone in type 2 diabetes patients with nonalcoholic Fatty liver disease.

BACKGROUND/PURPOSE: Nonalcoholic fatty liver disease (NAFLD) is a common chronic liver disease ranging in severity from steatosis to cirrhosis. Type 2 diabetes mellitus is a cause of primary NAFLD. Thiazolidinediones have been shown to enhance insulin sensitivity, improve glycemic control in type 2 diabetes patients and to improve the histologic markers of nonalcoholic steatohepatitis. This study aims to determine the safety and effectiveness of rosiglitazone in inadequately controlled type 2 diabetes patients with NAFLD. METHODS: Taiwanese type 2 diabetes patients with inadequate control on insulin secretagogues and metformin, with no history of significant alcohol ingestion, with mildly elevated serum aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT) and a diagnosis of fatty liver determined by ultrasonography were enrolled. Patients were treated for 24 weeks with rosiglitazone, 4-8 mg daily. Primary endpoints were change in AST and ALT levels from baseline and reduction in A1C < 6.5%. RESULTS: Out of a total of 68 patients, 60 (88.2%) completed the study treatment without serious adverse events. Treatment in two (2.9%) patients was discontinued due to elevated AST or ALT levels to more than three times the upper limit of normal, and noncompliance or loss of follow-up in six (8.8%) patients. Of the 60 patients who completed the study treatment, mean fasting plasma glucose, A1C, fasting plasma insulin, mean ALT and homeostasis model assessment for insulin resistance were all significantly reduced. Normal AST and ALT levels were achieved and maintained for at least three consecutive measurements and through to the end of the study period in 20 (33.3%) patients. Weight increased by a mean of 2.6 +/- 2.4 kg (p < 0.001). CONCLUSION: Rosiglitazone was reasonably well tolerated in patients with inadequately controlled type 2 diabetes and NAFLD. One-third of patients showed improved liver function after treatment.

Maternal embryonic leucine zipper kinase regulates pancreatic ductal, but not ß-cell, regeneration.

The maternal embryonic leucine zipper kinase (MELK) is expressed in stem/progenitor cells in some adult tissues, where it has been implicated in diverse biological processes, including the control of cell proliferation. Here, we described studies on its role in adult pancreatic regeneration in response to injury induced by duct ligation and ß-cell ablation. MELK expression was studied using transgenic mice expressing GFP under the control of the MELK promoter, and the role of MELK was studied using transgenic mice deleted in the MELK kinase domain. Pancreatic damage was initiated using duct ligation and chemical beta-cell ablation. By tracing MELK expression using a MELK promoter-GFP transgene, we determined that expression was extremely low in the normal pancreas. However, following duct ligation and ß-cell ablation, it became highly expressed in pancreatic ductal cells while remaining weakly expressed in α-cells and ß- cells. In a mutant mouse in which the MELK kinase domain was deleted, there was no effect on pancreatic development. There was no apparent effect on islet regeneration, either. However, following duct ligation there was a dramatic increase in the number of small ducts, but no change in the total number of duct cells or duct cell proliferation. In vitro studies indicated that this was likely due to a defect in cell migration. These results implicate MELK in the control of the response of the pancreas to injury, specifically controlling cell migration in normal and transformed pancreatic duct cells.

Adult pancreatic alpha-cells: a new source of cells for beta-cell regeneration.

Beta-cell deficit is the major pathological feature in type 1 and type 2 diabetes patients, and plays a key role in disease progression. In principle, beta-cell regeneration can occur by replication of pre-existing beta-cells, or by beta-cell neogenesis from stem/progenitors. Unfortunately, beta-cell replication is limited by the almost complete absence of beta-cells in patients with type 1 diabetes, and the increasing recognition that the beta-cell replicative capacity declines severely with age. Therefore, beta-cell neogenesis has received increasing interest. Many different cell types within the pancreas have been suggested as potential beta-cell stem/progenitor cells, but the data have been conflicting. In some cases, this may be due to different regeneration models. On the other hand, different results have been obtained with similar regeneration models, leading to confusion about the nature and existence of beta-cell neogenesis in adult animals. Here, we review the major candidates for adult regeneration pathways, and focus on the recent discovery that alpha-cells can function as a novel beta-cell progenitor. Of note, this is a pathway that appears to be unique to beta-cell neogenesis in the adult, as the embryonic pathway of beta-cell neogenesis does not proceed through a glucagon-positive intermediate. We conclude that beta-cell neogenesis from alpha-cells is a new pathway of potential therapeutic significance, making it of high importance to elucidate the molecular events in alpha- to beta-cell conversion.