276. PAX4 Gene Transfer Induces α-to-β Cell Transdifferentiation and Ameliorates Hyperglycemia

Abstract

The transcription factor Pax4 plays a critical role in the determination of the lineage of insulin-producing β-cells versus glucagon-producing α-cells during endocrine pancreas development. In this study, we explored whether Pax4 gene transfer into α-cells could convert them into functional β-cells, and thus provide therapeutic benefits for insulin-deficient diabetes. To accomplish that, we developed an adenoviral vector encoding CMV promoter driven human Pax4, Ad5.Pax4, and examined its functionality in the clonal α-cell line, aTC1.9. Our results showed that Pax4 induced insulin expression and reduced glucagon expression in aTC1.9 cells. More importantly, these cells exhibited functional glucose-stimulated insulin secretion, a key feature of functional β-cells. When injected into streptozotocin-induced diabetic mice, the Pax4-treated aTC1.9 cells significantly reduced blood glucose within 24 hours, and the mice showed better glucose tolerance, supporting that Pax4 gene transfer into aTC1.9 cells resulted in the formation of functional β-cells. Furthermore, treatment of primary human islets with Ad5. Pax4 resulted in significantly improved β-cell function. Although in the experimental setting, we were not able to distinguish pre-existing β-cells from converted β-cells, detection of triple positive cells (glucagon+/Pax4+/Insulin+) argued for the presence of α-to-β cell transitioning. This was further supported by quantification of glucagon and insulin double positive (bi-hormonal) cells, of which the number of bi-hormonal cells in Pax4-treated human islets was significantly higher than that in control groups. Finally, we found that direct administration of Ad5. Pax4 into the pancreas of insulin-deficient mice had therapeutic benefits. The significantly improved β-cell function in both human islets and mouse pancreas was consistent with Pax4-induced α-to-β cell conversion, although Pax4-mediated β-cell protection could have contributed as well. Taken together, our data demonstrate that manipulating Pax4 gene expression in α-cells represents a novel and viable therapeutic strategy for the treatment of insulin deficient diabetes.