Towards Pancreatic β-Cell Regeneration: Modulating Islet Microenvironment and Identifying Markers of β-Cell Maturation

Abstract

Regeneration of endogenous β-cells is a promising therapy to treat diabetes, but there are considerable gaps in our understanding of the microenvironmental signals necessary to stimulate β-cell proliferation and the unique ways human β-cells differ from rodents. Our group previously modulated the islet microenvironment using a mouse model in which vascular endothelial growth factor A (VEGF-A) overexpression causes β-cell loss and endothelial cell (EC) expansion, followed by β-cell proliferation and regeneration that requires infiltrating macrophages. To determine the role of proliferative and quiescent ECs, we conditionally inactivated the key receptor mediating VEGF-A signaling, VEGFR2, in ECs and found that EC signaling was necessary for maximal macrophage recruitment and phenotype activation. We also showed that ablation of VEGFR2 in quiescent ECs during the β-cell regenerative phase induced rapid vessel regression that promoted β-cell proliferation, possibly mediated by growth factor release from the extracellular matrix. Extending these findings to human pancreas development, we determined that intra-islet EC area was greatest during the first year of postnatal life and coincided with the peak of β-cell proliferation, suggesting that vascular arrangement or EC-derived signals may impact human β-cell proliferation. Next, to advance the methodologies for studying human islets, we identified two molecular markers of developing and mature human β-cells. Secretory granule membrane major glycoprotein 2 (GP2) marks a population of multipotent pancreatic progenitor cells in the neonatal human pancreas, and can be utilized to improve efficiency of generating β-like cells from stem cells. Nucleoside triphosphate diphosphohydrolase 3 (NTPDase3) is a cell surface marker of adult human β-cells, and is a unique tool for isolating live β-cells by flow cytometry and performing in vivo β-cell imaging. These two markers will further our knowledge of islet development and allow us to assess β-cell gene expression and mass during the disease process, which we demonstrated by utilizing our islet cell isolation strategy to reveal transcriptional dysregulation in α-cells from donors with type 1 diabetes. Together, this work provides a framework for future efforts aimed at promoting β-cell regeneration and increasing functional β-cell mass.