Maturation of adult β-cells revealed using a Pdx1/ insulin dual-reporter lentivirus

Abstract

The enigmatic process of β-cell maturation has significant implications for diabetes pathogenesis, and potential diabetes therapies. This study examined the dynamics and heterogeneity of insulin and pancreatic duodenal homeobox (Pdx)-1 gene expression in adult β-cells. Insulin and Pdx1 expression were monitored in human and mouse islet cells and MIN6 cells using a Pdx1-monomeric red fluorescent protein/insulin-enhanced green fluorescent protein dual-reporter lentivirus. The majority of fluorescent cells were highly positive for both Pdx1 and insulin. Cells expressing Pdxl but little or no insulin (Pdx1+/Inslow) comprised 15-25% of the total population. Time-lapse imaging demonstrated that Pdx1 +/Ins low primary β-cells and MIN6 cells could convert to Pdx1 +/Ins+ cells without cell division. Genes involved in the mature β-cell phenotype (Glut2, MafA) were expressed at higher levels in Pdx1+/Ins+ cells relative to Pdx1+/Ins low cells. Conversely, genes implicated in early β-cell development (MafB, Nkx2.2) were enriched in Pdx1+/Inslow cells. Sorted Pdx1 +/Inslow MIN6 cells had a higher replication rate and secreted less insulin relative to double- positive cells. Long-term phenotype tracking of Pdx1 +/Inslow cells showed two groups, one that matured into Pdx1 +/Ins+ cells and one that remained immature. These results demonstrate that adult β-cells pass through distinct maturation states, which is consistent with previously observed heterogeneity in insulin and Pdx1 expression in adult β-cells. At a given time, a proportion of adult β-cells share similar characteristics to functionally immature embryonic β-cell progenitors. The maturation of adult β-cells recapitulates development in that Pdx1 expression precedes the robust expression of insulin and other mature β-cell genes. These results have implications for harnessing the maturation process for therapeutic purposes. Copyright © 2009 by The Endocrine Society.