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Maturation of Adult β-Cells Revealed Using a Pdx1/Insulin Dual-Reporter Lentivirus

Michael Smith Laboratories (M.S., J.M.P.), Genetics Graduate Program (M.S.), and Departments of Cellular and Physiological Sciences (D.S.L., J.D.J.), Surgery (D.S.L., J.D.J.), and Chemical and Biological Engineering (J.M.P.), University of British Columbia, Vancouver, Canada V6T 1Z3

Address all correspondence and requests for reprints to: James D. Johnson, Ph.D., Department of Cellular and Physiological Sciences, University of British Columbia, 5358 Life Sciences Building, 2350 Health Sciences Mall, Vancouver, British Columbia, Canada V6T 1Z3. E-mail: jimjohn{at}interchange.ubc.ca.

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 Pdx1 but little or no insulin (Pdx1⁺/Ins^low) 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⁺/Ins^low cells. Sorted Pdx1⁺/Ins^low MIN6 cells had a higher replication rate and secreted less insulin relative to double-positive cells. Long-term phenotype tracking of Pdx1⁺/Ins^low 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.