Article

High Glucose Is Necessary for Complete Maturation of Pdx1-VP16-Expressing Hepatic Cells into Functional Insulin-Producing Cells

Department of Pathology, Immunology, and Laboratory Medicine, University of Florida College of Medicine, Gainesville, Florida, USA.
Diabetes (Impact Factor: 8.1). 01/2005; 53(12):3168-78. DOI: 10.2337/diabetes.53.12.3168
Source: PubMed

ABSTRACT

Pdx1 has been shown to convert hepatocytes into both exocrine and endocrine pancreatic cells in mice, but it fails to selectively convert hepatocytes into pure insulin-producing cells (IPCs). The molecular mechanisms underlying the transdifferentiation remain unclear. In this study, we generated a stably transfected rat hepatic cell line named WB-1 that expresses an active form of Pdx1 along with a reporter gene, RIP-eGFP. Our results demonstrate that Pdx1 induces the expression of multiple genes related to endocrine pancreas development and islet function in these liver cells. We do not however find any expression of the late-stage genes (Pax4, Pax6, Isl-1, and MafA) related to beta-cell development, and the cells do not secrete insulin upon the glucose challenge. Yet when WB-1 cells are transplanted into diabetic NOD-scid mice, these genes become activated and hyperglycemia is completely reversed. Detailed comparison of gene expression profiles between pre- and posttransplanted WB-1 cells demonstrates that the WB-1 cells have similar properties as that seen in pancreatic beta-cells. In addition, in vitro culture in high-glucose medium is sufficient to induce complete maturation of WB-1 cells into functional IPCs. In summary, we find that Pdx1-VP16 is able to selectively convert hepatic cells into pancreatic endocrine precursor cells. However, complete transdifferentiation into functional IPCs requires additional external factors, including high glucose or hyperglycemia. Thus, transdifferentiation of hepatocytes into functional IPCs may serve as a viable therapeutic option for patients with type 1 diabetes.

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    • "Upon transplantation, these pancreasderived oval cells can differentiate into functional hepatocytes and bile ducts [7]. The reciprocal conversion of rodent8910111213 and human1415161718 liver cells into pancreatic endocrine cells by transdifferentiation or direct cellular reprogramming has also been described. Liver cells have been induced to differentiate into insulin-producing cells by ectopic expression of pancreatic transcription factors, the best studied of which is PDX-1, a key regulator of pancreatic development and insulin expression in adult pancreatic beta cells [8, 10, 14,16171819. "
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    • "Based on our zebrafish and mouse data we hypothesize that one conserved function for pre-pancreatic insulin expression may be to suppress glucose production, as it can be teratogenic to embryos ([4] Akazawa, 2005; 23] Eriksson et al., 1991; 24] Freinkel, 1988; 44] Moley, 1999). Significantly, human, rodent, and apparently zebrafish preferentially utilize non-glucose substrates at early stages ([9] Biggers et al., 1967), further supporting this idea. "
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    • "Once again, IPF-1/ PDX-1 has proved to be a useful tool, with multiple groups successfully transdifferentiating rodent hepatic cells into insulin-producing cells via multiple genetic approaches66676869707172737475 . Most groups used adenovirusmediated gene transfer techniques to introduce transcription factors (especially PDX-1) into hepatic cells in vivo [66,68,72,73,75,76], whereas others found that in vitro high glucose concentrations and/or transplantation into a diabetic mouse were necessary to stimulate hepatic cell changes [67,71]. Regardless of the method used, amelioration of hyperglycaemia was achieved in these mouse models, giving hope to researchers searching for extra-pancreatic sources of insulin. "
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