IPF1/PDX1 Deficiency and β-Cell Dysfunction in Psammomys obesus, an Animal With Type 2 Diabetes
- Gil Leibowitz1,
- Sarah Ferber2,
- Åsa Apelqvist3,
- Helena Edlund3,
- David J. Gross1,
- Erol Cerasi1,
- Danielle Melloul1 and
- Nurit Kaiser1
- 1Department of Endocrinology and Metabolism, Hebrew University- Hadassah Medical Center, Jerusalem
- 2Institute of Endocrinology, Sheba Medical Center, Tel Hashomer, Israel
- 3Department of Microbiology, University of Umeå, Umeå, Sweden
The homeodomain transcription factor IPF1/PDX1 is required in β-cells for efficient expression of insulin, glucose transporter 2, and prohormone convertases 1/3 and 2. Psammomys obesus, a model of diet-responsive type 2 diabetes, shows markedly depleted insulin stores when given a high-energy (HE) diet. Despite hyperglycemia, insulin mRNA levels initially remained unchanged and then decreased gradually to 15% of the basal level by 3 weeks. Moreover, insulin gene expression was not increased when isolated P. obesus islets were exposed to elevated glucose concentrations. Consistent with these observations, no functional Ipf1/Pdx1 gene product was detected in islets of newborn or adult P. obesus using immunostaining, Western blot, DNA binding, and reverse transcriptase–polymerase chain reaction analyses. Other β-cell transcription factors (e.g., ISL-1, Nkx2.2, and Nkx6.1) were expressed in P. obesus islets, and the DNA binding activity of the insulin transcription factors RIPE3b1-Act and IEF1 was intact. Ipf1/Pdx1 gene transfer to isolated P. obesus islets normalized the defect in glucose-stimulated insulin gene expression and prevented the rapid depletion of insulin content after exposure to high glucose. Taken together, these results suggest that the inability of P. obesus islets to adapt to dietary overload, with depletion of insulin content as a consequence, results from IPF1/PDX1 deficiency. However, because not all animals become hyperglycemic on HE diet, additional factors may be important for the development of diabetes in this animal model.
Address correspondence and reprint requests to Gil Leibowitz, MD, Department of Endocrinology and Metabolism, Hadassah University Hospital, P.O. Box 12000, 91120 Jerusalem, Israel. E-mail:.
Received for publication 23 February 2001 and accepted in revised form 11 May 2001.
HE, high-energy; IRI, immunoreactive insulin; LE, low-energy; MOI, multiplicity of infection; PCR, polymerase chain reaction; RT, reverse transcriptase.