Development of diabetes mellitus in aging transgenic mice following suppression of pancreatic homeoprotein IDX-1
Melissa K. Thomas, … , Matthew S. Tenser, Joel F. Habener
Melissa K. Thomas, … , Matthew S. Tenser, Joel F. Habener
Published July 15, 2001
Citation Information: J Clin Invest. 2001;108(2):319-329. https://doi.org/10.1172/JCI12029.
View: Text | PDF
Article Article has an altmetric score of 3

Development of diabetes mellitus in aging transgenic mice following suppression of pancreatic homeoprotein IDX-1

Abstract

Monogenic forms of diabetes can result from mutations in genes encoding transcription factors. Mutations in the homeodomain transcription factor IDX-1, a critical regulator of pancreas development and insulin gene transcription, confer a strong predisposition to the development of diabetes mellitus in humans. To investigate the role of IDX-1 expression in the pathogenesis of diabetes, we developed a model for the inducible impairment of IDX-1 expression in pancreatic β cells in vivo by engineering an antisense ribozyme specific for mouse IDX-1 mRNA under control of the reverse tetracycline transactivator (rtTA). Doxycycline-induced impairment of IDX-1 expression reduced activation of the Insulin promoter but activated the Idx-1 promoter, suggesting that pancreatic β cells regulate IDX-1 transcription to maintain IDX-1 levels within a narrow range. In transgenic mice that express both rtTA and the antisense ribozyme construct, impaired IDX-1 expression elevated glycated hemoglobin levels, diminished glucose tolerance, and decreased insulin/glucose ratios. Metabolic phenotypes induced by IDX-1 deficiency were observed predominantly in male mice over 18 months of age, suggesting that cellular mechanisms to protect IDX-1 levels in pancreatic β cells decline with aging. We propose that even in the absence of Idx-1 gene mutations, pathophysiological processes that decrease IDX-1 levels are likely to impair glucose tolerance. Therapeutic strategies to attain normal glucose homeostasis by restoring normal IDX-1 levels may be of particular importance for older individuals with diabetes mellitus.

Authors

Melissa K. Thomas, Octavia N. Devon, Jee H. Lee, Andreas Peter, David A. Schlosser, Matthew S. Tenser, Joel F. Habener

×

Figure 2

Options: View larger image (or click on image) Download as PowerPoint
Impairment of IDX-1 expression in pancreatic β cells activates the Idx-1...
Impairment of IDX-1 expression in pancreatic β cells activates the Idx-1 promoter. (a) Inducible impairment of IDX-1 expression in clonal β cells. Double-stable rtTA/Tet-ASRZ-IDX-1 clonal βTC3 cell lines were treated, as indicated (+), with 1 μg/ml doxycycline for 72 hours before harvest. Whole-cell extracts from two clonal cell lines were analyzed by Western blotting with anti–IDX-1 antiserum (left panels). Doxycycline-dependent reduction in IDX-1 expression ranged from 54% to 70% (clone 1, right panel). (b) Idx-1 promoter activation in response to impairment of IDX-1 expression. Double-stable rtTA/Tet-ASRZ-IDX-1 clonal β cells were transfected with 5 μg –4.6 kb mouse Idx-1 promoter-luciferase reporter and treated, as indicated (+), with 1 μg/ml doxycycline for 48 hours before harvest. Data shown are the average ± SEM of three transfections in duplicate. Fold activation represents normalized luciferase activity relative to untreated transfected cells (**P ≤ 0.01). (c) Dexamethasone enhances doxycycline-induced impairment of IDX-1 expression. Double-stable rtTA/Tet-ASRZ-IDX-1 clonal β cell lines were treated with (+) or without (–) 1 μg/ml doxycycline (Dox) for 72 hours before harvest and 100 nM dexamethasone (Dex) for 48 hours before harvest. Western blots of whole-cell extracts from two clonal cell lines are shown (left panels). IDX-1 expression without doxycycline treatment was reduced 40–75% by dexamethasone, and the doxycycline-dependent reduction of IDX-1 expression was enhanced from 30% to 330% by dexamethasone (clone 3, right panel). (d) Overexpression of IDX-1 in β cells decreases Idx-1 promoter activation. MIN6 cells were transiently transfected with 0.5 μg pCMV-IDX-1 or pCMV empty expression vector, 3.5 μg pBluescript, and 1 μg –4.6 kb mouse Idx-1 promoter-luciferase reporter. Data shown are the average ± SEM of three transfections in duplicate. Percent activation is normalized to the activity of cells transfected with pCMV alone (**P ≤ 0.01).