BADERC-David Rhoads

David Rhoads, Ph.D.

Transcriptional Control of Carbohydrate-Responsive Genes

A number of intestinal transporters and enzymes for carbohydrate metabolism are both diurnally expressed and induced by dietary carbohydrate. The anticipatory nature of these behaviors, particularly of the diurnal periodicity, led us to hypothesize a genetically controlled adaptive mechanism. From our studies, we have concluded that a circadian transcriptional rhythm, conserved between rodents and primates and regulated in part by hepatocyte nuclear factor 1 (HNF1), underlies the circadian rhythm of enzyme activities observed in many tissues. We postulate that the rhythmicity in enzyme activities contributes to changes in carbohydrate tolerance and insulin sensitivity. To elucidate the transcriptional mechanism(s) regulating carbohydrate metabolism, we are characterizing the circadian control of carbohydrate-responsive genes and examining their regulation in mutant mice deficient in HNF1.

Human mutations in HNF1b cause maturity onset diabetes of the young (MODY5). To examine the role of HNF1b in pancreatic b cell function, we have used the Cre-LoxP strategy to generate mice deficient in this transcription factor specifically in b cells. Such mice are glucose intolerant, are defective in glucose-stimulated insulin secretion, and show derangements in b cell gene expression. Current studies are directed toward (i) defining the specific metabolic pathways affected by HNF1b deficiency and (ii) restoration of function in mutant b cells by transient expression of HNF1b or its target genes.

These studies will increase our understanding of the regulation of carbohydrate metabolism and its dysregulation in diabetes mellitus. Ultimately, we hope to identify targets amenable to pharmaceutical control of carbohydrate absorption in conditions such as obesity and diabetes.

References:

1. Hediger, M. A. and D. B. Rhoads. Molecular physiology of sodium-glucose cotransporters. Physiol Rev 1994; 74: 993-1026.

2. Rhoads, D. B., D. H. Rosenbaum, U. Unsal, K. J. Isselbacher, L. L. Levitsky. Circadian periodicity of intestinal SGLT1 mRNA levels is transcriptionally regulated. J Biol Chem 1998; 273: 9510-9516.

3. Tavakkolizadeh, A., U. V. Berger, K. R. Shen, L. L. Levitsky, M. J. Zinner, M. A. Hediger, S. W. Ashley, E. E. Whang, and D. B. Rhoads. Diurnal rhythmicity in intestinal SGLT-1 function, V_max, and mRNA expression topography. Am J Physiol 2001; 280: G209-215.

4. Sakaguchi, T., X. Gu, H. Golden, E. Suh, D. B. Rhoads, H.-C Reinecker. Cloning of the human claudin-2 5’-flanking region revealed a TATA-less promoter with conserved binding sites in mouse and human for caudal-related homeodomain proteins and hepatocyte nuclear factor-1a. J Biol Chem 2002; 277: 21361-21370.

5. Bodie, B. P., B. C. Fuchs, B. P. Hurley, J. L. Conroy, J. E. Suetterlin, K. K. Tanabe, D. B. Rhoads, S. F. Abcouwer, and W. W. Souba. Molecular and functional analysis of glutamine uptake in human hepatoma and liver-derived cells Am J Physiol 2002; 283: G1062-G1073.

6. Yang, F., T. Agulian, J. E. Sudati, D. B. Rhoads, and L. L. Levitsky. Developmental regulation of galactokinase in suckling mouse liver by the Egr-1 transcription factor. Pediatr Res. 55: 822-829, 2004.

7. Wang, L., Coffinier, C., Thomas, M.K., Gresh, L., Eddu, G., Manor, T., Levitsky, L.L., Yaniv, M., and Rhoads, D.B. Selective deletion of the Hnf1b (MODY5) gene in b-cells leads to altered gene expression and defective insulin release. Endocrinology. 145: 3941-3949, 2004.

8. Tavakkolizadeh, A., Ramsanahie, A., Levitsky, L.L., Zinner, M.J., Whang, E.E., Ashley, S.W., Rhoads, D.B. Differential role of vagus nerve in maintaining diurnal gene expression rhythms in the proximal small intestine. J Surg Res, in press 2005.






			David Rhoads, Ph.D. Transcriptional Control of Carbohydrate-Responsive Genes A number of intestinal transporters and enzymes for carbohydrate metabolism are both diurnally expressed and induced by dietary carbohydrate. The anticipatory nature of these behaviors, particularly of the diurnal periodicity, led us to hypothesize a genetically controlled adaptive mechanism. From our studies, we have concluded that a circadian transcriptional rhythm, conserved between rodents and primates and regulated in part by hepatocyte nuclear factor 1 (HNF1), underlies the circadian rhythm of enzyme activities observed in many tissues. We postulate that the rhythmicity in enzyme activities contributes to changes in carbohydrate tolerance and insulin sensitivity. To elucidate the transcriptional mechanism(s) regulating carbohydrate metabolism, we are characterizing the circadian control of carbohydrate-responsive genes and examining their regulation in mutant mice deficient in HNF1. Human mutations in HNF1b cause maturity onset diabetes of the young (MODY5). To examine the role of HNF1b in pancreatic b cell function, we have used the Cre-LoxP strategy to generate mice deficient in this transcription factor specifically in b cells. Such mice are glucose intolerant, are defective in glucose-stimulated insulin secretion, and show derangements in b cell gene expression. Current studies are directed toward (i) defining the specific metabolic pathways affected by HNF1b deficiency and (ii) restoration of function in mutant b cells by transient expression of HNF1b or its target genes. These studies will increase our understanding of the regulation of carbohydrate metabolism and its dysregulation in diabetes mellitus. Ultimately, we hope to identify targets amenable to pharmaceutical control of carbohydrate absorption in conditions such as obesity and diabetes. References: 1. Hediger, M. A. and D. B. Rhoads. Molecular physiology of sodium-glucose cotransporters. Physiol Rev 1994; 74: 993-1026. 2. Rhoads, D. B., D. H. Rosenbaum, U. Unsal, K. J. Isselbacher, L. L. Levitsky. Circadian periodicity of intestinal SGLT1 mRNA levels is transcriptionally regulated. J Biol Chem 1998; 273: 9510-9516. 3. Tavakkolizadeh, A., U. V. Berger, K. R. Shen, L. L. Levitsky, M. J. Zinner, M. A. Hediger, S. W. Ashley, E. E. Whang, and D. B. Rhoads. Diurnal rhythmicity in intestinal SGLT-1 function, V_max, and mRNA expression topography. Am J Physiol 2001; 280: G209-215. 4. Sakaguchi, T., X. Gu, H. Golden, E. Suh, D. B. Rhoads, H.-C Reinecker. Cloning of the human claudin-2 5’-flanking region revealed a TATA-less promoter with conserved binding sites in mouse and human for caudal-related homeodomain proteins and hepatocyte nuclear factor-1a. J Biol Chem 2002; 277: 21361-21370. 5. Bodie, B. P., B. C. Fuchs, B. P. Hurley, J. L. Conroy, J. E. Suetterlin, K. K. Tanabe, D. B. Rhoads, S. F. Abcouwer, and W. W. Souba. Molecular and functional analysis of glutamine uptake in human hepatoma and liver-derived cells Am J Physiol 2002; 283: G1062-G1073. 6. Yang, F., T. Agulian, J. E. Sudati, D. B. Rhoads, and L. L. Levitsky. Developmental regulation of galactokinase in suckling mouse liver by the Egr-1 transcription factor. Pediatr Res. 55: 822-829, 2004. 7. Wang, L., Coffinier, C., Thomas, M.K., Gresh, L., Eddu, G., Manor, T., Levitsky, L.L., Yaniv, M., and Rhoads, D.B. Selective deletion of the Hnf1b (MODY5) gene in b-cells leads to altered gene expression and defective insulin release. Endocrinology. 145: 3941-3949, 2004. 8. Tavakkolizadeh, A., Ramsanahie, A., Levitsky, L.L., Zinner, M.J., Whang, E.E., Ashley, S.W., Rhoads, D.B. Differential role of vagus nerve in maintaining diurnal gene expression rhythms in the proximal small intestine. J Surg Res, in press 2005.