Laboratory of Kim Brint Pedersen
Assistant Professor, PhD,
Louisiana State University Health Sciences Center, 2003

Biography
Kim Brint Pedersen received his Masters degree in Biology from the University of Copenhagen, Denmark in 1986. He was employed as a microbiologist in the Danish biotech company Novo Nordisk A/S 1986-1998. He received his Ph.D. degree from the Department of Biochemistry & Molecular Biology at LSUHSC, New Orleans in 2003. He continued his career in the Department of Biochemistry & Molecular Biology at LSUHSC, first as a postdoctoral researcher in the laboratory of Dr. Donald K. Scott 2003-2006, and from 2007 as an assistant professor.

Lisa Bothman and Dr. Pedersen

Ongoing research in his lab
Metabolic conditions such as obesity and diabetes have reached epidemic proportions in the US and in much of the industrialized world. Currently, a third of the US population is obese, and 7% has diabetes. A thorough understanding of metabolism is required for developing effective treatments or prevention of these conditions.             

We are studying the regulation of enzymes involved in intermediary metabolism. The activity and expression of many such enzymes are dependent on whether the organism is in a fed or fasted state. As signals of the fed and fasted states, insulin and glucagon can affect the enzyme activity and/or gene expression. An elevated glucose concentration is another signal of the fed state that can elicit activation or repression of various genes. Glucose signaling thus promotes the conversion of glucose to triglycerides in the liver in the fed state. In pancreatic beta-cells, a high blood glucose concentration is the most important signal for insulin secretion. Glucose also stimulates the expression of many proteins required for insulin secretion such as the glucose transporter GLUT2, pyruvate carboxylase (PC), and insulin itself. However, in the hyperglycemic condition of diabetes, the expression of these proteins is diminished compared to non-diabetic controls. This dysregulation is believed to contribute to beta-cell failure as diabetes progresses. The overall research goals of the lab are to understand the mechanisms of glucose-regulated gene expression in the pancreatic beta-cells, the mechanisms behind dysregulated gene expression in the diabetic state, and the impact of these mechanisms on beta-cell function.   
   
In pancreatic beta-cells, PC catalyzes the first step of so-called pyruvate cycling pathways, which consist of a series of mitochondrial and cytosolic reactions generating cytosolic NADPH. Pyruvate cycling is correlated with glucose-stimulated insulin secretion, and recent reports indicate that the concentration of PC can directly affect glucose-stimulated insulin secretion. We are currently studying the mechanisms whereby glucose stimulates expression of PC. In mammalian species, PC is expressed from at least two promoters with multiple 5’-untranslated regions. Mapping of promoters and exon sequences show that overall architecture of the promoter region is conserved in mammals (Fig. 1). Thus, PC promoter and exon sequences identified in rats have clear homologues in the genomes of cows and humans.

In insulin-secreting cells from rats, we have found that glucose induces expression of PC transcripts from both the distal and proximal promoter. We have discovered that glucose induction from the distal promoter occurs through a carbohydrate response element (ChoRE), which consists of two sequences related to the E-box motif (5’-CACGTG-3’) separated by 5 base pairs. As illustrated in Fig. 2, this ChoRE is evolutionarily well-conserved and located the same distance from the transcriptional start site in the three species.

For other well-known ChoREs, the glucose responsiveness is mediated by the transcription factor Carbohydrate Response Element Binding Protein (ChREBP) with its dimerization partner Max-Like protein X (Mlx).  We have shown that ChREBP/Mlx plays the same role in mediating glucose responsiveness from the distal PC promoter: The ChoRE sequence binds a protein complex containing both ChREBP and Mlx in vitro; ChREBP binds to the distal PC promoter in a glucose-dependent fashion in the living cell; and treatments that reduce the concentration of functional ChREBP/Mlx dimers result in a diminished glucose response. Other transcription factors such as Upstream Stimulatory Factor (USF)-1, USF-2, and E2A can also bind to the ChoRE. Competition between these transcription factors and ChREBP/Mlx affects the magnitude of the glucose response.

We use an insulinoma cell line, 832/13, as a model of pancreatic beta cells. We have discovered that a high glucose concentration decreases the concentration of ChREBP protein in this cell line. As a consequence, growing the cells at hyperglycemic conditions leads to subsequent lower glucose responsiveness of the distal PC promoter. Whether hyperglycemia-induced depletion of ChREBP contributes to diminished levels of PC and beta-cell dysfunction in diabetic animals will be studied in the future.

Pancreatic beta-cells have a much higher expression of PC than in most other cell types. Yet, the promoters are fairly weak when driving expression of reporter genes. There must therefore be enhancers interacting with the promoters. Ongoing research is aimed at identifying such interactions. We will use various approaches for these studies. Chromosomal regions that are well-conserved among rats, cows, and humans will the tested for enhancer activity. We are also developing screening methods for monitoring transcription factor binding and histone status in the whole 100 kb promoter region. These methods are based on chromatin immunoprecipitation combined with quantitative real-time PCR. Chromosome conformation capture procedures will be used for determining interactions with more remotely located enhancers or interactions with regions on different chromosomes.

A better understanding of acute and chronic effects of glucose on gene expression in pancreatic beta-cells may ultimately lead to new therapies for treating or preventing diabetes.

Recent Publications

Pedersen, K. B., Buckley, R. S., and Scioneaux, R, Glucose induces expression of rat pyruvate carboxylase through a carbohydrate response element in the distal gene promoter, Biochem. J., 426: 159-170, (2010)
Click here to read the entire article.

Collier, J.J., Zhang, P., Pedersen, K.B., Burke, S.J., Haycock, J.W., and Scott, D.K, c-Myc and ChREBP regulate glucose-mediated expression of the L-type pyruvate kinase gene in INS-1-derived 832/13 cells, Am. J. Physiol. Endocrinol 293: E48-E56, (2007).
Click here to read the entire article.

Pedersen, K.B., Zhang, P., Doumen, C., Charbonnet, M., Lu, D., Newgard, C., Haycock, J. W., Lange, A.J., and Scott, D. K., The Promoter for the Gene Encoding the Catalytic Subunit of Rat Glucose-6-phosphatase Contains Two Distinct Glucose-responsive Regions, Am. J. Physiol. Endocrinol. Metab., 292: E788-E801, (2007). Click here to read the entire article.

Nunez, B.S., Geng, C.-d., Pedersen, K.B.., Millro-Macklin, C.D., and Vedeckis W.V., . Interaction between the interferon signaling pathway and the human glucocorticoid receptor gene 1A promoter., Endocrinology, 146: 1449-1457, (2005).

Geng, C.-d., Pedersen, K.B., Nunez, B.S., and Vedeckis, W.V., Human glucocorticoid receptor alpha transcript splice variants with exon 2 deletions: evidence for tissue- and cell type-specific functions., Biochemistry, 44: 7395-7405, (2005).

Pedersen, K.B.; Geng, C.-d.; and Vedeckis, W. V., Three Mechanisms Are Involved in Glucocorticoid Receptor Autoregulation in a Human T-Lymphoblast Cell Line, Biochemistry, 43: 10851-10858, (2004).

Pedersen, K.B. and Vedeckis, W. V., Quantification and Glucocorticoid Regulation of Glucocorticoid Receptor Transcripts in Two Human Leukemic Cell Lines, Biochemistry, 42: 10978-10990, (2003).

To search for all of Dr. Pedersen's publications click here