- B.S. - University of New Mexico, 1978-1981
- Ph.D. - University of New Mexico, 1982-1986
- National Metabolism Training Program, Case Western Reserve University. Cleveland, Ohio, 1988-1990
- Cancer Research and Treatment Center, University of New Mexico, 1986-1988
- Co-Director, Obesity Cell Biology Program, Colorado Obesity Research Initiative, University of Colorado Denver, Aurora, CO, 2009-present
- Professor, Cardiovascular Pulmonary Research Laboratory, University of Colorado Denver, Denver, CO, 2004-present
- Director of Basic Research, Pulmonary and Critical Care Section, Veterans Affairs Medical Center, Denver, CO, 2001-2008
- Associate Professor, Cardiovascular Pulmonary Research Laboratory, University of Colorado Health Sciences Center, Denver, CO, 2001-2004
- Associate Faculty Member - Division of Allergy and Clinical Immunology, National Jewish Medical and Research Center, Denver, CO, 1998-2001
- Adjunct Associate Professor - Department of Biochemistry and Molecular Genetics, University of Colorado Health Sciences Center, Denver, CO, 1998-present
- Assistant Faculty Member - Division of Allergy and Clinical Immunology, National Jewish Medical and Research Center, Denver, CO, 1996-1999
- Adjunct Assistant Professor - Department of Biochemistry and Molecular Genetics, University of Colorado Health Sciences Center, Denver, CO, 1990-1999
- Assistant Faculty Member - Division of Basic Science, National Jewish Medical and Research Center, 1990-1996
- Heidi Miller
- Keith Fox
- Chrystelle Garat
- Paul Erickson
- John Psilas
Research in my laboratory focuses on two important medical conditions, obesity and pulmonary hypertension.
Obesity and weight gain are associated with increased morbidity and mortality, and affect a sizable and increasing population in the U.S. and other developed countries. Obesity and weight gain are characterized by an increase in the size of existing fat cells (adipocytes), as well as, an increase in the number of adipocytes in fat tissue. We are investigating the generation of new adipocytes in two research projects. The first project focuses on the developmental pathways by which adipocytes are generated from progenitor/stem cells. These two projects are described in more detail in the subsequent sections. The second project explores the role of a specific protein, the cAMP-Response Element Binding Protein (CREB), in initiating new adipocyte production.
Generation of New Adipocytes From Bone Marrow Stem Cells:
In these studies we are testing the hypothesis that stem cells from bone marrow may serve a source for new fat cells. It has generally been assumed that all new adipocytes are generated from preadipocytes or progenitor cells that reside within fat tissue. We have challenged this paradigm by demonstrating that some new fat cells are produced from bone marrow stem cells via myeloid intermediates. The marrow-derived adipocytes accumulate over time in a depot- and gender-specific manner with higher numbers in visceral versus subcutaneous fat, and in female rather than male mice. This differential accumulation is particularly interesting in view of global gene expression patterns in marrow-derived adipocytes showing decreased expression of mitochondrial and peroxisomal genes related to organelle biogenesis and lipid oxidation, and increased expression of inflammatory cytokine genes. Thus, differential accumulation of marrow-derived adipocytes may explain, in part, why fat in different parts of the body behaves differently, and why fat in the deep abdomen is linked to cardiovascular disease and diabetes. The results also explain the detrimental changes in adipose function with aging, adiposity and gender. We are now developing methods to improve the isolation of the marrow-derived adipocytes and further understand their relationship to conventional fat cells. We are also developing techniques to identify these novel fat cells in human fat tissue samples.
CREB and the Production of New Adipocytes:
Adipogenesis is the process by which new adipocytes are generated from progenitor cells and preadipocytes. This process is highly choreographed; involving the sequential expression of genes that not only drive the conversion process, but also ultimately give fat cells their distinctive features and functions. In previous biochemical and molecular studies using preadipocytes grown in culture, we demonstrated that CREB, a protein that regulates the expression of certain genes, plays an important role in initiating the conversion of preadipocytes to mature adipocytes, and also prevents death of mature fat cells. We are now using genetically-manipulated mouse models to explore the impact of CREB on adipose tissue development and expansion, and related changes in whole animal physiology. Preliminary data from these models indicates that loss of CREB in preadipocytes inhibits the development of fat tissue, while depletion of CREB in adipocytes increase body fat accumulation. These results suggest that CREB may be a target for therapies to prevent or reverse weight gain and obesity.
Hypoxia-induced pulmonary hypertension (PH) observed in chronic obstructive pulmonary diseases such as emphysema and chronic bronchitis, and sleep-related alveolar hypoventilation disorders is a major cause of morbidity and mortality. There has been a doubling of PH and increased death rate from this set of diseases in the past two decades. Despite major advances in the treatment of severe cardiopulmonary conditions, PH remains a deadly disease that is largely unresponsive to current treatment regimens. We are currently investigating two aspects of hypoxia-induced PH. The first aspect is the role of the transcription factor, cAMP-Response Element Binding Protein (CREB), in thickening of the pulmonary arterial wall under hypoxic conditions. The second aspect is whether factors unrelated to hypoxia such as inflammation may be responsible for the development of PH in obese individuals. Each of the aspects is discussed in more detail in the subsequent sections.
CREB in Pulmonary Hypertension:
We previously reported that levels of CREB, a protein that controls the expression of certain genes, is diminished in smooth muscle cells that comprise much of the pulmonary artery wall in rats and cows exposed to chronic hypoxia. In biochemical studies, we demonstrated that forced depletion of CREB in cultured smooth muscle cells stimulates cell proliferation, growth, migration and production of extracellular matrix. These same events occur during thickening of the pulmonary artery wall. We are now using genetically-engineered mice to further explore the impact of CREB on smooth muscle cell function and the development of pulmonary hypertension. Preliminary experiments indicate that forced depletion of CREB in smooth muscle cells in mice accelerates the development of PH in response to hypoxia, and is sufficient to elicit thickening of the arterial wall in the absence of hypoxia after many months. These results suggest that CREB plays a protective role in preventing detrimental changes in smooth muscle cell function.
Obesity and PH:
Obesity is associated with an increased incidence of PH. It has been generally assumed that obesity-related PH is due to intermittent or chronic hypoxia resulting decreased breathing ability or hypoventilation. However, obesity also results in numerous metabolic and inflammatory changes throughout the body. We hypothesize that these changes, unrelated to hypoxia, may also promote the development of PH. We are evaluating PH in several rodent models of obesity. Initial studies with lean versus obese rats showed increased pulmonary artery thickening and hypertension under normoxic conditions. No evidence of chronic or intermittent hypoxia in the fat rats has been detected. Thus, changes in pulmonary artery structure and function in the obese rats appears unrelated to hypoxia. We are now using rat and mouse models to determine what other obesity-related factors may account for the detrimental changes.
- Majka, S.M., K.E. Fox, J.C. Psilas, K.M. Helm, C.R. Childs, A.S. Acosta, M.V. Garcia, B.T. Woessner, T.R. Shade and D.J. Klemm. 2010. De Novo Generation of White Adipocytes from the Myeloid Lineage Via Mesenchymal Intermediates is Age, Adipose Depot and Gender Specific. Proceeding of the National Academy of Science USA. 107:14781-14786.
- Garat, C.V., J.T. Crossno, Jr., T.M. Sullivan, J.E.B. Reusch and D.J. Klemm. 2010. Thiazolidinediones Prevent PDGF-BB-Induced CREB Depletion in Pulmonary Artery Smooth Muscle Cells by Preventing Upregulation of Casein Kinase 2a’ Catalytic Subunit. Journal of Cardiovascular Pharmacology. 55:469-480.
- Takeda, K., M. Okamoto, S. De Langhe, E. Dill, M. Armstrong, N. Reisdorf, D. Irwin, M. Koster, J. Wilder, K. Stenamrk, J. West, D. Klemm, E. Gelfand, E. Nozik-Grayck and S. Majka. 2009. Peroxisome Proliferator Activated Receptor gamma Agonist Treatment Increases Septation and Angiogenesis and Decreases Airway Hyperresponsiveness in a Murine Model of Neonatal Chronic Lung Disease. Anatomical Record 292:1045-1061.
- Fox, K.E., L.A. Colton, P.F. Erickson, J.E. Friedman, H.C. Cha, P. Keller, O.A. MacDougald, and D.J. Klemm. 2009. Regulation of Cyclin D1 and Wnt10b Gene Expression by CREB During Early Adipogenesis Involves Differential Promoter Methylation. Journal of Biological Chemistry. 283:35096-35105.
- Irwin D, Helm K, Campbell N, Imamura M, Fagan KA, Harral J, Carr M, Young KA, Klemm DJ, Gebb SA, Dempsey EC, West J, Majka SM. Neonatal Lung Side Population Cells Demonstrate Endothelial Potential and are Altered in Response to Hyperoxia Induced Lung Simplification. Am J Physiol Lung Cell Mol Physiol. 293:L941-L951
- Schroeder-Gloeckler JM, Rahman SM, Janssen RC, Qiao L, Shao J, Roper M, Fischer SJ, Lowe E, Orlicky DJ, McManaman JL, Palmer C, Gitomer WL, Huang W, O'doherty RM, Becker TC, Klemm DJ, Jensen DR, Pulawa LK, Eckel RH, Friedman JE. 2007 CCAAT/enhancer-binding protein beta (C/EBPbeta ) deletion reduces adiposity, hepatic steatosis, and diabetes in Leprdb/db mice. J Biol Chem. 282:15717-15729.
- Crossno, J.T., Jr., J.E.B. Reusch, K.G. Morris, E.C. Dempsey, I.F. McMurtry, K.R. Stenmark and D.J. Klemm. 2007 Rosiglitazone Attenuates Hypoxia-Induced Pulmonary Arterial Remodeling. Am. J. Physiolo. Lung Cellular Mol. Physiol. 292:L885-97.
- Fox, K.E., D.M. Fankell, P. F. Erickson, S.M. Majka, J.T. Crossno and D.J. Klemm. 2006. Depletion of CREB/ATF1 Inhibits Adipogenic Conversion of 3T3-L1 Cells Ectopically Expressing C/EBP a, C/EBP b, or PPARg2. Journal of Biological Chemistry 281:40341-40353
- Crossno, J.T., Jr., S.M. Majka, T. Grazia, R.G. Gill and D.J. Klemm. 2006. Rosiglitazone Promotes Differentiation of Bone Marrow-Derived Circulating Progenitor Cells to Multilocular Adipocytes in Adipose Tissue. Journal of Clinical Investigation. 116:3220-3228.
- Garat, C.V., D. Fankell, P.F. Erickson, J.E.B. Reusch, N.N, Bauer, I.F. McMurtry and D.J. Klemm. 2006. PDGF-BB Induces Nuclear Export and Proteosomal Degradation of CREB via PI3-Kinase/Akt Signaling. Molecular and Cellular Biology 26:4934-4948.
- Zhang, J.W., D.J. Klemm, C. Vinson, and M.D. Lane. 2004. Transcriptional Regulation of the CCAAT/Enhancer Binding Protein beta Gene During Adipogenesis. Journal of Biological Chemistry 279:4471-4478.
- Reusch J.E., D.J. Klemm. 2002. Inhibition of cAMP-Response Element-Binding Protein Activity Decreases Protein Kinase B/Akt Expression in 3T3-L1 Adipocytes and Induces Apoptosis. Journal of Biological Chemistry. 277:1426-1432.
- Watson P.A., A. Nesterova, C.F. Burant, D.J. Klemm, J.E. Reusch. 2001. Diabetes-Related Changes in cAMP Response Element-Binding Protein Content Enhance Smooth Muscle Cell Proliferation and Migration. Journal of Biological Chemistry. 276:46142-46150.
- Klemm D.J., P.A. Watson, M.G.Frid, E.C. Dempsey, J. Schaack, L.A. Colton, A. Nesterova, K.R. Stenmark, J.E. Reusch. 2001. cAMP Response Element-Binding Protein Content is a Molecular Determinant of Smooth Muscle Cell Proliferation and Migration. Journal of Biological Chemistry. 276:46132-46141.
- Klemm D.J., J.W. Leitner, P. Watson, A. Nesterova, J.E. Reusch, M.L. Goalstone, B. Draznin. 2001. Insulin-Induced Adipocyte Differentiation. Activation of CREB Rescues Adipogenesis from the Arrest Caused by Inhibition of Prenylation. Journal of Biological Chemistry. 276:28430-28435.
- Reusch, J.E.-B., L.A. Colton, and D.J. Klemm. 2000. CREB Activation Induces Adipogenesis in NIH 3T3-L1 Cells. Molecular and Cellular Biology 20:1008-1020.