MECHANISMS OF LEPTIN RESISTANCE IN DIET-INDUCED OBESITY

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: NRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 0191003
• Grant No.: 2001-35200-10817
• Cumulative Award Amt.: $250,000.00
• Proposal No.: 2001-00828
• Project Start Date: Jul 1, 2001
• Project End Date: Jun 30, 2005
• Grant Year: 2001
• Program Code: [(N/A)]- (N/A)

Recipient Organization
PENNINGTON BIOMEDICAL RES CNTR
6400 PERKINS ROAD
BATON ROUGE,LA 70808

Performing Department
(N/A)

Non Technical Summary
Accumulation of excess adipose tissue is a known risk factor for hypertension, heart disease and noninsulin-dependent diabetes mellitus. The epidemic of obesity in Western society is strongly associated with consumption of high fat diets. A subset of this population is sensitive to the diabetes promoting effects of high fat in that their obesity progresses to insulin resistance and eventually diabetes. A similar variation in sensitivity to high fat diets has been documented among mouse strains. For instance, C57BL6/J mice develop an obese/diabetic syndrome when reared on high fat diets, while mice of the A/J strain develop none of these pathologies. Thus, the C57BL6/J mouse provides an excellent model to study the developmental stages of an obese/diabetic syndrome that is highly analogous to human noninsulin-dependent diabetes mellitus. The implications of these studies is that high fat diets inhibit the actions of the recently identified hormone, leptin, to limit food intake and/or stimulate energy utilization in the fat-sensitive C57BL6/J strain. In studies completed to date, we have found that high fat diets compromise the ability of the brain to sense cirulating, leptin and compromise the ability of adipose tissue to respond to signals from the brain. Thus, we will test the hypothesis that high fat diets limit the ability of leptin to regulate specific genes that are necessary to avoid obesity. Identification of such genes and understanding how they become dysregulated in fat-sensitive mouse strains will facilitate identification of their human homologues.

Animal Health Component

25%

Research Effort Categories

Basic

75%

Applied

25%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
702	3999	1010	100%

Knowledge Area
702 - Requirements and Function of Nutrients and Other Food Components;

Subject Of Investigation
3999 - Animal research, general;

Field Of Science
1010 - Nutrition and metabolism;

Keywords

obesity

dietary fats

leptin

sympathetic nervous system

adipocytes

gene expression

western blotting

hormones

signal transduction

ribonuclease

rna m

biochemical mechanisms

animal models

nutrient function

human nutrition

strains (genetics)

energy utilization

energy intake

receptors

human health

genetics

measurement

intermediates

proteins

Goals / Objectives
High fat diets induce leptin resistance in certain mouse strains and inhibit its ability to match rates of energy utilization to the rate of energy intake. The result is morbid obesity. The goals of the present work are to determine how consumption of a high fat diet compromises the appropriate upregulation of thermogenic capacity in adipose tissue by leptin. We will distinguish among several mechanisms including compromised transport of leptin across the blood brain barrier, compromised post receptor leptin signaling efficacy, and compromised ability of adipose tissue to respond to central effects of leptin.

Project Methods
The goals of the proposed studies will be accomplished by weaning fat-resistant and fat-sensitive mouse strains onto a high fat diet, and administering leptin peripherally and centrally to representative animals from each group at periodic intervals. The efficacy of leptin signaling will be assessed at both the level of the hypothalamus by examining immediate post-receptor signaling function and periphally by examining leptin effects of gene expression. Using ribonuclease protection assays to measure mRNA and specific antibodies to measure protein expression of signaling intermediates, we will extend our understanding of both the central and peripheral mechanisms which compromise leptins ability to upregulate uncoupling protein expression.

Progress 10/01/03 to 09/30/04

Outputs
The original aims of this proposal were (1) High fat diets induce leptin resistance in fat sensitive mouse strains by inhibiting leptin-mediated up regulation of thermogenic capacity in adipose tissue while fat-resistant mouse strains maintain their ability to increase thermogenic capacity in adipose tissue, and (2) High fat diets induce central leptin resistance by inhibiting leptin transport into the hypothalamus and peripheral leptin resistance in fat sensitive mouse strains by reducing the expression of the beta3-adrenergic receptor. Twelve papers have been published in peer-reviewed journals and an additional two manuscripts are in the submission/review or preparation process. Since our last progress report, we have conducted three additional studies to further delineate the development of both peripheral and central leptin resistance. In the first study, we treated A/J and C57BL/6J mice with a peroxisome proliferator-activated receptor gamma (PPAR gamma) agonist in the presence and absence of the beta 3-AR agonist, CL316,243 after various periods of consuming the high fat diet. Of particular interest was our finding that a combination treatment of obesity prone C57BL/6J mice with beta 3-AR agonist and PPAR gamma agonist led to a large synergistic induction of UCP1 in WAT and led to loss of weight. This finding is particularly significant because it shows that under appropriate conditions, the adaptive thermogenic processes can be reawakened and induced in WAT from obesity prone mouse strains. The work is described in reference 10 which has been submitted for editorial consideration. This finding further suggests that comparable pharmacologic regimens may be developed and used to treat obesity in humans. These findings have led to the funding and initiation of a clinical trial to test these principals in non-diabetic human subjects. Second, we have completed the analysis of samples from an experiment where different routes of leptin administration were used to distinguish between leptin resistance arising from compromised transport into the hypothalamus, compromised hypothalamic responsiveness, and compromised peripheral responsiveness to centrally-mediated but peripherally acting leptin-dependent signals (ie sympathetic nervous system outflow). We found comparable sensitivity to peripherally or centrally administered leptin in both strains at weaning but their response patterns quickly diverged thereafter. These studies demonstrate fundamental differences between obesity-prone and obesity-resistant mice respond to energy rich diets with respect to central and peripheral actions of leptin. The findings from this work extend our understanding of the components of leptin signaling and how they can become dysregulated during the development of obesity. Lastly, our work was featured in an article published in NRI Research Highlights (11)

Impacts
Obesity resulting from consumption of calorie-rich high-fat diets affects in excess of 100 million Americans. The development of leptin resistance is thought to be an underlying cause of diet-induced obesity, but the molecular basis of leptin resistance is poorly understood. A more complete understanding of leptin resistance will guide the development of preventative and rehabilitative treatment paradigms, and assist in the identification of molecular targets for drug development. Work supported by this project has advanced our understanding of the mechanisms and developmental sequence of leptin resistance.

Publications

• Commins, S., Watson, P.M., Padgett, M., and Gettys, T.W. 1999. Induction of uncoupling protein expression in brown and white adipose tissue by leptin. Endocrinology 140: 292-300.
• Commins, S. P., Thomas, S. A., Watson, P. M., Padgett, M. A., Palmiter, R., and Gettys, T. W. 1999. Norepinephrine is required for leptin effects on gene expression in brown and white adipose tissue. Endocrinology 140: 4772-4778.
• Watson, P.M., Commins, S.P., Beiler, R.J., Hatcher, H.C., and Gettys, T.W. 2000. Differential regulation of leptin expression and function in A/J vs C57BL/6J mice during diet-induced obesity. Am. J. Physiol. 279: E356-E365.
• Commins, S.P., Watson, P.M., Beiler, R.J., Levin, N., and Gettys, T.W. 2000. The beta3-adrenoceptor is necessary for centrally-mediated effects of leptin on gene expression in white but not brown adipose tissue. J. Biol. Chem. 275: 33059-33067.
• Commins, S.P., Watson, P.M. and Gettys, T.W. 2001. UCP1 is required for leptin-dependent decreases in epididymal, inguinal and retroperitoneal WAT in mice. Am. J. Physiol. 280: E372-E377.
• Demas, G.E., Bowers, R.R., Bartness, T.J., and Gettys, T.W. 2002. Photoperiodic Regulation of Gene Expression in Brown and White Adipose Tissue of Siberian Hamsters (Phodopus sungorus) American Journal of Physiology 282: R114-R121.
• Finkenbine, S.S., Gettys, T.W., and Burnett, K.G. 2002. Beta-adrenergic receptors on leukocytes of the channel catfish, lctularus punctatus. Comp. Biochem. Physiol. 131: 27-37.
• Prpic, V., Watson, P.M., Frampton, I.C., Sabol, M.A., Jezek, G.E. and Gettys, T.W. 2003. Differential mechanisms and development of leptin resistance in A/J vs C57BL/6J mice during diet-induced obesity. Endocrinology 144: 1155-1163.
• Prpic, V., Watson, P.M., Frampton, I.C., Sabol, M.A., Jezek, G.E. and Gettys, T.W. 2002. Adaptive changes in adipocyte gene expression differ in AKR/J and SWR/J mice during diet-induced obesity. J. Nutrition 132: 3325-3332.
• Gettys, T.W., Watson, P.M., Sabol, M.A., Hall, E., and Frampton, I.C. 2005. Induction of UCP1 by beta3-AR and PPARgamma agonists predicts the capacity for transdifferentiation in WAT during dietary obesity. (Submitted).
• Gettys, T.W. 2001. Mice serve as research models to study mechanisms of obesity. NRI Research Highlights 2001 No. 6.
• Leonard, N.R., Gettys, T.W., Dunn, A.J. 2003. Activation of beta2 and beta3-adrenoceptors increases brain tryptophan. J. Pharmacol. Exp. Therap. 305: 653-659.
• Gettys, T.W. 2004. Leptin. In Encyclopedia of Biological Chemistry. Ed., John H. Exton, Elsevier Press, Oxford, UK.
• Ott, V., Fasshauer, M., Meier, B., Dalski, A., Kraus, D., Gettys, T.W., Perwitz, N., and Klein, J. 2004. Ciliary neurotrophic factor influences endocrine adipocyte function: inhibition of leptin via PI-3 kinase. Mol. Cell. Endocrinol. 224: 21-27.

Progress 10/01/01 to 09/30/02

Outputs
We have shown that leptin is an important component of a feedback system between adipose tissue and the brain which functions to match rates of energy utilization with rates of energy intake. Leptin produces this response by regulating the process of adaptive thermogenesis in brown and white adipose tissue. This is accomplished by activating hypothalamic leptin receptors and increasing sympathetic stimulation of both tissues. We have shown that leptin functions less effectively in obesity-prone mice when they consume high fat diets and we have identified two mechanisms of compromised function. First, the ability of leptin to reach and activate leptin-responsive neurons in the hypothalamus is diminished. Second, the ability of adipose tissue to respond to sympathetic stimulation is altered such that the adaptive thermogenic response is compromised. These studies are directly relevant to humans in that leptin resistance is a hallmark of essentially all forms of human obesity. And although humans do not possess discrete brown adipose tissue depots like rodents, the responses of white adipose tissue to sympathetic stimulation are essential to the adaptive thermogenic response and preventing excess fat accumulation. Thus, the detailed knowledge gained through our mouse studies will improve our understanding of how leptin functions in humans and guide the development of effective treatments and interventional strategies.

Impacts
Obesity resulting from consumption of calorie-rich high-fat diets affects in excess of 100 million Americans. The development of leptin resistance is thought to be an underlying cause of diet-induced obesity, but the molecular basis of leptin resistance is poorly understood. A more complete understanding of leptin resistance will guide the development of of preventative and rehabilitative treatment paradigms, and assist in the identification of molecular targets for drug development. Work supported by this project has advanced our understanding of the mechanisms and developmental sequence of leptin resistance.

Publications

• Commins, S., Watson, P.M., Padgett, M., and Gettys, T.W. 1999. Induction of uncoupling protein expression in brown and white adipose tissue by leptin. Endocrinology 140: 292-300.
• Commins, S. P., Thomas, S. A., Watson, P. M., Padgett, M. A., Palmiter, R., and Gettys, T. W. 1999. Norepinephrine is required for leptin effects on gene expression in brown and white adipose tissue. Endocrinology 140: 4772-4778.
• Watson, P.M., Commins, S.P., Beiler, R.J., Hatcher, H.C., and Gettys, T.W. 2000. Differential regulation of leptin expression and function in A/J vs C57BL/6J mice during diet-induced obesity. Am. J. Physiol. 279: E356-E365.
• Commins, S.P., Watson, P.M., Beiler, R.J., Levin, N., and Gettys, T.W. 2000. The Beta3-adrenoceptor is necessary for centrally-mediated effects of leptin on gene expression in white but not brown adipose tissue. J. Biol. Chem. 275: 33059-33067.
• Commins, S.P., Watson, P.M. and Gettys, T.W. 2001. UCP1 is required for leptin-dependent decreases in epididymal, inguinal and retroperitoneal WAT in mice. Am. J. Physiol. 280: E372-E377.
• Demas, G.E., Bowers, R.R., Bartness, T.J., and Gettys, T.W. 2002. Photoperiodic Regulation of Gene Expression in Brown and White Adipose Tissue of Siberian Hamsters (Phodopus sungorus) American Journal of Physiology 282: R114-R121.
• Finkenbine, S.S., Gettys, T.W., and Burnett, K.G. 2002. Beta- adrenergic receptors on leukocytes of the channel catfish, lctularus punctatus. Comp. Biochem. Physiol. 131: 27-37.
• Prpic, V., Watson, P.M., Frampton, I.C., Sabol, M.A., Jezek, G.E. and Gettys, T.W. 2003. Differential mechanisms and development of leptin resistance in A/J vs C57BL/6J mice during diet-induced obesity. Endocrinology (in press).
• Prpic, V., Watson, P.M., Frampton, I.C., Sabol, M.A., Jezek, G.E. and Gettys, T.W. 2002. Adaptive changes in adipocyte gene expression differ in AKR/J and SWR/J mice during diet-induced obesity. J. Nutrition 132: 3325-3332.
• Gettys, T.W. 2001. Mice serve as research models to study mechanisms of obesity. NRI Research Highlights 2001 No. 6.