Showing papers by "University of Texas Southwestern Medical Center published in 2003"

Prospective identification of tumorigenic breast cancer cells

Abstract: Breast cancer is the most common malignancy in United States women, accounting for >40,000 deaths each year. These breast tumors are comprised of phenotypically diverse populations of breast cancer cells. Using a model in which human breast cancer cells were grown in immunocompromised mice, we found that only a minority of breast cancer cells had the ability to form new tumors. We were able to distinguish the tumorigenic (tumor initiating) from the nontumorigenic cancer cells based on cell surface marker expression. We prospectively identified and isolated the tumorigenic cells as CD44+CD24−/lowLineage− in eight of nine patients. As few as 100 cells with this phenotype were able to form tumors in mice, whereas tens of thousands of cells with alternate phenotypes failed to form tumors. The tumorigenic subpopulation could be serially passaged: each time cells within this population generated new tumors containing additional CD44+CD24−/lowLineage− tumorigenic cells as well as the phenotypically diverse mixed populations of nontumorigenic cells present in the initial tumor. The ability to prospectively identify tumorigenic cancer cells will facilitate the elucidation of pathways that regulate their growth and survival. Furthermore, because these cells drive tumor development, strategies designed to target this population may lead to more effective therapies.

Applications of magnetic nanoparticles in biomedicine

Abstract: The physical principles underlying some current biomedical applications of magnetic nanoparticles are reviewed. Starting from well-known basic concepts, and drawing on examples from biology and biomedicine, the relevant physics of magnetic materials and their responses to applied magnetic fields are surveyed. The way these properties are controlled and used is illustrated with reference to (i) magnetic separation of labelled cells and other biological entities; (ii) therapeutic drug, gene and radionuclide delivery; (iii) radio frequency methods for the catabolism of tumours via hyperthermia; and (iv) contrast enhancement agents for magnetic resonance imaging applications. Future prospects are also discussed.

From vulnerable plaque to vulnerable patient: a call for new definitions and risk assessment strategies: Part II.

Abstract: Atherosclerotic cardiovascular disease results in >19 million deaths annually, and coronary heart disease accounts for the majority of this toll. Despite major advances in treatment of coronary heart disease patients, a large number of victims of the disease who are apparently healthy die suddenly without prior symptoms. Available screening and diagnostic methods are insufficient to identify the victims before the event occurs. The recognition of the role of the vulnerable plaque has opened new avenues of opportunity in the field of cardiovascular medicine. This consensus document concludes the following. (1) Rupture-prone plaques are not the only vulnerable plaques. All types of atherosclerotic plaques with high likelihood of thrombotic complications and rapid progression should be considered as vulnerable plaques. We propose a classification for clinical as well as pathological evaluation of vulnerable plaques. (2) Vulnerable plaques are not the only culprit factors for the development of acute coronary syndromes, myocardial infarction, and sudden cardiac death. Vulnerable blood (prone to thrombosis) and vulnerable myocardium (prone to fatal arrhythmia) play an important role in the outcome. Therefore, the term "vulnerable patient" may be more appropriate and is proposed now for the identification of subjects with high likelihood of developing cardiac events in the near future. (3) A quantitative method for cumulative risk assessment of vulnerable patients needs to be developed that may include variables based on plaque, blood, and myocardial vulnerability. In Part I of this consensus document, we cover the new definition of vulnerable plaque and its relationship with vulnerable patients. Part II of this consensus document focuses on vulnerable blood and vulnerable myocardium and provide an outline of overall risk assessment of vulnerable patients. Parts I and II are meant to provide a general consensus and overviews the new field of vulnerable patient. Recently developed assays (eg, C-reactive protein), imaging techniques (eg, CT and MRI), noninvasive electrophysiological tests (for vulnerable myocardium), and emerging catheters (to localize and characterize vulnerable plaque) in combination with future genomic and proteomic techniques will guide us in the search for vulnerable patients. It will also lead to the development and deployment of new therapies and ultimately to reduce the incidence of acute coronary syndromes and sudden cardiac death. We encourage healthcare policy makers to promote translational research for screening and treatment of vulnerable patients.

Bmi-1 is required for maintenance of adult self-renewing haematopoietic stem cells.

Abstract: A central issue in stem cell biology is to understand the mechanisms that regulate the self-renewal of haematopoietic stem cells (HSCs), which are required for haematopoiesis to persist for the lifetime of the animal1. We found that adult and fetal mouse and adult human HSCs express the proto-oncogene Bmi-1. The number of HSCs in the fetal liver of Bmi-1-/- mice2 was normal. In postnatal Bmi-1-/- mice, the number of HSCs was markedly reduced. Transplanted fetal liver and bone marrow cells obtained from Bmi-1-/- mice were able to contribute only transiently to haematopoiesis. There was no detectable self-renewal of adult HSCs, indicating a cell autonomous defect in Bmi-1-/- mice. A gene expression analysis revealed that the expression of stem cell associated genes3, cell survival genes, transcription factors, and genes modulating proliferation including p16Ink4a and p19Arf was altered in bone marrow cells of the Bmi-1-/- mice. Expression of p16Ink4a and p19Arf in normal HSCs resulted in proliferative arrest and p53-dependent cell death, respectively. Our results indicate that Bmi-1 is essential for the generation of self-renewing adult HSCs.

Interferon and Granulopoiesis Signatures in Systemic Lupus Erythematosus Blood

Abstract: Systemic lupus erythematosus (SLE) is a prototype systemic autoimmune disease characterized by flares of high morbidity. Using oligonucleotide microarrays, we now show that active SLE can be distinguished by a remarkably homogeneous gene expression pattern with overexpression of granulopoiesis-related and interferon (IFN)-induced genes. Using the most stringent statistical analysis (Bonferroni correction), 15 genes were found highly up-regulated in SLE patients, 14 of which are targets of IFN and one, defensin DEFA-3, a major product of immature granulocytes. A more liberal correction (Benjamini and Hochberg correction) yielded 18 additional genes, 12 of which are IFN-regulated and 4 granulocyte-specific. Indeed immature neutrophils were identified in a large fraction of SLE patients white blood cells. High dose glucocorticoids, a standard treatment of disease flares, shuts down the interferon signature, further supporting the role of this cytokine in SLE. The expression of 10 genes correlated with disease activity according to the SLEDAI. The most striking correlation (P < 0.001, r = 0.55) was found with the formyl peptide receptor-like 1 protein that mediates chemotactic activities of defensins. Therefore, while the IFN signature confirms the central role of this cytokine in SLE, microarray analysis of blood cells reveals that immature granulocytes may be involved in SLE pathogenesis.

Cardiac progenitor cells from adult myocardium: Homing, differentiation, and fusion after infarction

Abstract: Potential repair by cell grafting or mobilizing endogenous cells holds particular attraction in heart disease, where the meager capacity for cardiomyocyte proliferation likely contributes to the irreversibility of heart failure. Whether cardiac progenitors exist in adult myocardium itself is unanswered, as is the question whether undifferentiated cardiac precursor cells merely fuse with preexisting myocytes. Here we report the existence of adult heart-derived cardiac progenitor cells expressing stem cell antigen-1. Initially, the cells express neither cardiac structural genes nor Nkx2.5 but differentiate in vitro in response to 5′-azacytidine, in part depending on Bmpr1a, a receptor for bone morphogenetic proteins. Given intravenously after ischemia/reperfusion, cardiac stem cell antigen 1 cells home to injured myocardium. By using a Cre/Lox donor/recipient pair (αMHC-Cre/R26R), differentiation was shown to occur roughly equally, with and without fusion to host cells.

The long-term effect of doxazosin, finasteride, and combination therapy on the clinical progression of benign prostatic hyperplasia.

Abstract: background Benign prostatic hyperplasia is commonly treated with alpha-adrenergic–receptor antagonists (alpha-blockers) or 5 a -reductase inhibitors. The long-term effect of these drugs, singly or combined, on the risk of clinical progression is unknown. methods We conducted a long-term, double-blind trial (mean follow-up, 4.5 years) involving 3047 men to compare the effects of placebo, doxazosin, finasteride, and combination therapy on measures of the clinical progression of benign prostatic hyperplasia. results The risk of overall clinical progression — defined as an increase above base line of at least 4 points in the American Urological Association symptom score, acute urinary retention, urinary incontinence, renal insufficiency, or recurrent urinary tract infection — was significantly reduced by doxazosin (39 percent risk reduction, P<0.001) and finasteride (34 percent risk reduction, P=0.002), as compared with placebo. The reduction in risk associated with combination therapy (66 percent for the comparison with placebo, P<0.001) was significantly greater than that associated with doxazosin (P<0.001) or finasteride (P<0.001) alone. The risks of acute urinary retention and the need for invasive therapy were significantly reduced by combination therapy (P<0.001) and finasteride (P<0.001) but not by doxazosin. Doxazosin (P<0.001), finasteride (P =0.001), and combination therapy (P<0.001) each resulted in significant improvement in symptom scores, with combination therapy being superior to both doxazosin (P=0.006) and finasteride (P<0.001) alone. conclusions Long-term combination therapy with doxazosin and finasteride was safe and reduced the risk of overall clinical progression of benign prostatic hyperplasia significantly more than did treatment with either drug alone. Combination therapy and finasteride alone reduced the long-term risk of acute urinary retention and the need for invasive therapy.

The Enzymes, Regulation, and Genetics of Bile Acid Synthesis

Abstract: ▪ Abstract The synthesis and excretion of bile acids comprise the major pathway of cholesterol catabolism in mammals. Synthesis provides a direct means of converting cholesterol, which is both hydrophobic and insoluble, into a water-soluble and readily excreted molecule, the bile acid. The biosynthetic steps that accomplish this transformation also confer detergent properties to the bile acid, which are exploited by the body to facilitate the secretion of cholesterol from the liver. This role in the elimination of cholesterol is counterbalanced by the ability of bile acids to solubilize dietary cholesterol and essential nutrients and to promote their delivery to the liver. The synthesis of a full complement of bile acids requires 17 enzymes. The expression of selected enzymes in the pathway is tightly regulated by nuclear hormone receptors and other transcription factors, which ensure a constant supply of bile acids in an ever changing metabolic environment. Inherited mutations that impair bile acid synth...

Cardiac Hypertrophy: The Good, the Bad, and the Ugly

Abstract: Cardiac hypertrophy is the heart's response to a variety of extrinsic and intrinsic stimuli that impose increased biomechanical stress. While hypertrophy can eventually normalize wall tension, it is associated with an unfavorable outcome and threatens affected patients with sudden death or progression to overt heart failure. Accumulating evidence from studies in human patients and animal models suggests that in most instances hypertrophy is not a compensatory response to the change in mechanical load, but rather is a maladaptive process. Accordingly, modulation of myocardial growth without adversely affecting contractile function is increasingly recognized as a potentially auspicious approach in the prevention and treatment of heart failure. In this review, we summarize recent insights into hypertrophic signaling and consider several novel antihypertrophic strategies.

The Metabolic Syndrome

Abstract: The National Cholesterol Education Program’s Adult Treatment Panel III (ATP III) report [1] added the metabolic syndrome, a multidimensional risk factor for cardiovascular disease (CVD), as a coequal partner of elevated low-density lipoprotein (LDL) cholesterol for risk-reduction therapies. Interest in the metabolic syndrome has increased greatly since the publication of the ATP III report. There are several aspects to the metabolic syndrome that deserve consideration for clinical practice: 1) major clinical outcomes, 2) metabolic components, 3) pathogenesis, 4) clinical criteria for diagnosis, 5) risk for clinical outcomes, and 6) therapeutic interventions.

Bmi-1 dependence distinguishes neural stem cell self-renewal from progenitor proliferation

Abstract: Stem cells persist throughout life by self-renewing in numerous tissues including the central and peripheral nervous systems. This raises the issue of whether there is a conserved mechanism to effect self-renewing divisions. Deficiency in the polycomb family transcriptional repressor Bmi-1 leads to progressive postnatal growth retardation and neurological defects. Here we show that Bmi-1 is required for the self-renewal of stem cells in the peripheral and central nervous systems but not for their survival or differentiation. The reduced self-renewal of Bmi-1-deficient neural stem cells leads to their postnatal depletion. In the absence of Bmi-1, the cyclin-dependent kinase inhibitor gene p16Ink4a is upregulated in neural stem cells, reducing the rate of proliferation. p16Ink4a deficiency partially reverses the self-renewal defect in Bmi-1-/- neural stem cells. This conserved requirement for Bmi-1 to promote self-renewal and to repress p16Ink4a expression suggests that a common mechanism regulates the self-renewal and postnatal persistence of diverse types of stem cell. Restricted neural progenitors from the gut and forebrain proliferate normally in the absence of Bmi-1. Thus, Bmi-1 dependence distinguishes stem cell self-renewal from restricted progenitor proliferation in these tissues.

Combined analysis of oligonucleotide microarray data from transgenic and knockout mice identifies direct SREBP target genes

Abstract: The synthesis of fatty acids and cholesterol, the building blocks of membranes, is regulated by three membrane-bound transcription factors: sterol regulatory element-binding proteins (SREBP)-1a, -1c, and -2. Their function in liver has been characterized in transgenic mice that overexpress each SREBP isoform and in mice that lack all three nuclear SREBPs as a result of gene knockout of SREBP cleavage-activating protein (SCAP), a protein required for nuclear localization of SREBPs. Here, we use oligonucleotide arrays hybridized with RNA from livers of three lines of mice (transgenic for SREBP-1a, transgenic for SREBP-2, and knockout for SCAP) to identify genes that are likely to be direct targets of SREBPs in liver. A total of 1,003 genes showed statistically significant increased expression in livers of transgenic SREBP-1a mice, 505 increased in livers of transgenic SREBP-2 mice, and 343 showed decreased expression in Scap–/– livers. A subset of 33 genes met the stringent combinatorial criteria of induction in both SREBP transgenics and decreased expression in SCAP-deficient mice. Of these 33 genes, 13 were previously identified as direct targets of SREBP action. Of the remaining 20 genes, 13 encode enzymes or carrier proteins involved in cholesterol metabolism, 3 participate in fatty acid metabolism, and 4 have no known connection to lipid metabolism. Through application of stringent combinatorial criteria, the transgenic/knockout approach allows identification of genes whose activities are likely to be controlled directly by one family of transcription factors, in this case the SREBPs.

Prevention of recurrent preterm delivery by 17 alpha-hydroxyprogesterone caproate.

Abstract: Background Women who have had a spontaneous preterm delivery are at greatly increased risk for preterm delivery in subsequent pregnancies. The results of several small trials have suggested that 17 alpha-hydroxyprogesterone caproate (17P) may reduce the risk of preterm delivery. Methods We conducted a double-blind, placebo-controlled trial involving pregnant women with a documented history of spontaneous preterm delivery. Women were enrolled at 19 clinical centers at 16 to 20 weeks of gestation and randomly assigned by a central data center, in a 2:1 ratio, to receive either weekly injections of 250 mg of 17P or weekly injections of an inert oil placebo; injections were continued until delivery or to 36 weeks of gestation. The primary outcome was preterm delivery before 37 weeks of gestation. Analysis was performed according to the intention-to-treat principle. Results Base-line characteristics of the 310 women in the progesterone group and the 153 women in the placebo group were similar. Treatment with 1...

Cytochrome C-Mediated Apoptosis

Abstract: Apoptosis, or programmed cell death, is involved in development, elimination of damaged cells, and maintenance of cell homeostasis. Deregulation of apoptosis may cause diseases, such as cancers, immune diseases, and neurodegenerative disorders. Apoptosis is executed by a subfamily of cysteine proteases known as caspases. In mammalian cells, a major caspase activation pathway is the cytochrome c-initiated pathway. In this pathway, a variety of apoptotic stimuli cause cytochrome c release from mitochondria, which in turn induces a series of biochemical reactions that result in caspase activation and subsequent cell death. In this review, we focus on the recent progress in understanding the biochemical mechanisms and regulation of the pathway, the roles of the pathway in physiology and disease, and their potential therapeutic values.

DNA damage and repair

Abstract: The aesthetic appeal of the DNA double helix initially hindered notions of DNA mutation and repair, which would necessarily interfere with its pristine state. But it has since been recognized that DNA is subject to continuous damage and the cell has an arsenal of ways of responding to such injury. Although mutations or deficiencies in repair can have catastrophic consequences, causing a range of human diseases, mutations are nonetheless fundamental to life and evolution.

GATA4 mutations cause human congenital heart defects and reveal an interaction with TBX5

Abstract: Congenital heart defects (CHDs) are the most common developmental anomaly and are the leading non-infectious cause of mortality in newborns. Only one causative gene, NKX2-5, has been identified through genetic linkage analysis of pedigrees with non-syndromic CHDs. Here, we show that isolated cardiac septal defects in a large pedigree were linked to chromosome 8p22-23. A heterozygous G296S missense mutation of GATA4, a transcription factor essential for heart formation, was found in all available affected family members but not in any control individuals. This mutation resulted in diminished DNA-binding affinity and transcriptional activity of Gata4. Furthermore, the Gata4 mutation abrogated a physical interaction between Gata4 and TBX5, a T-box protein responsible for a subset of syndromic cardiac septal defects. Conversely, interaction of Gata4 and TBX5 was disrupted by specific human TBX5 missense mutations that cause similar cardiac septal defects. In a second family, we identified a frame-shift mutation of GATA4 (E359del) that was transcriptionally inactive and segregated with cardiac septal defects. These results implicate GATA4 as a genetic cause of human cardiac septal defects, perhaps through its interaction with TBX5.

Adult chronic rhinosinusitis: Definitions, diagnosis, epidemiology, and pathophysiology

Abstract: Chronic rhinosinusitis Chronic rhinosinusitis (CRS) is a term that has been used to describe a number of entities characterized by chronic symptoms of nasal and sinus inflammation or infection. There has been a lack of consensus regarding definitions and treatments because CRS may be a spectrum of diseases with a range of appropriate treatments. The absence of widely accepted definitions for CRS has resulted in a paucity of research directed at understanding its pathophysiology and has hampered efforts to improve treatment. A Task Force was convened by the Sinus and Allergy Health Partnership to summarize much of the current and important information available regarding the prevalence, economic impact, pathophysiology, common inflammatory mediators, and the role of infectious microbes such as bacteria and fungi in CRS. The goal is to establish a standard and usable definition. Through this thorough review of the literature and the expert input from Task Force members, a definition was developed that serves to create a consistent baseline so that many of the currently debated or unanswered questions may be addressed. The new and more-specific Task Force definition is that “ Chronic rhinosinusitis is a group of disorders characterized by inflammation of the mucosa of the nose and paranasal sinuses of at least 12 weeks duration.” Recommended criteria for making the diagnosis of CRS for both clinical care and research were also outlined.

Efficacy and Safety of Plant Stanols and Sterols in the Management of Blood Cholesterol Levels

Abstract: Foods with plant stanol or sterol esters lower serum cholesterol levels. We summarize the deliberations of 32 experts on the efficacy and safety of sterols and stanols. A meta-analysis of 41 trials showed that intake of 2 g/d of stanols or sterols reduced low-density lipoprotein (LDL) by 10%; higher intakes added little. Efficacy is similar for sterols and stanols, but the food form may substantially affect LDL reduction. Effects are additive with diet or drug interventions: eating foods low in saturated fat and cholesterol and high in stanols or sterols can reduce LDL by 20%; adding sterols or stanols to statin medication is more effective than doubling the statin dose. A meta-analysis of 10 to 15 trials per vitamin showed that plasma levels of vitamins A and D are not affected by stanols or sterols. Alpha carotene, lycopene, and vitamin E levels remained stable relative to their carrier molecule, LDL. Beta carotene levels declined, but adverse health outcomes were not expected. Sterol-enriched foods increased plasma sterol levels, and workshop participants discussed whether this would increase risk, in view of the marked increase of atherosclerosis in patients with homozygous phytosterolemia. This risk is believed to be largely hypothetical, and any increase due to the small increase in plasma plant sterols may be more than offset by the decrease in plasma LDL. There are insufficient data to suggest that plant stanols or sterols either prevent or promote colon carcinogenesis. Safety of sterols and stanols is being monitored by follow-up of samples from the general population; however, the power of such studies to pick up infrequent increases in common diseases, if any exist, is limited. A trial with clinical outcomes probably would not answer remaining questions about infrequent adverse effects. Trials with surrogate end points such as intima-media thickness might corroborate the expected efficacy in reducing atherosclerosis. However, present evidence is sufficient to promote use of sterols and stanols for lowering LDL cholesterol levels in persons at increased risk for coronary heart disease.

Rheb is a direct target of the tuberous sclerosis tumour suppressor proteins.

Abstract: Mutations in the TSC1 or TSC2 genes cause tuberous sclerosis, a benign tumour syndrome in humans1,2. Tsc2 possesses a domain that shares homology with the GTPase-activating protein (GAP) domain of Rap1-GAP2, suggesting that a GTPase might be the physiological target of Tsc2. Here we show that the small GTPase Rheb (Ras homologue enriched in brain) is a direct target of Tsc2 GAP activity both in vivo and in vitro. Point mutations in the GAP domain of Tsc2 disrupted its ability to regulate Rheb without affecting the ability of Tsc2 to form a complex with Tsc1. Our studies identify Rheb as a molecular target of the TSC tumour suppressors.

Bacteria–host communication: The language of hormones

Abstract: The interbacterial communication system known as quorum sensing (QS) utilizes hormone-like compounds referred to as autoinducers to regulate bacterial gene expression. Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 is the agent responsible for outbreaks of bloody diarrhea in several countries. We previously proposed that EHEC uses a QS regulatory system to “sense” that it is within the intestine and activate genes essential for intestinal colonization. The QS system used by EHEC is the LuxS/autoinducer 2 (AI-2) system extensively involved in interspecies communication. The autoinducer AI-2 is a furanosyl borate diester whose synthesis depends on the enzyme LuxS. Here we show that an EHEC luxS mutant, unable to produce the bacterial autoinducer, still responds to a eukaryotic cell signal to activate expression of its virulence genes. We have identified this signal as the hormone epinephrine and show that β- and α-adrenergic antagonists can block the bacterial response to this hormone. Furthermore, using purified and in vitro synthesized AI-2 we showed that AI-2 is not the autoinducer involved in the bacterial signaling. EHEC produces another, previously undescribed autoinducer (AI-3) whose synthesis depends on the presence of LuxS. These results imply a potential cross-communication between the luxS/AI-3 bacterial QS system and the epinephrine host signaling system. Given that eukaryotic cell-to-cell signaling typically occurs through hormones, and that bacterial cell-to-cell signaling occurs through QS, we speculate that QS might be a “language” by which bacteria and host cells communicate.

Regulation of Interferon Regulatory Factor-3 by the Hepatitis C Virus Serine Protease

Abstract: Persistent infections with hepatitis C virus (HCV) are likely to depend on viral inhibition of host defenses. We show that the HCV NS3/4A serine protease blocks the phosphorylation and effector action of interferon regulatory factor-3 (IRF-3), a key cellular antiviral signaling molecule. Disruption of NS3/4A protease function by mutation or a ketoamide peptidomimetic inhibitor relieved this blockade and restored IRF-3 phosphorylation after cellular challenge with an unrelated virus. Furthermore, dominant-negative or constitutively active IRF-3 mutants, respectively, enhanced or suppressed HCV RNA replication in hepatoma cells. Thus, the NS3/4A protease represents a dual therapeutic target, the inhibition of which may both block viral replication and restore IRF-3 control of HCV infection.

Suppression of Ovarian Follicle Activation in Mice by the Transcription Factor Foxo3a

Abstract: Foxo transcription factors have been implicated in diverse biological processes, including metabolism, cellular stress responses, and aging Here, we show that Foxo3a-/- female mice exhibit a distinctive ovarian phenotype of global follicular activation leading to oocyte death, early depletion of functional ovarian follicles, and secondary infertility Foxo3a thus functions at the earliest stages of follicular growth as a suppressor of follicular activation In addition to providing a molecular entry point for studying the regulation of follicular growth, these results raise the possibility that accelerated follicular initiation plays a role in premature ovarian failure, a common cause of infertility and premature aging in women

Activation of peroxisome proliferator-activated receptor δ induces fatty acid β-oxidation in skeletal muscle and attenuates metabolic syndrome

Abstract: In this study, we defined the role of peroxisome proliferator-activated receptor beta/delta (PPARdelta) in metabolic homeostasis by using subtype selective agonists. Analysis of rat L6 myotubes treated with the PPARdelta subtype-selective agonist, GW501516, by the Affymetrix oligonucleotide microarrays revealed that PPARdelta controls fatty acid oxidation by regulating genes involved in fatty acid transport, beta-oxidation, and mitochondrial respiration. Similar PPARdelta-mediated gene activation was observed in the skeletal muscle of GW501516-treated mice. Accordingly, GW501516 treatment induced fatty acid beta-oxidation in L6 myotubes as well as in mouse skeletal muscles. Administration of GW501516 to mice fed a high-fat diet ameliorated diet-induced obesity and insulin resistance, an effect accompanied by enhanced metabolic rate and fatty acid beta-oxidation, proliferation of mitochondria, and a marked reduction of lipid droplets in skeletal muscles. Despite a modest body weight change relative to vehicle-treated mice, GW501516 treatment also markedly improved diabetes as revealed by the decrease in plasma glucose and blood insulin levels in genetically obese ob/ob mice. These data suggest that PPARdelta is pivotal to control the program for fatty acid oxidation in the skeletal muscle, thereby ameliorating obesity and insulin resistance through its activation in obese animals.