PMCC PMCC

Search tips
Search criteria

Advanced
Results 1-13 (13)
 

Clipboard (0)
None

Select a Filter Below

Journals
Year of Publication
2.  Adipose-Specific Deletion of TFAM Increases Mitochondrial Oxidation and Protects Mice against Obesity and Insulin Resistance 
Cell metabolism  2012;16(6):765-776.
Obesity and type 2 diabetes are associated with mitochondrial dysfunction in adipose tissue, but the role for adipose tissues mitochondria in the development of these disorders is currently unknown. To understand the impact of adipose tissue mitochondria on whole body metabolism, we have generated a mouse model with disruption of the mitochondrial transcription factor A (TFAM) specifically in fat. F-TFKO adipose tissue exhibit decreased mtDNA copy number, altered levels of proteins of the electron transport chain, and perturbed mitochondrial function with decreased Complex I activity and greater oxygen consumption and uncoupling. As a result, F-TFKO mice exhibit higher energy expenditure and are protected from age- and diet-induced obesity, insulin resistance and hepatosteatosis, despite a greater food intake. Thus, TFAM deletion in the adipose tissue increases mitochondrial oxidation that has positive metabolic effects suggesting that regulation of adipose tissue mitochondria may be a potential therapeutic target for the treatment of obesity.
doi:10.1016/j.cmet.2012.10.016
PMCID: PMC3529641  PMID: 23168219
Obesity; Brown adipose tissue; Mitochondrial function; mitochondrial bioenergetics; White adipose tissue; Insulin resistance; Diabetes
3.  Skeletal muscle Nur77 expression enhances oxidative metabolism and substrate utilization[S] 
Journal of Lipid Research  2012;53(12):2610-2619.
Mitochondrial dysfunction has been implicated in the pathogenesis of type 2 diabetes. Identifying novel regulators of mitochondrial bioenergetics will broaden our understanding of regulatory checkpoints that coordinate complex metabolic pathways. We previously showed that Nur77, an orphan nuclear receptor of the NR4A family, regulates the expression of genes linked to glucose utilization. Here we demonstrate that expression of Nur77 in skeletal muscle also enhances mitochondrial function. We generated MCK-Nur77 transgenic mice that express wild-type Nur77 specifically in skeletal muscle. Nur77-overexpressing muscle had increased abundance of oxidative muscle fibers and mitochondrial DNA content. Transgenic muscle also exhibited enhanced oxidative metabolism, suggestive of increased mitochondrial activity. Metabolomic analysis confirmed that Nur77 transgenic muscle favored fatty acid oxidation over glucose oxidation, mimicking the metabolic profile of fasting. Nur77 expression also improved the intrinsic respiratory capacity of isolated mitochondria, likely due to the increased abundance of complex I of the electron transport chain. These changes in mitochondrial metabolism translated to improved muscle contractile function ex vivo and improved cold tolerance in vivo. Our studies outline a novel role for Nur77 in the regulation of oxidative metabolism and mitochondrial activity in skeletal muscle.
doi:10.1194/jlr.M029355
PMCID: PMC3494265  PMID: 23028113
Nr4a; nuclear receptor; mitochondria
4.  Muscle-specific Deletion of Carnitine Acetyltransferase Compromises Glucose Tolerance and Metabolic Flexibility 
Cell Metabolism  2012;15(5):764-777.
Summary
The concept of “metabolic inflexibility” was first introduced to describe the failure of insulin resistant human subjects to appropriately adjust mitochondrial fuel selection in response to nutritional cues. This phenomenon has since gained increasing recognition as a core component of the metabolic syndrome, but the underlying mechanisms have remained elusive. Here, we identify an essential role for the mitochondrial matrix enzyme, carnitine acetyltransferase (CrAT), in regulating substrate switching and glucose tolerance. By converting acetyl-CoA to its membrane permeant acetylcarnitine ester, CrAT regulates mitochondrial and intracellular carbon trafficking. Studies in muscle-specific Crat knockout mice, primary human skeletal myocytes and human subjects undergoing L-carnitine supplementation support a model wherein CrAT combats nutrient stress, promotes metabolic flexibility and enhances insulin action by permitting mitochondrial efflux of excess acetyl moieties that otherwise inhibit key regulatory enzymes such as pyruvate dehydrogenase. These findings offer therapeutically relevant insights into the molecular basis of metabolic inflexibility.
doi:10.1016/j.cmet.2012.04.005
PMCID: PMC3348515  PMID: 22560225
5.  Metabolomic Profiling Reveals Mitochondrial-Derived Lipid Biomarkers That Drive Obesity-Associated Inflammation 
PLoS ONE  2012;7(6):e38812.
Obesity has reached epidemic proportions worldwide. Several animal models of obesity exist, but studies are lacking that compare traditional lard-based high fat diets (HFD) to “Cafeteria diets" (CAF) consisting of nutrient poor human junk food. Our previous work demonstrated the rapid and severe obesogenic and inflammatory consequences of CAF compared to HFD including rapid weight gain, markers of Metabolic Syndrome, multi-tissue lipid accumulation, and dramatic inflammation. To identify potential mediators of CAF-induced obesity and Metabolic Syndrome, we used metabolomic analysis to profile serum, muscle, and white adipose from rats fed CAF, HFD, or standard control diets. Principle component analysis identified elevations in clusters of fatty acids and acylcarnitines. These increases in metabolites were associated with systemic mitochondrial dysfunction that paralleled weight gain, physiologic measures of Metabolic Syndrome, and tissue inflammation in CAF-fed rats. Spearman pairwise correlations between metabolites, physiologic, and histologic findings revealed strong correlations between elevated markers of inflammation in CAF-fed animals, measured as crown like structures in adipose, and specifically the pro-inflammatory saturated fatty acids and oxidation intermediates laurate and lauroyl carnitine. Treatment of bone marrow-derived macrophages with lauroyl carnitine polarized macrophages towards the M1 pro-inflammatory phenotype through downregulation of AMPK and secretion of pro-inflammatory cytokines. Results presented herein demonstrate that compared to a traditional HFD model, the CAF diet provides a robust model for diet-induced human obesity, which models Metabolic Syndrome-related mitochondrial dysfunction in serum, muscle, and adipose, along with pro-inflammatory metabolite alterations. These data also suggest that modifying the availability or metabolism of saturated fatty acids may limit the inflammation associated with obesity leading to Metabolic Syndrome.
doi:10.1371/journal.pone.0038812
PMCID: PMC3373493  PMID: 22701716
6.  The Coactivator SRC-1 is an Essential Coordinator of Hepatic Glucose Production 
Cell metabolism  2010;12(6):606-618.
Gluconeogenesis makes a major contribution to hepatic glucose production, a process critical for survival in mammals. In this study, we identify the p160 family member, SRC-1, as a key coordinator of the hepatic gluconeogenic program in vivo. SRC-1 null mice displayed hypoglycemia secondary to a deficit in hepatic glucose production. Selective re-expression of SRC-1 in the liver restored blood glucose levels to a normal range. SRC-1 was found induced upon fasting to coordinate in a cell-autonomous manner, the gene expression of rate-limiting enzymes of the gluconeogenic pathway. At the molecular level, the main role of SRC-1 was to modulate the expression and the activity of C/EBPα through a feed-forward loop in which SRC-1 used C/EBPα to transactivate pyruvate carboxylase, a crucial gene for initiation of the gluconeogenic program. We propose that SRC-1, acts as a novel and critical mediator of glucose homeostasis in the liver by adjusting the transcriptional activity of key genes involved in the hepatic glucose production machinery.
doi:10.1016/j.cmet.2010.11.009
PMCID: PMC3024581  PMID: 21109193
7.  Regulation of mitochondrial morphology by APC/CCdh1-mediated control of Drp1 stability 
Molecular Biology of the Cell  2011;22(8):1207-1216.
Mitochondria form an interconnected network that undergoes dynamin-related protein 1 (Drp1)-dependent fission during mitosis. We demonstrate that changes in mitochondrial dynamics as cells exit mitosis are driven through ubiquitylation of Drp1 by the (anaphase- promoting complex/cyclosome and its coactivator Cdh1) APC/CCdh1 complex. Inhibition Drp1 degradation prevents the normal regrowth of mitochondrial networks during G1 phase.
Homeostatic maintenance of cellular mitochondria requires a dynamic balance between fission and fusion, and controlled changes in morphology are important for processes such as apoptosis and cellular division. Interphase mitochondria have been described as an interconnected network that fragments as cells enter mitosis, and this mitotic mitochondrial fragmentation is known to be regulated by the dynamin-related GTPase Drp1 (dynamin-related protein 1), a key component of the mitochondrial division machinery. Loss of Drp1 function and the subsequent failure of mitochondrial division during mitosis lead to incomplete cytokinesis and the unequal distribution of mitochondria into daughter cells. During mitotic exit and interphase, the mitochondrial network reforms. Here we demonstrate that changes in mitochondrial dynamics as cells exit mitosis are driven in part through ubiquitylation of Drp1, catalyzed by the APC/CCdh1 (anaphase-promoting complex/cyclosome and its coactivator Cdh1) E3 ubiquitin ligase complex. Importantly, inhibition of Cdh1-mediated Drp1 ubiquitylation and proteasomal degradation during interphase prevents the normal G1 phase regrowth of mitochondrial networks following cell division.
doi:10.1091/mbc.E10-07-0567
PMCID: PMC3078078  PMID: 21325626
8.  Insulin Resistance and Altered Systemic Glucose Metabolism in Mice Lacking Nur77 
Diabetes  2009;58(12):2788-2796.
OBJECTIVE
Nur77 is an orphan nuclear receptor with pleotropic functions. Previous studies have identified Nur77 as a transcriptional regulator of glucose utilization genes in skeletal muscle and gluconeogenesis in liver. However, the net functional impact of these pathways is unknown. To examine the consequence of Nur77 signaling for glucose metabolism in vivo, we challenged Nur77 null mice with high-fat feeding.
RESEARCH DESIGN AND METHODS
Wild-type and Nur77 null mice were fed a high-fat diet (60% calories from fat) for 3 months. We determined glucose tolerance, tissue-specific insulin sensitivity, oxygen consumption, muscle and liver lipid content, muscle insulin signaling, and expression of glucose and lipid metabolism genes.
RESULTS
Mice with genetic deletion of Nur77 exhibited increased susceptibility to diet-induced obesity and insulin resistance. Hyperinsulinemic-euglycemic clamp studies revealed greater high-fat diet–induced insulin resistance in both skeletal muscle and liver of Nur77 null mice compared with controls. Loss of Nur77 expression in skeletal muscle impaired insulin signaling and markedly reduced GLUT4 protein expression. Muscles lacking Nur77 also exhibited increased triglyceride content and accumulation of multiple even-chained acylcarnitine species. In the liver, Nur77 deletion led to hepatic steatosis and enhanced expression of lipogenic genes, likely reflecting the lipogenic effect of hyperinsulinemia.
CONCLUSIONS
Collectively, these data demonstrate that loss of Nur77 influences systemic glucose metabolism and highlight the physiological contribution of muscle Nur77 to this regulatory pathway.
doi:10.2337/db09-0763
PMCID: PMC2780886  PMID: 19741162
9.  SIRT3 regulates fatty acid oxidation via reversible enzyme deacetylation 
Nature  2010;464(7285):121-125.
Sirtuins are NAD+-dependent protein deacetylases and mediate adaptive responses to a variety of stresses, including calorie restriction and metabolic stress. Sirtuin 3 (SIRT3) is localized in the mitochondrial matrix where it regulates the acetylation levels of metabolic enzymes, including acetyl coenzyme A synthetase 21,2. Mice lacking both SIRT3 alleles appear phenotypically normal under basal conditions, but show marked hyperacetylation of several mitochondrial proteins3. We report that SIRT3 expression is upregulated during fasting in liver and brown adipose tissues. Livers from mice lacking SIRT3 show higher levels of fatty acid oxidation intermediate products and triglycerides during fasting associated with decreased levels of fatty acid oxidation when compared to wild-type mice. Mass spectrometry analysis of mitochondrial proteins shows that long-chain acyl CoA dehydrogenase (LCAD) is hyperacetylated at lysine 42 in the absence of SIRT3. LCAD is deacetylated in wild-type mice under fasted conditions and by SIRT3 in vitro and in vivo, and hyperacetylation of LCAD reduces its enzymatic activity. Mice lacking SIRT3 exhibit hallmarks of fatty acid oxidation disorders during fasting including reduced ATP levels and intolerance to cold exposure. These findings identify acetylation as a novel regulatory mechanism for mitochondrial fatty acid oxidation and demonstrate that SIRT3 modulates mitochondrial intermediary metabolism and fatty acid utilization during fasting.
doi:10.1038/nature08778
PMCID: PMC2841477  PMID: 20203611
11.  Chemical Knockout of Pantothenate Kinase Reveals the Metabolic and Genetic Program Responsible for Hepatic Coenzyme A Homeostasis 
Chemistry & biology  2007;14(3):291-302.
Summary
Coenzyme A (CoA) is the major acyl group carrier in intermediary metabolism. Hopantenate (HoPan), a competitive inhibitor of the pantothenate kinases, was used to chemically antagonize CoA biosynthesis. HoPan dramatically reduced liver CoA levels and the mice developed severe hypoglycemia. Insulin and corticosterone levels were reduced, glucagon levels were elevated in HoPan-treated mice and fasting accelerated the HoPan-induced hypoglycemia. Metabolic profiling revealed a large increase in carnitine, particularly acetylcarnitine, illustrating the role of carnitine in buffering acyl groups to maintain the unesterified CoASH level. HoPan treatment triggered significant changes in hepatic gene expression that substantially increased the thioesterases, which liberate CoASH from acyl-CoA, and increased pyruvate dehydrogenase kinase 1, which prevents the conversion of CoASH to acetyl-CoA. These results identify the metabolic re-arrangements that maintain the CoASH pool which is critical to mitochondrial functions, including gluconeogenesis, fatty acid oxidation, and the tricarboxylic acid and urea cycles.
doi:10.1016/j.chembiol.2007.01.013
PMCID: PMC1892532  PMID: 17379144
12.  Mig-6 Plays a Critical Role in the Regulation of Cholesterol Homeostasis and Bile Acid Synthesis 
PLoS ONE  2012;7(8):e42915.
The disruption of cholesterol homeostasis leads to an increase in cholesterol levels which results in the development of cardiovascular disease. Mitogen Inducible Gene 6 (Mig-6) is an immediate early response gene that can be induced by various mitogens, stresses, and hormones. To identify the metabolic role of Mig-6 in the liver, we conditionally ablated Mig-6 in the liver using the Albumin-Cre mouse model (Albcre/+Mig-6f/f; Mig-6d/d). Mig-6d/d mice exhibit hepatomegaly and fatty liver. Serum levels of total, LDL, and HDL cholesterol and hepatic lipid were significantly increased in the Mig-6d/d mice. The daily excretion of fecal bile acids was significantly decreased in the Mig-6d/d mice. DNA microarray analysis of mRNA isolated from the livers of these mice showed alterations in genes that regulate lipid metabolism, bile acid, and cholesterol synthesis, while the expression of genes that regulate biliary excretion of bile acid and triglyceride synthesis showed no difference in the Mig-6d/d mice compared to Mig-6f/f controls. These results indicate that Mig-6 plays an important role in cholesterol homeostasis and bile acid synthesis. Mice with liver specific conditional ablation of Mig-6 develop hepatomegaly and increased intrahepatic lipid and provide a novel model system to investigate the genetic and molecular events involved in the regulation of cholesterol homeostasis and bile acid synthesis. Defining the molecular mechanisms by which Mig-6 regulates cholesterol homeostasis will provide new insights into the development of more effective ways for the treatment and prevention of cardiovascular disease.
doi:10.1371/journal.pone.0042915
PMCID: PMC3422237  PMID: 22912762
13.  Genetic Networks of Liver Metabolism Revealed by Integration of Metabolic and Transcriptional Profiling 
PLoS Genetics  2008;4(3):e1000034.
Although numerous quantitative trait loci (QTL) influencing disease-related phenotypes have been detected through gene mapping and positional cloning, identification of the individual gene(s) and molecular pathways leading to those phenotypes is often elusive. One way to improve understanding of genetic architecture is to classify phenotypes in greater depth by including transcriptional and metabolic profiling. In the current study, we have generated and analyzed mRNA expression and metabolic profiles in liver samples obtained in an F2 intercross between the diabetes-resistant C57BL/6 leptinob/ob and the diabetes-susceptible BTBR leptinob/ob mouse strains. This cross, which segregates for genotype and physiological traits, was previously used to identify several diabetes-related QTL. Our current investigation includes microarray analysis of over 40,000 probe sets, plus quantitative mass spectrometry-based measurements of sixty-seven intermediary metabolites in three different classes (amino acids, organic acids, and acyl-carnitines). We show that liver metabolites map to distinct genetic regions, thereby indicating that tissue metabolites are heritable. We also demonstrate that genomic analysis can be integrated with liver mRNA expression and metabolite profiling data to construct causal networks for control of specific metabolic processes in liver. As a proof of principle of the practical significance of this integrative approach, we illustrate the construction of a specific causal network that links gene expression and metabolic changes in the context of glutamate metabolism, and demonstrate its validity by showing that genes in the network respond to changes in glutamine and glutamate availability. Thus, the methods described here have the potential to reveal regulatory networks that contribute to chronic, complex, and highly prevalent diseases and conditions such as obesity and diabetes.
Author Summary
Although numerous quantitative trait loci (QTL) influencing disease-related phenotypes have been detected through gene mapping and positional cloning, identifying individual genes and their potential roles in molecular pathways leading to disease remains a challenge. In this study, we include transcriptional and metabolic profiling in genomic analyses to address this limitation. We investigated an F2 intercross between the diabetes-resistant C57BL/6 leptinob/ob and the diabetes-susceptible BTBR leptinob/ob mouse strains that segregates for genotype and diabetes-related physiological traits; blood glucose, plasma insulin and body weight. Our study shows that liver metabolites (comprised of amino acids, organic acids, and acyl-carnitines) map to distinct genetic regions, thereby indicating that tissue metabolites are heritable. We also demonstrate that genomic analysis can be integrated with liver mRNA expression and metabolite profiling data to construct causal, testable networks for control of specific metabolic processes in liver. We apply an in vitro study to confirm the validity of this integrative method, and thus provide a novel approach to reveal regulatory networks that contribute to chronic, complex, and highly prevalent diseases and conditions such as obesity and diabetes.
doi:10.1371/journal.pgen.1000034
PMCID: PMC2265422  PMID: 18369453

Results 1-13 (13)