RESUMO
BACKGROUND: Carnitine palmitoyltransferase-1 (CPT1) is a rate-limiting step of mitochondrial ß-oxidation by controlling the mitochondrial uptake of long-chain acyl-CoAs. The muscle isoform, CPT1b, is the predominant isoform expressed in the heart. It has been suggested that inhibiting CPT1 activity by specific CPT1 inhibitors exerts protective effects against cardiac hypertrophy and heart failure. However, clinical and animal studies have shown mixed results, thereby creating concerns about the safety of this class of drugs. Preclinical studies using genetically modified animal models should provide a better understanding of targeting CPT1 to evaluate it as a safe and effective therapeutic approach. METHODS AND RESULTS: Heterozygous CPT1b knockout (CPT1b(+/-)) mice were subjected to transverse aorta constriction-induced pressure overload. These mice showed overtly normal cardiac structure/function under the basal condition. Under a severe pressure-overload condition induced by 2 weeks of transverse aorta constriction, CPT1b(+/-) mice were susceptible to premature death with congestive heart failure. Under a milder pressure-overload condition, CPT1b(+/-) mice exhibited exacerbated cardiac hypertrophy and remodeling compared with wild-type littermates. There were more pronounced impairments of cardiac contraction with greater eccentric cardiac hypertrophy in CPT1b(+/-) mice than in control mice. Moreover, the CPT1b(+/-) heart exhibited exacerbated mitochondrial abnormalities and myocardial lipid accumulation with elevated triglycerides and ceramide content, leading to greater cardiomyocyte apoptosis. CONCLUSIONS: CPT1b deficiency can cause lipotoxicity in the heart under pathological stress, leading to exacerbation of cardiac pathology. Therefore, caution should be exercised in the clinical use of CPT1 inhibitors.
Assuntos
Cardiomegalia/metabolismo , Cardiomegalia/patologia , Carnitina O-Palmitoiltransferase/deficiência , Ácidos Graxos/fisiologia , Animais , Pressão Sanguínea/fisiologia , Feminino , Masculino , Camundongos , Camundongos Knockout , Miócitos Cardíacos/metabolismo , Miócitos Cardíacos/patologia , Fenótipo , Vasoconstrição/fisiologiaRESUMO
We used a genome-wide single nucleotide polymorphism (SNP) approach to characterize the genomic structures of four representative C57BL/6 (B6) congenic mutant mouse lines to include the A) long-chain acyl-CoA dehydrogenase (Acadl), B) melanocortin 3 receptor (Mc3r), C) endothelial nitric oxide synthase (Nos3), and D) a replacement of mouse apolipoprotein E (Apoe) by human apolipoprotein E-2 (APOE2). We wanted to evaluate the size and flanking genes of the 129 strain origin mutant allele intervals on the B6 background. Additionally, we wanted to evaluate genetic drift among not only the four mutant lines and their respective B6 origin substrains, but also the drift between two commonly used B6 lines obtained from Jackson Laboratory and Taconic. Overall, we found a range of 129 origin interval sizes in the congenic mutant lines analyzed that ranged from a ~2.8 kb human sequence for APOE2 embedded in a 129S6 interval to the largest being a ~16 Mb fragment containing the targeted Nos3 (eNos) gene. Given the range of 129 strain interval sizes, we found 129 strain flanking genes via annotation in genome data bases ranging from one gene both upstream and downstream of the APOE2 allele to seven genes-upstream and five genes-downstream at the Nos3 locus. Furthermore, we found fourteen SNP differences between the Jackson Laboratory and Taconic B6 mice. These genetic differences were associated with marked adiposity differences between the two B6 substrains. This study demonstrates both the fidelity and the caveats of using congenic gene targeted mouse models and recognizing the importance of selecting the appropriately matched wild-type control mouse line.
Assuntos
Deriva Genética , Genoma , Genômica , Polimorfismo de Nucleotídeo Único , Característica Quantitativa Herdável , Alelos , Animais , Mapeamento Cromossômico , Loci Gênicos , Genótipo , Masculino , Camundongos Congênicos , Camundongos Endogâmicos C57BL , MutaçãoRESUMO
In rodents, the electroencephalogram (EEG) during paradoxical sleep and exploratory behavior is characterized by theta oscillations. Here we show that a deficiency in short-chain acyl-coenzyme A dehydrogenase (encoded by Acads) in mice causes a marked slowing in theta frequency during paradoxical sleep only. We found Acads expression in brain regions involved in theta generation, notably the hippocampus. Microarray analysis of gene expression in mice with mutations in Acads indicates overexpression of Glo1 (encoding glyoxylase 1), a gene involved in the detoxification of metabolic by-products. Administration of acetyl-L-carnitine (ALCAR) to mutant mice significantly recovers slow theta and Glo1 overexpression. Thus, an underappreciated metabolic pathway involving fatty acid beta-oxidation also regulates theta oscillations during sleep.
Assuntos
Encéfalo/enzimologia , Ácidos Graxos Dessaturases/deficiência , Ácidos Graxos/metabolismo , Sono REM , Ritmo Teta , Acetilcarnitina/administração & dosagem , Acil-CoA Desidrogenase , Animais , Modelos Animais de Doenças , Eletroencefalografia , Ácidos Graxos Dessaturases/genética , Ácidos Graxos Dessaturases/metabolismo , Immunoblotting , Técnicas Imunoenzimáticas , Hibridização In Situ , Lactoilglutationa Liase/metabolismo , Fígado/enzimologia , Masculino , Camundongos , Camundongos Endogâmicos AKR , Camundongos Endogâmicos BALB C , Camundongos Endogâmicos C57BL , Dados de Sequência Molecular , Nootrópicos/administração & dosagem , Análise de Sequência com Séries de Oligonucleotídeos , Oxirredução , Sono REM/efeitos dos fármacosRESUMO
The long-chain acyl-CoA dehydrogenase (LCAD) (Acadl=gene; LCAD=protein) deficient mouse model has been important in evaluating the role of mitochondrial fatty acid oxidation of long-chain fatty acids in metabolic disorders. The insertion vector-based gene targeting strategy used to generate this model has made it difficult to distinguish homozygous and heterozygous genotypes containing targeted Acadl alleles in LCAD-deficient mice. Herein, we describe the design and validation of Acadl SNP genotyping methods capable of distinguishing between heterozygous and homozygous LCAD-deficient mice. The Acadl SNP genotyping assays are effective at allelic discrimination of both C57BL/6 and 129 mouse strain-based Acadl alleles under conditions including, both low purity and quantity genomic DNA templates. This makes the method practical and provides the necessary tools for genotyping the LCAD-deficient mouse model.
Assuntos
Acil-CoA Desidrogenase de Cadeia Longa/deficiência , Acil-CoA Desidrogenase de Cadeia Longa/genética , Genótipo , Alelos , Animais , Sequência de Bases , Modelos Animais de Doenças , Ácidos Graxos/genética , Ácidos Graxos/metabolismo , Heterozigoto , Homozigoto , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Mitocôndrias/genética , Mitocôndrias/metabolismo , Dados de Sequência Molecular , Polimorfismo de Nucleotídeo ÚnicoRESUMO
Mouse models have been designed for a number of fatty acid oxidation defects. Studies in these mouse models have demonstrated that different pathogenetic mechanisms play a role in the pathophysiology of defects of fatty acid oxidation. Supplementation with L-carnitine does not prevent low tissue carnitine levels and induces acylcarnitine production having potentially toxic effects, as presented in very-long-chain acyl-CoA dehydrogenase (VLCAD)-deficient mice. Energy deficiency appears to be an important mechanism in the development of cardiomyopathy and skeletal myopathy in fatty acid oxidation defects and is also the underlying mechanism of cold intolerance. Hypoglycemia as one major clinical sign in all fatty acid oxidation defects occurs due to a reduced hepatic glucose output and an enhanced peripheral glucose uptake rather than to transcriptional changes that are also observed simultaneously, as presented in medium-chain acyl-CoA dehydrogenase (MCAD)-deficient mice. There are reports that an impaired fatty acid oxidation also plays a role in intrauterine life. The embryonic loss demonstrated for some enzyme defects in the mouse supports this hypothesis. However, the exact mechanisms are unknown. This observation correlates to maternal hemolysis, elevated liver enzymes, low platelets (HELLP) syndrome, as observed in pregnancies carrying a long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD)-deficient fetus. Synergistic heterozygosity has been shown in isolated patients and in mouse models to be associated with clinical phenotypes common to fatty acid oxidation disorders. Synergistic mutations may also modulate severity of the clinical phenotype and explain in part clinical heterogeneity of fatty acid oxidation defects. In summary, knowledge about the different pathogenetic mechanisms and the resulting pathophysiology allows the development of specific new therapies.
Assuntos
Metabolismo Energético , Ácidos Graxos/metabolismo , Erros Inatos do Metabolismo Lipídico/fisiopatologia , Mitocôndrias/enzimologia , Doenças Mitocondriais/fisiopatologia , Animais , Modelos Animais de Doenças , Metabolismo Energético/genética , Genótipo , Humanos , Erros Inatos do Metabolismo Lipídico/complicações , Erros Inatos do Metabolismo Lipídico/enzimologia , Erros Inatos do Metabolismo Lipídico/genética , Camundongos , Doenças Mitocondriais/complicações , Doenças Mitocondriais/enzimologia , Doenças Mitocondriais/genética , Oxirredução , Fenótipo , Especificidade da EspécieRESUMO
The fat-1 gene, derived from Caenorhabditis elegans, encodes for a fatty acid n-3 desaturase. In order to study the potential metabolic benefits of n-3 fatty acids, independent of dietary fatty acids, we developed seven lines of fat-1 transgenic mice (C57/BL6) controlled by the regulatory sequences of the adipocyte protein-2 (aP2) gene for adipocyte-specific expression (AP-lines). We were unable to obtain homozygous fat-1 transgenic offspring from the two highest expressing lines, suggesting that excessive expression of this enzyme may be lethal during gestation. Serum fatty acid analysis of fat-1 transgenic mice (AP-3) fed a high n-6 unsaturated fat (HUSF) diet had an n-6/n-3 fatty acid ratio reduced by 23% (P < 0.025) and the n-3 fatty acid eicosapentaenoic acid (EPA) concentration increased by 61% (P < 0.020). Docosahexaenoic acid (DHA) was increased by 19% (P < 0.015) in white adipose tissue. Male AP-3-fat-1 line of mice had improved glucose tolerance and reduced body weight with no change in insulin sensitivity when challenged with a high-carbohydrate (HC) diet. In contrast, the female AP-3 mice had reduced glucose tolerance and no change in insulin sensitivity or body weight. These findings indicate that male transgenic fat-1 mice have improved glucose tolerance likely due to increased insulin secretion while female fat-1 mice have reduced glucose tolerance compared to wild-type mice. Finally the inability of fat-1 transgenic mice to generate homozygous offspring suggests that prolonged exposure to increased concentrations of n-3 fatty acids may be detrimental to reproduction.
Assuntos
Peso Corporal , Proteínas de Caenorhabditis elegans/farmacologia , Ácidos Graxos Dessaturases/farmacologia , Ácidos Graxos Ômega-3/farmacologia , Glucose/metabolismo , Homeostase , Animais , Proteínas de Caenorhabditis elegans/genética , Ácidos Graxos Dessaturases/genética , Feminino , Intolerância à Glucose , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Reprodução , Fatores SexuaisRESUMO
Obesity is becoming recognized as a common co-morbidity with several disease states including cancer. There is tremendous interest to more fully understand the mechanistic connections between obesity and cancer. This commentary highlights the report by Byon et al in this issue of Laboratory Investigation. It provides an interpretation of their results in the context of other disease states involving obesity and its sequelae of excess fatty acids and increased plasminogen activator inhibitor-1 (PAI-1) concentrations. This includes obesity-related conditions, in particular metabolic syndrome, and its subphenotypes such as insulin resistance, and increased risk of myocardial infarction. The potential mechanistic tie-ins of obesity, elevated concentrations of fatty acids, as well as elevated PAI-1 levels with cancer and its risk for aggressiveness are discussed.
Assuntos
Ácidos Graxos/sangue , Neoplasias/fisiopatologia , Obesidade/fisiopatologia , Células Cultivadas , Comorbidade , Feminino , Humanos , Masculino , Neoplasias/sangue , Obesidade/sangue , Inibidor 1 de Ativador de Plasminogênio/sangue , Fatores de RiscoRESUMO
Cardiac hypertrophy is a common finding in human patients with inborn errors of long-chain fatty acid oxidation. Mice with either very long-chain acyl-coenzyme A dehydrogenase deficiency (VLCAD-/-) or long-chain acyl-coenzyme A dehydrogenase deficiency (LCAD-/-) develop cardiac hypertrophy. Cardiac hypertrophy, initially measured using heart/body weight ratios, was manifested most severely in LCAD-/- male mice. VLCAD-/- mice, as a group, showed a mild increase in normalized cardiac mass (8.8% hypertrophy compared with all wild-type (WT) mice). In contrast, LCAD-/- mice as a group showed more severe cardiac hypertrophy (32.2% increase compared with all WT mice). On the basis of a clear male predilection, we analyzed the role of dietary plant estrogenic compounds commonly found in mouse diets because of soy or alfalfa components providing natural phytoestrogens or isoflavones in cardioprotection of LCAD-/- mice. Male LCAD-/- mice fed an isoflavone-free test diet had more severe cardiac hypertrophy (58.1% hypertrophy compared with WT mice fed the same diet). There were no significant differences in the female groups fed any of the diets. Echocardiography measurement performed on male LCAD-deficient mice fed a standard diet at the age of approximately 3 months confirmed the substantial cardiac hypertrophy in these mice compared with WT controls. Left ventricular (LV) wall thickness of the interventricular septum and posterior wall was remarkably increased in LCAD-/- mice compared with that of WT controls. Accordingly, the calculated LV mass after normalization to body weight was increased by about 40% in the LCAD-/- mice compared with WT mice. In summary, we found that metabolic cardiomyopathy, expressed as hypertrophy, developed in mice because of either VLCAD deficiency or LCAD deficiency; however, LCAD deficiency was the most profound and seemed to be attenuated either by endogenous estrogen (in females) or by phytoestrogens present in the diet as isoflavones (in males).
Assuntos
Acil-CoA Desidrogenase de Cadeia Longa/deficiência , Cardiomegalia/enzimologia , Animais , Peso Corporal , Cardiomegalia/patologia , Cardiomegalia/prevenção & controle , Dieta , Modelos Animais de Doenças , Ecocardiografia , Feminino , Isoflavonas/uso terapêutico , Masculino , Camundongos , Camundongos Knockout , Miocárdio/patologia , Tamanho do Órgão , Fitoestrógenos/uso terapêuticoRESUMO
Carnitine palmitoyltransferase-1 (CPT-1) catalyzes the rate-limiting step of mitochondrial beta-oxidation of long chain fatty acids (LCFA), the most abundant fatty acids in mammalian membranes and in energy metabolism. Human deficiency of the muscle isoform CPT-1b is poorly understood. In the current study, embryos with a homozygous knockout of Cpt-1b were lost before embryonic day 9.5-11.5. Also, while there were normal percentages of CPT-1b+/- pups born from both male and female CPT-1b+/- mice crossed with wild-type mates, the number of CPT-1b+/- pups from CPT-1b+/- breeding pairs was under-represented (63% of the expected number). Northern blot analysis demonstrated approximately 50% Cpt-1b mRNA expression in brown adipose tissue (BAT), heart and skeletal muscles in the CPT-1b+/- male mice. Consistent with tissue-specific expression of Cpt-1b mRNA in muscle but not liver, CPT-1+/- mice had approximately 60% CPT-1 activity in skeletal muscle and no change in total liver CPT-1 activity. CPT-1b+/- mice had normal fasting blood glucose concentration. Consistent with expression of CPT-1b in BAT and muscle, approximately 7% CPT-1b+/- mice (n=30) developed fatal hypothermia following a 3h cold challenge, while none of the CPT-1b+/+ mice (n=30) did. With a prolonged cold challenge (6h), significantly more CPT-1b+/- mice developed fatal hypothermia (52% CPT-1b+/- mice vs. 21% CPT-1b+/+ mice), with increased frequency in females of both genotypes (67% female vs. 38% male CPT-1b+/- mice, and 33% female vs. 8% male CPT-1b+/+ mice). Therefore, lethality of homozygous CPT-1b deficiency in the mice is consistent with paucity of human cases.
Assuntos
Carnitina O-Palmitoiltransferase/deficiência , Perda do Embrião , Predisposição Genética para Doença , Hipotermia/genética , Músculo Esquelético/enzimologia , Animais , Carnitina O-Palmitoiltransferase/genética , Feminino , Genótipo , Homozigoto , Hipotermia/mortalidade , Isoenzimas/deficiência , Isoenzimas/genética , Masculino , Camundongos , Camundongos Knockout , Especificidade de ÓrgãosRESUMO
In the present paper, we describe a novel method which enables the analysis of tissue acylcarnitines and carnitine biosynthesis intermediates in the same sample. This method was used to investigate the carnitine and fatty acid metabolism in wild-type and LCAD-/- (long-chain acyl-CoA dehydrogenase-deficient) mice. In agreement with previous results in plasma and bile, we found accumulation of the characteristic C14:1-acylcarnitine in all investigated tissues from LCAD-/- mice. Surprisingly, quantitatively relevant levels of 3-hydroxyacylcarnitines were found to be present in heart, muscle and brain in wild-type mice, suggesting that, in these tissues, long-chain 3-hydroxyacyl-CoA dehydrogenase is rate-limiting for mitochondrial beta-oxidation. The 3-hydroxyacylcarnitines were absent in LCAD-/- tissues, indicating that, in this situation, the beta-oxidation flux is limited by the LCAD deficiency. A profound deficiency of acetylcarnitine was observed in LCAD-/- hearts, which most likely corresponds with low cardiac levels of acetyl-CoA. Since there was no carnitine deficiency and only a marginal elevation of potentially cardiotoxic acylcarnitines, we conclude from these data that the cardiomyopathy in the LCAD-/- mouse is caused primarily by a severe energy deficiency in the heart, stressing the important role of LCAD in cardiac fatty acid metabolism in the mouse.
Assuntos
Acil-CoA Desidrogenase de Cadeia Longa/deficiência , Carnitina/metabolismo , Ácidos Graxos/metabolismo , Animais , Química Encefálica , Rim/química , Fígado/química , Masculino , Camundongos , Camundongos Endogâmicos , Músculos/química , Testículo/químicaRESUMO
We investigated the effects of the HIV protease inhibitor ritonavir on body composition, serum lipids, and gene expression in C57BL/6 mice. Dual-energy X-ray absorptiometry measurements in ritonavir-treated male mice revealed whole-body lipoatrophy. In female mice fat reduction was restricted to the gonadal depot. A histopathological analysis showed no visible abnormalities in liver or adipose tissue from ritonavir-treated mice, although adipocytes were significantly smaller in diameter. Serum triglyceride levels were increased in ritonavir-treated male mice. Ritonavir was coadministered with the peroxisome proliferator-activated receptor alpha (PPARalpha) agonist gemfibrozil and the PPARgamma agonist rosiglitazone for 8 weeks. Neither drug alleviated the hypertriglyceridemia or lipoatrophy in ritonavir-treated male mice. Rather, gemfibrozil exacerbated the lipoatrophy. Ritonavir reduced basal expression of two PPARalpha target genes in liver, as well as the PPARgamma target gene phosphoenolpyruvate carboxykinase (PEPCK) in adipose tissues. Ritonavir partially inhibited induction of PPAR target genes by gemfibrozil and rosiglitazone. Gemfibrozil induced expression of fatty acid oxidation genes in liver, and this induction was less substantial when ritonavir was coadministered. Similarly, rosiglitazone induced expression of uncoupling protein-1, uncoupling protein-2, and PEPCK in adipose tissues, and this effect was partially inhibited by ritonavir. Thus, the effects of ritonavir on serum triglycerides and body composition may be due, at least in part, to an inhibition of PPAR function.
Assuntos
Ácidos Graxos/biossíntese , Inibidores da Protease de HIV/efeitos adversos , Lipodistrofia/induzido quimicamente , Fígado/efeitos dos fármacos , Ritonavir/efeitos adversos , Animais , Lipodistrofia/metabolismo , Fígado/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Esteróis/biossínteseRESUMO
Mitochondrial beta-oxidation of fatty acids is vital for energy production in periods of fasting and other metabolic stress. Human patients have been identified with inherited disorders of mitochondrial beta-oxidation of fatty acids with enzyme deficiencies identified at many of the steps in this pathway. Although these patients exhibit a range of disease processes, Reye-like illness (hypoketotic-hypoglycemia, hyperammonemia and fatty liver) and cardiomyopathy are common findings. There have been several mouse models developed to aid in the study of these disease conditions. The characterized mouse models include inherited deficiencies of very long-chain acyl-CoA dehydrogenase, long-chain acyl-CoA dehydrogenase, short-chain acyl-CoA dehydrogenase, mitochondrial trifunctional protein-alpha, and medium-/short-chain hydroxyacyl-CoA dehydrogenase. Mouse mutants developed, but presently incompletely characterized as models, include carnitine palmitoyltransferase-1a and medium-chain acyl-CoA dehydrogenase deficiencies. In general, the mouse models of disorders of mitochondrial fatty acid beta-oxidation have shown clinical signs that include Reye-like syndrome and cardiomyopathy, and many are cold intolerant. It is expected that these mouse models will provide vital contributions in understanding the mechanisms of disease pathogenesis of fatty acid oxidation disorders and the development of appropriate treatments and supportive care.
Assuntos
Modelos Animais de Doenças , Ácidos Graxos/metabolismo , Erros Inatos do Metabolismo/fisiopatologia , Mitocôndrias/enzimologia , Acil-CoA Desidrogenase , Acil-CoA Desidrogenase de Cadeia Longa/metabolismo , Animais , Regulação da Temperatura Corporal , Cardiomiopatias , Jejum , Humanos , Erros Inatos do Metabolismo/veterinária , Camundongos , Oxirredução , Síndrome de ReyeRESUMO
BACKGROUND: Carnitine palmitoyltransferase 1 (CPT1) is the rate-limiting enzyme governing the entry of long-chain acyl-CoAs into mitochondria. Treatments with CPT1 inhibitors protect against insulin resistance in short-term preclinical animal studies. We recently reported that mice with muscle isoform CPT1b deficiency demonstrated improved insulin sensitivity when fed a High Fat-Diet (HFD) for up to 5 months. In this follow up study, we further investigated whether the insulin sensitizing effects of partial CPT1b deficiency could be maintained under a prolonged HFD feeding condition. METHODS: We investigated the effects of CPT1b deficiency on HFD-induced insulin resistance using heterozygous CPT1b deficient (Cpt1b+/-) mice compared with Wild Type (WT) mice fed a HFD for a prolonged period of time (7 months). We assessed insulin sensitivity using hyperinsulinemic-euglycemic clamps. We also examined body composition, skeletal muscle lipid profile, and changes in the insulin signaling pathways of skeletal muscle, liver, and adipose tissue. RESULTS: We found that Cpt1b+/- mice became severely insulin resistant after 7 months of HFD feeding. Cpt1b+/- mice exhibited a substantially reduced glucose infusion rate and skeletal muscle glucose uptake. While Cpt1b+/- mice maintained a slower weight gain with less fat mass than WT mice, accumulation of lipid intermediates became evident in the muscle of Cpt1b+/- but not WT mice after 7 months of HFD feeding. Insulin signaling was impaired in the Cpt1b+/- as compared to the WT muscles. CONCLUSION: Partial CPT1b deficiency, mimicking CPT1b inhibition, may lead to impaired insulin signaling and insulin sensitivity under a prolonged HFD feeding condition. Therefore, further studies on the potential detrimental effects of prolonged therapy with CPT1 inhibition are necessary in the development of this potential therapeutic strategy.
RESUMO
BACKGROUND: Carnitine Palmitoyl Transferase 1 (CPT1) is the rate-limiting enzyme governing long-chain fatty acid entry into mitochondria. CPT1 inhibitors have been developed and exhibited beneficial effects against type II diabetes in short-term preclinical animal studies. However, the long-term effects of treatment remain unclear and potential non-specific effects of these CPT1 inhibitors hamper in-depth understanding of the potential molecular mechanisms involved. METHODS: We investigated the effects of restricting the activity of the muscle isoform CPT1b in mice using heterozygous CPT1b deficient (Cpt1b+/-) and Wild Type (WT) mice fed with a High Fat Diet (HFD) for 22 weeks. Insulin sensitivity was assessed using Glucose Tolerance Test (GTT), insulin tolerance test and hyperinsulinemic euglycemic clamps. We also examined body weight/composition, tissue and systemic metabolism/energetic status, lipid profile, transcript analysis, and changes in insulin signaling pathways. RESULTS: We found that Cpt1b+/- mice were protected from HFD-induced insulin resistance compared to WT littermates. Cpt1b+/- mice exhibited elevated whole body glucose disposal rate and skeletal muscle glucose uptake. Furthermore, Cpt1b+/- skeletal muscle showed diminished ex vivo palmitate oxidative capacity by ~40% and augmented glucose oxidation capacity by ~50% without overt change in whole body energy metabolism. HFD feeding Cpt1b+/- but not WT mice exhibited well-maintained insulin signaling in skeletal muscle, heart, and liver. CONCLUSION: The present study on a genetic model of CPT1b restriction supports the concept that partial CPT1b inhibition is a potential therapeutic strategy.
RESUMO
BACKGROUND: Abnormal fatty acid metabolism is an important feature in the mechanisms of insulin resistance and beta-cell dysfunction. Carnitine palmitoyltransferase-1a (CPT-1a, liver isoform) plays a pivotal role in the regulation of mitochondrial fatty acid oxidation. We investigated the role of CPT-1a in the development of impaired glucose tolerance using a mouse model for CPT-1a deficiency when challenged by either a high-carbohydrate (HCD) or a high-fat diet (HFD) for a total duration of up to 46 weeks. METHODS: Insulin sensitivity and glucose tolerance were assessed in heterozygous CPT-1a deficient (CPT-1a+/-) male mice after being fed either a HCD or a HFD for durations of 28 weeks and 46 weeks. Both glucose and insulin tolerance tests were used to investigate beta-cell function and insulin sensitivity. Differences in islet insulin content and hepatic steatosis were evaluated by morphological analysis. RESULTS: CPT-1a+/- mice were more insulin sensitive than CPT-1a+/+ mice when fed either HCD or HFD. The increased insulin sensitivity was associated with an increased expression of Cpt-1b (muscle isoform) in liver, as well as increased microvesicular hepatic steatosis compared to CPT-1a+/+ mice. CPT-1a+/- mice were more glucose tolerant than CPT-1a+/+ mice when fed the HCD, but there was no significant difference when fed HFD. Moreover, CPT-1a+/- mice fed HFD or HCD had fewer and smaller pancreatic islets than CPT-1a+/+ mice. CONCLUSIONS: CPT-1a deficiency preserved insulin sensitivity when challenged by long term feeding of either diet. Furthermore, CPT-1a deficient mice had distinct phenotypes dependent on the diet fed demonstrating that both diet and genetics collectively play a role in the development of impaired glucose tolerance.
RESUMO
Mitochondrial fatty acid oxidation provides an important energy source for cellular metabolism, and decreased mitochondrial fatty acid oxidation has been implicated in the pathogenesis of type 2 diabetes. Paradoxically, mice with an inherited deficiency of the mitochondrial fatty acid oxidation enzyme, very long-chain acyl-CoA dehydrogenase (VLCAD), were protected from high-fat diet-induced obesity and liver and muscle insulin resistance. This was associated with reduced intracellular diacylglycerol content and decreased activity of liver protein kinase Cvarepsilon and muscle protein kinase Ctheta. The increased insulin sensitivity in the VLCAD(-/-) mice were protected from diet-induced obesity and insulin resistance due to chronic activation of AMPK and PPARalpha, resulting in increased fatty acid oxidation and decreased intramyocellular and hepatocellular diacylglycerol content.
Assuntos
Acil-CoA Desidrogenase de Cadeia Longa/metabolismo , Resistência à Insulina , Obesidade/etiologia , Quinases Proteína-Quinases Ativadas por AMP , Acil-CoA Desidrogenase de Cadeia Longa/deficiência , Acil-CoA Desidrogenase de Cadeia Longa/genética , Animais , Gorduras na Dieta/farmacologia , Diglicerídeos/metabolismo , Humanos , Insulina/metabolismo , Isoenzimas/metabolismo , Fígado/enzimologia , Fígado/metabolismo , Masculino , Camundongos , Camundongos Knockout , Mitocôndrias/enzimologia , PPAR alfa/metabolismo , Proteína Quinase C/metabolismo , Proteína Quinase C-épsilon/metabolismo , Proteína Quinase C-theta , Proteínas Quinases/metabolismoAssuntos
Diabetes Mellitus Tipo 2/genética , Modelos Animais de Doenças , Ácidos Graxos/metabolismo , Alimentos Orgânicos , Resistência à Insulina/genética , Animais , Animais Geneticamente Modificados , Diabetes Mellitus Tipo 2/metabolismo , Genômica/métodos , Humanos , Resistência à Insulina/fisiologia , CamundongosRESUMO
Nutrigenetics is a genotype-based medical concept used in pursuit of individualized or personalized nutrition programs. That is, nutrigenetics is the study of what the effect of an individual's genetic make-up is on their response to diet or specific nutrients. Furthermore, the concept is that if an individual is genotyped at various genes for disease-associated risk alleles, a genotype-based diet or nutritional supplement regimen may be useful to overcome the genetic variation and reduce risk or prevent the disease altogether. The metabolic diseases considered in this article include obesity-related diseases and cardiovascular disease. The thesis of this article is that nutrigenetics, although an intuitively attractive approach to individualized nutrition, is not yet fully developed for evidence-based medical practice and is inappropriate as direct-to-the-consumer genetic testing. Although the genetic variations associated with disease risk can be determined, presently, relevant loci are too few in number, have modest effects at most, add little to the overall disease-risk prediction and any nutritional therapy based on genotype must be tested in case-control clinical trials.
RESUMO
Alterations in mitochondrial function have been implicated in the pathogenesis of insulin resistance and type 2 diabetes. However, it is unclear whether the reduced mitochondrial function is a primary or acquired defect in this process. To determine whether primary defects in mitochondrial beta-oxidation can cause insulin resistance, we studied mice with a deficiency of long-chain acyl-CoA dehydrogenase (LCAD), a key enzyme in mitochondrial fatty acid oxidation. Here, we show that LCAD knockout mice develop hepatic steatosis, which is associated with hepatic insulin resistance, as reflected by reduced insulin suppression of hepatic glucose production during a hyperinsulinemic-euglycemic clamp. The defects in insulin action were associated with an approximately 40% reduction in insulin-stimulated insulin receptor substrate-2-associated phosphatidylinositol 3-kinase activity and an approximately 50% decrease in Akt2 activation. These changes were associated with increased PKCepsilon activity and an aberrant 4-fold increase in diacylglycerol content after insulin stimulation. The increase in diacylglycerol concentration was found to be caused by de novo synthesis of diacylglycerol from medium-chain acyl-CoA after insulin stimulation. These data demonstrate that primary defects in mitochondrial fatty acid oxidation capacity can lead to diacylglycerol accumulation, PKCepsilon activation, and hepatic insulin resistance.
Assuntos
Acil-CoA Desidrogenase de Cadeia Longa/deficiência , Fígado Gorduroso/enzimologia , Resistência à Insulina/fisiologia , Fígado/enzimologia , Fígado/patologia , Mitocôndrias/enzimologia , Mitocôndrias/patologia , Acil Coenzima A/metabolismo , Animais , Calorimetria , Isótopos de Carbono , Diglicerídeos/biossíntese , Metabolismo Energético/efeitos dos fármacos , Fígado Gorduroso/patologia , Regulação da Expressão Gênica/efeitos dos fármacos , Glucose/metabolismo , Homeostase/efeitos dos fármacos , Insulina/farmacologia , Fígado/metabolismo , Camundongos , Mitocôndrias/efeitos dos fármacos , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/metabolismo , Oxirredução/efeitos dos fármacos , Proteína Quinase C-épsilon/metabolismo , Transdução de Sinais/efeitos dos fármacos , Triglicerídeos/biossínteseRESUMO
Muscular dystrophies include a diverse group of genetically heterogeneous disorders that together affect 1 in 2000 births worldwide. The diseases are characterized by progressive muscle weakness and wasting that lead to severe disability and often premature death. Rostrocaudal muscular dystrophy (rmd) is a new recessive mouse mutation that causes a rapidly progressive muscular dystrophy and a neonatal forelimb bone deformity. The rmd mutation is a 1.6-kb intragenic deletion within the choline kinase beta (Chkb) gene, resulting in a complete loss of CHKB protein and enzymatic activity. CHKB is one of two mammalian choline kinase (CHK) enzymes (alpha and beta) that catalyze the phosphorylation of choline to phosphocholine in the biosynthesis of the major membrane phospholipid phosphatidylcholine. While mutant rmd mice show a dramatic decrease of CHK activity in all tissues, the dystrophy is only evident in skeletal muscle tissues in an unusual rostral-to-caudal gradient. Minor membrane disruption similar to dysferlinopathies suggest that membrane fusion defects may underlie this dystrophy, because severe membrane disruptions are not evident as determined by creatine kinase levels, Evans Blue infiltration, and unaltered levels of proteins in the dystrophin-glycoprotein complex. The rmd mutant mouse offers the first demonstration of a defect in a phospholipid biosynthetic enzyme causing muscular dystrophy, representing a unique model for understanding mechanisms of muscle degeneration.