Differential regulation of carnitine palmitoyltransferase-I gene isoforms (CPT-I alpha and CPT-I beta) in the rat heart

Myoglobin Inhibits Breast Cancer Cell Fatty Acid Oxidation and Migration via Heme-dependent Oxidant Production and Not Fatty Acid Binding

The monomeric heme protein myoglobin (Mb), traditionally thought to be expressed exclusively in cardiac and skeletal muscle, is now known to be expressed in approximately 40% of breast tumors. While Mb expression is associated with better patient prognosis, the molecular mechanisms by which Mb limits cancer progression are unclear. In muscle, Mb's predominant function is oxygen storage and delivery, which is dependent on the protein's heme moiety. However, prior studies demonstrate that the low levels of Mb expressed in cancer cells preclude this function. Recent studies propose a novel fatty acid binding function for Mb via a lysine residue (K46) in the heme pocket. Given that cancer cells can upregulate fatty acid oxidation (FAO) to maintain energy production for cytoskeletal remodeling during cell migration, we tested whether Mb-mediated fatty acid binding modulates FAO to decrease breast cancer cell migration. We demonstrate that the stable expression of human Mb in MDA-MB-231 breast cancer cells decreases cell migration and FAO. Site-directed mutagenesis of Mb to disrupt Mb fatty acid binding did not reverse Mb-mediated attenuation of FAO or cell migration in these cells. In contrast, cells expressing Apo-Mb, in which heme incorporation was disrupted, showed a reversal of Mb-mediated attenuation of FAO and cell migration, suggesting that Mb attenuates FAO and migration via a heme-dependent mechanism rather than through fatty acid binding. To this end, we show that Mb's heme-dependent oxidant generation propagates dysregulated gene expression of migratory genes, and this is reversed by catalase treatment. Collectively, these data demonstrate that Mb decreases breast cancer cell migration, and this effect is due to heme-mediated oxidant production rather than fatty acid binding. The implication of these results will be discussed in the context of therapeutic strategies to modulate oxidant production and Mb in tumors.

Highlights

Myoglobin (Mb) expression in MDA-MB-231 breast cancer cells slows migration.Mb expression decreases mitochondrial respiration and fatty acid oxidation.Mb-dependent fatty acid binding does not regulate cell migration or respiration.Mb-dependent oxidant generation decreases mitochondrial metabolism and migration.Mb-derived oxidants dysregulate migratory gene expression.

Maturation of lipid metabolism in the fetal and newborn sheep heart

At birth, the fetus experiences a dramatic change in environment that is accompanied by a shift in myocardial fuel preference from lactate and glucose in fetal life to fatty acid oxidation after birth. We hypothesized that fatty acid metabolic machinery would mature during fetal life in preparation for this extreme metabolic transformation at birth. We quantified the pre- (94-day and 135-day gestation, term ∼147 days) and postnatal (5 ± 4 days postnatal) gene expression and protein levels for fatty acid transporters and enzymes in hearts from a precocial species, the sheep. Gene expression of fatty acid translocase (CD36), acyl-CoA synthetase long-chain 1 (ACSL1), carnitine palmitoyltransferase 1 (CPT1), hydroxy-acyl dehydrogenase (HADH), acetyl-CoA acetyltransferase (ACAT1), isocitrate dehydrogenase (IDH), and glycerol phosphate acyltransferase (GPAT) progressively increased through the perinatal period, whereas several genes [fatty acid transport protein 6 (FATP6), acyl-CoA synthetase long chain 3 (ACSL3), long-chain acyl-CoA dehydrogenase (LCAD), very long-chain acyl-CoA dehydrogenase (VLCAD), pyruvate dehydrogenase kinase (PDK4), phosphatidic acid phosphatase (PAP), and diacylglycerol acyltransferase (DGAT)] were stable in fetal hearts and had high expression after birth. Protein expression of CD36 and ACSL1 progressively increased throughout the perinatal period, whereas protein expression of carnitine palmitoyltransferase 1a (fetal isoform) (CPT1a) decreased and carnitine palmitoyltransferase 1b (adult isoform) (CPT1b) remained constitutively expressed. Using fluorescent-tagged long-chain fatty acids (BODIPY-C12), we demonstrated that fetal (125 ± 1 days gestation) cardiomyocytes produce 59% larger lipid droplets (P < 0.05) compared with newborn (8 ± 1 day) cardiomyocytes. These results provide novel insights into the perinatal maturation of cardiac fatty acid metabolism in a precocial species.NEW & NOTEWORTHY This study characterized the previously unknown expression patterns of genes that regulate the metabolism of free fatty acids in the perinatal sheep myocardium. This study shows that the prenatal myocardium prepares for the dramatic switch from carbohydrate metabolism to near complete reliance on free fatty acids postnatally. Fetal and neonatal cardiomyocytes also demonstrate differing lipid storage mechanisms where fetal cardiomyocytes form larger lipid droplets compared with newborn cardiomyocytes.

Impact of Prenatal Exposure to Maternal Diabetes and High-Fat Diet on Postnatal Myocardial Ketone Body Metabolism in Rats

Infants exposed to diabetic pregnancy are at higher risk of cardiomyopathy at birth and early onset cardiovascular disease (CVD) as adults. Using a rat model, we showed how fetal exposure to maternal diabetes causes cardiac disease through fuel-mediated mitochondrial dysfunction, and that a maternal high-fat diet (HFD) exaggerates the risk. Diabetic pregnancy increases circulating maternal ketones which can have a cardioprotective effect, but whether diabetes-mediated complex I dysfunction impairs myocardial metabolism of ketones postnatally remains unknown. The objective of this study was to determine whether neonatal rat cardiomyocytes (NRCM) from diabetes- and HFD-exposed offspring oxidize ketones as an alternative fuel source. To test our hypothesis, we developed a novel ketone stress test (KST) using extracellular flux analyses to compare real-time ß-hydroxybutyrate (βHOB) metabolism in NRCM. We also compared myocardial expression of genes responsible for ketone and lipid metabolism. NRCM had a dose-dependent increase in respiration with increasing concentrations of βHOB, demonstrating that both control and combination exposed NRCM can metabolize ketones postnatally. Ketone treatment also enhanced the glycolytic capacity of combination exposed NRCM with a dose-dependent increase in the glucose-mediated proton efflux rate (PER) from CO2 (aerobic glycolysis) alongside a decreased reliance on PER from lactate (anaerobic glycolysis). Expression of genes responsible for ketone body metabolism was higher in combination exposed males. Findings demonstrate that myocardial ketone body metabolism is preserved and improves fuel flexibility in NRCM from diabetes- and HFD-exposed offspring, which suggests that ketones might serve a protective role in neonatal cardiomyopathy due to maternal diabetes.

Acetylcarnitine Is Associated With Cardiovascular Disease Risk in Type 2 Diabetes Mellitus

OBJECTIVE

This study aimed to identify the association between specific short-chain acylcarnitines and cardiovascular disease (CVD) in type 2 diabetes mellitus (T2DM).

METHOD

We retrieved 1,032 consecutive patients with T2DM who meet the inclusion and exclusion criteria from the same tertiary care center and extracted clinical information from electronic medical records from May 2015 to August 2016. A total of 356 T2DM patients with CVD and 676 T2DM patients without CVD were recruited. Venous blood samples were collected by finger puncture after 8 h fasting and stored as dried blood spots. Restricted cubic spline (RCS) analysis nested in binary logistic regression was used to identify possible cutoff points and obtain the odds ratios (ORs) and 95% confidence intervals (CIs) of short-chain acylcarnitines for CVD risk in T2DM. The Ryan-Holm step-down Bonferroni procedure was performed to adjust p-values. Stepwise forward selection was performed to estimate the effects of acylcarnitines on CVD risk.

RESULT

The levels of C2, C4, and C6 were elevated and C5-OH was decreased in T2DM patients with CVD. Notably, only elevated C2 was still associated with increased CVD inT2DM after adjusting for potential confounders in the multivariable model (OR = 1.558, 95%CI = 1.124-2.159, p = 0.008). Furthermore, the association was independent of previous adjusted demographic and clinical factors after stepwise forward selection (OR = 1.562, 95%CI = 1.132-2.154, p = 0.007).

CONCLUSIONS

Elevated C2 was associated with increased CVD risk in T2DM.

Myocardium Metabolism in Physiological and Pathophysiological States: Implications of Epicardial Adipose Tissue and Potential Therapeutic Targets

The main energy substrate of adult cardiomyocytes for their contractility are the fatty acids. Its metabolism generates high ATP levels at the expense of high oxygen consumption in the mitochondria. Under low oxygen supply, they can get energy from other substrates, mainly glucose, lactate, ketone bodies, etc., but the mitochondrial dysfunction, in pathological conditions, reduces the oxidative metabolism. In consequence, fatty acids are stored into epicardial fat and its accumulation provokes inflammation, insulin resistance, and oxidative stress, which enhance the myocardium dysfunction. Some therapies focused on improvement the fatty acids entry into mitochondria have failed to demonstrate benefits on cardiovascular disorders. Oppositely, those therapies with effects on epicardial fat volume and inflammation might improve the oxidative metabolism of myocardium and might reduce the cardiovascular disease progression. This review aims at explain (a) the energy substrate adaptation of myocardium in physiological conditions, (b) the reduction of oxidative metabolism in pathological conditions and consequences on epicardial fat accumulation and insulin resistance, and (c) the reduction of cardiovascular outcomes after regulation by some therapies.

Tributyrin Inhibits Ethanol-Induced Epigenetic Repression of CPT-1A and Attenuates Hepatic Steatosis and Injury

Ethanol-mediated down-regulation of carnitine palmitoyltransferase-1 (CPT-1A) gene expression plays a major role in the development of hepatic steatosis; however, the underlying mechanisms are not completely elucidated. Tributyrin, a butyrate prodrug that can inhibit histone deacetylase (HDAC) activity, attenuates hepatic steatosis and injury. The present study examined the beneficial effect of tributyrin/butyrate in attenuating ethanol-induced pathogenic epigenetic mechanisms affecting CPT-1A promoter-histone modifications and gene expression and hepatic steatosis/injury.

METHODS

Mice were fed a liquid Lieber-DeCarli diet (Research Diet Inc, New Brunswick, NJ) with or without ethanol for 4 weeks. In a subset of mice, tributyrin (2 g/kg) was administered orally by gavage. Primary rat hepatocytes were treated with 50 mmol/L ethanol and/or 2 mmol/L butyrate. Gene expression and epigenetic modifications at the CPT-1A promoter were analyzed by chromatin immunoprecipitation analysis.

RESULTS

In vivo, ethanol induced hepatic CPT-1A promoter histone H3K9 deacetylation, which is indicative of a repressive chromatin state, and decreased CPT-1A gene expression. Our data identified HDAC1 as the predominant HDAC causing CPT-1A promoter histone H3K9 deacetylation and epigenetic down-regulation of gene expression. Significantly, Specificity Protein 1 (SP1) and Hepatocyte Nuclear Factor 4 Alpha (HNF4α) participated in the recruitment of HDAC1 to the proximal and distal regions of CPT-1A promoter, respectively, and mediated transcriptional repression. Importantly, butyrate, a dietary HDAC inhibitor, attenuated ethanol-induced recruitment of HDAC1 and facilitated p300-HAT binding by enabling SP1/p300 interaction at the proximal region and HNF4α/peroxisomal proliferator-activated receptor-γ coactivator-1α/p300 interactions at the distal region, leading to promoter histone acetylation and enhanced CPT-1A transcription.

CONCLUSIONS

This study identifies HDAC1-mediated repressive epigenetic mechanisms that underlie an ethanol-mediated decrease in CPT-1A expression. Importantly, tributyrin/butyrate inhibits HDAC1, rescues CPT-1A expression, and attenuates ethanol-mediated hepatic steatosis and injury, suggesting its potential use in therapeutic strategies for alcoholic liver disease.

The less weight loss due to modest food restriction drove more fat accumulation in striped hamsters refed with high-fat diet

Food restriction (FR) has been commonly used to decrease body fat, reducing the risk of overweight in humans and animals. However, the lost weight has been shown to be followed by overweight when food restriction ends. It remains uncertain whether the weight loss drives the overweight, or not. In the present study, striped hamsters were restricted by 15%, 30% and 40% of ad libitum food intake for 2 weeks, followed by high-fat refeeding for 6 weeks (FR15%-Re, FR30%-Re and FR40%-Re). The hamsters in FR15%, FR30% and FR40% groups decreased by 21.1%, 37.8% and 50.0% in fat mass (P < 0.01), and 16.8%, 42.8% and 53.4% in leptin levels (P < 0.01) compared with the hamsters fed ad libitum. The FR15%-Re, FR30%-Re and FR40%-Re groups showed 77.0%, 37.2% and 23.7% more body fat than ad libitum group (P < 0.01). The FR15%-Re group showed considerable decreases in gene expression of arcuate nucleus co-expressing proopiomelanocortin (POMC), cocaine - and amphetamineregulated transcript (CART) and the long isoform of leptin receptor (LepRb) in the hypothalamus and of several genes associated with fatty acid transport to mitochondria and β-oxidation in brown adipose tissue and liver. It suggests that less weight loss is likely to drive more fat accumulation when food restriction ends, in which the impaired function of LepRb, POMC and CART in the brain and fatty acid oxidation in brown adipose tissue and liver may be involved.

Molecular characterization and tissue distribution of carnitine palmitoyltransferases in Chinese mitten crab Eriocheir sinensis and the effect of dietary fish oil replacement on their expression in the hepatopancreas

The carnitine palmitoyltransferase (CPT) family includes CPT 1 and CPT 2 that transport long-chain fatty acids into the mitochondrial compartment for β-oxidation. In this study, three isoforms (CPT 1α, CPT 1β and CPT 2) of the CPT family were cloned from Chinese mitten crab (Eriocheir sinensis) and their complete coding sequences (CDS) were obtained. Sequence analysis revealed deduced amino acid sequences of 915, 775 and 683 amino acids, respectively. Gene expression analysis revealed a broad tissue distribution for all three isoforms, with high CPT 1α and CPT 2 mRNA levels in the hepatopancreas of males and females. In males, CPT 1β was highly expressed in gill, heart, brain ganglia and muscle, while in females, CPT 1β-mRNA levels were relatively high in muscle, hepatopancreas and ovary tissue. The effects of dietary fish oil replacement on the expression of the three CPT isoforms in the hepatopancreas during gonadal development were investigated using five experimental diets formulated with replacement of 0, 25, 50, 75 and 100% fish oil by 1:1 rapeseed oil: soybean oil. The results showed that Diets 2# and 5# yielded higher CPT 1α and CPT 2 mRNA expression in males (P < 0.05), while in females, expression of all three CPT isoforms increased then declined in the hepatopancreas with increasing dietary fish oil replacement. The observed changes in CPT gene expression varied in different isoforms and gender, suggesting the three CPT genes might play different roles in fatty acid β-oxidation in E. sinensis.

Hepatic Lipogenesis and Brain Fatty Acid Profile in Response to Different Dietary n6/n3 Ratios and DHA/EPA Supplementation in Streptozotocin Treated Rats

SCOPE

We investigated the interaction between streptozotocin (STZ)-induced diabetes and dietary n6/n3 ratio, and its influence on lipogenesis.

METHODS AND RESULTS

The animals were treated with STZ and fed with different dietary n6/n3 ratios: 1, 7, and 60, or supplemented with DHA/EPA. Gene expression was assessed by RT-PCR and protein expression by western blotting and immunohistochemistry. Fatty acid profile was determined by GC-MS. Pancreas and liver histology were assessed by hematoxylin and eosin (H&E) staining. STZ-induced characteristic changes in all STZ treated groups, including: increased blood glucose, decreased body mass, increased lipid peroxidation and CD36 expression, decreased 16:1n7 and 18:1n7, increases in 20:3n6, decreases in phospholipid (PL) content of 20:4n6, as well as decreases in the expression of SREBP1c, Δ-9-desaturase (Δ9D), and Δ-5-desaturase (Δ5D). Additionally, other changes occurred that were dependent on the n6/n3 ratio. Among the diabetic groups, the lower n6/n3 ratio caused higher lipid peroxidation and CD36 expression, a greater decrease in 20:4n6 and decreased Δ6-desaturase (Δ6D) expression, while the higher n6/n3 ratio caused increased partitioning of 20:4n6 into hepatic neutral lipids (NL), a decrease in 20:5n3 content, and increased β-oxidation.

CONCLUSION

Presented data suggest that the n6/n3 ratio could significantly influence lipogenesis, lipid peroxidation, and β-oxidation in STZ-induced diabetes, which could have clinical significance.

Cardiac Med1 deletion promotes early lethality, cardiac remodeling, and transcriptional reprogramming

The mediator complex, a multisubunit nuclear complex, plays an integral role in regulating gene expression by acting as a bridge between transcription factors and RNA polymerase II. Genetic deletion of mediator subunit 1 (Med1) results in embryonic lethality, due in large part to impaired cardiac development. We first established that Med1 is dynamically expressed in cardiac development and disease, with marked upregulation of Med1 in both human and murine failing hearts. To determine if Med1 deficiency protects against cardiac stress, we generated two cardiac-specific Med1 knockout mouse models in which Med1 is conditionally deleted (Med1cKO mice) or inducibly deleted in adult mice (Med1cKO-MCM mice). In both models, cardiac deletion of Med1 resulted in early lethality accompanied by pronounced changes in cardiac function, including left ventricular dilation, decreased ejection fraction, and pathological structural remodeling. We next defined how Med1 deficiency alters the cardiac transcriptional profile using RNA-sequencing analysis. Med1cKO mice demonstrated significant dysregulation of genes related to cardiac metabolism, in particular genes that are coordinated by the transcription factors Pgc1α, Pparα, and Errα. Consistent with the roles of these transcription factors in regulation of mitochondrial genes, we observed significant alterations in mitochondrial size, mitochondrial gene expression, complex activity, and electron transport chain expression under Med1 deficiency. Taken together, these data identify Med1 as an important regulator of vital cardiac gene expression and maintenance of normal heart function.NEW & NOTEWORTHY Disruption of transcriptional gene expression is a hallmark of dilated cardiomyopathy; however, its etiology is not well understood. Cardiac-specific deletion of the transcriptional coactivator mediator subunit 1 (Med1) results in dilated cardiomyopathy, decreased cardiac function, and lethality. Med1 deletion disrupted cardiac mitochondrial and metabolic gene expression patterns.

A systems genetics approach identifies Trp53inp2 as a link between cardiomyocyte glucose utilization and hypertrophic response

Cardiac failure has been widely associated with an increase in glucose utilization. The aim of our study was to identify factors that mechanistically bridge this link between hyperglycemia and heart failure. Here, we screened the Hybrid Mouse Diversity Panel (HMDP) for substrate-specific cardiomyocyte candidates based on heart transcriptional profile and circulating nutrients. Next, we utilized an in vitro model of rat cardiomyocytes to demonstrate that the gene expression changes were in direct response to substrate abundance. After overlaying candidates of interest with a separate HMDP study evaluating isoproterenol-induced heart failure, we chose to focus on the gene Trp53inp2 as a cardiomyocyte glucose utilization-specific factor. Trp53inp2 gene knockdown in rat cardiomyocytes reduced expression and protein abundance of key glycolytic enzymes. This resulted in reduction of both glucose uptake and glycogen content in cardiomyocytes stimulated with isoproterenol. Furthermore, this reduction effectively blunted the capacity of glucose and isoprotereonol to synergistically induce hypertrophic gene expression and cell size expansion. We conclude that Trp53inp2 serves as regulator of cardiomyocyte glycolytic activity and can consequently regulate hypertrophic response in the context of elevated glucose content.NEW & NOTEWORTHY Here, we apply a novel method for screening transcripts based on a substrate-specific expression pattern to identify Trp53inp2 as an induced cardiomyocyte glucose utilization factor. We further show that reducing expression of the gene could effectively blunt hypertrophic response in the context of elevated glucose content.

Streptozotocin diabetes increases mRNA expression of ketogenic enzymes in the rat heart

BACKGROUND

Diabetic cardiomyopathy develops in insulin-dependent diabetic patients who have no hypertension, cardiac hypertrophy or vascular disease. Diabetes increases cardiac fatty acid oxidation, but cardiac hypertrophy limits fatty acid oxidation. Here we examined effects of diabetes on gene expression in rat hearts.

METHODS

We used oligonucleotide microarrays to examine effects of insulindependent diabetes in the rat heart. RTQ PCR confirmed results of microarrays. Specific antibodies were used to examine changes in the mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2).

RESULTS

A surprising result of diabetes was increased mRNA encoding all enzymes of the ketone body synthesis pathway. Increased mRNA expression for these enzymes was confirmed by RTQ PCR. The mRNA encoding HMGCS2, the rate-controlling enzyme, was 27 times greater in diabetic hearts. Total HMGCS2 protein increased 8-fold in diabetic hearts, but no difference was found in HMGCS2 protein in control vs. diabetic liver.

CONCLUSIONS

Insulin-dependent diabetes induced the enzymes of ketone body synthesis in the heart, including HMGCS2, as well as increasing enzymes of fatty acid oxidation.

GENERAL SIGNIFICANCE

The mammalian heart does not export ketone bodies to other tissues, but rather is a major consumer of ketone bodies. Induction of HMGCS2, which is normally expressed only in the fetal and newborn heart, may indicate an adaptation by the heart to combat "metabolic inflexibility" by shifting the flux of excess intramitochondrial acetyl-CoA derived from elevated fatty acid oxidation into ketone bodies, liberating free CoA to balance the acetyl-CoA/CoA ratio in favor of increased glucose oxidation through the pyruvate dehydrogenase complex.

Circadian and Dopaminergic Regulation of Fatty Acid Oxidation Pathway Genes in Retina and Photoreceptor Cells

The energy metabolism of the retina might comply with daily changes in energy demand and is impaired in diabetic retinopathy-one of the most common causes of blindness in Europe and the USA. The aim of this study was to investigate putative adaptation of energy metabolism in healthy and diabetic retina. Hence expression analysis of metabolic pathway genes was performed using quantitative polymerase chain reaction, semi-quantitative western blot and immunohistochemistry. Transcriptional profiling of key enzymes of energy metabolism identified transcripts of mitochondrial fatty acid β-oxidation enzymes, i.e. carnitine palmitoyltransferase-1α (Cpt-1α) and medium chain acyl-CoA dehydrogenase (Acadm) to display daily rhythms with peak values during daytime in preparations of the whole retina and microdissected photoreceptors. The cycling of both enzymes persisted in constant darkness, was dampened in mice deficient for dopamine D4 (D4) receptors and was altered in db/db mice-a model of diabetic retinopathy. The data of the present study are consistent with circadian clock-dependent and dopaminergic regulation of fatty acid oxidation in retina and its putative disturbance in diabetic retina.

Molecular characterization and nutritional regulation of carnitine palmitoyltransferase (CPT) family in grass carp (Ctenopharyngodon idellus)

The carnitine palmitoyltransferase (CPT) gene family plays an essential role in fatty acid β-oxidation in the mitochondrion. We identified six isoforms of the CPT family in grass carp and obtained their complete coding sequences (CDS). The isoforms included CPT 1α1a, CPT 1α1b, CPT 1α2a, CPT 1α2b, CPT 1β, and CPT 2, which may have resulted from fish-specific genome duplication. Sequence analysis showed that the predicted protein structure was different among the CPT gene family members in grass carp. The N-terminal domain of grass carp CPT 1α1a, CPT 1α1b, CPT 1α2a, and CPT 1α2b contained two transmembrane region domains and two acyltransferase choActase domains that exist in human and mouse proteins also; however, only one acyltransferase choActase domain was found in grass carp CPT 1β. The grass carp CPT 2 had two acyltransferase choActase domains. The grass carp CPT 1α1b, CPT 1α2a, CPT 1α2b, and CPT 1β contained 18 coding exons, while CPT 1α1a and CPT 2 consisted of 17 coding exons and 5 coding exons, respectively. The mRNA of the six CPT isoforms was expressed in a wide range of tissues, but the mRNA abundance of each CPT showed tissue-dependent expression patterns. The expression of CPT 1α1a, CPT 1α2a, and CPT 1β at 48h post-feeding was significantly increased in the liver (P<0.01, P<0.05, and P<0.01, respectively). The diverse responses of multiple isoforms in the liver during nutritional limitation suggest that they may play different roles in fatty acid β-oxidation.

Effect of DanQi Pill on PPARα, lipid disorders and arachidonic acid pathway in rat model of coronary heart disease

Background

Danqi pill (DQP) is one of the most widely prescribed formulas and has been shown to have remarkable protective effect on coronary heart disease (CHD). However, its regulatory effects on lipid metabolism disorders haven’t been comprehensively studied so far. We aimed to explore the effects of DQP on Peroxisome Proliferator activated receptors α (PPARα), lipid uptake-transportation-metabolism pathway and arachidonic acid (AA)-mediated inflammation pathway in rats with CHD.

Methods

80 Sprague-Dawley (SD) Rats were randomly divided into sham group, model group, positive control group and DQP group. Rat model of CHD was induced by ligation of left ventricle anterior descending artery and fed with high fat diet in all but the sham group. Rats in sham group only underwent thoracotomy. After surgery, rats in the positive control and DQP group received daily treatments of pravastatin and DQP respectively. At 28 days after surgery, rats were sacrificed and plasma lipids were evaluated by plasma biochemical detection. Western blot and PCR were applied to evaluate the expressions of PPARα, proteins involved in lipid metabolism and AA pathways.

Results

Twenty eight days after surgery, dyslipidemia developed in CHD model rats, as illustrated by elevated plasma lipid levels. Expressions of apolipoprotein A-I (ApoA-I), cluster of differentiation 36 (CD36) and fatty acid binding protein (FABP) in the heart tissues of model group were down-regulated compared with those in sham group. Expressions of carnitine palmitoyl transferase I (CPT-1A) and lipoproteinlipase (LPL) were also reduced significantly. In addition, levels of phospholipase A2 (PLA2) and cyclooxygenase 2 (COX-2) were up-regulated. Expressions of Nuclear factor-κB (NF- κB) and signal transducer and activator of transcription 3 (STAT3) also increased. Furthermore, Expression of PPARα decreased in the model group. DQP significantly up-regulated expressions of ApoA-I and FABP, as well as the expressions of CPT-1A and CD36. In addition, DQP down-regulated expressions of PLA2, COX-2 and NF-κB in inflammation pathway. Levels of STAT3 and LPL were not affected by DQP treatment. In particular, DQP up-regulated PPARα level significantly.

Conclusions

DQP could effectively regulate lipid uptake-transportation-metabolism process in CHD model rats, and the effect is achieved mainly by activating ApoA-I-CD36-CPT-1A molecules. Interestingly, DQP can up-regulate expression of PPARα significantly. The anti-inflammatory effect of DQP is partly exerted by inhibiting expressions of PLA2-COX2 -NF-κB pathway.

L-carnitine and PPARα-agonist fenofibrate are involved in the regulation of Carnitine Acetyltransferase (CrAT) mRNA levels in murine liver cells

Background

The carnitine acetyltransferase (CrAT) is a mitochondrial matrix protein that directly influences intramitochondrial acetyl-CoA pools. Murine CrAT is encoded by a single gene located in the opposite orientation head to head to the PPP2R4 gene, sharing a very condensed bi-directional promoter. Since decreased CrAT expression is correlated with metabolic inflexibility and subsequent pathological consequences, our aim was to reveal and define possible activators of CrAT transcription in the normal embryonic murine liver cell line BNL CL. 2 and via which nuclear factors based on key metabolites mainly regulate hepatic expression of CrAT. Here we describe a functional characterization of the CrAT promoter region under conditions of L-carnitine deficiency and supplementation as well as fenofibrate induction in cell culture cells.

Results

The murine CrAT promoter displays some characteristics of a housekeeping gene: it lacks a TATA-box, is very GC-rich and harbors two Sp1 binding sites. Analysis of the promoter activity of CrAT by luciferase assays uncovered a L-carnitine sensitive region within −342 bp of the transcription start. Electrophoretic mobility shift and supershift assays proved the sequence element (−228/-222) to be an L-carnitine sensitive RXRα binding site, which also showed sensitivity to application of anti-PPARα and anti-PPARbp antibodies. In addition we analysed this specific RXRα/PPARα site by Southwestern Blotting technique and could pin down three protein factors binding to this promoter element. By qPCR we could quantify the nutrigenomic effect of L-carnitine itself and fenofibrate.

Conclusions

Our results indicate a cooperative interplay of L-carnitine and PPARα in transcriptional regulation of murine CrAT, which is of nutrigenomical relevance. We created experimental proof that the muCrAT gene clearly is a PPARα target. Both L-carnitine and fenofibrate are inducers of CrAT transcripts, but the important hyperlipidemic drug fenofibrate being a more potent one, as a consequence of its pharmacological interaction.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-514) contains supplementary material, which is available to authorized users.

Cardiac metabolism in heart failure: implications beyond ATP production

The heart has a high rate of ATP production and turnover that is required to maintain its continuous mechanical work. Perturbations in ATP-generating processes may therefore affect contractile function directly. Characterizing cardiac metabolism in heart failure (HF) revealed several metabolic alterations called metabolic remodeling, ranging from changes in substrate use to mitochondrial dysfunction, ultimately resulting in ATP deficiency and impaired contractility. However, ATP depletion is not the only relevant consequence of metabolic remodeling during HF. By providing cellular building blocks and signaling molecules, metabolic pathways control essential processes such as cell growth and regeneration. Thus, alterations in cardiac metabolism may also affect the progression to HF by mechanisms beyond ATP supply. Our aim is therefore to highlight that metabolic remodeling in HF not only results in impaired cardiac energetics but also induces other processes implicated in the development of HF such as structural remodeling and oxidative stress. Accordingly, modulating cardiac metabolism in HF may have significant therapeutic relevance that goes beyond the energetic aspect.

Hypoxic regulation of hand1 controls the fetal-neonatal switch in cardiac metabolism

This study reveals a novel pathway that responds to hypoxia and modulates energy metabolism by cardiomyocytes in the mouse heart, thereby determining oxygen consumption.

Cardiomyocytes are vulnerable to hypoxia in the adult, but adapted to hypoxia in utero. Current understanding of endogenous cardiac oxygen sensing pathways is limited. Myocardial oxygen consumption is determined by regulation of energy metabolism, which shifts from glycolysis to lipid oxidation soon after birth, and is reversed in failing adult hearts, accompanying re-expression of several “fetal” genes whose role in disease phenotypes remains unknown. Here we show that hypoxia-controlled expression of the transcription factor Hand1 determines oxygen consumption by inhibition of lipid metabolism in the fetal and adult cardiomyocyte, leading to downregulation of mitochondrial energy generation. Hand1 is under direct transcriptional control by HIF1α. Transgenic mice prolonging cardiac Hand1 expression die immediately following birth, failing to activate the neonatal lipid metabolising gene expression programme. Deletion of Hand1 in embryonic cardiomyocytes results in premature expression of these genes. Using metabolic flux analysis, we show that Hand1 expression controls cardiomyocyte oxygen consumption by direct transcriptional repression of lipid metabolising genes. This leads, in turn, to increased production of lactate from glucose, decreased lipid oxidation, reduced inner mitochondrial membrane potential, and mitochondrial ATP generation. We found that this pathway is active in adult cardiomyocytes. Up-regulation of Hand1 is protective in a mouse model of myocardial ischaemia. We propose that Hand1 is part of a novel regulatory pathway linking cardiac oxygen levels with oxygen consumption. Understanding hypoxia adaptation in the fetal heart may allow development of strategies to protect cardiomyocytes vulnerable to ischaemia, for example during cardiac ischaemia or surgery.

Regulation of oxygen usage in cardiomyocytes is of great medical interest, because adult cardiac tissue is extremely vulnerable to hypoxia during myocardial infarction and cardiac surgery. While some progress has been made toward protecting cardiomyocytes from hypoxia in these circumstances, it has been limited by a lack of understanding of endogenous oxygen-sensing pathways. In contrast to adult cardiac tissue, embryonic cardiomyocytes are highly resistant to hypoxia, although the mechanisms underlying this have hitherto been unclear. Using mice we show that the transcription factor Hand1 is expressed at high levels in the fetal heart, under direct control of HIF1α signaling, a pathway well known to respond to hypoxia. We show that Hand1 expression decreases at birth as the neonate is exposed to higher levels of oxygen. By experimentally increasing Hand1 expression in the neonatal heart, we see lower oxygen consumption in cardiomyocytes and this is caused by Hand1 repressing key regulatory genes involved in cardiomyocyte lipid metabolism. This has the effect of decreasing mitochondrial ATP generation via the tricarboxylic acid cycle. Furthermore, we show that increasing Hand1 expression in adult transgenic hearts is protective against myocardial infarction, suggesting that a hypoxia–Hand1 pathway may also be of importance in the adult heart.

Nuclear corepressors mediate the repression of phospholipase A2 group IIa gene transcription by thyroid hormone

Secretory phospholipase A2 group IIa (PLA2g2a) is associated with inflammation, hyperlipidemia, and atherogenesis. Transcription of the PLA2g2a gene is induced by multiple cytokines. Here, we report the surprising observation that thyroid hormone (T3) inhibited PLA2g2a gene expression in human and rat hepatocytes as well as in rat liver. Moreover, T3 reduced the cytokine-mediated induction of PLA2g2a, suggesting that the thyroid status may modulate aspects of the inflammatory response. In an effort to dissect the mechanism of repression by T3, we cloned the PLA2g2a gene and identified a negative T3 response element in the promoter. This T3 receptor (TRβ)-binding site differed considerably from consensus T3 stimulatory elements. Using in vitro and in vivo binding assays, we found that TRβ bound directly to the PLA2g2a promoter as a heterodimer with the retinoid X receptor. Knockdown of nuclear corepressor or silencing mediator for retinoid and thyroid receptors by siRNA blocked the T3 inhibition of PLA2g2a. Using chromatin immunoprecipitation assays, we showed that nuclear corepressor and silencing mediator for retinoid and thyroid receptors were associated with the PLA2g2a gene in the presence of T3. In contrast with the established role of T3 to promote coactivator association with TRβ, our experiments demonstrate a novel inverse recruitment mechanism in which liganded TRβ recruits corepressors to inhibit PLA2g2a expression.

Role of sirtuin 1 in the regulation of hepatic gene expression by thyroid hormone

Sirtuin 1 (SIRT1) is a nuclear deacetylase that modulates lipid metabolism and enhances mitochondrial activity. SIRT1 targets multiple transcription factors and coactivators. Thyroid hormone (T(3)) stimulates the expression of hepatic genes involved in mitochondrial fatty acid oxidation and gluconeogenesis. We reported that T(3) induces genes for carnitine palmitoyltransferase (cpt1a), pyruvate dehydrogenase kinase 4 (pdk4), and phosphoenolpyruvate carboxykinase (pepck). SIRT1 increases the expression of these genes via the activation of several factors, including peroxisome proliferator-activated receptor α, estrogen-related receptor α, and peroxisome proliferator-activated receptor γ coactivator (PGC-1α). Previously, we reported that PGC-1α participates in the T(3) induction of cpt1a and pdk4 in the liver. Given the overlapping targets of T(3) and SIRT1, we investigated whether SIRT1 participated in the T(3) regulation of these genes. Resveratrol is a small phenolic compound whose actions include the activation of SIRT1. Addition of resveratrol increased the T(3) induction of the pdk4 and cpt1a genes in hepatocytes. Furthermore, expression of SIRT1 in hepatocytes mimicked resveratrol in the regulation of gene expression by T(3). The deacetylase activity of SIRT1 was required and PGC-1α was deacetylated following addition of T(3). We found that SIRT1 interacted directly with T(3) receptor (TRβ). Knockdown of SIRT1 decreased the T(3) induction of cpt1a and pdk4 and reduced the T(3) inhibition of sterol response element binding protein (srebp-1c) both in isolated hepatocytes and in rat liver. Our results indicate that SIRT1 contributes to the T(3) regulation of hepatic genes.

Serum metabonomics coupled with Ingenuity Pathway Analysis characterizes metabolic perturbations in response to hypothyroidism induced by propylthiouracil in rats

A serum metabonomic profiling method based on ultra-performance liquid chromatography/time-of-flight mass spectrometry (UHPLC/TOF-MS) was applied to investigate the metabolic changes in hypothyroid rats induced by propylthiouracil (PTU). With Significance Analysis of Microarray (SAM) for classification and selection of biomarkers, 13 potential biomarkers in rat serum were screened out. Furthermore, Ingenuity Pathway Analysis (IPA) was introduced to deeply analyze unique pathways of hypothyroidism that were primarily involved in sphingolipid metabolism, fatty acid transportation, phospholipid metabolism and phenylalanine metabolism. Our results demonstrated that the metabonomic approach integrating with IPA was a promising tool for providing a novel methodological clue to systemically dissect the underlying molecular mechanism of hypothyroidism.

Peroxisome proliferator activated receptor alpha (PPARalpha) and PPAR gamma coactivator (PGC-1alpha) induce carnitine palmitoyltransferase IA (CPT-1A) via independent gene elements

Long chain fatty acids and pharmacologic ligands for the peroxisome proliferator activated receptor alpha (PPARalpha) activate expression of genes involved in fatty acid and glucose oxidation including carnitine palmitoyltransferase-1A (CPT-1A) and pyruvate dehydrogenase kinase 4 (PDK4). CPT-1A catalyzes the transfer of long chain fatty acids from acyl-CoA to carnitine for translocation across the mitochondrial membranes and is an initiating step in the mitochondrial oxidation of long chain fatty acids. PDK4 phosphorylates and inhibits the pyruvate dehydrogenase complex (PDC) which catalyzes the conversion of pyruvate to acetyl-CoA in the glucose oxidation pathway. The activity of CPT-1A is modulated both by transcriptional changes as well as by malonyl-CoA inhibition. In the liver, CPT-1A and PDK4 gene expression are induced by starvation, high fat diets and PPARalpha ligands. Here, we characterized a binding site for PPARalpha in the second intron of the rat CPT-1A gene. Our studies indicated that WY14643 and long chain fatty acids induce CPT-1A gene expression through this element. In addition, we found that mutation of the PPARalpha binding site reduced the expression of CPT-1A-luciferase vectors in the liver of fasted rats. We had demonstrated previously that CPT-1A was stimulated by the peroxisome proliferator activated receptor gamma coactivator (PGC-1) via sequences in the first intron of the rat CPT-1A gene. Surprisingly, PGC-1alpha did not enhance CPT-1A transcription through the PPARalpha binding site in the second intron. Following knockdown of PGC-1alpha with short hairpin RNA, the CPT-1A and PDK4 genes remained responsive to WY14643. Overall, our studies indicated that PPARalpha and PGC-1alpha stimulate transcription of the CPT-1A gene through different regions of the CPT-1A gene.

Regulatory enzymes of mitochondrial beta-oxidation as targets for treatment of the metabolic syndrome

Insulin sensitizers like metformin generally act through pathways triggered by adenosine monophosphate-activated protein kinase. Carnitine palmitoyltransferase 1 (CPT1) controls mitochondrial beta-oxidation and is inhibited by malonyl-CoA, the product of acetyl-CoA carboxylase (ACC). The adenosine monophosphate-activated protein kinase-ACC-CPT1 axis tightly regulates mitochondrial long-chain fatty acid oxidation. Evidence indicates that ACC2, the isoform located in close proximity to CPT1, is the major regulator of CPT1 activity. ACC2 as well as CPT1 are therefore potential targets to treat components of the metabolic syndrome such as obesity and insulin resistance. Reversible inhibitors of the liver isoform of CPT1, developed to prevent ketoacidosis and hyperglycemia, have been found to be associated with side effects like hepatic steatosis. However, stimulation of systemic CPT1 activity may be an attractive means to accelerate peripheral fatty acid oxidation and hence improve insulin sensitivity. Stimulation of CPT1 can be achieved by elimination or inhibition of ACC2 activity and through activating transcription factors like peroxisome proliferator-activated receptors and their protein partners. The latter leads to enhanced CPT1 gene expression. Recent developments are discussed, including a recently identified CPT1 isoform, i.e. CPT1C. This protein is highly expressed in the brain and may provide a target for new tools to prevent obesity.

Mass spectrometric demonstration of the presence of liver carnitine palmitoyltransferase-I (CPT-I) in heart mitochondria of adult rats

The carnitine palmitoyltransferase-I (CPT-I) enzymes catalyze the regulated step in overall mitochondrial fatty acid oxidation. The liver and muscle isoforms are expressed in liver and skeletal muscle respectively with the isoforms exhibiting different kinetic properties and apparent molecular weight masses. In contrast, the heart expresses both isoforms at the mRNA level. However, for the expression of the liver isoform at the protein level only indirect evidence is available, such as tagging with radiolabeled CPT-I inhibitors followed by SDS-PAGE separation and kinetic analysis using inhibitors. The importance of fatty acid oxidation in the heart and the potential regulation via the liver isoform of CPT-I demands proof of the liver isoform in the heart. Using a proteomic approach in the present study we demonstrate that rat heart mitochondria (a) contain both the muscle and liver isoforms; (b) both proteins retain their C- and N-termini; (c) the N-terminal alanine residues are acetylated; (d) and in rat heart mitochondria the liver isoform is phosphorylated on tyrosine 281. By providing amino acid sequence information this is the first unequivocal demonstration that the liver isoform of CPT-I is expressed at the protein level in adult rat heart mitochondria and that the apparent smaller molecular size of the muscle isoform is not due to proteolytic truncation.

Maternal dietary L-carnitine supplementation influences fetal carnitine status and stimulates carnitine palmitoyltransferase and pyruvate dehydrogenase complex activities in swine

Effects of increasing maternal L-carnitine on carnitine status and energy metabolism in the fetus were evaluated by feeding pregnant swine a corn-soybean-based diet containing either 0 or 50 mg/kg added L-carnitine (n = 10/treatment) during the first 70 d of gestation. Carnitine, carnitine palmitoyltransferase (CPT), and pyruvate dehydrogenase complex (PDHC) activities were analyzed in tissues collected from fetuses on d 55 and 70. Maternal L-carnitine supplementation increased both fetal free and long-chain carnitine concentrations by 45% in liver and free carnitine by 31% in heart tissues but did not affect kidney tissue. Elevations in free and acylcarnitines increased with gestational age from 55 to 70 d in liver but not in heart and kidney. The increased carnitine concentrations resulted in a 45% increase in PDHC activity in heart and liver on d 70 of gestation but did not affect kidney and liver on d 55 of gestation. The increases in carnitine concentrations were accompanied by a 70% increase in hepatic CPT activity in 70-d-old fetuses, but activities in heart and kidney were unaffected. The Michaelis constant (K(m)) of CPT for carnitine in fetal tissues was not influenced by carnitine supplementation (P > 0.1). Notably, the concentrations of carnitine measured on d 70 were only 25-40% of the K(m) values in liver, 60-70% in heart, and 30-40% in kidney (P < 0.001). We conclude that carnitine ingestion during pregnancy increases fetal carnitine concentrations and stimulates heart PDHC and liver CPT activity without altering carnitine K(m).

Rat liver mitochondrial carnitine palmitoyltransferase-I, hepatic carnitine, and malonyl-CoA: effect of starvation

Hepatic mitochondrial fatty acid oxidation and ketogenesis increase during starvation. Carnitine palmitoyltransferase I (CPT-I) catalyses the rate-controlling step in the overall pathway and retains its control over beta-oxidation under fed, starved and diabetic conditions. To determine the factors contributing to the reported several-fold increase in fatty acid oxidation in perfused livers, we measured the V(max) and K(m) values for palmitoyl-CoA and carnitine, the K(i) (and IC(50)) values for malonyl-CoA in isolated liver mitochondria as well as the hepatic malonyl-CoA and carnitine contents in control and 48 h starved rats. Since CPT-I is localized in the mitochondrial outer membrane and in contact sites, the kinetic properties of CPT-I also was determined in these submitochondrial structures. After 48 h starvation, there is: (a) a significant increase in K(i) and decrease in hepatic malonyl-CoA content; (b) a decreased K(m) for palmitoyl-CoA; and (c) increased catalytic activity (V(max)) and CPT-I protein abundance that is significantly greater in contact sites compared with outer membranes. Based on these changes the estimated increase in mitochondrial fatty acid oxidation is significantly less than that observed in perfused liver. This suggests that CPT-I is regulated in vivo by additional mechanism(s) lost during mitochondrial isolation or/and that mitochondrial oxidation of peroxisomal beta-oxidation products contribute to the increased ketogenesis by bypassing CPT-I. Furthermore, the greater increase in CPT-I protein in contact sites as compared to outer membranes emphasizes the significance of contact sites in hepatic fatty acid oxidation.

Thyroid hormone regulation of heart metabolism

Thyroid hormone regulates cardiac metabolism through multiple mechanisms. Traditionally, most cardiac metabolic studies have focused on presumed transcriptional actions by defining thyroid hormone-induced changes in mRNA or protein levels. Recent studies have established metabolic pathways in heart that rapidly respond to thyroid hormone. Functions have also been implicated for thyroid hormone receptors, which are separate from their transcriptional actions. Finally, thyroid through ligand binding may play a direct role in transactivation of mitochondrial DNA. This review will explore these newly identified modes of thyroid action on metabolism in heart.

Mitochondrial uncoupling protein 3 and its role in cardiac- and skeletal muscle metabolism

Uncoupling protein 3 (UCP3), is primarily expressed in skeletal muscle mitochondria and has been suggested to be involved in mediating energy expenditure via uncoupling, hereby dissipating the mitochondrial proton gradient necessary for adenosine triphosphate (ATP) synthesis. Although some studies support a role for UCP3 in energy metabolism, other studies pointed towards a function in fatty acid metabolism. Thus, the protein is up regulated or high when fatty acid supply to the mitochondria exceeds the capacity to oxidize fatty acids and down regulated or low when oxidative capacity is high or improved. Irrespective of the exact operating mechanism, UCP3 seems to protect mitochondria against lipid-induced oxidative stress, which makes this protein a potential player in the development of type 2 diabetes mellitus. Next to skeletal muscle, UCP3 is also expressed in cardiac muscle where its role is relatively unexplored. Interestingly, energy deficiency in cardiac muscle is associated to heart failure and UCP3 might contribute to this energy deficiency. It has been suggested that UCP3 decreases energy status via uncoupling of mitochondrial respiration, but the available data does not provide a unified answer. In fact, the results obtained regarding cardiac UCP3 are very similar as in skeletal muscle, implying that its physiological function can be extrapolated. Therefore, cardiac UCP3 can just as well serve to protect the heart against lipid-induced oxidative stress, similar to the function described for skeletal muscle UCP3. The present review will deal with the available literature on both skeletal muscle- and cardiac UCP3 to elucidate its physiological function in these tissues.

Hormonal and nutritional regulation of muscle carnitine palmitoyltransferase I gene expression in vivo

Transgenic mice carrying the human heart muscle carnitine palmitoyltransferase I (M-CPTI) gene fused to a CAT reporter gene were generated to study the regulation of M-CPTI gene expression. When the mice were fasted for 48 h, CAT activity and mRNA levels increased by more than 2-fold in heart and skeletal muscle, but not liver or kidney. In the diabetic transgenic mice, there was a 2- to 3-fold increase in CAT activity and CAT mRNA levels in heart and skeletal muscle which upon insulin administration reverted to that observed with the control insulin sufficient transgenic mice. Feeding a high fat diet increased CAT activity and mRNA levels by 2- to 4-fold in heart and skeletal muscle of the transgenic mice compared to the control transgenic mice on regular diet. Overall, the M-CPTI promoter was found to be necessary for the tissue-specific hormonal and dietary regulation of the gene expression.

Regulation of carnitine palmitoyltransferase I (CPT-Ialpha) gene expression by the peroxisome proliferator activated receptor gamma coactivator (PGC-1) isoforms

The peroxisome proliferator activated receptor gamma coactivators (PGC-1) have important roles in mitochondrial biogenesis and metabolic control in a variety of tissues. There are multiple isoforms of PGC-1 including PGC-1alpha and PGC-1beta. Both the PGC-1alpha and beta isoforms promote mitochondrial biogenesis and fatty acid oxidation, but only PGC-1alpha stimulates gluconeogenesis in the liver. Carnitine palmitoyltransferase I (CPT-I) is a key enzyme regulating mitochondrial fatty acid oxidation. In these studies, we determined that PGC-1beta stimulated expression of the "liver" isoform of CPT-I (CPT-Ialpha) but that PGC-1beta did not induce pyruvate dehydrogenase kinase 4 (PDK4) which is a regulator of pyruvate metabolism. The CPT-Ialpha gene is induced by thyroid hormone. We found that T3 increased the expression of PGC-1beta and that PGC-1beta enhanced the T3 induction of CPT-Ialpha. The thyroid hormone receptor interacts with PGC-1beta in a ligand dependent manner. Unlike PGC-1alpha, the interaction of PGC-1beta and the T3 receptor does not occur exclusively through the leucine-X-X-leucine-leucine motif in PGC-1beta. We have found that PGC-1beta is associated with the CPT-Ialpha gene in vivo. Overall, our results demonstrate that PGC-1beta is a coactivator in the T3 induction of CPT-Ialpha and that PGC-1beta has similarities and differences with the PGC-1alpha isoform.

Transcriptomic analysis of the cardiac left ventricle in a rodent model of diabetic cardiomyopathy: molecular snapshot of a severe myocardial disease

Heart disease is the major cause of death in diabetes, a disorder characterized by chronic hyperglycemia and cardiovascular complications. Diabetic cardiomyopathy (DCM) is increasingly recognized as a major contributor to diastolic dysfunction and heart failure in diabetes, but its molecular basis has remained obscure, in part because of its multifactorial origins. Here we employed comparative transcriptomic methods with quantitative verification of selected transcripts by reverse transcriptase quantitative PCR to characterize the molecular basis of DCM in rats with streptozotocin-induced diabetes of 16-wk duration. Diabetes caused left ventricular disease that was accompanied by significant changes in the expression of 1,614 genes, 749 of which had functions assignable by Gene Ontology classification. Genes corresponding to proteins expressed in mitochondria accounted for a disproportionate number of those whose expression was significantly modified in DCM, consistent with the idea that the mitochondrion is a key target of the pathogenic processes that cause myocardial disease in diabetes. Diabetes also induced global perturbations in the expression of genes regulating cardiac fatty acid metabolism, whose dysfunction is likely to play a key role in the promotion of oxidative stress, thereby contributing to the pathogenesis of diabetic myocardial disease. In particular, these data point to impaired regulation of mitochondrial beta-oxidation as central in the mechanisms that generate DCM pathogenesis. This study provides a comprehensive molecular snapshot of the processes leading to myocardial disease in diabetes.

Fatty acid metabolism, the central nervous system, and feeding

A potential role for fatty acid metabolism in the regulation of energy balance in the brain or in the periphery has been considered only recently. Fatty acid synthase (FAS) catalyzes the synthesis of long-chain fatty acids, whereas the breakdown of fatty acids by beta-oxidation is regulated by carnitine palmitoyltransferase-1, the rate-limiting enzyme for the entry of fatty acids into the mitochondria for oxidation. While the question of the physiological role of fatty acid metabolism remains to be resolved, studies indicate that inhibition of FAS or stimulation of carnitine palmitoyltransferase-1 using cerulenin or synthetic FAS inhibitors reduces food intake and incurs profound and reversible weight loss. Several hypotheses regarding the mechanisms by which these small molecules mediate their effects have been entertained. Centrally, these compounds alter the expression of hypothalamic neuropeptides, generally reducing the expression of orexigenic peptides. Whether through central, peripheral, or combined central and peripheral mechanisms, these compounds also increase energy consumption to augment weight loss. In vitro and in vivo studies indicate that at least part of C75's effects is mediated by modulation of adenosine monophosphate-activated protein kinase, a member of an energy-sensing kinase family. These compounds, with chronic treatment, also alter gene expression peripherally to favor a state of enhanced energy consumption. Together, these effects raise the possibility that pharmacological alterations in fatty acid synthesis/degradation may serve as a target for obesity therapeutics.

Effects of insulin-like growth factor-I on the maturation of metabolism in neonatal rat cardiomyocytes

Myocardial metabolism shifts during the perinatal period from predominant utilization of glucose towards oxidation of fatty acids. Expression of enzymes of the fatty acid oxidation (FAO) pathway is under the control of the nuclear receptor/transcription factor peroxisome proliferator-activated receptor alpha (PPARalpha). Insulin-like Growth Factor-I (IGF-I) plays an important role in the post-natal growth and differentiation of the heart. We determined the influence of IGF-I on the maturation of myocardial metabolism. In neonatal rat cardiac myocytes, expression of the FAO enzymes MCAD and M-CPT I was induced by treatment with the specific PPARalpha agonist WY-14643. Concomitant treatment with IGF-I enhanced the expression of both FAO enzymes. By comparison, treatment with FGF-2, which is required for myocyte differentiation of cardiac precursors, did not increase WY-14643-induced expression of FAO enzymes. Despite stimulation of FAO enzyme expression, IGF-I did not further enhance WY-14643-stimulated palmitate oxidation. In contrast, IGF-I relieved WY-14643-mediated inhibition of glucose uptake and promoted storage of fatty acids into cellular neutral lipids. In conclusion, IGF-I promotes a more mature pattern of FAO gene expression but, because of insulin-like metabolic effects, does not concomitantly enhance oxidation of fatty acids.

Thyroid hormone controls myocardial substrate metabolism through nuclear receptor-mediated and rapid posttranscriptional mechanisms

Thyroid hormone regulates metabolism through transcriptional and posttranscriptional mechanisms. The integration of these mechanisms in heart is poorly understood. Therefore, we investigated control of substrate flux into the citric acid cycle (CAC) by thyroid hormone using retrogradely perfused isolated hearts (n = 20) from control (C) and age-matched thyroidectomized rats (T). We determined substrate flux and fractional contributions (Fc) to the CAC by 13C-NMR spectroscopy and isotopomer analyses in hearts perfused with [1,3-(13)C]acetoacetic acid (0.17 mM), L-[3-(13)C]lactic acid (LAC, 1.2 mM), [U-13C]long-chain mixed free fatty acids (FFA, 0.35 mM), and unlabeled glucose. Some T hearts were supplied triiodothyronine (T3, 10 nM; TT) for 60 min. Prolonged hypothyroid state reduced myocardial oxygen consumption, although T3 produced no significant change. Hypothyroidism reduced overall CAC(flux) but selectively altered only FFA(flux) among the individual substrates, though LAC(flux) trended upward. T3 rapidly decreased lactate Fc and flux. 13C labeling of glutamine through glutamate was increased in T with further enhancement in TT. The glutamate-to-glutamine ratio was significantly lower in T and TT. Immunoblots detected a decrease in hypothyroid hearts for muscle carnitine palmitoyltransferase I (CPT I) and a marked increase in pyruvate dehydrogenase kinase (PDK)-2 with no changes in liver CPT I, PDK-4, or hexokinase 2. TT, but not T, displayed elevated glutamine synthetase (GS) expression. These studies showed that T3 regulates cardiac metabolism through integration of several mechanisms, including changes in oxidative enzyme content and rapid modulation of individual substrates fluxes. T3 also moderates forward glutamine flux, possibly by increasing the overall activity of GS.

Cloning of the rat pyruvate dehydrogenase kinase 4 gene promoter: activation of pyruvate dehydrogenase kinase 4 by the peroxisome proliferator-activated receptor gamma coactivator

The pyruvate dehydrogenase complex catalyzes the conversion of pyruvate to acetyl-CoA in mitochondria and is a key regulatory enzyme in the metabolism of glucose to acetyl-CoA. Phosphorylation of pyruvate dehydrogenase by the pyruvate dehydrogenase kinases (PDK) inhibits pyruvate dehydrogenase complex activity. There are four PDK isoforms, and expression of PDK4 and PDK2 genes is elevated in starvation and diabetes, allowing glucose to be conserved while fatty acid oxidation is increased. In these studies we have investigated the transcriptional mechanisms by which the expression of the PDK4 gene is increased. The peroxisome proliferator-activated receptor gamma coactivator (PGC-1alpha) stimulates the expression of genes involved in hepatic gluconeogenesis and mitochondrial fatty acid oxidation. We have found that PGC-1alpha will induce the expression of both the PDK2 and PDK4 genes in primary rat hepatocytes and ventricular myocytes. We cloned the promoter for the rat PDK4 gene. Hepatic nuclear factor 4 (HNF4), which activates many genes in the liver, will induce PDK4 expression. Although HNF4 and PGC-1alpha interact to stimulate several genes encoding gluconeogenic enzymes, the induction of PDK4 does not involve interactions of PGC-1alpha with HNF4. Using the chromatin immunoprecipitation assay, we have demonstrated that HNF4 and PGC-1alpha are associated with the PDK4 gene in vivo. Our data suggest that by inducing PDK genes PGC-1alpha will direct pyruvate away from metabolism into acetyl-CoA and toward the formation of oxaloacetate and into the gluconeogenic pathway.

Fatty acid metabolism is enhanced in type 2 diabetic hearts

The metabolic phenotype of hearts has been investigated using rodent models of type 2 diabetes which exhibit obesity and insulin resistance: db/db and ob/ob mice, and Zucker fatty and ZDF rats. In general, cardiac fatty acid (FA) utilization is enhanced in type 2 diabetic hearts, with increased rates of FA oxidation (db/db, ob/ob and ZDF models) and increased FA esterification into cellular triacylglycerols (db/db hearts). Hearts from db/db and ob/ob mice and ZDF rat hearts all have elevated levels of myocardial triacylglycerols, consistent with enhanced FA utilization. A number of mechanisms may be responsible for enhanced FA utilization in type 2 diabetic hearts: (i) increased FA uptake into cardiac myocytes and into mitochondria; (ii) altered mitochondrial function, with up-regulation of uncoupling proteins; and (iii) stimulation of peroxisome proliferator-activated receptor-alpha. Enhanced cardiac FA utilization in rodent type 2 diabetic models is associated with reduced cardiac contractile function, perhaps as a consequence of lipotoxicity and/or reduced cardiac efficiency. Similar results have been obtained with human type 2 diabetic hearts, suggesting that pharmacological interventions that can reduce cardiac FA utilization may have beneficial effects on contractile function.

Peroxisomal proliferator activated receptor gamma coactivator (PGC-1alpha) stimulates carnitine palmitoyltransferase I (CPT-Ialpha) through the first intron

Peroxisomal proliferator activated receptor gamma coactivator-1 (PGC-1alpha) is a transcriptional coactivator that promotes mitochondrial biogenesis and energy metabolism in brown fat, skeletal muscle and heart. Previous studies demonstrated that PGC-1alpha is present at low levels in the liver but that the hepatic abundance of PGC-1alpha is elevated in diabetic and fasted animals. Elevated PGC-1alpha expression is associated with increased fatty acid oxidation and hepatic glucose production. Carnitine palmitoyltransferase-I (CPT-I) is a rate controlling step in the mitochondrial oxidation of long chain fatty acids. CPT-I transfers the acyl moiety from fatty acyl-CoA to carnitine for the translocation of long chain fatty acids across the mitochondrial membrane. There are two isoforms of CPT-I including a liver isoform CPT-Ialpha and a muscle isoform CPT-Ibeta. Here, we characterized the regulation of CPT-Ialpha isoform by PGC-1alpha. PGC-1alpha stimulates CPT-Ialpha primarily through multiple sites in the first intron. We found that PGC-1alpha can induce CPT-Ialpha gene expression in cardiac myocytes and primary hepatocytes. Our results indicate that PGC-1alpha elevates the expression of CPT-Ialpha via a unique mechanism that utilizes elements within the intron.

Expression of genes participating in regulation of fatty acid and glucose utilization and energy metabolism in developing rat hearts

The heart is a unique organ that can use several fuels for energy production. During development, the heart undergoes changes in fuel supply, and it must be able to respond to these changes. We have examined changes in the expression of several genes that regulate fuel transport and metabolism in rat hearts during early development. At birth, there was increased expression of fatty acid transporters and enzymes of fatty acid metabolism that allow fatty acids to become the major source of energy for cardiac muscle during the first 2 wk of life. At the same time, expression of genes that control glucose transport and oxidation was downregulated. After 2 wk, expression of genes for glucose uptake and oxidation was increased, and expression of genes for fatty acid uptake and utilization was decreased. Expression of carnitine palmitoyltransferase I (CPT I) isoforms during development was different from published data obtained from rabbit hearts. CPT Iα and Iβ isoforms were both highly expressed in hearts before birth, and both increased further at birth. Only after the second week did CPT Iα expression decrease appreciably below the level of CPT Iβ expression. These results represent another example of different expression patterns of CPT I isoforms among various mammalian species. In rats, changes in gene expression followed nutrient availability during development and may render cardiac fatty acid oxidation less sensitive to factors that influence malonyl-CoA content (e.g., fluctuations in glucose concentration) and thereby favor fatty acid oxidation as an energy source for cardiomyocytes in early development.

Peroxisomal proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1 alpha) enhances the thyroid hormone induction of carnitine palmitoyltransferase I (CPT-I alpha)

Carnitine palmitoyltransferase I (CPT-I) catalyzes the rate-controlling step in the pathway of mitochondrial fatty acid oxidation. Thyroid hormone will stimulate the expression of the liver isoform of CPT-I (CPT-I alpha). This induction of CPT-I alpha gene expression requires the thyroid hormone response element in the promoter and sequences within the first intron. The peroxisomal proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1 alpha) is a coactivator that promotes mitochondrial biogenesis, mitochondrial fatty acid oxidation, and hepatic gluconeogenesis. In addition, PGC-1 alpha will stimulate the expression of CPT-I alpha in primary rat hepatocytes. Here we report that thyroid hormone will increase PGC-1 alpha mRNA and protein levels in rat hepatocytes. In addition, overexpression of PGC-1 alpha will enhance the thyroid hormone induction of CPT-I alpha indicating that PGC-1 alpha is a coactivator for thyroid hormone. By using chromatin immunoprecipitation assays, we show that PGC-1 alpha is associated with both the thyroid hormone response element in the CPT-I alpha gene promoter and the first intron of the CPT-I alpha gene. Our data demonstrate that PGC-1 alpha participates in the stimulation of CPT-I alpha gene expression by thyroid hormone and suggest that PGC-1 alpha is a coactivator for thyroid hormone.

Nondiabetic ketoacidosis caused by severe hyperthyroidism

Severe hyperthyroidism is not included in the traditional differential diagnosis of ketoacidosis. However, thyroid hormone has well-documented lipolytic effects on adipocytes and may also promote hepatic beta-oxidation. We present a case in which a woman with severe hyperthyroidism developed otherwise unexplained ketoacidosis during the acute phase of her illness. We propose that thyrotoxicosis was a significant contributor to ketoacidosis in this patient and that severe hyperthyroidism should be added to the differential diagnosis of ketoacidosis.

Myocardial carnitine palmitoyltransferase I expression and long-chain fatty acid oxidation in fetal and newborn lambs

Carnitine palmitoyltransferase I (CPT I) catalyzes the conversion of acyl-CoA to acylcarnitine at the outer mitochondrial membrane and is a key enzyme in the control of long-chain fatty acid (LC-FA) oxidation. Because myocardial LC-FA oxidation increases dramatically after birth, we determined the extent to which CPT I expression contributes to these changes in the perinatal lamb. We measured the steady-state level of transcripts of the CPT1A and CPT1B genes, which encode the liver (L-CPT I) and muscle CPT I (M-CPT I) isoforms, respectively, as well as the amount of these proteins, their total activity, and the amount of carnitine in left ventricular tissue from fetal and newborn lambs. We compared these data with previously obtained myocardial FA oxidation rates in vivo in the same model. The results showed that CPT1B was already expressed before birth and that total CPT I expression transiently increased after birth. The protein level of M-CPT I was high throughout development, whereas that of L-CPT I was only transiently upregulated in the first week after birth. The total CPT I activity in vitro also increased after birth. However, the increase in myocardial FA oxidation measured in vivo (112-fold) by far exceeded the increase in gene expression (2.2-fold), protein amount (1.1-fold), and enzyme activity (1.2-fold) in vitro. In conclusion, these results stress the importance of substrate supply per se in the postnatal increase in myocardial FA oxidation. M-CPT I is expressed throughout perinatal development, making it a primary target for metabolic modulation of myocardial FA oxidation.

Expression of three carnitine palmitoyltransferase-I isoforms in 10 regions of the rat brain during feeding, fasting, and diabetes

Inhibition of carnitine palmitoyltransferase-I (CPT-I) activity in the brain has been shown to decrease food intake in rats. We examined the expression of mRNA encoding all three known CPT-I isoforms (alpha, beta, and gamma in 10 different major regions of the rat brain in normal, chow-fed rats, in fasting rats, and in insulin-dependent diabetic rats. Compared with the effects of fasting and diabetes on CPT-I mRNA in the liver and heart, there was either less effect or no effect depending on the particular brain region examined. These results suggest that the regulation of CPT-I mRNA levels is different in the brain than in other tissues. A surprising result of this study was the discovery of very high, unique expression of CPT-Ibeta (the muscle isoform) in the cerebellum.

Cloning and expression of the liver and muscle isoforms of ovine carnitine palmitoyltransferase 1: residues within the N-terminus of the muscle isoform influence the kinetic properties of the enzyme

The nucleotide sequence data reported will appear in DDBJ, EMBL, GenBank(R) and GSDB Nucleotide Sequence Databases; the sequences of ovine CPT1A and CPT1B cDNAs have the accession numbers Y18387 and AJ272435 respectively and the partial adipose tissue and liver CPT1A clones have the accession numbers Y18830 and Y18829 respectively. Fatty acid and ketone body metabolism differ considerably between monogastric and ruminant species. The regulation of the key enzymes involved may differ accordingly. Carnitine palmitoyltransferase 1 (CPT 1) is the key locus for the control of long-chain fatty acid beta-oxidation and liver ketogenesis. Previously we showed that CPT 1 kinetics in sheep and rat liver mitochondria differ. We cloned cDNAs for both isoforms [liver- (L-) and muscle- (M-)] of ovine CPT 1 in order to elucidate the structural features of these proteins and their genes ( CPT1A and CPT1B ). Their deduced amino acid sequences show a high degree of conservation compared with orthologues from other mammalian species, with the notable exception of the N-terminus of ovine M-CPT 1. These differences were also present in bovine M-CPT 1, whose N-terminal sequence we determined. In addition, the 5'-end of the sheep CPT1B cDNA suggested a different promoter architecture when compared with previously characterized CPT1B genes. Northern blotting revealed differences in tissue distribution for both CPT1A and CPT1B transcripts compared with other species. In particular, ovine CPT1B mRNA was less tissue restricted, and the predominant transcript in the pancreas was CPT1B. Expression in yeast allowed kinetic characterization of the two native enzymes, and of a chimaera in which the distinctive N-terminal segment of ovine M-CPT 1 was replaced with that from rat M-CPT 1. The ovine N-terminal segment influences the kinetics of the enzyme for both its substrates, such that the K (m) for palmitoyl-CoA is decreased and that for carnitine is increased for the chimaera, relative to the parental ovine M-CPT 1.

Upstream stimulatory factor represses the induction of carnitine palmitoyltransferase-Ibeta expression by PGC-1

Transcriptional regulation of carnitine palmitoyltransferase-1beta (CPT-1beta) is coordinated with contractile gene expression through cardiac-enriched transcription factors, GATA4 and SRF. Metabolic modulation of CPT-1beta promoter activity has been described with the stimulation of gene expression by oleate that is mediated through the peroxisome proliferator-activated receptor (PPAR) pathway. The coactivator, peroxisomal proliferator-activated receptor gamma coactivator (PGC-1), enhances gene expression through interactions with nuclear hormone receptors and the myocyte enhancer factor 2 (MEF2) family. PGC-1 and MEF2A synergistically activate CPT-1beta promoter activity. This stimulation is enhanced by mutation of the E-box sequences that flank the MEF2A binding site. These elements bind the upstream stimulatory factors (USF1 and USF2), which activate transcription in CV-1 fibroblasts. However, overexpression of the USF proteins in myocytes depresses CPT-1beta activity and significantly reduces MEF2A and PGC-1 synergy. Co-immunoprecipitation studies demonstrate that PGC-1 and USF2 proteins can physically interact. Our studies demonstrate that PGC-1 stimulates CPT-1beta gene expression through MEF2A. USF proteins have a novel role in repressing the expression of the CPT-1beta gene and modulating the induction by the coactivator, PGC-1.

A thyroid hormone response unit formed between the promoter and first intron of the carnitine palmitoyltransferase-Ialpha gene mediates the liver-specific induction by thyroid hormone

Carnitine palmitoyltransferase-I (CPT-I) catalyzes the rate-controlling step of fatty acid oxidation. CPT-I converts long-chain fatty acyl-CoAs to acylcarnitines for translocation across the mitochondrial membrane. The mRNA levels and enzyme activity of the liver isoform, CPT-Ialpha, are greatly increased in the liver of hyperthyroid animals. Thyroid hormone (T3) stimulates CPT-Ialpha transcription far more robustly in the liver than in non-hepatic tissues. We have shown that the thyroid hormone receptor (TR) binds to a thyroid hormone response element (TRE) located in the CPT-Ialpha promoter. In addition, elements in the first intron participate in the T3 induction of CPT-Ialpha gene expression, but the CPT-Ialpha intron alone cannot confer a T3 response. We found that deletion of sequences in the first intron between +653 and +744 decreased the T3 induction of CPT-Ialpha. Upstream stimulatory factor (USF) and CCAAT enhancer binding proteins (C/EBPs) bind to elements within this region, and these factors are required for the T3 response. The binding of TR and C/EBP to the CPT-Ialpha gene in vivo was shown by the chromatin immunoprecipitation assay. We determined that TR can physically interact with USF-1, USF-2, and C/EBPalpha. Transgenic mice were created that carry CPT-Ialpha-luciferase transgenes with or without the first intron of the CPT-Ialpha gene. In these mouse lines, the first intron is required for T3 induction as well as high levels of hepatic expression. Our data indicate that the T3 stimulates CPT-Ialpha gene expression in the liver through a T3 response unit consisting of the TRE in the promoter and additional factors, C/EBP and USF, bound in the first intron.