Fatty Acids For Energy Production Research Articles

Stimulation of neutral lipid synthesis via viral growth factor signaling and ATP citrate lyase during vaccinia virus infection.

Fatty acid metabolism can provide various products essential for viral infections. How vaccinia virus (VACV), the prototype of poxviruses, modulates fatty acid metabolism is not well understood. Here, we show that VACV infection results in increased neutral lipid droplet synthesis, the organelles that play a crucial role in storing and mobilizing fatty acids for energy production via β-oxidation. Citrate is the first tricarboxylic acid (TCA) cycle intermediate that can be transported to the cytosol to be converted to acetyl-CoA for de novo fatty acid biosynthesis. We found that VACV infection stimulates the S455 phosphorylation of ATP citrate lyase (ACLY), a pivotal enzyme that links citrate metabolism with lipid metabolism. We demonstrate that the inhibition of neutral lipid droplet synthesis and ACLY severely suppresses VACV replication. Remarkably, we found that virus growth factor (VGF)-induced signaling is essential for the VACV-mediated upregulation of ACLY phosphorylation and neutral lipid droplets. Finally, we report that VGF-induced EGFR-Akt pathway and ACLY phosphorylation are important for VACV stimulation of neutral lipid synthesis. These findings identified a new way of rewiring cell metabolism by a virus and a novel function for VGF in the governance of virus-host interactions through the induction of a key enzyme at the crossroads of the TCA cycle and fatty acid metabolism. Our study also provides a mechanism for the role played by VGF and its downstream signaling cascades in the modulation of lipid metabolism in VACV-infected cells.IMPORTANCENeutral lipid droplets are vital players in cellular metabolism. Here, we showed that VACV induces neutral lipid droplet synthesis in infected primary human foreskin fibroblasts and identified the cellular and viral factors needed. We identified VACV encoded growth factor (VGF) as an essential viral factor that induces cellular EGFR-Akt signaling to increase lipid droplets. Interestingly, VACV increases the S455 phosphorylation of ACLY, a key metabolic enzyme that sits at the crossroads of carbohydrate and lipid metabolism in a VGF-EGFR-Akt-dependent manner. We also found that ACLY is vital for VACV-induced lipid droplet synthesis. Our findings identified the modulation of ACLY by a virus and identified it as a potential target for antiviral development against pathogenic poxviruses. Our study also expands the role of growth factor signaling in boosting VACV replication by targeting fatty acid metabolism.

Inhibition of Drp1-Filamin Protein Complex Prevents Hepatic Lipid Droplet Accumulation by Increasing Mitochondria-Lipid Droplet Contact.

Lipid droplet (LD) accumulation in hepatocytes is one of the major symptoms associated with fatty liver disease. Mitochondria play a key role in catabolizing fatty acids for energy production through β-oxidation. The interplay between mitochondria and LD assumes a crucial role in lipid metabolism, while it is obscure how mitochondrial morphology affects systemic lipid metabolism in the liver. We previously reported that cilnidipine, an already existing anti-hypertensive drug, can prevent pathological mitochondrial fission by inhibiting protein-protein interaction between dynamin-related protein 1 (Drp1) and filamin, an actin-binding protein. Here, we found that cilnidipine and its new dihydropyridine (DHP) derivative, 1,4-DHP, which lacks Ca2+ channel-blocking action of cilnidipine, prevent the palmitic acid-induced Drp1-filamin interaction, LD accumulation and cytotoxicity of human hepatic HepG2 cells. Cilnidipine and 1,4-DHP also suppressed the LD accumulation accompanied by reducing mitochondrial contact with LD in obese model and high-fat diet-fed mouse livers. These results propose that targeting the Drp1-filamin interaction become a new strategy for the prevention or treatment of fatty liver disease.

ACSM1 and ACSM3 Regulate Fatty Acid Metabolism to Support Prostate Cancer Growth and Constrain Ferroptosis.

Solid tumors are highly reliant on lipids for energy, growth, and survival. In prostate cancer, the activity of the androgen receptor (AR) is associated with reprogramming of lipid metabolic processes. Here, we identified acyl-CoA synthetase medium chain family members 1 and 3 (ACSM1 and ACSM3) as AR-regulated mediators of prostate cancer metabolism and growth. ACSM1 and ACSM3 were upregulated in prostate tumors compared with nonmalignant tissues and other cancer types. Both enzymes enhanced proliferation and protected prostate cancer cells from death in vitro, whereas silencing ACSM3 led to reduced tumor growth in an orthotopic xenograft model. ACSM1 and ACSM3 were major regulators of the prostate cancer lipidome and enhanced energy production via fatty acid oxidation. Metabolic dysregulation caused by loss of ACSM1/3 led to mitochondrial oxidative stress, lipid peroxidation, and cell death by ferroptosis. Conversely, elevated ACSM1/3 activity enabled prostate cancer cells to survive toxic levels of medium chain fatty acids and promoted resistance to ferroptosis-inducing drugs and AR antagonists. Collectively, this study reveals a tumor-promoting function of medium chain acyl-CoA synthetases and positions ACSM1 and ACSM3 as key players in prostate cancer progression and therapy resistance. Significance: Androgen receptor-induced ACSM1 and ACSM3 mediate a metabolic pathway in prostate cancer that enables the utilization of medium chain fatty acids for energy production, blocks ferroptosis, and drives resistance to clinically approved antiandrogens.

Probiotic-Derived Heptelidic Acid Demonstrates Therapeutic Efficacy Against Pediatric B-Cell Acute Lymphoblastic Leukemia

Introduction Pediatric B-cell acute lymphoblastic leukemia (B-ALL) is known to be sensitive to chemotherapy. However, approximately 15-20% of pediatric B-ALL patients experience relapse, and survival rates after relapse can drop to 5-10%. Therefore, new drugs need to be developed. Probiotics are live microorganisms with potential health benefits. Heptelidic acid (HA) from the probiotic Aspergillus oryzae has been shown to exert antitumor effects against pancreatic cancer, lung cancer, thyroid cancer, breast cancer and melanoma in vivo as well as in vitro. In this study, we assessed the antitumor effects of HA in B-ALL, which is the most common type of pediatric cancer. Methods Two B-ALL cell lines (JM1 and Reh), four CD34 + hematopoietic stem cells (HSCs) and three high-risk patient-derived B-ALL cells (s90: age < 1 year old, s96: age > 10 years old, s98: relapse) collected from the spleen or bone marrow of a patient-derived xenograft (PDX) model were used in this study. Cytotoxicity of HA was assessed by MTS assay. GAPDH activity and intracellular ATP contents were measured, as HA binds to cysteine 152 of GAPDH, a crucial region for its enzymatic activity and ATP production in glycolysis. The synergistic effects of HA with therapeutics, vincristine (VCR), doxorubicin (DXR) and L-asparaginase (L-Asp), were evaluated. GAPDH is involved not only in glucose metabolism but also in amino acid and fatty acids for energy production. Therefore, we analyzed whether HA exerted cytotoxicity under glucose, amino acid or fatty acid-deprived conditions in Reh cells. To analyze the underlying mechanism for HA's cytotoxicity against B-ALL, cell cycle analysis by flowcytometry, western blotting of cleaved PARP, caspase assays, and inhibitory assays using specific inhibitors for PCD mechanisms, such as RIPK-1 inhibitor, MLKL inhibitor, and autophagy inhibitor, were conducted. In vivo studies were done using a B-ALL PDX model. Oral administration of 0.5mg/kg HA was carried out for 21 days, while intraperitoneal injection of 0.15mg/kg VCR was performed once per week for 3 cycles in the HA-VCR combinational therapeutic efficacy study. Results HA exhibited significant cytotoxicity in JM1 (IC50: 169 ng/ml), Reh (IC50: 126.5 ng/ml), and three samples obtained from PDX mice (s90 IC50: 66.6 ng/ml, s96 IC50: 89.9 ng/ml, and s98 IC50: 275.6 ng/ml), while sparing CD34 + HSCs. GAPDH activity of CD34+ HSCs was significantly lower than both B-ALL cell lines and patient-derived cells. The cytotoxic effect of HA was associated with the reduction of GAPDH activity and ATP contents, suggesting glycolysis inhibition. Glucose deprivation induced significant reduction of cell viability, and HA showed the cytotoxicity in amino acid and fatty acid deprived media in Reh cells. Oral daily administration of HA prolonged the survival of the B-ALL PDX mice (34.5 days, n=8) compared to control mice (28 days, n=7) without causing body weight loss (p<0.05) (Figure 1A). The effects of over 0.5mg/kg of HA was confirmed by the reduction in GAPDH activity observed in leukemia cells isolated from the bone marrow. HA demonstrated synergistic effects when combined with chemotherapeutic agents, especially VCR. The combination therapy of HA and VCR resulted in improved survival outcomes in the B-ALL PDX model (49 days, n=5) compared to single-agent treatments (HA: 28 days, n=5, VCR: 40 days, n=5) and control groups (26 days, n=5) (p<0.05) (Figure 1B). Mechanistic studies revealed that HA induced PCD in B-ALL cells. HA treatment caused G2/M arrest (Control: 18.8%, HA: 27.6% in JM1; Control: 13.3%, HA: 18.3% in Reh), and this was accompanied by increased cleavage of PARP, a hallmark of PCD, in both cell lines. Moreover, the cytotoxicity of HA was attenuated by RIPK1 inhibition in JM1 and Reh. Conclusion We have demonstrated that B-ALL cells utilize glucose for their survival and HA is cytotoxic in B-ALL cells by disrupting glycolysis through the inhibition of GAPDH. The therapeutic efficacy of HA is further enhanced when combined with chemotherapeutic agents. The underlying mechanisms of HA involve the induction of RIPK-1 mediated PCD. This is the first study to demonstrate HA as a novel therapeutic agent for B-ALL.

A new strategy for screening novel functional genes involved in reduction of lipid droplet accumulation.

Lipid droplets (LDs) are organelles that store excess lipids and provide fatty acids for energy production during starvation. LDs are also essential for cellular maintenance, but excessive accumulation of LDs triggers various cancers in addition to metabolic diseases such as diabetes. In this study, we aimed to develop a strategy to identify new genes that reduces accumulation of LDs in cancer cells using an RNA interference (RNAi) screening system employing artificial sequence-enriched shRNA libraries. Monitoring LDs by fluorescent activated cell sorting, the subsequently collected cumulative LDs cells, and shRNA sequence analysis identified a clone that potentially functioned to accumulate LDs. The clone showed no identical sequence to human Refseq. It showed very similar sequence to seven genes by allowing three mismatches. Among these genes, we identified the mediator complex subunit 6 (MED6) gene as a target of this shRNA. Silencing of MED6 led to an increase in LD accumulation and expression of the marker genes, PLIN2 and DGAT1, in fatty cells. MED6 is a member of the mediator complex that regulates RNA polymerase II transcription through transcription factor II. Some mediator complexes play important roles in both normal and pathophysiological transcription processes. These results suggest that MED6 transcriptionally regulates the genes involved in lipid metabolism and suppresses LD accumulation.

Increased cardiac PFK-2 protects against high-fat diet-induced cardiomyopathy and mediates beneficial systemic metabolic effects

A healthy heart adapts to changes in nutrient availability and energy demands. In metabolic diseases like type 2 diabetes (T2D), increased reliance on fatty acids for energy production contributes to mitochondrial dysfunction and cardiomyopathy. A principal regulator of cardiac metabolism is 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2), which is a central driver of glycolysis. We hypothesized that increasing PFK-2 activity could mitigate cardiac dysfunction induced by high-fat diet (HFD). Wild type (WT) and cardiac-specific transgenic mice expressing PFK-2 (GlycoHi) were fed a low fat or HFD for 16weeks to induce metabolic dysfunction. Metabolic phenotypes were determined by measuring mitochondrial bioenergetics and performing targeted quantitative proteomic and metabolomic analysis. Increasing cardiac PFK-2 had beneficial effects on cardiac and mitochondrial function. Unexpectedly, GlycoHi mice also exhibited sex-dependent systemic protection from HFD, including increased glucose homeostasis. These findings support improving glycolysis via PFK-2 activity can mitigate mitochondrial and functional changes that occur with metabolic syndrome.

Links between autophagy and lipid droplet dynamics.

Autophagy is a catabolic process in which cytoplasmic components are delivered to vacuoles or lysosomes for degradation and nutrient recycling. Autophagy-mediated degradation of membrane lipids provides a source of fatty acids for the synthesis of energy-rich, storage lipid esters such as triacylglycerol (TAG). In eukaryotes, storage lipids are packaged into dynamic subcellular organelles, lipid droplets. In times of energy scarcity, lipid droplets can be degraded via autophagy in a process termed lipophagy to release fatty acids for energy production via fatty acid β-oxidation. On the other hand, emerging evidence suggests that lipid droplets are required for the efficient execution of autophagic processes. Here, we review recent advances in our understanding of metabolic interactions between autophagy and TAG storage, and discuss mechanisms of lipophagy. Free fatty acids are cytotoxic due to their detergent-like properties and their incorporation into lipid intermediates that are toxic at high levels. Thus, we also discuss how cells manage lipotoxic stresses during autophagy-mediated mobilization of fatty acids from lipid droplets and organellar membranes for energy generation.

The FABP12/PPARγ pathway promotes metastatic transformation by inducing epithelial-to-mesenchymal transition and lipid-derived energy production in prostate cancer cells.

Early stage localized prostate cancer (PCa) has an excellent prognosis; however, patient survival drops dramatically when PCa metastasizes. The molecular mechanisms underlying PCa metastasis are complex and remain unclear. Here, we examine the role of a new member of the fatty acid-binding protein (FABP) family, FABP12, in PCa progression. FABP12 is preferentially amplified and/or overexpressed in metastatic compared to primary tumors from both PCa patients and xenograft animal models. We show that FABP12 concurrently triggers metastatic phenotypes (induced epithelial-to-mesenchymal transition (EMT) leading to increased cell motility and invasion) and lipid bioenergetics (increased fatty acid uptake and accumulation, increased ATP production from fatty acid β-oxidation) in PCa cells, supporting increased reliance on fatty acids for energy production. Mechanistically, we show that FABP12 is a driver of PPARγ activation which, in turn, regulates FABP12's role in lipid metabolism and PCa progression. Our results point to a novel role for a FABP-PPAR pathway in promoting PCa metastasis through induction of EMT and lipid bioenergetics.

Untargeted UPLC-MS metabolomics reveals multiple changes of urine composition in healthy adult volunteers after consumption of curcuma longa L. extract.

Curcuma longa L. is used as food supplement to prevent diseases, although limited studies have been performed on healthy subjects up to now. In the present work, an untargeted UPLC-MS metabolomics approach was applied to study the changes of 24-hours urinary composition on healthy volunteers due to a 28-days daily consumption of a dried C. longa extract containing a standardized amount of curcuminoids. Changes in the excretion of different metabolites were observed after supplementation. Curcumin and two metabolic derivatives (hexahydrocurcumin and dihydrocurcumin) were detected in urine, indicating the absorption of the main curcuminoid from the extract and its further metabolism by liver and gut microbiota. For the first time ar-turmerone, the main apolar constituent of curcuma, was detected in urine in intact form, and its presence was confirmed by a targeted GC-MS analysis. The increase of tetranor-PGJM and tetranor-PGDM, two prostaglandin-D2 metabolites, was observed, being related to the anti-inflammatory effect exerted by curcuma. The variation of the amounts of HPAG, PAG, proline-betaine and hydroxyphenyllactic acid indicate that the supplementation induced changes to the activity of gut microbiota. Finally, the reduced excretion of niacin metabolites (nicotinuric acid, trigonelline and 2PY) and medium- and short-chain acylcarnitines suggests that curcuma could induce the mitochondrial β-oxidation of fatty acids for energy production in healthy subjects. Overall, the results indicate that a prolonged daily consumption of a dried curcuma extract exerts multiple effects on healthy subjects, furthermore they show the opportunity offered by untargeted metabolomics for the study of the bioactivity of natural extracts in healthy human volunteers.

Diversion of Carbon Flux from Sugars to Lipids Improves the Growth of an Arabidopsis Starchless Mutant.

Inactivation of ADP-glucose pyrophosphorylase1 (ADG1) causes a starchless phenotype in Arabidopsis. Mutants defective in ADG1 show severe growth retardation in day/night conditions but exhibit similar growth to wild type under continuous light, implying that starch plays an important role in supporting respiration, metabolism and growth at night. In addition to carbohydrates, lipids and proteins can serve as alternative respiratory substrates for the energy production in mature plants. To test the role of lipids in plant growth, we generated transgenic plants overexpressing phospholipid:diacylglycerol acyltransferase1 (PDAT1) in adg1. We found that PDAT1 overexpression caused an increase in both fatty acid synthesis and turnover and increased the accumulation of triacylglycerol (TAG) at the expense of sugars, and enhanced the growth of adg1. We demonstrated that unlike sugars, which were metabolized within a few hours of darkness, TAG breakdown was slow, occurring throughout the entire dark period. The slow pace of TAG hydrolysis provided a sustained supply of fatty acids for energy production, thereby alleviating energy deficiency at night and thereby improving the growth of the starchless mutants. We conclude that lipids can contribute to plant growth by providing a constant supply of fatty acids as an alternative energy source in mature starchless mutant plants.

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SUN-077 In Utero Growth Restriction Induces an Early Metabolic Shift in Fetal Rat Heart

Adverse uterine environment may expose newborns to develop metabolic diseases later in their life. The in-utero growth restriction (IUGR) is an immediate outcome of a sub-optimal womb environment, where the fetus cannot reach its full growth potential. We have developed an animal model of IUGR based on a low-sodium diet given to dams during the last week of gestation. We showed that the isocaloric low-sodium diet reduces maternal blood volume expansion, causing poor placental perfusion, low placental weight and subsequent IUGR in offspring. Redistribution of blood flow in the fetus was observed, causing a preferential perfusion to major organs, such as the heart. Consistent with this, adult offspring showed an increase in blood pressure and remodeling of cardiomyocytes occurs in adult female, suggesting metabolic changes in cardiac function. In this study, we address whether the IUGR induced-stress leads to metabolic changes in fetal cardiomyocytes to adapt their energy-production process and lipid utilization. At 22 days of gestation, hearts were collected from IUGR and control fetuses, and homogenized. Gene expression profile as well as protein levels were analyzed. We observed an increased expression of critical genes involved in lipid metabolism, such as long chain fatty acid receptor CD36, carnitine palmitoyltransferase CPT1a, and also key enzymes of long chain fatty acid beta-oxidation in IUGR heart. In addition, our results indicate an increase in mitochondrial biogenesis. To address whether changes in lipid metabolite profile might prevail, we performed lipidomic MS analysis in heart homogenates. Lipidomics showed significant accumulation of very long and long-chain fatty acids in the context of IUGR and when comparing males and females. These changes could be reminiscent of an adaptation in the use of fatty acids for energy production. Altogether, these findings suggest that fetal IUGR cardiac cells may rely more on the use of lipids as an energy source, compared to same age control cells. Such alterations in energy metabolism in fetal IUGR cardiomyocytes are consistent with an early metabolic shift to favor lipids as the main energy source. This shift normally occurs in the neonatal life to adapt to an extra-uterine environment. Therefore, our findings suggest that adaptation to an altered placental perfusion results in an early cardiac metabolic remodeling that might predispose individuals to metabolic disorders later in their life. Sources of Research Support: Fond de Recherche Québécois en Santé (FRQS) and Canadian Institutes of Health Research (CIHR).

L-カルニチンの食餌性給与は歩行運動を付加したラットの エネルギー合成に対する長鎖脂肪酸の均等利用を誘起する

L-カルニチンの食餌性給与は歩行運動を付加したラットの エネルギー合成に対する長鎖脂肪酸の均等利用を誘起する

Embryonic lethality in mice due to carnitine transporter OCTN2 defect and placental carnitine deficiency

l-Carnitine plays a crucial role in uptake and subsequent β-oxidation of long-chain fatty acids in the mitochondria. Placental trophoblast cells oxidize long-chain fatty acids for energy production. Here we present data showing that l-carnitine deficiency due to a defect in the carnitine transporter OCTN2 (SLC22A5) in a mouse model leads to embryonic lethality. Placental levels of l-carnitine are reduced to <10% of normal and deficiency of l-carnitine is associated with markedly reduced expression of several growth factors and transforming growth factor β (TGF-β) genes. This report links for the first time reduced l-carnitine levels in the placenta to embryonic lethality.

Anesthetic Management of a Patient With Carnitine-Acylcarnitine Translocase Deficiency

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare disorder of mitochondrial fatty acid metabolism that results in an acute encephalopathic and/or myopathic disorder. Carnitine and CACT play an essential role in the transport of fatty acids into the mitochondria. The deficiency leads to the reduced transport of long-chain fatty acids into the mitochondria, thereby limiting the use of fatty acids for energy production especially during prolonged fasting, febrile illnesses, increased muscular activity, and other periods of systemic stress. We present the anesthetic management of a 10-year-old girl, diagnosed with CACT deficiency at birth, who presented for multiple osteotomies. The preoperative evaluation of such patients is presented, previous reports of anesthetic care are reviewed, and options for intraoperative care are discussed. J Med Cases. 2018;9(5):127-130 doi: https://doi.org/10.14740/jmc3044w

Anesthetic Management of a Patient With Carnitine-Acylcarnitine Translocase Deficiency

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare disorder of mitochondrial fatty acid metabolism that results in an acute encephalopathic and/or myopathic disorder. Carnitine and CACT play an essential role in the transport of fatty acids into the mitochondria. The deficiency leads to the reduced transport of long-chain fatty acids into the mitochondria, thereby limiting the use of fatty acids for energy production especially during prolonged fasting, febrile illnesses, increased muscular activity, and other periods of systemic stress. We present the anesthetic management of a 10-year-old girl, diagnosed with CACT deficiency at birth, who presented for multiple osteotomies. The preoperative evaluation of such patients is presented, previous reports of anesthetic care are reviewed, and options for intraoperative care are discussed. J Med Cases. 2018;9(5):127-130 doi: https://doi.org/10.14740/jmc3044w

Dietary Supplementation with L-Carnitine Induces Equal Utilization of Long-Chain Fatty Acids for Energy Production in Rats Trained with Walking

Dietary Supplementation with LCarnitine Induces Equal Utilization of Long-Chain Fatty Acids for Energy Production in Rats Trained with Walking The present experiment was conducted to evaluate the effects of L-carnitine supplementation on the fatty acid composition of epididymal adipose tissue and femoral muscle in rats trained with walking. The rats were assigned to four groups receiving dietary treatments to evaluate the effects of supplementation with 0 ppm L-carnitine or 50 ppm L-carnitine in combination with two types of exercise: free moving and walking (4 h/day at a speed of 840 m/h). L-carnitine supplementation significantly increased its level in the blood plasma. There was a main effect of L-carnitine supplementation on body weight gain and blood plasma triglyceride level, with both parameters reduced by L-carnitine supplementation. The results of the fatty acid composition analysis revealed that walking reduced the C16:0 level, resulting in a low total saturated fatty acid (SFA) proportion. Dietary L-carnitine suppressed the decrease in the C16:0 proportion observed in the walking group and accelerated the use of fatty acids for energy production so that it was the same as in the control condition. There was no specific relation between L-carnitine and fatty acid type. In conclusion, the current results suggest that dietary supplementation with L-carnitine reversed the unbalanced fatty acid degradation caused by walking without L-carnitine supplementation.

Incretin-related drug therapy in heart failure.

The new pharmacological classes of GLP-1 agonists and DPP-4 inhibitors are now widely used in diabetes and have been postulated as beneficial in heart failure. These proposed benefits arise from the inter-related pathophysiologies of diabetes and heart failure (diabetes increases the risk of heart failure, and heart failure can induce insulin resistance) and also in light of the dysfunctional myocardial energetics seen in heart failure. The normal heart utilizes predominantly fatty acids for energy production, but there is some evidence to suggest that increased myocardial glucose uptake may be beneficial for the failing heart. Thus, GLP-1 agonists, which stimulate glucose-dependent insulin release and enhance myocardial glucose uptake, have become a focus of investigation in both animal models and humans with heart failure. Limited pilot data for GLP-1 agonists shows potential improvements in systolic function, hemodynamics, and quality of life, forming the basis for current phase II trials.

Rapid Inhibition of Pyruvate Dehydrogenase: An Initiating Event in High Dietary Fat-Induced Loss of Metabolic Flexibility in the Heart

Cardiac function depends on the ability to switch between fatty acid and glucose oxidation for energy production in response to changes in substrate availability and energetic stress. In obese and diabetic individuals, increased reliance on fatty acids and reduced metabolic flexibility are thought to contribute to the development of cardiovascular disease. Mechanisms by which cardiac mitochondria contribute to diet-induced metabolic inflexibility were investigated. Mice were fed a high fat or low fat diet for 1 d, 1 wk, and 20 wk. Cardiac mitochondria isolated from mice fed a high fat diet displayed a diminished ability to utilize the glycolytically derived substrate pyruvate. This response was rapid, occurring within the first day on the diet, and persisted for up to 20 wk. A selective increase in the expression of pyruvate dehydrogenase kinase 4 and inhibition of pyruvate dehydrogenase are responsible for the rapid suppression of pyruvate utilization. An important consequence is that pyruvate dehydrogenase is sensitized to inhibition when mitochondria respire in the presence of fatty acids. Additionally, increased expression of pyruvate dehydrogenase kinase 4 preceded any observed diet-induced reductions in the levels of glucose transporter type 4 and glycolytic enzymes and, as judged by Akt phosphorylation, insulin signaling. Importantly, diminished insulin signaling evident at 1 wk on the high fat diet did not occur in pyruvate dehydrogenase kinase 4 knockout mice. Dietary intervention leads to a rapid decline in pyruvate dehydrogenase kinase 4 levels and recovery of pyruvate dehydrogenase activity indicating an additional form of regulation. Finally, an overnight fast elicits a metabolic response similar to that induced by high dietary fat obscuring diet-induced metabolic changes. Thus, our data indicate that diet-induced inhibition of pyruvate dehydrogenase may be an initiating event in decreased oxidation of glucose and increased reliance of the heart on fatty acids for energy production.

Alteration of cardiac glucose metabolism in association to low birth weight: Experimental evidence in lambs with left ventricular hypertrophy

ObjectiveIntrauterine growth restriction that results in low birth weight (LBW) has been linked to the onset of pathological cardiac hypertrophy. An altered transition from a fetal to an adult energy metabolism phenotype, with increased reliance on glucose rather than fatty acids for energy production, could help explain this connection. We have therefore investigated cardiac metabolism in relation to left ventricular hypertrophy in LBW lambs, at 21days after birth. Materials/MethodsThe expression of regulatory molecules involved in cardiac glucose and fatty acid metabolism was measured using real-time PCR and Western blotting. A section of the left ventricle was fixed for Periodic Acid Schiff staining to determine tissue glycogen content. ResultsThere was increased abundance of insulin signalling pathway proteins (phospho-insulin receptor, insulin receptor and phospho-Akt) and the glucose transporter (GLUT)-1, but no change in GLUT-4 or glycogen content in the heart of LBW compared to ABW lambs. There was, however, increased abundance of cardiac pyruvate dehydrogenase kinase 4 (PDK-4) in LBW compared to ABW lambs. There were no significant changes in the mRNA expression of components of the peroxisome proliferator activated receptor regulatory complex or proteins involved in fatty acid metabolism. ConclusionWe concluded that LBW induced left ventricular hypertrophy was associated with increased GLUT-1 and PDK-4, suggesting increased glucose uptake, but decreased efficacy for the conversion of glucose to ATP. A reduced capacity for energy conversion could have significant implications for vulnerability to cardiovascular disease in adults who are born LBW.