Fatty Acid Beta-oxidation Enzymes Research Articles

Dysregulated lipid metabolism is associated with kidney allograft fibrosis

BackgroundInterstitial fibrosis and tubular atrophy (IF/TA), a histologic feature of kidney allograft destruction, is linked to decreased allograft survival. The role of lipid metabolism is well-acknowledged in the area of chronic kidney diseases; however, its role in kidney allograft fibrosis is still unclarified. In this study, how lipid metabolism contributes to kidney allografts fibrosis was examined.MethodsA comprehensive bioinformatic comparison between IF/TA and normal kidney allograft in the Gene Expression Omnibus (GEO) database was conducted. Further validations through transcriptome profiling or pathological staining of human recipient biopsy samples and in rat models of kidney transplantation were performed. Additionally, the effects of enhanced lipid metabolism on changes in the fibrotic phenotype induced by TGF-β1 were examined in HK-2 cell.ResultsIn-depth analysis of the GEO dataset revealed a notable downregulation of lipid metabolism pathways in human kidney allografts with IF/TA. This decrease was associated with increased level of allograft rejection, inflammatory responses, and epithelial mesenchymal transition (EMT). Pathway enrichment analysis showed the downregulation in mitochondrial LC-fatty acid beta-oxidation, fatty acid beta-oxidation (FAO), and fatty acid biosynthesis. Dysregulated fatty acid metabolism was also observed in biopsy samples from human kidney transplants and in fibrotic rat kidney allografts. Notably, the areas affected by IF/TA had increased immune cell infiltration, during which increased EMT biomarkers and reduced CPT1A expression, a key FAO enzyme, were shown by immunohistochemistry. Moreover, under TGF-β1 induction, activating CPT1A with the compound C75 effectively inhibited migration and EMT process in HK-2 cells.ConclusionsThis study reveal a critical correlation between dysregulated lipid metabolism and kidney allograft fibrosis. Enhancing lipid metabolism with CPT1A agonists could be a therapeutic approach to mitigate kidney allografts fibrosis.

Proteomics reveals defective peroxisomal fatty acid oxidation during the progression of acute kidney injury and repair

Acute kidney injury (AKI) is characterized by a rapid decrease in renal function with high mortality and risk of progression to chronic kidney disease (CKD). Ischemia and reperfusion injury (IRI) is one of the major causes of AKI. However, the cellular and molecular responses of the kidney to IRI are complex and not fully understood. Herein, we conducted unbiased proteomics and bioinformatics analyses in an IRI mouse model on days 3, 7, and 21, and validated the results using IRI, unilateral ureteral obstruction (UUO), and biopsies from patients with AKI or CKD. The results indicated an obvious temporal expression profile of differentially expressed proteins and highlighted impaired lipid metabolism during the progression of AKI to CKD. Acyl-coenzyme A oxidase 1 (Acox1), the first rate-limiting enzyme of peroxisomal fatty acid beta-oxidation, was then selected, and its disturbed expression in the two murine models validated the proteomic findings. Accordingly, Acox1 expression was significantly downregulated in renal biopsies from patients with AKI or CKD, and its expression was negatively correlated with kidney injury score. Furthermore, in contrast to the decreased Acox1 expression, lipid droplet accumulation was remarkably increased in these renal tissues, suggesting dysregulation of fatty acid oxidation. In conclusion, our results suggest that defective peroxisomal fatty acid oxidation might be a common pathological feature in the transition from AKI to CKD, and that Acox1 is a promising intervention target for kidney injury and repair.

Abstract 4852: Metabolomic rewiring in endocrine therapy resistant estrogen receptor positive breast cancer

Abstract Breast cancer (BC) is one of the most commonly diagnosed cancers worldwide and the most common in women in the United States. The majority of the BC are estrogen receptor alpha positive (ER+) and are likely to respond to endocrine therapy. Tamoxifen and fulvestrant are the most widely used hormonal treatments for ER+ BC. However, nearly half of patients receiving endocrine therapy suffer from the risk of recurrence due to either intrinsic or acquired resistance. Thus, it is vital to understand the mechanisms of resistance to endocrine therapy in ER+ BC. Metabolic reprogramming is one of the significant hallmarks of cancer and it is now known that many tumors utilize mitochondrial oxidative phosphorylation (OXPHOS) for their energy needs. Our lab previously reported that metastatic triple-negative breast cancer (TNBC), which does not express ER, has a high energy dependency on mitochondrial fatty acid beta-oxidation (FAO). In this project, we developed a gene signature by integrating the transcriptomic, metabolomic, and lipidomic data from FAO rate-limiting gene (CPT1) modulated TNBC cells. Our signature represented the FAO-regulated gene set relevant to metabolic or lipidomic changes. We discovered a significant reliance on this TNBC signature in endocrine-resistant ER+ BC. Clinical data suggests that our gene signature predicts the survival of endocrine-treated ER+ BC patients. Though increased fatty acid consumption is reported in tamoxifen-resistant cells, the role of FAO in endocrine treatment resistance is largely unclear. We then analyzed the metabolic reprogramming in ER+ BC cell lines after tamoxifen or fulvestrant therapy. Molecular, genetic, and metabolic analyses suggested that endocrine therapy-induce AMPK-FAO-OXPHOS signal activation in ER+ BC cells. Furthermore, the knockdown of CPT1, the rate-limiting enzyme of FAO, or treatment with FAO inhibitors significantly enhanced the response to endocrine therapies. We have also reported that FAO induces the autophosphorylation of the c-Src proto-oncogene in TNBC tumors. Thus, we analyzed this phenomenon in the endocrine-resistant ER+ BC cells. As expected, endocrine therapy-induced FAO activated the Src pathway in ER+ BC also. Moreover, in vitro, and in vivo studies confirmed that endocrine-resistant ER+ BC cells have increased sensitivity to FAO, OXPHOS, and Src inhibitors. Finally, analysis of clinical data suggests that low expression of FAO rate-limiting genes in the ER+ primary tumors have better recurrence-free and distant metastasis-free survival after endocrine therapy. Overall, our findings suggest that the gene signature generated from FAO-modulated TNBC cells predicts response to endocrine therapy in ER+ BC. Moreover, metabolic reprogramming in endocrine-resistant ER+ tumors induce FAO, OXPHOS, and Src pathways, providing potential targets to overcome endocrine-resistance ER+ BC patients. Citation Format: Songyeon Ahn, Junhyoung Park, Sandra L. Grimm, Badrajee WB Piyarathna, Nagireddy Putluri, Gokul Das, Cristian Coarfa, Benny A. Kaipparettu. Metabolomic rewiring in endocrine therapy resistant estrogen receptor positive breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4852.

The Regulators of Peroxisomal Acyl-Carnitine Shuttle CROT and CRAT Promote Metastasis in Melanoma

Circulating tumor cells (CTCs) are the key link between a primary tumor and distant metastases, but once in the bloodstream loss of adhesion induces cell death. To identify mechanisms relevant for melanoma CTC survival we performed RNAseq and discovered that detached melanoma cells and isolated melanoma CTCs rewire lipid metabolism by up-regulating fatty acid transport and fatty acid beta-oxidation (FAO) related genes. In melanoma patients high expression of fatty acid transporters and FAO enzymes significantly correlates with reduced progression free and overall survival. Amongst the highest expressed regulators in melanoma CTCs were the carnitine-transferases CROT and CRAT, which control the shuttle of peroxisome derived medium-chain fatty acids (MCFAs) towards mitochondria to fuel mitochondrial FAO. Knockdown of CROT or CRAT and short-term treatment with peroxisomal or mitochondrial FAO inhibitors thioridazine or ranolazine suppressed melanoma metastasis in mice. CROT and CRAT depletion could be rescued by MCFA supplementation, indicating that the peroxisomal supply of fatty acids is crucial for the survival of non-adherent melanoma cells. Our study identifies targeting the fatty acid based cross-talk between peroxisomes and mitochondria as a potential therapeutic opportunity to challenge melanoma progression. Moreover, the discovery of the anti-metastatic activity of the FDA-approved drug ranolazine carries translational potential.

Altered adipose tissue macrophage populations in people with HIV on integrase inhibitor-containing antiretroviral therapy.

Objective:Antiretroviral therapy (ART) extends the life of people with HIV (PWH), but these individuals are at increased risk for obesity, dyslipidemia, diabetes, and cardiovascular disease. These comorbidities may be a consequence of HIV-related chronic inflammation and/or adverse effects of ART on tissue regulatory adipose tissue macrophages (ATMs). We sought to determine the effects of HIV/ART on metabolically beneficial ATM populations and functions.Design:We examined subcutaneous ATMs from PWH on integrase inhibitor-containing ART (n = 5) and uninfected persons (n = 9). We complemented these studies with ex vivo and in vitro analyses of peripheral blood mononuclear cell (PBMC) and murine macrophage lipid metabolism and fatty acid oxidation gene expression.Methods:ATM populations were examined by flow cytometry. Macrophage lipid metabolism and fatty acid oxidation gene expression were examined by Seahorse assay and quantitative PCR.Results:Adipose tissue from PWH had reduced populations of metabolically activated CD9+ ATMs compared to that of uninfected controls (P < 0.001). PBMCs of PWH had lower fatty acid metabolism compared to those of uninfected controls (P < 0.01). Analysis of murine macrophages revealed that dolutegravir reduced lipid metabolism (P < 0.001) and increased expression of the fatty acid beta-oxidation enzyme enoyl-CoA hydratase, short chain 1 (P < 0.05).Conclusions:We report the loss of metabolically beneficial ATM populations in PWH on ART, altered fatty acid metabolism of blood immune cells, and evidence that dolutegravir alters macrophage fatty acid metabolism. Future studies should examine direct or indirect effects and mechanisms of dolutegravir, and other integrase inhibitors and ART classes, on fatty acid beta-oxidation.

HADHB, a fatty acid beta-oxidation enzyme, is a potential prognostic predictor in malignant lymphoma

In haematological malignancies, such as malignant lymphoma, reprogramming of fatty acid metabolism favours tumour cell survival and drug resistance. Hydroxyacyl-CoA dehydrogenase trifunctional multienzyme complex subunit alpha (HADHA), an enzyme involved in fatty acid beta-oxidation (FAO), is overexpressed in high-grade lymphoma and is a predictor of poor prognosis in diffuse large B-cell lymphoma (DLBCL). HADHB forms a heterodimer with HADHA and functions as an FAO enzyme together with HADHA; however, the relevance of its expression in malignant lymphoma is unknown. In this study, we investigated the roles and antitumour effects of HADHB expression in malignant lymphoma. Immunohistochemical analysis showed that HADHB was frequently overexpressed in the high-grade lymphoma subtype. HADHB overexpression was observed in 68% (87/128) of DLBCL cases and was an independent predictor of poor prognosis (p=0.001). Invitro analysis demonstrated that HADHB knockdown suppressed cell proliferation in LCL-K and MD901 cells (p<0.05). Additionally, treatment with the FAO inhibitor, ranolazine, increased cell death in control cells compared with that in HADHB knockdown LCL-K and MD901 cells (p<0.01). Cell death was also suppressed by the ferroptosis inhibitor, ferrosatin-1, in LCL-K and MD901 cells (p<0.05). Collectively, these findings provide basic evidence for the development of new cell death-based therapies for refractory malignant lymphoma. We plan to perform prospective studies and preclinical studies using animal models to confirm these results.

Fatty acid beta oxidation enzyme HADHA is a novel potential therapeutic target in malignant lymphoma

Cancer cells, including malignant lymphoma cells, alter their metabolism, termed “metabolic reprograming,” on initiation of malignant transformation as well as upon accumulation of genetic abnormalities. Here, to identify a novel therapeutic target involved in the metabolic changes during malignant lymphoma, we performed global analyses combined with shotgun proteomics, in silico database analysis, and clinic-pathologic analysis of nonneoplastic lymphoid tissue and malignant lymphoma tissue and verified the molecular functions in vitro. In total, 2002 proteins were detected from both samples and proteins related to fatty acid beta-oxidation (FAO) were detected more frequently in malignant lymphoma tissue. Consequently, the most frequently detected protein, the mitochondrial trifunctional enzyme subunit-alpha (HADHA), was identified as a potential target. Immunohistochemical analyses revealed that HADHA tended to be overexpressed in a high-grade subtype of malignant lymphoma tissue. Clinicopathologic study revealed that HADHA overexpression was correlated with significantly worse overall survival (P= 0.013) and was an independent prognostic predictor in diffuse large B-cell lymphoma (P= 0.027). In vitro, downregulation of HADHA negatively regulated cell growth by causing G0/G1 arrest (P= 0.0008) similar to treatment with etomoxir, an inhibitor of FAO (P= 0.032). Moreover, downregulation of HADHA increased the susceptibility to doxorubicin (P= 0.002) and etoposide (P= 0.004). Moreover, these phenotypes were confirmed in an HADHA knockout system. Thus, we provide a basis for a novel therapeutic strategy through the regulation of HADHA and FAO in patients with refractory malignant lymphoma.

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).

Targeting Myocardial Metabolism for the Treatment of Stable Angina

The goals of pharmacological treatment of stable angina pectoris are to improve quality of life by reducing the severity and/or frequency of symptoms and also the long-term prognosis. Patients with coronary artery disease have viable but dysfunctional myocardium. The metabolism of the ischemic myocardium is characterized by a shift from fatty acid to glucose as a preferred substrate and a decline in the levels of ATP. Targeting myocardial metabolism as a pharmacologic approach for chronic angina is based on the concept that metabolic adaptive mechanisms during ischemia resemble fetal energy metabolism by shifting substrate use towards glucose metabolism. Potential pharmacologic approaches should target i) the suppression of lipolysis and the plasma fatty acid levels and subsequent uptake and oxidation by the heart, ii) direct inhibition of the enzymes of fatty acid beta-oxidation, iii) inhibition of carnitine palmitoyl transferase- I (CPT-1). Currently, there are no approved medications directly targeting myocardial metabolism. However, in the last two years a number of medications indirectly targeting cardiac metabolism have been tested in small clinical trials, and some of them appear to be promising potential therapies for stable angina. This review summarizes the main aspects of myocardial metabolism and focuses on the therapeutic approaches that could offer clinical benefit in patients with stable angina.

Global transcriptome analysis of Atlantic cod (Gadus morhua) liver after in vivo methylmercury exposure suggests effects on energy metabolism pathways

Methylmercury (MeHg) is a widely distributed contaminant polluting many aquatic environments, with health risks to humans exposed mainly through consumption of seafood. The mechanisms of toxicity of MeHg are not completely understood. In order to map the range of molecular targets and gain better insights into the mechanisms of toxicity, we prepared Atlantic cod (Gadus morhua) 135k oligonucleotide arrays and performed global analysis of transcriptional changes in the liver of fish treated with MeHg (0.5 and 2mg/kg of body weight) for 14days. Inferring from the observed transcriptional changes, the main pathways significantly affected by the treatment were energy metabolism, oxidative stress response, immune response and cytoskeleton remodeling. Consistent with known effects of MeHg, many transcripts for genes in oxidative stress pathways such as glutathione metabolism and Nrf2 regulation of oxidative stress response were differentially regulated. Among the differentially regulated genes, there were disproportionate numbers of genes coding for enzymes involved in metabolism of amino acids, fatty acids and glucose. In particular, many genes coding for enzymes of fatty acid beta-oxidation were up-regulated. The coordinated effects observed on many transcripts coding for enzymes of energy pathways may suggest disruption of nutrient metabolism by MeHg. Many transcripts for genes coding for enzymes in the synthetic pathways of sulphur containing amino acids were also up-regulated, suggesting adaptive responses to MeHg toxicity. By this toxicogenomics approach, we were also able to identify many potential biomarker candidate genes for monitoring environmental MeHg pollution. These results based on changes on transcript levels, however, need to be confirmed by other methods such as proteomics.

1-Butanol synthesis by Escherichia coli cells through butyryl-CoA formation by heterologous enzymes of clostridia and native enzymes of fatty acid β-oxidation

Anaerobic biosynthesis of 1-butanol from glucose is investigated in recombinant Escherichia coli strains which form butyryl-CoA using the heterologous enzyme complex of clostridia or as a result of a reversal in the action of native enzymes of the fatty acid beta-oxidation pathway. It was revealed that when the basic pathways of acetic and lactic acid formation are inactivated due to deletions in the ackA, pta, poxB, and ldhA genes, the efficiency of butyryl-CoA biosynthesis and its reduced product, i.e., 1-butanol, by two types of recombinant stains is comparable. The limiting factor for 1-butanol production by the obtained strains is the low substrate specificity of the basic CoA-dependent alcohol/aldehyde AdhE dehydrogenase from E. coli to butyryl-CoA. It was concluded that, in order to construct an efficient 1-butanol producer based on a model strain synthesizing butyryl-CoA as a result of a reversal in fatty acid beta-oxidation enzymes, it is necessary to provide intensive formation of acetyl-CoA and enhanced activity of alternative alcohol and aldehyde dehydrogenases in the cells of a strain.

Upregulation of Fatty Acyl-CoA Thioesterases in the Heart and Skeletal Muscle of Rats Fed a High-Fat Diet

In rodent models of diet-induced obesity, prolonged high-fat feeding increases the cellular uptake of fatty acids and causes lipotoxicity in the heart and skeletal muscle, where substrate overload to beta-oxidation generates mitochondrial stress. We examined the hypothesis that, because of its catalytic properties, acyl-CoA thioesterase (ACOT) would counteract these detrimental situations by modulating intracellular acyl-CoA levels. Rats were fed a low- or high-fat diet for up to 20 weeks, and the expressions of ACOT isoforms and fatty acid beta-oxidation enzymes were analyzed by western blotting. The expressions of ACOT1, ACOT2 and ACOT7 proteins in the heart and soleus muscle were significantly increased, by 2.0-7.6-fold, in rats fed the high-fat diet as compared with the low-fat diet group. These effects were accompanied by increases in carnitine palmitoyltransferase and acyl-CoA oxidase expression. However, ACOT was not induced in the extensor digitorum longus muscle or the liver. Subcellular fractionation of heart and soleus muscle homogenates confirmed expression of both the cytosolic and mitochondrial ACOT isoforms. These results underscore the functional relationship between ACOT and fatty acid oxidation, and suggest adaptive upregulation of ACOT to protect against fatty acid oversupply in the heart and skeletal muscle.

Anti-obese property of fucoxanthin is partly mediated by altering lipid-regulating enzymes and uncoupling proteins of visceral adipose tissue in mice.

This study investigated the anti-obesity effects of fucoxanthin in diet-induced obesity mice fed a high-fat diet (20% fat, wt/wt). The mice were supplemented with two doses of fucoxanthin (0.05 and 0.2%, wt/wt) for 6 wk. Fucoxanthin significantly lowered body weight and visceral fat-pads weights compared with the control group without altering food intake. In epididymal adipose tissue of fucoxanthin-fed mice, adipocyte sizes and mRNA expression of lipogenic and fatty acid beta-oxidation enzymes were significantly altered in a dose-dependent manner. Plasma leptin level was significantly lower in the fucoxanthin groups than in the control group, while the adiponectin level was elevated. Fucoxanthin significantly down-regulated various lipogenic enzyme activities in epididymal adipose tissue with a simultaneous decrease in fatty acid beta-oxidation activity. The 0.2% fucoxanthin supplement led to increase mRNA expression of uncoupling protein-1 (UCP-1) and UCP-3 in brown adipose tissue and that of UCP-2 in the epididymal white adipose tissue. However, the 0.05% fucoxanthin only elevated UCP-1 mRNA expression in epididymal white adipose tissue. These results suggest that the anti-obesity effect of fucoxanthin could be mediated by altering lipid-regulating enzymes and UCPs in the visceral fat tissues and plasma adipokine levels.

Immunohistochemical and DNA microarray analysis of rat retinal Müller cells

Gene expression and localization of nutrient‐metabolizing enzymes in retinal Müller cells were examined in order to clarify the meaning of fatty acid beta‐oxidation in the retina. Adult rat retinal tissues and isolated Müller cells from the retina were subjected to western blot analysis, immuno‐fluorescent microscopy and immuno‐electron microscopy for mitochondrial fatty acid beta‐oxidation enzymes. Gene expression of fatty acid beta‐oxidation enzymes and related nutrient‐metabolizing genes were analyzed by DNA microarray. Western blot analysis on adult retina and DNA microarray analysis showed that all the fatty acid beta‐oxidation enzyme examined and their gene expressions are present in the retina but small amount about 1/10 of liver tissue. Immuno‐histochemistry at light and electron microscopy showed all these are present only in Müller cells in the retina and isolated Müller cells, in contrast, they are not present in retinal neurons. Mitochondrial fatty acid beta‐oxidation system was shown to be present in retina, and the Müller cells were sole localization of mitochondrial fatty acid beta‐oxidation system in the retina.

Proteomic Analysis of Highly Purified Peroxisomes from Etiolated Soybean Cotyledons

To identify previously unknown peroxisomal proteins, we established an optimized method for isolating highly purified peroxisomes from etiolated soybean cotyledons using Percoll density gradient centrifugation followed by iodixanol density gradient centrifugation. Proteins in highly purified peroxisomes were separated by two-dimensional PAGE. We performed peptide mass fingerprinting of proteins separated in the gel with matrix-assisted laser desorption ionization time-of-flight mass spectrometry and used the peptide mass fingerprints to search a non-redundant soybean expressed sequence tag database. We succeeded in assigning 92 proteins to 70 sequences in the database. Among them, proteins encoded by 30 sequences were judged to be located in peroxisomes. These included enzymes for fatty acid beta-oxidation, the glyoxylate cycle, photorespiratory glycolate metabolism, stress response and metabolite transport. We also show experimental evidence that plant peroxisomes contain a short-chain dehydrogenase/reductase family protein, enoyl-CoA hydratase/isomerase family protein, 3-hydroxyacyl-CoA dehydrogenase-like protein and a voltage-dependent anion-selective channel protein.

Valproic acid metabolism and its effects on mitochondrial fatty acid oxidation: A review

Valproic acid (VPA; 2-n-propylpentanoic acid) is widely used as a major drug in the treatment of epilepsy and in the control of several types of seizures. Being a simple fatty acid, VPA is a substrate for the fatty acid beta-oxidation (FAO) pathway, which takes place primarily in mitochondria. The toxicity of valproate has long been considered to be due primarily to its interference with mitochondrial beta-oxidation. The metabolism of the drug, its effects on enzymes of FAO and their cofactors such as CoA and/or carnitine will be reviewed. The cumulative consequences of VPA therapy in inborn errors of metabolism (IEMs) and the importance of recognizing an underlying IEM in cases of VPA-induced steatosis and acute liver toxicity are two different concepts that will be emphasized.

Simulated hyperglycemia in rat cardiomyocytes: A proteomics approach for improved analysis of cellular alterations

Diabetic hyperglycemia can lead to stress-related cellular apoptosis of cardiac tissue. However, the mechanism by which hyperglycemia inflicts this damage on the structure and function of the heart is unclear. In this study, we examined the relationship between proteome alterations, mitochondrial function, and major biochemical and electrophysiological changes affecting cardiac performance during simulated short-term hyperglycemia. Two-dimensional comparative proteomics analysis of rat hearts perfused with glucose at high (30 mM) or control (5.5 mM) levels revealed that glucose loading alters cardiomyocyte proteomes. It increased expression levels of initial enzymes of the tricarboxylic acid cycle, and of enzymes of fatty acid beta-oxidation, with consequent up-regulation of enzymes of mitochondrial electron transport. It also markedly decreased expression of enzymes of glycolysis and the final steps of the tricarboxylic acid cycle. Glucose loading increased the rate of Bax-independent apoptosis. High glucose increased the duration of the action potential and elevated level of intracellular cytoplasmic calcium. Surprisingly, glucose loading did not influence levels of nitric oxide or mitochondrial superoxide in isolated cardiomyocytes. In summary, short-term simulated hyperglycemia attenuated expression of many anti-apoptotic proteins. This effect was apparently mediated via alterations in multiple biochemical pathways that collectively increased apoptotic susceptibility.

Nine 3-ketoacyl-CoA thiolases (KATs) and acetoacetyl-CoA thiolases (ACATs) encoded by five genes in Arabidopsis thaliana are targeted either to peroxisomes or cytosol but not to mitochondria

The sub-cellular location of enzymes of fatty acid beta-oxidation in plants is controversial. In the current debate the role and location of particular thiolases in fatty acid degradation, fatty acid synthesis and isoleucine degradation are important. The aim of this research was to determine the sub-cellular location and hence provide information about possible functions of all the putative 3-ketoacyl-CoA thiolases (KAT) and acetoacetyl-CoA thiolases (ACAT) in Arabidopsis. Arabidopsis has three genes predicted to encode KATs, one of which encodes two polypeptides that differ at the N-terminal end. Expression in Arabidopsis cells of cDNAs encoding each of these KATs fused to green fluorescent protein (GFP) at their C-termini showed that three are targeted to peroxisomes while the fourth is apparently cytosolic. The four KATs are also predicted to have mitochondrial targeting sequences, but purified mitochondria were unable to import any of the proteins in vitro. Arabidopsis also has two genes encoding a total of five different putative ACATs. One isoform is targeted to peroxisomes as a fusion with GFP, while the others display no targeting in vivo as GFP fusions, or import into isolated mitochondria. Analysis of gene co-expression clusters in Arabidopsis suggests a role for peroxisomal KAT2 in beta-oxidation, while KAT5 co-expresses with genes of the flavonoid biosynthesis pathway and cytosolic ACAT2 clearly co-expresses with genes of the cytosolic mevalonate biosynthesis pathway. We conclude that KATs and ACATs are present in the cytosol and peroxisome, but are not found in mitochondria. The implications for fatty acid beta-oxidation and for isoleucine degradation in mitochondria are discussed.

Abstract 605: ERK5 Activation Regulates PPARalpha Activity and Subsequent Cardioprotection After Ischemia/Reperfusion

Background: The strong cardioprotective effect of erythropoietin (EPO) and heme oxygenase-1 (HO-1) have been reported, but the mechanism are not understood. Previously we found that activation of big MAP kinase 1 (BMK1/ERK5) inhibits cardiac injury after myocardial ischemia and reperfusion. The hinge-helix 1 region of peroxisome proliferator-activated receptor gamma1 (PPARgamma1) mediates interaction with extra-cellular signal-regulated kinase 5(ERK5). We hypothesize that ERK5 activation induced by insulin growth factor-1(IGF-1), erythropoietin(EPO) and heme oxygenase-1(HO-1) is a “key modulator” of PPARa activity and provides a cardioprotective effect after I/R. Thus the aim of this study was to explore the mechanism of the protective effect of EPO, HO-1 and IGF-1 via ERK5 activation. Method and Results: We have found that EPO, HO-1 and IGF-1 stimulate ERK5 activation in the heart, and increase PPARa activity via an ERK5 dependent manner. To prove the role of ERK5 kinase/PPARa activation in IGF-1, EPO and HO-1 mediated cardioprotection after I/R, we characterized the unique role of ERK5 in IGF-1, EPO and HO-1-mediated PPARa activation. In cardiomyocytes, IGF-1, EPO and HO-1 mediate endogenous ERK5 association with endogenous PPARa but not phosphorylation of the PPARa. Activation of ERK5 by Ad-CA-MEK5a trigged the induction of mCPT-1 and PDK4, which promote fatty acid beta-oxidation (FAO) enzyme pathway via increasing PPARa transcriptional activation. Also we found that increased apoptosis in cardiomyocytes incubated by H2O2 compared to non-treated group( 3– 4 times increase H2O2 group vs. wildtype group). However HO-1 induction, EPO and IGF-1 treatment blocked the increased apoptosis induced by H2O2 stimulation. To determine the role of ERK5 kinase in EPO-mediated cardioprotection in vivo, we used the I/R mouse model in CA-MEK5a transgenic mice. Our preliminary experiments suggest a smaller infarction size in CA-MEK5a transgenic mice hearts compared to control hearts. Conclusion: We propose a key role for PPARa and subsequent activation of FAO enzyme induced by EPO and HO-1 mediated cardioprotection. These factors are induced by ERK5 activation. These data suggest that ERK5 is a critical factor and therefore a future therapeutic target.

The Crystal Structure of a Plant 3-Ketoacyl-CoA Thiolase Reveals the Potential for Redox Control of Peroxisomal Fatty Acid β-Oxidation

Crystal structures of peroxisomal Arabidopsis thaliana 3-ketoacyl-CoA thiolase (AtKAT), an enzyme of fatty acid beta-oxidation, are reported. The subunit, a typical thiolase, is a combination of two similar alpha/beta domains capped with a loop domain. The comparison of AtKAT with the Saccharomyces cerevisiae homologue (ScKAT) structure reveals a different placement of subunits within the functional dimers and that a polypeptide segment forming an extended loop around the open catalytic pocket of ScKAT converts to alpha-helix in AtKAT, and occludes the active site. A disulfide is formed between Cys192, on this helix, and Cys138, a catalytic residue. Access to Cys138 is determined by the structure of this polypeptide segment. AtKAT represents an oxidized, previously unknown inactive form, whilst ScKAT is the reduced and active enzyme. A high level of sequence conservation is observed, including Cys192, in eukaryotic peroxisomal, but not mitochondrial or prokaryotic KAT sequences, for this labile loop/helix segment. This indicates that KAT activity in peroxisomes is influenced by a disulfide/dithiol change linking fatty acid beta-oxidation with redox regulation.