Molecular identification and characterization of two medium-chain acyl-CoA synthetases, MACS1 and the Sa gene product

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.

Pyruvate dehydrogenase operates as an intramolecular nitroxyl generator during macrophage metabolic reprogramming

M1 macrophages enter a glycolytic state when endogenous nitric oxide (NO) reprograms mitochondrial metabolism by limiting aconitase 2 and pyruvate dehydrogenase (PDH) activity. Here, we provide evidence that NO targets the PDH complex by using lipoate to generate nitroxyl (HNO). PDH E2-associated lipoate is modified in NO-rich macrophages while the PDH E3 enzyme, also known as dihydrolipoamide dehydrogenase (DLD), is irreversibly inhibited. Mechanistically, we show that lipoate facilitates NO-mediated production of HNO, which interacts with thiols forming irreversible modifications including sulfinamide. In addition, we reveal a macrophage signature of proteins with reduction-resistant modifications, including in DLD, and identify potential HNO targets. Consistently, DLD enzyme is modified in an HNO-dependent manner at Cys477 and Cys484, and molecular modeling and mutagenesis show these modifications impair the formation of DLD homodimers. In conclusion, our work demonstrates that HNO is produced physiologically. Moreover, the production of HNO is dependent on the lipoate-rich PDH complex facilitating irreversible modifications that are critical to NO-dependent metabolic rewiring.

RNA Sequencing Reveals the Wound Repair Mechanism of Cuyuxunxi Prescription in Surgical Patients with Anal Fistulas

BACKGROUND

Anal fistula is one of the most common colorectal and perirectal diseases in the world. Cuyuxunxi (CYXX) prescription is an efficient herbal fumigant used to promote the surgical wound healing of anal fistulas.

OBJECTIVE

This study aimed to explore the underlying molecular mechanism of CYXX prescription on surgical wound healing of anal fistulas.

METHODS

Ten patients with anal fistula were randomized into a control group or treatment group. The wound surface of patients in the control group was rinsed by normal saline, while that in the treatment group was rinsed by CYXX prescription. The wound tissues of patients with anal fistulas seven days after the surgery were collected for hematoxylin-eosin (HE) staining and RNA sequencing. The expressions of differentially expressed genes (DEGs) were validated by real-time quantitative PCR (RT-qPCR).

RESULTS

HE staining showed that CYXX treatment reduced the infiltration of inflammatory cells. A total of 472 DEGs, including 141 up-regulated genes and 331 down-regulated genes, were identified. These genes were significantly related to skin development, xenobiotic stimulus, and inflammation. In addition, the consistency rate of RT-qPCR and sequencing results was 83.33%, which showed a high relative reliability of the sequencing results.

CONCLUSION

CYXX prescription could improve epidermis repair and reduce inflammatory responses.

Hepatic Transcriptome Profiling Reveals Lack of Acsm3 Expression in Polydactylous Rats with High-Fat Diet-Induced Hypertriglyceridemia and Visceral Fat Accumulation

Metabolic syndrome (MetS) is an important cause of worldwide morbidity and mortality. Its complex pathogenesis includes, on the one hand, sedentary lifestyle and high caloric intake, and, on the other hand, there is a clear genetic predisposition. PD (Polydactylous rat) is an animal model of hypertriglyceridemia, insulin resistance, and obesity. To unravel the genetic and pathophysiologic background of this phenotype, we compared morphometric and metabolic parameters as well as liver transcriptomes among PD, spontaneously hypertensive rat, and Brown Norway (BN) strains fed a high-fat diet (HFD). After 4 weeks of HFD, PD rats displayed marked hypertriglyceridemia but without the expected hepatic steatosis. Moreover, the PD strain showed significant weight gain, including increased weight of retroperitoneal and epididymal fat pads, and impaired glucose tolerance. In the liver transcriptome, we found 5480 differentially expressed genes, which were enriched for pathways involved in fatty acid beta and omega oxidation, glucocorticoid metabolism, oxidative stress, complement activation, triacylglycerol and lipid droplets synthesis, focal adhesion, prostaglandin synthesis, interferon signaling, and tricarboxylic acid cycle pathways. Interestingly, the PD strain, contrary to SHR and BN rats, did not express the Acsm3 (acyl-CoA synthetase medium-chain family member 3) gene in the liver. Together, these results suggest disturbances in fatty acid utilization as a molecular mechanism predisposing PD rats to hypertriglyceridemia and fat accumulation.

Enhanced lipid metabolism induces the sensitivity of dormant cancer cells to 5-aminolevulinic acid-based photodynamic therapy

Cancer can develop into a recurrent metastatic disease with latency periods of years to decades. Dormant cancer cells, which represent a major cause of recurrent cancer, are relatively insensitive to most chemotherapeutic drugs and radiation. We previously demonstrated that cancer cells exhibited dormancy in a cell density-dependent manner. Dormant cancer cells exhibited increased porphyrin metabolism and sensitivity to 5-aminolevulinic acid-based photodynamic therapy (ALA-PDT). However, the metabolic changes in dormant cancer cells or the factors that enhance porphyrin metabolism have not been fully clarified. In this study, we revealed that lipid metabolism was increased in dormant cancer cells, leading to ALA-PDT sensitivity. We performed microarray analysis in non-dormant and dormant cancer cells and revealed that lipid metabolism was remarkably enhanced in dormant cancer cells. In addition, triacsin C, a potent inhibitor of acyl-CoA synthetases (ACSs), reduced protoporphyrin IX (PpIX) accumulation and decreased ALA-PDT sensitivity. We demonstrated that lipid metabolism including ACS expression was positively associated with PpIX accumulation. This research suggested that the enhancement of lipid metabolism in cancer cells induces PpIX accumulation and ALA-PDT sensitivity.

Acetate Metabolism in Archaea: Characterization of an Acetate Transporter and of Enzymes Involved in Acetate Activation and Gluconeogenesis in Haloferax volcanii

The haloarchaeon Haloferax volcanii grows on acetate as sole carbon and energy source. The genes and proteins involved in uptake and activation of acetate and in gluconeogenesis were identified and analyzed by characterization of enzymes and by growth experiments with the respective deletion mutants. (i) An acetate transporter of the sodium: solute-symporter family (SSF) was characterized by kinetic analyses of acetate uptake into H. volcanii cells. The functional involvement of the transporter was proven with a Δssf mutant. (ii) Four paralogous AMP-forming acetyl-CoA synthetases that belong to different phylogenetic clades were shown to be functionally involved in acetate activation. (iii) The essential involvement of the glyoxylate cycle as an anaplerotic sequence was concluded from growth experiments with an isocitrate lyase knock-out mutant excluding the operation of the methylaspartate cycle reported for Haloarcula species. (iv) Enzymes involved in phosphoenolpyruvate synthesis from acetate, namely two malic enzymes and a phosphoenolpyruvate synthetase, were identified and characterized. Phylogenetic analyses of haloarchaeal malic enzymes indicate a separate evolutionary line distinct from other archaeal homologs. The exclusive function of phosphoenolpyruvate synthetase in gluconeogenesis was proven by the respective knock-out mutant. Together, this is a comprehensive study of acetate metabolism in archaea.

High-fat but not normal-fat intake of extra virgin olive oil modulates the liver proteome of mice

PURPOSE

The metabolic benefits of the Mediterranean diet have been largely attributed to its olive oil content. Whether the ingested fat amount is relevant to these effects is not clear. We thus compared the effects of high-fat and normal-fat intake of extra-virgin olive oil (EVOO) on the liver proteome.

METHODS

Three groups of mice were fed for 12 weeks with either normal-fat diets containing either soybean oil (control, C) or EVOO (NO) or a high-fat EVOO diet (HO). Body weight and food intake were measured weekly and serum parameters were analyzed. The liver was processed for data-independent acquisition mass spectrometry-based proteomics. The differentially expressed proteins among the groups were submitted to pathway enrichment analysis.

RESULTS

The consumption of HO diet reduced food intake and serum triglycerides, while it preserved body weight gain, adiposity, and glycemia. However, it increased serum cholesterol and liver mass. The proteomic analysis showed 98 altered proteins, which were allocated in 27 significantly enriched pathways. The pathway analysis suggested stimulation of mitochondrial and peroxissomal β-oxidation, and inhibition of lipid synthesis and gluconeogenesis in the HO group. Although the NO group failed to show significant liver proteome alterations, it presented reduced body fat, body weight gain, and serum triglycerides and glucose levels.

CONCLUSION

The data indicate that the intake of the HO diet induced hepatic adjustments, which were partially successful in counteracting the detrimental outcomes of a high-fat feeding. Contrastingly, the NO diet had beneficial effects which were not accompanied by significant modifications on hepatic proteome.

Approaches to studying the genomic architecture of complex birth defects

Every year nearly 6 percent of children worldwide are born with a serious congenital malformation, resulting in death or lifelong disability. In the United States, birth defects remain one of the leading causes of infant mortality. Among the common structural congenital defects are conditions known as neural tube defects (NTDs). These are a class of malformation of the brain and spinal cord where the neural tube fails to close during the neurulation. Although NTDs remain among the most pervasive and debilitating of all human developmental anomalies, there is insufficient understanding of their etiology. Previous studies have proposed that complex birth defects like NTDs are likely omnigenic, involving interconnected gene regulatory networks with associated signals throughout the genome. Advances in technologies have allowed researchers to more critically investigate regulatory gene networks in ever increasing detail, informing our understanding of the genetic basis of NTDs. Employing a systematic analysis of these complex birth defects using massively parallel DNA sequencing with stringent bioinformatic algorithms, it is possible to approach a greater level of understanding of the genomic architecture underlying NTDs. Herein, we present a brief overview of different approaches undertaken in our laboratory to dissect out the genetics of susceptibility to NTDs. This involves the use of mouse models to identify candidate genes, as well as large scale whole genome/whole exome (WGS/WES) studies to interrogate the genomic landscape of NTDs. The goal of this research is to elucidate the gene-environment interactions contributing to NTDs, thus encouraging global research efforts in their prevention.

Genes lost during the transition from land to water in cetaceans highlight genomic changes associated with aquatic adaptations

The transition from land to water in whales and dolphins (cetaceans) was accompanied by remarkable adaptations. To reveal genomic changes that occurred during this transition, we screened for protein-coding genes that were inactivated in the ancestral cetacean lineage. We found 85 gene losses. Some of these were likely beneficial for cetaceans, for example, by reducing the risk of thrombus formation during diving (F12 and KLKB1), erroneous DNA damage repair (POLM), and oxidative stress-induced lung inflammation (MAP3K19). Additional gene losses may reflect other diving-related adaptations, such as enhanced vasoconstriction during the diving response (mediated by SLC6A18) and altered pulmonary surfactant composition (SEC14L3), while loss of SLC4A9 relates to a reduced need for saliva. Last, loss of melatonin synthesis and receptor genes (AANAT, ASMT, and MTNR1A/B) may have been a precondition for adopting unihemispheric sleep. Our findings suggest that some genes lost in ancestral cetaceans were likely involved in adapting to a fully aquatic lifestyle.

Unravelling the genetic basis of schizophrenia and bipolar disorder with GWAS: A systematic review

OBJECTIVES

To systematically review findings of GWAS in schizophrenia (SZ) and in bipolar disorder (BD); and to interpret findings, with a focus on identifying independent replications.

METHOD

PubMed search, selection and review of all independent GWAS in SZ or BD, published since March 2011, i.e. studies using non-overlapping samples within each article, between articles, and with those of the previous review (Li et al., 2012).

RESULTS

From the 22 GWAS included in this review, the genetic associations surviving standard GWAS-significance were for genetic markers in the regions of ACSL3/KCNE4, ADCY2, AMBRA1, ANK3, BRP44, DTL, FBLN1, HHAT, INTS7, LOC392301, LOC645434/NMBR, LOC729457, LRRFIP1, LSM1, MDM1, MHC, MIR2113/POU3F2, NDST3, NKAPL, ODZ4, PGBD1, RENBP, TRANK1, TSPAN18, TWIST2, UGT1A1/HJURP, WHSC1L1/FGFR1 and ZKSCAN4. All genes implicated across both reviews are discussed in terms of their function and implication in neuropsychiatry.

CONCLUSION

Taking all GWAS to date into account, AMBRA1, ANK3, ARNTL, CDH13, EFHD1 (albeit with different alleles), MHC, PLXNA2 and UGT1A1 have been implicated in either disorder in at least two reportedly non-overlapping samples. Additionally, evidence for a SZ/BD common genetic basis is most strongly supported by the implication of ANK3, NDST3, and PLXNA2.

Fatty acid activation in thermogenic adipose tissue

Channeling carbohydrates and fatty acids to thermogenic tissues, including brown and beige adipocytes, have garnered interest as an approach for the management of obesity-related metabolic disorders. Mitochondrial fatty acid oxidation (β-oxidation) is crucial for the maintenance of thermogenesis. Upon cellular fatty acid uptake or following lipolysis from triglycerides (TG), fatty acids are esterified to coenzyme A (CoA) to form active acyl-CoA molecules. This enzymatic reaction is essential for their utilization in β-oxidation and thermogenesis. The activation and deactivation of fatty acids are regulated by two sets of enzymes called acyl-CoA synthetases (ACS) and acyl-CoA thioesterases (ACOT), respectively. The expression levels of ACS and ACOT family members in thermogenic tissues will determine the substrate availability for β-oxidation, and consequently the thermogenic capacity. Although the role of the majority of ACS and ACOT family members in thermogenesis remains unclear, recent proceedings link the enzymatic activities of ACS and ACOT family members to metabolic disorders and thermogenesis. Elucidating the contributions of specific ACS and ACOT family members to trafficking of fatty acids towards thermogenesis may reveal novel targets for modulating thermogenic capacity and treating metabolic disorders.

Lipoic acid metabolism and mitochondrial redox regulation

Lipoic acid is an essential cofactor for mitochondrial metabolism and is synthesized de novo using intermediates from mitochondrial fatty-acid synthesis type II, S-adenosylmethionine and iron-sulfur clusters. This cofactor is required for catalysis by multiple mitochondrial 2-ketoacid dehydrogenase complexes, including pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and branched-chain ketoacid dehydrogenase. Lipoic acid also plays a critical role in stabilizing and regulating these multienzyme complexes. Many of these dehydrogenases are regulated by reactive oxygen species, mediated through the disulfide bond of the prosthetic lipoyl moiety. Collectively, its functions explain why lipoic acid is required for cell growth, mitochondrial activity, and coordination of fuel metabolism.

SucStruct: Prediction of succinylated lysine residues by using structural properties of amino acids

Post-Translational Modification (PTM) is a biological reaction which contributes to diversify the proteome. Despite many modifications with important roles in cellular activity, lysine succinylation has recently emerged as an important PTM mark. It alters the chemical structure of lysines, leading to remarkable changes in the structure and function of proteins. In contrast to the huge amount of proteins being sequenced in the post-genome era, the experimental detection of succinylated residues remains expensive, inefficient and time-consuming. Therefore, the development of computational tools for accurately predicting succinylated lysines is an urgent necessity. To date, several approaches have been proposed but their sensitivity has been reportedly poor. In this paper, we propose an approach that utilizes structural features of amino acids to improve lysine succinylation prediction. Succinylated and non-succinylated lysines were first retrieved from 670 proteins and characteristics such as accessible surface area, backbone torsion angles and local structure conformations were incorporated. We used the k-nearest neighbors cleaning treatment for dealing with class imbalance and designed a pruned decision tree for classification. Our predictor, referred to as SucStruct (Succinylation using Structural features), proved to significantly improve performance when compared to previous predictors, with sensitivity, accuracy and Mathew's correlation coefficient equal to 0.7334-0.7946, 0.7444-0.7608 and 0.4884-0.5240, respectively.

Time Course Analysis of Skeletal Muscle Pathology of GDE5 Transgenic Mouse

Glycerophosphodiesterase 5 (GDE5) selectively hydrolyses glycerophosphocholine to choline and is highly expressed in type II fiber-rich skeletal muscles. We have previously generated that a truncated mutant of GDE5 (GDE5dC471) that lacks phosphodiesterase activity and shown that transgenic mice overexpressing GDE5dC471 in skeletal muscles show less skeletal muscle mass than control mice. However, the molecular mechanism and pathophysiological features underlying decreased skeletal muscle mass in GDE5dC471 mice remain unclear. In this study, we characterized the skeletal muscle disorder throughout development and investigated the primary cause of muscle atrophy. While type I fiber-rich soleus muscle mass was not altered in GDE5dC471 mice, type II fiber-rich muscle mass was reduced in 8-week-old GDE5dC471 mice. Type II fiber-rich muscle mass continued to decrease irreversibly in 1-year-old transgenic mice with an increase in apoptotic cell. Adipose tissue weight and blood triglyceride levels in 8-week-old and 1-year-old transgenic mice were higher than those in control mice. This study also demonstrated compensatory mRNA expression of neuromuscular junction (NMJ) components, including nicotinic acetylcholine receptors (α1, γ, and ε subunits) and acetylcholinesterase in type II fiber-rich quadriceps muscles in GDE5dC471 mice. However, we did not observe morphological changes in NMJs associated with skeletal muscle atrophy in GDE5dC471 mice. We also found that HSP70 protein levels are significantly increased in the skeletal muscles of 2-week-old GDE5dC471 mice and in mouse myoblastic C2C12 cells overexpressing GDE5dC471. These findings suggest that GDE5dC471 mouse is a novel model of early-onset irreversible type II fiber-rich myopathy associated with cellular stress.

Xenobiotic/medium chain fatty acid: CoA ligase - a critical review on its role in fatty acid metabolism and the detoxification of benzoic acid and aspirin

INTRODUCTION

Activation of fatty acids by the acyl-CoA synthetases (ACSs) is the vital first step in fatty acid metabolism. The enzymatic and physiological characterization of the human xenobiotic/medium chain fatty acid: CoA ligases (ACSMs) has been severely neglected even though xenobiotics, such as benzoate and salicylate, are detoxified through this pathway.

AREAS COVERED

This review will focus on the nomenclature and substrate specificity of the human ACSM ligases; the biochemical and enzymatic characterization of ACSM1 and ACSM2B; the high sequence homology of the ACSM2 genes (ACSM2A and ACSM2B) as well as what is currently known regarding disease association studies.

EXPERT OPINION

Several discrepancies exist in the current literature that should be taken note of. For example, the single nucleotide polymorphisms (SNPs) reported to be associated with aspirin metabolism and multiple risk factors of metabolic syndrome are incorrect. Kinetic data on the substrate specificity of the human ACSM ligases are non-existent and currently no data exist on the influence of SNPs on the enzyme activity of these ligases. One of the biggest obstacles currently in the field is that glycine conjugation is continuously studied as a one-step process, which means that key regulatory factors of the two individual steps remain unknown.

Assembly of Lipoic Acid on Its Cognate Enzymes: an Extraordinary and Essential Biosynthetic Pathway

Although the structure of lipoic acid and its role in bacterial metabolism were clear over 50 years ago, it is only in the past decade that the pathways of biosynthesis of this universally conserved cofactor have become understood. Unlike most cofactors, lipoic acid must be covalently bound to its cognate enzyme proteins (the 2-oxoacid dehydrogenases and the glycine cleavage system) in order to function in central metabolism. Indeed, the cofactor is assembled on its cognate proteins rather than being assembled and subsequently attached as in the typical pathway, like that of biotin attachment. The first lipoate biosynthetic pathway determined was that of Escherichia coli, which utilizes two enzymes to form the active lipoylated protein from a fatty acid biosynthetic intermediate. Recently, a more complex pathway requiring four proteins was discovered in Bacillus subtilis, which is probably an evolutionary relic. This pathway requires the H protein of the glycine cleavage system of single-carbon metabolism to form active (lipoyl) 2-oxoacid dehydrogenases. The bacterial pathways inform the lipoate pathways of eukaryotic organisms. Plants use the E. coli pathway, whereas mammals and fungi probably use the B. subtilis pathway. The lipoate metabolism enzymes (except those of sulfur insertion) are members of PFAM family PF03099 (the cofactor transferase family). Although these enzymes share some sequence similarity, they catalyze three markedly distinct enzyme reactions, making the usual assignment of function based on alignments prone to frequent mistaken annotations. This state of affairs has possibly clouded the interpretation of one of the disorders of human lipoate metabolism.

Genome-Wide Association Study with Targeted and Non-targeted NMR Metabolomics Identifies 15 Novel Loci of Urinary Human Metabolic Individuality

Genome-wide association studies with metabolic traits (mGWAS) uncovered many genetic variants that influence human metabolism. These genetically influenced metabotypes (GIMs) contribute to our metabolic individuality, our capacity to respond to environmental challenges, and our susceptibility to specific diseases. While metabolic homeostasis in blood is a well investigated topic in large mGWAS with over 150 known loci, metabolic detoxification through urinary excretion has only been addressed by few small mGWAS with only 11 associated loci so far. Here we report the largest mGWAS to date, combining targeted and non-targeted ¹H NMR analysis of urine samples from 3,861 participants of the SHIP-0 cohort and 1,691 subjects of the KORA F4 cohort. We identified and replicated 22 loci with significant associations with urinary traits, 15 of which are new (HIBCH, CPS1, AGXT, XYLB, TKT, ETNPPL, SLC6A19, DMGDH, SLC36A2, GLDC, SLC6A13, ACSM3, SLC5A11, PNMT, SLC13A3). Two-thirds of the urinary loci also have a metabolite association in blood. For all but one of the 6 loci where significant associations target the same metabolite in blood and urine, the genetic effects have the same direction in both fluids. In contrast, for the SLC5A11 locus, we found increased levels of myo-inositol in urine whereas mGWAS in blood reported decreased levels for the same genetic variant. This might indicate less effective re-absorption of myo-inositol in the kidneys of carriers. In summary, our study more than doubles the number of known loci that influence urinary phenotypes. It thus allows novel insights into the relationship between blood homeostasis and its regulation through excretion. The newly discovered loci also include variants previously linked to chronic kidney disease (CPS1, SLC6A13), pulmonary hypertension (CPS1), and ischemic stroke (XYLB). By establishing connections from gene to disease via metabolic traits our results provide novel hypotheses about molecular mechanisms involved in the etiology of diseases.

Human metabolism is influenced by genetic and environmental factors defining a person’s metabolic individuality. This individuality is linked to personal differences in the ability to react on metabolic challenges and in the susceptibility to specific diseases. By investigating how common variants in genetic regions (loci) affect individual blood metabolite levels, the substantial contribution of genetic inheritance to metabolic individuality has been demonstrated previously. Meanwhile, more than 150 loci influencing metabolic homeostasis in blood are known. Here we shift the focus to genetic variants that modulate urinary metabolite excretion, for which only 11 loci were reported so far. In the largest genetic study on urinary metabolites to date, we identified 15 additional loci. Most of the 26 loci also affect blood metabolite levels. This shows that the metabolic individuality seen in blood is also reflected in urine, which is expected when urine is regarded as “diluted blood”. Nonetheless, we also found loci that appear to primarily influence metabolite excretion. For instance, we identified genetic variants near a gene of a transporter that change the capability for renal re-absorption of the transporter’s substrate. Thus, our findings could help to elucidate molecular mechanisms influencing kidney function and the body’s detoxification capabilities.

Genetic association of ACSM1 variation with schizophrenia and major depressive disorder in the Han Chinese population

Schizophrenia (SCZ) and major depressive disorder (MDD) are two of the most common and severe mental disorders, the etiologies of which are not yet clearly elucidated. The ACSM1 gene has been identified as a susceptibility gene for SCZ in two previous genome-wide association studies (GWAS). ACSM1 catalyzes the activation of fatty acids and plays an important role in the metabolic system. Some evidence has suggested that ACSM1 contributes to a genetic risk for MDD. The present study aimed to evaluate the common genetic risk of the ACSM1 gene in these two disorders in the Han Chinese population. In total, 1235 patients with SCZ, 1045 patients with MDD and 1235 control subjects of Chinese origin were recruited. Six single nuclear polymorphisms (SNPs) in ACSM1 were genotyped to test their associations with SCZ and MDD. SNP rs163234 was found to be significantly associated with both SCZ (permutated Pallele=1.700×10(-3), OR=1.350 [95% CI=1.152-1.581]) and MDD (permutated Pallele=4.800×10(-3), OR=1.329 [95% CI=1.127-1.567]). SNP rs433598 showed a strong association with SCZ (permutated Pallele=4.300×10(-3), OR=1.303 [95% CI=1.117-1.520]). Haplotype analysis of the blocks containing the two positive markers also revealed a significant association. This is the first study to assess the possible association of the ACSM1 gene with a genetic susceptibility for MDD. Our data are the first to suggest a positive association of the ACSM1 gene with a genetic susceptibility for SCZ and MDD in the Han Chinese population.

The Streptomyces coelicolor lipoate-protein ligase is a circularly permuted version of the Escherichia coli enzyme composed of discrete interacting domains

Lipoate-protein ligases are used to scavenge lipoic acid from the environment and attach the coenzyme to its cognate proteins, which are generally the E2 components of the 2-oxoacid dehydrogenases. The enzymes use ATP to activate lipoate to its adenylate, lipoyl-AMP, which remains tightly bound in the active site. This mixed anhydride is attacked by the ϵ-amino group of a specific lysine present on a highly conserved acceptor protein domain, resulting in the amide-linked coenzyme. The Streptomyces coelicolor genome encodes only a single putative lipoate ligase. However, this protein had only low sequence identity (<25%) to the lipoate ligases of demonstrated activity and appears to be a circularly permuted version of the known lipoate ligase proteins in that the canonical C-terminal domain seems to have been transposed to the N terminus. We tested the activity of this protein both by in vivo complementation of an Escherichia coli ligase-deficient strain and by in vitro assays. Moreover, when the domains were rearranged into a protein that mimicked the arrangement found in the canonical lipoate ligases, the enzyme retained complementation activity. Finally, when the two domains were separated into two proteins, both domain-containing proteins were required for complementation and catalysis of the overall ligase reaction in vitro. However, only the large domain-containing protein was required for transfer of lipoate from the lipoyl-AMP intermediate to the acceptor proteins, whereas both domain-containing proteins were required to form lipoyl-AMP.

Determination of acyl-CoA esters and acyl-CoA synthetase activity in mouse brain areas by liquid chromatography-electrospray ionization-tandem mass spectrometry

The acyl-CoA levels and the acyl-CoA synthetase activities in 7 areas of mouse brain were determined by liquid chromatography-electrospray ionization-tandem mass spectrometry. Twenty-one acyl-CoA esters of C2:0, C4:0, C6:0, C8:0, C10:0, C12:0, C14:1, C14:0, C16:0, C16:1, C18:0, C18:1, C18:2, C18:3, C20:0, C20:4, C20:5, C22:0, C22:5, C22:6 and C24:0 were detected in the olfactory bulb, cerebral cortex, hippocampus, cerebellum, hypothalamus, midbrain and medulla oblongata. The brain areas contained primarily the acyl-CoAs of the C16:0, C18:0, C18:1, C20:4 and C22:6 species. The relative abundances of the acyl-CoAs of C16:0, C18:0 and C18:1 were considerably higher than those of C20:4 and C22:6. The levels of medium-chain acyl-CoAs were only 1.2% that of the long-chain acyl-CoAs. The differences in the acyl-CoA synthetase activities in each area of mouse brain were less dramatic. The order of the acyl-CoA synthetase activities for fatty acids of different chain lengths was palmitic acid>arachidonic acid>docosahexaenoic acid>octanoic acid. The analytical method proved to be very useful for the analysis of the acyl-CoA profile of tissues. Our results have important implications for understanding the regulation of acyl-CoA synthetase activity and long-chain fatty acid turnover in the phospholipids in the brain.

A medium-chain fatty acid as an alternative energy source in mouse preimplantation development

To further optimize the culturing of preimplantation embryos, we undertook metabolomic analysis of relevant culture media using capillary electrophoresis time-of-flight mass spectrometry (CE-TOFMS). We detected 28 metabolites: 23 embryo-excreted metabolites including 16 amino acids and 5 media-derived metabolites (e.g., octanoate, a medium-chain fatty acid (MCFA)). Due to the lack of information on MCFAs in mammalian preimplantation development, this study examined octanoate as a potential alternative energy source for preimplantation embryo cultures. No embryos survived in culture media lacking FAs, pyruvate, and glucose, but supplementation of octanoate rescued the embryonic development. Immunoblotting showed significant expression of acyl-CoA dehydrogenase and hydroxyacyl-CoA dehydrogenase, important enzymes for ß-oxidation of MCFAs, in preimplantation embryo. Furthermore, CE-TOFMS traced [1-¹³C₈] octanoate added to the culture media into intermediate metabolites of the TCA cycle via ß-oxidation in mitochondria. These results are the first demonstration that octanoate could provide an efficient alternative energy source throughout preimplantation development.

Characterization of an archaeal medium-chain acyl coenzyme A synthetase from Methanosarcina acetivorans

Short- and medium-chain acyl coenzyme A (acyl-CoA) synthetases catalyze the formation of acyl-CoA from an acyl substrate, ATP, and CoA. These enzymes catalyze mechanistically similar two-step reactions that proceed through an enzyme-bound acyl-AMP intermediate. Here we describe the characterization of a member of this enzyme family from the methane-producing archaeon Methanosarcina acetivorans. This enzyme, a medium-chain acyl-CoA synthetase designated Macs(Ma), utilizes 2-methylbutyrate as its preferred substrate for acyl-CoA synthesis but cannot utilize acetate and thus cannot catalyze the first step of acetoclastic methanogenesis in M. acetivorans. When propionate or other less favorable acyl substrates, such as butyrate, 2-methylpropionate, or 2-methylvalerate, were utilized, the acyl-CoA was not produced or was produced at reduced levels. Instead, acyl-AMP and PP(i) were released in the absence of CoA, whereas in the presence of CoA, the intermediate was broken down into AMP and the acyl substrate, which were released along with PP(i). These results suggest that although acyl-CoA synthetases may have the ability to utilize a broad range of substrates for the acyl-adenylate-forming first step of the reaction, the intermediate may not be suitable for the thioester-forming second step. The Macs(Ma) structure has revealed the putative acyl substrate- and CoA-binding pockets. Six residues proposed to form the acyl substrate-binding pocket, Lys(256), Cys(298), Gly(351), Trp(259), Trp(237), and Trp(254), were targeted for alteration. Characterization of the enzyme variants indicates that these six residues are critical in acyl substrate binding and catalysis, and even conservative alterations significantly reduced the catalytic ability of the enzyme.

Effect of salicylic acid and diclofenac on the medium-chain and long-chain acyl-CoA formation in the liver and brain of mouse

Medium-chain and long-chain acyl-CoA esters are key metabolites in fatty acid metabolism. Effects of salicylic acid on the in vivo formation of acyl-CoAs in mouse liver and brain were investigated. Further, inhibition of the medium-chain and long-chain acyl-CoA synthetases by salicylic acid and diclofenac was determined in mouse liver and brain mitochondria. Acyl-CoA esters were analyzed by liquid chromatography-tandem mass spectrometry. The amounts of medium-chain acyl-CoAs (C(6), C(8) and C(10)) were less than long-chain acyl-CoAs (C(16:0), C(18:0), C(18:1) and C(20:4)) in both liver and brain. The administration of salicylic acid decreased the levels of both the medium-chain (C(6), C(8) and C(10)) and long-chain acyl-CoAs (C(16:0), C(18:0), C(18:1) and C(20:4)) in liver. In brain, however, only long-chain acyl-CoAs were decreased. The level of salicylyl-CoA detected in brain was about 12% of that in liver. Salicylic acid had a strong inhibitory activity (IC(50) = 0.1 mm) for the liver mitochondrial formation of hexanoyl-CoA from hexanoic acid, whereas diclofenac was weak (IC(50) = 4.4 mm). In contrast, diclofenac (IC(50) = 1.4 mm) inhibited the liver mitochondrial long-chain acyl-CoA synthetases more potently than salicylic acid (IC(50) = 25.5 mm). Similar inhibitory activities for the acyl-CoA synthetases were obtained in the case of the brain and liver mitochondria, except for the weak inhibition of brain medium-chain acyl-CoA synthetases by salicylic acid (IC(50) = 1.8 mm). These findings suggest that salicylic acid and diclofenac exhibit different mechanisms of inhibition of fatty acid metabolism depending on the length of the acyl chain and tissues, and they may contribute to the further understanding of the toxic effects associated with these drugs.

Comparative analyses of disease risk genes belonging to the acyl-CoA synthetase medium-chain (ACSM) family in human liver and cell lines

The human ACSM1, 2A and B, 3, and 5 genes, located on chromosome 16p12-13, encode for enzymes catalyzing the activation of medium-chain length fatty acids. Association studies have linked several polymorphisms of these genes to traits of insulin resistance syndrome. In our study, ACSM transcripts showed 3 to >400-fold higher expression levels in human liver when compared to cell lines by qRT-PCR. This difference was also evident at the protein level, as shown for ACSM2. In liver, ACSM2 was the most abundant transcript, showing sixfold (vs. ACSM3) to >300-fold higher expression levels (vs. ACSM1). Mitochondrial localization of the ACSM2 protein and the presence of an N-terminal targeting sequence were shown by GFP-tagging. We have shown ACSM2B to be the predominant transcript in human liver, and genetic variations of this gene could therefore play an important role in disease susceptibility.

Structural snapshots for the conformation-dependent catalysis by human medium-chain acyl-coenzyme A synthetase ACSM2A

Acyl-CoA synthetases belong to the superfamily of adenylate-forming enzymes, and catalyze the two-step activation of fatty acids or carboxylate-containing xenobiotics. The carboxylate substrate first reacts with ATP to form an acyl-adenylate intermediate, which then reacts with CoA to produce an acyl-CoA ester. Here, we report the first crystal structure of a medium-chain acyl-CoA synthetase ACSM2A, in a series of substrate/product/cofactor complexes central to the catalytic mechanism. We observed a substantial rearrangement between the N- and C-terminal domains, driven purely by the identity of the bound ligand in the active site. Our structures allowed us to identify the presence or absence of the ATP pyrophosphates as the conformational switch, and elucidated new mechanistic details, including the role of invariant Lys557 and a divalent magnesium ion in coordinating the ATP pyrophosphates, as well as the involvement of a Gly-rich P-loop and the conserved Arg472-Glu365 salt bridge in the domain rearrangement.

Human SA gene polymorphisms are associated with non-high-density lipoprotein cholesterol in postmenopausal women: a pilot study

OBJECTIVE

The purpose of the study is to evaluate the associations between polymorphisms of the human SA (SAH) gene, an acyl-CoA synthetase gene, with dyslipidemia and phenotypes of the insulin resistance syndrome in postmenopausal women.

METHODS

One hundred and forty-two postmenopausal women were recruited for the study. Each subject received anthropometric and blood pressure measurements, fasting sampling for lipids, and a 75-g oral glucose tolerance test for insulin resistance. Genotypes of two polymorphisms in the promoter region (c.-962ins/del, c.-451G>A), one missense variant (c.1077G>C, p.K359N) in exon 8, and one in intron 12 (A>G) of the SAH gene, were determined.

RESULTS

There were significant differences in genetic distribution of the SAH gene promoter I/D polymorphism between the two groups of subjects by non-high-density lipoprotein cholesterol (non-HDL-C) levels (p=0.004). The subjects with the DD genotype was associated with high levels of non-HDL-C (>160 mg/dL) as compared with the ID or II genotypes (p=0.002). Furthermore, three haplotypes were constructed based on the promoter I/D and the exon 8 G/C polymorphisms. Homozygosity for SAH haplotype 3 was associated with increased adiposity, insulin resistance, and elevated levels of non-HDL-C in the post menopausal women. The subjects with haplotype 3 had double the risk to have higher non-HDL-C levels than those with haplotype 1.

CONCLUSION

Our results suggest that the polymorphisms of the SAH gene are associated with non-HDL-C levels in postmenopausal women. Further studies with larger sample sizes or different populations are warranted to confirm our preliminary findings.

Xenobiotic incorporation into pyruvate dehydrogenase complex can occur via the exogenous lipoylation pathway

Lipoylated enzymes such as the E2 component of pyruvate dehydrogenase complex (PDC-E2) are targets for autoreactive immune responses in primary biliary cirrhosis, with lipoic acid itself forming a component of the dominant auto-epitopes. A candidate mechanism for the initiation of tolerance breakdown in this disease is immune recognition of neo-antigens formed by xenobiotic substitution of normal proteins. Importantly, sensitization with proteins artificially substituted with the lipoic acid analogue xenobiotic 6-bromohexanoic acid (6BH) can induce an immune response that cross-reacts with PDC-E2. This study investigated the potential of recombinant lipoylation enzymes lipoate activating enzyme and lipoyl-AMP(GMP):N-lysine lipoyl transferase to aberrantly incorporate xenobiotics into PDC-E2. It was found that these enzymes could incorporate lipoic acid analogues including octanoic and hexanoic acids and the xenobiotic 6BH into PDC-E2. The efficiency of incorporation of these analogues showed a variable dependence on activation by adenosine triphosphate (ATP) or guanosine triphosphate (GTP), with ATP favoring the incorporation of hexanoic acid and 6BH whereas GTP enhanced substitution by octanoic acid. Importantly, competition studies showed that the relative incorporation of both 6BH and lipoic acid could be regulated by the balance between ATP and GTP, with the formation of 6BH-substituted PDC-E2 predominating in an ATP-rich environment.

CONCLUSION

Using a well-defined system in vitro we have shown that an important xenobiotic can be incorporated into PDC in place of lipoic acid by the exogenous lipoylation system; the relative levels of lipoic acid and xenobiotic incorporation may be determined by the balance between ATP and GTP. These observations suggest a clear mechanism for the generation of an auto-immunogenic neo-antigen of relevance for the pathogenesis of primary biliary cirrhosis.

Hereditary and acquired diseases of acyl-coenzyme A metabolism

Coenzyme A (CoA) sequestration, toxicity or redistribution (CASTOR) is predicted to occur in many hereditary and acquired conditions in which the degradation of organic acyl esters of CoA is impaired. The resulting accumulation of CoA esters and reduction of acetyl-CoA and free CoA (CoASH) will then trigger a cascade of reactions leading to clinical disease. Most conditions detected by expanded neonatal screening are CASTOR diseases. We review acyl-CoA metabolism, including CoASH synthesis, transesterification of acyl-CoAs to glycine, glutamate or l-carnitine and hydrolysis of CoA esters. Because acyl-CoAs do not cross biological membranes, their main toxicity is intracellular, primarily within mitochondria. Treatment measures directed towards removal of circulating metabolites do not address this central problem of intracellular acyl-CoA accumulation. Treatments usually involve the restriction of dietary precursors and administration of agents like l-carnitine and glycine, which can accept the transfer of acyl groups from acyl-CoA, liberating CoASH. Many hereditary CASTOR patients are chronically ill, with persistent symptoms and continuously abnormal metabolites in blood and urine despite good compliance with treatment. Conversely, asymptomatic patients are also common in hereditary CASTOR conditions. Future challenges include the understanding of pathophysiologic mechanisms in CASTOR diseases, the discovery of reliable predictors of outcome in individual patients and the establishment of therapeutic trials with sufficient numbers of patients to permit solid therapeutic conclusions.

Evidence for 26 distinct acyl-coenzyme A synthetase genes in the human genome

Acyl-coenzyme A synthetases (ACSs) catalyze the fundamental, initial reaction in fatty acid metabolism. "Activation" of fatty acids by thioesterification to CoA allows their participation in both anabolic and catabolic pathways. The availability of the sequenced human genome has facilitated the investigation of the number of ACS genes present. Using two conserved amino acid sequence motifs to probe human DNA databases, 26 ACS family genes/proteins were identified. ACS activity in either humans or rodents was demonstrated previously for 20 proteins, but 6 remain candidate ACSs. For two candidates, cDNA was cloned, protein was expressed in COS-1 cells, and ACS activity was detected. Amino acid sequence similarities were used to assign enzymes into subfamilies, and subfamily assignments were consistent with acyl chain length preference. Four of the 26 proteins did not fit into a subfamily, and bootstrap analysis of phylograms was consistent with evolutionary divergence. Three additional conserved amino acid sequence motifs were identified that likely have functional or structural roles. The existence of many ACSs suggests that each plays a unique role, directing the acyl-CoA product to a specific metabolic fate. Knowing the full complement of ACS genes in the human genome will facilitate future studies to characterize their specific biological functions.

AMP-forming acetyl-CoA synthetases in Archaea show unexpected diversity in substrate utilization

Adenosine monophosphate (AMP)-forming acetyl-CoA synthetase (ACS; acetate:CoA ligase (AMP-forming), EC 6.2.1.1) is a key enzyme for conversion of acetate to acetyl-CoA, an essential intermediate at the junction of anabolic and catabolic pathways. Phylogenetic analysis of putative short and medium chain acyl-CoA synthetase sequences indicates that the ACSs form a distinct clade from other acyl-CoA synthetases. Within this clade, the archaeal ACSs are not monophyletic and fall into three groups composed of both bacterial and archaeal sequences. Kinetic analysis of two archaeal enzymes, an ACS from Methanothermobacter thermautotrophicus (designated as MT-ACS1) and an ACS from Archaeoglobus fulgidus (designated as AF-ACS2), revealed that these enzymes have very different properties. MT-ACS1 has nearly 11-fold higher affinity and 14-fold higher catalytic efficiency with acetate than with propionate, a property shared by most ACSs. However, AF-ACS2 has only 2.3-fold higher affinity and catalytic efficiency with acetate than with propionate. This enzyme has an affinity for propionate that is almost identical to that of MT-ACS1 for acetate and nearly tenfold higher than the affinity of MT-ACS1 for propionate. Furthermore, MT-ACS1 is limited to acetate and propionate as acyl substrates, whereas AF-ACS2 can also utilize longer straight and branched chain acyl substrates. Phylogenetic analysis, sequence alignment and structural modeling suggest a molecular basis for the altered substrate preference and expanded substrate range of AF-ACS2 versus MT-ACS1.

High-fat diet, muscular lipotoxicity and insulin resistance

A high dietary fat intake and low physical activity characterize the current Western lifestyle. Dietary fatty acids do not stimulate their own oxidation and a surplus of fat is stored in white adipose tissue, liver, heart and muscle. In these organs intracellular lipids serve as a rapidly-available energy source during, for example, physical activity. However, under conditions of elevated plasma fatty acid levels and high dietary fat intake, conditions implicated in the development of modern diseases such as obesity and type 2 diabetes mellitus, fat accumulation in liver and muscle (intramyocellular lipids; IMCL) is associated with the development of insulin resistance. Recent data suggest that IMCL are specifically harmful when combined with reduced mitochondrial function, both conditions that characterize type 2 diabetes. In the (pre)diabetic state reduced expression of the transcription factor PPARgamma co-activator-1alpha (PGC-1alpha), which is involved in mitochondrial biogenesis, has been suggested to underlie the reduced mitochondrial function. Importantly, the reduction in PGC-1alpha may be a result of low physical activity, consumption of high-fat diets and high plasma fatty acid levels. Mitochondrial function can also be impaired as a result of enhanced mitochondrial damage by reactive oxygen species. Fatty acids in the vicinity of mitochondria are particularly prone to lipid peroxidation. In turn, lipid peroxides can induce oxidative damage to mitochondrial RNA, DNA and proteins. The mitochondrial protein uncoupling protein 3, which is induced under high-fat conditions, may serve to protect mitochondria against lipid-induced oxidative damage, but is reduced in the prediabetic state. Thus, muscular lipotoxicity may impair mitochondrial function and may be central to insulin resistance and type 2 diabetes mellitus.

Transcriptional regulation of the macs1-fadD1 operon encoding two acyl-CoA synthases involved in the physiological differentiation of Streptomyces coelicolor

The long-chain acyl-CoA synthase (ACS) FadD1 plays an important role in timing the levels of antibiotic production in Streptomyces coelicolor. fadD1 and macs1, encoding a putative medium-chain ACS, are part of a two-gene operon, whose expression is induced during the stationary phase of growth. Here it is reported that transcription of the macs1-fadD1 operon is positively regulated by AcsR, a LuxR-type transcriptional regulator. In an acsR mutant, expression of the macs1-fadD1 genes loses its normal up-regulation and the mutant becomes deficient in antibiotic production, in a clear correlation with the phenotype shown by a fadD1 null mutant. The absence of macs1-fadD1 induction in the acsR mutant was restored by complementation with a wild-type copy of the acsR gene, showing a strict link between AcsR and induction of the macs1-fadD1 operon. Gel mobility shift assays and DNase I footprinting indicated that AcsR binds to specific sequences about +162 nucleotides downstream of the macs1 transcriptional start site. In the putative operator sequence three almost identical direct tandem repeats of seven nucleotides were identified where the central sequence is essential for AcsR recognition and binding. Transcriptional fusions of the divergent pacsR and pmacs1 promoters indicated that AcsR does not regulate its own transcription, and that it binds to the operator region to control exclusively the growth-phase induction of the macs1-fadD1 operon.

Modulation of adipocyte lipogenesis by octanoate: involvement of reactive oxygen species

Background

Octanoate is a medium-chain fatty acid (MCFA) that is rich in milk and tropical dietary lipids. It also accounts for 70% of the fatty acids in commercial medium chain triglycerides (MCT). Use of MCT for weight control tracks back to early 1950s and is highlighted by recent clinical trials. The molecular mechanisms of the weight reduction effect remain not completely understood. The findings of significant amounts of MCFA in adipose tissue in MCT-fed animals and humans suggest a direct influence of MCFA on fat cell functions.

Methods

3T3-L1 adipocytes were treated with octanoate in a high glucose culture medium supplemented with 10% fetal bovine serum and 170 nM insulin. The effects on lipogenesis, fatty acid oxidation, cellular concentration of reactive oxygen species (ROS), and the expression and activity of peroxisome proliferator receptor gamma (PPARγ) and its associated lipogenic genes were assessed. In selected experiments, long-chain fatty acid oleate, PPARγ agonist troglitazone, and antioxidant N-acetylcysteine were used in parallel. Effects of insulin, L-carnitine, and etomoxir on β-oxidation were also measured.

Results

β-oxidation of octanoate was primarily independent of CPT-I. Treatment with octanoate was linked to an increase in ROS in adipocytes, a decrease in triglyceride synthesis, and reduction of lipogenic gene expression. Co-treatment with troglitazone, N-acetylcysteine, or over-expression of glutathione peroxidase largely reversed the effects of octanoate.

Conclusion

These findings suggest that octanoate-mediated inactivation of PPARγ might contribute to the down regulation of lipogenic genes in adipocytes, and ROS appears to be involved as a mediator in this process.

Purification, characterization, and mass spectrometric sequencing of a medium chain acyl-CoA synthetase from mouse liver mitochondria and comparisons with the homologues of rat and bovine

Medium chain acyl-CoA synthetases catalyze the first reaction of amino acid conjugation of many xenobiotic carboxylic acids and fatty acid metabolism. This paper reports studies on purification, characterization, and the partial amino acid sequence of mouse liver enzyme. The medium chain acyl-CoA synthetase was isolated from mouse liver mitochondria. The purified enzyme catalyzes this reaction not only for straight medium chain fatty acids but also for aromatic and arylacetic acids. Maximal activity was found with hexanoic acid. High activities were obtained with benzoic acid having methyl, pentyl, and methoxy groups in the para- or meta-positions of the benzene ring. However, the enzyme was less active with valproic acid and ketoprofen. Salicylic acid exhibited no activity. The medium chain acyl-CoA synthetases from mouse and bovine liver mitochondria were subjected to in-gel tryptic digestion, followed by LC-MS/MS sequence analysis. The amino acid sequence of each tryptic peptide of mouse liver mitochondrial medium chain acyl-CoA synthetase differed from that from bovine liver mitochondria only in one or two amino acids. LC-MS/MS analysis provided the information about these differences in amino acid sequences. In addition, we compared the properties of this protein with the homologues from rat and bovine.

The L513S polymorphism in medium-chain acyl-CoA synthetase 2 (MACS2) is associated with risk factors of the metabolic syndrome in a Caucasian study population

Enzymes of the medium-chain acyl-CoA synthetase (MACS) family catalyze the ligation of medium chain fatty acids with CoA to produce medium-chain-acyl-CoA. At least four members of the MACS gene family are clustered on human chromosome 16p12. Association studies in the Japanese Suita cohort of MACS polymorphisms and various phenotypes revealed the contribution of the Leu513Ser polymorphism in MACS2 to multiple risk factors of the metabolic syndrome. Here, we investigated the association between this polymorphism and different risk factors in the Caucasian Metabolic Intervention Cohort Kiel. Seven hundred and sixteen male subjects aged 45-65 years were recruited for a standard oral glucose tolerance test and the postprandial assessment of metabolic parameters after an oral metabolic tolerance test (oMTT; 1017 kcal, 51.6% fat, 29.6% carbohydrates, 11.9% protein). The MACS2 Leu513Ser polymorphism was determined by TaqMan-Assay in 705 subjects. Postprandial triglyceride levels following oMTT [area under the curve (AUC)] were significantly higher in subjects carrying the Ser allele compared to subjects homozygous for the Leu allele (1690 +/- 100 mg x h/dL versus 1514 +/- 39 mg x h/dL, p = 0.04). Significant differences between genotype groups were also found for fasting (108 +/- 1.9 mg/dL versus 104 +/- 0.66 mg/dL, p = 0.04) and postprandial (AUC 535 +/- 11 versus 512 +/- 4.0, p = 0.02) glucose levels as well as for high-density-lipoprotein, body mass index, waist circumference, systolic and diastolic blood pressure. Carriers of the Ser allele also show an increased risk of impaired glucose metabolism (OR: 1.48, 95% confidence interval: 0.98-2.27, p = 0.07), adiposity (1.8, 1.16-2.81, p = 0.01) and hypertension (1.5, 0.99-2.17, p = 0.06). In conclusion, our results suggest an involvement of the MACS2 Leu513Ser polymorphism in the development of the metabolic syndrome in Caucasian population. Additionally, the higher triglyceride and glucose levels after an oMTT support a possible functional impact of the polymorphism in vivo.

Involvement of UCP3 in mild uncoupling and lipotoxicity

Although vital to life, mitochondria are also the major source of ROS production, which may have unwanted detrimental effects on DNA, RNA and protein structures Therefore, mitochondria must exhibit well-developed mechanisms to regulate its ROS production. One such mechanism might be mild uncoupling of the mitochondrial respiratory chain, thereby lowering the proton gradient across the inner mitochondrial membrane and directly lowering ROS production. Mitochondrial uncoupling proteins have been shown to possess mild uncoupling activity and may therefore be important regulator of mitochondrial ROS production. The skeletal muscle isoform of the uncoupling protein family, UCP3, seems to be specifically active under conditions of high fatty acid availability. Although the exact function of UCP3 is not yet unravelled, UCP3 is activated by lipid peroxides and suggested to export fatty acid anions and/or peroxides from the mitochondrial matrix, thereby specifically protecting fatty acids from ROS-induced oxidative damage. Protein levels of UCP3 are reduced with aging and in the (pre)-diabetic state, both conditions characterized by increased levels of oxidative damage to lipids and proteins and reduced mitochondrial function. Whether UCP3 is causally related to mitochondrial dysfunction and is essential in the prevention and treatment of lipid-induced mitochondrial dysfunction requires further study.

Two medium-chain acyl-coenzyme A synthetase genes, SAH and MACS1, are associated with plasma high-density lipoprotein cholesterol levels, but they are not associated with essential hypertension

BACKGROUND AND OBJECTIVES

SAH has been proposed as a candidate gene for essential hypertension (EH) because elevated expression of SAH was observed in the kidneys of spontaneously hypertensive rats. Recently, a homology search of SAH in the human genome revealed the presence of the SAH gene family, which includes SAH, MACS1, MACS2, and MACS3. SAH and MACS1 are located within a 150-kb region on human chromosome 16p13.11. SAH and MACS1 are thought to function as acyl-coenzyme A synthetases, which are involved in fatty acid metabolism. In the present study, we analyzed six single nucleotide polymorphisms (SNPs) in the SAH and MACS1 genes in a Japanese population, and examined whether these SNPs contribute to EH and multiple risk factors.

METHODS AND RESULTS

We performed association studies of six SNPs in 287 EH patients and 259 normotensive subjects. Multiple logistic linear regression analysis revealed that the allele frequencies of these six SNPs in SAH and MACS1 genes were not significantly different between EH patients and normotensives. SNP in exon 8 of the A/G polymorphism of the MACS1 gene and the G/T SNP in intron 3 of the SAH gene were associated with plasma levels of plasma high-density lipoprotein cholesterol.

CONCLUSIONS

SNPs in the MACS1 and SAH genes contribute to plasma levels of high-density lipoprotein cholesterol.

Starvation response in mouse liver shows strong correlation with life-span-prolonging processes

We have monitored global changes in gene expression in mouse liver in response to fasting and sugar-fed conditions using high-density microarrays. From ∼20,000 different genes, the significantly regulated ones were grouped into specific signaling and metabolic pathways. Striking changes in lipid signaling cascade, insulin and dehydroepiandrosterone (DHEA) hormonal pathways, urea cycle and S-adenosylmethionine-based methyl transfer systems, and cell apoptosis regulators were observed. Since these pathways have been implicated to play a role in the aging process, and since we observe significant overlap of genes regulated upon starvation with those regulated upon caloric restriction, our analysis suggests that starvation may elicit a stress response that is also elicited during caloric restriction. Therefore, many of the signaling and metabolic components regulated during fasting may be the same as those which mediate caloric restriction-dependent life-span extension.

Isolation, sequencing, and expression of a cDNA for the HXM-A form of xenobiotic/medium-chain fatty acid:CoA ligase from human liver mitochondria

The purification of xenobiotic/medium-chain fatty acid:CoA ligases (XM-ligases) from human liver mitochondria resulted in the isolation of two chromatographically separable forms (HXM-A and HXM-B). These two forms were purified to near homogeneity, cleaved with cyanogen bromide, the resulting peptides separated, and the N-terminus of two of the peptides partially sequenced. Identical sequences were obtained for HXM-A and HXM-B for the two peptides. These sequences were used to design probes for screening a human liver cDNA library. This resulted in the isolation of two overlapping cDNAs. Using these sequences we were able to design PCR primers that resulted in the isolation of a full-length cDNA from a human cDNA library. The cDNA contained 1731 bp of open reading frame and coded for a 64230-Da protein. This protein bears 56.2% amino acid homology to the MACS1 (medium-chain acyl-CoA synthetase) enzyme, 58.7% homology to the bovine XL-III XM-ligase, and 81.5% homology to the bovine XL-I XM-ligase. The cDNA could be expressed in COS cells, and the expressed enzyme had greater benzoate activity than phenylacetate activity, which is consistent with the known substrate specificity of HXM-A.

Analysis of the role of the SA gene in blood pressure regulation by gene targeting

The SA gene is expressed in the proximal tubule of the kidney and may be involved in blood pressure (BP) regulation. However, direct evidence for this is lacking. We constructed and analyzed an SA-null mouse in which exons 2 and 3 of the SA gene (including the start codon) had been deleted by homologous recombination. Basal BP and BP changes in response to increased salt and to treatment with losartan were compared between mice homozygous for the targeted SA allele (SA-/- mice) and littermates carrying the wild-type allele (SA+/+ mice). Molecular and biochemical analysis confirmed the lack of SA gene product in SA-/- mice. SA-/- mice grew normally, were fertile, and had no overt phenotype. With both indirect and direct techniques, basal BP was similar in SA-/- and SA+/+ mice. A high salt diet for 4 weeks caused a significant increase in BP in SA-/- and SA+/+, mice but there was no difference between the 2 strains. Losartan caused a significant decrease in BP, but again the response was similar between SA-/- and SA+/+ mice, as were their kidney renin mRNA levels. SA is not involved in the regulation of either basal or salt related BP, and the lack of differential effect in SA-/- mice is not a consequence of compensatory activation of the renin-angiotensin system.

An acyl-CoA synthetase gene family in chromosome 16p12 may contribute to multiple risk factors

We recently reported that genetic polymorphisms of SAH, an acyl-CoA synthetase for fatty acids, might contribute to multiple risk factors, especially hypertriglyceridemia. There are at least 4 members in this SAH gene family, SAH, MACS1, MACS2, and MACS3, and these 4 members are clustered in human Ch16p12. It is possible either that the previously observed associations were due to linkage disequilibrium with truly important polymorphisms in other members of the SAH gene family or that other polymorphisms in this gene family may also influence multiple risk factors. Thus, we performed association studies between genetic polymorphisms in this SAH region and multiple risk factors, using a large cohort representing the general population in Japan. The L513S polymorphism in MACS2 was shown to significantly influence the triglyceride level and the waist-to-hip ratio. The previously observed associations between an SAH polymorphism and the waist-to-hip ratio appear to be due to linkage disequilibrium with the L513S polymorphism. Haplotype analysis indicated that a haplotype defined by the I/D polymorphism of SAH and the L513S polymorphism in MACS2 was highly significantly associated with the triglyceride level. This study confirmed the importance of this chromosomal region in the pathogenesis of hypertriglyceridemia and visceral obesity.

O-MACS, a novel member of the medium-chain acyl-CoA synthetase family, specifically expressed in the olfactory epithelium in a zone-specific manner

In rodents, the olfactory epithelium (OE) can be divided into four topographically distinct zones, and each member of the odorant receptor (OR) gene family is expressed only in one particular zone. To study the functional significance of the zonal structure of the OE, we searched for genes expressed in a zone-specific manner by using the differential display method. Among the clones isolated from the rat OE, we characterized a novel olfactory protein termed O-MACS, a member of the medium-chain acyl-CoA synthetase family. The o-macs gene encodes a protein of 580 amino acids, sharing 56-63% identity with other MACS family proteins. RT-PCR analysis demonstrated that the o-macs gene is expressed only in the OE, unlike other MACS family genes. In situ hybridization revealed that the o-macs transcripts are present in the neuronal cell layer of olfactory sensory neurons (OSNs) as well as in the supporting and basal cell layers in the most dorso-medial area (zone 1) of the OE. Developmental analysis revealed that the o-macs gene is already expressed on embryonic day 11.5, before the onset of the OR gene expression, in a restricted area within the rat olfactory placode. Recombinant O-MACS protein tagged with c-Myc and His6 demonstrated an acyl-CoA synthetase activity for fatty acid activation, and protein localization to mitochondria like other MACS family proteins. The present study indicates that this novel protein may play important roles in processing odorants in a zone-specific manner, or the zonal patterning of the OE during development.

Familial juvenile hyperuricaemic nephropathy (FJHN): linkage analysis in 15 families, physical and transcriptional characterisation of the FJHN critical region on chromosome 16p11.2 and the analysis of seven candidate genes

Familial juvenile hyperuricaemic nephropathy (FJHN) is an autosomal dominant renal disease characterised by juvenile onset of hyperuricaemia, gouty arthritis, and progressive renal failure at an early age. Recent studies in four kindreds showed linkage of a gene for FJHN to the same genomic interval on chromosome 16p11.2, where the gene for the phenotypically similar medullary cystic disease type 2 (MCKD2) has been localised. In this study we performed linkage analysis in additional 15 FJHN families. Linkage of FJHN to 16p11.2 was confirmed in six families, which suggests that, in a large proportion of FJHN kindreds, the disease is likely to be caused by a gene or genes located outside of 16p11.2. Haplotype analysis of the new and previously analysed families provided two non-overlapping critical regions on 16p11.2-FJHN1, delimited by markers D16S499-D16S3036 and FJHN2, delimited by markers D16S412-D16S3116. Considering MCKD2 to be a distinct molecular entity, the analysis suggests that as many as three kidney disease genes may be located in close proximity on 16p11.2. From genomic databases we compiled integrated physical and transcription maps of whole critical genomic region in which 45 known genes and 129 predicted loci have been localised. We selected, analysed and found no pathogenic mutations in seven candidate genes. The linkage and haplotype analysis reported here demonstrates the genetic heterogeneity of FJHN. The report of integrated physical and mostly in-silico predicted transcription maps of the FJHN critical region provides a basis for precise experimental annotation of the current transcript map, which is essential for final identification of the FJHN gene(s).

Role of genetic polymorphism in the SA gene on the blood pressure and prognosis of renal function in patients with immunoglobulin A nephropathy

The SA gene has been shown to be much more highly expressed in the kidneys of spontaneously hypertensive rats than in the corresponding wild-type strain. Genetic polymorphism of this gene has been shown to play a role in human hypertension, although the details of this association remain controversial. We investigated the possible associations between SA gene polymorphism and both hypertension and the prognosis of renal function in patients with immunoglobulin A nephropathy (IgAN). Genomic DNA was isolated from the peripheral blood of 367 individuals, including 274 patients with histologically proven IgAN and 100 controls without any history of renal disease. The SA genotype was determined by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) with Pst I. The frequencies of genotypes and alleles were not different between the patients with IgAN and those without renal disease. In the group without renal disease, the SA gene polymorphism was not associated with hypertension. However, in the patients with IgAN the A1 allele frequency was significantly higher in the hypertensives than in the normotensives. The renal survival of the patients with the A2 allele tended to be better than that of those without the A2 allele. The findings thus suggest that SA gene polymorphism may be associated with the renal prognosis of IgAN through its effect on blood pressure. Further, they suggest that the sensitivity to this gene polymorphism increases in patients with renal injury.

A stationary-phase acyl-coenzyme A synthetase of Streptomyces coelicolor A3(2) is necessary for the normal onset of antibiotic production

The fadD1 and macs1 genes of Streptomyces coelicolor are part of a two-gene operon. Both genes encode putative acyl coenzyme A synthetases (ACSs). The amino acid sequence of FadD1 has high homology with those of several ACSs, while MACS1 has the closest homology with medium-chain ACSs, broadly known as SA proteins. Like FadD of Escherichia coli, FadD1 also has a broad substrate specificity, although saturated long-chain fatty acids appears to be the preferred substrate. fadD1 is a growth-phase-regulated gene, and its mRNA is detected only during the stationary phase of growth. Interestingly, a mutation in fadD1 alters the levels of another ACS or ACSs, both at the stationary phase and at the exponential phase of growth, at least when glucose is used as a main carbon source. The mutant also shows a severe deficiency in antibiotic production, and at least for Act biosynthesis, this deficiency seems to be related to delayed expression of the Act biosynthetic genes. Antibiotic production is restored by the introduction of a wt fadD1 allele into the cell, demonstrating a strict link between ACS activity and the biosynthesis of secondary metabolites. The results of this study indicate that the ACSs may be useful targets for the design of rational approaches to improving antibiotic production.