beta-oxidation of fatty acids in mitochondria, peroxisomes, and bacteria: a century of continued progress

Engineering nature for gaseous hydrocarbon production

The development of sustainable routes to the bio-manufacture of gaseous hydrocarbons will contribute widely to future energy needs. Their realisation would contribute towards minimising over-reliance on fossil fuels, improving air quality, reducing carbon footprints and enhancing overall energy security. Alkane gases (propane, butane and isobutane) are efficient and clean-burning fuels. They are established globally within the transportation industry and are used for domestic heating and cooking, non-greenhouse gas refrigerants and as aerosol propellants. As no natural biosynthetic routes to short chain alkanes have been discovered, de novo pathways have been engineered. These pathways incorporate one of two enzymes, either aldehyde deformylating oxygenase or fatty acid photodecarboxylase, to catalyse the final step that leads to gas formation. These new pathways are derived from established routes of fatty acid biosynthesis, reverse β-oxidation for butanol production, valine biosynthesis and amino acid degradation. Single-step production of alkane gases in vivo is also possible, where one recombinant biocatalyst can catalyse gas formation from exogenously supplied short-chain fatty acid precursors. This review explores current progress in bio-alkane gas production, and highlights the potential for implementation of scalable and sustainable commercial bioproduction hubs.

MmbR, a master transcription regulator that controls fatty acid β-oxidation genes in Mycolicibacterium smegmatis

An unusually high lipid content and a complex lipid profile are the most distinctive features of the mycobacterial cell envelope. However, our understanding of the regulatory mechanism underlying mycobacterial lipid metabolism is limited, and the major regulators responsible for lipid homeostasis remain to be characterized. Here, we identified MmbR as a novel master regulator that is essential for maintaining lipid homeostasis in Mycolicibacterium smegmatis. We found that MmbR controls fatty acid β-oxidation and modulates biofilm formation in Mycolicibacterium smegmatis. Although MmbR possesses the properties of nucleoid-associated proteins, it acts as a TetR-like transcription factor, directly regulating and intensively repressing the expression of a group of core genes involved in fatty acid β-oxidation. Furthermore, both long-chain acyl-Coenzyme A and fatty acids appear to regulate the signal molecules modulated by MmbR. The deletion of mmbR led to a significant reduction in intracellular fatty acid content and a decrease in the relative lipid composition of the biofilm. The lack of mmbR led to morphological changes in the mycobacterial colony, defects in biofilm formation and enhanced sensitivity to anti-tuberculosis drugs. Our study is the first to establish a link between the transcriptional regulation of fatty acid β-oxidation genes and lipid homeostasis in mycobacteria.

Identification and characterization of two isoforms of acyl-coenzyme A oxidase 1 gene and their expression in fasting-induced grass carp Ctenopharyngodon idella adipocyte lipolysis

Acyl-coenzyme A oxidases 1 (ACOX1) is the first rate-limiting enzyme responsible for peroxisomal β-oxidation. In the present study, two mRNA variants, ACOX1a and ACOX1b, transcribed from a single gene, were for the first time isolated and characterized from grass carp Ctenopharyngodon idella, both encoding putative peptides of 660 amino acids. Analysis of the exon-intron structures clarified that grass carp ACOX1a and ACOX1b comprise 14 coding exons and correspond to 3a and 3b isoforms of exon 3 splicing variants. Both ACOX1a and ACOX1b mRNAs were expressed in a wide range of tissues, but the abundance of each ACOX1 mRNA showed the tissue-dependent expression patterns. Time-course analysis of ACOX1 expressions indicated that the level of ACOX1a mRNA reached an almost maximal level at day 2, while that of ACOX1b mRNA reached an almost maximal level at day 8 during grass carp primary preadipocyte differentiation. In fasting-induced adipocyte lipolysis, only ACOX1a showed a significant increase in adipocyte, indicating that two ACOX1 isoforms may serve somewhat different roles in the peroxisomal β-oxidation. These results suggested that grass carp ACOX1a and ACOX1b were differently modulated by fasting in adipocyte. In addition, we found that mitochondrial β-oxidation might dominate at the early stage of fasting in adipocytes, indicating that mitochondria and peroxisomes might possess different capacities in fasting-induced adipocytes fatty acid oxidation.

Fatty Acid Synthase Beta Dehydratase in the Lipid Biosynthesis Pathway Is Required for Conidiogenesis, Pigmentation and Appressorium Formation in Magnaporthe oryzae S6

Lipid biosynthesis produces glycerol, which is important in fueling turgor pressure necessary for germination and penetration of plant host by fungi. As the relationship between pathogenicity and the lipid biosynthetic pathway is not fully understood, we have elucidated the role of the fatty acid synthase beta subunit dehydratase (FAS1) gene in lipid biosynthesis. The FAS1 gene was silenced through homologous double crossover in Magnaporthe oryzae strain S6 to study the effect on lipid biosynthesis. The vegetative growth of Δfas1 mutants show the highest drop on oleic acid (between 10 and 50%), while the mycelial dry weight of mutants dropped significantly on all media. Conidiation of FAS1 mutants show a ~10- and ~5-fold reduction on oatmeal and Potato Dextrose Agar (PDA), respectively. Mutants formed mycelium that were mildly pigmented, indicating that the deletion of FAS1 may have affected melanin biosynthesis. Biochemical and gene expression studies concluded that the fatty acid degradation pathway might have been interrupted by FAS1 deletion. FAS1 mutants showed no enzyme activity on glucose or olive oil, suggesting that the mutants may lack functional peroxisomes and be defective in β-oxidation of fatty acids, hence explaining the reduced lipid deposits in the spores.

Leishmania Encodes a Bacterium-like 2,4-Dienoyl-Coenzyme A Reductase That Is Required for Fatty Acid β-Oxidation and Intracellular Parasite Survival

Leishmania spp. are protozoan parasites that cause a spectrum of important diseases in humans. These parasites develop as extracellular promastigotes in the digestive tract of their insect vectors and as obligate intracellular amastigotes that infect macrophages and other phagocytic cells in their vertebrate hosts. Promastigote-to-amastigote differentiation is associated with marked changes in metabolism, including the upregulation of enzymes involved in fatty acid β-oxidation, which may reflect adaptation to the intracellular niche. Here, we have investigated the function of one of these enzymes, a putative 2,4-dienoyl-coenzyme A (CoA) reductase (DECR), which is specifically required for the β-oxidation of polyunsaturated fatty acids. The Leishmania DECR shows close homology to bacterial DECR proteins, suggesting that it was acquired by lateral gene transfer. It is present in other trypanosomatids that have obligate intracellular stages (i.e., Trypanosoma cruzi and Angomonas) but is absent from dixenous parasites with an exclusively extracellular lifestyle (i.e., Trypanosoma brucei). A DECR-green fluorescent protein (GFP) fusion protein was localized to the mitochondrion in both promastigote and amastigote stages, and the levels of expression increased in the latter stages. A Leishmania major Δdecr null mutant was unable to catabolize unsaturated fatty acids and accumulated the intermediate 2,4-decadienoyl-CoA, confirming DECR's role in β-oxidation. Strikingly, the L. major Δdecr mutant was unable to survive in macrophages and was avirulent in BALB/c mice. These findings suggest that β-oxidation of polyunsaturated fatty acids is essential for intracellular parasite survival and that the bacterial origin of key enzymes in this pathway could be exploited in developing new therapies.IMPORTANCE The Trypanosomatidae are protozoan parasites that infect insects, plants, and animals and have evolved complex monoxenous (single host) and dixenous (two hosts) lifestyles. A number of species of Trypanosomatidae, including Leishmania spp., have evolved the capacity to survive within intracellular niches in vertebrate hosts. The adaptations, metabolic and other, that are associated with development of intracellular lifestyles remain poorly defined. We show that genomes of Leishmania and Trypanosomatidae that can survive intracellularly encode a 2,4-dienoyl-CoA reductase that is involved in catabolism of a subclass of fatty acids. The trypanosomatid enzyme shows closest similarity to the corresponding bacterial enzymes and is located in the mitochondrion and essential for intracellular growth of Leishmania The findings suggest that acquisition of this gene by lateral gene transfer from bacteria by ancestral monoxenous Trypanosomatidae likely contributed to the development of a dixenous lifestyle of these parasites.

Comparing Early Eukaryotic Integration of Mitochondria and Chloroplasts in the Light of Internal ROS Challenges: Timing is of the Essence

When trying to reconstruct the evolutionary trajectories during early eukaryogenesis, one is struck by clear differences in the developments of two organelles of endosymbiotic origin: the mitochondrion and the chloroplast. From a symbiogenic perspective, eukaryotic development can be interpreted as a process in which many of the defining eukaryotic characteristics arose as a result of mutual adaptions of both prokaryotes (an archaeon and a bacterium) involved. This implies that many steps during the bacterium-to-mitochondrion transition trajectory occurred in an intense period of dramatic and rapid changes. In contrast, the subsequent cyanobacterium-to-chloroplast development in a specific eukaryotic subgroup, leading to the photosynthetic lineages, occurred in a full-fledged eukaryote. The commonalities and differences in the two trajectories shed an interesting light on early, and ongoing, eukaryotic evolutionary driving forces, especially endogenous reactive oxygen species (ROS) formation. Differences between organellar ribosomes, changes to the electron transport chain (ETC) components, and mitochondrial codon reassignments in nonplant mitochondria can be understood when mitochondrial ROS formation, e.g., during high energy consumption in heterotrophs, is taken into account.IMPORTANCE The early eukaryotic evolution was deeply influenced by the acquisition of two endosymbiotic organelles - the mitochondrion and the chloroplast. Here we discuss the possibly important role of reactive oxygen species in these processes.

Identification and characterization of a protein Bro1 essential for sophorolipids synthesis in Starmerella bombicola

Sophorolipids (SLs) are surface-active molecules produced by the non-pathogenic yeast Starmerella bombicola CGMCC 1576. Several genes involved in the synthesis of SLs have been identified. However, the regulation mechanism of the synthesis pathway for SLs has not been investigated. We recently discovered a protein in S. bombicola, which is structurally related to Yarrowia lipolytica YlBro1. To identify the function of the protein SbBro1 in S. bombicola, the deletion, overexpression, and complementary mutant strains were constructed. We found that the deletion mutant no longer produced SLs. Transcriptome analysis indicated that the expression levels of the key enzyme genes of SLs biosynthetic pathway were significantly down-regulated in the Δbro1, especially the expression level of cyp52m1 encoding the first rate-limiting enzyme in SL synthesis pathway was down-regulated 13-folds and the expression of fatty acid β-oxidation-related enzymes was also down-regulated. This study can give insight into the regulation of SL synthesis.

Mitochondrial adaptations in liver and skeletal muscle to pro-longevity nutritional and genetic interventions: the crosstalk between calorie restriction and CYB5R3 overexpression in transgenic mice

Calorie restriction without malnutrition (CR) is considered as the most effective nongenetic nor pharmacological intervention that promotes healthy aging phenotypes and can extend lifespan in most model organisms. Lifelong CR leads to an increase of cytochrome b₅ reductase-3 (CYB5R3) expression and activity. Overexpression of CYB5R3 confers some of the salutary effects of CR, although the mechanisms involved might be independent because key aspects of energy metabolism and lipid profiles of tissues go in opposite ways. It is thus important to study if some of the metabolic adaptations induced by CR are affected by CYB5R3 overexpression. CYB5R3 overexpression greatly preserved body and liver weight in mice under CR conditions. In liver, CR did not modify mitochondrial abundance, but lead to increased expression of mitofusin Mfn2 and TFAM, a transcription factor involved in mitochondrial biogenesis. These changes were prevented by CYB5R3 overexpression but resulted in a decreased expression of a different mitochondrial biogenesis-related transcription factor, Nrf1. In skeletal muscle, CR strongly increased mitochondrial mass, mitofusin Mfn1, and Nrf1. However, CYB5R3 mice on CR did not show increase in muscle mitochondrial mass, regardless of a clear increase in expression of TFAM and mitochondrial complexes in this tissue. Our results support that CYB5R3 overexpression significantly modifies the metabolic adaptations of mice to CR.

Omics Integration for Mitochondria Systems Biology

Significance: Elucidation of the central importance of mitophagy in homeostasis of cells and organisms emphasizes that mitochondrial functions extend far beyond short-term needs for energy production. In mitochondria systems biology, the mitochondrial genome, proteome, and metabolome operate as a functional network in coordination of cell activities. Organization occurs through subnetworks that are interconnected by membrane potential, transport activities, allosteric and cooperative interactions, redox signaling mechanisms, rheostatic control by post-translational modifications, and metal ion homeostasis. These subnetworks enable use of varied energy precursors, defense against environmental stressors, and macromolecular rewiring to titrate energy production, biosynthesis, and detoxification according to cell-specific needs. Rewiring mechanisms, termed mitochondrial reprogramming, enhance fitness to respond to metabolic resources and challenges from the environment. Maladaptive responses can cause cell death. Maladaptive rewiring can cause disease. In cancer, adaptive rewiring can interfere with effective treatment. Recent Advances: Many recent advances have been facilitated by the development of new omics tools, which create opportunities to use data-driven analysis of omics data to address these complex adaptive and maladaptive mechanisms of mitochondrial reprogramming in human disease. Critical Issues: Application of omics integration to model systems reveals a critical role for metal ion homeostasis broadly impacting mitochondrial reprogramming. Importantly, data show that trans-omics associations are more robust and biologically relevant than single omics associations. Future Directions: Application of omics integration to mitophagy research creates new opportunities to link the complex, interactive functions of mitochondrial form and function in mitochondria systems biology.

CPT1A-mediated Fat Oxidation, Mechanisms, and Therapeutic Potential

Energy homeostasis during fasting or prolonged exercise depends on mitochondrial fatty acid oxidation (FAO). This pathway is crucial in many tissues with high energy demand and its disruption results in inborn FAO deficiencies. More than 15 FAO genetic defects have been currently described, and pathological variants described in circumpolar populations provide insights into its critical role in metabolism. The use of fatty acids as energy requires more than 2 dozen enzymes and transport proteins, which are involved in the activation and transport of fatty acids into the mitochondria. As the key rate-limiting enzyme of FAO, carnitine palmitoyltransferase I (CPT1) regulates FAO and facilitates adaptation to the environment, both in health and in disease, including cancer. The CPT1 family of proteins contains 3 isoforms: CPT1A, CPT1B, and CPT1C. This review focuses on CPT1A, the liver isoform that catalyzes the rate-limiting step of converting acyl-coenzyme As into acyl-carnitines, which can then cross membranes to get into the mitochondria. The regulation of CPT1A is complex and has several layers that involve genetic, epigenetic, physiological, and nutritional modulators. It is ubiquitously expressed in the body and associated with dire consequences linked with genetic mutations, metabolic disorders, and cancers. This makes CPT1A an attractive target for therapeutic interventions. This review discusses our current understanding of CPT1A expression, its role in heath and disease, and the potential for therapeutic opportunities targeting this enzyme.

Identification of putative Type-I sex pheromone biosynthesis-related genes expressed in the female pheromone gland of Streltzoviella insularis

Species-specific sex pheromones play key roles in moth sexual communication. Although the general pathway of Type-I sex pheromone biosynthesis is well established, only a handful of genes encoding enzymes involved in this pathway have been characterized. Streltzoviella insularis is a destructive wood-boring pest of many street trees in China, and the female sex pheromone of this species comprises a blend of (Z)-3-tetradecenyl acetate, (E)-3-tetradecenyl acetate, and (Z)-5-dodecenyl acetate. This organism therefore provides an excellent model for research on the diversity of genes and molecular mechanisms involved in pheromone production. Herein, we assembled the pheromone gland transcriptome of S. insularis by next-generation sequencing and identified 74 genes encoding candidate key enzymes involved in the fatty acid biosynthesis, β-oxidation, and functional group modification. In addition, tissue expression patterns further showed that an acetyl-CoA carboxylase and two desaturases were highly expressed in the pheromone glands compared with the other tissues, indicating possible roles in S. insularis sex pheromone biosynthesis. Finally, we proposed putative S. insularis biosynthetic pathways for sex pheromone components and highlighted candidate genes. Our findings lay a solid foundation for understanding the molecular mechanisms underpinning S. insularis sex pheromone biosynthesis, and provide potential targets for disrupting chemical communication that could assist the development of novel pest control methods.

The Role of Mitochondrial Calcium Signaling in the Pathophysiology of Cancer Cells

The pioneering work of Richard Altman on the presence of mitochondria in cells set in motion a field of research dedicated to uncovering the secrets of the mitochondria. Despite limitations in studying the structure and function of the mitochondria, advances in our understanding of this organelle prompted the development of potential treatments for various diseases, from neurodegenerative conditions to muscular dystrophy and cancer. As the powerhouses of the cell, the mitochondria represent the essence of cellular life and as such, a selective advantage for cancer cells. Much of the function of the mitochondria relies on Ca²⁺ homeostasis and the presence of effective Ca²⁺ signaling to maintain the balance between mitochondrial function and dysfunction and subsequently, cell survival. Ca²⁺ regulates the mitochondrial respiration rate which in turn increases ATP synthesis, but too much Ca²⁺ can also trigger the mitochondrial apoptosis pathway; however, cancer cells have evolved mechanisms to modulate mitochondrial Ca²⁺ influx and efflux in order to sustain their metabolic demand and ensure their survival. Therefore, targeting the mitochondrial Ca²⁺ signaling involved in the bioenergetic and apoptotic pathways could serve as potential approaches to treat cancer patients. This chapter will review the role of Ca²⁺ signaling in mediating the function of the mitochondria and its involvement in health and disease with special focus on the pathophysiology of cancer.

Temporal Dynamics of the Soil Metabolome and Microbiome During Simulated Anaerobic Soil Disinfestation

Significant interest exists in engineering the soil microbiome to attain suppression of soil-borne plant diseases. Anaerobic soil disinfestation (ASD) has potential as a biologically regulated disease control method; however, the role of specific metabolites and microbial community dynamics contributing to ASD mediated disease control is mostly uncharacterized. Understanding the trajectory of co-evolutionary processes leading to syntrophic generation of functional metabolites during ASD is a necessary prelude to the predictive utilization of this disease management approach. Consequently, metabolic and microbial community profiling were used to generate highly dimensional datasets and network analysis to identify sequential transformations through aerobic, facultatively anaerobic, and anaerobic soil phases of the ASD process and distinct groups of metabolites and microorganisms linked with those stages. Transient alterations in abundance of specific microbial groups, not consistently accounted for in previous studies of the ASD process, were documented in this time-course study. Such events initially were associated with increases and subsequent diminution in highly labile metabolites conferred by the carbon input. Proliferation and dynamic compositional changes in the Firmicutes community continued throughout the anaerobic phase and was linked to temporal changes in metabolite abundance including accumulation of small chain organic acids, methyl sulfide compounds, hydrocarbons, and p-cresol with antimicrobial properties. Novel potential modes of disease control during ASD were identified and the importance of the amendment and "community metabolism" for temporally supplying specific classes of labile compounds were revealed.

Characteristics and optimised fermentation of a novel magnetotactic bacterium, Magnetospirillum sp. ME-1

Magnetotactic bacteria (MTB) can biosynthesise magnetosomes, which have great potential for commercial applications. A new MTB strain, Magnetospirillum sp. ME-1, was isolated and cultivated from freshwater sediments of East Lake (Wuhan, China) using the limiting dilution method. ME-1 had a chain of 17 ± 4 magnetosomes in the form of cubooctahedral crystals with a shape factor of 0.89. ME-1 was closest to Magnetospirillum sp. XM-1 according to 16S rRNA gene sequence similarity. Compared with XM-1, ME-1 possessed an additional copy of mamPA and a larger mamO in magnetosome-specific genes. ME-1 had an intact citric acid cycle, and complete pathway models of ammonium assimilation and dissimilatory nitrate reduction. Potential carbon and nitrogen sources in these pathways were confirmed to be used in ME-1. Adipate was determined to be used in the fermentation medium as a new kind of dicarboxylic acid. The optimised fermentation medium was determined by orthogonal tests. The large-scale production of magnetosomes was achieved and the magnetosome yield (wet weight) reached 120 mg L-1 by fed-batch cultivation of ME-1 at 49 h in a 10-L fermenter with the optimised fermentation medium. This study may provide insights into the isolation and cultivation of other new MTB strains and the production of magnetosomes.

Structure-toxicity relationships of saturated and unsaturated free fatty acids for elucidating the lipotoxic effects in human EndoC-βH1 beta-cells

Lipotoxicity has been considered a major cause for beta-cell dysfunction in type 2 diabetes mellitus. However, the underlying mechanisms are still unclear. To achieve a better understanding of the toxicity a wide range of structurally different free fatty acids (FFAs) has been analyzed in human EndoC-βH1 beta-cells. Exposure of human EndoC-βH1 beta-cells to physiological saturated and monounsaturated long-chain FFAs induced apoptosis. Particularly noteworthy was that the toxicity increased more rapidly with increasing chain length of saturated than of unsaturated FFAs. The highest toxicity was observed in the presence of very long-chain FFAs (C20-C22), whereas polyunsaturated FFAs were not toxic. Long-chain FFAs increased peroxisomal hydrogen peroxide generation slightly, while very long-chain FFAs increased hydrogen peroxide generation more potently in both peroxisomes and mitochondria. The greater toxicity of very long-chain FFAs was accompanied by hydroxyl radical formation, along with cardiolipin peroxidation and ATP depletion. Intriguingly, only saturated very long-chain FFAs activated ER stress. On the other hand saturated very long-chain FFAs did not induce lipid droplet formation in contrast to long-chain FFAs and unsaturated very long-chain FFAs. The present data highlight the importance of structure-activity relationship analyses for the understanding of the mechanisms of lipotoxicity. Chain length and degree of saturation of FFAs are crucial factors for the toxicity of FFAs, with peroxisomal, mitochondrial, and ER stress representing the major pathogenic factors for induction of lipotoxicity. The results might provide a guide for the composition of a healthy beta-cell protective diet.

Effect of moisture on wheat grains lipid patterns and infection with Fusarium graminearum

Suitable conditions of temperature and humidity are required to maintain wheat grains quality, but during processing and storage, the grains can be exposed to adverse environmental conditions and presence of infectious fungi. Fusarium graminearum, the main causal agent of Fusarium head blight on wheat, affects crop yields and grain quality by alteration of their biochemical components and mycotoxin contamination, which reduces the possibilities of wheat end use and compromises food safety. Lipid degradation by hydrolytic, oxidative and microbial deterioration is the predominant cause of the loss of sensory acceptability, nutritional value and baking quality. The aim of this research was to determine the influence of adverse environmental conditions -as the increasing moisture - on lipid patterns of whole wheat flours contaminated with F. graminearum in relation to the infection degree. In vitro cultures of F. graminearum were carried out on wheat grains under different degrees of relative humidity (11, 50, 75 and 100%) throughout 45 days of incubation at 28 °C. The fungal biomass measured by q-PCR increased proportionally with the humidity. A decrease in the signals of saturated (palmitic and estearic) and unsaturated (oleic, linoleic and linolenic) fatty acids, analyzed as fatty acid methyl esters (FAMEs) by GC-MS, was observed in relation with the humidity and infection degree. The degradation rate of the lipids was high during the first 15 days of incubation, reaching the fatty acids content, values around 20-40% of those found in the control. From that moment on, the rate of degradation was slower or even null. It was observed that in all treatments, the linolenic acid reached the highest degradation ratio in comparison with the other fatty acids, which may be caused by the action of lipoxygenases. The lipase activity and the content of deoxynivalenol were also determinate on the flours. The lipase activity increased until day 25 of incubation reaching twice the initial value. The deoxynivalenol content also increased along incubation while fatty acids decreased. Our results demonstrated that the magnitude in the signal of fatty acids in whole wheat flours varied in relation to the degree of humidity and fungal infection of the grains from which they were obtained. Otherwise, lipids and their oxidation products are related with the pathogenesis and production of mycotoxins. These observations highlight the importance of an adequate manipulation of wheat grains on the processing chain to prevent quality changes and mycotoxins contamination.

Melatonin reduces intramuscular fat deposition by promoting lipolysis and increasing mitochondrial function

In obesity and diabetes, intramuscular fat (IMF) content correlates markedly with insulin sensitivity, which makes IMF manipulation an area of therapeutic interest. Melatonin, an important circadian rhythm-regulating hormone, reportedly regulates fat deposition, but its effects on different types of adipose vary. Little is known about the role of melatonin in IMF deposition. Here, using intramuscular preadipocytes in pigs, we investigated to determine whether melatonin affects or regulates IMF deposition. We found that melatonin greatly inhibited porcine intramuscular preadipocyte proliferation. Although melatonin administration significantly upregulated the expression of adipogenic genes, smaller lipid droplets were formed in intramuscular adipocytes. Additional investigation demonstrated that melatonin promoted lipolysis of IMF by activating protein kinase A and the signaling of ERK1/2. Moreover, melatonin increased thermogenesis in intramuscular adipocytes by enhancing mitochondrial biogenesis and mitochondrial respiration. A mouse model, in which untreated controls were compared with mice that received 3 weeks of melatonin treatment, verified the effect of melatonin on IMF deposition. In conclusion, melatonin reduces IMF deposition by upregulating lipolysis and mitochondrial bioactivities. These data establish a link between melatonin signaling and lipid metabolism in mammalian models and suggest the potential for melatonin administration to treat or prevent obesity and related diseases.

Crystal structure of human mitochondrial trifunctional protein, a fatty acid β-oxidation metabolon

Membrane-bound mitochondrial trifunctional protein (TFP) catalyzes β-oxidation of long chain fatty acyl-CoAs, employing 2-enoyl-CoA hydratase (ECH), 3-hydroxyl-CoA dehydrogenase (HAD), and 3-ketothiolase (KT) activities consecutively. Inherited deficiency of TFP is a recessive genetic disease, manifesting in hypoketotic hypoglycemia, cardiomyopathy, and sudden death. We have determined the crystal structure of human TFP at 3.6-Å resolution. The biological unit of the protein is α₂β₂ The overall structure of the heterotetramer is the same as that observed by cryo-EM methods. The two β-subunits make a tightly bound homodimer at the center, and two α-subunits are bound to each side of the β₂ dimer, creating an arc, which binds on its concave side to the mitochondrial innermembrane. The catalytic residues in all three active sites are arranged similarly to those of the corresponding, soluble monofunctional enzymes. A structure-based, substrate channeling pathway from the ECH active site to the HAD and KT sites is proposed. The passage from the ECH site to the HAD site is similar to those found in the two bacterial TFPs. However, the passage from the HAD site to the KT site is unique in that the acyl-CoA intermediate can be transferred between the two sites by passing along the mitochondrial inner membrane using the hydrophobic nature of the acyl chain. The 3'-AMP-PPi moiety is guided by the positively charged residues located along the "ceiling" of the channel, suggesting that membrane integrity is an essential part of the channel and is required for the activity of the enzyme.

Disruption of putative short-chain acyl-CoA dehydrogenases compromised free radical scavenging, conidiogenesis, and pathogenesis of Magnaporthe oryzae

Short-chain acyl-CoA dehydrogenase (Scad) mediated β-oxidation serves as the fastest route for generating essential energies required to support the survival of organisms under stress or starvation. In this study, we identified three putative SCAD genes in the genome of the globally destructive rice blast pathogen Magnaporthe oryzae, named as MoSCAD1, MoSCAD2, and MoSCAD3. To elucidate their function, we deployed targeted gene deletion strategy to investigate individual and the combined influence of MoSCAD genes on growth, stress tolerance, conidiation and pathogenicity of the rice blast fungus. First, localization and co-localization results obtained from this study showed that MoScad1 localizes to the endoplasmic reticulum (ER), MoScad2 localizes exclusively to the mitochondria while MoScad3 partially localizes to the mitochondria and peroxisome at all developmental stages of M. oryzae. Results obtained from this investigation showed that the deletion of MoSCAD1 and MoSCAD2 caused a minimal but significant reduction in the growth of ΔMoscad1 and ΔMoscad2 strains, while, growth characteristics exhibited by the ΔMoscad3 strain was similar to the wild-type strain. Furthermore, we observed that deletion of MoSCAD2 resulted in drastic reduction in conidiation, delayed conidia germination, triggered the development of abnormal appressorium and suppressed host penetration and colonization efficiencies of the ΔMoscad1 strain. This study provides first material evidence confirming the possible existence of ER β-oxidation pathway in M. oryzae. We also infer that mitochondria β-oxidation rather than peroxisomal and ER β-oxidation play an essential role in the vegetative growth, conidiation, appressorial morphogenesis and progression of pathogenesis in M. oryzae.

Cardiolipin-deficient cells depend on anaplerotic pathways to ameliorate defective TCA cycle function

Previous studies have shown that the cardiolipin (CL)-deficient yeast mutant, crd1Δ, has decreased levels of acetyl-CoA and decreased activities of the TCA cycle enzymes aconitase and succinate dehydrogenase. These biochemical phenotypes are expected to lead to defective TCA cycle function. In this study, we report that signaling and anaplerotic metabolic pathways that supplement defects in the TCA cycle are essential in crd1Δ mutant cells. The crd1Δ mutant is synthetically lethal with mutants in the TCA cycle, retrograde (RTG) pathway, glyoxylate cycle, and pyruvate carboxylase 1. Glutamate levels were decreased, and the mutant exhibited glutamate auxotrophy. Glyoxylate cycle genes were up-regulated, and the levels of glyoxylate metabolites succinate and citrate were increased in crd1Δ. Import of acetyl-CoA from the cytosol into mitochondria is essential in crd1Δ, as deletion of the carnitine-acetylcarnitine translocase led to lethality in the CL mutant. β-oxidation was functional in the mutant, and oleate supplementation rescued growth defects. These findings suggest that TCA cycle deficiency caused by the absence of CL necessitates activation of anaplerotic pathways to replenish acetyl-CoA and TCA cycle intermediates. Implications for Barth syndrome, a genetic disorder of CL metabolism, are discussed.

Metabolic profiling analysis upon acylcarnitines in tissues of hepatocellular carcinoma revealed the inhibited carnitine shuttle system caused by the downregulated carnitine palmitoyltransferase 2

The carnitine shuttle system (CSS) plays a crucial role in the transportation of fatty acyls during fatty acid β-oxidation for energy supplementation, especially in cases of high energy demand, such as in cancer. In this study, to systematically characterize alterations of the CSS in hepatocellular carcinoma (HCC), acylcarnitine metabolic profiling was carried out on 80 pairs of HCC tissues and adjacent noncancerous tissues (ANTs) by using ultra-performance liquid chromatography coupled to mass spectrometry. Twenty-four acylcarnitines classified into five categories were identified and characterized between HCCs and ANTs. Notably, increased saturated long-chain acylcarnitines (LCACs) and decreased short- and medium-chain acylcarnitines (S/MCACs) were simultaneously observed in HCC samples. Subsequent correlation network and heatmap analysis indicated low correlations between LCACs and S/MCACs. The mRNA and protein expressions of carnitine palmitoyltransferase 2 (CPT2) was significantly downregulated in HCC samples, whereas CPT1A expression was not significantly changed. Correspondingly, the relative levels of S/MCACs were reduced and those of LCACs were increased in BEL-7402/CPT2-knockdown cells compared to negative controls. Both results suggested that decreased shuttling efficiency in HCC might be associated with downregulation of CPT2. In addition, decreases in the mRNA expression of acetyl-CoA acyltransferase 2 were also observed in HCC tissues and BEL-7402/CPT2-knockdown cells, suggesting potential low β-oxidation efficiency, which was consistent with the increased expression of stearoyl-CoA desaturase 1 in both samples. The systematic strategy applied in our study illustrated decreased shuttling efficiency of the carnitine shuttle system in HCC and can provide biologists with an in-depth understanding of β-oxidation in HCC.

Investigating the Role of Mitochondria in Type 2 Diabetes - Lessons from Lipidomics and Proteomics Studies of Skeletal Muscle and Liver

Mitochondrial dysfunction is discussed as a key player in the pathogenesis of type 2 diabetes mellitus (T2Dm), a highly prevalent disease rapidly developing as one of the greatest global health challenges of this century. Data however about the involvement of mitochondria, central hubs in bioenergetic processes, in the disease development are still controversial. Lipid and protein homeostasis are under intense discussion to be crucial for proper mitochondrial function. Consequently proteomics and lipidomics analyses might help to understand how molecular changes in mitochondria translate to alterations in energy transduction as observed in the healthy and metabolic diseases such as T2Dm and other related disorders. Mitochondrial lipids integrated in a tool covering proteomic and functional analyses were up to now rarely investigated, although mitochondrial lipids might provide a possible lynchpin in the understanding of type 2 diabetes development and thereby prevention. In this chapter state-of-the-art analytical strategies, pre-analytical aspects, potential pitfalls as well as current proteomics and lipidomics-based knowledge about the pathophysiological role of mitochondria in the pathogenesis of type 2 diabetes will be discussed.

Dietary sn-2 palmitic triacylglycerols reduced faecal lipids, calcium contents and altered lipid metabolism in Sprague-Dawley rats

In this study, the impact of dietary sn-2 palmitic triacylglycerol (sn-2 PTAG) on faecal lipids, calcium excretion and lipid metabolic alternation was investigated in Sprague-Dawley (SD) rats fed with high-fat diet containing either palm olein (PO, sn-2 palmitic acid (PA) of 14.8%), sn-2 PTAG50 (sn-2 PA of 56.4%) or sn-2 PTAG70 (sn-2 PA of 72.4%), respectively. After 4-week feeding period, SD rats fed with sn-2 PTAGs showed reduced faecal soap fatty acids, neutral lipid and calcium excretion compared to those of PO-fed rats, whereas a significant difference was only observed for the sn-2 PTAG70-fed rats (p < .05). Moreover, dietary sn-2 PTAG70 also showed a significant effect on decreasing serum triacylglycerol (TAG) level, reducing perirenal adipocyte size and regulating lipid metabolism in small intestine and perirenal adipose tissue of SD rats. Significantly increased mRNA levels of genes involved in intestinal lipid anabolism as well as lipid catabolism were both observed in the sn-2 PTAG70-fed rats (p < .05). Meanwhile, dietary sn-2 PTAG70 also significantly up-regulated lipolysis, mitochondrial fatty acid oxidation and thermogenesis-related gene and protein levels in perirenal adipose tissue, which might be correlated with the reduced perirenal adipocyte size. Taken together, our findings indicated that sn-2 PTAG70 may have some beneficial effects on intestinal lipid utilisation and lipid metabolic activity for energy supply in visceral adipose tissue.

Epigenetic-Transcriptional Regulation of Fatty Acid Metabolism and Its Alterations in Leukaemia

In recent years fatty acid metabolism has gained greater attention in haematologic cancers such as acute myeloid leukaemia. The oxidation of fatty acids provides fuel in the form of ATP and NADH, while fatty acid synthesis provides building blocks for cellular structures. Here, we will discuss how leukaemic cells differ from healthy cells in their increased reliance on fatty acid metabolism. In order to understand how these changes are achieved, we describe the main pathways regulating fatty acid metabolism at the transcriptional level and highlight the limited knowledge about related epigenetic mechanisms. We explore these mechanisms in the context of leukaemia and consider the relevance of the bone marrow microenvironment in disease management. Finally, we discuss efforts to interfere with fatty acid metabolism as a therapeutic strategy along with the use of metabolic parameters as biomarkers.

Bioengineering triacetic acid lactone production in Yarrowia lipolytica for pogostone synthesis

Yarrowia lipolytica is an oleaginous yeast that is recognized for its ability to accumulate high levels of lipids, which can serve as precursors to biobased fuels and chemicals. Polyketides, such as triacetic acid lactone (TAL), can also serve as a precursor for diverse commodity chemicals. This study used Y. lipolytica as a host organism for the production of TAL via expression of the 2-pyrone synthase gene from Gerbera hybrida. Induction of lipid biosynthesis by nitrogen-limited growth conditions increased TAL titers. We also manipulated basal levels of TAL production using a DNA cut-and-paste transposon to mobilize and integrate multiple copies of the 2-pyrone synthase gene. Strain modifications and batch fermentation in nitrogen-limited medium yielded TAL titers of 2.6 g/L. Furthermore, we show that minimal medium allows TAL to be readily concentrated at >94% purity and converted at 96% yield to pogostone, a valuable antibiotic. Modifications of this reaction scheme yielded diverse related compounds. Thus, oleaginous organisms have the potential to be flexible microbial biofactories capable of economical synthesis of platform chemicals and the generation of industrially relevant molecules.

Specific enzyme functionalities of Fusarium oxysporum compared to host plants

The genus Fusarium contains some of the most studied and important species of plant pathogens that economically affect world agriculture and horticulture. Fusarium spp. are ubiquitous fungi widely distributed in soil, plants as well as in different organic substrates and are also considered as opportunistic human pathogens. The identification of specific enzymes essential to the metabolism of these fungi is expected to provide molecular targets to control the diseases they induce to their hosts. Through applications of traditional techniques of sequence homology comparison by similarity search and Markov modeling, this report describes the characterization of enzymatic functionalities associated to protein targets that could be considered for the control of root rots induced by Fusarium oxysporum. From the analysis of 318 F. graminearum enzymes, we retrieved 30 enzymes that are specific of F. oxysporum compared to 15 species of host plants. By comparing these 30 specific enzymes of F. oxysporum with the genome of Arabidopsis thaliana, Brassica rapa, Glycine max, Jatropha curcas and Ricinus communis, we found 7 key specific enzymes whose inhibition is expected to affect significantly the development of the fungus and 5 specific enzymes that were considered here to be secondary because they are inserted in pathways with alternative routes.

Fatty Acid-Stimulated Insulin Secretion vs. Lipotoxicity

Fatty acid (FA)-stimulated insulin secretion (FASIS) is reviewed here in contrast to type 2 diabetes etiology, resulting from FA overload, oxidative stress, intermediate hyperinsulinemia, and inflammation, all converging into insulin resistance. Focusing on pancreatic islet β-cells, we compare the physiological FA roles with the pathological ones. Considering FAs not as mere amplifiers of glucose-stimulated insulin secretion (GSIS), but as parallel insulin granule exocytosis inductors, partly independent of the K_ATP channel closure, we describe the FA initiating roles in the prediabetic state that is induced by retardations in the glycerol-3-phosphate (glucose)-promoted glycerol/FA cycle and by the impaired GPR40/FFA1 (free FA1) receptor pathway, specifically in its amplification by the redox-activated mitochondrial phospholipase, iPLA2γ. Also, excessive dietary FAs stimulate intestine enterocyte incretin secretion, further elevating GSIS, even at low glucose levels, thus contributing to diabetic hyperinsulinemia. With overnutrition and obesity, the FA overload causes impaired GSIS by metabolic dysbalance, paralleled by oxidative and metabolic stress, endoplasmic reticulum stress and numerous pro-apoptotic signaling, all leading to decreased β-cell survival. Lipotoxicity is exerted by saturated FAs, whereas ω-3 polyunsaturated FAs frequently exert antilipotoxic effects. FA-facilitated inflammation upon the recruitment of excess M1 macrophages into islets (over resolving M2 type), amplified by cytokine and chemokine secretion by β-cells, leads to an inevitable failure of pancreatic β-cells.

Hematopoietic stem cell fate through metabolic control

Hematopoietic stem cells maintain a quiescent state in the bone marrow to preserve their self-renewal capacity, but also undergo cell divisions as required. Organelles such as the mitochondria sustain cumulative damage during these cell divisions and this damage may eventually compromise the cells' self-renewal capacity. Hematopoietic stem cell divisions result in either self-renewal or differentiation, with the balance between the two affecting hematopoietic homeostasis directly; however, the heterogeneity of available hematopoietic stem cell-enriched fractions, together with the technical challenges of observing hematopoietic stem cell behavior, has long hindered the analysis of individual hematopoietic stem cells and prevented the elucidation of this process. Recent advances in genetic models, metabolomics analyses, and single-cell approaches have revealed the contributions made to hematopoietic stem cell self-renewal by metabolic cues, mitochondrial biogenesis, and autophagy/mitophagy, which have highlighted mitochondrial quality control as a key factor in the equilibrium of hematopoietic stem cells. A deeper understanding of precisely how specific modes of metabolism control hematopoietic stem cells fate at the single-cell level is therefore not only of great biological interest, but will also have clear clinical implications for the development of therapies for hematological diseases.

Fatty Acid Oxidation Is Required for Myxococcus xanthus Development

Myxococcus xanthus cells produce lipid bodies containing triacylglycerides during fruiting body development. Fatty acid β-oxidation is the most energy-efficient pathway for lipid body catabolism. In this study, we used mutants in fadJ (MXAN_5371 and MXAN_6987) and fadI (MXAN_5372) homologs to examine whether β-oxidation serves an essential developmental function. These mutants contained more lipid bodies than the wild-type strain DK1622 and 2-fold more flavin adenine dinucleotide (FAD), consistent with the reduced consumption of fatty acids by β-oxidation. The β-oxidation pathway mutants exhibited differences in fruiting body morphogenesis and produced spores with thinner coats and a greater susceptibility to thermal stress and UV radiation. The MXAN_5372/5371 operon is upregulated in sporulating cells, and its expression could not be detected in csgA, fruA, or mrpC mutants. Lipid bodies were found to persist in mature spores of DK1622 and wild strain DK851, suggesting that the roles of lipid bodies and β-oxidation may extend to spore germination.IMPORTANCE Lipid bodies act as a reserve of triacylglycerides for use when other sources of carbon and energy become scarce. β-Oxidation is essential for the efficient metabolism of fatty acids associated with triacylglycerides. Indeed, the disruption of genes in this pathway has been associated with severe disorders in animals and plants. Myxococcus xanthus, a model organism for the study of development, is ideal for investigating the complex effects of altered lipid metabolism on cell physiology. Here, we show that β-oxidation is used to consume fatty acids associated with lipid bodies and that the disruption of the β-oxidation pathway is detrimental to multicellular morphogenesis and spore formation.

Lipid metabolism and benzo[a]pyrene degradation by Fusarium solani: an unexplored potential

In a search for indigenous soil saprotrophic fungi for bioremediation purposes, Fusarium solani, a saprotrophic fungus belonging to the phylum Ascomycota, was isolated from a fossil carbon contaminated soil. The effect of the carbon source, glucose or olive oil, was investigated in vitro on the biomass produced by F. solani and on the degradation of benzo[a]pyrene (BaP) in mineral medium. After only 12 days of incubation, BaP degradation by F. solani was higher (37.4%) with olive oil used as the carbon source than the one obtained with glucose (4.2%). Catalase activity increased in the presence of olive oil (3.4 μkat mg^-1 protein) in comparison with glucose (2.1 μkat mg^-1 protein). When olive oil was used as the carbon source, BaP degradation increased up to 76.0% in the presence of a specific catalase inhibitor, 3-Amino-1,2,4-triazole (2 mM). This metabolic engineering strategy based both on the use of olive oil as carbon source (cultivation strategy) and on the blocking of the catalase activity could be an innovative and promising approach for fungal biodegradation of BaP and consequently for bioremediation of soil contaminated with polycyclic aromatic hydrocarbons.

Skeletal muscle overexpression of short isoform Sirt3 altered mitochondrial cardiolipin content and fatty acid composition

Cardiolipin (CL) is a phospholipid at the heart of mitochondrial metabolism, which plays a key role in mitochondrial function and bioenergetics. Among mitochondrial activity regulators, SIRT3 plays a crucial role in controlling the acetylation status of many enzymes participating in the energy metabolism in particular concerning lipid metabolism and fatty acid oxidation. Data suggest that possible connection may exist between SIRT3 and CL status that has not been evaluated in skeletal muscle. In the present study, we have characterized skeletal muscle lipids as well as mitochondrial lipids composition in mice overexpressing long (SIRT3-M1) and short (SIRT3-M3) isoforms of SIRT3. Particular attention has been paid for CL. We reported no alteration in muscle lipids content and fatty acids composition between the two mice SIRT3 strains and the control mice. However, mitochondrial CL content was significantly decreased in SIRT3-M3 mice and associated to an upregulation of tafazzin gene expression. In addition, mitochondrial phospholipids and fatty acids composition was altered with an increase in the PC/PE ratio and arachidonic acid content and a reduction in the MUFA/SFA ratio. These modifications in mitochondrial membrane composition are associated with a reduction in the enzymatic activities of mitochondrial respiratory chain complexes I and IV. In spite of these mitochondrial enzymatic alterations, skeletal muscle mitochondrial respiration remained similar in SIRT3-M3 and control mice. Surprisingly, none of those metabolic alterations were detected in mitochondria from SIRT3-M1 mice. In conclusion, our data indicate a specific action of the shorter SIRT3 isoform on lipid mitochondrial membrane biosynthesis and functioning.

Flavin-Based Electron Bifurcation, Ferredoxin, Flavodoxin, and Anaerobic Respiration With Protons (Ech) or NAD+ (Rnf) as Electron Acceptors: A Historical Review

Flavin-based electron bifurcation is a newly discovered mechanism, by which a hydride electron pair from NAD(P)H, coenzyme F₄₂₀H₂, H₂, or formate is split by flavoproteins into one-electron with a more negative reduction potential and one with a more positive reduction potential than that of the electron pair. Via this mechanism microorganisms generate low- potential electrons for the reduction of ferredoxins (Fd) and flavodoxins (Fld). The first example was described in 2008 when it was found that the butyryl-CoA dehydrogenase-electron-transferring flavoprotein complex (Bcd-EtfAB) of Clostridium kluyveri couples the endergonic reduction of ferredoxin (E₀′ = −420 mV) with NADH (−320 mV) to the exergonic reduction of crotonyl-CoA to butyryl-CoA (−10 mV) with NADH. The discovery was followed by the finding of an electron-bifurcating Fd- and NAD-dependent [FeFe]-hydrogenase (HydABC) in Thermotoga maritima (2009), Fd-dependent transhydrogenase (NfnAB) in various bacteria and archaea (2010), Fd- and H₂-dependent heterodisulfide reductase (MvhADG-HdrABC) in methanogenic archaea (2011), Fd- and NADH-dependent caffeyl-CoA reductase (CarCDE) in Acetobacterium woodii (2013), Fd- and NAD-dependent formate dehydrogenase (HylABC-FdhF2) in Clostridium acidi-urici (2013), Fd- and NADP-dependent [FeFe]-hydrogenase (HytA-E) in Clostridium autoethanogrenum (2013), Fd(?)- and NADH-dependent methylene-tetrahydrofolate reductase (MetFV-HdrABC-MvhD) in Moorella thermoacetica (2014), Fd- and NAD-dependent lactate dehydrogenase (LctBCD) in A. woodii (2015), Fd- and F₄₂₀H₂-dependent heterodisulfide reductase (HdrA2B2C2) in Methanosarcina acetivorans (2017), and Fd- and NADH-dependent ubiquinol reductase (FixABCX) in Azotobacter vinelandii (2017). The electron-bifurcating flavoprotein complexes known to date fall into four groups that have evolved independently, namely those containing EtfAB (CarED, LctCB, FixBA) with bound FAD, a NuoF homolog (HydB, HytB, or HylB) harboring FMN, NfnB with bound FAD, or HdrA harboring FAD. All these flavoproteins are cytoplasmic except for the membrane-associated protein FixABCX. The organisms—in which they have been found—are strictly anaerobic microorganisms except for the aerobe A. vinelandii. The electron-bifurcating complexes are involved in a variety of processes such as butyric acid fermentation, methanogenesis, acetogenesis, anaerobic lactate oxidation, dissimilatory sulfate reduction, anaerobic- dearomatization, nitrogen fixation, and CO₂ fixation. They contribute to energy conservation via the energy-converting ferredoxin: NAD⁺ reductase complex Rnf or the energy-converting ferredoxin-dependent hydrogenase complex Ech. This Review describes how this mechanism was discovered.

Novel alternative splicing variants of <i>ACOX1</i> and their differential expression patterns in goats

Abstract. As the first and rate-limiting enzyme of the peroxisomal β-oxidation pathway, acyl-coenzyme A oxidase 1 (ACOX1), which is regulated by peroxisome proliferator-activated alfa (PPARα), is vital for fatty acid oxidation and deposition, especially in the lipid metabolism of very long-chain fatty acids. Alternative splicing events of ACOX1 have been detected in rodents, Nile tilapia, zebra fish and humans but not in goats. Herein, we identified a novel splice variant of the ACOX1 gene, which was designated as ACOX1-SV1, in addition to the complete transcript, ACOX1, in goats. The length of the ACOX1-SV1 coding sequence was 1983 bp, which presented a novel exon 2 variation owing to alternative 5′-splice site selection in exon 2 and partial intron 1, compared to that in ACOX1. The protein sequence analysis indicated that ACOX1-SV1 was conserved across different species. Reverse-transcription quantitative real-time polymerase chain reaction (RT-qPCR) analysis showed that these two isoforms were expressed spatially and differently in different tissue types. ACOX1 and ACOX1-SV1 were expressed at high levels in liver, spleen, brain and adipose tissue in kid goats, and they were abundantly expressed in the fat, liver and spleen of adults. Interestingly, whether in kids or in adults, in fat, the mRNA level of ACOX1 was considerably higher than that of ACOX1-SV1. In contrast, in the liver, the expression of ACOX1-SV1 was considerably higher than that of ACOX1. This differential expression patterns showed the existence of a tissue-dependent splice regulation. These novel findings for ACOX1 should provide new insights for further studies on the function of ACOX1 and its variants that should aid in the breeding of goats with improved meat quality.

The monounsaturated fatty acid oleate is the major physiological toxic free fatty acid for human beta cells

Free fatty acids (FFAs) can cause glucose intolerance and diabetes. Lipotoxicity to the pancreatic beta cells is considered to be a major underlying cause for this phenomenon. The aim of this study was to analyse the toxicity profile of FFAs in the human EndoC-βH1 beta-cell line and to compare the results with isolated rat and human islets with special reference to the physiologically most prevalent FFAs palmitic acid (PA) and oleic acid (OA). Toxicity after a 2-day incubation with the different FFAs was analysed by the caspase-3 assay and confirmed by the propidium iodide and annexin V staining tests. The long-chain saturated PA (C16:0) and the monounsaturated OA (C18:1) were both toxic to human EndoC-βH1 beta cells and pseudoislets, as well as to rat islets, and, as confirmed in a pilot experiment, also to human islets. Furthermore, OA provided no protection against the toxicity of PA. Likewise, elaidic acid (EA, the trans isomer of OA; trans-OA) was significantly toxic, in contrast to the non-metabolisable analogues methylated PA (MePA) and methylated OA (MeOA). Fatty acids with a chain length  < C16 were not toxic in EndoC-βH1 beta cells. Caspase-3 was also activated by linoleic acid (LA)(C18:2) but not by γ-linolenic acid (γ-LNA)(C18:3). Overall, only long-chain FFAs with chain lengths  > C14, which generate hydrogen peroxide in the peroxisomal beta-oxidation, were toxic. This conclusion is also supported by the toxicity of the branched-chain FFA pristanic acid, which is exclusively metabolised in the peroxisomal beta-oxidation. The lack of a protective effect of the monounsaturated fatty acid OA has important consequences for a beta-cell protective lipid composition of a diet. A cardioprotective diet with a high OA content does not fulfil this requirement.

Structural insight into the substrate specificity of acyl-CoA oxidase1 from Yarrowia lipolytica for short-chain dicarboxylyl-CoAs

Acyl-CoA oxidase (ACOX) plays an important role in fatty acid degradation. The enzyme catalyzes the first reaction in peroxisomal fatty acid β-oxidation by reducing acyl-CoA to 2-trans-enoyl-CoA. The yeast Yarrowia lipolytica is able to utilize fatty acids, fats, and oil as carbon sources to produce valuable bioproducts. We determined the crystal structure of ACOX1 from Y. lipolytica (YlACOX1) at a resolution of 2.5 Å. YlACOX1 forms a homodimer, and the monomeric structure is composed of four domains, the Nα, Nβ, Cα1, and Cα2. The FAD cofactor is bound at the dimerization interface between the Nβ- and Cα1-domains. The substrate-binding tunnel formed by the interface between the Nα-, Nβ-, and Cα1-domains is located proximal to FAD. Amino acid and structural comparisons of YlACOX1 with other ACOXs show that the substrate-binding pocket of YlACOX1 is much smaller than that of the medium- or long-chain ACOXs but is rather similar to that of the short-chain ACOXs. Moreover, the hydrophilicity of residues constituting the end region of the substrate-binding pocket in YlACOX1 is quite similar to those in the short-chain ACOXs but different from those of the medium- or long-chain ACOXs. These observations provide structural insights how YlACOX1 prefers short-chain dicarboxylyl-CoAs as a substrate.

The Mitochondrion of Euglena gracilis

In the presence of oxygen, Euglena gracilis mitochondria function much like mammalian mitochondria. Under anaerobiosis, E. gracilis mitochondria perform a malonyl-CoA independent synthesis of fatty acids leading to accumulation of wax esters, which serve as the sink for electrons stemming from glycolytic ATP synthesis and pyruvate oxidation. Some components (enzymes and cofactors) of Euglena's anaerobic energy metabolism are found among the anaerobic mitochondria of invertebrates, others are found among hydrogenosomes, the H₂-producing anaerobic mitochondria of protists.

Chemistry and biology of reactive species with special reference to the antioxidative defence status in pancreatic β-cells

BACKGROUND

Diabetes mellitus is a serious metabolic disease. Dysfunction and subsequent loss of the β-cells in the islets of Langerhans through apoptosis ultimately cause a life-threatening insulin deficiency. The underlying reason for the particular vulnerability of the β-cells is an extraordinary sensitivity to the toxicity of reactive oxygen and nitrogen species (ROS and RNS) due to its low antioxidative defense status.

SCOPE REVIEW

This review considers the different aspects of the chemistry and biology of the biologically most important reactive species and their chemico-biological interactions in the β-cell toxicity of proinflammatory cytokines in type 1 diabetes and of lipotoxicity in type 2 diabetes development.

MAJOR CONCLUSION

The weak antioxidative defense equipment in the different subcellular organelles makes the β-cells particularly vulnerable and prone to mitochondrial, peroxisomal and ER stress. Looking upon the enzyme deficiencies which are responsible for the low antioxidative defense status of the pancreatic β-cells it is the lack of enzymatic capacity for H₂O₂ inactivation at all major subcellular sites.

GENERAL SIGNIFICANCE

Diabetes is the most prevalent metabolic disorder with a steadily increasing incidence of both type 1 and type 2 diabetes worldwide. The weak protection of the pancreatic β-cells against oxidative stress is a major reason for their particular vulnerability. Thus, careful protection of the β-cells is required for prevention of the disease.

Coenzyme A thioester formation of 11- and 15-oxo-eicosatetraenoic acid

Release of arachidonic acid (AA) by cytoplasmic phospholipase A2 (cPLA2), followed by metabolism through cyclooxygenase-2 (COX-2) and 15-hydroxyprostaglandin dehydrogenase (15-PGDH), results in the formation of the eicosanoids 11-oxo- and 15-oxo-eicosatetraenoic acid (oxo-ETE). Both 11-oxo- and 15-oxo-ETE have been identified in human biospecimens but their function and further metabolism is poorly described. The oxo-ETEs contain an α,β-unsaturated ketone and a free carboxyclic acid, and thus may form Michael adducts with a nucleophile or a thioester with the free thiol of Coenzyme A (CoA). To examine the potential for eicosanoid-CoA formation, which has not previously been a metabolic route examined for this class of lipids, we applied a semi-targeted neutral loss scanning approach following arachidonic acid treatment in cell culture and detected inducible long-chain acyl-CoAs including a predominant AA-CoA peak. Interestingly, a series of AA-inducible acyl-CoAs at lower abundance but higher mass, likely corresponding to eicosanoid metabolites, was detected. Using a targeted LC-MS/MS approach we detected the formation of CoA thioesters of both 11-oxo- and 15-oxo-ETE and monitored the kinetics of their formation. Subsequently, we demonstrated that these acyl-CoA species undergo up to four double bond reductions. We confirmed the generation of 15-oxo-ETE-CoA in human platelets via LC-high resolution MS. Acyl-CoA thioesters of eicosanoids may provide a route to generate reducing equivalents, substrates for fatty acid oxidation, and substrates for acyl-transferases through cPLA2-dependent eicosanoid metabolism outside of the signaling contexts traditionally ascribed to eicosanoid metabolites.

Self-renewal of a purified Tie2+ hematopoietic stem cell population relies on mitochondrial clearance

A single hematopoietic stem cell (HSC) is capable of reconstituting hematopoiesis and maintaining homeostasis by balancing self-renewal and cell differentiation. The mechanisms of HSC division balance, however, are not yet defined. Here we demonstrate, by characterizing at the single-cell level a purified and minimally heterogeneous murine Tie2⁺ HSC population, that these top hierarchical HSCs preferentially undergo symmetric divisions. The induction of mitophagy, a quality control process in mitochondria, plays an essential role in self-renewing expansion of Tie2⁺ HSCs. Activation of the PPAR (peroxisome proliferator-activated receptor)-fatty acid oxidation pathway promotes expansion of Tie2⁺ HSCs through enhanced Parkin recruitment in mitochondria. These metabolic pathways are conserved in human TIE2⁺ HSCs. Our data thus identify mitophagy as a key mechanism of HSC expansion and suggest potential methods of cell-fate manipulation through metabolic pathways.

Anaerobic biodegradation of soybean biodiesel and diesel blends under sulfate-reducing conditions

Biotransformation of soybean biodiesel and its biodiesel/petrodiesel blends were investigated under sulfate-reducing conditions. Three blends of biodiesel, B100, B50, and B0, were treated using microbial cultures pre-acclimated to B100 (biodiesel only) and B80 (80% biodiesel and 20% petrodiesel). Results indicate that the biodiesel could be effectively biodegraded in the presence or absence of petrodiesel, whereas petrodiesel could not be biodegraded at all under sulfate-reducing conditions. The kinetics of biodegradation of individual Fatty Acid Methyl Ester (FAME) compounds and their accompanying sulfate-reduction rates were studied using a serum bottle test. As for the biodegradation of individual FAME compounds, the biodegradation rates for the saturated FAMEs decreased with increasing carbon chain length. For unsaturated FAMEs, biodegradation rates increased with increasing number of double bonds. The presence of petrodiesel had a greater effect on the rate of biodegradation of biodiesel than on the extent of removal.

Cytochrome b5 reductase and the control of lipid metabolism and healthspan

Cytochrome b₅ reductases (CYB5R) are required for the elongation and desaturation of fatty acids, cholesterol synthesis and mono-oxygenation of cytochrome P450 enzymes, all of which are associated with protection against metabolic disorders. However, the physiological role of CYB5R in the context of metabolism, healthspan and aging remains ill-defined. We generated CYB5R-overexpressing flies (CYB5R-OE) and created a transgenic mouse line overexpressing CYB5R3 (CYB5R3-Tg) in the C57BL/6J background to investigate the function of this class of enzymes as regulators of metabolism and age-associated pathologies. Gender- and/or stage-specific induction of CYB5R, and pharmacological activation of CYB5R with tetrahydroindenoindole extended fly lifespan. Increased expression of CYB5R3 was associated with significant improvements in several metabolic parameters that resulted in modest lifespan extension in mice. Diethylnitrosamine-induced liver carcinogenesis was reduced in CYB5R3-Tg mice. Accumulation of high levels of long-chain polyunsaturated fatty acids, improvement in mitochondrial function, decrease in oxidative damage and inhibition of chronic pro-inflammatory pathways occurred in the transgenic animals. These results indicate that CYB5R represents a new target in the study of genes that regulate lipid metabolism and healthspan.