Malonyl-CoA: the regulator of fatty acid synthesis and oxidation

The emerging role of the mitochondrial fatty-acid synthase (mtFASII) in the regulation of energy metabolism

Malonyl-CoA synthetase (ACSF3) catalyzes the first step of the mitochondrial fatty acid biosynthesis (mtFASII). Mutations in ACSF3 cause CMAMMA a rare inborn error of metabolism. The clinical phenotype is very heterogeneous, with some patients presenting with neurologic manifestations. In some children, presenting symptoms such as coma, ketoacidosis and hypoglycemia are suggestive of an intermediary metabolic disorder. The overall pathophysiological mechanisms are not understood. In order to study the role of mtFASII in the regulation of energy metabolism we performed a comprehensive metabolic phenotyping with Seahorse technology proteomics in fibroblasts from healthy controls and ACSF3 patients. SILAC-based proteomics and lipidomic analysis were performed to investigate the effects of hypofunctional mtFASII on proteome and lipid homeostasis of complex lipids. Our data clearly confirmed an impaired mitochondrial flexibility characterized by reduced mitochondrial respiration and glycolytic flux due to a lower lipoylation degree. These findings were accompanied by the adaptational upregulation of β-oxidation and by the reduction of anaplerotic amino acids as compensatory mechanism to address the required energy need. Finally, lipidomic analysis demonstrated that the content of the bioactive lipids sphingomyelins and cardiolipins was strongly increased. Our data clearly demonstrate the role of mtFASII in metabolic regulation. Moreover, we show that mtFASII acts as mediator in the lipid-mediated signaling processes in the regulation of energy homeostasis and metabolic flexibility.

Lingguizhugan decoction attenuates diet-induced obesity and hepatosteatosis via gut microbiota

BACKGROUND

Obesity is a major risk factor for a variety of diseases such as diabetes, nonalcoholic fatty liver disease, and cardiovascular diseases. Restricting energy intake, or caloric restriction (CR), can reduce body weight and improve metabolic parameters in overweight or obese patients. We previously found that Lingguizhugan decoction (LZD) in combination with CR can effectively lower plasma lipid levels in patients with metabolic syndrome. However, the mechanism underlying CR and LZD treatment is still unclear.

AIM

To investigate whether CR and LZD improve metabolic parameters by modulating gut microbiota.

METHODS

We extracted the water-soluble components out of raw materials and dried as LZD extracts. Eight-week old male C57BL/6 mice were treated with a 3-d treatment regime that included 24 h-fasting followed by gavage of LZD extracts for 2 consecutive days, followed by a normal diet (ND) ad libitum for 16 wk. To test the effects of gut microbiota on diet-induced obesity, 8-wk old male C57BL/6 mice received fecal microbiota transplantation (FMT) from CR and LZD-treated mice every 3 d and were fed with high-fat diet (HFD) ad libitum for 16 wk. Control mice received either saline gavage or FMT from ND-fed mice receiving saline gavage as mentioned above. Body weight was monitored bi-weekly. Food consumption of each cage hosting five mice was recorded weekly. To monitor blood glucose, total cholesterol, and total triglycerides, blood samples were collected via submandibular bleeding after 6 h fasting. Oxygen consumption rate was monitored with metabolic cages. Feces were collected, and fecal DNA was extracted. Profiles of gut microbiota were mapped by metagenomic sequencing.

RESULTS

We found that CR and LZD treatment significantly reduced the body weight of mice fed with ND (28.71 ± 0.29 vs 28.05 ± 0.15, P < 0.05), but did not affect plasma total cholesterol or total triglyceride levels. We then transplanted the fecal microbiota collected from CR and LZD-treated mice under ND feeding to HFD-fed mice. Intriguingly, transplanting the mice with fecal microbiota from CR and LZD-treated mice potently reduced body weight (44.95 ± 1.02 vs 40.53 ± 0.97, P < 0.001). FMT also reduced HFD-induced hepatosteatosis, in addition to improved glycemic control. Mechanistic studies found that FMT increased OCR of the mice and suppressed the expression and protein abundance of lipogenic genes in the liver. Metagenomic analysis revealed that HFD drastically altered the profile of gut microbiota, and FMT modified the profile of the gut microbiota.

CONCLUSION

Our study suggests that CR and LZD improve metabolic parameters by modulating gut microbiota.

The PPAR-microbiota-metabolic organ trilogy to fine-tune physiology

The human gut is colonized by commensal microorganisms, predominately bacteria that have coevolved in symbiosis with their host. The gut microbiota has been extensively studied in recent years, and many important findings on how it can regulate host metabolism have been unraveled. In healthy individuals, feeding timing and type of food can influence not only the composition but also the circadian oscillation of the gut microbiota. Host feeding habits thus influence the type of microbe-derived metabolites produced and their concentrations throughout the day. These microbe-derived metabolites influence many aspects of host physiology, including energy metabolism and circadian rhythm. Peroxisome proliferator-activated receptors (PPARs) are a group of ligand-activated transcription factors that regulate various metabolic processes such as fatty acid metabolism. Similar to the gut microbiota, PPAR expression in various organs oscillates diurnally, and studies have shown that the gut microbiota can influence PPAR activities in various metabolic organs. For example, short-chain fatty acids, the most abundant type of metabolites produced by anaerobic fermentation of dietary fibers by the gut microbiota, are PPAR agonists. In this review, we highlight how the gut microbiota can regulate PPARs in key metabolic organs, namely, in the intestines, liver, and muscle. Knowing that the gut microbiota impacts metabolism and is altered in individuals with metabolic diseases might allow treatment of these patients using noninvasive procedures such as gut microbiota manipulation.-Oh, H. Y. P., Visvalingam, V., Wahli, W. The PPAR-microbiota-metabolic organ trilogy to fine-tune physiology.

Role of Gender in Regulation of Redox Homeostasis in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is one of the diseases with a well-established gender dimorphism. The prevalence of PAH is increased in females with a ratio of 4:1, while poor survival prognosis is associated with the male gender. Nevertheless, the specific contribution of gender in disease development and progression is unclear due to the complex nature of the PAH. Oxidative and nitrosative stresses are important contributors in PAH pathogenesis; however, the role of gender in redox homeostasis has been understudied. This review is aimed to overview the possible sex-specific mechanisms responsible for the regulation of the balance between oxidants and antioxidants in relation to PAH pathobiology.

Combined docosahexaenoic acid and thyroid hormone supplementation as a protocol supporting energy supply to precondition and afford protection against metabolic stress situations

Liver preconditioning (PC) refers to the development of an enhanced tolerance to injuring stimuli. For example, the protection from ischemia-reperfusion (IR) in the liver that is obtained by previous maneuvers triggering beneficial molecular and functional changes. Recently, we have assessed the PC effects of thyroid hormone (T_3; single dose of 0.1 mg/kg) and n-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs; daily doses of 450 mg/kg for 7 days) that abrogate IR injury to the liver. This feature is also achieved by a combined T₃ and the n-3 LCPUFA docosahexaenoic acid (DHA) using a reduced period of supplementation of the FA (daily doses of 300 mg/kg for 3 days) and half of the T₃ dosage (0.05 mg/kg). T₃ -dependent protective mechanisms include (i) the reactive oxygen species (ROS)-dependent activation of transcription factors nuclear factor-κB (NF-κB), AP-1, signal transducer and activator of transcription 3, and nuclear factor erythroid-2-related factor 2 (Nrf2) upregulating the expression of protective proteins. (ii) ROS-induced endoplasmic reticulum stress affording proper protein folding. (iii) The autophagy response to produce FAs for oxidation and ATP supply and amino acids for protein synthesis. (iv) Downregulation of inflammasome nucleotide-bonding oligomerization domain leucine-rich repeat containing family pyrin containing 3 and interleukin-1β expression to prevent inflammation. N-3 LCPUFAs induce antioxidant responses due to Nrf2 upregulation, with inflammation resolution being related to production of oxidation products and NF-κB downregulation. Energy supply to achieve liver PC is met by the combined DHA plus T₃ protocol through upregulation of AMPK coupled to peroxisome proliferator-activated receptor-γ coactivator 1α signaling. In conclusion, DHA plus T₃ coadministration favors hepatic bioenergetics and lipid homeostasis that is of crucial importance in acute and clinical conditions such as IR, which may be extended to long-term or chronic situations including steatosis in obesity and diabetes. © 2019 IUBMB Life, 71(9):1211-1220, 2019.

Redox control of non-shivering thermogenesis

Background

Thermogenic adipocytes reorganize their metabolism during cold exposure. Metabolic reprogramming requires readily available bioenergetics substrates, such as glucose and fatty acids, to increase mitochondrial respiration and produce heat via the uncoupling protein 1 (UCP1). This condition generates a finely-tuned production of mitochondrial reactive oxygen species (ROS) that support non-shivering thermogenesis.

Scope of review

Herein, the findings underlining the mechanisms that regulate ROS production and control of the adaptive responses tuning thermogenesis in adipocytes are described. Furthermore, this review describes the metabolic responses to substrate availability and the consequence of mitochondrial failure to switch fuel oxidation in response to changes in nutrient availability. A framework to control mitochondrial ROS threshold to maximize non-shivering thermogenesis in adipocytes is provided.

Major conclusions

Thermogenesis synchronizes fuel oxidation with an acute and transient increase of mitochondrial ROS that promotes the activation of redox-sensitive thermogenic signaling cascade and UCP1. However, an overload of substrate flux to mitochondria causes a massive and damaging mitochondrial ROS production that affects mitochondrial flexibility. Finding novel thermogenic redox targets and manipulating ROS concentration in adipocytes appears to be a promising avenue of research for improving thermogenesis and counteracting metabolic diseases.

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Mitochondrial ROS support non-shivering thermogenesis.

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Thermogenic ROS are tightly related to mitochondrial metabolic reorganization.

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Uncontrolled mitochondrial ROS production is causative of metabolic inflexibility.

Genomic, Transcriptomic, and Epigenomic Features Differentiate Genes That Are Relevant for Muscular Polyunsaturated Fatty Acids in the Common Carp

Polyunsaturated fatty acids (PUFAs) are a set of important nutrients that mainly include arachidonic acid (ARA4), docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and α-linolenic acid (ALA). Recently, fish-derived PUFAs have been associated with cardiovascular health, fetal development, and improvement of brain functions. Studies have shown that fish muscular tissues are rich in PUFAs, which are influenced by various factors, including genetic variations, regulatory profiles, and methylation status of desaturase genes during fatty acid desaturation and elongation processes. However, the genetic mechanism and the pathways involved in fatty acid metabolism in fishes remain unclear. The overall aim of this study was to assess differences in gene expression responses among fishes with different fatty acid levels. To achieve this goal, we conducted genome-wide association analysis (GWAS) using a 250K SNP array in a population of 203 samples of common carp (Cyprinus carpio) and identified nine SNPs and 15 genes associated with muscular PUFA content. Then, RNA-Seq and whole genome bisulfite sequencing (WGBS) of different groups with high and low EPA, DHA, ARA4, and ALA contents in muscle, liver and brain tissues were conducted, resulting in 6,750 differentially expressed genes and 5,631 genes with differentially methylated promoters. Gene ontology and KEGG pathway enrichment analyses of RNA-Seq and WGBS results identified enriched pathways for fatty acid metabolism, which included the adipocytokine signaling pathway, ARA4 and linoleic acid metabolism pathway, and insulin signaling pathway. Integrated analysis indicated significant correlations between gene expression and methylation status among groups with high and low PUFA contents in muscular tissues. Taken together, these multi-level results uncovered candidate genes and pathways that are associated with fatty acid metabolism and paved the way for further genomic selection and carp breeding for PUFA traits.

Docosahexaenoic acid-thyroid hormone combined protocol as a novel approach to metabolic stress disorders: Relation to mitochondrial adaptation via liver PGC-1α and sirtuin1 activation

Docosahexaenoic acid (DHA) and 3,3',5-triiodothyronine (T₃ ) combined protocol affords protection against liver injury via AMPK signaling supporting energy requirements. The aim of this work was to test the hypothesis that a DHA + T₃ accomplish mitochondrial adaptation through downstream upregulation of PPAR-γ coactivator 1α (PGC-1α). Male Sprague-Dawley rats were given daily oral doses of 300 mg DHA/kg or saline (controls) for three consecutive days, followed by 0.05 mg T₃ /kg (or hormone vehicle) ip at the fourth day, or single dose of 0.1 mg T₃ /kg alone. Liver mRNA levels were assayed by qPCR, NAD⁺ /NADH ratios, hepatic proteins, histone 3 acetylation and serum T₃ and β-hydroxybutyrate levels were determined by specific ELISA kits. Combined DHA + T₃ protocol led to increased liver AMPK, PGC-1α, NRF-2, COX-IV, and β-ATP synthase mRNAs, with concomitant higher protein levels of COX-IV and NRF-2, 369% enhancement in the NAD⁺ /NADH ratio, 47% decrease in histone 3 acetylation and 162% increase in serum levels of β-hydroxybutyrate over control values. These changes were reproduced by the higher dose of T₃ without major alterations by DHA or T₃ alone. In conclusion, liver mitochondrial adaptation by DHA + T₃ is associated with PGC-1α upregulation involving enhanced transcription of the coactivator, which may be contributed by PGC-1α deacetylation and phosphorylation by SIRT1 and AMPK activation, respectively. This contention is supported by NRF-2-dependent enhancement in COX-1 and β-ATP synthase induction with higher fatty acid oxidation resulting in a significant ketogenic response, which may represent a suitable strategy for hepatic steatosis with future clinical applications. © 2018 BioFactors, 45(2):271-278, 2019.

3-ketodihydrosphingosine reductase mutation induces steatosis and hepatic injury in zebrafish

3-ketodihydrosphingosine reductase (KDSR) is the key enzyme in the de novo sphingolipid synthesis. We identified a novel missense kdsr^I105R mutation in zebrafish that led to a loss of function, and resulted in progression of hepatomegaly to steatosis, then hepatic injury phenotype. Lipidomics analysis of the kdsr^I105R mutant revealed compensatory activation of the sphingolipid salvage pathway, resulting in significant accumulation of sphingolipids including ceramides, sphingosine and sphingosine 1-phosphate (S1P). Ultrastructural analysis revealed swollen mitochondria with cristae damage in the kdsr^I105R mutant hepatocytes, which can be a cause of hepatic injury in the mutant. We found elevated sphingosine kinase 2 (sphk2) expression in the kdsr^I105R mutant. Genetic interaction analysis with the kdsr^I105R and the sphk2^wc1 mutants showed that sphk2 depletion suppressed liver defects observed in the kdsr^I105R mutant, suggesting that liver defects were mediated by S1P accumulation. Further, both oxidative stress and ER stress were completely suppressed by deletion of sphk2 in kdsr^I105R mutants, linking these two processes mechanistically to hepatic injury in the kdsr^I105R mutants. Importantly, we found that the heterozygous mutation in kdsr induced predisposed liver injury in adult zebrafish. These data point to kdsr as a novel genetic risk factor for hepatic injury.

Will Studies in Nonalcoholic Steatohepatitis Help Manage Alcoholic Steatohepatitis?

Hepatic steatosis and steatohepatitis have several etiologies; the most common are alcoholic steatohepatitis (ASH) and obesity/metabolic syndrome-induced steatohepatitis, also known as nonalcoholic steatohepatitis (NASH). Although the etiology of these 2 conditions is different, they share pathways to disease progression and severity. They also have differences in physiologic pathways, and shared and divergent mechanisms can be therapeutic targets. There is no approved pharmacologic therapy for NASH, but several molecules are under study. Focus remains on modulation of insulin resistance, oxidative stress, the inflammatory cascade, hepatic fibrosis, and cell death. This review provides an overview of pathophysiologic similarities and differences between ASH and NASH.

Metabolic adaptation and maladaptation in adipose tissue

Adipose tissue possesses the remarkable capacity to control its size and function in response to a variety of internal and external cues, such as nutritional status and temperature. The regulatory circuits of fuel storage and oxidation in white adipocytes and thermogenic adipocytes (brown and beige adipocytes) play a central role in systemic energy homeostasis, whereas dysregulation of the pathways is closely associated with metabolic disorders and adipose tissue malfunction, including obesity, insulin resistance, chronic inflammation, mitochondrial dysfunction, and fibrosis. Recent studies have uncovered new regulatory elements that control the above parameters and provide new mechanistic opportunities to reprogram fat cell fate and function. In this Review, we provide an overview of the current understanding of adipocyte metabolism in physiology and disease and also discuss possible strategies to alter fuel utilization in fat cells to improve metabolic health.

Effect of ethanol on lipid metabolism

Hepatic lipid metabolism is a series of complex processes that control influx and efflux of not only hepatic lipid pools, but also organismal pools. Lipid homeostasis is usually tightly controlled by expression, substrate supply, oxidation and secretion that keep hepatic lipid pools relatively constant. However, perturbations of any of these processes can lead to lipid accumulation in the liver. Although it is thought that these responses are hepatic arms of the 'thrifty genome', they are maladaptive in the context of chronic fatty liver diseases. Ethanol is likely unique among toxins, in that it perturbs almost all aspects of hepatic lipid metabolism. This complex response is due in part to the large metabolic demand placed on the organ by alcohol metabolism, but also appears to involve more nuanced changes in expression and substrate supply. The net effect is that steatosis is a rapid response to alcohol abuse. Although transient steatosis is largely an inert pathology, the chronicity of alcohol-related liver disease seems to require steatosis. Better and more specific understanding of the mechanisms by which alcohol causes steatosis may therefore translate into targeted therapies to treat alcohol-related liver disease and/or prevent its progression.

A clinical and computational study on anti-obesity effects of hydroxycitric acid

Hydroxycitric acid (HCA), a major active ingredient of Garcinia cambogia extracts, is known to suppress body weight gain and fat synthesis in animals and humans. But the underlying mechanism of HCA action is not fully understood. Clinical study on 100 obese individuals for a period of 3 months was performed followed by a computational study aimed to investigate the effects of HCA treatment on human subjects at anthropometric and plasma lipid profile levels. A detailed hepatic metabolic model was used to incorporate the effect of HCA at the metabolic pathway level. Perturbation analysis of ATP citrate lyase activity in the metabolic pathway was performed to simulate the net effect of HCA. Significant reductions in body weight, triceps, subscapular, and mid axillary measurements as well as in serum triglyceride, cholesterol, HDL and LDL levels were observed following HCA dosage. During the study, half of the subjects experienced a decline in body weight and the remainder experienced an increase in body weight. However, analysis of fat mass with the help of empirical correlations clearly showed significant reduction in the mean values due to HCA dosage in both cases. An extra increase in fat free mass was responsible for offsetting the decrease in fat mass for the subjects who experienced an increase in body weight during the trials. Perturbation analysis showed a net reduction in fatty acid, triglyceride and cholesterol synthesis along with urea cycle fluxes under lipogenetic conditions. Moreover, protein synthesis fluxes increased under these conditions. These results indicate that HCA treatment can reduce body weight gain and fat accumulation in obese subjects along with improving their anthropometric parameters and metabolic state.

Hydroxycitric acid (HCA), a major active ingredient of Garcinia cambogia extracts, is known to suppress body weight gain and fat synthesis in animals and humans.

Role of the malonyl-CoA synthetase ACSF3 in mitochondrial metabolism

Malonyl-CoA is a central metabolite in fatty acid biochemistry. It is the rate-determining intermediate in fatty acid synthesis but is also an allosteric inhibitor of the rate-setting step in mitochondrial long-chain fatty acid oxidation. While these canonical cytoplasmic roles of malonyl-CoA have been well described, malonyl-CoA can also be generated within the mitochondrial matrix by an alternative pathway: the ATP-dependent ligation of malonate to Coenzyme A by the malonyl-CoA synthetase ACSF3. Malonate, a competitive inhibitor of succinate dehydrogenase of the TCA cycle, is a potent inhibitor of mitochondrial respiration. A major role for ACSF3 is to provide a metabolic pathway for the clearance of malonate by the generation of malonyl-CoA, which can then be decarboxylated to acetyl-CoA by malonyl-CoA decarboxylase. Additionally, ACSF3-derived malonyl-CoA can be used to malonylate lysine residues on proteins within the matrix of mitochondria, possibly adding another regulatory layer to post-translational control of mitochondrial metabolism. The discovery of ACSF3-mediated generation of malonyl-CoA defines a new mitochondrial metabolic pathway and raises new questions about how the metabolic fates of this multifunctional metabolite intersect with mitochondrial metabolism.

Lipopolysaccharide (LPS)-induced septic shock causes profound changes in myocardial energy metabolites in pigs

INTRODUCTION

Energy deficiency is a cause for myocardial dysfunction during septic shock. In rodents, septic shock decreases the oxidation of long-chain fatty acids and glucose in the myocardium causing energy deficiency. However, the effect of septic shock on myocardial energy metabolites in large animals and human is unknown.

OBJECTIVES

Investigate the effects of septic shock on myocardial energy metabolites in domestic pigs.

METHODS

Seventeen female pigs divided into control and lipopolysaccharide (LPS)-induced septic shock groups. Myocardial metabolites were analyzed ex vivo by ¹H nuclear magnetic resonance spectroscopy and liquid chromatography-tandem mass spectrometry. Gene and protein expression analysis were analyzed by real-time PCR and western blot.

RESULTS

Septic shock was associated with an increase in myocardial levels of short- and medium-chain acylcarnitines, lactate, alanine, and pyruvate dehydrogenase kinase 4 gene expression. COX-2 and prostaglandin E4 receptor gene expression also increased in the septic myocardium, although the only elevated eicosanoid in the septic animals was thromboxane B2. Myocardial levels of niacin, taurine, glutamate, glutamine, and glutathione were higher, and hypoxanthine levels lower in septic pigs than controls.

CONCLUSIONS

In pigs, septic shock induced by LPS caused myocardial changes directed to decrease the oxidation of medium- and short-chain fatty acid without an effect on long-chain fatty acid oxidation. The increase in myocardial levels of lactate, alanine, and pyruvate dehydrogenase kinase 4 gene expression suggest that septic shock decreases pyruvate dehydrogenase complex activity and glucose oxidation. Homeostasis of niacin, taurine, glutamate, glutamine, glutathione, hypoxanthine and thromboxane B2 is also affected in the septic myocardium.

Key regulators of lipid metabolism drive endocrine resistance in invasive lobular breast cancer

Background

Invasive lobular breast carcinoma (ILC) is a histological subtype of breast cancer that is characterized by loss of E-cadherin and high expression of estrogen receptor alpha (ERα). In many cases, ILC is effectively treated with adjuvant aromatase inhibitors (AIs); however, acquired AI resistance remains a significant problem.

Methods

To identify underlying mechanisms of acquired anti-estrogen resistance in ILC, we recently developed six long-term estrogen-deprived (LTED) variant cell lines from the human ILC cell lines SUM44PE (SUM44; two lines) and MDA-MB-134VI (MM134; four lines). To better understand mechanisms of AI resistance in these models, we performed transcriptional profiling analysis by RNA-sequencing followed by candidate gene expression and functional studies.

Results

MM134 LTED cells expressed ER at a decreased level and lost growth response to estradiol, while SUM44 LTED cells retained partial ER activity. Our transcriptional profiling analysis identified shared activation of lipid metabolism across all six independent models. However, the underlying basis of this signature was distinct between models. Oxysterols were able to promote the proliferation of SUM44 LTED cells but not MM134 LTED cells. In contrast, MM134 LTED cells displayed a high expression of the sterol regulatory element-binding protein 1 (SREBP1), a regulator of fatty acid and cholesterol synthesis, and were hypersensitive to genetic or pharmacological inhibition of SREBPs. Several SREBP1 downstream targets involved in fatty acid synthesis, including FASN, were induced, and MM134 LTED cells were more sensitive to etomoxir, an inhibitor of the rate-limiting enzyme in beta-oxidation, than their respective parental control cells. Finally, in silico expression analysis in clinical specimens from a neo-adjuvant endocrine trial showed a significant association between the increase of SREBP1 expression and lack of clinical response, providing further support for a role of SREBP1 in the acquisition of endocrine resistance in breast cancer.

Conclusions

Our characterization of a unique series of AI-resistant ILC models identifies the activation of key regulators of fatty acid and cholesterol metabolism, implicating lipid-metabolic processes driving estrogen-independent growth of ILC cells. Targeting these changes may prove a strategy for prevention and treatment of endocrine resistance for patients with ILC.

Electronic supplementary material

The online version of this article (10.1186/s13058-018-1041-8) contains supplementary material, which is available to authorized users.

Role of the Pyruvate Dehydrogenase Complex in Metabolic Remodeling: Differential Pyruvate Dehydrogenase Complex Functions in Metabolism

Mitochondrial dysfunction is a hallmark of metabolic diseases such as obesity, type 2 diabetes mellitus, neurodegenerative diseases, and cancers. Dysfunction occurs in part because of altered regulation of the mitochondrial pyruvate dehydrogenase complex (PDC), which acts as a central metabolic node that mediates pyruvate oxidation after glycolysis and fuels the Krebs cycle to meet energy demands. Fine-tuning of PDC activity has been mainly attributed to post-translational modifications of its subunits, including the extensively studied phosphorylation and de-phosphorylation of the E1α subunit of pyruvate dehydrogenase (PDH), modulated by kinases (pyruvate dehydrogenase kinase [PDK] 1-4) and phosphatases (pyruvate dehydrogenase phosphatase [PDP] 1-2), respectively. In addition to phosphorylation, other covalent modifications, including acetylation and succinylation, and changes in metabolite levels via metabolic pathways linked to utilization of glucose, fatty acids, and amino acids, have been identified. In this review, we will summarize the roles of PDC in diverse tissues and how regulation of its activity is affected in various metabolic disorders.

1,25-Dihydroxyvitamin D regulates lipid metabolism and glucose utilization in differentiated 3T3-L1 adipocytes

It is well established that adipose tissue can both store and metabolize vitamin D. The active form of vitamin D, 1,25 dihydroxyvitamin D [1,25(OH)₂D], regulates adipocyte differentiation and inflammation, highlighting the multifaceted role that vitamin D plays in adipose tissue physiology. However, there is limited evidence regarding vitamin D regulation of mature adipocyte lipid metabolism. We hypothesize that 1,25(OH)₂D alters lipid and glucose metabolism in differentiated 3T3-L1 adipocytes to reduce triacylglycerol (TAG) accumulation. In this study, 1,25(OH)₂D (10 nmol/L) stimulated a 21% reduction in TAG accumulation in differentiated 3T3-L1 adipocytes after 4 days (P = .01) despite a significant increase in fatty acid uptake (P < .01). Additionally, 1,25(OH)₂D stimulated a 2.5-fold increase in ¹⁴CO₂ production from [1-¹⁴C] palmitic acid (P < .01), indicative of an elevated rate of fatty acid β-oxidation, while stimulating a 9% reduction in de novo fatty acid synthesis (P = .03). Interestingly, d-[U-¹³C]glucose incorporation into fatty acids was reduced by 30% in response to 1,25(OH)₂D (P < .01), indicating a reduced contribution of glucose as a substrate for de novo lipogenesis. Consistent with these findings, mRNA expression of the anaplerotic enzyme pyruvate carboxylase was reduced by 41% (P < .01). In summary, 1,25(OH)₂D stimulated fatty acid oxidation and reduced TAG accumulation in differentiated adipocytes. Furthermore, 1,25(OH)₂D reduced glucose utilization as a substrate for fatty acid synthesis potentially by downregulating pyruvate carboxylase and stimulating glucose disposal as glycerol. Collectively, these 1,25(OH)₂D-induced changes in lipid metabolism and glucose utilization may contribute to the reduction in TAG accumulation and be protective against excessive fat mass accumulation and associated metabolic disorders.

Human-based systems: Mechanistic NASH modelling just around the corner?

Non-alcoholic steatohepatitis (NASH) is a chronic liver disease characterized by excessive triglyceride accumulation in the liver accompanied by inflammation, cell stress and apoptosis. It is the tipping point to the life-threatening stages of non-alcoholic fatty liver disease (NAFLD). Despite the high prevalence of NASH, up to five percent of the global population, there are currently no approved drugs to treat this disease. Animal models, mostly based on specific diets and genetic modifications, are often employed in anti-NASH drug development. However, due to interspecies differences and artificial pathogenic conditions, they do not represent the human situation accurately and are inadequate for testing the efficacy and safety of potential new drugs. Human-based in vitro models provide a more legitimate representation of the human NASH pathophysiology and can be used to investigate the dysregulation of cellular functions associated with the disease. Also in silico methodologies and pathway-based approaches using human datasets, may contribute to a more accurate representation of NASH, thereby facilitating the quest for new anti-NASH drugs. In this review, we describe the molecular components of NASH and how human-based tools can contribute to unraveling the pathogenesis of this disease and be used in anti-NASH drug development. We also propose a roadmap for the development and application of human-based approaches for future investigation of NASH.

HEPATOKIN1 is a biochemistry-based model of liver metabolism for applications in medicine and pharmacology

The epidemic increase of non-alcoholic fatty liver diseases (NAFLD) requires a deeper understanding of the regulatory circuits controlling the response of liver metabolism to nutritional challenges, medical drugs, and genetic enzyme variants. As in vivo studies of human liver metabolism are encumbered with serious ethical and technical issues, we developed a comprehensive biochemistry-based kinetic model of the central liver metabolism including the regulation of enzyme activities by their reactants, allosteric effectors, and hormone-dependent phosphorylation. The utility of the model for basic research and applications in medicine and pharmacology is illustrated by simulating diurnal variations of the metabolic state of the liver at various perturbations caused by nutritional challenges (alcohol), drugs (valproate), and inherited enzyme disorders (galactosemia). Using proteomics data to scale maximal enzyme activities, the model is used to highlight differences in the metabolic functions of normal hepatocytes and malignant liver cells (adenoma and hepatocellular carcinoma).

In silico models of cells can provide insight into the causes and effects of disease states and reduce the need for in vivo studies. Here, the authors present a kinetic model of hepatocyte metabolism including energy, carbohydrate, lipid and nitrogen metabolism and hormonal and allosteric regulation of enzymatic activity.

Proteomics of the Rat Myocardium during Development of Type 2 Diabetes Mellitus Reveals Progressive Alterations in Major Metabolic Pathways

Congestive heart failure and poor clinical outcome after myocardial infarction are known complications in patients with type-2 diabetes mellitus (T2DM). Protein alterations may be involved in the mechanisms underlying these disarrays in the diabetic heart. Here we map proteins involved in intracellular metabolic pathways in the Zucker diabetic fatty rat heart as T2DM develops using MS based proteomics. The prediabetic state only induced minor pathway changes, whereas onset and late T2DM caused pronounced perturbations. Two actin-associated proteins, ARPC2 and TPM3, were up-regulated at the prediabetic state indicating increased actin dynamics. All differentially regulated proteins involved in fatty acid metabolism, both peroxisomal and mitochondrial, were up-regulated at late T2DM, whereas enzymes of branched chain amino acid degradation were all down-regulated. At both onset and late T2DM, two members of the serine protease inhibitor superfamily, SERPINA3K and SERPINA3L, were down-regulated. Furthermore, we found alterations in proteins involved in clearance of advanced glycation end-products and lipotoxicity, DCXR and CBR1, at both onset and late T2DM. These proteins deserve elucidation with regard to their role in T2DM pathogenesis and their respective role in the deterioration of the diabetic heart. Data are available via ProteomeXchange with identifiers PXD009538, PXD009554, and PXD009555.

Glycine N-methyltransferase deletion in mice diverts carbon flux from gluconeogenesis to pathways that utilize excess methionine cycle intermediates

Glycine N-methyltransferase (GNMT) is the most abundant liver methyltransferase regulating the availability of the biological methyl donor, S-adenosylmethionine (SAM). Moreover, GNMT has been identified to be down-regulated in hepatocellular carcinoma (HCC). Despite its role in regulating SAM levels and association of its down-regulation with liver tumorigenesis, the impact of reduced GNMT on metabolic reprogramming before the manifestation of HCC has not been investigated in detail. Herein, we used ²H/¹³C metabolic flux analysis in conscious, unrestrained mice to test the hypothesis that the absence of GNMT causes metabolic reprogramming. GNMT-null (KO) mice displayed a reduction in blood glucose that was associated with a decline in both hepatic glycogenolysis and gluconeogenesis. The reduced gluconeogenesis was due to a decrease in liver gluconeogenic precursors, citric acid cycle fluxes, and anaplerosis and cataplerosis. A concurrent elevation in both hepatic SAM and metabolites of SAM utilization pathways was observed in the KO mice. Specifically, the increase in metabolites of SAM utilization pathways indicated that hepatic polyamine synthesis and catabolism, transsulfuration, and de novo lipogenesis pathways were increased in the KO mice. Of note, these pathways utilize substrates that could otherwise be used for gluconeogenesis. Also, this metabolic reprogramming occurs before the well-documented appearance of HCC in GNMT-null mice. Together, these results indicate that GNMT deletion promotes a metabolic shift whereby nutrients are channeled away from glucose formation toward pathways that utilize the elevated SAM.

Paediatric fatty liver disease (PeFLD): All is not NAFLD - Pathophysiological insights and approach to management

The recognition of a pattern of steatotic liver injury where histology mimicked alcoholic liver disease, but alcohol consumption was denied, led to the identification of non-alcoholic fatty liver disease (NAFLD). Non-alcoholic fatty liver disease has since become the most common chronic liver disease in adults owing to the global epidemic of obesity. However, in paediatrics, the term NAFLD seems incongruous: alcohol consumption is largely not a factor and inherited metabolic disorders can mimic or co-exist with a diagnosis of NAFLD. The term paediatric fatty liver disease may be more appropriate. In this article, we summarise the known causes of steatosis in children according to their typical, clinical presentation: i) acute liver failure; ii) neonatal or infantile jaundice; iii) hepatomegaly, splenomegaly or hepatosplenomegaly; iv) developmental delay/psychomotor retardation and perhaps most commonly; v) the asymptomatic child with incidental discovery of abnormal liver enzymes. We offer this model as a means to provide pathophysiological insights and an approach to management of the ever more complex subject of fatty liver.

A Fatty Acid Oxidation-Dependent Metabolic Shift Regulates Adult Neural Stem Cell Activity

Hippocampal neurogenesis is important for certain forms of cognition, and failing neurogenesis has been implicated in neuropsychiatric diseases. The neurogenic capacity of hippocampal neural stem/progenitor cells (NSPCs) depends on a balance between quiescent and proliferative states. Here, we show that the rate of fatty acid oxidation (FAO) regulates the activity of NSPCs. Quiescent NSPCs show high levels of carnitine palmitoyltransferase 1a (Cpt1a)-dependent FAO, which is downregulated in proliferating NSPCs. Pharmacological inhibition and conditional deletion of Cpt1a in vitro and in vivo leads to altered NSPC behavior, showing that Cpt1a-dependent FAO is required for stem cell maintenance and proper neurogenesis. Strikingly, manipulation of malonyl-CoA, the metabolite that regulates levels of FAO, is sufficient to induce exit from quiescence and to enhance NSPC proliferation. Thus, the data presented here identify a shift in FAO metabolism that governs NSPC behavior and suggest an instructive role for fatty acid metabolism in regulating NSPC activity.

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A metabolic shift defines NSPC quiescence versus proliferation

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Quiescent NSPCs require high levels of FAO

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Changing levels of a single metabolite is sufficient to induce NSPC proliferation

Effect of Toxicants on Fatty Acid Metabolism in HepG2 Cells

Impairment of hepatic fatty acid metabolism can lead to liver steatosis and injury. Testing drugs for interference with hepatic fatty acid metabolism is therefore important. To find out whether HepG2 cells are suitable for this purpose, we investigated the effect of three established fatty acid metabolism inhibitors and of three test compounds on triglyceride accumulation, palmitate metabolism, the acylcarnitine pool and dicarboxylic acid accumulation in the cell supernatant and on ApoB-100 excretion in HepG2 cells. The three established inhibitors [etomoxir, methylenecyclopropylacetic acid (MCPA), and 4-bromocrotonic acid (4-BCA)] depleted mitochondrial ATP at lower concentrations than cytotoxicity occurred, suggesting mitochondrial toxicity. They inhibited palmitate metabolism at similar or lower concentrations than ATP depletion, and 4-BCA was associated with cellular fat accumulation. They caused specific changes in the acylcarnitine pattern and etomoxir an increase of thapsic (C18 dicarboxylic) acid in the cell supernatant, and did not interfere with ApoB-100 excretion (marker of VLDL export). The three test compounds (amiodarone, tamoxifen, and the cannabinoid WIN 55,212-2) depleted the cellular ATP content at lower concentrations than cytotoxicity occurred. They all caused cellular fat accumulation and inhibited palmitate metabolism at similar or higher concentrations than ATP depletion. They suppressed medium-chain acylcarnitines in the cell supernatant and amiodarone and tamoxifen impaired thapsic acid production. Tamoxifen and WIN 55,212-2 decreased cellular ApoB-100 excretion. In conclusion, the established inhibitors of fatty acid metabolism caused the expected effects in HepG2 cells. HepG cells proved to be useful for the detection of drug-associated toxicities on hepatocellular fatty acid metabolism.

Mitochondria regulate cardiac contraction through ATP-dependent and independent mechanisms

The multipurpose organelle mitochondria play an essential role(s) in controlling cardiac muscle contraction. Mitochondria, not only function as the powerhouses and the energy source of myocytes but also modulate intracellular Ca²⁺ homeostasis, the production of intermediary metabolites/reactive oxygen species (ROS), and other cellular processes. Those molecular events can substantially influence myocardial contraction. Mitochondrial dysfunction is usually associated with cardiac remodelling, and is the causal factor of heart contraction defects in many cases. The manipulation of mitochondria or mitochondria-relevant pathways appears to be a promising therapeutic approach to treat the diseases.

GSEA of mouse and human mitochondriomes reveals fatty acid oxidation in astrocytes

The prevalent view in neuroenergetics is that glucose is the main brain fuel, with neurons being mostly oxidative and astrocytes glycolytic. Evidence supporting that astrocyte mitochondria are functional has been overlooked. Here we sought to determine what is unique about astrocyte mitochondria by performing unbiased statistical comparisons of the mitochondriome in astrocytes and neurons. Using MitoCarta, a compendium of mitochondrial proteins, together with transcriptomes of mouse neurons and astrocytes, we generated cell-specific databases of nuclear genes encoding for mitochondrion proteins, ranked according to relative expression. Standard and in-house Gene Set Enrichment Analyses (GSEA) of five mouse transcriptomes revealed that genes encoding for enzymes involved in fatty acid oxidation (FAO) and amino acid catabolism are consistently more expressed in astrocytes than in neurons. FAO and oxidative-metabolism-related genes are also up-regulated in human cortical astrocytes versus the whole cortex, and in adult astrocytes versus fetal astrocytes. We thus present the first evidence of FAO in human astrocytes. Further, as shown in vitro, FAO coexists with glycolysis in astrocytes and is inhibited by glutamate. Altogether, these analyses provide arguments against the glucose-centered view of energy metabolism in astrocytes and reveal mitochondria as specialized organelles in these cells.

Multi-tissue transcriptomic study reveals the main role of liver in the chicken adaptive response to a switch in dietary energy source through the transcriptional regulation of lipogenesis

Background

Because the cost of cereals is unstable and represents a large part of production charges for meat-type chicken, there is an urge to formulate alternative diets from more cost-effective feedstuff. We have recently shown that meat-type chicken source is prone to adapt to dietary starch substitution with fat and fiber. The aim of this study was to better understand the molecular mechanisms of this adaptation to changes in dietary energy sources through the fine characterization of transcriptomic changes occurring in three major metabolic tissues – liver, adipose tissue and muscle – as well as in circulating blood cells.

Results

We revealed the fine-tuned regulation of many hepatic genes encoding key enzymes driving glycogenesis and de novo fatty acid synthesis pathways and of some genes participating in oxidation. Among the genes expressed upon consumption of a high-fat, high-fiber diet, we highlighted CPT1A, which encodes a key enzyme in the regulation of fatty acid oxidation. Conversely, the repression of lipogenic genes by the high-fat diet was clearly associated with the down-regulation of SREBF1 transcripts but was not associated with the transcript regulation of MLXIPL and NR1H3, which are both transcription factors. This result suggests a pivotal role for SREBF1 in lipogenesis regulation in response to a decrease in dietary starch and an increase in dietary PUFA. Other prospective regulators of de novo hepatic lipogenesis were suggested, such as PPARD, JUN, TADA2A and KAT2B, the last two genes belonging to the lysine acetyl transferase (KAT) complex family regulating histone and non-histone protein acetylation. Hepatic glycogenic genes were also down-regulated in chickens fed a high-fat, high-fiber diet compared to those in chickens fed a starch-based diet. No significant dietary-associated variations in gene expression profiles was observed in the other studied tissues, suggesting that the liver mainly contributed to the adaptation of birds to changes in energy source and nutrients in their diets, at least at the transcriptional level. Moreover, we showed that PUFA deposition observed in the different tissues may not rely on transcriptional changes.

Conclusion

We showed the major role of the liver, at the gene expression level, in the adaptive response of chicken to dietary starch substitution with fat and fiber.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4520-5) contains supplementary material, which is available to authorized users.

Current and future pharmacological therapies for NAFLD/NASH

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent liver disease worldwide, and there is no approved pharmacotherapy. The efficacy of vitamin E and pioglitazone has been established in nonalcoholic steatohepatitis (NASH), a progressive form of NAFLD. GLP-1RA and SGLT2 inhibitors, which are currently approved for use in diabetes, have shown early efficacy in NASH, and also have beneficial cardiovascular or renal effects. Innovative NASH therapies include four main pathways. The first approach is targeting hepatic fat accumulation. Medications in this approach include modulation of peroxisome proliferator-activator receptors (e.g., pemafibrate, elafibranor), medications targeting farnesoid X receptor axis [obeticholic acid; OCA)], inhibitors of de novo lipogenesis (aramchol, ACC inhibitor), and fibroblast growth factor-21 analogues. A second target is oxidative stress, inflammation, and apoptosis. This class of drug includes apoptosis signaling kinase 1 (ASK1) inhibitor and emricasan (an irreversible caspase inhibitor). A third target is intestinal microbiomes and metabolic endotoxemia. Several agents are in ongoing trials, including IMMe124, TLR4 antagonist, and solithromycin (macrolide antibiotics). The final target is hepatic fibrosis, which is strongly associated with all-cause or liver-related mortality in NASH. Antifibrotic agents are a cysteine-cysteine motif chemokine receptor-2/5 antagonist (cenicriviroc; CVC) and galectin 3 antagonist. Among a variety of medications in development, four agents such as OCA, elafibranor, ASK1 inhibitor, and CVC are currently being evaluated in an international phase 3 trial for the treatment of NASH. Within the next few years, the availability of therapeutic options for NASH will hopefully curb the rising trend of NASH-related diseases.

Sodium-glucose cotransporter-2 inhibitors induced eu-glycemic diabetic ketoacidosis: The first report in a type 2 diabetic (T2D) Taiwanese and literature review of possible pathophysiology and contributing factors

Sodium-glucose cotransporter-2 (SGLT-2) inhibitors are the newest class of oral antidiabetic drugs (OADs), approved to be a second-line OAD for type 2 diabetes in Taiwan since 2016. The U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) had both released statements associating the use of SGLT-2 inhibitors may increase the risk of eu-glycemic diabetic ketoacidosis (euDKA). This review reveals the possible pathophysiology with a chain of metabolic adaptions to decrease plasma glucose and increase plasma ketone bodies through pancreas, kidney, liver and adipose tissue. Moreover, euDKA is a potential and rare complication of treatment with SGLT-2 inhibitors when coexisting with triggering factors. It is an emerging challenge for clinical physicians and patients treated with SGLT-2 inhibitors. Therefore, first report of SGLT-2 inhibitor induced euDKA in a T2D Taiwanese and literature review of possible pathophysiology and contributing factors are presented in order to make more attentions in public.

(Pro)renin Receptor Inhibition Reprograms Hepatic Lipid Metabolism and Protects Mice From Diet-Induced Obesity and Hepatosteatosis

RATIONALE

An elevated level of plasma LDL (low-density lipoprotein) is an established risk factor for cardiovascular disease. Recently, we reported that the (pro)renin receptor ([P]RR) regulates LDL metabolism in vitro via the LDLR (LDL receptor) and SORT1 (sortilin-1), independently of the renin-angiotensin system.

OBJECTIVES

To investigate the physiological role of (P)RR in lipid metabolism in vivo.

METHODS AND RESULTS

We used N-acetylgalactosamine modified antisense oligonucleotides to specifically inhibit hepatic (P)RR expression in C57BL/6 mice and studied the consequences this has on lipid metabolism. In line with our earlier report, hepatic (P)RR silencing increased plasma LDL-C (LDL cholesterol). Unexpectedly, this also resulted in markedly reduced plasma triglycerides in a SORT1-independent manner in C57BL/6 mice fed a normal- or high-fat diet. In LDLR-deficient mice, hepatic (P)RR inhibition reduced both plasma cholesterol and triglycerides, in a diet-independent manner. Mechanistically, we found that (P)RR inhibition decreased protein abundance of ACC (acetyl-CoA carboxylase) and PDH (pyruvate dehydrogenase). This alteration reprograms hepatic metabolism, leading to reduced lipid synthesis and increased fatty acid oxidation. As a result, hepatic (P)RR inhibition attenuated diet-induced obesity and hepatosteatosis.

CONCLUSIONS

Collectively, our study suggests that (P)RR plays a key role in energy homeostasis and regulation of plasma lipids by integrating hepatic glucose and lipid metabolism.

Acetyl-CoA Carboxylase 1-Dependent Protein Acetylation Controls Breast Cancer Metastasis and Recurrence

Breast tumor recurrence and metastasis represent the main causes of cancer-related death in women, and treatments are still lacking. Here, we define the lipogenic enzyme acetyl-CoA carboxylase (ACC) 1 as a key player in breast cancer metastasis. ACC1 phosphorylation was increased in invading cells both in murine and human breast cancer, serving as a point of convergence for leptin and transforming growth factor (TGF) β signaling. ACC1 phosphorylation was mediated by TGFβ-activated kinase (TAK) 1, and ACC1 inhibition was indispensable for the elevation of cellular acetyl-CoA, the subsequent increase in Smad2 transcription factor acetylation and activation, and ultimately epithelial-mesenchymal transition and metastasis induction. ACC1 deficiency worsened tumor recurrence upon primary tumor resection in mice, and ACC1 phosphorylation levels correlated with metastatic potential in breast and lung cancer patients. Given the demonstrated effectiveness of anti-leptin receptor antibody treatment in halting ACC1-dependent tumor invasiveness, our work defines a "metabolocentric" approach in metastatic breast cancer therapy.

Design and application of genetically-encoded malonyl-CoA biosensors for metabolic engineering of microbial cell factories

Malonyl-CoA is the basic building block for synthesizing a range of important compounds including fatty acids, phenylpropanoids, flavonoids and non-ribosomal polyketides. Centering around malonyl-CoA, we summarized here the various metabolic engineering strategies employed recently to regulate and control malonyl-CoA metabolism and improve cellular productivity. Effective metabolic engineering of microorganisms requires the introduction of heterologous pathways and dynamically rerouting metabolic flux towards products of interest. Transcriptional factor-based biosensors translate an internal cellular signal to a transcriptional output and drive the expression of the designed genetic/biomolecular circuits to compensate the activity loss of the engineered biosystem. Recent development of genetically-encoded malonyl-CoA sensor has stood out as a classical example to dynamically reprogram cell metabolism for various biotechnological applications. Here, we reviewed the design principles of constructing a transcriptional factor-based malonyl-CoA sensor with superior detection limit, high sensitivity and broad dynamic range. We discussed various synthetic biology strategies to remove pathway bottleneck and how genetically-encoded metabolite sensor could be deployed to improve pathway efficiency. Particularly, we emphasized that integration of malonyl-CoA sensing capability with biocatalytic function would be critical to engineer efficient microbial cell factory. Biosensors have also advanced beyond its classical function of a sensor actuator for in situ monitoring of intracellular metabolite concentration. Applications of malonyl-CoA biosensors as a sensor-invertor for negative feedback regulation of metabolic flux, a metabolic switch for oscillatory balancing of malonyl-CoA sink pathway and source pathway and a screening tool for engineering more efficient biocatalyst are also presented in this review. We envision the genetically-encoded malonyl-CoA sensor will be an indispensable tool to optimize cell metabolism and cost-competitively manufacture malonyl-CoA-derived compounds.

Intestinal SIRT3 overexpression in mice improves whole body glucose homeostasis independent of body weight

OBJECTIVE

Intestinal metabolism might play a greater role in regulating whole body metabolism than previously believed. We aimed to enhance enterocyte metabolism in mice and investigate if it plays a role in diet-induced obesity (DIO) and its comorbidities.

METHODS

Using the cre-loxP system, we overexpressed the mitochondrial NAD+ dependent protein deacetylase SIRT3 in enterocytes of mice (iSIRT3 mice). We chronically fed iSIRT3 mice and floxed-SIRT3 control (S3fl) mice a low-fat, control diet (CD) or a high-fat diet (HFD) and then phenotyped the mice.

RESULTS

There were no genotype differences in any of the parameters tested when the mice were fed CD. Also, iSIRT3 mice were equally susceptible to the development of DIO as S3fl mice when fed HFD. They were, however, better able than S3fl mice to regulate their blood glucose levels in response to exogenous insulin and glucose, indicating that they were protected from developing insulin resistance. This improved glucose homeostasis was accompanied by an increase in enterocyte metabolic activity and an upregulation of ketogenic gene expression in the small intestine.

CONCLUSION

Enhancing enterocyte oxidative metabolism can improve whole body glucose homeostasis.

Insights into the Hexose Liver Metabolism-Glucose versus Fructose

High-fructose intake in healthy men is associated with characteristics of metabolic syndrome. Extensive knowledge exists about the differences between hepatic fructose and glucose metabolism and fructose-specific mechanisms favoring the development of metabolic disturbances. Nevertheless, the causal relationship between fructose consumption and metabolic alterations is still debated. Multiple effects of fructose on hepatic metabolism are attributed to the fact that the liver represents the major sink of fructose. Fructose, as a lipogenic substrate and potent inducer of lipogenic enzyme expression, enhances fatty acid synthesis. Consequently, increased hepatic diacylglycerols (DAG) are thought to directly interfere with insulin signaling. However, independently of this effect, fructose may also counteract insulin-mediated effects on liver metabolism by a range of mechanisms. It may drive gluconeogenesis not only as a gluconeogenic substrate, but also as a potent inducer of carbohydrate responsive element binding protein (ChREBP), which induces the expression of lipogenic enzymes as well as gluconeogenic enzymes. It remains a challenge to determine the relative contributions of the impact of fructose on hepatic transcriptome, proteome and allosterome changes and consequently on the regulation of plasma glucose metabolism/homeostasis. Mathematical models exist modeling hepatic glucose metabolism. Future models should not only consider the hepatic adjustments of enzyme abundances and activities in response to changing plasma glucose and insulin/glucagon concentrations, but also to varying fructose concentrations for defining the role of fructose in the hepatic control of plasma glucose homeostasis.

Review article: new treatments in non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease is the fastest growing cause of liver disease in the Western world, yet there is no approved pharmacotherapy. While lifestyle modifications remain the mainstay of treatment, only a proportion of individuals are able to make or sustain them, and so more treatment options are required.

AIM

To review the potential benefit of drugs used in clinical practice, those entering phase II trials, and compounds being investigated in pre-clinical studies.

METHODS

A literature search was performed using PubMed to identify relevant studies; linked references were also reviewed.

RESULTS

Vitamin E and pioglitazone have shown efficacy in non-alcoholic steatohepatitis (NASH), but long-term safety concerns, specifically bladder cancer and osteoporosis with pioglitazone, have limited their use. GLP-1 analogues and SGLT-2 inhibitors are currently approved for use in diabetes, have shown early efficacy in NASH and also have beneficial cardiovascular effects. Peroxisome proliferator-activator receptors and FXR agonists have potent effects on lipogenesis, inflammation and fibrosis, respectively, with their efficacy and safety being currently tested in phase 3. As inflammation and apoptosis are key features of NASH agents modulating these pathways are of interest; CCR2/5 antagonists downregulate inflammatory pathways and reduce fibrosis with caspase and apoptosis signal-regulating kinase 1 inhibitors reducing apoptosis and fibrosis.

CONCLUSIONS

Rising demand and an improved understanding of NASH pathophysiology has led to a surge in development of new therapies. Tailoring pharmacotherapy to the dominant pathogenic pathway in a given patient along with use of combination therapy is likely to represent the future direction in treatment of patients with NASH.

AMPK activation: Role in the signaling pathways of neuroinflammation and neurodegeneration

Adenosine monophosphate-activated protein kinase (AMPK) is an evolutionarily conserved sensor of cellular energy status and has been reported to be involved in chronic inflammatory disorders. AMPK is expressed in immune cells, such as dendritic cells, macrophages, lymphocytes and neutrophils, and is an important regulator of inflammatory responses through the regulation of complex signaling networks in part by inhibiting downstream cascade pathways, such as nuclear factor kB, which is a key regulator of innate immunity and inflammation, as well as acting as a negative regulator of toll-like receptors. Recent data suggest that AMPK dysregulation may participate in neurodegenerative diseases, such as multiple sclerosis, Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis and neuropathies. However, there are conflicting reports on the benefits or detrimental effects of AMPK in distinct pathological conditions. This paper offers a review of the recent literature on the pharmacological modulation of the AMPK system as a potential molecular target in the management of neurodegenerative diseases.

Inflammasomes on the Crossroads of Innate Immune Recognition and Metabolic Control

Inflammasomes are protein complexes formed upon encounter of microbial or damage-associated stimuli. The main output of inflammasome assembly is activation of caspase-1, a protease involved in both pro-inflammatory and host-protective responses. Defined bacterial or viral ligands have been identified for the inflammasome-forming receptors AIM2, NLRP1, and NLRC4. The signals activating other inflammasomes, NLRP3, NLRP6, and pyrin, are less well understood. Recent studies implicated several low-molecular-weight compounds traditionally linked to metabolism, not immunity, in modulation of inflammasome signaling. Furthermore, genetic, pharmacological, or pathogen-mediated interference with energy metabolism also affects inflammasome activation. Here we review the findings on how microbial- and host-derived metabolites regulate activation of the NLRP3 and NLRP6 inflammasomes. We discuss the different models of how glycolysis and mitochondrial metabolism control the NLRP3 inflammasome. Finally, we summarize the findings on metabolic control of pyrin and point to open questions to be addressed to broaden our understanding of metabolism-inflammasome interactions.

Tibolone Preserves Mitochondrial Functionality and Cell Morphology in Astrocytic Cells Treated with Palmitic Acid

Obesity has been associated with increased chronic neuroinflammation and augmented risk of neurodegeneration. This is worsened during the normal aging process when the levels of endogenous gonadal hormones are reduced. In this study, we have assessed the protective actions of tibolone, a synthetic steroid with estrogenic actions, on T98G human astrocytic cells exposed to palmitic acid, a saturated fatty acid used to mimic obesity in vitro. Tibolone improved cell survival, and preserved mitochondrial membrane potential in palmitic acid-treated astrocytic cells. Although we did not find significant actions of tibolone on free radical production, it modulated astrocytic morphology after treatment with palmitic acid. These data suggest that tibolone protects astrocytic cells by preserving both mitochondrial functionality and morphological complexity.

Reviewing the impact of lipid synthetic flux on Th17 function

CD4+ T helper 17 cells (Th17) acquire specific effector functions in response to activation and instructional signals. Accumulating evidence indicates that specific cellular lipid metabolic pathways play essential roles in regulating the differentiation and function of Th17 cells. Mechanistic studies reveal that metabolic fluxes through both the cholesterol and long chain fatty acid biosynthetic pathways are important in controlling RORγ transcriptional activity through their ability to generate lipid ligands of RORγ. Genetic and pharmacologic studies demonstrate that altering the flux through these lipid biosynthetic pathways impacts the generation of IL-17 as well as the balance of Th17 and CD4+ regulatory T cells (Tregs). In this mini-review, we briefly introduce the mechanics of cholesterol and long chain fatty acid biosynthesis. We also discuss the evidence underlying the unique role that these lipid metabolic pathways play in intrinsically regulating the fate and function of Th17 cells under normal and pathogenic conditions.

The Mammalian Malonyl-CoA Synthetase ACSF3 Is Required for Mitochondrial Protein Malonylation and Metabolic Efficiency

Malonyl-coenzyme A (malonyl-CoA) is a central metabolite in mammalian fatty acid biochemistry generated and utilized in the cytoplasm; however, little is known about noncanonical organelle-specific malonyl-CoA metabolism. Intramitochondrial malonyl-CoA is generated by a malonyl-CoA synthetase, ACSF3, which produces malonyl-CoA from malonate, an endogenous competitive inhibitor of succinate dehydrogenase. To determine the metabolic requirement for mitochondrial malonyl-CoA, ACSF3 knockout (KO) cells were generated by CRISPR/Cas-mediated genome editing. ACSF3 KO cells exhibited elevated malonate and impaired mitochondrial metabolism. Unbiased and targeted metabolomics analysis of KO and control cells in the presence or absence of exogenous malonate revealed metabolic changes dependent on either malonate or malonyl-CoA. While ACSF3 was required for the metabolism and therefore detoxification of malonate, ACSF3-derived malonyl-CoA was specifically required for lysine malonylation of mitochondrial proteins. Together, these data describe an essential role for ACSF3 in dictating the metabolic fate of mitochondrial malonate and malonyl-CoA in mammalian metabolism.

Fructose Consumption in the Development of Obesity and the Effects of Different Protocols of Physical Exercise on the Hepatic Metabolism

Fructose consumption has been growing exponentially and, concomitant with this, the increase in the incidence of obesity and associated complications has followed the same behavior. Studies indicate that fructose may be a carbohydrate with greater obesogenic potential than other sugars. In this context, the liver seems to be a key organ for understanding the deleterious health effects promoted by fructose consumption. Fructose promotes complications in glucose metabolism, accumulation of triacylglycerol in the hepatocytes, and alterations in the lipid profile, which, associated with an inflammatory response and alterations in the redox state, will imply a systemic picture of insulin resistance. However, physical exercise has been indicated for the treatment of several chronic diseases. In this review, we show how each exercise protocol (aerobic, strength, or a combination of both) promote improvements in the obesogenic state created by fructose consumption as an improvement in the serum and liver lipid profile (high-density lipoprotein (HDL) increase and decrease triglyceride (TG) and low-density lipoprotein (LDL) levels) and a reduction of markers of inflammation caused by an excess of fructose. Therefore, it is concluded that the practice of aerobic physical exercise, strength training, or a combination of both is essential for attenuating the complications developed by the consumption of fructose.

Personal model-assisted identification of NAD+ and glutathione metabolism as intervention target in NAFLD

To elucidate the molecular mechanisms underlying non‐alcoholic fatty liver disease (NAFLD), we recruited 86 subjects with varying degrees of hepatic steatosis (HS). We obtained experimental data on lipoprotein fluxes and used these individual measurements as personalized constraints of a hepatocyte genome‐scale metabolic model to investigate metabolic differences in liver, taking into account its interactions with other tissues. Our systems level analysis predicted an altered demand for NAD⁺ and glutathione (GSH) in subjects with high HS. Our analysis and metabolomic measurements showed that plasma levels of glycine, serine, and associated metabolites are negatively correlated with HS, suggesting that these GSH metabolism precursors might be limiting. Quantification of the hepatic expression levels of the associated enzymes further pointed to altered de novo GSH synthesis. To assess the effect of GSH and NAD⁺ repletion on the development of NAFLD, we added precursors for GSH and NAD⁺ biosynthesis to the Western diet and demonstrated that supplementation prevents HS in mice. In a proof‐of‐concept human study, we found improved liver function and decreased HS after supplementation with serine (a precursor to glycine) and hereby propose a strategy for NAFLD treatment.

Adipose tissue NAD+-homeostasis, sirtuins and poly(ADP-ribose) polymerases -important players in mitochondrial metabolism and metabolic health

Obesity, a chronic state of energy overload, is characterized by adipose tissue dysfunction that is considered to be the major driver for obesity associated metabolic complications. The reasons for adipose tissue dysfunction are incompletely understood, but one potential contributing factor is adipose tissue mitochondrial dysfunction. Derangements of adipose tissue mitochondrial biogenesis and pathways associate with obesity and metabolic diseases. Mitochondria are central organelles in energy metabolism through their role in energy derivation through catabolic oxidative reactions. The mitochondrial processes are dependent on the proper NAD⁺/NADH redox balance and NAD⁺ is essential for reactions catalyzed by the key regulators of mitochondrial metabolism, sirtuins (SIRTs) and poly(ADP-ribose) polymerases (PARPs). Notably, obesity is associated with disturbed adipose tissue NAD⁺ homeostasis and the balance of SIRT and PARP activities. In this review we aim to summarize existing literature on the maintenance of intracellular NAD⁺ pools and the function of SIRTs and PARPs in adipose tissue during normal and obese conditions, with the purpose of comprehending their potential role in mitochondrial derangements and obesity associated metabolic complications. Understanding the molecular mechanisms that are the root cause of the adipose tissue mitochondrial derangements is crucial for developing new effective strategies to reverse obesity associated metabolic complications.

Mechanism for leptin's acute insulin-independent effect to reverse diabetic ketoacidosis

The mechanism by which leptin reverses diabetic ketoacidosis (DKA) is unknown. We examined the acute insulin-independent effects of leptin replacement therapy in a streptozotocin-induced rat model of DKA. Leptin infusion reduced rates of lipolysis, hepatic glucose production (HGP), and hepatic ketogenesis by 50% within 6 hours and were independent of any changes in plasma glucagon concentrations; these effects were abrogated by coinfusion of corticosterone. Treating leptin- and corticosterone-infused rats with an adipose triglyceride lipase inhibitor blocked corticosterone-induced increases in plasma glucose concentrations and rates of HGP and ketogenesis. Similarly, adrenalectomized type 1 diabetic (T1D) rats exhibited decreased rates of lipolysis, HGP, and ketogenesis; these effects were reversed by corticosterone infusion. Leptin-induced decreases in lipolysis, HGP, and ketogenesis in DKA were also nullified by relatively small increases (15 to 70 pM) in plasma insulin concentrations. In contrast, the chronic glucose-lowering effect of leptin in a STZ-induced mouse model of poorly controlled T1D was associated with decreased food intake, reduced plasma glucagon and corticosterone concentrations, and decreased ectopic lipid (triacylglycerol/diacylglycerol) content in liver and muscle. Collectively, these studies demonstrate marked differences in the acute insulin-independent effects by which leptin reverses fasting hyperglycemia and ketoacidosis in a rodent model of DKA versus the chronic pleotropic effects by which leptin reverses hyperglycemia in a non-DKA rodent model of T1D.