Hepatic Fatty Acid Β-oxidation Research Articles

MnO2 nanoparticles trigger hepatic lipotoxicity and mitophagy via mtROS-dependent Hsf1Ser326 phosphorylation

Manganese (Mn) is an essential element for maintaining normal metabolism in vertebrates. Mn dioxide nanoparticles (MnO2 NPs), a novel Mn source, have shown great potentials in biological and biomedical applications due to their distinct physical and chemical properties. However, little is known about potential adverse effects on animal or cellular metabolism. Here, we investigated whether and how dietary MnO2 NPs affect hepatic lipid metabolism in vertebrates. We found that, excessive MnO2 NPs intake increased hepatic and mitochondrial Mn content, promoted hepatic lipotoxic disease and lipogenesis, and inhibited hepatic lipolysis and fatty acid β-oxidation. Moreover, excessive MnO2 NPs intake induced hepatic mitochondrial oxidative stress, damaged mitochondrial function, disrupted mitochondrial dynamics and activated mitophagy. Importantly, we uncovered that mtROS-activated phosphorylation of heat shock factor 1 (Hsf1) at Ser326 residue mediated MnO2 NPs-induced hepatic lipotoxic disease and mitophagy. Mechanistically, MnO2 NPs-induced lipotoxicity and mitophagy were via mtROS-induced phosphorylation and nucleus translocation of Hsf1 and its DNA binding capacity to plin2/dgat1 and bnip3 promoters, respectively. Overall, our findings uncover novel mechanisms by which mtROS-mediated mitochondrial dysfunction and phosphorylation of Hsf1S326 contribute to MnO2 NPs-induced hepatic lipotoxicity and mitophagy, which provide new insights into the effects of metal oxides nanoparticles on hepatotoxicity in vertebrates.

Changes in Plasma Pyruvate and TCA Cycle Metabolites upon Increased Hepatic Fatty Acid Oxidation and Ketogenesis in Male Wistar Rats.

Altered hepatic mitochondrial fatty acid β-oxidation and associated tricarboxylic acid (TCA) cycle activity contributes to lifestyle-related diseases, and circulating biomarkers reflecting these changes could have disease prognostic value. This study aimed to determine hepatic and systemic changes in TCA-cycle-related metabolites upon the selective pharmacologic enhancement of mitochondrial fatty acid β-oxidation in the liver, and to elucidate the mechanisms and potential markers of hepatic mitochondrial activity. Male Wistar rats were treated with 3-thia fatty acids (e.g., tetradecylthioacetic acid (TTA)), which target mitochondrial biogenesis, mitochondrial fatty acid β-oxidation, and ketogenesis predominantly in the liver. Hepatic and plasma concentrations of TCA cycle intermediates and anaplerotic substrates (LC-MS/MS), plasma ketones (colorimetric assay), and acylcarnitines (HPLC-MS/MS), along with associated TCA-cycle-related gene expression (qPCR) and enzyme activities, were determined. TTA-induced hepatic fatty acid β-oxidation resulted in an increased ratio of plasma ketone bodies/nonesterified fatty acid (NEFA), lower plasma malonyl-CoA levels, and a higher ratio of plasma acetylcarnitine/palmitoylcarnitine (C2/C16). These changes were associated with decreased hepatic and increased plasma pyruvate concentrations, and increased plasma concentrations of succinate, malate, and 2-hydroxyglutarate. Expression of several genes encoding TCA cycle enzymes and the malate-oxoglutarate carrier (Slc25a11), glutamate dehydrogenase (Gdh), and malic enzyme (Mdh1 and Mdh2) were significantly increased. In conclusion, the induction of hepatic mitochondrial fatty acid β-oxidation by 3-thia fatty acids lowered hepatic pyruvate while increasing plasma pyruvate, as well as succinate, malate, and 2-hydroxyglutarate.

Thyroid Dysfunction Induced by Fungicide Famoxadone Exposure Contributes to Nonalcoholic Fatty Liver Disease in Male Mice: In Vivo, In Vitro, and In Silico Studies.

Thyroid dysfunction has become a serious public health problem, which is considered a trigger of nonalcoholic fatty liver disease (NAFLD). Pesticide exposure could contribute to thyroid dysfunction and NAFLD, but the relationship between these factors remains unclear. In this study, the effects of subchronic famoxadone exposure on thyroid and liver at no observed adverse effect level (NOEL) related concentrations were investigated using in vivo, in vitro, and in silico models. Famoxadone caused hepatic steatosis, lipid metabolism disorder, and liver oxidative stress and induced NAFLD in male mice. The suppression of hepatic fatty acid β-oxidation was the key factor of NAFLD, which was highly associated with hypothalamic-pituitary-thyroid (HPT) axis hormones disorder. Famoxadone disrupted thyroid hormone biosynthesis by causing thyroid follicle aberrations and abnormal HPT axis-related gene expression. In vitro studies confirmed that famoxadone inhibited the transport of thyroxine (T4) into hepatocytes and the conversion of T4 to triiodothyronine (T3). In silico studies verified that famoxadone interfered with the binding of thyroid hormones to proteins mediating thyroid hormone transport, conversion, and activation. This study comprehensively reported the association between NAFLD and thyroid dysfunction caused by famoxadone, providing new perspectives for the health risk evaluation of pesticides with a similar structure in mammals.

Perilipin5 protects against non-alcoholic steatohepatitis by increasing 11-Dodecenoic acid and inhibiting the occurrence of ferroptosis

BackgroundNon-alcoholic steatohepatitis (NASH) is a major contributor to liver cirrhosis and hepatocellular carcinoma. There remains no effective pharmacological therapy. The hepatic lipid metabolism and fatty acid β-oxidation are regulated by Perilipin5 (Plin5). However, it is yet unknown how Plin5 affects NASH and the molecular process.MethodsHigh-fat, high-cholesterol and high-fructose (HFHC) diets were used to mimic the progression of NASH in wild type (WT) mice and Plin5 knockout (Plin5 KO) mice. The degree of ferroptosis was measured by detecting the expression of key genes of ferroptosis and the level of lipid peroxide. The degree of NASH was judged by observing the morphology of the liver, detecting the expression of inflammation and fibrosis related genes of liver damage. Plin5 was overexpressed in the liver of mice by tail vein injection of adenovirus, and the process of NASH was simulated by methionine choline deficiency (MCD) diet. The occurrence of ferroptosis and NASH was detected by the same detection method. Targeted lipidomics sequencing was used to detect the difference in free fatty acid expression in the WT Plin5 KO group. Finally, it was verified in cell experiments to further study the effect of free fatty acids on ferroptosis of hepatocytes.ResultsIn various NASH models, hepatic Plin5 was dramatically reduced. Plin5 knockout (KO) worsened NASH-associated characteristics in mice given a high-fat/high-cholesterol (HFHC) diet, such as lipid accumulation, inflammation and hepatic fibrosis. It has been shown that ferroptosis is involved in NASH progression. We revealed that Plin5 KO in mice aggravated the degree of ferroptosis in NASH models. Conversely, overexpression of Plin5 significantly alleviated ferroptosis and further ameliorated progression of MCD-induced NASH. Analysis of livers obtained from HFHC diet-fed mice by targeted lipidomics revealed that 11-Dodecenoic acid was significantly decreased in Plin5 KO mice. Addition of 11-Dodecenoia acid to Plin5 knockdown hepatocytes effectively prevented ferroptosis.ConclusionOur study demonstrates that Plin5 protects against NASH progression by increasing 11-Dodecenoic acid level and further inhibiting ferroptosis, suggesting that Plin5 has therapeutic potential as a target for the management of NASH.

257-LB: Defining the Stage-Dependent Transcriptome and Methylome in the Mouse Liver during Perinatal Metabolic Maturation

A mammalian liver serves as an extramedullary hematopoietic organ during fetus, and matures into a metabolic organ after birth, thereby adapting to the changes in nutritional environment. PPARα-dependent DNA demethylation upregulates hepatic fatty acid β-oxidation (FAO) genes in the postnatal mouse liver to produce energy from breast milk lipids. However, the detailed interaction between DNA methylation (DNAme) and gene expression in the liver through perinatal stages remain poorly understood. Here, we perform an integrative analysis of transcriptome and methylome of the mice liver at fetal, neonatal, and postweaning stages. While the level of global DNAme gradually increased from fetal to postweaning stages, we found a drastic loss of DNAme in specific regions that are associated with metabolic pathways such as FAO, gluconeogenesis, and amino acid metabolism within the neonatal stage in concordance with the activation of such metabolic processes. Moreover, in silico analysis predicted transcription factors, such as HNF4α, PPARα, NR1H2, and NR1H3, as key epigenetic regulators within lactation period. We also observed an inactivation of erythrocyte development with a concordant gain of DNAme. This analysis extends the epigenetic landscape for understanding the hepatic maturation during early life, and suggests the importance of lactation period in epigenetic regulation. Disclosure S. Yano: None. N. Sato: None. H. Araki: None. F. Miura: None. T. Ito: None. Y. Ogawa: None.

Coordinated transcriptional upregulation of oxidative metabolism proteins in long-lived endocrine mutant mice.

Caloric restriction (CR), which extends lifespan in rodents, leads to increased hepatic fatty acid β-oxidation and oxidative phosphorylation (OXPHOS), with parallel changes in proteins and their mRNAs. Genetic mutants that extend lifespan, including growth hormone receptor knockout (GHRKO) and Snell dwarf (SD) mice, have lower respiratory quotient, suggesting increased reliance on fatty acid oxidation, but the molecular mechanism(s) of this metabolic shift have not yet been worked out. Here we show that both GHRKO and SD mice have significantly higher mRNA and protein levels of enzymes involved in mitochondrial and peroxisomal fatty acid β-oxidation. In addition, multiple subunits of OXPHOS complexes I-IV are upregulated in GHRKO and SD livers, and Complex V subunit ATP5a is upregulated in liver of GHRKO mice. Expression of these genes is regulated by a group of nuclear receptors and transcription factors including peroxisome proliferator-activated receptors (PPARs) and estrogen-related receptors (ERRs). We found that levels of these nuclear receptors and their co-activator PGC-1α were unchanged or downregulated in liver of GHRKO and SD mice. In contrast, NCOR1, a co-repressor for the same receptors, was significantly downregulated in the two long-lived mouse models, suggesting a plausible mechanism for the changes in FAO and OXPHOS proteins. Hepatic levels of HDAC3, a co-factor for NCOR1 transcriptional repression, were also downregulated. The role of NCOR1 is well established in the contexts of cancer and metabolic disease, but may provide new mechanistic insights into metabolic control in long-lived mouse models.

Insoluble Dietary Fiber from Soybean Residue (Okara) Exerts Anti-Obesity Effects by Promoting Hepatic Mitochondrial Fatty Acid Oxidation.

Numerous investigations have shown that insoluble dietary fiber (IDF) has a potentially positive effect on obesity due to a high-fat diet (HFD). Our previous findings based on proteomic data revealed that high-purity IDF from soybean residue (okara) (HPSIDF) prevented obesity by regulating hepatic fatty acid synthesis and degradation pathways, while its intervention mechanism is uncharted. Consequently, the goal of this work is to find out the potential regulatory mechanisms of HPSIDF on hepatic fatty acid oxidation by determining changes in fatty acid oxidation-related enzymes in mitochondria and peroxisomes, the production of oxidation intermediates and final products, the composition and content of fatty acids, and the expression levels of fatty acid oxidation-related proteins in mice fed with HFD. We found that supplementation with HPSIDF significantly ameliorated body weight gain, fat accumulation, dyslipidemia, and hepatic steatosis caused by HFD. Importantly, HPSIDF intervention promotes medium- and long-chain fatty acid oxidation in hepatic mitochondria by improving the contents of acyl-coenzyme A oxidase 1 (ACOX1), malonyl coenzyme A (Malonyl CoA), acetyl coenzyme A synthase (ACS), acetyl coenzyme A carboxylase (ACC), and carnitine palmitoyl transferase-1 (CPT-1). Moreover, HPSIDF effectively regulated the expression levels of proteins involved with hepatic fatty acid β-oxidation. Our study indicated that HPSIDF treatment prevents obesity by promoting hepatic mitochondrial fatty acid oxidation.

Abstract 684: Hepatic Oxalate Overproduction As A Driver And Therapeutic Target In NASH And Atherosclerosis

Affecting one third of the global population, with no pharmacotherapy available, nonalcoholic fatty liver disease (NAFLD) has become the leading cause of chronic liver disease. Surprisingly, the major cause of death in patients with NAFLD, particularly in those with the more severe nonalcoholic steatohepatitis (NASH), is atherosclerotic cardiovascular disease (CVD). Thus, there is a critical need to identify targetable pathways for concurrent treatment of NASH and atherosclerotic CVD, which has been hampered by limited understanding of the pathophysiology and metabolic pathways linking these two diseases. Recently, we and others uncovered oxalate metabolism commonly dysregulated in NAFLD and CVD. Using unbiased transcriptomics, we identified suppression of genes that limit oxalate production in livers from humans and mice with NASH. Alanine-glyoxylate aminotransferase (AGXT), a liver-specific enzyme that detoxifies glyoxylate, the oxalate precursor, was reduced and oxalate was markedly increased in correlation with NASH severity. Remarkably, oxalate was also increased both in patients and mice with atherosclerosis. In our mouse models of hepatic oxalate overproduction ( Agxt -/- and Agxt -/- / Apoe -/- ), both NASH and atherosclerosis were increased with suppressed hepatic fatty acid β-oxidation (FAO) and induction of proinflammatory pathways. In hepatocytes, oxalate induced mitochondrial dysfunction and lipid accumulation while downregulating peroxisome proliferator-activated receptor α (PPARα), inhibiting FAO and upregulating C-C motif chemokine ligand 5 (CCL5). Importantly, limiting hepatic oxalate production via hepatocyte-specific overexpression of AGXT (AAV8-TBG-AGXT) reduced NASH and atherosclerosis in mice by stimulating FAO and attenuating proinflammatory responses. Together, our findings uncover hepatic oxalate overproduction as a dysregulated metabolic pathway linking NASH and atherosclerotic CVD, highlighting the potential of oxalate reduction for concurrent treatment of these two prominent diseases.

Quantitative proteomics reveals Polygonum perfoliatum L. ameliorates hepatic steatosis by promoting PPARs/CPT1A/CPT2-mediated fatty acid β-oxidation.

Non-alcoholic fatty liver disease (NAFLD) is a predominant contributor to end-stage liver disease in the forthcoming decades. Polygonum perfoliatum L. (PPL) is an herbal medicine with anti-lipid peroxidation and anti-inflammatory properties. However, detailed hepatoprotective effects of PPL against NAFLD and its underlying mechanisms are not fully understood. Here, we found that PPL protects against high fat diet (HFD)-induced hepatic steatosis, lipid peroxidation, and glucose-lipid metabolism dysfunction in NAFLD mice. We therefore performed a label-free quantitative proteomic profiling analysis to determine the effect of PPL treatment on liver tissue proteomics and identified that activated PPARs/CPT1A/CPT2-mediated hepatic fatty acid β-oxidation (FAO) process was significantly altered. In vitro treatment of hepatocytes with PPL confirmed this altered process and FAO inhibitor etomoxir (ETO) attenuated the lipid-lowering activity of PPL in hepatocytes. Ultra-high-performance liquid chromatography/Q Exactive-HFX (UPLC/QE-HFX) was used to determine the material basis of anti-NAFLD activity of PPL. Our results have demonstrated the efficacy and potential mechanisms of PPL as an effective pharmacological therapy of NAFLD.

Resmetirom: An Orally Administered, Smallmolecule, Liver-directed, β-selective THR Agonist for the Treatment of Non-alcoholic Fatty Liver Disease and Non-alcoholic Steatohepatitis.

Non-alcoholic fatty liver disease (NAFLD) encompasses a spectrum of fatty liver disease, including non-alcoholic fatty liver (NAFL) and its more progressive form, non-alcoholic steatohepatitis (NASH). The prevalence of NAFLD/NASH along with type 2 diabetes and obesity is rising worldwide. In those who develop NASH, unlike those with bland steatosis (NAFL), lipotoxic lipids drive hepatocyte injury, inflammation and stellate cell activation leading to progressive accumulation of collagen or fibrosis, ultimately leading to cirrhosis and increased risk of hepatocellular carcinoma. Hypothyroidism is associated with NAFLD/NASH; specifically, intrahepatic hypothyroidism drives lipotoxicty in preclinical models. Agonists of thyroid hormone receptor (THR)-β, which is primarily found in the liver, can promote lipophagy, mitochondrial biogenesis and mitophagy, stimulating increased hepatic fatty acid β-oxidation, and thereby decreasing the burden of lipotoxic lipids, while promoting low-density lipoprotein (LDL) uptake and favourable effects on lipid profiles. A number of THR-β agonists are currently being investigated for NASH. This review focuses on resmetirom, an orally administered, once-daily, small-molecule, liver-directed, ß-selective THR agonist, as it is furthest along in development. Data from completed clincal studies outlined in this review demonstrate that resmetirom is effective in reducing hepatic fat content as measured by magnetic resonance imaging-derived proton density fat fraction, reduces liver enzymes, improves non-i nvasive markers of liver fibrogenesis and decreases liver stiffness, while eliciting a favourable cardiovascular profile with a reduction in serum lipids, including LDL cholesterol. Topline phase III biopsy data showed resolution of NASH and/or fibrosis improvement after 52 weeks of treatment, with more detailed peer-reviewed findings anticipated in order to certify these findings. Longer term clinical outcomes from both MAESTRO-NASH and MAESTRO-NASH OUTCOMES will be a pivotal juncture in the drug's road towards being approved as a NASH therapeutic.

Hif-2α regulates lipid metabolism in alcoholic fatty liver disease through mitophagy

BackgroundDisordered lipid metabolism plays an essential role in both the initiation and progression of alcoholic fatty liver disease (AFLD), and fatty acid β-oxidation is increasingly considered as a crucial factor for controlling lipid metabolism. Hif-2α is a member of the Hif family of nuclear receptors, which take part in regulating hepatic fatty acid β-oxidation. However, its functional role in AFLD and the underlying mechanisms remain unclear.ResultsHif-2α was upregulated in EtOH-fed mice and EtOH-treated AML-12 cells. Inhibition or silencing of Hif-2α led to increased fatty acid β-oxidation and BNIP3-dependent mitophagy. Downregulation of Hif-2α activates the PPAR-α/PGC-1α signaling pathway, which is involved in hepatic fatty acid β-oxidation, by mediating BNIP3-dependent mitophagy, ultimately delaying the progression of AFLD.ConclusionsHif-2α induces liver steatosis, which promotes the progression of AFLD. Here, we have described a novel Hif-2α-BNIP3-dependent mitophagy regulatory pathway interconnected with EtOH-induced lipid accumulation, which could be a potential therapeutic target for the prevention and treatment of AFLD.

Ethanolic extract of root from Arctium lappa L ameliorates obesity and hepatic steatosis in rats by regulating the AMPK/ACC/CPT-1 pathway.

Burdock (Arctium lappa L) root is eaten as a vegetable in many countries and used as an ethnomedicine because of its various pharmacological effects. The objective of this study was to investigate the underlying mechanisms of ethanolic extract of root from Arctium lappa L root (ALE) to lose weight and regulate lipid metabolism. The results showed that ALE can regulate lipid metabolism level and inhibit the weight gain of rats induced by the high-sugar and high-fat diet. The contents of triglyceride and cholesterol in the liver of obese rats significantly reduced, and hepatic steatosis was ameliorated. In addition, this study identified that ALE enhanced hepatic fatty acid β-oxidation and ameliorated hepatic steatosis by activating AMPK/ACC/CPT-1 pathway. These results indicated that ALE has a potential preventive and therapeutic effect on metabolic-associated fatty liver disease and obesity. PRACTICAL APPLICATIONS: Obesity is already a global health problem. Obesity causes accumulation of triglycerides, which leads to hepatic steatosis. Long-term steatosis causes liver damage and metabolic fatty liver disease. Plant-derived functional foods or herbal medicines have better effects on weight loss and liver protection, which are more conducive to long-term use with less toxic side effects. As a medicinal and edible plant material, Arctium lappa L root has the effect in losing weight. Our study showed that ethanolic extract of Arctium lappa L root effectively regulates lipid metabolism and inhibits hepatic steatosis. Arctium lappa L root may be used as a therapeutic drug and functional food raw material for obesity and fatty liver disease.

KHK, PNPLA3 and PPAR as Novel Targets for the Anti-Steatotic Action of Bempedoic Acid.

Bempedoic acid (BemA) is an ATP-citrate lyase (ACLY) inhibitor used to treat hypercholesterolemia. We studied the anti-steatotic effect of BemA, and the mechanisms involved, in a model of fatty liver in female rats obtained through the administration of a high-fat diet supplemented with liquid fructose (HFHFr) for three months. In the third month, a group of rats was treated with BemA (30 mg/kg/day) by gavage. Plasma analytes, liver histology, adiposity, and the expression of key genes controlling fatty acid metabolism were determined, and PPAR agonism was explored by using luciferase reporter assays. Our results showed that, compared to HFHFr, BemA-treated rats exhibited lower body weight, higher liver/body weight, and reduced hepatic steatosis. In addition to ACLY inhibition, we found three novel mechanisms that could account for the anti-steatotic effect: (1) reduction of liver ketohexokinase, leading to lower fructose intake and reduced de novo lipogenesis; (2) increased expression of patatin-like phospholipase domain-containing protein 3, a protein related to the export of liver triglycerides to blood; and (3) PPARα agonist activity, leading to increased hepatic fatty acid β-oxidation. In conclusion, BemA may represent a novel approach to treat hepatic steatosis, and therefore to avoid progression to advanced stages of non-alcoholic fatty liver disease.

Consumption of Low Dose Fucoxanthin Does Not Prevent Hepatic and Adipose Inflammation and Fibrosis in Mouse Models of Diet-Induced Obesity.

Fucoxanthin (FCX) is a xanthophyll carotenoid present in brown seaweed. The goal of this study was to examine whether FCX supplementation could attenuate obesity-associated metabolic abnormalities, fibrosis, and inflammation in two diet-induced obesity (DIO) mouse models. C57BL/6J mice were fed either a high-fat/high-sucrose/high-cholesterol (HFC) diet or a high-fat/high-sucrose (HFS) diet. The former induces more severe liver injury than the latter model. In the first study, male C57BL/6J mice were fed an HFC diet, or an HFC diet containing 0.015% or 0.03% (w/w) FCX powder for 12 weeks to develop obesity-induced nonalcoholic steatohepatitis (NASH). In the second study, mice were fed an HFS diet or an HFS diet containing 0.01% FCX powder for 8 weeks. FCX did not change body weight gain and serum lipid profiles compared to the HFC or HFS controls. No significant differences were present in liver triglyceride and total cholesterol, hepatic fat accumulation, and serum alanine aminotransferase levels between control and FCX-fed mice regardless of whether they were on an HFC or HFS diet. FCX did not mitigate mRNA abundance of genes involved in lipid synthesis, cholesterol metabolism, inflammation, and fibrosis in the liver and white adipose tissue, while hepatic fatty acid β-oxidation genes were significantly elevated by FCX in both HFC and HFS feeding studies. Additionally, in the soleus muscle, FCX supplementation significantly elevated genes that regulate mitochondrial biogenesis and fatty acid β-oxidation, concomitantly increasing mitochondrial DNA copy number, compared with HFC. In summary, FCX supplementation had minor effects on hepatic and white adipose inflammation and fibrosis in two different DIO mouse models.

Natural Garlic Organosulfur Compounds Prevent Metabolic Disorder of Lipid and Glucose by Increasing Gut Commensal Bacteroides acidifaciens.

A number of reports of the effects of garlic on gut microbiota revealed that the active garlic organosulfur compounds (OSCs) are destabilized by the action of alliinase during garlic preparation. In this study, garlic alliinase was deactivated to obtain stable garlic OSCs. Experiments with C57BL/6J mice fed with lipid and glucose metabolic disorder-inducing Western diet (WD) revealed that stable garlic OSCs prevented the disorder by increasing the relative abundance of gut Bacteroides acidifaciens. Molecular analysis indicated that garlic OSCs inhibited dyslipidemia and fatty liver by increasing taurine and subsequently promoting hepatic fatty acid β-oxidation. In parallel, garlic OSCs could meliorate glucose homeostasis by inhibiting dipeptidyl peptidase-4 (DPP-4) and hepatic gluconeogenesis. In vitro bacterial culture experiments revealed that garlic OSCs directly increased the growth of gut Bacteroides acidifaciens. The results of this study demonstrate that the molecular mechanism of the preventive effect of garlic OSCs on the WD-induced metabolic disorder is attributed to the enhanced growth of Bacteroides acidifaciens and the consequent increase in taurine.

Abstract 145: Glycine Metabolism Links Atherosclerosis And NASH: Studies In Humans, Nonhuman Primates And Mice

A major cause of death in patients with nonalcoholic steatohepatitis (NASH) is cardiovascular disease driven by accelerated atherosclerosis. The mechanisms linking NASH and atherosclerosis remain unclear and there is an urgent need to identify new pathways as targets for NASH without increasing, and preferably while decreasing, atherosclerosis. Lower circulating glycine is emerging as a common feature in both atherosclerosis and NASH, but the mechanisms behind reduced glycine, its potential as a causative factor and a therapeutic target are unclear. Applying unbiased transcriptomics and metabolomics, we uncovered impaired glycine biosynthesis in humans and mice with atherosclerosis and NASH. Hepatic glycine biosynthetic genes were downregulated with a most significant suppression of alanine-glyoxylate aminotransferase ( AGXT ). Functional deficiencies of AGXT lead to oxalate accumulation and we found decreased glycine/oxalate ratio in both NASH and atherosclerosis. In mice, dietary and genetic ( Agxt –/– and Agxt -/- / Apoe -/- ) approaches to limit glycine availability exacerbated NASH and atherosclerosis with suppressed hepatic fatty acid β-oxidation (FAO) and enhanced inflammation as the underlying pathways. These effects were reversed by glycine supplementation and AAV8-mediated AGXT overexpression. We explored glycine-based compounds as potential therapies for atherosclerosis and NASH and identified a tripeptide (Gly-Gly-L-Leu, DT-109) that protected mice from NASH and atherosclerosis by modulating FAO, glutathione synthesis and the gut microbiome. We further developed a dietary model in cynomolgus monkeys that closely mimics human NASH. DT-109 ameliorated NASH and showed anti-atherogenic properties in monkeys by modulating similar pathways observed in the mice. Altogether, impaired glycine metabolism links atherosclerosis and NASH and can be targeted for the simultaneous treatment of these diseases.

Chicory polysaccharides alleviate high-fat diet-induced non-alcoholic fatty liver disease via alteration of lipid metabolism- and inflammation-related gene expression

Administration of chicory polysaccharides (CP) can modify lipid metabolism, improve dyslipidemia, and reduce liver inflammation, all of which may help alleviate non-alcoholic fatty liver disease (NAFLD). However, the underlying mechanisms remain unclear. This study aimed to gain further understanding of the potential molecular mechanisms that mediate the protective effects of CP against NAFLD via transcriptomic and metabolomic analyses. Hepatic RNA-sequencing analysis demonstrated that long-term intake of CP restored expression of lipid metabolism-related genes Xbp1, Insig2, and Cth in NAFLD rats, thereby inhibiting de novo lipogenesis. Moreover, CP consumption restored expression levels of genes involved in pro-inflammatory responses, such as Irf1. In addition, metabolic data confirmed that CP treatment increased levels of L-palmitoylcarnitine and hexadecanoyl-CoA, implying that CP administration can promote hepatic fatty acid β-oxidation. The present results demonstrate the underlying mechanisms of CP in high-fat diet-induced NAFLD rats and suggest that CP treatment might provide a dietary therapeutic tool for the treatment of NAFLD in humans.

Inhibition of Fatty Acid Translocase (FAT/CD36) Palmitoylation Enhances Hepatic Fatty Acid β-Oxidation by Increasing Its Localization to Mitochondria and Interaction with Long-Chain Acyl-CoA Synthetase 1.

Aims: Impaired fatty acid oxidation (FAO) in mitochondria of hepatocytes causes lipid accumulation and excessive production of reactive oxygen species (ROS) and oxidative damage, leading to nonalcoholic fatty liver disease (NAFLD). Fatty acid translocase (FAT/cluster of differentiation 36 [CD36]), a transmembrane protein that facilitates the uptake of long-chain fatty acids (LCFAs), is recently found to be involved in FAO. The function of FAT/CD36 is associated with its subcellular localization. Palmitoylation, one of the most common lipid modifications, is generally thought to regulate FAT/CD36 subcellular localization. Here, we aimed to investigate the role of palmitoylation in FAT/CD36 localization to mitochondria and its influence on FAO in hepatocytes. Results: We demonstrated that FAT/CD36 exists on the mitochondria of hepatocytes. Palmitoylation of FAT/CD36 was significantly upregulated in NAFLD. Inhibition of FAT/CD36 palmitoylation resulted in an obvious increase in the distribution of FAT/CD36 to mitochondria of hepatocytes. Depalmitoylated FAT/CD36 on the mitochondrial membrane continues functioning by facilitating fatty acid trafficking to mitochondria. Abundant mitochondrial FAT/CD36 interacted with long-chain acyl-CoA synthetase 1 (ACSL1), and thus, more LCFAs were transported to ACSL1. This led to an increase in the generation of long-chain acyl-CoA, contributing to the enhancement of FAO and alleviating NAFLD. Innovation and Conclusion: This work revealed that inhibiting FAT/CD36 palmitoylation alleviates NAFLD by promoting FAT/CD36 localization to the mitochondria of hepatocytes. Mitochondrial FAT/CD36 functions as a molecular bridge between LCFAs and ACSL1 to increase the production of long-chain acyl-CoA, thus promoting FAO, thereby avoiding lipid accumulation and overproduction of ROS in hepatocytes. Antioxid. Redox Signal. 36, 1081-1100.

Intestinal farnesoid X receptor signaling controls hepatic fatty acid oxidation

In addition to maintaining bile acid, cholesterol and glucose homeostasis, farnesoid X receptor (FXR) also regulates fatty acid β-oxidation (FAO). To explore the different roles of hepatic and intestinal FXR in liver FAO, FAO-associated metabolites, including acylcarnitines and fatty acids, and FXR target gene mRNAs were profiled using an integrated metabolomic and transcriptomic analysis in control (Fxrfl/fl), liver-specific Fxr-null (FxrΔHep) and intestine-specific Fxr-null (FxrΔIE) mice, treated either with the FXR agonist obeticholic acid (OCA) or vehicle (VEH). Activation of FXR by OCA treatment significantly increased fatty acyl-CoA hydrolysis (Acot1) and decreased FAO-associated mRNAs in Fxrfl/fl mice, resulting in reduced levels of total acylcarnitines and relative accumulation of long/medium chain acylcarnitines and fatty acids in liver. FxrΔHep mice responded to OCA treatment in a manner similar to Fxrfl/fl mice while FxrΔIE mice responded differently, thus illustrating that intestinal FXR plays a critical role in the regulation of hepatic FAO. A significant negative-correlation between intestinal FXR-FGF15 and hepatic CREB-PGC1A pathways was observed after both VEH and OCA treatment, suggesting that OCA-induced activation of the intestinal FXR-FGF15 axis downregulates hepatic PGC1α signaling via inactivation of hepatic CREB, thus repressing FAO. This mechanism was confirmed in experiments based on human recombinant FGF19 treatment and intestinal Fgf15-null mice. This study revealed an important role for the intestinal FXR-FGF15 pathway in hepatic FAO repression.

Acetyl-CoA derived from hepatic mitochondrial fatty acid β-oxidation aggravates inflammation by enhancing p65 acetylation

SummaryAcetylation coordinates many biological processes to ensure cells respond appropriately to nutrients. However, how acetylation regulates lipid surplus-induced inflammation remains poorly understood. Here, we found that a high-fat diet (HFD) enhanced mitochondrial fatty acid β-oxidation, which enhanced acetyl-CoA levels in the liver of the large yellow croaker. The HFD activated ACLY to govern the “citrate transport” to transfer acetyl-CoA from the mitochondria to the nucleus. Elevated acetyl-CoA activated CBP to increase p65 acetylation and then aggravated inflammation. SIRT1 was deactivated with a decline in NAD+/NADH, which further aggravated inflammation. Therefore, acetylation-dependent regulation of transcription factor activity is an adaptation to proinflammatory stimuli under nutrient stress, which was also confirmed in AML12 hepatocytes. In vitro octanoate stimulation further verified that acetyl-CoA derived from fatty acid β-oxidation mediated acetylation homeostasis in the nucleus. The broad therapeutic prospects of intermediate metabolites and acetyltransferases/deacetylases might provide critical insights for the treatment of metabolic diseases in vertebrates.