Peroxisomal β-oxidation regulates whole body metabolism, inflammatory vigor, and pathogenesis of nonalcoholic fatty liver disease

Western Diet and fecal microbiota transplantation alter phenotypic, liver fatty acids, and gut metagenomics and metabolomics in Mtarc2 knockout mice

Background

The mitochondrial amidoxime-reducing component-2 (Mtarc) enzyme complex is located on the outer mitochondrial membrane and may be involved in lipid metabolism regulation.

Aim

This study evaluated the impact of fecal microbiota transplantation (FMT) on phenotypic outcomes, liver accumulation of fatty acids (FAs), and modifications to the gut microbial community, as well as the abundance of short-chain fatty acids (SCFAs) and amino acids (AAs), in both sexes of Mtarc2 knockout (Mtarc2-KO) and C57BL/6 N mice fed a Western Diet (WD).

Methodology

Mice were fed a WD (study groups) or normal diet (control groups) and were subjected to intestinal flushing with either a polyethylene glycol (PEG) solution (study groups) or water (control groups); this was followed by intragastrical administration of a human feces suspension (study groups) or water (control groups). Liver FA composition and fecal SCFAs and AAs were measured by mass spectrometry. Metagenomic-based analysis was performed by sequencing the variable V3 and V4 regions of the bacterial 16 S rRNA gene.

Principal findings

Weight gain in C57BL/6 N mice fed a WD was significantly higher than in Mtarc2-KO mice. Compared with water only, intestinal cleansing with PEG resulted in significantly lower weight gain in C57BL/6 N mice but not in Mtarc2-KO mice. FMT did not affect body weight in C57BL/6 N mice, and decreased in Mtarc2-KO females and males fed a ND and a WD, respectively. No significant differences in liver FAs composition were found between mouse strains. While PEG treatment significantly affected liver FAs composition, FMT modulated FAs levels to a much smaller extent. However, neither intestinal cleansing nor FMT affected the microscopic findings of fatty liver. WD feeding affected bacterial diversity, taxonomy and SCFAs and AAs abundances in Mtarc2-KO and C57BL/6 N mice not subjected to PEG treatment. Both intestinal cleansing alone and FMT modulated gut bacterial composition, especially in C57BL/6 N mice, and metabolite abundances in Mtarc2-KO mice.

Conclusion

WD and FMT differentially modified phenotypic parameters, liver FA composition, and gut bacteria in comparisons between Mtarc2-KO and C57BL/6 N. This suggests the Mtarc complex plays a significant role in regulating energy metabolism in mice.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12263-025-00772-x.

Revisiting the Pathogenesis of X-Linked Adrenoleukodystrophy

BACKGROUND

X-ALD is a white matter (WM) disease caused by mutations in the ABCD1 gene encoding the transporter of very-long-chain fatty acids (VLCFAs) into peroxisomes. Strikingly, the same ABCD1 mutation causes either devastating brain inflammatory demyelination during childhood or, more often, progressive spinal cord axonopathy starting in middle-aged adults. The accumulation of undegraded VLCFA in glial cell membranes and myelin has long been thought to be the central mechanism of X-ALD.

METHODS

This review discusses studies in mouse and drosophila models that have modified our views of X-ALD pathogenesis.

RESULTS

In the Abcd1 knockout (KO) mouse that mimics the spinal cord disease, the late manifestations of axonopathy are rapidly reversed by ABCD1 gene transfer into spinal cord oligodendrocytes (OLs). In a peroxin-5 KO mouse model, the selective impairment of peroxisomal biogenesis in OLs achieves an almost perfect phenocopy of cerebral ALD. A drosophila knockout model revealed that VLCFA accumulation in glial myelinating cells causes the production of a toxic lipid able to poison axons and activate inflammatory cells. Other mouse models showed the critical role of OLs in providing energy substrates to axons. In addition, studies on microglial changing substates have improved our understanding of neuroinflammation.

CONCLUSIONS

Animal models supporting a primary role of OLs and axonal pathology and a secondary role of microglia allow us to revisit of X-ALD mechanisms. Beyond ABCD1 mutations, pathogenesis depends on unidentified contributors, such as genetic background, cell-specific epigenomics, potential environmental triggers, and stochasticity of crosstalk between multiple cell types among billions of glial cells and neurons.

NPC86 Increases LncRNA Gas5 In Vivo to Improve Insulin Sensitivity and Metabolic Function in Diet-Induced Obese Diabetic Mouse Model

In the United States, an estimated 38 million individuals (10% of the population) have type 2 diabetes mellitus (T2D), while approximately 97.6 million adults (38%) have prediabetes. Long noncoding RNAs (lncRNAs) are critical regulators of gene expression and metabolism. We were the first to demonstrate that lncRNA Growth Arrest-Specific Transcript 5 (GAS5 (human)/gas5 (mouse)) is decreased in the serum of T2D patients and established GAS5 as a biomarker for T2D diagnosis and onset prediction, now validated by other groups. We further demonstrated that GAS5 depletion impaired glucose uptake, decreased insulin receptor levels, and inhibited insulin signaling in human adipocytes, highlighting its potential as a therapeutic target in T2D. To address this, we developed NPC86, a small-molecule compound that stabilizes GAS5 by disrupting its interaction with UPF-1, an RNA helicase involved in nonsense-mediated decay (NMD) that regulates RNA stability. NPC86 increased GAS5 and insulin receptor (IR) levels, enhanced insulin signaling, and improved glucose uptake in vitro. In this study, we tested the efficacy of NPC86 in vivo in a diet-induced obese diabetic (DIOD) mouse model, and NPC86 treatment elevated gas5 levels, improved glucose tolerance, and enhanced insulin sensitivity, with no observed toxicity or weight changes. A transcriptomics analysis of adipose tissue revealed the upregulation of insulin signaling and metabolic pathways, including oxidative phosphorylation and glycolysis, while inflammatory pathways were downregulated. These findings highlight NPC86's therapeutic potential in T2D.

Total glucosides of Picrorhizae Rhizome alleviate non-alcoholic steatohepatitis (NASH) by specifically targeting acyl-CoA oxidase 1

Nonalcoholic steatohepatitis (NASH), a chronic liver disease characterized by the accumulation of fat in the liver, is highly prevalent on a global scale. In this study, we investigated the effects of total glucosides of Picrorhizae Rhizome (TGPR), the primary active ingredients in traditional Chinese herbal medicine derived from Picrorhiza scrophulariiflora Pennell. TGPR is known for its efficiency in attenuating NASH, in mouse models induced by methionine-choline deficient (MCD) diet or high-fat diet (HFD). Our findings indicated that TGPR exhibited efficacy in reducing hepatic steatosis and lowering serum lipid levels, specifically triglyceride and total cholesterol in the NASH model. Meanwhile, TGPR exhibited a suppressive effect on the production of pro-inflammatory cytokines. Mechanistically, we identified acyl-CoA oxidase 1 (Acox1) as a crucial cellular target of TGPR, influencing lipid metabolism and ATP production to treat NASH. Additionally, we found that the major components of TGPR, including Picroside I, Picroside II, and Picroside IV, exhibit significant binding abilities to the target Acox1 at its catalytic C-terminal α-domain, stabilizing its protein expression. TGPR binding to Acox1 facilitated the degradation of fatty acids via the Acox1-mediated MAPK signaling pathways, and consequently plays a role in regulating energy metabolism and reducing liver inflammation. In summary, our study demonstrates that TGPR effectively counteracts NASH by specifically targeting Acox1, thereby providing a significant clinical solution for the treatment of NASH.

Integrator complex subunit 6 promotes hepatocellular steatosis via β-catenin-PPARγ axis

Hepatic adipogenesis has common mechanisms with adipocyte differentiation such as PPARγ involvement and the induction of adipose tissue-specific molecules. A previous report demonstrated that integrator complex subunit 6 (INTS6) is required for adipocyte differentiation. This study aimed to investigate INTS6 expression and its role in hepatic steatosis progression. The expression of INTS6 and PPARγ was examined in the liver of a mouse model of steatohepatitis and in paired liver biopsy samples from 11 patients with severe obesity and histologically proven metabolic dysfunction associated steatohepatitis (MASH) before and one year after bariatric surgery. To induce hepatocellular steatosis in vitro, an immortalized human hepatocyte cell line Hc3716 was treated with free fatty acids. In the steatohepatitis mouse model, we observed hepatic induction of INTS6, PPARγ, and adipocyte-specific genes. In contrast, β-catenin which negatively regulates PPARγ was reduced. Biopsied human livers demonstrated a strong positive correlation (r2 = 0.8755) between INTS6 and PPARγ mRNA levels. After bariatric surgery, gene expressions of PPARγ, FABP4, and CD36 were mostly downregulated. In our in vitro experiments, we observed a concentration-dependent increase in Oil Red O staining in Hc3716 cells after treatment with the free fatty acids. Alongside this change, the expression of INTS6, PPARγ, and adipocyte-specific genes was induced. INTS6 knockdown using siRNA significantly suppressed cellular lipid accumulation together with induction of β-catenin and PPARγ downregulation. Collectively, INTS6 expression closely correlates with PPARγ. INTS6 suppression significantly reduced hepatocyte steatosis via β-catenin-PPARγ axis, indicating that INTS6 could be a novel therapeutic target for treating MASH.

Genome-Wide Analysis Reveals Copy Number Variant Gene TGFBR3 Regulates Pig Back Fat Deposition

BFT is closely related to meat quality and lean meat percentage in pigs. The BFT traits of European LW pigs significantly differ from those of Chinese indigenous fatty MZ pigs. CNV is a prevalent genetic variation that plays an important role in economically important traits in pigs. However, the potential contribution of CNV to BFT in LW and MZ pigs remains unclear. In this study, whole-genome CNV detection was performed using next-generation sequencing data from LW and MZ pigs, and transcriptome data from back fat tissue of 180-day-old LW and MZ pigs were integrated for expression quantitative trait loci (eQTL) analysis. We identified a copy number variation in the TGFBR3 gene associated with BFT, showing a dose effect between the genome and transcriptome levels of the TGFBR3 gene. In porcine preadipocytes, TGFBR3 expression continuously increased during differentiation. Knockdown of TGFBR3 using specific siRNA inhibited preadipocyte differentiation and proliferation. Our study provides insights into the genetic regulation of pork quality and offers a theoretical basis for improving carcass quality by modulating BFT in pigs.

Pemafibrate abrogates SLD in a rat experimental dietary model, inducing a shift in fecal bile acids and microbiota composition

BACKGROUND AND AIMS

Drugs resolving steatotic liver disease (SLD) could prevent the evolution of metabolic dysfunction associated SLD (MASLD) to more aggressive forms but must show not only efficacy, but also a high safety profile. Repurposing of drugs in clinical use, such as pemafibrate and mirabegron, could facilitate the finding of an effective and safe drug-treatment for SLD.

APPROACH AND RESULTS

The SLD High Fat High Fructose (HFHFr) rat model develops steatosis without the influence of other metabolic disturbances, such as obesity, inflammation, or type 2 diabetes. Further, liver fatty acids are provided, as in human pathology, both from dietary origin and de novo lipid synthesis. We used the HFHFr model to evaluate the efficacy of pemafibrate and mirabegron, alone or in combination, in the resolution of SLD, analyzing zoometric, biochemical, histological, transcriptomic, fecal metabolomic and microbiome data. We provide evidence showing that pemafibrate, but not mirabegron, completely reverted liver steatosis, due to a direct effect on liver PPARα-driven fatty acid catabolism, without changes in total energy consumption, subcutaneous, perigonadal and brown fat, blood lipids and body weight. Moreover, pemafibrate treatment showed a neutral effect on whole-body glucose metabolism, but deeply modified fecal bile acid composition and microbiota.

CONCLUSIONS

Pemafibrate administration reverts liver steatosis in the HFHFr dietary rat SLD model without altering parameters related to metabolic or organ toxicity. Our results strongly support further clinical research to reposition pemafibrate for the treatment of SLD/MASLD.

Effects of different energy levels in low-protein diet on liver lipid metabolism in the late-phase laying hens through the gut-liver axis

BACKGROUND

The energy/protein imbalance in a low-protein diet induces lipid metabolism disorders in late-phase laying hens. Reducing energy levels in the low-protein diet to adjust the energy-to-protein ratio may improve fat deposition, but this also decreases the laying performance of hens. This study investigated the mechanism by which different energy levels in the low-protein diet influences liver lipid metabolism in late-phase laying hens through the enterohepatic axis to guide feed optimization and nutrition strategies. A total of 288 laying hens were randomly allocated to the normal-energy and normal-protein diet group (positive control: CK) or 1 of 3 groups: low-energy and low-protein diet (LL), normal-energy and low-protein diet (NL), and high-energy and low-protein diet (HL) groups. The energy-to-protein ratios of the CK, LL, NL, and HL diets were 0.67, 0.74, 0.77, and 0.80, respectively.

RESULTS

Compared with the CK group, egg quality deteriorated with increasing energy intake in late-phase laying hens fed low-protein diet. Hens fed LL, NL, and HL diets had significantly higher triglyceride, total cholesterol, acetyl-CoA carboxylase, and fatty acid synthase levels, but significantly lower hepatic lipase levels compared with the CK group. Liver transcriptome sequencing revealed that genes involved in fatty acid beta-oxidation (ACOX1, HADHA, EHHADH, and ACAA1) were downregulated, whereas genes related to fatty acid synthesis (SCD, FASN, and ACACA) were upregulated in LL group compared with the CK group. Comparison of the cecal microbiome showed that in hens fed an LL diet, Lactobacillus and Desulfovibrio were enriched, whereas riboflavin metabolism was suppressed. Cecal metabolites that were most significantly affected by the LL diet included several vitamins, such as riboflavin (vitamin B2), pantethine (vitamin B5 derivative), pyridoxine (vitamin B6), and 4-pyridoxic acid.

CONCLUSION

A lipid metabolism disorder due to deficiencies of vitamin B2 and pantethine originating from the metabolism of the cecal microbiome may be the underlying reason for fat accumulation in the liver of late-phase laying hens fed an LL diet. Based on the present study, we propose that targeting vitamin B2 and pantethine (vitamin B5 derivative) might be an effective strategy for improving lipid metabolism in late-phase laying hens fed a low-protein diet.

Chronic treatment with glucagon-like peptide-1 and glucagon receptor co-agonist causes weight loss-independent improvements in hepatic steatosis in mice with diet-induced obesity

OBJECTIVES

Co-agonists at the glucagon-like peptide-1 and glucagon receptors (GLP1R/GCGR) show promise as treatments for metabolic dysfunction-associated steatotic liver disease (MASLD). Although most co-agonists to date have been heavily GLP1R-biased, glucagon directly acts on the liver to reduce fat content. The aims of this study were to investigate a GCGR-biased co-agonist as treatment for hepatic steatosis in mice.

METHODS

Mice with diet-induced obesity (DIO) were treated with Dicretin, a GLP1/GCGR co-agonist with high potency at the GCGR, Semaglutide (GLP1R monoagonist) or food restriction over 24 days, such that their weight loss was matched. Hepatic steatosis, glucose tolerance, hepatic transcriptomics, metabolomics and lipidomics at the end of the study were compared with Vehicle-treated mice.

RESULTS

Dicretin lead to superior reduction of hepatic lipid content when compared to Semaglutide or equivalent weight loss by calorie restriction. Markers of glucose tolerance and insulin resistance improved in all treatment groups. Hepatic transcriptomic and metabolomic profiling demonstrated many changes that were unique to Dicretin-treated mice. These include some known targets of glucagon signaling and others with as yet unclear physiological significance.

CONCLUSIONS

Our study supports the development of GCGR-biased GLP1/GCGR co-agonists for treatment of MASLD and related conditions.

Essential phospholipids impact cytokine secretion and alter lipid-metabolizing enzymes in human hepatocyte cell lines

BACKGROUND

Essential phospholipids (EPL) are hepatoprotective.

METHODS

The effects on interleukin (IL)-6 and -8 secretion and on certain lipid-metabolizing enzymes of non-cytotoxic concentrations of EPL (0.1 and 0.25 mg/ml), polyenylphosphatidylcholine (PPC), and phosphatidylinositol (PtdIns) (both at 0.1 and 1 mg/ml), compared with untreated controls, were assessed in human hepatocyte cell lines (HepG2, HepaRG, and steatotic HepaRG).

RESULTS

Lipopolysaccharide (LPS)-induced IL-6 secretion was significantly decreased in HepaRG cells by most phospholipids, and significantly increased in steatotic HepaRG cells with at least one concentration of EPL and PtdIns. LPS-induced IL-8 secretion was significantly increased in HepaRG and steatotic HepaRG cells with all phospholipids. All phospholipids significantly decreased amounts of fatty acid synthase in steatotic HepaRG cells and the amounts of acyl-CoA oxidase in HepaRG cells. Amounts of lecithin cholesterol acyltransferase were significantly decreased in HepG2 and HepaRG cells by most phospholipids, and significantly increased with 0.1 mg/ml PPC (HepaRG cells) and 1 mg/ml PtdIns (steatotic HepaRG cells). Glucose-6-phosphate dehydrogenase activity was unaffected by any phospholipid in any cell line.

CONCLUSIONS

EPL, PPC, and PtdIns impacted the secretion of pro-inflammatory cytokines and affected amounts of several key lipid-metabolizing enzymes in human hepatocyte cell lines. Such changes may help liver function improvement, and provide further insights into the EPL's mechanism of action.

Dietary dicarboxylic acids provide a nonstorable alternative fat source that protects mice against obesity

Dicarboxylic fatty acids are generated in the liver and kidney in a minor pathway called fatty acid ω-oxidation. The effects of consuming dicarboxylic fatty acids as an alternative source of dietary fat have not been explored. Here, we fed dodecanedioic acid, a 12-carbon dicarboxylic (DC12), to mice at 20% of daily caloric intake for 9 weeks. DC12 increased metabolic rate, reduced body fat, reduced liver fat, and improved glucose tolerance. We observed DC12-specific breakdown products in liver, kidney, muscle, heart, and brain, indicating that oral DC12 escaped first-pass liver metabolism and was utilized by many tissues. In tissues expressing the "a" isoform of acyl-CoA oxidase-1 (ACOX1), a key peroxisomal fatty acid oxidation enzyme, DC12 was chain shortened to the TCA cycle intermediate succinyl-CoA. In tissues with low peroxisomal fatty acid oxidation capacity, DC12 was oxidized by mitochondria. In vitro, DC12 was catabolized even by adipose tissue and was not stored intracellularly. We conclude that DC12 and other dicarboxylic acids may be useful for combatting obesity and for treating metabolic disorders.

Characterization and Comparison Analysis of Milk Fat Globule Membrane Proteins between Human and Porcine Milk

This study aimed to explore the differences in milk fat globule membrane (MFGM) proteins between human milk (HM) and porcine milk (PM) using a label-free quantitative proteomic approach. A total of 3920 and 4001 MFGM proteins were identified between PM and HM, respectively. Among them, 3520 common MFGM proteins were detected, including 956 significant differentially expressed MFGM proteins (DEPs). Gene ontology (GO) enrichment analysis showed that the DEPs were highly enriched in the lipid metabolic process and intrinsic component of membrane. Kyoto Encyclopedia of Genes and Genomes pathways suggested that protein processing in the endoplasmic reticulum was the most highly enriched pathway, followed by peroxisome, complement, and coagulation cascades. This study reflects the difference in the composition of MFGM proteins between HM and PM and provides a scientific and systematic reference for the development of MFGM protein nutrition.

Molecular mechanisms in MASLD/MASH-related HCC

Liver cancer is the third leading cause of cancer-related deaths and ranks as the sixth most prevalent cancer type globally. NAFLD or metabolic dysfunction-associated steatotic liver disease, and its more severe manifestation, NASH or metabolic dysfunction-associated steatohepatitis (MASH), pose a significant global health concern, affecting approximately 20%-25% of the population. The increased prevalence of metabolic dysfunction-associated steatotic liver disease and MASH is parallel to the increasing rates of obesity-associated metabolic diseases, including type 2 diabetes, insulin resistance, and fatty liver diseases. MASH can progress to MASH-related HCC (MASH-HCC) in about 2% of cases each year, influenced by various factors such as genetic mutations, carcinogen exposure, immune microenvironment, and microbiome. MASH-HCC exhibits distinct molecular and immune characteristics compared to other causes of HCC and affects both men and women equally. The management of early to intermediate-stage MASH-HCC typically involves surgery and locoregional therapies, while advanced HCC is treated with systemic therapies, including anti-angiogenic therapies and immune checkpoint inhibitors. In this comprehensive review, we consolidate previous research findings while also providing the most current insights into the intricate molecular processes underlying MASH-HCC development. We delve into MASH-HCC-associated genetic variations and somatic mutations, disease progression and research models, multiomics analysis, immunological and microenvironmental impacts, and discuss targeted/combined therapies to overcome immune evasion and the biomarkers to recognize treatment responders. By furthering our comprehension of the molecular mechanisms underlying MASH-HCC, our goal is to catalyze the advancement of more potent treatment strategies, ultimately leading to enhanced patient outcomes.

ACOX1-mediated peroxisomal fatty acid oxidation contributes to metabolic reprogramming and survival in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is still an incurable disease, with many patients developing resistance to conventional and targeted therapies. To better understand the physiology of CLL and facilitate the development of innovative treatment options, we examined specific metabolic features in the tumor CLL B-lymphocytes. We observed metabolic reprogramming, characterized by a high level of mitochondrial oxidative phosphorylation activity, a low glycolytic rate, and the presence of C2- to C6-carnitine end-products revealing an unexpected, essential role for peroxisomal fatty acid beta-oxidation (pFAO). Accordingly, downmodulation of ACOX1 (a rate-limiting pFAO enzyme overexpressed in CLL cells) was enough to shift the CLL cells' metabolism from lipids to a carbon- and amino-acid-based phenotype. Complete blockade of ACOX1 resulted in lipid droplet accumulation and caspase-dependent death in CLL cells, including those from individuals with poor cytogenetic and clinical prognostic factors. In a therapeutic translational approach, ACOX1 inhibition spared non-tumor blood cells from CLL patients but led to the death of circulating, BCR-stimulated CLL B-lymphocytes and CLL B-cells receiving pro-survival stromal signals. Furthermore, a combination of ACOX1 and BTK inhibitors had a synergistic killing effect. Overall, our results highlight a less-studied but essential metabolic pathway in CLL and pave the way towards the development of new, metabolism-based treatment options.

Metabolic-associated fatty liver disease: a selective review of pathogenesis, diagnostic approaches, and therapeutic strategies

Background

Metabolic associated fatty liver disease (MAFLD) is a novel terminology introduced in 2020 to provide a more accurate description of fatty liver disease associated with metabolic dysfunction. It replaces the outdated term nonalcoholic fatty liver disease (NAFLD) and aims to improve diagnostic criteria and tailored treatment strategies for the disease. NAFLD, the most prevalent liver disease in western industrialized nations, has been steadily increasing in prevalence and is associated with serious complications such as cirrhosis and hepatocellular carcinoma. It is also linked to insulin resistance syndrome and cardiovascular diseases. However, current studies on NAFLD have limitations in meeting necessary histological endpoints.

Objective

This literature review aims to consolidate recent knowledge and discoveries concerning MAFLD, integrating the diverse aspects of the disease. Specifically, it focuses on analyzing the diagnostic criteria for MAFLD, differentiating it from NAFLD and alcoholic fatty liver disease (AFLD), and exploring the epidemiology, clinical manifestations, pathogenesis, and management approaches associated with MAFLD. The review also explores the associations between MAFLD and other conditions. It discusses the heightened mortality risk associated with MAFLD and its link to chronic kidney disease (CKD), showing that MAFLD exhibits enhanced diagnostic accuracy for identifying patients with CKD compared to NAFLD. The association between MAFLD and incident/prevalent CKD is supported by cohort studies and meta-analyses.

Conclusion

This literature review highlights the importance of MAFLD as a distinct terminology for fatty liver disease associated with metabolic dysfunction. The review provides insights into the diagnostic criteria, associations with CKD, and management approaches for MAFLD. Further research is needed to develop more accurate diagnostic tools for advanced fibrosis in MAFLD and to explore the underlying mechanisms linking MAFLD with other conditions. This review serves as a valuable resource for researchers and healthcare professionals seeking a comprehensive understanding of MAFLD.

PEX13 is a potential immunotherapeutic indicator and prognostic biomarker for various tumors including PAAD

The peroxisome serves a significant role in the occurrence and development of cancers. Specifically, the peroxisomal biogenesis factor 13 (PEX13) is crucial to the occurrence of peroxisomes. However, the biological function of PEX13 in cancers remains unclear. To address this, various portals and databases such as The Cancer Genome Atlas Program, The Genotype-Tissue Expression project, the Gene Expression Profiling Interactive Analysis 2, cBioPortal, the Genomic Identification of Significant Targets In Cancer 2.0, Tumor Immune Estimation Resource 2, SangerBox, LinkedOmics, DAVID and STRING were applied to extract and analyze PEX13 data in tumors. The correlations between PEX13 and prognosis, genetic alterations, PEX13-related gene enrichment analysis, weighted gene co-expression network analysis (WGCNA), protein interaction, long non-coding (lnc)RNA/circular (circ)RNA-micro (mi)RNA network and tumor immunity were explored in various tumors. The lncRNA-miRNA-PEX13 and circRNA-miRNA-PEX13 regulatory networks were identified via miRabel, miRDB, TargetScan and ENCORI portals and Cytoscape tool. In vitro assays were applied to verify the biological functions of PEX13 in pancreatic adenocarcinoma (PAAD) cells. The findings revealed that PEX13 is upregulated in various tumors and high PEX13 mRNA expression is associated with poor prognosis in patients with multiple cancers. Genetic alterations in PEX13 such as amplification, mutation and deep deletion have been found in multiple cancers. PEX13-related genes were associated with T cell receptor, signaling pathway and hippo signaling pathway through 'biological process' subontology of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses. Through WGCNA analysis, it was discovered that PEX13 hub genes were mainly enriched in the Rap1, ErbB and AMPK signaling pathways in PAAD. Immune analysis showed that PEX13 was significantly related to tumor infiltration immune cells, immune checkpoint genes, microsatellite instability, TMB and tumor purity in a variety of tumors. Cell Counting Kit-8, wound healing, Transwell and colony formation assays displayed that PEX13 knockdown could suppress PAAD cell proliferation, migration, invasion, and colony formation in vitro, respectively. Overall, PEX13 is a potential predictor of immunotherapeutic and prognostic biomarkers in various malignant tumors, including ACC, KICH, LGG, LIHC and PAAD.

Metabolic-Dysfunction-Associated Steatotic Liver Disease-Its Pathophysiology, Association with Atherosclerosis and Cardiovascular Disease, and Treatments

Metabolic-dysfunction-associated steatotic liver disease (MASLD) is a chronic liver disease that affects more than a quarter of the global population and whose prevalence is increasing worldwide due to the pandemic of obesity. Obesity, impaired glucose metabolism, high blood pressure and atherogenic dyslipidemia are risk factors for MASLD. Therefore, insulin resistance may be closely associated with the development and progression of MASLD. Hepatic entry of increased fatty acids released from adipose tissue, increase in fatty acid synthesis and reduced fatty acid oxidation in the liver and hepatic overproduction of triglyceride-rich lipoproteins may induce the development of MASLD. Since insulin resistance also induces atherosclerosis, the leading cause for death in MASLD patients is cardiovascular disease. Considering that the development of cardiovascular diseases determines the prognosis of MASLD patients, the therapeutic interventions for MASLD should reduce body weight and improve coronary risk factors, in addition to an improving in liver function. Lifestyle modifications, such as improved diet and increased exercise, and surgical interventions, such as bariatric surgery and intragastric balloons, have shown to improve MASLD by reducing body weight. Sodium glucose cotransporter 2 inhibitors (SGLT2i) and glucagon-like peptide-1 receptor agonists (GLP-1RAs) have been shown to improve coronary risk factors and to suppress the occurrence of cardiovascular diseases. Both SGLT2i and GLP-1 have been reported to improve liver enzymes, hepatic steatosis and fibrosis. We recently reported that the selective peroxisome proliferator-activated receptor-alpha (PPARα) modulator pemafibrate improved liver function. PPARα agonists have multiple anti-atherogenic properties. Here, we consider the pathophysiology of MASLD and the mechanisms of action of such drugs and whether such drugs and the combination therapy of such drugs could be the treatments for MASLD.

Administration of Linoleoylethanolamide Reduced Weight Gain, Dyslipidemia, and Inflammation Associated with High-Fat-Diet-Induced Obesity

Acylethanolamides (NAEs) are bioactive lipids derived from diet fatty acids that modulate important homeostatic functions, including appetite, fatty acid synthesis, mitochondrial respiration, inflammation, and nociception. Among the naturally circulating NAEs, the pharmacology of those derived from either arachidonic acid (Anandamide), oleic acid (OEA), and palmitic acid (PEA) have been extensively characterized in diet-induced obesity. For the present work, we extended those studies to linoleoylethanolamide (LEA), one of the most abundant NAEs found not only in plasma and body tissues but also in foods such as cereals. In our initial study, circulating concentrations of LEA were found to be elevated in overweight humans (body mass index (BMI, Kg/m2) > 25) recruited from a representative population from the south of Spain, together with AEA and the endocannabinoid 2-Arachidonoyl glycerol (2-AG). In this population, LEA concentrations correlated with the circulating levels of cholesterol and triglycerides. In order to gain insight into the pharmacology of LEA, we administered it for 14 days (10 mg/kg i.p. daily) to obese male Sprague Dawley rats receiving a cafeteria diet or a standard chow diet for 12 consecutive weeks. LEA treatment resulted in weight loss and a reduction in circulating triglycerides, cholesterol, and inflammatory markers such as Il-6 and Tnf-alpha. In addition, LEA reduced plasma transaminases and enhanced acetyl-CoA-oxidase (Acox) and Uncoupling protein-2 (Ucp2) expression in the liver of the HFD-fed animals. Although the liver steatosis induced by the HFD was not reversed by LEA, the overall data suggest that LEA contributes to the homeostatic signals set in place in response to diet-induced obesity, potentially contributing with OEA to improve lipid metabolism after high fat intake. The anti-inflammatory response associated with its administration suggests its potential for use as a nutrient supplement in non-alcoholic steatohepatitis.

Lactobacillus helveticus Isolated from Raw Milk Improves Liver Function, Hepatic Steatosis, and Lipid Metabolism in Non-Alcoholic Fatty Liver Disease Mouse Model

Here, we show that Lactiplantibacillus plantarum LP158 (LP158), Lactobacillus helveticus HY7804 (HY7804), and Lacticaseibacillus paracasei LPC226 (LPC226) isolated from raw milk alleviate non-alcoholic fatty acid disease (NAFLD) in a C57BL/6 mouse model. Lactic acid bacteria (LAB) were screened for their ability to inhibit fatty acid accumulation in palmitic acid (PA)-treated HepG2 cells, and three strains were selected based on the results. We also investigated hemolytic activity and antibiotic resistance of the three strains. LP158, HY7804, and LPC226 suppressed expression of mRNA encoding genes related to lipogenesis, and increased expression of genes related to β-oxidation, in a PA-induced HepG2 cell model. Moreover, when LP158, HY7804, and LPC226 were administered at 109 CFU/kg/day for 8 weeks to mice with dietary-induced NAFLD, they all modulated blood biochemistry markers and reduced steatosis in liver tissue. Also, all three strains significantly reduced expression of mRNA encoding lipogenesis genes (Fasn, Acaca, and Srebp-1c) and inflammatory factors (Tnfα and Ccl-2) and fibrosis factors, and increased expression of a β-oxidation gene (Acox1) in the liver. In particular, HY7804 showed the strongest effects both in vitro and in vivo. Therefore, HY7804, LP158, and LPC226 can be proposed as potential supplements that can improve NAFLD through anti-steatosis, anti-inflammatory, and anti-fibrotic effects.

TM4SF5-mediated abnormal food-intake behavior and apelin expression facilitate non-alcoholic fatty liver disease features

Transmembrane 4 L six family member 5 (TM4SF5) engages in non-alcoholic steatohepatitis (NASH), although its mechanistic roles are unclear. Genetically engineered Tm4sf5 mice fed ad libitum normal chow or high-fat diet for either an entire day or a daytime-feeding (DF) pattern were analyzed for metabolic parameters. Compared to wild-type and Tm4sf5-/- knockout mice, hepatocyte-specific TM4SF5-overexpressing Alb-TGTm4sf5-Flag (TG) mice showed abnormal food-intake behavior during the mouse-inactive daytime, increased apelin expression, increased food intake, and higher levels of NASH features. DF or exogenous apelin injection of TG mice caused severe hepatic pathology. TM4SF5-mediated abnormal food intake was correlated with peroxisomal β-oxidation, mTOR activation, and autophagy inhibition, with triggering NASH phenotypes. Non-alcoholic fatty liver disease (NAFLD) patients' samples revealed a correlation between serum apelin and NAFLD activity score. Altogether, these observations suggest that hepatic TM4SF5 may cause abnormal food-intake behaviors to trigger steatohepatitic features via the regulation of peroxisomal β-oxidation, mTOR, and autophagy.

Lipid and glucose metabolism in senescence

Senescence is an inevitable biological process. Disturbances in glucose and lipid metabolism are essential features of cellular senescence. Given the important roles of these types of metabolism, we review the evidence for how key metabolic enzymes influence senescence and how senescence-related secretory phenotypes, autophagy, apoptosis, insulin signaling pathways, and environmental factors modulate glucose and lipid homeostasis. We also discuss the metabolic alterations in abnormal senescence diseases and anti-cancer therapies that target senescence through metabolic interventions. Our work offers insights for developing pharmacological strategies to combat senescence and cancer.

AN1284 attenuates steatosis, lipogenesis, and fibrosis in mice with pre-existing non-alcoholic steatohepatitis and directly affects aryl hydrocarbon receptor in a hepatic cell line

Non-alcoholic steatohepatitis (NASH) is an aggressive form of fatty liver disease with hepatic inflammation and fibrosis for which there is currently no drug treatment. This study determined whether an indoline derivative, AN1284, which significantly reduced damage in a model of acute liver disease, can reverse steatosis and fibrosis in mice with pre-existing NASH and explore its mechanism of action. The mouse model of dietary-induced NASH reproduces most of the liver pathology seen in human subjects. This was confirmed by RNA-sequencing analysis. The Western diet, given for 4 months, caused steatosis, inflammation, and liver fibrosis. AN1284 (1 mg or 5 mg/kg/day) was administered for the last 2 months of the diet by micro-osmotic-pumps (mps). Both doses significantly decreased hepatic damage, liver weight, hepatic fat content, triglyceride, serum alanine transaminase, and fibrosis. AN1284 (1 mg/kg/day) given by mps or in the drinking fluid significantly reduced fibrosis produced by carbon tetrachloride injections. In human HUH7 hepatoma cells incubated with palmitic acid, AN1284 (2.1 and 6.3 ng/ml), concentrations compatible with those in the liver of mice treated with AN1284, decreased lipid formation by causing nuclear translocation of the aryl hydrocarbon receptor (AhR). AN1284 downregulated fatty acid synthase (FASN) and sterol regulatory element-binding protein 1c (SREBP-1c) and upregulated Acyl-CoA Oxidase 1 and Cytochrome P450-a1, genes involved in lipid metabolism. In conclusion, chronic treatment with AN1284 (1mg/kg/day) reduced pre-existing steatosis and fibrosis through AhR, which affects several contributors to the development of fatty liver disease. Additional pathways are also influenced by AN1284 treatment.

Insulin resistance and adipose tissue interactions as the cornerstone of metabolic (dysfunction)-associated fatty liver disease pathogenesis

The relationship between metabolic derangements and fatty liver development are undeniable, since more than 75% of patients with type 2 diabetes mellitus present with fatty liver. There is also significant epidemiological association between insulin resistance (IR) and metabolic (dysfunction)-associated fatty liver disease (MAFLD). For little more than 2 years, the nomenclature of fatty liver of non-alcoholic origin has been intended to change to MAFLD by multiple groups. While a myriad of reasons for which MAFLD is thought to be of metabolic origin could be exposed, the bottom line relies on the role of IR as an initiator and perpetuator of this disease. There is a reciprocal role in MAFLD development and IR as well as serum glucose concentrations, where increased circulating glucose and insulin result in increased de novo lipogenesis by sterol regulatory element-binding protein-1c induced lipogenic enzyme stimulation; therefore, increased endogenous production of triglycerides. The same effect is achieved through impaired suppression of adipose tissue (AT) lipolysis in insulin-resistant states, increasing fatty acid influx into the liver. The complementary reciprocal situation occurs when liver steatosis alters hepatokine secretion, modifying fatty acid metabolism as well as IR in a variety of tissues, including skeletal muscle, AT, and the liver. The aim of this review is to discuss the importance of IR and AT interactions in metabolic altered states as perhaps the most important factor in MAFLD pathogenesis.

BAFF and APRIL counterregulate susceptibility to inflammation-induced preterm birth

Clinical evidence points to a function for B cell-activating factor (BAFF) in pregnancy. However, direct roles for BAFF-axis members in pregnancy have not been examined. Here, via utility of genetically modified mice, we report that BAFF promotes inflammatory responsiveness and increases susceptibility to inflammation-induced preterm birth (PTB). In contrast, we show that the closely related A proliferation-inducing ligand (APRIL) decreases inflammatory responsiveness and susceptibility to PTB. Known BAFF-axis receptors serve a redundant function in signaling BAFF/APRIL presence in pregnancy. Treatment with anti-BAFF/APRIL monoclonal antibodies or BAFF/APRIL recombinant proteins is sufficient to manipulate susceptibility to PTB. Notably, macrophages at the maternal-fetal interface produce BAFF, while BAFF and APRIL presence divergently shape macrophage gene expression and inflammatory function. Overall, our findings demonstrate that BAFF and APRIL play divergent inflammatory roles in pregnancy and provide therapeutic targets for mitigating risk of inflammation-induced PTB.

Thermoneutral housing shapes hepatic inflammation and damage in mouse models of non-alcoholic fatty liver disease

Introduction

Inflammation is a common unifying factor in experimental models of non-alcoholic fatty liver disease (NAFLD) progression. Recent evidence suggests that housing temperature-driven alterations in hepatic inflammation correlate with exacerbated hepatic steatosis, development of hepatic fibrosis, and hepatocellular damage in a model of high fat diet-driven NAFLD. However, the congruency of these findings across other, frequently employed, experimental mouse models of NAFLD has not been studied.

Methods

Here, we examine the impact of housing temperature on steatosis, hepatocellular damage, hepatic inflammation, and fibrosis in NASH diet, methionine and choline deficient diet, and western diet + carbon tetrachloride experimental models of NAFLD in C57BL/6 mice.

Results

We show that differences relevant to NAFLD pathology uncovered by thermoneutral housing include: (i) augmented NASH diet-driven hepatic immune cell accrual, exacerbated serum alanine transaminase levels and increased liver tissue damage as determined by NAFLD activity score; (ii) augmented methionine choline deficient diet-driven hepatic immune cell accrual and increased liver tissue damage as indicated by amplified hepatocellular ballooning, lobular inflammation, fibrosis and overall NAFLD activity score; and (iii) dampened western diet + carbon tetrachloride driven hepatic immune cell accrual and serum alanine aminotransferase levels but similar NAFLD activity score.

Discussion

Collectively, our findings demonstrate that thermoneutral housing has broad but divergent effects on hepatic immune cell inflammation and hepatocellular damage across existing experimental NAFLD models in mice. These insights may serve as a foundation for future mechanistic interrogations focused on immune cell function in shaping NAFLD progression.

p27Kip1 Deficiency Impairs Brown Adipose Tissue Function Favouring Fat Accumulation in Mice

The aim of this work was to investigate the effect of the whole-body deletion of p27 on the activity of brown adipose tissue and the susceptibility to develop obesity and glucose homeostasis disturbances in mice, especially when subjected to a high fat diet. p27 knockout (p27^-/-) and wild type (WT) mice were fed a normal chow diet or a high fat diet (HFD) for 10-weeks. Body weight and composition were assessed. Insulin and glucose tolerance tests and indirect calorimetry assays were performed. Histological analysis of interscapular BAT (iBAT) was carried out, and expression of key genes/proteins involved in BAT function were characterized by qPCR and Western blot. iBAT activity was estimated by ¹⁸F-fluorodeoxyglucose (¹⁸FDG) uptake with microPET. p27^-/- mice were more prone to develop obesity and insulin resistance, exhibiting increased size of all fat depots. p27^-/- mice displayed a higher respiratory exchange ratio. iBAT presented larger adipocytes in p27^-/- HFD mice, accompanied by downregulation of both Glut1 and uncoupling protein 1 (UCP1) in parallel with defective insulin signalling. Moreover, p27^-/- HFD mice exhibited impaired response to cold exposure, characterized by a reduced iBAT ¹⁸FDG uptake and difficulty to maintain body temperature when exposed to cold compared to WT HFD mice, suggesting reduced thermogenic capacity. These data suggest that p27 could play a role in BAT activation and in the susceptibility to develop obesity and insulin resistance.

Mouse Models to Study Peroxisomal Functions and Disorders: Overview, Caveats, and Recommendations

During the last three decades many mouse lines were created or identified that are deficient in one or more peroxisomal functions. Different methodologies were applied to obtain global, hypomorph, cell type selective, inducible, and knockin mice. Whereas some models closely mimic pathologies in patients, others strongly deviate or no human counterpart has been reported. Often, mice, apparently endowed with a stronger transcriptional adaptation, have to be challenged with dietary additions or restrictions in order to trigger phenotypic changes. Depending on the inactivated peroxisomal protein, several approaches can be taken to validate the loss-of-function. Here, an overview is given of the available mouse models and their most important characteristics.

The peroxisome: an up-and-coming organelle in immunometabolism

Peroxisomes are essential metabolic organelles, well known for their roles in the metabolism of complex lipids and reactive ionic species. In the past 10 years, peroxisomes have also been cast as central regulators of immunity. Lipid metabolites of peroxisomes, such as polyunsaturated fatty acids (PUFAs), are precursors for important immune mediators, including leukotrienes (LTs) and resolvins. Peroxisomal redox metabolism modulates cellular immune signaling such as nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation. Additionally, peroxisomal β-oxidation and ether lipid synthesis control the development and aspects of the activation of both innate and adaptive immune cells. Finally, peroxisome number and metabolic activity have been linked to inflammatory diseases. These discoveries have opened avenues of investigation aimed at targeting peroxisomes for therapeutic intervention in immune disorders, inflammation, and cancer.

The physiological functions of human peroxisomes

Peroxisomes are subcellular organelles that play a central role in human physiology by catalyzing a range of unique metabolic functions. The importance of peroxisomes for human health is exemplified by the existence of a group of usually severe diseases caused by an impairment in one or more peroxisomal functions. Among others these include the Zellweger spectrum disorders, X-linked adrenoleukodystrophy, and Refsum disease. To fulfill their role in metabolism, peroxisomes require continued interaction with other subcellular organelles including lipid droplets, lysosomes, the endoplasmic reticulum, and mitochondria. In recent years it has become clear that the metabolic alliance between peroxisomes and other organelles requires the active participation of tethering proteins to bring the organelles physically closer together, thereby achieving efficient transfer of metabolites. This review intends to describe the current state of knowledge about the metabolic role of peroxisomes in humans, with particular emphasis on the metabolic partnership between peroxisomes and other organelles and the consequences of genetic defects in these processes. We also describe the biogenesis of peroxisomes and the consequences of the multiple genetic defects therein. In addition, we discuss the functional role of peroxisomes in different organs and tissues and include relevant information derived from model systems, notably peroxisomal mouse models. Finally, we pay particular attention to a hitherto underrated role of peroxisomes in viral infections.

Role of acyl-coenzyme A oxidase 1 (ACOX1) on palmitate-induced inflammation and ROS production of macrophages in large yellow croaker (Larimichthys crocea)

Acyl-coenzyme A oxidase 1 (ACOX1) is the rate-limiting enzyme in peroxisomal β-oxidation, and it plays an essential role in mediating the inflammatory response and reactive oxygen species (ROS) metabolism in mammals. However, the role of ACOX1 in fish has not been completely elucidated. Herein, this study was conducted to investigate the role of large yellow croaker (Larimichthys crocea) ACOX1 (Lc-ACOX1) on palmitate (PA)-induced inflammation and ROS production. In this study, Lc-ACOX1 was cloned and characterized. The full-length CDS of Lc-acox1 was 1986 bp, encoding 661 amino acids. Tissue distribution results showed that the gene expression of Lc-acox1 was the highest in the intestine and the lowest in the spleen. Moreover, results showed that the mRNA expression of Lc-acox1 was upregulated by PA, with elevated pro-inflammatory gene expression, including il-1β, il-6, il-8, tnf-α, cox2 and ifn-γ, as well as ROS content in macrophages of large yellow croaker. Furthermore, the role of Lc-ACOX1 in inflammation induced by PA was investigated by using the ACOX1 inhibitor TDYA. Treatment of macrophages with TDYA reduced the mRNA expression of pro-inflammatory genes induced by PA. Moreover, inhibition of ACOX1 reduced the elevated level of ROS caused by PA and increased the mRNA expression of antioxidant genes. In conclusion, this study first identified that fish ACOX1 was involved in the PA-induced inflammatory response and ROS production.

A diet-induced murine model for non-alcoholic fatty liver disease with obesity and insulin resistance that rapidly develops steatohepatitis and fibrosis

Non-alcoholic fatty liver disease (NAFLD) has become the leading cause of chronic liver disease worldwide. Patients with NAFLD often suffer steatohepatitis, which can progress to cirrhosis and hepatocellular carcinoma. The presence of visceral obesity or type 2 diabetes mellitus (T2DM) is a major risk factor and potential therapeutic target for NAFLD. The establishment of animal models with these metabolic comorbidities and with the rapid progression of the disease is needed for developing treatments for NAFLD but remains to be archived. In the present study, KK-A^y mice, widely used as T2DM models, or C57BL6 mice were fed a high-fat, high-fructose, and high-cholesterol diet supplemented with cholic acid (NAFLD diet). The KK-A^y mice fed a NAFLD diet exhibited remarkable obesity and insulin resistance. A prominent accumulation of triglycerides and cholesterol in the liver was observed at 4 weeks. These mice developed steatohepatitis at 4 weeks and fibrosis at 12 weeks. In contrast, C57BL6 mice fed a NAFLD diet remained lean, although they still developed steatohepatitis and fibrosis. In summary, we established a diet-induced murine NAFLD model with the rapid development of steatohepatitis and fibrosis, bearing obesity and insulin resistance. This model could be useful as preclinical models for drug development of NAFLD.

Carotenoids in orange carrots mitigate non-alcoholic fatty liver disease progression

Background

Carotenoids are abundant in colored fruits and vegetables. Non-alcoholic fatty liver disease (NAFLD) is a global burden and risk factor for end-stage hepatic diseases. This study aims to compare the anti-NAFLD efficacy between carotenoid-rich and carotenoid-deficient vegetables.

Materials and methods

Male C57BL/6J mice were randomized to one of four experimental diets for 15 weeks (n = 12 animals/group): Low-fat diet (LFD, 10% calories from fat), high-fat diet (HFD, 60% calories from fat), HFD with 20% white carrot powders (HFD + WC), or with 20% orange carrot powders (HFD + OC).

Results

We observed that carotenoids in the orange carrots reduced HFD-induced weight gain, better than white carrots. Histological and triglyceride (TG) analyses revealed significantly decreased HFD-induced hepatic lipid deposition and TG content in the HFD + WC group, which was further reduced in the HFD + OC group. Western blot analysis demonstrated inconsistent changes of fatty acid synthesis-related proteins but significantly improved ACOX-1 and CPT-II, indicating that orange carrot carotenoids had the potential to inhibit NAFLD by improving β-oxidation. Further investigation showed significantly higher mRNA and protein levels of PPARα and its transcription factor activity.

Conclusion

Carotenoid-rich foods may display more potent efficacy in mitigating NAFLD than those with low carotenoid levels.

Molecular mechanisms of metabolic associated fatty liver disease (MAFLD): functional analysis of lipid metabolism pathways

The metabolic-associated fatty liver disease (MAFLD) is a condition of fat accumulation in the liver in combination with metabolic dysfunction in the form of overweight or obesity and insulin resistance. It is also associated with an increased cardiovascular disease risk, including hypertension and atherosclerosis. Hepatic lipid metabolism is regulated by a combination of the uptake and export of fatty acids, de novo lipogenesis, and fat utilization by β-oxidation. When the balance between these pathways is altered, hepatic lipid accumulation commences, and long-term activation of inflammatory and fibrotic pathways can progress to worsen the liver disease. This review discusses the details of the molecular mechanisms regulating hepatic lipids and the emerging therapies targeting these pathways as potential future treatments for MAFLD.

Akkermansia muciniphila Enhances Egg Quality and the Lipid Profile of Egg Yolk by Improving Lipid Metabolism

Akkermansia muciniphila (A. muciniphila) has shown potential as a probiotic for the prevention and treatment of non-alcoholic fatty liver disease in both humans and mice. However, relatively little is known about the effects of A. muciniphila on lipid metabolism, productivity, and product quality in laying hens. In this study, we explored whether A. muciniphila supplementation could improve lipid metabolism and egg quality in laying hens and sought to identify the underlying mechanism. In the first experiment, 80 Hy-Line Brown laying hens were divided into four groups, one of which was fed a normal diet (control group), while the other three groups were administered a high-energy, low-protein diet to induce fatty liver hemorrhagic syndrome (FLHS). Among the three FLHS groups, one was treated with phosphate-buffered saline, one with live A. muciniphila, and one with pasteurized A. muciniphila. In the second experiment, 140 Hy-Line Brown laying hens were divided into two groups and respectively fed a basal diet supplemented or not with A. muciniphila lyophilized powder. The results showed that, in laying hens with FLHS, treatment with either live or pasteurized A. muciniphila efficiently decreased body weight, abdominal fat deposition, and lipid content in both serum and the liver; downregulated the mRNA expression of lipid synthesis-related genes and upregulated that of lipid transport-related genes in the liver; promoted the growth of short-chain fatty acids (SCFAs)-producing microorganisms and increased the cecal SCFAs content; and improved the yolk lipid profile. Additionally, the supplementation of lyophilized powder of A. muciniphila to aged laying hens reduced abdominal fat deposition and total cholesterol (TC) levels in both serum and the liver, suppressed the mRNA expression of cholesterol synthesis-related genes in the liver, reduced TC content in the yolk, increased eggshell thickness, and reshaped the composition of the gut microbiota. Collectively, our findings demonstrated that A. muciniphila can modulate lipid metabolism, thereby, promoting laying hen health as well as egg quality and nutritive value. Live, pasteurized, and lyophilized A. muciniphila preparations all have the potential for use as additives for improving laying hen production.

Enteromorpha polysaccharide and yeast glycoprotein mixture improves growth, antioxidant activity, serum lipid profile and regulates lipid metabolism in broiler chickens

This study aimed to analyze the growth performance, antioxidant activity, serum lipid profile, meat quality, and lipid metabolism of broiler chickens fed mixtures containing Enteromorpha polysaccharide (EP) and yeast glycoprotein (YG). A total of 400 one-day-old broiler chickens were randomly divided into 4 treatment groups of 10 replicates with 10 birds each replicate. The dietary treatments consisted of the control group (fed basal diet), and diets supplemented with Enteromorpha polysaccharide (EP; 400 mg/kg), yeast glycoprotein (YG;400 mg/kg), and EP+YG (200 mg/kg EP + 200 mg/kg YG). Compared with the control group, EP+YG supplementation enhanced growth performance and significantly reduced (P < 0.05) serum total triglyceride (TG), cholesterol (CHOL), and low-density lipoprotein LDL levels, and increased high-density lipoprotein (HDL) levels. Besides, birds fed EP+YG supplemented diet exhibited higher (P < 0.05) serum catalase (CAT), total antioxidant capacity, superoxide dismutase (SOD), and lower malonaldehyde (MDA) activities, and upregulated expressions of related genes, such as nuclear factor-erythroid factor 2-related factor 2 (NRF2), SOD1, and glutathione peroxidase 4 (GPX4) in the liver and intestinal tissues than the control group. Interestingly, higher (P < 0.05) serum SOD and lower MDA contents were observed in the EP+YG group than in either EP or YG group, suggesting a synergetic effect. Breast meat from EP+YG supplemented group had significantly higher redness value (a*), and lower pH24, total saturated fatty acid profiles, C14:0, C16:0, C18:0 fatty acid, atherogenic index, and thrombogenicity index than meat from the control group (P < 0.05). Furthermore, the mRNA expressions of fatty acid synthesis genes were downregulated (P < 0.05), whereas lipid β-oxidation-related genes were upregulated (P < 0.05) in the liver of the EP+YG supplemented group than in the control group. Overall, our data suggest that dietary EP+YG inclusion may have a synergistic effect, and therefore improve growth performance, regulate serum biochemical indexes, enhance antioxidant activity, and modulate lipid metabolism in broilers, indicating that it is a potential feed additive for chickens.

Overexpression of NAG-1/GDF15 prevents hepatic steatosis through inhibiting oxidative stress-mediated dsDNA release and AIM2 inflammasome activation

Mitochondrial dysfunction and oxidative stress-mediated inflammasome activation play critical roles in the pathogenesis of the non-alcoholic fatty liver disease (NAFLD). Non-steroidal anti-inflammatory drug (NSAID)-activated gene-1 (NAG-1), or growth differentiation factor-15 (GDF15), is associated with many biological processes and diseases, including NAFLD. However, the role of NAG-1/GDF15 in regulating oxidative stress and whether this process is associated with absent in melanoma 2 (AIM2) inflammasome activation in NAFLD are unknown. In this study, we revealed that NAG-1/GDF15 is significantly downregulated in liver tissues of patients with steatosis compared to normal livers using the Gene Expression Omnibus (GEO) database, and in free fatty acids (FFA, oleic acid/palmitic acid, 2:1)-induced HepG2 and Huh-7 cellular steatosis models. Overexpression of NAG-1/GDF15 in transgenic (Tg) mice significantly alleviated HFD-induced obesity and hepatic steatosis, improved lipid homeostasis, enhanced fatty acid β-oxidation and lipolysis, inhibited fatty acid synthesis and uptake, and inhibited AIM2 inflammasome activation and the secretion of IL-18 and IL-1β, as compared to their wild-type (WT) littermates without reducing food intake. Furthermore, NAG-1/GDF15 overexpression attenuated FFA-induced triglyceride (TG) accumulation, lipid metabolism deregulation, and AIM2 inflammasome activation in hepatic steatotic cells, while knockdown of NAG-1/GDF15 demonstrated opposite effects. Moreover, NAG-1/GDF15 overexpression inhibited HFD- and FFA-induced oxidative stress and mitochondrial damage which in turn reduced double-strand DNA (dsDNA) release into the cytosol, while NAG-1/GDF15 siRNA showed opposite effects. The reduced ROS production and dsDNA release may be responsible for attenuated AIM2 activation by NAG-1/GDF15 upon fatty acid overload. In conclusion, our results provide evidence that other than regulating lipid homeostasis, NAG-1/GDF15 protects against hepatic steatosis through a novel mechanism via suppressing oxidative stress, mitochondrial damage, dsDNA release, and AIM2 inflammasome activation.

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NAG-1/GDF15 is downregulated in human steatotic liver and FFA-induced liver cells.

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NAG-1/GDF15 inhibits hepatic steatosis and improves lipid homeostasis.

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AIM2 inflammasome is activated in steatosis models and is inhibited by NAG-1/GDF15.

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NAG-1/GDF15 reduces oxidative stress and mitochondrial damage in steatosis models.

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NAG-1/GDF15 inhibits mitochondrial dsDNA release and thus inhibits AIM2 activation.

Spermidine Ameliorates Nonalcoholic Steatohepatitis through Thyroid Hormone-Responsive Protein Signaling and the Gut Microbiota-Mediated Metabolism of Bile Acids

Spermidine, a natural polyamine and physiological autophagy inducer, is involved in various physiological processes. However, the impact and mechanism of spermidine on nonalcoholic steatohepatitis (NASH) remains unclarified. We found that daily spermidine intake was significantly lower in volunteers with liver dysfunction than the healthy controls, and the serum and fecal spermidine levels were negatively correlated with the NASH phenotypes. Spermidine supplementation significantly attenuated hepatic lipid accumulation, insulin resistance, hepatic inflammation, and fibrosis in NASH mice induced by a western diet. The ameliorating effect of spermidine on lipid accumulation might be partly regulated by thyroid hormone-responsive protein (THRSP) signaling and autophagy. Moreover, spermidine altered the profile of hepatic bile acids (BAs) and microbial composition and function. Furthermore, spermidine reversed the progression of hepatic steatosis, inflammation, and fibrosis in mice with preexisting NASH. Therefore, spermidine ameliorates NASH partly through the THRSP signaling and the gut microbiota-mediated metabolism of BAs, suggesting that spermidine might be a viable therapy for NASH.

Peroxisomes Regulate Cellular Free Fatty Acids to Modulate Mast Cell TLR2, TLR4, and IgE-Mediated Activation

Mast cells are specialized, tissue resident, immune effector cells able to respond to a wide range of stimuli. MCs are involved in the regulation of a variety of physiological functions, including vasodilation, angiogenesis and pathogen elimination. In addition, MCs recruit and regulate the functions of many immune cells such as dendritic cells, macrophages, T cells, B cells and eosinophils through their selective production of multiple cytokines and chemokines. MCs generate and release multi-potent molecules, such as histamine, proteases, prostanoids, leukotrienes, heparin, and many cytokines, chemokines, and growth factors through both degranulation dependent and independent pathways. Recent studies suggested that metabolic shifts dictate the activation and granule content secretion by MCs, however the metabolic signaling promoting these events is at its infancy. Lipid metabolism is recognized as a pivotal immunometabolic regulator during immune cell activation. Peroxisomes are organelles found across all eukaryotes, with a pivotal role in lipid metabolism and the detoxification of reactive oxygen species. Peroxisomes are one of the emerging axes in immunometabolism. Here we identified the peroxisome as an essential player in MCs activation. We determined that lack of functional peroxisomes in murine MCs causes a significant reduction of interleukin-6, Tumor necrosis factor and InterleukinL-13 following immunoglobulin IgE-mediated and Toll like receptor 2 and 4 activation compared to the Wild type (WT) BMMCs. We linked these defects in cytokine release to defects in free fatty acids homeostasis. In conclusion, our study identified the importance of peroxisomal fatty acids homeostasis in regulating mast cell-mediated immune functions.

Dietary Enteromorpha polysaccharide-Zn supplementation regulates amino acid and fatty acid metabolism by improving the antioxidant activity in chicken

Background

Enteromorpha prolifera (E. prolifera) polysaccharide has become a promising feed additive with a variety of physiological activities, such as anti-oxidant, anti-cancer, anti-diabetic, immunomodulatory, hypolipidemic, and cation chelating ability. However, whether Enteromorpha polysaccharide-trace element complex supplementation regulates amino acid and fatty acid metabolism in chicken is largely unknown. This study was conducted to investigate the effects of E. prolifera polysaccharide (EP)-Zn supplementation on growth performance, amino acid, and fatty acid metabolism in chicken.

Methods

A total of 184 one-day-old Ross-308 broiler chickens were randomly divided into two treatment groups with 8 replicates, 12 chickens per replicate, and fed either the basal diet (control group) or basal diet plus E. prolifera polysaccharide-Zinc (400 mg EP-Zn/kg diet).

Results

Dietary EP-Zn supplementation significantly increased (P < 0.05) the body weight, average daily gain, muscle antioxidant activity, serum HDL level, and reduced serum TG and LDL concentration. In addition, dietary EP-Zn supplementation could modulate ileal amino acid digestibility and upregulate the mRNA expression of amino acid transporter genes in the jejunum, ileum, breast muscle, and liver tissues (P < 0.05). Compared with the control group, breast meat from chickens fed EP-Zn had higher (P < 0.05) Pro and Asp content, and lower (P < 0.05) Val, Phe, Gly, and Cys free amino acid content. Furthermore, EP-Zn supplementation upregulated (P < 0.05) the mRNA expressions of mTOR and anti-oxidant related genes, while down-regulated protein degradation related genes in the breast muscle. Breast meat from EP-Zn supplemented group had significantly lower (P < 0.05) proportions of Σn-3 PUFA, and a higher percentage of Σn-6 PUFA and the ratio of n-6/n-3 PUFA. Besides, EP-Zn supplementation regulated lipid metabolism by inhibiting the gene expression of key enzymes involved in the fatty acid synthesis and activating genes that participated in fatty acid oxidation in the liver tissue.

Conclusions

It is concluded that EP-Zn complex supplementation regulates apparent ileal amino acid digestibility, enhances amino acid metabolism, and decreases oxidative stress-associated protein breakdown, thereby improving the growth performance. Furthermore, it promotes fatty acid oxidation and restrains fat synthesis through modulating lipid metabolism-related gene expression.

Graphical abstract

Chronic angiotensin receptor activation promotes hepatic triacylglycerol accumulation during an acute glucose challenge in obese-insulin-resistant OLETF rats

PURPOSE

Angiotensin receptor blockers (ARBs) can ameliorate metabolic syndrome (MetS)-associated dyslipidemia, hepatic steatosis, and glucose intolerance, suggesting that angiotensin receptor (AT1) over-activation contributes to impaired lipid and glucose metabolism, which is characteristic of MetS. The aim of this study was to evaluate changes in the lipid profile and proteins of fatty acid uptake, triacylglycerol (TAG) synthesis, and β-oxidation to better understand the links between AT1 overactivation and non-alcoholic fatty liver disease (NAFLD) during MetS.

METHODS

Four groups of 25-week-old-rats were used: (1) untreated LETO, (2) untreated OLETF, (3) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d × 8 weeks) and (4) OLETF ± ARB (MINUS; 10 mg olmesartan/kg/d × 4 weeks, then removed until dissection). To investigate the dynamic shifts in metabolism, animals were dissected after an oral glucose challenge (fasting, 3 and 6 h post-glucose).

RESULTS

Compared to OLETF, plasma total cholesterol and TAG remained unchanged in ARB. However, liver TAG was 55% lesser in ARB than OLETF, and remained lower throughout the challenge. Basal CD36 and ApoB were 28% and 29% lesser, respectively, in ARB than OLETF. PRDX6 abundance in ARB was 45% lesser than OLETF, and it negatively correlated with liver TAG in ARB.

CONCLUSIONS

Chronic blockade of AT1 protects the liver from TAG accumulation during glucose overload. This may be achieved by modulating NEFA uptake and increasing TAG export via ApoB. Our study highlights the contributions of AT1 signaling to impaired hepatic substrate metabolism and the detriments of a high-glucose load and its potential contribution to steatosis during MetS.

GP73 is a TBC-domain Rab GTPase-activating protein contributing to the pathogenesis of non-alcoholic fatty liver disease without obesity

The prevalence of non-obese nonalcoholic fatty liver disease (NAFLD) is increasing worldwide with unclear etiology and pathogenesis. Here, we show GP73, a Golgi protein upregulated in livers from patients with a variety of liver diseases, exhibits Rab GTPase-activating protein (GAP) activity regulating ApoB export. Upon regular-diet feeding, liver-GP73-high mice display non-obese NAFLD phenotype, characterized by reduced body weight, intrahepatic lipid accumulation, and gradual insulin resistance development, none of which can be recapitulated in liver-GAP inactive GP73-high mice. Common and specific gene expression signatures associated with GP73-induced non-obese NAFLD and high-fat diet (HFD)-induced obese NAFLD are revealed. Notably, metformin inactivates the GAP activity of GP73 and alleviates GP73-induced non-obese NAFLD. GP73 is pathologically elevated in NAFLD individuals without obesity, and GP73 blockade improves whole-body metabolism in non-obese NAFLD mouse model. These findings reveal a pathophysiological role of GP73 in triggering non-obese NAFLD and may offer an opportunity for clinical intervention.

Dysregulation of lipid metabolism and transport contribute to the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Here the authors identify GP73 as a TBC-domain Rab GTPase-activating protein that regulates very low-density lipoprotein export and promotes NAFLD development in mice.

Integrative lipidomic and transcriptomic study unravels the therapeutic effects of saikosaponins A and D on non-alcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has become one of the most prominent causes of chronic liver diseases and malignancies. However, few therapy has been approved. Radix Bupleuri (RB) is the most frequently used herbal medicine for the treatment of liver diseases. In the current study, we aim to systemically evaluate the therapeutic effects of saikosaponin A (SSa) and saikosaponin D (SSd), the major bioactive monomers in RB, against NAFLD and to investigate the underlying mechanisms. Our results demonstrated that both SSa and SSd improved diet-induced NAFLD. Integrative lipidomic and transcriptomic analysis revealed that SSa and SSd modulated glycerolipid metabolism by regulating related genes, like Lipe and Lipg. SSd profoundly suppressed the fatty acid biosynthesis by downregulating Fasn and Acaca expression and promoted fatty acid degradation by inducing Acox1 and Cpt1a expression. Bioinformatic analysis further predicted the implication of master transcription factors, including peroxisome proliferator-activated receptor alpha (PPARα), in the protective effects of SSa and SSd. These results were further confirmed in vitro in mouse primary hepatocytes. In summary, our study uncoded the complicated mechanisms underlying the promising anti-steatosis activities of saikosaponins (SSs), and provided critical evidence inspiring the discovery of innovative therapies based on SSa and SSd for the treatment of NAFLD and related complications.

Transcriptomic bases of a polyphenism

Polyphenism-in which multiple distinct phenotypes are produced from a single genotype owing to differing environmental conditions-is commonplace, but its molecular bases are poorly understood. Here, we examine the transcriptomic bases of a polyphenism in Mexican spadefoot toads (Spea multiplicata). Depending on their environment, their tadpoles develop into either a default "omnivore" morph or a novel "carnivore" morph. We compared patterns of gene expression among sibships that exhibited high versus low production of carnivores when reared in conditions that induce the carnivore morph versus those that do not. We found that production of the novel carnivore morph actually involved changes in fewer genes than did the maintenance of the default omnivore morph in the inducing environment. However, only body samples showed this pattern; head samples showed the opposite pattern. We also found that changes to lipid metabolism (especially cholesterol biosynthesis) and peroxisome contents and function might be crucial for establishing and maintaining differences between the morphs. Thus, our findings suggest that carnivore phenotype might have originally evolved following the breakdown of robustness mechanisms that maintain the default omnivore phenotype, and that the carnivore morph is developmentally regulated by lipid metabolism and peroxisomal form, function, and/or signaling. This study also serves as a springboard for further exploration into the nature and causes of plasticity in an emerging model system.

Aging mitigates the severity of obesity-associated metabolic sequelae in a gender independent manner

BACKGROUND

Understanding gender-associated bias in aging and obesity-driven metabolic derangements has been hindered by the inability to model severe obesity in female mice.

METHODS

Here, using chow- or high fat diet (HFD)-feeding regimens at standard (TS) and thermoneutral (TN) housing temperatures, the latter to model obesity in female mice, we examined the impact of gender and aging on obesity-associated metabolic derangements and immune responsiveness. Analysis included quantification of: (i) weight gain and adiposity; (ii) the development and severity of glucose dysmetabolism and non-alcoholic fatty liver disease (NAFLD); and (iii) induction of inflammatory pathways related to metabolic dysfunction.

RESULTS

We show that under chow diet feeding regimen, aging was accompanied by increased body weight and white adipose tissue (WAT) expansion in a gender independent manner. HFD feeding regimen in aged, compared to young, male mice at TS, resulted in attenuated glucose dysmetabolism and hepatic steatosis. However, under TS housing conditions only aged, but not young, HFD fed female mice developed obesity. At TN however, both young and aged HFD fed female mice developed severe obesity. Independent of gender or housing conditions, aging attenuated the severity of metabolic derangements in HFD-fed obese mice. Tempered severity of metabolic derangements in aged mice was associated with increased splenic frequency of regulatory T (Treg) cells, Type I regulatory (Tr1)-like cells and circulating IL-10 levels and decreased vigor of HFD-driven induction of inflammatory pathways in adipose and liver tissues.

CONCLUSION

Our findings suggest that aging-associated altered immunological profile and inflammatory vigor may play a dominant role in the attenuation of obesogenic diet-driven metabolic dysfunction.

PKM2-dependent metabolic skewing of hepatic Th17 cells regulates pathogenesis of non-alcoholic fatty liver disease

Emerging evidence suggests a key contribution to non-alcoholic fatty liver disease (NAFLD) pathogenesis by Th17 cells. The pathogenic characteristics and mechanisms of hepatic Th17 cells, however, remain unknown. Here, we uncover and characterize a distinct population of inflammatory hepatic CXCR3+Th17 (ihTh17) cells sufficient to exacerbate NAFLD pathogenesis. Hepatic ihTh17 cell accrual was dependent on the liver microenvironment and CXCR3 axis activation. Mechanistically, the pathogenic potential of ihTh17 cells correlated with increased chromatin accessibility, glycolytic output, and concomitant production of IL-17A, IFNγ, and TNFα. Modulation of glycolysis using 2-DG or cell-specific PKM2 deletion was sufficient to reverse ihTh17-centric inflammatory vigor and NAFLD severity. Importantly, ihTh17 cell characteristics, CXCR3 axis activation, and hepatic expression of glycolytic genes were conserved in human NAFLD. Together, our data show that the steatotic liver microenvironment regulates Th17 cell accrual, metabolism, and competence toward an ihTh17 fate. Modulation of these pathways holds potential for development of novel therapeutic strategies for NAFLD.

A BAFF/APRIL axis regulates obesogenic diet-driven weight gain

The impact of immune mediators on weight homeostasis remains underdefined. Interrogation of resistance to diet-induced obesity in mice lacking a negative regulator of Toll-like receptor signaling serendipitously uncovered a role for B cell activating factor (BAFF). Here we show that overexpression of BAFF in multiple mouse models associates with protection from weight gain, approximating a log-linear dose response relation to BAFF concentrations. Gene expression analysis of BAFF-stimulated subcutaneous white adipocytes unveils upregulation of lipid metabolism pathways, with BAFF inducing white adipose tissue (WAT) lipolysis. Brown adipose tissue (BAT) from BAFF-overexpressing mice exhibits increased Ucp1 expression and BAFF promotes brown adipocyte respiration and in vivo energy expenditure. A proliferation-inducing ligand (APRIL), a BAFF homolog, similarly modulates WAT and BAT lipid handling. Genetic deletion of both BAFF and APRIL augments diet-induced obesity. Lastly, BAFF/APRIL effects are conserved in human adipocytes and higher BAFF/APRIL levels correlate with greater BMI decrease after bariatric surgery. Together, the BAFF/APRIL axis is a multifaceted immune regulator of weight gain and adipose tissue function.

Dapagliflozin Alleviates Hepatic Steatosis by Restoring Autophagy via the AMPK-mTOR Pathway

As a newly approved oral hypoglycaemic agent, the sodium-glucose cotransporter 2 (SGLT2) inhibitor dapagliflozin, which is derived from the natural product phlorizin can effectively reduce blood glucose. Recent clinical studies have found that dapagliflozin alleviates non-alcoholic fatty liver disease (NAFLD), but the specific mechanism remains to be explored. This study aimed to investigate the underlying mechanism of dapagliflozin in alleviating hepatocyte steatosis in vitro and in vivo. We fed the spontaneous type 2 diabetes mellitus rats with high-fat diets and cultured human normal liver LO2 cells and human hepatocellular carcinoma HepG2 cells with palmitic acid (PA) to induce hepatocellular steatosis. Dapagliflozin attenuated hepatic lipid accumulation both in vitro and in vivo. In Zucker diabetic fatty (ZDF) rats, dapagliflozin reduced hepatic lipid accumulation via promoting phosphorylation of acetyl-CoA carboxylase 1 (ACC1), and upregulating lipid β-oxidation enzyme acyl-CoA oxidase 1 (ACOX1). Furthermore, dapagliflozin increased the expression of the autophagy-related markers LC3B and Beclin1, in parallel with a drop in p62 level. Similar effects were observed in PA-stimulated LO2 cells and HepG2 cells. Dapagliflozin treatment could also significantly activated AMPK and reduced the phosphorylation of mTOR in ZDF rats and PA-stimulated LO2 cells and HepG2 cells. We demonstrated that dapagliflozin ameliorates hepatic steatosis by decreasing lipogenic enzyme, while inducing fatty acid oxidation enzyme and autophagy, which could be associated with AMPK activation. Moreover, our results indicate that dapagliflozin induces autophagy via the AMPK-mTOR pathway. These findings reveal a novel clinical application and functional mechanism of dapagliflozin in the treatment of NAFLD.

Cholesterol-binding translocator protein TSPO regulates steatosis and bile acid synthesis in nonalcoholic fatty liver disease

Translocator protein (TSPO, 18 kDa) levels increase in parallel with the evolution of simple steatosis (SS) to nonalcoholic steatohepatitis (NASH) in nonalcoholic fatty liver disease (NAFLD). However, TSPO function in SS and NASH is unknown. Loss of TSPO in hepatocytes in vitro downregulated acetyl-CoA acetyltransferase 2 and increased free cholesterol (FC). FC accumulation induced endoplasmic reticulum stress via IRE1A and protein kinase RNA-like ER kinase/ATF4/CCAAT-enhancer-binding protein homologous protein pathways and autophagy. TSPO deficiency activated cellular adaptive antioxidant protection; this adaptation was lost upon excessive FC accumulation. A TSPO ligand 19-Atriol blocked cholesterol binding and recapitulated many of the alterations seen in TSPO-deficient cells. These data suggest that TSPO deficiency accelerated the progression of SS. In NASH, however, loss of TSPO ameliorated liver fibrosis through downregulation of bile acid synthesis by reducing CYP7A1 and CYP27A1 levels and increasing farnesoid X receptor expression. These studies indicate a dynamic and complex role for TSPO in the evolution of NAFLD.

How does hepatic lipid accumulation lead to lipotoxicity in non-alcoholic fatty liver disease?

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD), characterized as excess lipid accumulation in the liver which is not due to alcohol use, has emerged as one of the major health problems around the world. The dysregulated lipid metabolism creates a lipotoxic environment which promotes the development of NAFLD, especially the progression from simple steatosis (NAFL) to non-alcoholic steatohepatitis (NASH).

PURPOSEAND AIM

This review focuses on the mechanisms of lipid accumulation in the liver, with an emphasis on the metabolic fate of free fatty acids (FFAs) in NAFLD and presents an update on the relevant cellular processes/mechanisms that are involved in lipotoxicity. The changes in the levels of various lipid species that result from the imbalance between lipolysis/lipid uptake/lipogenesis and lipid oxidation/secretion can cause organellar dysfunction, e.g. ER stress, mitochondrial dysfunction, lysosomal dysfunction, JNK activation, secretion of extracellular vesicles (EVs) and aggravate (or be exacerbated by) hypoxia which ultimately lead to cell death. The aim of this review is to provide an overview of how abnormal lipid metabolism leads to lipotoxicity and the cellular mechanisms of lipotoxicity in the context of NAFLD.