Accumulation Of Lipid Droplets In Liver Research Articles

FBXL5 promotes lipid accumulation in alcoholic fatty liver disease by promoting the ubiquitination and degradation of TFEB

BackgroundAlcoholic fatty liver disease (AFLD) is characterized by abnormal lipid droplet accumulation in liver. Epigenetic regulation plays an important role in the pathogenesis of AFLD. Comprehensive bioinformatics analysis revealed that an E3 ubiquitin ligase, F-box and leucine-rich repeats protein 5 (FBXL5), was significantly upregulated in AFLD mice. MethodsThe mouse model of AFLD was established by feeding Lieber-DeCarli liquid diet containing ethanol. An in vitro model of AFLD was established by treating HepG2 cells with ethanol (EtOH). The FBXL5 expression was assessed by quantitative real-time PCR (qRT-PCR) and western blotting assays. The levels of triglyceride (TG), alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lipid accumulation were analyzed by enzyme-linked immunosorbent assay (ELISA) and Nile red staining. ResultsThe FBXL5 expression was markedly up-regulated in in vivo and in vitro models of AFLD compared with controls. Functionally, FBXL5 knockdown alleviated lipid accumulation in EtOH-treated HepG2 cells. Mechanistically, FBXL5 directly interacted with transcription factor EB (TFEB) and accelerated its ubiquitination-mediated degradation. TFEB knockdown reversed the effect of FBXL5 inhibition on decreasing EtOH-induced lipid accumulation. ConclusionOur data suggest that FBXL5 promotes lipid accumulation in AFLD by promoting the ubiquitination and degradation of TFEB.

A novel HIF2A mutation causes dyslipidemia and promotes hepatic lipid accumulation

Hypoxia-inducible factor-2α (HIF-2α) is a transcription factor responsible for regulating genes related to angiogenesis and metabolism. This study aims to explore the effect of a previously unreported mutation c.C2473T (p.R825S) in the C-terminal transactivation domain (CTAD) of HIF-2α that we detected in tissue of patients with liver disease. We sequenced available liver and matched blood samples obtained during partial liver resection or liver transplantation performed for clinical indications including hepatocellular carcinoma and liver failure. In tandem, we constructed cell lines and a transgenic mouse model bearing the corresponding identified mutation in HIF-2α from which we extracted primary hepatocytes. Lipid accumulation was evaluated in these cells and liver tissue from the mouse model using Oil Red O staining and biochemical measurements. We identified a mutation in the CTAD of HIF-2α (c.C2473T; p.R825S) in 5 of 356 liver samples obtained from patients with hepatopathy and dyslipidemia. We found that introduction of this mutation into the mouse model led to an elevated triglyceride level, lipid droplet accumulation in liver of the mutant mice and in their extracted primary hepatocytes, and increased transcription of genes related to hepatic fatty acid transport and synthesis in the mutant compared to the control groups. In mutant mice and cells, the protein levels of nuclear HIF-2α and its target perilipin-2 (PLIN2), a lipid droplet-related gene, were also elevated. Decreased lipophagy was observed in mutant groups. Our study defines a subpopulation of dyslipidemia that is caused by this HIF-2α mutation. This may have implications for personalized treatment.

Impacts of polypropylene microplastics on lipid profiles of mouse liver uncovered by lipidomics analysis and Raman spectroscopy

Microplastics (MPs) are emerging contaminants, and there are only limited studies reporting the impacts of some MPs on liver lipid metabolism in animals. In this study, we investigated the accumulation of polypropylene-MPs in mouse liver and unraveled the change in lipid metabolic profiles by both lipidomics and Raman spectroscopy. Polypropylene-MP exposure did not cause obvious health symptoms, but hematoxylin-eosin staining showed pathological changes that polypropylene-MPs induced lipid droplet accumulation in liver. Lipidomics results showed a significant change in lipid metabolic profiles and the most influenced categories were triglycerides, fatty acids, free fatty acids and lysophosphatidylcholine, implying the effects of polypropylene-MPs on the hemostasis of lipid droplet biogenesis and catabolism. Most altered lipids contained unsaturated bonds and polyunsaturated phospholipids, possibly affecting the fluidity and curvature of membrane surfaces. Raman spectroscopy confirmed that the major spectral alterations of liver tissues were related to lipids, evidencing the altered lipid metabolism and cell membrane components in the presence of polypropylene-MPs. Our findings firstly disclosed the impacts of polypropylene-MPs on lipid metabolisms in mouse liver and hinted at their detrimental disturbance on membrane properties, cellular lipid storage and oxidation regulation, helping our deeper understanding on the toxicities and corresponding risks of polypropylene-MPs to mammals.

Safety evaluation and hypolipidemic effect of aqueous-ethanol and hot-water extracts from E Se tea in rats

E Se tea, processed by the fresh leaves of Malus toringoides (Rehd.) Hughes, is a traditional herbal tea with various human benefits. The present study was aimed to evaluate the toxicity and hypolipidemic effect of aqueous-ethanol extract (EE) and hot-water extract (WE) from E Se tea. Eight main chemical constituents in EE and WE were respectively identified and quantified by UHPLC-HRMS/MS. EE is rich in TPC and TFC, while WE had higher TPS content. Both EE and WE exhibited strong antioxidant activity with no significant difference. The acute toxicity study revealed that the LD50 values were higher than 5000 mg/kg, while both WE and EE had no significant adverse effect in rats by subacute toxicity assay. However, the triglyceride (TG) content in experiment groups (male) and highest doses groups (female) significantly decreased. Furthermore, the hypolipidemic effect of WE and EE were performed on high fat diet induced hyperlipidemic rats. The result exhibited that either WE or EE could effectively regulate lipid droplet accumulation in liver, and reduce the adipocyte size. These results demonstrated that these two extracts from E Se tea could be regarded as a potential functional dietary supplement in preventing and treating diet induced metabolic diseases.

Bisphenol A inhibits autophagosome-lysosome fusion and lipid droplet degradation

Bisphenol A (BPA) is an artificial xenoestrogen widely used in consumer products containing polycarbonate plastics and epoxy resins. Exposure to BPA occurs through various channels, including ingestion of contaminated food and water. Autophagy is an important catabolic pathway that plays an important role in liver lipid metabolism. Evidence suggests that BPA exposure causes abnormal lipid droplet accumulation in liver, but the mechanism remains unknown. Here, we investigate the function of BPA in lipid metabolism and autophagy. BPA exposure increases lipid droplet and ROS accumulation which is accompanied by a defect in the fusion of the autophagosome to the lysosome. BPA exposure decreases the translocation of Stx17 to lysosome resulting in the autophagogome-lysosome fusion defect. There is no defect in the formation of the autophagosome indicated by increased LC3-II, p62 level, GFP/mRFP-LC3 ratios and decreased colocalization between LAMP2 with LC3. Mechanistically, BPA exposure reduces autophagy SNARE complex formation. Promoting autophagy by autophagy inducer (Torin2) partially reverses lipid droplet accumulation caused by BPA exposure. In summary, our results demonstrate BPA exposure inhibits autophagy resulting in decreased lipid droplet degradation and increased ROS levels. These results also provide a novel implication between autophagosome-lysosome fusion.

Triclosan-induced liver injury in zebrafish (Danio rerio) via regulating MAPK/p53 signaling pathway

Long-term exposure of triclosan (TCS), an important antimicrobial agent, can lead to deleterious effects on liver growth and development. However, the related mechanisms on TCS-induced hepatocyte injury remain unclear. Herein, we found that after long-time TCS exposure to adult zebrafish (Danio rerio) from 6 hpf (hours post-fertilization) to 90 dpf (days post-fertilization), the body weight and hepatic weight were significantly increased in concomitant with a large amount of lipid droplet accumulation in liver. Also, TCS exposure resulted in occurrence of oxidative stress by increasing the concentrations of malondialdehyde and reducing the activity of superoxide dismutase both in zebrafish larvae (120 hpf) and adult liver. By H&E staining, we observed a series of abnormal phenomena such as severely hepatocellular atrophy and necrosis, as well as prominently increased hepatic plate gap in TCS-exposure treatment groups. Through AO staining, TCS induced obvious apoptosis in larval heart and liver; through TUNEL assay, a concentration-dependent apoptosis was found to mainly occur in adult liver and its surrounding tissues. The mRNA and protein expression of anti-apoptotic protein Bcl-2 decreased, while that of pro-apoptosis protein Bax significantly increased, identifying that liver injury was closely related to hepatocyte apoptosis. The significant up-regulation of MAPK and p53 at both mRNA and protein levels proved that TCS-induced hepatocyte apoptosis was closely related to activating the MAPK/p53 signaling pathway. These results strongly suggest that long-term TCS-exposure may pose a great injury to zebrafish liver development by means of activating MAPK/p53 apoptotic signaling pathway, also lay theoretical foundation for further assessing TCS-induced ecological healthy risk.

Cytochrome P450 1A1 (CYP1A1) protects against nonalcoholic fatty liver disease caused by Western diet containing benzo[a]pyrene in mice

The Western diet contributes to nonalcoholic fatty liver disease (NAFLD) pathogenesis. Benzo[a]pyrene (BaP), a prototypical environmental pollutant produced by combustion processes, is present in charcoal-grilled meat. Cytochrome P450 1A1 (CYP1A1) metabolizes BaP, resulting in either detoxication or metabolic activation in a context-dependent manner. To elucidate a role of CYP1A1-BaP in NAFLD pathogenesis, we compared the effects of a Western diet, with or without oral BaP treatment, on the development of NAFLD in Cyp1a1(−/−) mice versus wild-type mice. A Western diet plus BaP induced lipid-droplet accumulation in liver of Cyp1a1(−/−) mice, but not wild-type mice. The hepatic steatosis observed in Cyp1a1(−/−) mice was associated with increased cholesterol, triglyceride and bile acid levels. Cyp1a1(−/−) mice fed Western diet plus BaP had changes in expression of genes involved in bile acid and lipid metabolism, and showed no increase in Cyp1a2 expression but did exhibit enhanced Cyp1b1 mRNA expression, as well as hepatic inflammation. Enhanced BaP metabolic activation, oxidative stress and inflammation may exacerbate metabolic dysfunction in liver of Cyp1a1(−/−) mice. Thus, Western diet plus BaP induces NAFLD and hepatic inflammation in Cyp1a1(−/−) mice in comparison to wild-type mice, indicating a protective role of CYP1A1 against NAFLD pathogenesis.

Resveratrol Ameliorates Lipid Droplet Accumulation in Liver Through a SIRT1/ ATF6-Dependent Mechanism

Background/Aims: Lipid droplets (LDs) are dynamic organelles that store neutral lipids during times of energy excess, and an increased accumulation of LDs in the liver is closely linked to hepatic steatosis. Our previous studies suggested that resveratrol (RSV) supplement could improve hepatic steatosis, but the underlying mechanism, particularly which related to LD accumulation, has not yet been elucidated. Methods: A high-fat diet (HFD) and palmitic acid were used to induce hepatic steatosis in mouse liver and hepatocytes, respectively. The effects of RSV on LD accumulation were analyzed in vivo and in vitro. The effects of RSV on the expression levels of LD-associated genes (ATF6, Fsp27β/CIDEC, CREBH, and PLIN1) were measured by qRT-PCR and western blot assays, followed by KD or overexpression of SIRT1 and ATF6 with small interfering RNAs or overexpressed plasmids, respectively. The dual luciferase reporter assay, chromatin immunoprecipitation assay, coimmunoprecipitation, and proximity ligation assay were utilized to clarify the mechanism of transcriptional regulation and possible interaction between SIRT1 and ATF6. Results: There was a significant increase in the accumulation of LDs in liver and hepatocytes during the process of HFD-induced steatosis, respectively, which was significantly inhibited by RSV supplementation. RSV notably activated SIRT1 expression and decreased the expression levels of ATF6, Fsp27β/CIDEC, CREBH, and PLIN1, which are associated with LD accumulation. Interestingly, the inhibitory effects of RSV on LD accumulation and the associated expression of genes in hepatocytes were abrogated or strengthened with SIRT1 silencing or overexpression, respectively. On the contrary, the benefits of RSV in hepatocytes were eliminated or aggravated when transfected with the overexpressed ATF6 or ATF6 siRNA, respectively. Furthermore, we found that RSV stimulated SIRT1 expression significantly, which was followed by increased deacetylation and inactivation of ATF6, resulting in a positive feedback loop for SIRT1 transcription associated with ATF6 binding to the SIRT1 promoter region. Conclusion: Taken together, these findings indicate that RSV supplementation improves hepatic steatosis by ameliorating the accumulation of LDs, and this might be partially mediated by a SIRT1/ATF6-dependent mechanism.