Lipid Accumulation In Hepatocytes Research Articles

CCN1/Integrin α5β1 Instigates Free Fatty Acid-Induced Hepatocyte Lipid Accumulation and Pyroptosis through NLRP3 Inflammasome Activation

Hyperlipidemia with high blood levels of free fatty acids (FFA) is the leading cause of non-alcoholic steatohepatitis. CCN1 is a secreted matricellular protein that drives various cellular functions, including proliferation, migration, and differentiation. However, its role in mediating FFA-induced pro-inflammatory cell death and its underlying molecular mechanisms have not been characterized. In this study, we demonstrated that CCN1 was upregulated in the livers of obese mice. The increase in FFA-induced CCN1 was evaluated in vitro by treating hepatocytes with a combination of oleic acid and palmitic acid (2:1). Gene silencing using specific small interfering RNAs (siRNA) revealed that CCN1 participated in FFA-induced intracellular lipid accumulation, caspase-1 activation, and hepatocyte pyroptosis. Next, we identified integrin α5β1 as a potential receptor of CCN1. Co-immunoprecipitation demonstrated that the binding between CCN1 and integrin α5β1 increased in hepatocytes upon FFA stimulation in the livers of obese mice. Similarly, the protein levels of integrin α5 and β1 were increased in vitro and in vivo. Experiments with specific siRNAs confirmed that integrin α5β1 played a part in FFA-induced intracellular lipid accumulation, NLRP3 inflammasome activation, and pyroptosis in hepatocytes. In conclusion, these results provide novel evidence that the CCN1/integrin α5β1 is a novel mediator that drives hepatic lipotoxicity via NLRP3-dependent pyroptosis.

Sclerostin aggravates insulin signaling in skeletal muscle and hepatic steatosis via upregulation of ER stress by mTOR-mediated inhibition of autophagy under hyperlipidemic conditions.

Recently, sclerostin (SCL), a circulating glycoprotein, was proposed to be a novel myokine involved in developing metabolic disorders. The association between SCL levels and insulin resistance in skeletal muscle, liver, and adipose tissue was studied in individuals with aggravated glucose tolerance. Thus, we hypothesized that elevated circulating SCL might affect skeletal muscle insulin signaling and hepatic lipid metabolism, and aimed to investigate the effects of SCL on skeletal muscle insulin resistance and hepatic steatosis in obesity using in vitro and in vivo experimental models under hyperlipidemic conditions. In the current study, we found elevated SCL messenger RNA expression levels in myocytes in obese patients. In addition to a higher blood level, SCL was expressed at an elevated level in the skeletal muscle of mice fed a high-fat diet (HFD). Higher SCL release levels and expression were also noticed in palmitate-treated C2C12 myocytes. SCL suppression by in vivo transfection improves skeletal muscle insulin resistance and hepatic steatosis in HFD-fed mice. The treatment of C2C12 myocytes with recombinant SCL aggravated insulin signaling. Furthermore, treatment with SCL augmented lipogenic lipid deposition in human primary hepatocytes. Treatment with SCL upregulated mammalian target of rapamycin (mTOR) phosphorylation and suppressed autophagy markers, thereby causing endoplasmic reticulum (ER) stress. 4-Phenylbutyric acid, a pharmacological ER stress inhibitor, abolished the effects of SCL on insulin signaling in C2C12 myocytes and lipid accumulation in primary hepatocytes. In conclusion, SCL promotes skeletal muscle insulin resistance and hepatic steatosis by upregulating ER stress via the mTOR/autophagy-mediated pathway. The present study suggests that antagonizing SCL might be a novel therapeutic strategy for simultaneously managing insulin resistance and hepatic steatosis in obesity.

Low abundance of mitophagy markers is associated with reactive oxygen species overproduction in cows with fatty liver and causes reactive oxygen species overproduction and lipid accumulation in calf hepatocytes.

Mitochondria are the main site of fatty acid oxidation and reactive oxygen species (ROS) formation. Damaged or dysfunctional mitochondria induce oxidative stress and increase the risk of lipid accumulation. During the process of mitophagy, PTEN induced kinase 1 (PINK1) accumulates on damaged mitochondria and recruits cytoplasmic Parkin to mitochondria. As an autophagy receptor protein, sequestosome-1 (p62) binds Parkin-ubiquitinated outer mitochondrial membrane proteins and microtubule-associated protein 1 light chain 3 (LC3) to facilitate degradation of damaged mitochondria. In nonruminants, clearance of dysfunctional mitochondria through the PINK1/Parkin-mediated mitophagy pathway contributes to reducing ROS production and maintaining metabolic homeostasis. Whether PINK1/Parkin-mediated mitophagy plays a similar role in dairy cow liver is not well known. Thus, the objective of this study was to investigate mitophagy status in dairy cows with fatty liver and its role in free fatty acid (FFA)-induced oxidative stress and lipid accumulation. Liver and blood samples were collected from healthy dairy cows (n = 10) and cows with fatty liver (n = 10) that had a similar number of lactations (median = 3, range = 2 to 4) and days in milk (median = 6 d, range = 3 to 9 d). Calf hepatocytes were isolated from 5 healthy newborn female Holstein calves (1 d of age, 30-40 kg). Hepatocytes were transfected with small interfering RNA targeted against PRKN for 48 h or transfected with PRKN overexpression plasmid for 36 h, followed by treatment with FFA (0.3 or 1.2 mM) for 12 h. Mitochondria were isolated from fresh liver tissue or calf hepatocytes. Serum concentrations of β-hydroxybutyrate were higher in dairy cows with fatty liver. Hepatic malondialdehyde (MDA) and hydrogen peroxide (H2O2) were greater in cows with fatty liver. The lower protein abundance of PINK1, Parkin, p62, and LC3-II in hepatic mitochondrial fraction of dairy cows with fatty liver indicated the mitophagy was impaired. In hepatocytes, knockdown of PRKN decreased protein abundance of p62 and LC3-II in the mitochondrial fraction, and increased contents of triacylglycerol (TG), MDA, and H2O2. In addition, protein abundances of PINK1, Parkin, p62, and LC3-II were lower in the mitochondrial fraction from hepatocytes treated with 1.2 mM FFA than the hepatocytes treated with 0.3 mM FFA, whereas the content of TG, MDA, and H2O2 increased. In 1.2 mM FFA-treated hepatocytes, PRKN overexpression increased protein abundance of p62 and LC3-II in the mitochondrial fraction and decreased contents of TG, MDA, and H2O2. Together, our data demonstrate that low abundance of mitophagy markers is associated with ROS overproduction in dairy cows with fatty liver and impaired mitophagy induced by a high concentration of FFA promotes ROS production and lipid accumulation in female calf hepatocytes.

Depletion of hepatic stellate cells inhibits hepatic steatosis in mice.

Hepatic stellate cells (HSCs), the main source of extracellular matrix in hepatic fibrogenesis, produce various cytokines, growth factors, and morphogenetic proteins. Among these, several factors are known to promote hepatocyte lipid accumulation, suggesting that HSCs can be efficient therapeutic targets for non-alcoholic steatohepatitis (NASH). This study aimed to investigate the effects of HSC depletion on the development of hepatic steatosis and fibrosis in a murine NASH model. C57BL/6 mice were treated with gliotoxin (GTX), an apoptosis inducer of activated HSCs under the feeding of a choline-deficient l-amino acid-defined high-fat diet for 4weeks. For in vitro study, Hc3716 cells, immortalized human hepatocytes, were treated with fatty acids in the presence or absence of LX2, immortalized HSCs. Choline-deficient l-amino acid-defined high-fat diet increased pronounced hepatic steatosis, which was attenuated by GTX treatment, together with a reduction in the number of activated HSCs. This change was associated with the downregulation of the peroxisome proliferator-activated receptor gamma (PPARγ) and its downstream genes, including adipocyte protein 2, cluster of differentiation 36 (CD36), and fatty acid transport protein 1, all of which increase the fatty acid uptake into hepatocytes. As expected, GTX treatment improved hepatic fibrosis. Co-culture of hepatocytes with HSCs enhanced intracellular lipid accumulation, together with the upregulation of PPARγ and CD36 protein expressions. In addition to the improvement in hepatic fibrogenesis, depletion of HSCs had a favorable effect on hepatic lipid metabolism in a mouse NASH model, suggesting that HSCs are potentially efficient targets for the treatment of NASH.

Pentoxifylline attenuates nonalcoholic fatty liver by inhibiting hepatic macrophage polarization to the M1 phenotype

BackgroundNonalcoholic fatty liver (NAFL), recognized as one of the most common causes of chronic liver diseases, is increasingly prevalent worldwide. Pentoxifylline, a derivative of theobromine extracted from Theobroma cacao and tea, has been studied for effects on blood viscosity, tissue oxygenation and inflammation. However, its effects on hepatic lipid accumulation and the potential mechanisms remain unclear. PurposeThis study aimed to investigate the therapeutic effects of pentoxifylline on high-fat diet-induced NAFL and to explore the corresponding molecular mechanisms. MethodsNAFL mice were injected with or without 25, 50 or 100 mg/kg pentoxifylline for 2 weeks. Hepatic steatosis was observed by haematoxylin-eosin staining and Oil Red O staining, the levels of serum total cholesterol, triglyceride were detected by biochemical kits, and insulin resistance was evaluated by glucose and insulin tolerance tests. In addition, we measured the frequencies of macrophage and its polarization subsets in the liver using flow cytometry and immunofluorescence. The expressions of proteins associated with macrophage polarization signaling pathways were assessed by Western blotting and flow cytometry histograms. Molecular docking and cellular thermal shift assay were conducted to identify and verify the target protein of pentoxifylline in macrophage. ResultsPentoxifylline significantly alleviated hepatic lipid accumulation, reduced blood lipid levels and improved insulin resistance. Strikingly, the excessive M1 macrophages in NAFL development was abolished by pentoxifylline. And pentoxifylline was further evidenced it failed to reduce hepatocyte lipid accumulation in the absence of macrophages in vitro. Mechanistically, pentoxifylline competed with LPS for binding to toll-like receptor 4, dramatically inhibiting the TLR4/MyD88/NF-κB signaling pathway. ConclusionPentoxifylline attenuated NAFL by inhibiting hepatic macrophage M1 polarization, indicating that pentoxifylline could be a therapeutic candidate for NAFL. This study first observed that M1 macrophages were increased in NAFL mice and then revealed the molecule targeted by pentoxifylline. In addition, we provided evidence that macrophage targeting may be an emerging strategy for NAFL treatment.

Network Pharmacology Analysis and Experimental Validation to Explore the Anti-inflammatory Mechanism of Asiatic Acid on Alcoholic Steatohepatitis.

Objective The mechanism of action of asiatic acid (AA) on alcoholic steatohepatitis (ASH) was investigated using network pharmacology and experiments. Methods Through data retrieval, network construction, and enrichment analysis, the potential mechanism of AA in the treatment of alcoholic steatohepatitis was explored. Animal and cell models were established in this study. Animal Model. The mouse model was divided into six groups: normal group; model group; low, medium, and high AA group; and silibinin-positive group. Cell Model. An in vitro inflammatory model of RAW264.7 cells was established by alcohol stimulation. Results Compared with the model group, the low, medium, and high AA group showed decreased serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), triglyceride (TG), and total cholesterol (T-CHO). The inflammatory factor tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), and interleukin 6 (IL-6) in a dose-dependent manner were decreased. In addition, hematoxylin-eosin staining showed that liver tissue damage and inflammatory cell infiltration in mice were significantly reduced with increasing doses. Further, oil red staining showed that lipid accumulation in hepatocytes in the low, medium, and high AA group was significantly reduced, with increasing dose. In addition, in the cellular model, real-time reverse transcriptase-polymerase chain reaction (Real-Time RT-PCR) and enzyme-linked immunosorbent assay (ELISA) results showed that AA could alleviate alcohol-induced cellular inflammation, while western blot and immunofluorescence results showed that AA might alleviate alcohol-induced cellular inflammation by inhibiting the nuclear factor-κB (NF-κB) pathway. Conclusion This study provides multiple lines of evidence that asiatic acid may alleviate alcoholic hepatitis in mice by modulating the NF-κB pathway.

Role of lysosomal acid lipase in PPAR-mediated reduction of lipid accumulation in hepatocytes

Background and Aims : Lysosomal acid lipase (LAL) catalyzes the hydrolysis of cholesteryl esters and triglycerides in the lysosomal compartment. Recently, it was shown that NAFLD patients can develop an acquired LAL deficiency which is rescued by PPAR-alpha activation. Aim of the study was to investigate the role of other isoform-specific and dual PPAR agonists on lipid accumulation and LAL activity using an in vitro model of steatosis.

The aqueous extract of Phragmites rhizome improves hepatic steatosis in obese mice via the AMPK-mediated inhibition of ER stress

Phragmites rhizome has been documented to have antioxidative stress and anti-inflammation properties in several pathogenic models. We aimed to investigate the therapeutic effects and molecular mechanism of the aqueous extract of Phragmites rhizome (AP) in in vitro and in vivo hepatic steatosis models. We found that treatment with AP dose-dependently reduced lipid accumulation and endoplasmic reticulum (ER) stress in palmitate-treated human primary hepatocytes and attenuated hepatic steatosis and ER stress in high-fat diet (HFD)-fed mice. AMPK phosphorylation and autophagy markers in hepatocytes were augmented by AP. siRNA targeting AMPK or 3-methyladenine (3-MA) abolished the impacts of AP on palmitate-treated hepatocytes. These results suggest that AP treatment suppresses hepatic ER stress through AMPK/autophagy signaling, leading to attenuation of hepatic steatosis. The present study may provide a novel therapeutic approach for treating nonalcoholic fatty liver disease (NAFLD) and ER stress-mediated metabolic diseases using natural substances.

Niclosamide Exposure at Environmentally Relevant Concentrations Efficaciously Inhibited the Growth and Disturbed the Liver-Gut Axis of Adult Male Zebrafish.

In the current study, adult male zebrafish fed a normal diet (ND) or high-fat diet (HFD) were exposed to niclosamide (NIC) at environmentally relevant concentrations to reveal the accumulation and distribution in different tissues and evaluate the effects on liver-gut axis. Chemical analysis indicated that the liver bore a greater burden of NIC compared with the brain and gonads in adult zebrafish, and the HFD-fed fish bore greater burden in their liver and brain than those ND-fed fish. The indications from body weight, growth rate, body mass index, micro-CT images, biochemical and pathological changes confirmed that NIC can efficaciously curb weight gain and improve overloads of in plasma insulin and glucose in HFD-fed zebrafish. However, the potential effects on liver-gut axis in ND-fed zebrafish were also elucidated: NIC disturbed mitochondrial energy production, inhibited the glycemic and triacylglycerol biosynthesis but promoted triacylglycerol and free fatty acid catabolism, therefore reduced lipid accumulation in hepatocytes; NIC also impaired the physical barrier, evoked inflammatory and oxidative stress and led to microbiota dysbiosis in the intestine. There findings highlighted the necessity for evaluating its potential impacts on the health of wild animals as well as human beings upon long-term exposure.

Role of MCPIP1 protein in lipid metabolism, liver homeostasis and non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is characterized by excessive accumulation of lipids in hepatocytes. Among NAFLD patients, in 25% of them this disease progress to nonalcoholic steatohepatitis, which is characterized additionally by the development of inflammation and fibrosis of liver. Currently, it is estimated that 24% of the world’s population suffers from NAFLD. MCPIP1 protein is an RNase described as a negative regulator of inflammation. Also, MCPIP1 plays a role in lipid metabolism because it inhibits the process of adipogenesis and mice with a deletion of Zc3h12a gene are characterized by dyslipidemia and reduced body fat content. In the case of ischemia-reperfusion injury in liver, MCPIP1 is protective against the inflammation and damage of this organ. Lipid accumulation by hepatocytes is associated with a decrease of Mcpip1 level. In addition, MCPIP1 may influence the PPARγ-mediated lipogenesis process. Presence of Mcpip1 in both myeloid leukocytes and liver epithelial cells is crucial for the maintenance of liver homeostasis.

Protective effects of monoammonium glycyrrhizinate on fatty deposit degeneration induced in primary calf hepatocytes by sodium oleate administration in vitro

In this study we investigated the effect of MAG on fatty deposit-induced degeneration of primary calf hepatocytes induced by sodium oleate. Primary hepatocytes were isolated from dairy calves and cultured before allocation to the following treatment groups: control (untreated), model (starved for 12 h before treatment with 0.25 mM sodium oleate to induce steatosis-like changes, and the MAG group pretreated with MAG (0.1, 0.25, 0.5, and 1.5 mM) for 12 h before sodium oleate treatment (0.25 mM) for 12 h). To evaluate the effect of MAG on fat-induced degradation of primary hepatocytes, we evaluated lipid deposition, cell viability, apoptosis rate, alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity in the culture supernatant, and expression of oxidant and antioxidant enzymes (LDH, MDA, GSH, and CAT), as well as the expression of lipid metabolism-related genes (PPARα, SREBP-1c, ChREBP, CPT1, CPT2, and MTP) and apoptosis-related genes (Cyt-c, Caspase 9, Caspase 8, Caspase 3, Bax, and Bcl-2). MAG significantly reduced lipid accumulation in hepatocytes induced by sodium oleate (P < 0.05), increased cell viability, decreased the apoptosis rate (P < 0.05), and significantly decreased ALT and AST activity in the culture supernatant (P < 0.05). MAG significantly decreased MDA levels in cells and LDH levels in the culture supernatant, while GSH and CAT levels were increased (P < 0.05). MAG significantly increased the expression of the lipid transport- and metabolism-related genes MTP, PPARα, CPT1 and CPT2, and decreased ChREBP expression (P < 0.05). At concentrations higher than 0.25 mM, MAG significantly decreased SREBP-1c expression (P < 0.05). MAG significantly decreased the expression of the apoptosis-related genes Cyt-c, Caspase 9, Caspase 8, Caspase3 and Bax, while Bcl-2 expression was increased (P < 0.05). These findings demonstrate that MAG improves the antioxidant capacity of hepatocytes and effectively reduces lipid deposition by inhibiting the expression of lipid metabolism- and apoptosis-related genes.

Tyrosol Ameliorates Liver Inflammatory Response in a Mouse Model of Nonalcoholic Fatty Liver Disease (NFALD) by Regulating JAK1/STAT3

Nonalcoholic fatty liver disease (NAFLD) is becoming one of the major health issues globally. NAFLD is usually associated with obesity and other metabolic syndromes, and there is no specific cure to address this issue so far. Featured by lipid accumulation in hepatocytes, and later progressing to fibrosis, inflammatory responses are involved in the various levels of the pathological changes. In the present study, we added a natural compound, tyrosol, which in our previous study had demonstrated anti-inflammatory properties, to a high-fat diet-induced NAFLD mouse model and investigated whether tyrosol could mitigate the liver damage by attenuating the inflammation response. The treatment with tyrosol significantly improved the liver function and decreased the fasting glucose level in NAFLD mice. Morphologically, our results showed that tyrosol could reduce the fat deposition and lipid droplets accumulation in liver tissue. The key regulating factors, JAK1 and STAT3, were increased in NAFLD mice, but tyrosol treatment could effectively prevent the upregulation. The expression levels of pro-inflammatory cytokine genes in liver tissue of the NAFLD mice were upregulated, which could be effectively prevented by the treatment with tyrosol. Overall, in the high-fat diet-induced NAFLD mouse model, tyrosol could improve the liver function and, more importantly, ameliorate the inflammatory response triggered by the high-fat diet. Although our data here are consistent with the previous report that tyrosol could exert beneficial effects on the NAFLD animal model, we also provide solid evidence that tyrosol is able to conquer the inflammatory response in liver, which is related to the high-fat-diet feeding. Tyrosol could be a promising candidate for the treatment of NAFLD in the future.

Dietary supplementation of salidroside alleviates liver lipid metabolism disorder and inflammatory response to promote hepatocyte regeneration via PI3K/AKT/Gsk3-β pathway

Fatty liver hemorrhagic syndrome (FLHS) is a chronic hepatic disease which occurs when there is a disorder in lipid metabolism. FLHS is often observed in caged laying hens and characterized by a decrease in egg production and dramatic increase of mortality. Salidroside (SDS) is an herbal drug which has shown numerous pharmacological activities, such as protecting mitochondrial function, attenuating cell apoptosis and inflammation, and promoting antioxidant defense system. We aimed to determine the therapeutic effects of SDS on FLHS in laying hens and investigate the underlying mechanisms through which SDS operates these functions. We constructed oleic acid (OA)-induced fatty liver model in vitro and high-fat diet-induced FLHS of laying hens in vivo. The results indicated that SDS inhibited OA-induced lipid accumulation in chicken primary hepatocytes, increased hepatocyte activity, elevated the mRNA expression of proliferation related genes PCNA, CDK2, and cyclinD1 and increased the protein levels of PCNA and CDK2 (P < 0.05), as well as decreased the cleavage levels of Caspase-9, Caspase-8, and Caspase-3 and apoptosis in hepatocytes (P < 0.05). Moreover, SDS promoted the phosphorylation levels of PDK1, AKT, and Gsk3-β, while inhibited the PI3K inhibitor (P < 0.05). Additionally, we found that high-fat diet-induced FLHS hens had heavier body weight, liver weight, and abdominal fat weight, and severe steatosis in histology, compared with the control group (Con). However, hens fed with SDS maintained lighter body weight, liver weight, and abdominal fat weight, as well as normal liver without hepatic steatosis. In addition, high-fat diet-induced FLHS hens had high levels of serum total cholesterol (TC), triglyceride (TG), alanine transaminase (ALT), and aspartate aminotransferase (AST) compared to the Con group, however, in the Model+SDS group, the levels of TC, TG, ALT, and AST decreased significantly, whereas the level of superoxide dismutase (SOD) increased significantly (P < 0.05). We also found that SDS significantly decreased the mRNA expression abundance of PPARγ, SCD, and FAS in the liver, as well as increased levels of PPARα and MTTP, and decreased the mRNA expression of TNF-α, IL-1β, IL-6, and IL-8 in the Model+SDS group (P < 0.05). In summary, this study showed that 0.3 mg/mL SDS attenuated ROS generation, inhibited lipid accumulation and hepatocyte apoptosis, and promoted hepatocyte proliferation by targeting the PI3K/AKT/Gsk3-β pathway in OA-induced fatty liver model in vitro, and 20 mg/kg SDS alleviated high-fat-diet-induced hepatic steatosis, oxidative stress, and inflammatory response in laying hens in vivo.

Amelioration of high-fat diet (HFD) + CCl4 induced NASH/NAFLD in CF-1 mice by activation of SIRT-1 using cinnamoyl sulfonamide hydroxamate derivatives: in-silico molecular modelling and in-vivo prediction

Non-alcoholic fatty liver disease (NAFLD) is one of the major hepatic metabolic disorders that occurs because of the accumulation of lipids in hepatocytes in the form of free fatty acids (FFA) and triglycerides (TG) which become non-alcoholic steatohepatitis (NASH). NOTCH-1 receptors act as novel targets for the development of NAFLD/NASH, where overexpression of NOTCH-1 receptor alters the lipid metabolism in hepatocytes leading to NAFLD. SIRT-1 deacetylates the NOTCH-1 receptor and inhibits NAFLD. Hence, computer-aided drug design (CADD) was used to check the SIRT-1 activation ability of cinnamic sulfonyl hydroxamate derivatives (NMJ 1–8), resveratrol, and vorinostat. SIRT-1 (PDB ID: 5BTR) was docked with eight hydroxamate derivatives and vorinostat using Schrödinger software. Based on binding energy obtained (– 26.31 to – 47.34 kcal/mol), vorinostat, NMJ-2, NMJ-3, NMJ-5 were selected for induced-fit docking (IFD) and results were within – 750.70 to – 753.22 kcal/mol. Qikprop tool was used to analyse the pre pharmacokinetic parameters (ADME analysis) of all hydroxamate compounds. As observed in the molecular dynamic (MD) study, NMJ-2, NMJ-3 were showing acceptable results for activation of SIRT-1. Based on these predictions, in-vivo studies were conducted in CF1 mice, where NMJ-3 showed significant (p < 0.05) changes in lipid profile and anti-oxidant parameters (Catalase, SOD, GSH, nitrite, and LPO) and plasma insulin levels. NMJ-3 treatment also reduced inflammation, fibrosis, and necrosis in liver samples.

LncRNA MALAT1 Promotes PPARα/CD36-Mediated Hepatic Lipogenesis in Nonalcoholic Fatty Liver Disease by Modulating miR-206/ARNT Axis.

Long non-coding RNAs (lncRNAs) are known to play crucial roles in nonalcoholic fatty liver disease (NAFLD). This research sought to explore mechanisms by which lncRNA MALAT1 regulates the progression of NAFLD. Thus, in order to detect the function of MALAT1 in NAFLD, in vitro and in vivo model of NAFLD were established. Then, fatty acid uptake and triglyceride level were investigated by BODIPY labeled-fatty acid uptake assay and Oil red O staining, respectively. The expressions of MALAT1, miR-206, ARNT, PPARα and CD36 were detected by western blotting and qPCR. Dual luciferase, RIP and ChIP assay were used to validate the relation among MALAT1, miR-206, ARNT and PPARα. The data revealed expression of MALAT1 was up-regulated in vitro and in vivo in NAFLD, and knockdown of MALAT1 suppressed FFA-induced lipid accumulation in hepatocytes. Meanwhile, MALAT1 upregulated the expression of ARNT through binding with miR-206. Moreover, miR-206 inhibitor reversed MALAT1 knockdown effects in decreased lipid accumulation in FFA-treated hepatocytes. Furthermore, ARNT could inhibit the expression of PPARα via binding with PPARα promoter. Knockdown of MALAT1 significantly upregulated the level of PPARα and downregulated the expression of CD36, while PPARα knockdown reversed these phenomena. MALAT1 regulated PPARα/CD36 -mediated hepatic lipid accumulation in NAFLD through regulation of miR-206/ARNT axis. Thus, MALAT1/miR-206/ARNT might serve as a therapeutic target against NAFLD.

Dectin-1 plays a deleterious role in high fat diet-induced NAFLD of mice through enhancing macrophage activation.

The innate immune response and inflammation contribute to hepatic steatosis and non-alcoholic fatty liver disease (NAFLD). Dectin-1 is a pathogen recognition receptor in innate immunity. In this study, we investigated the role of Dectin-1 in the pathogenesis of NAFLD. We first showed that Dectin-1 expression was significantly elevated in liver tissues of patients with NASH. NAFLD was induced in mice by feeding high fat diet (HFD) for 24 weeks. At the end of treatment, mice were sacrificed, and their blood and liver tissues were collected for analyses. We showed HFD feeding also increased liver Dectin-1 levels in mice, associated with macrophage infiltration. Either gene knockout or co-administration of a Dectin-1 antagonist laminarin (150 mg/kg twice a day, ip, from 16th week to 24th week) largely protected the livers from HFD-induced lipid accumulation, fibrosis, and elaboration of inflammatory responses. In primary mouse peritoneal macrophages (MPMs), challenge with palmitate (PA, 200 μM), an abundant saturated fatty acid found in NAFLD, significantly activated Dectin-1 signaling pathway, followed by transcriptionally regulated production of pro-inflammatory cytokines. Dectin-1 was required for hepatic macrophage activation and inflammatory factor induction. Condition media generated from Dectin-1 deficient macrophages failed to cause hepatocyte lipid accumulation and hepatic stellate activation. In conclusion, this study provides the primary evidence supporting a deleterious role for Dectin-1 in NAFLD through enhancing macrophage pro-inflammatory responses and suggests that it can be targeted to prevent inflammatory NAFLD.

Mechanisms of ductular reaction in non-alcoholic steatohepatitis.

Non-alcoholic fatty liver disease (NAFLD) is a disease spectrum caused in part by insulin resistance and genetic predisposition. This disease is primarily characterized by excessive lipid accumulation in hepatocytes in the absence of alcohol abuse and other causes of liver damage. Histologically, NAFLD is divided into several periods: simple steatosis, non-alcoholic steatohepatitis (NASH), hepatic fibrosis, cirrhosis, and hepatocellular carcinoma. With the increasing prevalence of obesity and hyperlipidemia, NAFLD has become the main cause of chronic liver disease worldwide. As a result, the pathogenesis of this disease is drawing increasing attention. Ductular reaction (DR) is a reactive bile duct hyperplasia caused by liver injury that involves hepatocytes, cholangiocytes, and hepatic progenitor cells. Recently, DR is shown to play a pivotal role in simple steatosis progression to NASH or liver fibrosis, providing new research and treatment options. This study reviews several DR signaling pathways, including Notch, Hippo/YAP-TAZ, Wnt/β-catenin, Hedgehog, HGF/c-Met, and TWEAK/Fn14, and their role in the occurrence and development of NASH.

Upregulation of hepatic CD36 via glucocorticoid receptor activation contributes to dexamethasone-induced liver lipid metabolism disorder in mice

Glucocorticoids such as dexamethasone (DEX) are widely prescribed to treat numerous conditions and diseases. However, glucocorticoid-induced liver lipid metabolism disorder, even nonalcoholic fatty liver disease, has caused extensive attention. Since fatty acid transporters such as CD36 and FATP play crucial roles in hepatic fatty acid uptake, this work examined their potential involvement in DEX-induced liver lipid accumulation. Chronic DEX administration (1–5 mg/kg/day over 28 days) induced hepatic lipid accumulation in mice. Fatty acid uptake in HepG2 cells and mouse primary hepatocytes was also stimulated after incubation with 0.5–2 μM DEX. Meanwhile, qPCR and western blotting demonstrated dose-dependent upregulation of CD36 expression by DEX in the mouse liver and in cultured hepatocytes. Glucocorticoid receptor (GR) inhibition with mifepristone (RU486) and siRNA-mediated GR knockdown attenuated lipid accumulation in hepatocytes by inhibiting DEX-induced CD36 upregulation, and direct binding of GR to the CD36 promoter was demonstrated by luciferase reporter and chromatin immunoprecipitation assays. These results indicate that DEX promotes free fatty acid uptake leading to hepatic steatosis by upregulating CD36 expression via activation of GR. Thus, strategies aimed at inhibiting GR/CD36 expression or activity might help prevent or reduce the onset and progression of hepatic lipid metabolism disorders induced by glucocorticoid drugs.

DDX17 protects hepatocytes against oleic acid/palmitic acid-induced lipid accumulation

Hepatic lipid accumulation is an initiation factor in fatty liver disease, and promoting a reduction in hepatic lipid accumulation is an important treatment strategy. DEAD box RNA helicase 17 (DDX17) is a member of the DEAD-box family and a molecular chaperone. Previous studies have demonstrated that DDX17 is a transcriptional coregulator of tumorigenesis, inflammation, and macrophage cholesterol efflux. The liver is the main site for lipid metabolism, and metabolic (dysfunction)-associated fatty liver disease (MAFLD) is one of the most common chronic liver diseases. However, the impact of DDX17 on hepatic lipid accumulation has not been verified. In this study, we found, for the first time, that oleic acid/palmitic acid (OA/PA)-induced lipid accumulation was largely abrogated by DDX17 overexpression in both HepG2 (a human hepatocellular carcinoma line) and Hep1-6 (a murine hepatocellular carcinoma line) cells, and this effect was due to a marked reduction in cellular triglyceride (TG) content. Moreover, the overexpression of DDX17 was accompanied by a significant decrease in the expression of genes involved in de novo fatty acid synthesis (FAS, ACC, and SCD-1) in both HepG2 and Hep1-6 cells. In conclusion, DDX17 protected against OA/PA-induced lipid accumulation in hepatocytes through de novo lipogenesis inhibition.

Calycosin-7-O-β-D-glucoside attenuates palmitate-induced lipid accumulation in hepatocytes through AMPK activation

Calycosin-7-O-β-D-glucoside (CG) is the major component of Astragali Radix (AR), a traditional Chinese drug. As reported, CG could attenuate cerebral ischemia/reperfusion injury, protect blood-brain barrier integrity, and ameliorate myocardial infarction. To date, whether CG has a protective effect on metabolic diseases remains to be elucidated. In the present study, CG could attenuate palmitate-induced lipid accumulation in hepatocytes in a dose-dependent manner, with down-regulation of lipogenesis related genes expression and up-regulation of lipids β-oxidation related genes expression. CG could decrease the triglyceride (TG) content from 0.30 mmol/g protein to 0.21 mmol/g protein and reduce the total cholesterol (TC) content from 0.39 mmol/g protein to 0.26 mmol/g protein. Moreover, CG stimulated the phosphorylation of AMP-activated protein kinase (AMPK), and the protective effect of CG on hepatocytes was partially reversed both by the inhibitor of AMPK signaling pathway and overexpression of AMPK-DN. Our findings revealed that CG could ameliorate palmitate-induced lipids accumulation in hepatocytes via AMPK activation and it may be a promising therapeutic medicine for hepatic steatosis.