HDMCP uncouples yeast mitochondrial respiration and alleviates steatosis in L02 and hepG2 cells by decreasing ATP and H2O2 levels: a novel mechanism for NAFLD

Deficiency of the mitochondrial transporter SLC25A47 minimally impacts hepatic lipid metabolism in fasted and diet-induced obese mice

OBJECTIVE

The peroxisome proliferator-activated receptor-alpha (PPARα) plays a central role in lipid metabolism in the liver by stimulating the expression of hundreds of genes. Accordingly, regulation by PPARα could be a screening tool to identify novel genes involved in hepatic lipid metabolism. Previously, the mitochondrial transporter SLC25A47 was suggested to play a role in energy metabolism and liver-specific uncoupling, but further research is lacking.

METHODS

We explored the potential role of SLC25A47 through in vitro studies and using mice overexpressing and lacking SLC25A47.

RESULTS

SLC25A47 was identified as a PPARα-regulated and fasting-induced gene in human and mouse hepatocytes. Adenoviral-mediated overexpression of SLC25A47 minimally impacted metabolic parameters during fasting and high-fat feeding. During high-fat feeding, SLC25A47 ablation also did not influence any metabolic parameters, apart from a minor improvement in glucose tolerance. In fasted mice, SLC25A47 ablation was associated with modest, reproducible, and likely indirect reductions in plasma triglycerides and glycerol. SLC25A47 ablation did not influence energy expenditure. Depending on the nutritional status, metabolomic analysis showed modest alterations in plasma, liver, and hepatic mitochondrial levels of various metabolites related to amino acid metabolism, TCA cycle, and fatty acid metabolism. No major and consistent alterations in levels of specific metabolites were found that establish the substrate for and function of SLC25A47.

CONCLUSION

Collectively, our results hint at a role of SLC25A47 in amino acid and fatty acid metabolism, yet suggest that SLC25A47 is dispensable for hepatic lipid homeostasis during fasting and high-fat feeding.

Hepatic mitochondrial NAD + transporter SLC25A47 activates AMPKα mediating lipid metabolism and tumorigenesis

BACKGROUND AIMS

SLC25A47 was initially identified as a mitochondrial HCC-downregulated carrier protein, but its physiological functions and transport substrates are unknown. We aimed to investigate the physiological role of SLC25A47 in hepatic metabolism.

APPROACH RESULTS

In the treatment of hepatocytes with metformin, we found that metformin can transcriptionally activate the expression of Slc25a47 , which is required for AMP-activated protein kinase α (AMPKα) phosphorylation. Slc25a47 -deficient mice had increased hepatic lipid content, triglycerides, and cholesterol levels, and we found that Slc25a47 deficiency suppressed AMPKα phosphorylation and led to an increased accumulation of nuclear SREBPs, with elevated fatty acid and cholesterol biosynthetic activities. Conversely, when Slc25a47 was overexpressed in mouse liver, AMPKα was activated and resulted in the inhibition of lipogenesis. Moreover, using a diethylnitrosamine-induced mouse HCC model, we found that the deletion of Slc25a47 promoted HCC tumorigenesis and development through the activated mammalian target of rapamycin cascade. Employing homology modeling of SLC25A47 and virtual screening of the human metabolome database, we demonstrated that NAD + was an endogenous substrate for SLC25A47, and the activity of NAD + -dependent sirtuin 3 declined in Slc25a47 -deficient mice, followed by inactivation of AMPKα.

CONCLUSIONS

Our findings reveal that SLC25A47, a hepatocyte-specific mitochondrial NAD + transporter, is one of the pharmacological targets of metformin and regulates lipid homeostasis through AMPKα, and may serve as a potential drug target for treating NAFLD and HCC.

The Slc25a47 locus is a novel determinant of hepatic mitochondrial function implicated in liver fibrosis

BACKGROUND & AIMS

Transporters of the SLC25 mitochondrial carrier superfamily bridge cytoplasmic and mitochondrial metabolism by channeling metabolites across mitochondrial membranes and are pivotal for metabolic homeostasis. Despite their physiological relevance as gatekeepers of cellular metabolism, most of the SLC25 family members remain uncharacterized. We undertook a comprehensive tissue distribution analysis of all Slc25 family members across metabolic organs and identified SLC25A47 as a liver-specific mitochondrial carrier.

METHODS

We used a murine loss-of-function model to unravel the role of this transporter in mitochondrial and hepatic homeostasis. We performed extensive metabolic phenotyping and molecular characterization of newly generated Slc25a47^hep-/- and Slc25a47-Fgf21^hep-/- mice.

RESULTS

Slc25a47^hep-/- mice displayed a wide variety of metabolic abnormalities, as a result of sustained energy deficiency in the liver originating from impaired mitochondrial respiration. This mitochondrial phenotype was associated with an activation of the mitochondrial stress response (MSR) in the liver, and the development of fibrosis, which was exacerbated upon feeding a high-fat high-sucrose diet. The MSR induced the secretion of several mitokines, amongst which FGF21 played a preponderant role on systemic physiology. To dissect the FGF21-dependent and -independent physiological changes induced in Slc25a47^hep-/- mice, we generated a double Slc25a47-Fgf21^hep-/- mouse model and demonstrated that several aspects of the hypermetabolic state were driven by hepatic secretion of FGF21. On the other hand, the metabolic fuel inflexibility observed in Slc25a47^hep-/- mice could not be rescued with the genetic removal of Fgf21.

CONCLUSION

Collectively, our data place the Slc25a47 locus at the center of mitochondrial homeostasis, which upon dysfunction triggers robust liver-specific and systemic adaptive stress responses. The prominent role of the Slc25a47 locus in hepatic fibrosis identifies this carrier, or its transported metabolite, as a potential target for therapeutic intervention.

LAY SUMMARY

Herein, we report the importance of a locus containing a liver-specific gene coding for a mitochondrial transport protein called SLC25A47. Mitochondria are the powerhouses of cells. They are crucial for metabolism and energy generation. We show that mice with genetic disruption of the Slc25a47 locus cannot maintain mitochondrial homeostasis (balance), leading to wide-ranging problems in the liver that have far-reaching physiological consequences.

Oxidative Stress-A Key Player in the Course of Alcohol-Related Liver Disease

Oxidative stress is known to be an inseparable factor involved in the presentation of liver disorders. Free radicals interfere with DNA, proteins, and lipids, which are crucial in liver metabolism, changing their expression and biological functions. Additionally, oxidative stress modifies the function of micro-RNAs, impairing the metabolism of hepatocytes. Free radicals have also been proven to influence the function of certain transcriptional factors and to alter the cell cycle. The pathological appearance of alcohol-related liver disease (ALD) constitutes an ideal example of harmful effects due to the redox state. Finally, ethanol-induced toxicity and overproduction of free radicals provoke irreversible changes within liver parenchyma. Understanding the underlying mechanisms associated with the redox state in the course of ALD creates new possibilities of treatment for patients. The future of hepatology may become directly dependent on the effective action against reactive oxygen species. This review summarizes current data on the redox state in the natural history of ALD, highlighting the newest reports on this topic.

Inducible hepatic expression of CREBH mitigates diet-induced obesity, insulin resistance, and hepatic steatosis in mice

Cyclic AMP-responsive element-binding protein H (CREBH encoded by Creb3l3) is a transcription factor that regulates the expression of genes that control lipid and glucose metabolism as well as inflammation. CREBH is upregulated in the liver under conditions of overnutrition, and mice globally lacking the gene (CREBH-/-) are highly susceptible to diet-induced obesity, insulin resistance, and hepatic steatosis. The net protective effects of CREBH have been attributed in large part to the activities of fibroblast growth factor (Fgf)-21 (Fgf21), a target gene that promotes weight loss, improves glucose homeostasis, and reduces hepatic lipid accumulation. To explore the possibility that activation of the CREBH-Fgf21 axis could ameliorate established effects of high-fat feeding, we generated an inducible transgenic hepatocyte-specific CREBH overexpression mouse model (Tg-rtTA). Acute overexpression of CREBH in livers of Tg-rtTA mice effectively reversed diet-induced obesity, insulin resistance, and hepatic steatosis. These changes were associated with increased activities of thermogenic brown and beige adipose tissues in Tg-rtTA mice, leading to reductions in fat mass, along with enhanced insulin sensitivity and glucose tolerance. Genetically silencing Fgf21 in Tg-rtTA mice abrogated the CREBH-mediated reductions in body weight loss, but only partially reversed the observed improvements in glucose metabolism. These findings reveal that the protective effects of CREBH activation may be leveraged to mitigate diet-induced obesity and associated metabolic abnormalities in both Fgf21-dependent and Fgf21-independent pathways.

Computational studies of the mitochondrial carrier family SLC25. Present status and future perspectives

The members of the mitochondrial carrier family, also known as solute carrier family 25 (SLC25), are transmembrane proteins involved in the translocation of a plethora of small molecules between the mitochondrial intermembrane space and the matrix. These transporters are characterized by three homologous domains structure and a transport mechanism that involves the transition between different conformations. Mutations in regions critical for these transporters’ function often cause several diseases, given the crucial role of these proteins in the mitochondrial homeostasis. Experimental studies can be problematic in the case of membrane proteins, in particular concerning the characterization of the structure–function relationships. For this reason, computational methods are often applied in order to develop new hypotheses or to support/explain experimental evidence. Here the computational analyses carried out on the SLC25 members are reviewed, describing the main techniques used and the outcome in terms of improved knowledge of the transport mechanism. Potential future applications on this protein family of more recent and advanced in silico methods are also suggested.

Oxidative stress in alcohol-related liver disease

Alcohol consumption is one of the leading causes of the global burden of disease and results in high healthcare and economic costs. Heavy alcohol misuse leads to alcohol-related liver disease, which is responsible for a significant proportion of alcohol-attributable deaths globally. Other than reducing alcohol consumption, there are currently no effective treatments for alcohol-related liver disease. Oxidative stress refers to an imbalance in the production and elimination of reactive oxygen species and antioxidants. It plays important roles in several aspects of alcohol-related liver disease pathogenesis. Here, we review how chronic alcohol use results in oxidative stress through increased metabolism via the cytochrome P450 2E1 system producing reactive oxygen species, acetaldehyde and protein and DNA adducts. These trigger inflammatory signaling pathways within the liver leading to expression of pro-inflammatory mediators causing hepatocyte apoptosis and necrosis. Reactive oxygen species exposure also results in mitochondrial stress within hepatocytes causing structural and functional dysregulation of mitochondria and upregulating apoptotic signaling. There is also evidence that oxidative stress as well as the direct effect of alcohol influences epigenetic regulation. Increased global histone methylation and acetylation and specific histone acetylation inhibits antioxidant responses and promotes expression of key pro-inflammatory genes. This review highlights aspects of the role of oxidative stress in disease pathogenesis that warrant further study including mitochondrial stress and epigenetic regulation. Improved understanding of these processes may identify novel targets for therapy.

Antagonizing circRNA_002581-miR-122-CPEB1 axis alleviates NASH through restoring PTEN-AMPK-mTOR pathway regulated autophagy

Circular RNAs (circRNAs) have been shown to play critical roles in cancer biology, but their functions in nonalcoholic steatohepatitis (NASH) remain unexplored. Full length of circRNA_002581 was amplified and sequenced, followed by RNA immunoprecipitation, RNA-Fluorescence in Situ Hybridization and dual luciferase reporter gene analysis to confirm the existence of the circRNA_002581–miR-122–CPEB1 regulatory axis in vitro. CircRNA_002581 knockdown was used to study its roles in high concentration of free fatty acids-induced NASH-like cell model and a methionine and choline deficiency (MCD) diet-induced NASH mice model. Autophagy flux and related potential PTEN–AMPK–mTOR pathway were tested by western blot. CircRNA_002581 overexpression significantly relieved the inhibitory role of miR-122 on its target CPEB1 by sponging miR-122. CircRNA_002581 knockdown markedly attenuated lipid droplet accumulation, reduced the levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), pro-inflammatory cytokines, apoptosis, H₂O₂, and increased ATP level in both mice and cellular models of NASH. Mechanistically, circRNA_002581 interference significantly rescue the defective autophagy evidenced by increased autophagosome number, upregulated LC3-II/I level, and decreased p62 level. Further chloroquine-mediated total autophagy inhibition antagonizes the protective effect of circRNA_002581 knockdown. Finally, CPEB1–PTEN–AMPK–mTOR pathway is shown to link the autophagy and circRNA_002581 knockdown-mediated NASH alleviation. CircRNA_002581–miR-122–CPEB1 axis actively participates in the pathogenesis of NASH through PTEN–AMPK–mTOR pathway-related autophagy suppression. Targeting circRNA_002581 is a potential therapeutic strategy for NASH through partial autophagy restoration.

Lotus Seedpod Extracts Reduced Lipid Accumulation and Lipotoxicity in Hepatocytes

Non-alcoholic fatty liver disease (NAFLD) is closely associated with metabolic disorders, including hepatic lipid accumulation and lipotoxicity. Plant-derived polyphenols have attracted considerable attention in the prevention of NAFLD. Lotus seedpod, rich in polyphenols, is a traditional Chinese herbal medicine. Previous studies have showed that lotus seedpod possess radioprotective, antioxidant, anti-cancer, and anti-inflammatory activities. In this study, the in vitro hepatoprotective effect of lotus seedpod extract (LSE) and its main component epigallocatechin (EGC) was examined. Firstly, oleic acid (OA), an unsaturated fatty acid, was used to induce the phenotype of NAFLD in human hepatocytes, HepG2 cells. LSE dose-dependently improved the OA-induced viability loss of HepG2 cells. Non-cytotoxic concentrations of LSE or EGC abolished intracellular lipid accumulation and oxidative stress in the OA-treated cells. In addition, LSE and EGC showed a minor effect on autophagy, and potential in reducing OA-induced occurrence of apoptosis confirmed by morphological and biochemical features, including an increase in the formation of apoptotic bodies, the exposure of phosphatidylserine, and activation of caspases. Molecular data showed the anti-apoptotic effect of LSE might be mediated via downregulation of the mitochondrial pathway. Our data imply that EGC-enriched LSE potentially could be developed as an anti-NAFLD agent.

Multi-omics insights into functional alterations of the liver in insulin-deficient diabetes mellitus

OBJECTIVE

The liver regulates the availability of insulin to other tissues and is the first line insulin response organ physiologically exposed to higher insulin concentrations than the periphery. Basal insulin during fasting inhibits hepatic gluconeogenesis and glycogenolysis, whereas postprandial insulin peaks stimulate glycogen synthesis. The molecular consequences of chronic insulin deficiency for the liver have not been studied systematically.

METHODS

We analyzed liver samples of a genetically diabetic pig model (MIDY) and of wild-type (WT) littermate controls by RNA sequencing, proteomics, and targeted metabolomics/lipidomics.

RESULTS

Cross-omics analyses revealed increased activities in amino acid metabolism, oxidation of fatty acids, ketogenesis, and gluconeogenesis in the MIDY samples. In particular, the concentrations of the ketogenic enzyme 3-hydroxy-3-methylglutaryl-CoA synthase 2 (HMGCS2) and of retinol dehydrogenase 16 (RDH16), which catalyzes the first step in retinoic acid biogenesis, were highly increased. Accordingly, elevated levels of retinoic acid, which stimulates the expression of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PCK1), were measured in the MIDY samples. In contrast, pathways related to extracellular matrix and inflammation/pathogen defense response were less active than in the WT samples.

CONCLUSIONS

The first multi-omics study of a clinically relevant diabetic large animal model revealed molecular signatures and key drivers of functional alterations of the liver in insulin-deficient diabetes mellitus. The multi-omics data set provides a valuable resource for comparative analyses with other experimental or clinical data sets.

Protective effects of cichoric acid on H2O2-induced oxidative injury in hepatocytes and larval zebrafish models

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease with a broad spectrum of liver injury. Oxidant stress is believed to be the pathogenesis of NAFLD as the "second hit". Hydrogen peroxide is widely used as an oxidant reagent to induce the oxidant injury of cells and larval zebrafish. Recently, cichoric acid is being studied extensively for its obesity attenuating, hepatic steatosis reduction and anti-oxidant effects. In this study, to identify whether CRA could protect the H₂O₂ induced oxidant injury via anti-oxidant impact by using L02 and HepG2 hepatocytes as in vitro and larval zebrafish as in vivo injury models, and evaluated the protective and anti-oxidant effects of CRA by pretreated it on both in vitro and in vivo models. CRA was found to reduce the production of ROS and MDA, activate the anti-oxidant enzymes SOD and GSH-px, and pathways Keap1-Nrf2 and HO-1. These results demonstrated that CRA might protect the liver injury by its anti-oxidant effect, which could be a potential therapeutic agent of NAFLD.

Association between urine retinol-binding protein levels and nonalcoholic fatty liver disease: A cross-sectional study in Chinese population

OBJECTIVE

The prevalence of nonalcoholic fatty liver disease (NAFLD) has been rapidly increased, becoming a public health problem worldwide. Our objective was to investigate the association between urine retinol-binding protein (RBP) and NAFLD in a Chinese population and develop a multivariate logistic regression model for NAFLD prediction.

METHODS

A total of 317 NAFLD patients and 391 healthy controls were enrolled in this cross-sectional study based on inclusion and exclusion criteria, from whom fasting urine and blood were collected for further study. Urine RBP level and other parameters were measured and compared between NAFLD subjects and controls.

RESULTS

Urine RBP levels (expressed by RBP/creatinine ratio) in NAFLD patients were significantly higher than controls (median 133.1 mg/g vs 110.7 mg/g; P < .001). Urine RBP/creatinine ratio was verified as an independent factor for NAFLD prediction after adjustment in multivariate logistic regression. The area under curve (AUC) of receiver operating characteristic (ROC) was 0.889 with the 95% confidence interval from 0.867 to 0.912.With a cutoff point of 0.215, the sensitivity and specificity of urine RBP/creatinine ratio in NAFLD prediction were 81.1% and 84.5%, respectively.

CONCLUSION

Our results demonstrated that urine RBP/creatinine ratio was an independent risk factor for NAFLD while the predictive model for NAFLD diagnosis is noninvasive with high sensitivity and specificity.

MiR-30e-UCP2 pathway regulates alcoholic hepatitis progress by influencing ATP and hydrogen peroxide expression

To investigate the expression of miR-30e-UCP2 pathway in different stages of alcoholic liver disease (ALD) and its capacity and mechanism in regulating alcoholic hepatitis (AH) progress. C57BL/6 mice were fed with Lieber-DeCaril (LD) diet for 4 and 12 weeks to establish models of alcoholic fat infiltration (AFI) and AH. Based on AFI feeding, the alcoholic hepatic fibrosis (AHF) was set up with additional 4 weeks 5% carbon tetrachloride intra-abdominal injection twice per week. Serum lipid and inflammation related makers were detected while H-E staining for hepatic steatosis/ inflammation and Sirius staining for hepatic fibrosis were conducted. The apoptosis degree was tested by TUNEL plot while the hydrogen peroxide (H2O2) and ATP levels were tested by colorimetric method. MiR-30e and UCP2 over-expression were carried out by synthesizing miR-30e mimic and inserting UCP2 sequence into pCDNA3.1 plasmid. Different stages of ALD were established as indicated by increased serum TG, Tch, ALT, AST, apoptosis degree and hyaluronic acid levels as well as the typical lipid deposition, inflammatory cell infiltration and fibrosis formation in AFI, AH and AHF stages. A stepwise decreased miR-30e and increased UCP2 level was identified from AFI to AHF (p<0.05). MiR-30e over-expression significantly decreased UCP2 level. After successful miR-30e over-expression in AH, its inflammation level was decreased, followed by significantly increased ATP and H2O2 levels. Therefore, MiR-30e-UCP2 pathway participates in different stages of ALD and its therapeutic effect on AH may be through influencing oxidative stress and energy metabolism.

Expression and putative role of mitochondrial transport proteins in cancer

Cancer cells undergo major changes in energy and biosynthetic metabolism. One of them is the Warburg effect, in which pyruvate is used for fermentation rather for oxidative phosphorylation. Another major one is their increased reliance on glutamine, which helps to replenish the pool of Krebs cycle metabolites used for other purposes, such as amino acid or lipid biosynthesis. Mitochondria are central to these alterations, as the biochemical pathways linking these processes run through these organelles. Two membranes, an outer and inner membrane, surround mitochondria, the latter being impermeable to most organic compounds. Therefore, a large number of transport proteins are needed to link the biochemical pathways of the cytosol and mitochondrial matrix. Since the transport steps are relatively slow, it is expected that many of these transport steps are altered when cells become cancerous. In this review, changes in expression and regulation of these transport proteins are discussed as well as the role of the transported substrates. This article is part of a Special Issue entitled Mitochondria in Cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.

8-Methoxypsoralen disrupts MDR3-mediated phospholipids efflux and bile acid homeostasis and its relevance to hepatotoxicity

Since its discovery in 1987, multidrug resistance 3 P-glycoprotein (MDR3) had recognized to play a crucial role in the translocation of phospholipids from the inner to outer leaflets of bile canalicular membranes. An increasing number of reports suggest that drug-mediated functional disruption of MDR3 is responsible for drug-induced cholestasis. 8-Methoxypsoralen (8-MOP) is used clinically to treat psoriasis, vitiligo and other skin disorders. However, psoralens safety for long-term use is a concern. In the current study, we evaluate 8-MOP's potential hepatotoxicity and effects on bile formation. Sprague Dawley (SD) rats were treated daily 200mg/kg or 400mg/kg of 8-MOP orally for 28 days. The result showed a prominent decrease in biliary phospholipids output, which associated with the down-regulation of MDR3. Elevated bile acid serum level and increased biliary bile acid outputs were observed in 8-MOP-treated groups. The disturbance of bile acid homeostasis was associated with changes in enzymes and proteins involved in bile acid synthesis, regulation and transport. Human liver cell line L02 was used to determine on the mRNA and protein levels of MDR3. Cells treated with 8-MOP reveled a decrease in fluorescent PC (phosphatidylcholine) secretion into the pseudocanaliculi (formed between adjacent cells) compared with untreated cells. Our investigation represent the first evidence that 8-MOP can induce cholestatic liver injury by disturbing MDR3-mediated phospholipids efflux and bile acid homeostasis.

Effect of miR-146 targeted HDMCP up-regulation in the pathogenesis of nonalcoholic steatohepatitis

BACKGROUNDS/AIMS

Mitochondrial dysfunction plays an important role inthe pathogenesis of nonalcoholic steatohepatitis (NASH), where uncoupling protein (UCP) is actively involved. We previously reported the uncoupling activity of HDMCP and its role in liver steatosis. We now aim to investigate the degree and therapeutic effect of HDMCP in NASH and the regulatory role of miR-146 on HDMCP.

METHODS

NASH animal model was established by feeding BALB/c mice with MCD diet while L02 cell was cultured with high concentration of fatty acid (HFFA) for 72h to mimic the steatosis and inflammation of NASH in-vitro appearance. The steatosis level was assessed by H-E/oil-red staining and serum/supernatant marker detection. The inflammation activity was evaluated by levels of Hepatic activity index, transwell, apoptosis degree (TUNEL/flow cytometry) and serum/supernatant marker. HDMCP level was detected by western blot and miRNA expression was tested by qRT-PCR. NASH severity change was recorded after RNA interference while the regulatory role of miR-146 on HDMCP was confirmed by dual luciferase report system. The H2O2 and ATP levels were measured for mechanism exploration.

RESULTS

Increased HDMCP expression was identified in NASH animal model and HFFA-72h cultured L02 cell. Moreover, under regulation of miR-146, NASH alleviation was achieved after HDMCP downregulation in both in vivo and in vitro, according to the declination of steatosis and inflammation related markers. Though H2O2 and ATP levels were increased and decreased in NASH models, HDMCP down regulation both increased their levels.

CONCLUSIONS

The miR-146-HDMCP-ATP/H2O2 pathway may provide novel mechanism and treatment option for NASH.

miRNA-133a-UCP2 pathway regulates inflammatory bowel disease progress by influencing inflammation, oxidative stress and energy metabolism

AIM

To investigate the role of the miR-133a-UCP2 pathway in the pathogenesis of inflammatory bowel disease (IBD) and to explore the potential downstream mechanisms with respect to inflammation, oxidative stress and energy metabolism.

METHODS

C57BL/6 mice were fed dextran sulfate sodium (DSS) liquid for 7 consecutive days, followed by the administration of saline to the DSS group, UCP2 siRNA to the UCP2 group and a miR-133a mimic to the miR-133a group on days 8 and 11. Body weight, stool consistency and rectal bleeding were recorded daily, and these composed the disease activity index (DAI) score for the assessment of disease severity. After cervical dislocation was performed on day 14, the length of the colon in each mouse was measured, and colonic tissue was collected for further study, which included the following: haematoxylin and eosin staining, UCP2 and miR-133a detection by immunohistochemical staining, western blot and quantitative real-time PCR, measurement of apoptosis by TUNEL assay, and the assessment of inflammation (TNF-α, IL-1β, IL-6 and MCP1), oxidative stress (H2O2 and MDA) and metabolic parameters (ATP) by ELISA and colorimetric methods.

RESULTS

An animal model of IBD was successfully established, as shown by an increased DAI score, shortened colon length and specific pathologic changes, along with significantly increased UCP2 and decreased miR-133a levels. Compared with the DSS group, the severity of IBD was alleviated in the UCP2 and the miR-133a groups after successful UCP2 knockdown and miR-133a overexpression. The extent of apoptosis, as well as the levels of TNF-α, IL-1β, MDA and ATP, were significantly increased in both the UCP2 and miR-133a groups compared with the DSS group.

CONCLUSION

The miR-133a-UCP2 pathway participates in IBD by altering downstream inflammation, oxidative stress and markers of energy metabolism, which provides novel clues and potential therapeutic targets for IBD.

The Pathogenesis of Nonalcoholic Fatty Liver Disease: Interplay between Diet, Gut Microbiota, and Genetic Background

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world, and it comprises a spectrum of hepatic abnormalities from simple hepatic steatosis to steatohepatitis, fibrosis, cirrhosis, and liver cancer. While the pathogenesis of NAFLD remains incompletely understood, a multihit model has been proposed that accommodates causal factors from a variety of sources, including intestinal and adipose proinflammatory stimuli acting on the liver simultaneously. Prior cellular and molecular studies of patient and animal models have characterized several common pathogenic mechanisms of NAFLD, including proinflammation cytokines, lipotoxicity, oxidative stress, and endoplasmic reticulum stress. In recent years, gut microbiota has gained much attention, and dysbiosis is recognized as a crucial factor in NAFLD. Moreover, several genetic variants have been identified through genome-wide association studies, particularly rs738409 (Ile748Met) in PNPLA3 and rs58542926 (Glu167Lys) in TM6SF2, which are critical risk alleles of the disease. Although a high-fat diet and inactive lifestyles are typical risk factors for NAFLD, the interplay between diet, gut microbiota, and genetic background is believed to be more important in the development and progression of NAFLD. This review summarizes the common pathogenic mechanisms, the gut microbiota relevant mechanisms, and the major genetic variants leading to NAFLD and its progression.

Bioenergetic cues shift FXR splicing towards FXRα2 to modulate hepatic lipolysis and fatty acid metabolism

Objective

Farnesoid X receptor (FXR) plays a prominent role in hepatic lipid metabolism. The FXR gene encodes four proteins with structural differences suggestive of discrete biological functions about which little is known.

Methods

We expressed each FXR variant in primary hepatocytes and evaluated global gene expression, lipid profile, and metabolic fluxes. Gene delivery of FXR variants to Fxr^−/− mouse liver was performed to evaluate their role in vivo. The effects of fasting and physical exercise on hepatic Fxr splicing were determined.

Results

We show that FXR splice isoforms regulate largely different gene sets and have specific effects on hepatic metabolism. FXRα2 (but not α1) activates a broad transcriptional program in hepatocytes conducive to lipolysis, fatty acid oxidation, and ketogenesis. Consequently, FXRα2 decreases cellular lipid accumulation and improves cellular insulin signaling to AKT. FXRα2 expression in Fxr^−/− mouse liver activates a similar gene program and robustly decreases hepatic triglyceride levels. On the other hand, FXRα1 reduces hepatic triglyceride content to a lesser extent and does so through regulation of lipogenic gene expression. Bioenergetic cues, such as fasting and exercise, dynamically regulate Fxr splicing in mouse liver to increase Fxrα2 expression.

Conclusions

Our results show that the main FXR variants in human liver (α1 and α2) reduce hepatic lipid accumulation through distinct mechanisms and to different degrees. Taking this novel mechanism into account could greatly improve the pharmacological targeting and therapeutic efficacy of FXR agonists.

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FXR variants regulate discrete gene programs with distinct biological outcomes.

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FXRα2 (but not α1) enhances fatty acid handling and insulin responsiveness.

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FXRα1 and α2 reduce liver lipid content through different mechanisms.

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Fasting and physical exercise dynamically regulate Fxr splicing in liver.

Hugan Qingzhi medication ameliorates hepatic steatosis by activating AMPK and PPARα pathways in L02 cells and HepG2 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Hugan Qingzhi tablet (HQT), a lipid- lowering traditional Chinese medicine formula, has been used for the prevention and treatment of nonalcoholic fatty liver (NAFLD).

AIM OF THE STUDY

This study was realized to evaluate the effects of HQT-medicated serum on hepatic steatosis using in vitro experiments with cells and explore the relevant mechanisms with method of serum pharmacology.

MATERIALS AND METHODS

A model of hepatic steatosis in the L02 and HepG2 cells was induced by free fatty acid (FFA). The components in the HQT-medicated serum were assayed by high-performance liquid chromatography. Intracellular lipid droplets were detected by Oil Red O staining, and their ultrastructure was examined by transmission electron microscope. The biochemical parameters, including triglyceride (TG), lactate dehydrogenase (LDH), aspartate aminotransferase (AST) and alanine aminotransferase (ALT), total antioxidant capacity (T-AOC), malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione (GSH), were measured with commercial kits. Furthermore, the expression of adiponectin, AMP-activated protein kinase (AMPK) phosphorylation, sterol regulatory element-binding protein 1 (SREBP-1), peroxisome proliferator activated receptor-α (PPARα), carnitine palmitoyltransferase 1 (CPT-1), and acetyl-CoA oxidase 1 (ACOX1) was analyzed by Western blot and/or quantitative reverse transcription-polymerase chain reaction (qRT-PCR).

RESULTS

Moderate- and high-dose HQT-medicated serum reduced (P<0.05 or P<0.01) the accumulation of lipid droplets and the cellular TG content in L02 and HepG2 cells. They caused significant reductions (P<0.01) in LDH, AST, ALT and MDA and significant increase (P<0.05 or P<0.01) in T-AOC in the culture medium. They also caused increase (P<0.05 or P<0.01) in GSH level and SOD activity in FFA-induced steatotic L02 and HepG2 cells. Furthermore, moderate- and high-dose HQT-medicated serum enhanced (P<0.01) adiponectin expression in a concentration-dependent manner and increased (P<0.05 or P<0.01) the phosphorylation of AMPK and the expression of PPARα, CPT-1, and ACOX1, and reduced (P<0.05 or P<0.01) the expression of SREBP-1.

CONCLUSION

The results suggested that HQT-medicated serum exerts a preventive effect against hepatic steatosis, and the potential mechanism might be activation of AMPK and PPARα pathways.

In vitro effects of active components of Polygonum Multiflorum Radix on enzymes involved in the lipid metabolism

ETHNOPHARMACOLOGY RELEVANCE

Raw and processed Polygoni Multiflori Radix (PMR and PMRP) are used in the prevention and treatment of non-alcoholic fatty liver disease (NAFLD), hyperlipidemia or related diseases. In our previous research, 2, 3, 5, 4'-tetrahydroxy-stilbene-2-O-β-D-glucoside (TSG) displayed the most important role in the total cholesterol (TC) lowering effect among all the chemical constituents of Polygonum multiflorum. Emodin and physcion displayed more favorable triglyceride (TG) reducing effects than TSG. However, there are few researches focus on the approach and mechanism of how do Polygonum multiflorum exhibit good lipid regulation activity. The targeted sites of active substances of Polygonum multiflorum are still not clearly elucidated. This research pays close attention to how major chemical components of Polygonum multiflorum affect the TC and TG contents in liver cells.

MATERIALS AND METHODS

In this research, a sensitive, accurate and rapid in vitro model, steatosis hepatic L02 cell, was used to explore target sites of active chemical substances of Polygonum multiflorum for 48h. Steatosis hepatic L02 cell was exposed to emodin, physcion and TSG, respectively. The contents of four key enzymes in the pathway of synthesis and decomposition of TC and TG were investigated after exposure. Meanwhile, the contents of lipid transfer protein were also tested. The diacylgycerol acyltransferase 1 (DGAT1) controlled the biosynthesis of TG from free fatty acids while 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoA reductase) limited the biosynthesis of TC. Hepatic triglyceride lipase (HTGL) and cholesterol 7α-hydroxylase (CYP7A) played the key role in the lipolysis procedure of TG and TC.

RESULTS

The synthesis of TC and TG in steatosis L02 cells were apparently increased in the model group compared to the control group. Intracellular contents of HMG-CoA reductase and DGAT1 increased 32.33% and 56.52%, while contents of CYP7A and HTGL decreased 21.61% and 47.37%. Emodin, physcion and TSG all showed down-regulation effects on HMG-CoA reductase, while up-regulation effects on CYP7A. The most remarkable effect on HMG-CoA reductase was found on emodin. Emodin could reduce the DGAT1 content from 438.44 ± 4.51 pg/mL in model group to 192.55 ± 9.85 pg/mL (100 μm). The content of HTGL in 300 μm physcion group was 3.15 ± 0.15 U/mL, which was more significantly effective than the control, lovastatin and fenofibrate group.

CONCLUSIONS

TSG could raise the content of CYP7A and then promote the lipolysis of cholesterol. Moreover, TSG also showed the best LDL-reducing effect. Emodin could inhibit HMG-CoA reductase and DGAT1, which were key enzymes in the synthesis of TC and TG. Physcion increased the content of HTGL, and then could boost the lipolysis of triglyceride. At the same time, physcion showed the best VLDL-reducing effect. In view of the above conclusions, we contributed the lipid regulation activity to an overall synergy of TSG, emodin and physcion.

Proteomic analysis of liver mitochondria from rats with nonalcoholic steatohepatitis

AIM: To explore mitochondrial dysfunction in nonalcoholic steatohepatitis (NASH) by analyzing the proteome of liver mitochondria from a NASH model.

METHODS: The NASH rat model was established by feeding rats a fat-rich diet for 24 wk and was confirmed using hematoxylin and eosin staining of liver tissue and by changes in the levels of serum alanine transaminase, aspartate aminotransferase, triglyceride, total cholesterol and other markers. Liver mitochondria from each group were isolated using differential centrifugation. The mitochondrial samples were lyzed, purified and further analyzed using two-dimensional electrophoresis combined with matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry. Bioinformatic analyses of assigned gene ontology and biological pathway was used to study functional enrichments in the abundant proteomic data.

RESULTS: Eight up-regulated and sixteen down-regulated proteins were identified that showed greater than 1.5-fold differences between the controls and the NASH group. These dysregulated proteins were predicted to be involved in different metabolic processes including fatty acid β-oxidation processes, lipid metabolic processes, cell-cycle arrest, cell polarity maintenance, and adenosine triphosphate/sex hormone metabolic processes. Novel proteins that may be involved in NASH pathogenesis including the trifunctional enzyme Hadha, thyroxine, prohibitin, aldehyde dehydrogenase ALDH1L2, UDP-glucuronosyltransferase 2B31, and carbamoyl-phosphate synthase were identified using bioinformatics tools. The decreased expression of Hadha in NASH liver was verified by Western blotting, which was used as a complementary technique to confirm the proteomic results.

CONCLUSION: This novel report on the liver mitochondrial proteome of a NASH model may provide a reservoir of information on the pathogenesis and treatment of NASH.

Physiological and pathological roles of mitochondrial SLC25 carriers

The mitochondrion relies on compartmentalization of certain enzymes, ions and metabolites for the sake of efficient metabolism. In order to fulfil its activities, a myriad of carriers are properly expressed, targeted and folded in the inner mitochondrial membrane. Among these carriers, the six-transmembrane-helix mitochondrial SLC25 (solute carrier family 25) proteins facilitate transport of solutes with disparate chemical identities across the inner mitochondrial membrane. Although their proper function replenishes building blocks needed for metabolic reactions, dysfunctional SLC25 proteins are involved in pathological states. It is the purpose of the present review to cover the current knowledge on the role of SLC25 transporters in health and disease.

Enhanced antitumor activity by the combination of dasatinib and combretastatin A-4 in vitro and in vivo

The present study showed that the combination of dasatinib and combretastatin A-4 (CA-4) exhibited synergistic cytotoxicity in multiple types of cancer, including ovarian, hepatocellular, lung and prostate carcinoma. The enhanced apoptosis induced by dasatinib plus CA-4 was accompanied by a greater extent of mitochondrial depolarization, caspase-3 activation and PARP cleavage in HO-8910 cells. Furthermore, elevated expression of Mcl-1 led to a reduced apoptosis induced by dasatinib plus CA-4, highlighting that downregulated Mcl-1 was necessary for the potentiating effect of dasatinib to CA-4-triggered apoptosis. A clear increase in γ-H2AX expression was observed in the dasatinib+CA-4 group compared with the mono-treatment groups, indicating that dasatinib plus CA-4 may induce double-strand breaks (DSBs) in HO-8910 cells. Moreover, the increased anticancer efficacy of dasatinib combined with CA-4 was further validated in a human HO-8910 ovarian cancer xenograft model in nude mice. Our study is the first to show that the combination of dasatinib with CA-4 could be a novel and promising therapeutic approach for the treatment of cancer.

Transition from hepatic steatosis to steatohepatitis: unique microRNA patterns and potential downstream functions and pathways

BACKGROUND AND AIM

This study aimed to explore the unique miRNA responsible for transition from hepatic steatosis to steatohepatitis and to investigate the functions and pathways of their downstream targets.

METHODS

Microarray and stem-loop reverse transcription-polymerase chain reaction were utilized to detect dysregulated miRNA in a rat model. SAM, PAM and clustering analysis were jointly applied to calculate significantly changed miRNA. The targets of miRNA were predicted through web server "microrna." The functions and pathways of those predicted genes were analyzed using databases of Gene Ontology and KEGG by the web server "DAVID."

RESULTS

Fourteen upregulated and six downregulated miRNA were selected as an accurate molecular signature in distinguishing hepatic steatohepatitis from steatosis. Through Gene ontology, 499 and 287 enriched functional categories were found for the target genes of upregulated and downregulated miRNA, including ion homeostasis, protein transport and so on. Through KEGG, 46 and 41 enriched pathways were collected for the target genes of upregulated and downregulated miRNA, including apoptosis, fatty acid metabolism and so on. Analysis of common target genes of all downregulated miRNA revealed potential involvement of ion transport and the membrane structure in steatohepatitis.

CONCLUSION

We reported the dysregulated miRNA in transition from hepatic steatosis to steatohepatitis and showed potential clinical application in disease differentiation. This study provided data reservoir for miRNA exploration and revealed novel disease-specific Gene Ontology functions and KEGG pathways such as uncoupling-protein-guided membrane change. Our data contributes to further researches on the pathogenesis and treatment of non-alcoholic steatohepatitis.

Lipid regulation effects of Polygoni Multiflori Radix, its processed products and its major substances on steatosis human liver cell line L02

ETHNOPHARMACOLOGICAL RELEVANCE

Raw and processed Polygoni Multiflori Radix (PMR) are used in the prevention and treatment of non-alcoholic fatty liver disease (NAFLD), hyperlipidemia or related diseases. However, few researches compared the activities of raw and processed PMR on lipid metabolism regulation. Moreover, the active substances of Polygonum multiflorum are still not clearly elucidated.

MATERIALS AND METHODS

In this research, a sensitive, accurate and rapid in vitro model, steatosis hepatic L02 cell, was applied to compare the relative activities of raw and processed PMR on lipid metabolism regulation. Furthermore, the lipid regulation activities of emodin, physcion and 2,3,5,4'-tetrahydroxy-stilbene-2-O-β-d-glucoside (TSG) were evaluated. The steatosis L02 cells were obtained after cultured with 1% fat emulsion-10% fetal bovine serum (FBS)-RPMI 1640 medium for 48h. Contents of total cholesterol (TC), triglyceride (TG) and low-density lipoprotein cholesterol (LDL-C) in L02 cells are evaluated after exposure.

RESULTS

The intracellular TG contents were increased from 16.50±1.29mmol/L to 34.40±1.36mmol/L in steatosis L02 cells, while the intracellular contents of TC were increased from 5.07±1.80mmol/L to 11.79±0.54mmol/L. Water extract of raw PMR showed much remarkable TG-regulation and TC-regulation effects than its processed products. Emodin displayed the best TG regulation activity while TSG showed the best TC regulation activity. At the same time, the exposure of emodin and physcion could reduce the LDL-C contents in steatosis L02 cells.

CONCLUSIONS

On account of these in vitro results, raw PMR might have more satisfactory effects in clinic treatment of NAFLD or hyperlipidemia characterized by the elevation of cholesterol than processed PMR.

Hepatocyte steatosis increases the expression of adhesion molecules in endothelial cells

Background: Non-alcoholic fatty liver disease is considered a hepatic manifestation of the metabolic syndrome. It is associated with endothelial dysfunction as an early event of generalized atherosclerosis. However, it is unclear whether steatotic hepatocytes influence endothelial function directly. Objective: Explore the influence of hepatocyte steatosis on the function of endothelial cells. Methods: Oleic and palmitic acid (2:1 mixture, final concentration: 1 mM for 24 hours) was used to induce a normal adult hepatocyte strain (L-02) for transformation into steatosis cells. This was followed by oil red O staining and transmission electron microscopy (TEM) for verification. The culture solution of steatotic L-02 cells was filtered and collected, and added into the culture substrate of human umbilical vein endothelial cells (HUVECs). The expression of vascular cellular adhesion molecule -1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and E-selectin in HUVECs was detected by real-time polymerase chain reaction and Western blot assays. The apoptosis and proliferation of HUVECs was determined using flow cytometry. The experimental results were compared with the controls. Results: Oil red O staining and microscopic observation showed that the cytoplasm of induced L-02 cells contained a large amount of red lipid droplets. TEM results showed that the cytoplasm had lipid accumulation, swelling mitochondria, fewer cristae, and reduced number of rough endoplasmic reticula accompanied with degranulation. However, these changes were not observed in normal L-02 cells. As to the group of HUVECs treated by the filtrate of steatosis L-02 cells, the mRNA and protein expression of VCAM-1, ICAM-1, and E-selectin was higher than that in the control group. The difference was statistically significant (p <0.01). No significant difference was found when HUVECs apoptosis and proliferation were assessed by flow cytometry. Conclusion: Secretion from steatotic hepatocytes could boost the expression of VCAM-1, ICAM-1, and E-selectin in endothelial cells, indicating that hepatocyte steatosis could induce endothelial cell dysfunction. The proliferation and apoptosis of endothelial cells did not change, suggesting that hepatocyte steatosis had no influence on the viability of endothelial cells under this condition.

Quantitative proteomics identification of phosphoglycerate mutase 1 as a novel therapeutic target in hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide with poor prognosis due to resistance to conventional chemotherapy and limited efficacy of radiotherapy. There is an urgent need to develop novel biomarkers for early diagnosis, as well as to identify new drug targets for therapeutic interventions.

PATIENTS AND METHODS

54 paired HCC samples and 21 normal liver tissues were obtained from West China Hospital of Sichuan University. Informed consent was obtained from all the patients or their relatives prior to analysis, and the project was approved by the Institutional Ethics Committee of Sichuan University. Stable Isotope Labeling with Amino Acids in Cell Culture (SILAC)-based proteomics was employed to profile the differentially expressed proteins between a HepG2 human hepatoma cell line and an immortal hepatic cell line L02. Validation of PGAM1 expression was performed by semi-quantitative RT-PCR, immunoblot and immunohistochemistry using clinical samples. shRNA expressing plasmids specifically targeting PGAM1 were designed and constructed by GenePharma Corporation (Shanghai, China), and were utilized to silence expression of PGAM1 in vitro and in vivo. Cell proliferation was measured by a combination of colony formation assay and Ki67 staining. Apoptosis was examined by flow cytometry and TUNEL assay.

RESULTS

A total of 63 dysregulated proteins were identified, including 51 up-regulated proteins, and 12 down-regulated proteins (over 2-fold, p < 0.01). Phosphoglycerate mutase 1 (PGAM1) was found markedly upregulated. Clinico-pathological analysis indicated that overexpression of PGAM1 was associated with 66.7% HCC, and strongly correlated with poor differentiation and decreased survival rates (p < 0.01). shRNAs-mediated repression of PGAM1 expression resulted in significant inhibition in liver cancer cell growth both in vitro and in vivo.

CONCLUSION

Our studies suggested that PGAM1 plays an important role in hepatocarcinogenesis, and should be a potential diagnostic biomarker, as well as an attractive therapeutic target for hepatocellular carcinoma.