Hepatic Interferon Regulatory Factor 6 Alleviates Liver Steatosis and Metabolic Disorder by Transcriptionally Suppressing Peroxisome Proliferator-Activated Receptor γ in Mice

Interferon regulatory factor 1 contributes to metabolic dysfunction associated steatotic liver disease

AIMS

Non-alcoholic fatty liver disease (NAFLD) or metabolic dysfunction associated steatotic liver disease (MASLD), has reached epidemic levels in multiple regions worldwide and contributes to cirrhosis and hepatocellular carcinoma. We have previously reported that the CC motif chemokine ligand 11 (CCL11) is a key regulator of MASLD. Expression of interferon regulatory factor 1 (IRF1) can be up-regulated by CCL11 treatment in hepatocytes, the relevance of which is not clear. In the present study we investigated the role of IRF1 in NAFLD pathogenesis.

METHODS AND MATERIALS

MASLD was investigated in mice fed a high-fat high carbohydrate (HFHC) diet or in the genetically predisposed obese mice (db/db).

KEY FINDINGS

Hepatocytes from CCL11 knockout mice displayed a less severe MASLD phenotype, when treated with palmitic acid (PA), compared to wild type hepatocytes, which could be normalized by IRF1 over-expression. On the contrary, IRF1 knockdown in hepatocytes significantly down-regulated expression of pro-inflammatory mediators and dampened lipid accumulation induced by PA treatment. More importantly, IRF1 knockdown in hepatocytes led to amelioration of MASLD in mice. RNA-seq and CUT&Tag-seq identified pro-MASLD genes, including Osbpl3, Ddit4, and Ccl2, as potential targets for IRF1 in hepatocytes.

SIGNIFICANCE

Our data reveal a novel regulatory role of IRF1 in MASLD pathogenesis. Targeting IRF1 can be considered as a reasonable approach for MASLD intervention.

Molecular docking- and reporter-based screening identify dicoumarol against ER stress-induced liver injury in mice through inhibiting IRE1α activity

AIMS

Drug-induced liver injury is among the most challenging liver disorders. Endoplasmic reticulum (ER) is responsible for the correct protein folding and secretion, which are highly active in hepatocytes. Failure in maintaining the proper protein folding under pathological condition or external stimuli leads to the unfolded protein response (UPR) to restore ER homeostasis or induce cell death. IRE1α pathway is the most conserved UPR branch with diverse physiological and pathological functions. This study aimed to screen for natural compounds to alleviate hepatic ER stress and liver injury by modulating IRE1α activity.

MATERIALS AND METHODS

ATP-competitive molecules from chemical libraries were recognized by virtual screening for targeting the IRE1α kinase domain. IRE1α activity-based XBP1s-reporter cell lines with flow cytometric analysis were employed to validate candidates from chemical libraries. Then the functions of the top candidate compound on IRE1α signaling were analyzed followed by the treatment with ER stress agonists in vitro. Finally, the candidate compound was used to treat ER stress-induced acute liver injury to evaluate its protective effect in vivo.

KEY FINDINGS

Dicoumarol (DIC) was discovered as a potential inhibitor of IRE1α activation in HEK293T cells, HepG2 cells and primary hepatocytes. Particularly, DIC ameliorates tunicamycin (Tm)- and carbon tetrachloride (CCl4)-induced acute hepatic ER stress to protect against liver injury.

SIGNIFICANCE

This study established a drug screening strategy against IRE1α activation and identified potential new therapeutic effects of DIC in treating liver injury-related diseases.

Hepatic AKAP1 deficiency exacerbates diet-induced MASLD by enhancing GPAT1-mediated lysophosphatidic acid synthesis

Metabolic dysfunction-associated steatotic liver disease (MASLD), closely associated with obesity, can progress to metabolic dysfunction-associated steatohepatitis when the liver undergoes overt inflammatory damage. A-kinase anchoring protein 1 (AKAP1) has been shown to control lipid accumulation in brown adipocytes. However, the role of AKAP1 signaling in hepatic lipid metabolism and MASLD remains poorly understood. Here, we showed that hepatocyte-specific AKAP1 deficiency exacerbated hepatic steatosis and steatohepatitis in male mice subjected to a high-fat diet and fast-food diet, respectively. Mechanistically, AKAP1 directly phosphorylated and inactivated glycerol-3-phosphate acyltransferase 1 (GPAT1) in a PKA-dependent manner, thus suppressing lysophosphatidic acid (LPA) production. Increased endogenous LPA in hepatocytes promoted hepatocellular triglyceride (TG) synthesis and initiated pronounced inflammatory response in Kupffer cells. Restoring hepatic AKAP1 or repressing LPA levels via GPAT1 knockdown alleviated MASLD exacerbation. Overall, AKAP1 plays a protective role against MASLD by inhibiting GPAT1 activity, highlighting the potential of targeting AKAP1/PKA/GPAT1 signalosome for MASLD therapy.

IRF8 aggravates nonalcoholic fatty liver disease via BMAL1/PPARγ axis

Non-alcoholic fatty liver disease (NAFLD) is a hepatic metabolic syndrome arising from lipid metabolic imbalance, with its prevalence increasing globally. In this study, we observed a significant up-regulation of interferon regulatory factor 8 (IRF8) in the liver of NAFLD model mice and patients. Overexpression of IRF8 induced lipid accumulation in the mouse primary hepatocytes. Mice with adeno-associated virus-mediated IRF8 overexpression exhibited hepatic steatosis due to up-regulated peroxisome proliferator-activated receptor γ (PPARγ) expression and increased fatty acid uptake and lipogenesis. In vitro, small interfering RNA-mediated IRF8 knockdown attenuated triglyceride accumulation by dampening PPARγ expression through transcriptional inhibition of brain and muscle ARNT-like 1. The PPARγ-specific antagonist GW9662 abolished the effect of IRF8 overexpression. Furthermore, adeno-associated virus-mediated IRF8 knockdown in the mouse liver markedly alleviated hepatic steatosis and obesity-related metabolic syndrome. These findings indicate that IRF8 plays a vital role in modulating hepatic lipid metabolism in a PPARγ-dependent manner and provide a previously unknown insight into NAFLD therapeutic strategies.

Gallic acid mitigates high-fat and high-carbohydrate diet-induced steatohepatitis by modulating the IRF6/PPARγ signaling pathway

Gallic acid (GA), a natural organic phenolic compound, is an abundant plant food bioactive substance present in many medicinal herbs. GA has anti-oxidative, anti-inflammatory and anticancer activities on multiple metabolic disorders. The present study was carried out to uncover the alleviating effects of GA on metabolic dysfunction-associated steatohepatitis (MASH) and the underlying mechanisms of its action. In this study, a mouse model of MASH induced by high-fat and high-carbohydrate diet was used to test the impact of GA on metabolic disorders. We found that GA administration attenuated obesity and fatty liver, relieved insulin resistance, and mitigated hepatic steatosis, inflammation and liver injury. Transcriptome sequencing (RNA-seq) of mouse liver tissues identified 154 differentially expressed genes (DEGs) among the NCD, HFHC, and GA groups. Bioinformatic analysis of these DEGs revealed significant enrichment in lipid metabolism function and the PPARγ signaling pathway, which were further validated. Overexpression of PPARγ significantly reduced the therapeutic effect of GA both in vitro and in vivo. Notably, the transcription factor interferon regulatory factor 6 (IRF6), a protective factor in metabolic stress, which was predicted as the upstream regulator, was significantly upregulated by GA. Furthermore, it was verified that GA's anti-lipid deposition effect depends on the negative regulation of IRF6 on PPARγ using knocking-down strategy. Taken together, GA increases hepatic IRF6 expression, which mitigates lipid accumulation of hepatocytes and subsequent liver damage via inhibiting the PPARγ signaling pathway. These findings suggest a novel strategy for MASH management based on pharmacological intervention with GA.

Liver-innervating vagal sensory neurons are indispensable for the development of hepatic steatosis and anxiety-like behavior in diet-induced obese mice

The visceral organ-brain axis, mediated by vagal sensory neurons, is essential for maintaining various physiological functions. Here, we investigate the impact of liver-projecting vagal sensory neurons on energy balance, hepatic steatosis, and anxiety-like behavior in mice under obesogenic conditions. A small subset of vagal sensory neurons innervate the liver and project centrally to the nucleus of the tractus solitarius, area postrema, and dorsal motor nucleus of the vagus, and peripherally to the periportal areas in the liver. The loss of these neurons prevents diet-induced obesity, and these outcomes are associated with increased energy expenditure. Although males and females exhibit improved glucose homeostasis following disruption of liver-projecting vagal sensory neurons, only male mice display increased insulin sensitivity. Furthermore, the loss of liver-projecting vagal sensory neurons limits the progression of hepatic steatosis. Intriguingly, mice lacking liver-innervating vagal sensory neurons also exhibit less anxiety-like behavior compared to control mice. Modulation of the liver-brain axis may aid in designing effective treatments for both psychiatric and metabolic disorders associated with obesity and MAFLD.

Effects of moderate intensity exercise on liver metabolism in mice based on multi-omics analysis

Physical exercise is beneficial to keep physical and mental health. The molecular mechanisms underlying exercise are still worth exploring. The healthy adult mice after six weeks of moderate-intensity exercise (experimental group) and sedentary mice (control group) were used to perform transcriptomic, proteomic, lactylation modification, and metabolomics analysis. In addition, gene sets related to hypoxia, glycolysis, and fatty acid metabolism were used to aid in the screening of hub genes. The mMCP-counter was employed to evaluate infiltration of immune cells in murine liver tissues. Transcriptomics analysis revealed 82 intersection genes related to hypoxia, glycolysis, and fatty acid metabolism. Proteomics and lactylation modification analysis identified 577 proteins and 141 differentially lactylation modification proteins. By overlapping 82 intersection genes with 577 differentially expressed proteins and 141 differentially lactylation modification proteins, three hub genes (Aldoa, Acsl1, and Hadhb) were obtained. The immune infiltration analysis revealed a decreased score for monocytes/macrophages and an increased score for endothelial cells in the experimental group. Then, 459 metabolites in positive mode and 181 metabolites in negative mode were identified. The "Metabolic pathways" (mmu01100) was a common pathway between intersection genes-enriched pathways and metabolites-enriched pathways. These findings highlight the pivotal roles of hub genes in the glycolysis and fatty acid metabolism under the context of chronic exercise.

Cav3.2 deletion attenuates nonalcoholic fatty liver disease in mice

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease and represents the main cause of liver cirrhosis and hepatocellular carcinoma. Cav3.2 is a T-type calcium channel that is widely present in tissues throughout the body and plays a vital role in energy and metabolic balance. However, the effects of Cav3.2 on the NFALD remain unclear. Here, we investigated the role of Cav3.2 channel in the development and progression of NAFLD. After 16 weeks on a high-fat diets (HFD), Cav3.2 knockout (Cav3.2 KO) improved hepatic steatosis, liver injury and metabolic syndrome in an NAFLD mouse model. We provided evidence that Cav3.2 KO inhibited HFD-induced hepatic oxidative stress, inflammation and hepatocyte apoptosis. In addition, Cav3.2 KO also attenuated hepatic lipid accumulation, oxidative stress, inflammation and hepatocyte apoptosis in palmitic acid/oleic acid (PAOA)-treated primary hepatocytes. These results suggest that therapeutic approaches targeting Cav3.2 provide effective approaches for treating NAFLD.

Liver-innervating vagal sensory neurons are indispensable for the development of hepatic steatosis and anxiety-like behavior in diet-induced obese mice

The visceral organ-brain axis, mediated by vagal sensory neurons, is essential for maintaining various physiological functions. Here, we investigate the impact of liver-projecting vagal sensory neurons on energy balance, hepatic steatosis, and anxiety-like behavior in mice under obesogenic conditions. A small subset of vagal sensory neurons in both the left and right ganglia innervate the liver and project centrally to the nucleus of the tractus solitarius, area postrema, and dorsal motor nucleus of the vagus, and peripherally to the periportal areas in the liver. Surprisingly, the loss of liver-projecting vagal sensory neurons via caspase-induced selective destruction of advillin-positive neurons prevents diet-induced obesity, and these outcomes are associated with increased energy expenditure. Although males and females exhibit improved glucose homeostasis following disruption of liver-projecting vagal sensory neurons, only male mice display increased insulin sensitivity. Furthermore, the loss of liver-projecting vagal sensory neurons limits the progression of hepatic steatosis in mice fed a steatogenic diet. Intriguingly, mice lacking liver-innervating vagal sensory neurons also exhibit less anxiety-like behavior compared to control mice. Therefore, modulation of the liver-brain axis may aid in designing effective treatments for both psychiatric and metabolic disorders associated with obesity and MAFLD.

Daphnetin ameliorates hepatic steatosis by suppressing peroxisome proliferator-activated receptor gamma (PPARG) in ob/ob mice

Non-alcoholic fatty liver disease (NAFLD) is the predominant metabolic liver disorder and currently lacks effective and safe pharmaceutical interventions. Daphnetin (DA), a natural coumarin derivative with anti-inflammatory and antioxidant activities, is a promising agent for NAFLD treatment. In this study, we evaluated the effects and mechanisms of DA on hepatic lipid metabolism in ob/ob mice. Our results showed that DA effectively ameliorates glucose metabolism and hepatic lipid accumulation in ob/ob mice. Metabolomics and RNA sequencing (RNA-seq), combined with GEO data analysis, suggest that DA primarily modulates the peroxisome proliferator-activated receptor gamma (PPARG) pathway, as validated in vivo in ob/ob mice. Mechanistically, DA selectively targets PPARG in hepatic cells by inhibiting PPARG promoter activity and downregulating its expression, resulting in decreased transcription of downstream lipid metabolism-related genes, including fatty acid binding protein 4 (Fabp4), cluster of differentiation 36 (Cd36), and fatty acid synthase (Fasn). This effect was abolished in PPARG-deficient HepG2 cells subjected to palmitic acid (PA) insult. Our findings provide evidence that DA acts as a selective suppressor of hepatic PPARG, suggesting an attractive strategy by targeting PPARG for the prevention of hepatic steatosis.

The multiple roles of interferon regulatory factor family in health and disease

Interferon Regulatory Factors (IRFs), a family of transcription factors, profoundly influence the immune system, impacting both physiological and pathological processes. This review explores the diverse functions of nine mammalian IRF members, each featuring conserved domains essential for interactions with other transcription factors and cofactors. These interactions allow IRFs to modulate a broad spectrum of physiological processes, encompassing host defense, immune response, and cell development. Conversely, their pivotal role in immune regulation implicates them in the pathophysiology of various diseases, such as infectious diseases, autoimmune disorders, metabolic diseases, and cancers. In this context, IRFs display a dichotomous nature, functioning as both tumor suppressors and promoters, contingent upon the specific disease milieu. Post-translational modifications of IRFs, including phosphorylation and ubiquitination, play a crucial role in modulating their function, stability, and activation. As prospective biomarkers and therapeutic targets, IRFs present promising opportunities for disease intervention. Further research is needed to elucidate the precise mechanisms governing IRF regulation, potentially pioneering innovative therapeutic strategies, particularly in cancer treatment, where the equilibrium of IRF activities is of paramount importance.

Estrogen Induces LCAT to Maintain Cholesterol Homeostasis and Suppress Hepatocellular Carcinoma Development

Hepatocellular carcinoma (HCC) is an aggressive disease that occurs predominantly in men. Estrogen elicits protective effects against HCC development. Elucidation of the estrogen-regulated biological processes that suppress HCC could lead to improved prevention and treatment strategies. Here, we performed transcriptomic analyses on mouse and human liver cancer and identified lecithin cholesterol acyltransferase (LCAT) as the most highly estrogen-upregulated gene and a biomarker of favorable prognosis. LCAT upregulation inhibited HCC in vitro and in vivo and mediated estrogen-induced suppression of HCC in an ESR1-dependent manner. LCAT facilitated high-density lipoprotein cholesterol production and uptake via the LDLR and SCARB1 pathways. Consistently, high HDL-C levels corresponded to a favorable prognosis in HCC patients. The enhanced HDL-C absorption induced by LCAT impaired SREBP2 maturation, which ultimately suppressed cholesterol biosynthesis and dampened HCC cell proliferation. HDL-C alone inhibited HCC growth comparably to the cholesterol-lowering drug lovastatin, and SREBF2 overexpression abolished the inhibitory activity of LCAT. Clinical observations and cross-analyses of multiple databases confirmed the correlation of elevated LCAT and HDL-C levels to reduced cholesterol synthesis and improved HCC patient prognosis. Furthermore, LCAT deficiency mimicked whereas LCAT overexpression abrogated the tumor growth-promoting effects of ovariectomy in HCC-bearing female mice. Most importantly, HDL-C and LCAT delayed the development of subcutaneous tumors in nude mice, and HDL-C synergized with lenvatinib to eradicate orthotopic liver tumors. Collectively, this study reveals that estrogen upregulates LCAT to maintain cholesterol homeostasis and to dampen hepatocarcinogenesis. LCAT and HDL-C represent potential prognostic and therapeutic biomarkers for targeting cholesterol homeostasis as a strategy for treating HCC. Significance: Estrogen mediates the sex differences in hepatocellular carcinoma development by reducing cholesterol biosynthesis through activation of an LCAT/HDL-C axis, providing strategies for improving liver cancer prevention, prognosis, and treatment.

Hepatotoxicity of oral exposure to 2-methyl-4-nitroaniline: toxicity prediction and in vivo evaluation

2-Methyl-4-nitroaniline (MNA), an intermediate in the synthesis of azo dyes, is widely distributed in various environmental media and organisms. Although there is speculation regarding MNA's potential to be hepatotoxic, the underlying mechanisms of its hepatotoxicity and its definitive diagnostic process remain largely unexplored. In this research. In the present study, we initially predicted the toxicity and possible toxic effect pathways of MNA using ProTox-II, and found that MNA binds to the PPARγ receptor (binding energy －6.118 kcal/mol) with a potential PPARγ agonist effect. Subsequently, in vivo exposure evaluation was conducted on Wistar rats to assess the impact of MNA after a 90-day exposure period, by detecting serum biochemical indexes, hematological indexes, urinary indexes, inflammatory factors, liver histopathological observations and liver tissue PPARγ mRNA expression. The results showed that MNA causes liver function abnormalities, liver histopathological changes and inflammatory response, along with a pronounced increase in PPARγ mRNA levels. This study suggests that the hepatotoxic mechanism of MNA may be related to its possible upregulation of PPARγ expression, increased liver dysfunction and inflammatory responses. Based on these results, the benchmark dose lower limit (BMDL) of 1.503 mg/kg for male Wistar rats was also established, providing a vital benchmark for determining the safety threshold of MNA. Our data highlight the hepatotoxic mechanism of MNA and contribute to a better understanding of its potential etiological diagnosis.

The Role of Interferon Regulatory Factors in Liver Diseases

The interferon regulatory factors (IRFs) family comprises 11 members that are involved in various biological processes such as antiviral defense, cell proliferation regulation, differentiation, and apoptosis. Recent studies have highlighted the roles of IRF1-9 in a range of liver diseases, including hepatic ischemia-reperfusion injury (IRI), alcohol-induced liver injury, Con A-induced liver injury, nonalcoholic fatty liver disease (NAFLD), cirrhosis, and hepatocellular carcinoma (HCC). IRF1 is involved in the progression of hepatic IRI through signaling pathways such as PIAS1/NFATc1/HDAC1/IRF1/p38 MAPK and IRF1/JNK. The regulation of downstream IL-12, IL-15, p21, p38, HMGB1, JNK, Beclin1, β-catenin, caspase 3, caspase 8, IFN-γ, IFN-β and other genes are involved in the progression of hepatic IRI, and in the development of HCC through the regulation of PD-L1, IL-6, IL-8, CXCL1, CXCL10, and CXCR3. In addition, IRF3-PPP2R1B and IRF4-FSTL1-DIP2A/CD14 pathways are involved in the development of NAFLD. Other members of the IRF family also play moderately important functions in different liver diseases. Therefore, given the significance of IRFs in liver diseases and the lack of a comprehensive compilation of their molecular mechanisms in different liver diseases, this review is dedicated to exploring the molecular mechanisms of IRFs in various liver diseases.

Morphological Changes Induced by TKS4 Deficiency Can Be Reversed by EZH2 Inhibition in Colorectal Carcinoma Cells

BACKGROUND

The scaffold protein tyrosine kinase substrate 4 (TKS4) undergoes tyrosine phosphorylation by the epidermal growth factor receptor (EGFR) pathway via Src kinase. The TKS4 deficiency in humans is responsible for the manifestation of a genetic disorder known as Frank-Ter Haar syndrome (FTHS). Based on our earlier investigation, the absence of TKS4 triggers migration, invasion, and epithelial-mesenchymal transition (EMT)-like phenomena while concurrently suppressing cell proliferation in HCT116 colorectal carcinoma cells. This indicates that TKS4 may play a unique role in the progression of cancer. In this study, we demonstrated that the enhancer of zeste homolog 2 (EZH2) and the histone methyltransferase of polycomb repressive complex 2 (PRC2) are involved in the migration, invasion, and EMT-like changes in TKS4-deficient cells (KO). EZH2 is responsible for the maintenance of the trimethylated lysine 27 on histone H3 (H3K27me3).

METHODS

We performed transcriptome sequencing, chromatin immunoprecipitation, protein and RNA quantitative studies, cell mobility, invasion, and proliferation studies combined with/without the EZH2 activity inhibitor 3-deazanoplanocine (DZNep).

RESULTS

We detected an elevation of global H3K27me3 levels in the TKS4 KO cells, which could be reduced with treatment with DZNep, an EZH2 inhibitor. Inhibition of EZH2 activity reversed the phenotypic effects of the knockout of TKS4, reducing the migration speed and wound healing capacity of the cells as well as decreasing the invasion capacity, while the decrease in cell proliferation became stronger. In addition, inhibition of EZH2 activity also reversed most epithelial and mesenchymal markers. We investigated the wider impact of TKS4 deletion on the gene expression profile of colorectal cancer cells using transcriptome sequencing of wild-type and TKS4 knockout cells, particularly before and after treatment with DZNep. Additionally, we observed changes in the expression of several protein-coding genes and long non-coding RNAs that showed a recovery in expression levels following EZH2 inhibition.

CONCLUSIONS

Our results indicate that the removal of TKS4 causes a notable disruption in the gene expression pattern, leading to the disruption of several signal transduction pathways. Inhibiting the activity of EZH2 can restore most of these transcriptomics and phenotypic effects in colorectal carcinoma cells.

A crosstalk between epigenetic modulations and non-alcoholic fatty liver disease progression

Non-alcoholic fatty liver disease (NAFLD) has recently emerged as a major public health concern worldwide due to its rapidly rising prevalence and its potential to progress into end-stage liver disease. While the precise pathophysiology underlying NAFLD remains incompletely understood, it is strongly associated with various environmental triggers and other metabolic disorders. Epigenetics examines changes in gene expression that are not caused by alterations in the DNA sequence itself. There is accumulating evidence that epigenetics plays a key role in linking environmental cues to the onset and progression of NAFLD. Our understanding of how epigenetic mechanisms contribute to NAFLD pathophysiology has expanded considerably in recent years as research on the epigenetics of NAFLD has developed. This review summarizes recent insights into major epigenetic processes that have been implicated in NAFLD pathogenesis including DNA methylation, histone acetylation, and microRNAs that have emerged as promising targets for further investigation. Elucidating epigenetic mechanisms in NAFLD may uncover novel diagnostic biomarkers and therapeutic targets for this disease. However, many questions have remained unanswered regarding how epigenetics promotes NAFLD onset and progression. Additional studies are needed to further characterize the epigenetic landscape of NAFLD and validate the potential of epigenetic markers as clinical tools. Nevertheless, an enhanced understanding of the epigenetic underpinnings of NAFLD promises to provide key insights into disease mechanisms and pave the way for novel prognostic and therapeutic approaches.

Swimming exercise ameliorates insulin resistance and nonalcoholic fatty liver by negatively regulating PPARγ transcriptional network in mice fed high fat diet

BACKGROUND

Recent findings elucidated hepatic PPARγ functions as a steatogenic-inducer gene that activates de novo lipogenesis, and is involved in regulation of glucose homeostasis, lipid accumulation, and inflammation response. This study delved into a comprehensive analysis of how PPARγ signaling affects the exercise-induced improvement of insulin resistance (IR) and non-alcoholic fatty liver disease (NAFLD), along with its underlying mechanism.

METHODS

Chronic and acute swimming exercise intervention were conducted in each group mice. IR status was assessed by GTT and ITT assays. Serum inflammatory cytokines were detected by Elisa assays. PPARγ and its target genes expression were detected by qPCR assay. Relative protein levels were quantified via Western blotting. ChIP-qPCR assays were used to detect the enrichment of PPARγ on its target genes promoter.

RESULTS

Through an exploration of a high-fat diet (HFD)-induced IR and NAFLD model, both chronic and acute swimming exercise training led to significant reductions in body weight and visceral fat mass, as well as hepatic lipid accumulation. The exercise interventions also demonstrated a significant amelioration in IR and the inflammatory response. Meanwhile, swimming exercise significantly inhibited PPARγ and its target genes expression induced by HFD, containing CD36, SCD1 and PLIN2. Furthermore, swimming exercise presented significant modulation on regulatory factors of PPARγ expression and transcriptional activity.

CONCLUSION

The findings suggest that swimming exercise can improve lipid metabolism in IR and NAFLD, possibly through PPARγ signaling in the liver of mice.

Differences in DNA methylation of HAMP in blood cells predicts the development of type 2 diabetes

OBJECTIVES

Better disease management can be achieved with earlier detection through robust, sensitive, and easily accessible biomarkers. The aim of the current study was to identify novel epigenetic biomarkers determining the risk of type 2 diabetes (T2D).

METHODS

Livers of 10-week-old female New Zealand Obese (NZO) mice, slightly differing in their degree of hyperglycemia and liver fat content and thereby in their diabetes susceptibility were used for expression and methylation profiling. We screened for differences in hepatic expression and DNA methylation in diabetes-prone and -resistant mice, and verified a candidate (HAMP) in human livers and blood cells. Hamp expression was manipulated in primary hepatocytes and insulin-stimulated pAKT was detected. Luciferase reporter assays were conducted in a murine liver cell line to test the impact of DNA methylation on promoter activity.

RESULTS

In livers of NZO mice, the overlap of methylome and transcriptome analyses revealed a potential transcriptional dysregulation of 12 hepatokines. The strongest effect with a 52% decreased expression in livers of diabetes-prone mice was detected for the Hamp gene, mediated by elevated DNA methylation of two CpG sites located in the promoter. Hamp encodes the iron-regulatory hormone hepcidin, which had a lower abundance in the livers of mice prone to developing diabetes. Suppression of Hamp reduces the levels of pAKT in insulin-treated hepatocytes. In liver biopsies of obese insulin-resistant women, HAMP expression was significantly downregulated along with increased DNA methylation of a homologous CpG site. In blood cells of incident T2D cases from the prospective EPIC-Potsdam cohort, higher DNA methylation of two CpG sites was related to increased risk of incident diabetes.

CONCLUSIONS

We identified epigenetic changes in the HAMP gene which may be used as an early marker preceding T2D.

Peroxisome Proliferator-Activated Receptor-γ as a Target and Regulator of Epigenetic Mechanisms in Nonalcoholic Fatty Liver Disease

Peroxisome proliferator-activated receptor-γ (PPARγ) belongs to the superfamily of nuclear receptors that control the transcription of multiple genes. Although it is found in many cells and tissues, PPARγ is mostly expressed in the liver and adipose tissue. Preclinical and clinical studies show that PPARγ targets several genes implicated in various forms of chronic liver disease, including nonalcoholic fatty liver disease (NAFLD). Clinical trials are currently underway to investigate the beneficial effects of PPARγ agonists on NAFLD/nonalcoholic steatohepatitis. Understanding PPARγ regulators may therefore aid in unraveling the mechanisms governing the development and progression of NAFLD. Recent advances in high-throughput biology and genome sequencing have greatly facilitated the identification of epigenetic modifiers, including DNA methylation, histone modifiers, and non-coding RNAs as key factors that regulate PPARγ in NAFLD. In contrast, little is still known about the particular molecular mechanisms underlying the intricate relationships between these events. The paper that follows outlines our current understanding of the crosstalk between PPARγ and epigenetic regulators in NAFLD. Advances in this field are likely to aid in the development of early noninvasive diagnostics and future NAFLD treatment strategies based on PPARγ epigenetic circuit modification.

Therapeutic role of Artemether in the prevention of hepatic steatosis through miR‐34a‐5p/PPARα pathway

Artemether (ATM) is a natural antimalarial drug that can also regulate glucose and lipid metabolism. However, little is known regarding its pharmacological action in metabolic dysfunction-associated fatty liver disease (MAFLD), and the underlying mechanisms remain undetermined. The aim of this study was to explore the therapeutic effects of ATM against hepatic steatosis and the possible mechanisms. ATM significantly decreased blood glucose levels, improved glucose tolerance, reduced inflammatory response, and alleviated hepatic steatosis in the ob/ob mouse model as well as the high-fat diet-fed mice. ATM also inhibited lipid accumulation in murine hepatocytes in vitro. Using RNA sequencing, miR-34a-5p and peroxisome proliferator-activated receptor-α (PPARα) were identified as important regulators during ATM treatment. ATM administration downregulated miR-34a-5p expression and miR-34a-5p abrogated the inhibitory effects of ATM on PO (palmitate + oleate)-induced lipid accumulation as well as triglycerides levels in murine hepatocytes. Furthermore, the expression of PPARα, a target gene of miR-34a-5p, was upregulated by ATM and PPARα inhibitor MK-886 abolished the positive effect of ATM. Consequently, PPARα agonist fenofibrate reversed the decreased mitochondrial fatty acid β-oxidation induced by miR-34a-5p mimics after ATM treatment, thereby leading to attenuation of intracellular lipid accumulation. Taken together, ATM is a promising therapeutic agent against MAFLD that reduces lipid deposition by suppressing miR-34a-5p and upregulating PPARα.

Plasma PFOA and PFOS Levels, DNA Methylation, and Blood Lipid Levels: A Pilot Study

Exposure to perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) is associated with blood lipids in adults, but the underlying mechanisms remain unclear. This pilot study aimed to investigate the associations between PFOA or PFOS and epigenome-wide DNA methylation and assess the mediating effect of DNA methylation on the PFOA/PFOS-blood lipid association. We measured plasma PFOA/PFOS and leukocyte DNA methylation in 98 patients enrolled from the hospital between October 2018 and August 2019. The median plasma PFOA/PFOS levels were 0.85 and 2.29 ng/mL. Plasma PFOA and PFOS levels were significantly associated with elevated total cholesterol (TC) and low-density lipoprotein cholesterol (LDL) levels. There were 63/87 CpG positions and 8/11 differentially methylated regions (DMRs) associated with plasma PFOA/PFOS levels, respectively. In addition, 5 CpG positions (annotated to AFF3, CREB5, NRG2, USF2, and intergenic region) and one DMR annotated to IRF6 may mediate the association between plasma PFOA/PFOS and LDL levels (mediated proportion from 7.29 to 46.77%); two CpG positions may mediate the association between plasma PFOA/PFOS and TC levels (annotated to CREB5 and USF2, mediated proportion is around 30%). The data suggest that PFOA/PFOS exposure alters DNA methylation. More importantly, the association of PFOA/PFOS with lipid indicators was partly mediated by DNA methylation changes in lipid metabolism-related genes.

Energy substrate metabolism and oxidative stress in metabolic cardiomyopathy

Metabolic cardiomyopathy is an emerging cause of heart failure in patients with obesity, insulin resistance, and diabetes. It is characterized by impaired myocardial metabolic flexibility, intramyocardial triglyceride accumulation, and lipotoxic damage in association with structural and functional alterations of the heart, unrelated to hypertension, coronary artery disease, and other cardiovascular diseases. Oxidative stress plays an important role in the development and progression of metabolic cardiomyopathy. Mitochondria are the most significant sources of reactive oxygen species (ROS) in cardiomyocytes. Disturbances in myocardial substrate metabolism induce mitochondrial adaptation and dysfunction, manifested as a mismatch between mitochondrial fatty acid oxidation and the electron transport chain (ETC) activity, which facilitates ROS production within the ETC components. In addition, non-ETC sources of mitochondrial ROS, such as β-oxidation of fatty acids, may also produce a considerable quantity of ROS in metabolic cardiomyopathy. Augmented ROS production in cardiomyocytes can induce a variety of effects, including the programming of myocardial energy substrate metabolism, modulation of metabolic inflammation, redox modification of ion channels and transporters, and cardiomyocyte apoptosis, ultimately leading to the structural and functional alterations of the heart. Based on the above mechanistic views, the present review summarizes the current understanding of the mechanisms underlying metabolic cardiomyopathy, focusing on the role of oxidative stress.

Role of Oxidative Stress in Liver Disorders

Oxygen is vital for life as it is required for many different enzymatic reactions involved in intermediate metabolism and xenobiotic biotransformation. Moreover, oxygen consumption in the electron transport chain of mitochondria is used to drive the synthesis of ATP to meet the energetic demands of cells. However, toxic free radicals are generated as byproducts of molecular oxygen consumption. Oxidative stress ensues not only when the production of reactive oxygen species (ROS) exceeds the endogenous antioxidant defense mechanism of cells, but it can also occur as a consequence of an unbalance between antioxidant strategies. Given the important role of hepatocytes in the biotransformation and metabolism of xenobiotics, ROS production represents a critical event in liver physiology, and increasing evidence suggests that oxidative stress contributes to the development of many liver diseases. The present review, which is part of the special issue “Oxidant stress in Liver Diseases”, aims to provide an overview of the sources and targets of ROS in different liver diseases and highlights the pivotal role of oxidative stress in cell death. In addition, current antioxidant therapies as treatment options for such disorders and their limitations for future trial design are discussed.

Integrative network analysis revealed the molecular function of folic acid on immunological enhancement in a sheep model

We previously observed the beneficial role of folic acid supplemented from maternal or offspring diet on lamb growth performance and immunity. Twenty-four Hu lambs from four groups (mother received folic acid or not, offspring received folic acid or not) were used in the current study, which was conducted consecutively to elucidate the molecular regulatory mechanisms of folic acid in lambs by analyzing blood metabolome, liver transcriptome, and muscle transcriptome. Serum metabolomics analysis showed that L-homocitrulline, hyodeoxycholic acid, 9-Hpode, palmitaldehyde, N-oleoyl glycine, hexadecanedioic acid, xylose, 1,7-dimethylxanthine, nicotinamide, acetyl-N-formyl-5-methoxykynurenamine, N6-succinyl adenosine, 11-cis-retinol, 18-hydroxycorticosterone, and 2-acetylfuran were down-regulated and methylisobutyrate was up-regulated by the feeding of folic acid from maternal and/or offspring diets. Meanwhile, folic acid increased the abundances of S100A12 and IRF6 but decreased TMEM25 in the liver. In the muscle, RBBP9, CALCR, PPP1R3D, UCP3, FBXL4, CMBL, and MTFR2 were up-regulated, CYP26B1 and MYH9 were down-regulated by the feeding of folic acid. The pathways of bile secretion, biosynthesis of unsaturated fatty acids, linoleic acid metabolism, and herpes simplex virus 1 infection were changed by folic acid in blood, liver, or muscle. Further integrated analysis revealed potential interactions among the liver, blood, and muscle, and the circulating metabolites, hub gene, and pathways, which might be the predominant acting targets of folic acid in animals. These findings provide fundamental information on the beneficial function of folic acid no matter from maternal or offspring, in regulating animal lipid metabolism and immune enhancement, providing a theoretical basis for the use of folic acid from the view of animal health care.

OTUB1 alleviates NASH through inhibition of the TRAF6-ASK1 signaling pathways

BACKGROUND AND AIMS

NAFLD is considered as the hepatic manifestation of the metabolic syndrome, which includes insulin resistance, obesity and hyperlipidemia. NASH is a progressive stage of NAFLD with severe hepatic steatosis, hepatocyte death, inflammation, and fibrosis. Currently, no pharmacological interventions specifically tailored for NASH are approved. Ovarian tumor domain, ubiquitin aldehyde binding 1 (OTUB1), the founding member of deubiquitinases, regulates many metabolism-associated signaling pathways. However, the role of OTUB1 in NASH is unclarified.

METHODS AND RESULTS

We demonstrated that mice with Otub1 deficiency exhibited aggravated high-fat diet-induced and high-fat high-cholesterol (HFHC) diet-induced hyperinsulinemia and liver steatosis. Notably, hepatocyte-specific overexpression of Otub1 markedly alleviated HFHC diet-induced hepatic steatosis, inflammatory responses, and liver fibrosis. Mechanistically, we identified apoptosis signal-regulating kinase 1 (ASK1) as a key candidate target of OTUB1 through RNA-sequencing analysis and immunoblot analysis. Through immunoprecipitation-mass spectrometry analysis, we further found that OTUB1 directly bound to tumor necrosis factor receptor-associated factor 6 (TRAF6) and suppressed its lysine 63-linked polyubiquitination, thus inhibiting the activation of ASK1 and its downstream pathway.

CONCLUSIONS

OTUB1 is a key suppressor of NASH that inhibits polyubiquitinations of TRAF6 and attenuated TRAF6-mediated ASK1 activation. Targeting the OTUB1-TRAF6-ASK1 axis may be a promising therapeutic strategy for NASH.

Liver Steatosis: A Marker of Metabolic Risk in Children

Obesity is one of the greatest health challenges affecting children of all ages and ethnicities. Almost 19% of children and adolescents worldwide are overweight or obese, with an upward trend in the last decades. These reports imply an increased risk of fat accumulation in hepatic cells leading to a series of histological hepatic damages gathered under the acronym NAFLD (Non-Alcoholic Fatty Liver Disease). Due to the complex dynamics underlying this condition, it has been recently renamed as 'Metabolic Dysfunction Associated Fatty Liver Disease (MAFLD)', supporting the hypothesis that hepatic steatosis is a key component of the large group of clinical and laboratory abnormalities of Metabolic Syndrome (MetS). This review aims to share the latest scientific knowledge on MAFLD in children in an attempt to offer novel insights into the complex dynamics underlying this condition, focusing on the novel molecular aspects. Although there is still no treatment with a proven efficacy for this condition, starting from the molecular basis of the disease, MAFLD's therapeutic landscape is rapidly expanding, and different medications seem to act as modifiers of liver steatosis, inflammation, and fibrosis.

The Role of Interferon Regulatory Factors in Non-Alcoholic Fatty Liver Disease and Non-Alcoholic Steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) is becoming the most common chronic liver disease with many metabolic comorbidities, such as obesity, diabetes, and cardiovascular diseases. Non-alcoholic steatohepatitis (NASH), an advanced form of NAFLD, accompanies the progression of hepatic steatosis, inflammation, cell death, and varying degree of liver fibrosis. Interferons (IFNs) have been shown to play important roles in the pathogenesis of NAFLD and NASH. Their regulating transcriptional factors such as interferon regulatory factors (IRFs) can regulate IFN expression, as well as genes involved in macrophage polarization, which are implicated in the pathogenesis of NAFLD and advanced liver disease. In this review, the roles of IRF-involved signaling pathways in hepatic inflammation, insulin resistance, and immune cell activation are reviewed. IRFs such as IRF1 and IRF4 are also involved in the polarization of macrophages that contribute to critical roles in NAFLD or NASH pathogenesis. In addition, IRFs have been shown to be regulated by treatments including microRNAs, PPAR modulators, anti-inflammatory agents, and TLR agonists or antagonists. Modulating IRF-mediated factors through these treatments in chronic liver disease can ameliorate the progression of NAFLD to NASH. Furthermore, adenoviruses and CRISPR activation plasmids can also be applied to regulate IRF-mediated effects in chronic liver disease. Pre-clinical and clinical trials for evaluating IRF regulators in NAFLD treatment are essential in the future direction.

The transcription factor zinc fingers and homeoboxes 2 alleviates NASH by transcriptional activation of phosphatase and tensin homolog

BACKGROUND AND AIMS

NASH, which is a common clinical condition predisposing to advanced liver diseases, has become a worldwide epidemic. A large and growing unmet therapeutic need for this condition reflects incomplete understanding of its pathogenesis. In the current study, we identified a transcription factor, zinc fingers and homeoboxes 2 (ZHX2), in hepatocytes as a protective factor against steatohepatitis.

APPROACH AND RESULTS

We found that hepatic ZHX2 was significantly suppressed in NASH models and steatotic hepatic cells. Hepatocyte-specific ablation of ZHX2 exacerbated NASH-related phenotypes in mice, including lipid accumulation, enhanced inflammation, and hepatic fibrosis. Conversely, hepatocyte-specific overexpression of ZHX2 significantly alleviated the progression of NASH in an experimental setting. Integrated analysis of transcriptomic profiling and chromatin immunoprecipitation sequencing data demonstrated that the phosphatase and tensin homolog (PTEN) was a target gene of ZHX2 in hepatocyte. ZHX2 bound to the promoter of PTEN gene and subsequently promoted the transcription of PTEN, which mediated the beneficial role of ZHX2 against NASH.

CONCLUSIONS

The current findings demonstrate a protective role of ZHX2 against NASH progression by transcriptionally activating PTEN. These findings shed light on the therapeutic potential of targeting ZHX2 for treating NASH and related metabolic disorders.

A conventional immune regulator mitochondrial antiviral signaling protein blocks hepatic steatosis by maintaining mitochondrial homeostasis

BACKGROUND AND AIMS

Although the prevalence of NAFLD has risen dramatically to 25% of the adult population worldwide, there are as yet no approved pharmacological interventions for the disease because of uncertainty about the underlying molecular mechanisms. It is known that mitochondrial dysfunction is an important factor in the development of NAFLD. Mitochondrial antiviral signaling protein (MAVS) is a critical signaling adaptor for host defenses against viral infection. However, the role of MAVS in mitochondrial metabolism during NAFLD progression remains largely unknown.

APPROACH AND RESULTS

Based on expression analysis, we identified a marked down-regulation of MAVS in hepatocytes during NAFLD progression. By using MAVS global knockout and hepatocyte-specific MAVS knockout mice, we found that MAVS is protective against diet-induced NAFLD. MAVS deficiency induces extensive mitochondrial dysfunction during NAFLD pathogenesis, which was confirmed as impaired mitochondrial respiratory capacity and membrane potential. Metabolomics data also showed the extensive metabolic disorders after MAVS deletion. Mechanistically, MAVS interacts with the N-terminal stretch of voltage-dependent anion channel 2 (VDAC2), which is required for the ability of MAVS to influence mitochondrial function and hepatic steatosis.

CONCLUSIONS

In hepatocytes, MAVS plays an important role in protecting against NAFLD by helping to regulate healthy mitochondrial function. These findings provide insights regarding the metabolic importance of conventional immune regulators and support the possibility that targeting MAVS may represent an avenue for treating NAFLD.

MicroRNA-137-3p Improves Nonalcoholic Fatty Liver Disease through Activating AMPKα

Nonalcoholic fatty liver disease (NAFLD) is one of the most common chronic liver diseases worldwide and can develop to nonalcoholic steatohepatitis and later hepatic cirrhosis with a high prevalence to hepatocellular carcinoma. Oxidative stress and chronic hepatic inflammation are implicated in the pathogenesis of NAFLD. MicroRNA-137-3p (miR-137-3p) are associated with oxidative stress and inflammation; however, its role and mechanism in NAFLD remain unclear. Mice were fed with a high-fat diet (HFD) for 24 weeks to establish the NAFLD model. To overexpress or suppress hepatic miR-137-3p expression, mice were intraperitoneally injected with the agomir, antagomir, or respective controls of miR-137-3p at a dose of 100 mg/kg weekly for 6 consecutive weeks before the mice were sacrificed. To validate the involvement of AMP-activated protein kinase alpha (AMPKα) or cAMP-specific phosphodiesterase 4D (PDE4D), HFD mice were intraperitoneally injected with 20 mg/kg compound C or 0.5 mg/kg rolipram every other day for 8 consecutive weeks before the mice were sacrificed. Hepatic miR-137-3p expression was significantly decreased in mice upon HFD stimulation. miR-137-3p agomir alleviated, while miR-137-3p antagomir facilitated HFD-induced oxidative stress, inflammation, and hepatic dysfunction in mice. Mechanistically, we revealed that miR-137-3p is directly bound to the 3'-untranslated region of PDE4D and subsequently increased hepatic cAMP level and protein kinase A activity, thereby activating the downstream AMPKα pathway. In summary, miR-137-3p improves NAFLD through activating AMPKα and it is a promising therapeutic candidate to treat NAFLD.

Fatty Acid Synthase-Suppressor Screening Identifies Sorting Nexin 8 as a Therapeutic Target for NAFLD

BACKGROUND AND AIMS

NAFLD is the most prevalent chronic liver disease without any Food and Drug Administration-approved pharmacological intervention in clinic. Fatty acid synthase (FASN) is one of the most attractive targets for NAFLD treatment because of its robust rate-limiting capacity to control hepatic de novo lipogenesis. However, the regulatory mechanisms of FASN in NAFLD and potential therapeutic strategies targeting FASN remain largely unknown.

METHODS AND RESULTS

Through a systematic interactomics analysis of FASN-complex proteins, we screened and identified sorting nexin 8 (SNX8) as a binding partner of FASN. SNX8 directly bound to FASN and promoted FASN ubiquitination and subsequent proteasomal degradation. We further demonstrated that SNX8 mediated FASN protein degradation by recruiting the E3 ligase tripartite motif containing 28 (TRIM28) and enhancing the TRIM28-FASN interaction. Notably, Snx8 interference in hepatocytes significantly deteriorated lipid accumulation in vitro, whereas SNX8 overexpression markedly blocked hepatocyte lipid deposition. Furthermore, the aggravating effect of Snx8 deletion on NAFLD was validated in vivo as hepatic steatosis and lipogenic pathways in the liver were significantly exacerbated in Snx8-knockout mice compared to wild-type controls. Consistently, hepatocyte-specific overexpression of Snx8 in vivo markedly suppressed high-fat, high-cholesterol diet (HFHC)-induced hepatic steatosis. Notably, the protective effect of SNX8 against NAFLD was largely dependent on FASN suppression.

CONCLUSIONS

These data indicate that SNX8 is a key suppressor of NAFLD that promotes FASN proteasomal degradation. Targeting the SNX8-FASN axis is a promising strategy for NAFLD prevention and treatment.

Liver Fibrosis and MAFLD: From Molecular Aspects to Novel Pharmacological Strategies

Metabolic-associated fatty liver disease (MAFLD) is a new disease definition, and this nomenclature MAFLD was proposed to renovate its former name, non-alcoholic fatty liver disease (NAFLD). MAFLD/NAFLD have shared and predominate causes from nutrition overload to persistent liver damage and eventually lead to the development of liver fibrosis and cirrhosis. Unfortunately, there is an absence of effective treatments to reverse MAFLD/NAFLD-associated fibrosis. Due to the significant burden of MAFLD/NAFLD and its complications, there are active investigations on the development of novel targets and pharmacotherapeutics for treating this disease. In this review, we cover recent discoveries in new targets and molecules for antifibrotic treatment, which target pathways intertwined with the fibrogenesis process, including lipid metabolism, inflammation, cell apoptosis, oxidative stress, and extracellular matrix formation. Although marked advances have been made in the development of antifibrotic therapeutics, none of the treatments have achieved the endpoints evaluated by liver biopsy or without significant side effects in a large-scale trial. In addition to the discovery of new druggable targets and pharmacotherapeutics, personalized medication, and combinatorial therapies targeting multiple profibrotic pathways could be promising in achieving successful antifibrotic interventions in patients with MAFLD/NAFLD.

Green Tea and Epigallocatechin Gallate (EGCG) for the Management of Nonalcoholic Fatty Liver Diseases (NAFLD): Insights into the Role of Oxidative Stress and Antioxidant Mechanism

Nonalcoholic fatty liver diseases (NAFLD) represent a set of liver disorders progressing from steatosis to steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma, which induce huge burden to human health. Many pathophysiological factors are considered to influence NAFLD in a parallel pattern, involving insulin resistance, oxidative stress, lipotoxicity, mitochondrial dysfunction, endoplasmic reticulum stress, inflammatory cascades, fibrogenic reaction, etc. However, the underlying mechanisms, including those that induce NAFLD development, have not been fully understood. Specifically, oxidative stress, mainly mediated by excessive accumulation of reactive oxygen species, has participated in the multiple NAFLD-related signaling by serving as an accelerator. Ameliorating oxidative stress and maintaining redox homeostasis may be a promising approach for the management of NAFLD. Green tea is one of the most important dietary resources of natural antioxidants, above which epigallocatechin gallate (EGCG) notably contributes to its antioxidative action. Accumulative evidence from randomized clinical trials, systematic reviews, and meta-analysis has revealed the beneficial functions of green tea and EGCG in preventing and managing NAFLD, with acceptable safety in the patients. Abundant animal and cellular studies have demonstrated that green tea and EGCG may protect against NAFLD initiation and development by alleviating oxidative stress and the related metabolism dysfunction, inflammation, fibrosis, and tumorigenesis. The targeted signaling pathways may include, but are not limited to, NRF2, AMPK, SIRT1, NF-κB, TLR4/MYD88, TGF-β/SMAD, and PI3K/Akt/FoxO1, etc. In this review, we thoroughly discuss the oxidative stress-related mechanisms involved in NAFLD development, as well as summarize the protective effects and underlying mechanisms of green tea and EGCG against NAFLD.

P2Y2R Deficiency Ameliorates Hepatic Steatosis by Reducing Lipogenesis and Enhancing Fatty Acid β-Oxidation through AMPK and PGC-1α Induction in High-Fat Diet-Fed Mice

Non-alcoholic fatty liver disease (NAFLD) is a chronic metabolic liver disease associated with obesity and insulin resistance. Activation of the purinergic receptor P2Y2R has been reported to promote adipogenesis, inflammation and dyslipidemia in adipose tissues in obese mice. However, the role of P2Y2R and its mechanisms in NAFLD remain unknown. We hypothesized that P2Y2R deficiency may play a protective role in NAFLD by modulating lipid metabolism in the liver. In this study, we fed wild type and P2Y2R knockout mice with a high-fat diet (HFD) for 12 weeks and analyzed metabolic phenotypes. First, P2Y2R deficiency effectively improved insulin resistance with a reduction in body weight and plasma insulin. Second, P2Y2R deficiency attenuated hepatic lipid accumulation and injury with reduced alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Third, P2Y2R deficiency decreased the expression of fatty acid synthesis mediators (cluster of differentiation (CD36), fatty acid synthase (FAS), and stearoyl-CoA desaturase 1 (SCD1)); and increased the expression of adipose triglyceride lipase (ATGL), a lipolytic enzyme. Mechanistically, P2Y2R deficiency increased the AMP-activated protein kinase (AMPK) activity to improve mitochondrial fatty acid β-oxidation (FAO) by regulating acetyl-CoA carboxylase (ACC) and carnitine palmitoyltransferase 1A (CPT1A)-mediated FAO pathway. In addition, P2Y2R deficiency increased peroxisome proliferator-activated gamma co-activator-1α (PGC-1α)-mediated mitochondrial biogenesis. Conclusively, P2Y2R deficiency ameliorated HFD-induced hepatic steatosis by enhancing FAO through AMPK signaling and PGC-1α pathway, suggesting P2Y2R as a promising therapeutic target for NAFLD.

Immunity as Cornerstone of Non-Alcoholic Fatty Liver Disease: The Contribution of Oxidative Stress in the Disease Progression

Non-alcoholic fatty liver disease (NAFLD) is considered the hepatic manifestation of metabolic syndrome and has become the major cause of chronic liver disease, especially in western countries. NAFLD encompasses a wide spectrum of hepatic histological alterations, from simple steatosis to steatohepatitis and cirrhosis with a potential development of hepatocellular carcinoma. Non-alcoholic steatohepatitis (NASH) is characterized by lobular inflammation and fibrosis. Several studies reported that insulin resistance, redox unbalance, inflammation, and lipid metabolism dysregulation are involved in NAFLD progression. However, the mechanisms beyond the evolution of simple steatosis to NASH are not clearly understood yet. Recent findings suggest that different oxidized products, such as lipids, cholesterol, aldehydes and other macromolecules could drive the inflammation onset. On the other hand, new evidence indicates innate and adaptive immunity activation as the driving force in establishing liver inflammation and fibrosis. In this review, we discuss how immunity, triggered by oxidative products and promoting in turn oxidative stress in a vicious cycle, fuels NAFLD progression. Furthermore, we explored the emerging importance of immune cell metabolism in determining inflammation, describing the potential application of trained immune discoveries in the NASH pathological context.

Cardiolipin Synthase 1 Ameliorates NASH Through Activating Transcription Factor 3 Transcriptional Inactivation

BACKGROUND AND AIMS

NASH is an increasingly prevalent disease that is the major cause of liver dysfunction. Previous research has indicated that adipose cardiolipin synthase 1 (CRLS1) levels are associated with insulin sensitivity; however, the precise roles of CRLS1 and underlying mechanisms involving CRLS1 in the pathological process of NASH have not been elucidated.

APPROACH AND RESULTS

Here, we discovered that CRLS1 was significantly down-regulated in genetically obese and diet-induced mice models. In vitro studies demonstrated that overexpression of CRLS1 markedly attenuated hepatic steatosis and inflammation in hepatocytes, whereas short hairpin RNA-mediated CRLS1 knockdown aggravated these abnormalities. Moreover, high-fat diet-induced insulin resistance and hepatic steatosis were significantly exacerbated in hepatocyte-specific Crls1-knockout (Crls1-HKO) mice. It is worth noting that Crls1 depletion significantly aggravated high-fat and high-cholesterol diet-induced inflammatory response and fibrosis during NASH development. RNA-sequencing analysis systematically demonstrated a prominently aggravated lipid metabolism disorder in which inflammation and fibrosis resulted from Crls1 deficiency. Mechanically, activating transcription factor 3 (ATF3) was identified as the key differentially expressed gene in Crls1-HKO mice through transcriptomic analysis, and our investigation further showed that CRLS1 suppresses ATF3 expression and inhibits its activity in palmitic acid-stimulated hepatocytes, whereas ATF3 partially reverses lipid accumulation and inflammation inhibited by CRLS1 overexpression under metabolic stress.

CONCLUSIONS

In conclusion, CRLS1 ameliorates insulin resistance, hepatic steatosis, inflammation, and fibrosis during the pathological process of NASH by inhibiting the expression and activity of ATF3.

Soluble Klotho Improves Hepatic Glucose and Lipid Homeostasis in Type 2 Diabetes

Type 2 diabetes (T2D) is one of the most escalating global metabolic diseases, which is highly associated with insulin resistance (IR) and risk of combination with nonalcoholic fatty liver disease (NAFLD). Previous studies suggest that soluble klotho (sKL) could serve as a circulating hormone to mediate energy metabolism, but the detailed mechanism is poorly understood. In this study, we generated T2D models of wild-type (WT), sKL heterozygous (KL ^+/-), and sKL transgenic (TgKL) mice continuously fed a high-fat diet (HFD) and constructed L02 cell lines that stably overexpress sKL to investigate the effect of sKL on hepatic glucose and lipid metabolism. Surprisingly, we discovered that sKL deficiency resulted in exacerbated diabetic phenotypes and hepatic glucolipid metabolism disorders in HFD-fed KL ^+/- diabetic mice (KL ^+/- DM), whereas TgKL diabetic mice (TgKL DM) exhibited ameliorated diabetic phenotypes and decreased IR. Mechanistic studies in vitro and in vivo demonstrated that sKL could inhibit the PI3K/AKT/mTORC1 signaling to upregulate peroxisome proliferator-activated receptor α (PPARα) expression by directly interacting with type 1 insulin-like growth factor receptor (IGF1R) in HFD-fed T2D mice. Thus, sKL could improve hepatic glucolipid homeostasis to ameliorate diabetic phenotypes and lipid accumulation and may function as a potential therapeutic target for the treatment of T2D and reduce the risk of NAFLD.

C-Jun/C7ORF41/NF-κB axis mediates hepatic inflammation and lipid accumulation in NAFLD

Nonalcoholic fatty liver disease (NAFLD) is an expanding health problem worldwide. Although many studies have made great efforts to elucidate the pathogenesis of NAFLD, the molecular basis remains poorly understood. Here, we showed that hepatic C7ORF41, a critical regulator of innate immune response, was markedly decreased in diet or genetic-induced NAFLD model. We also demonstrated that C7ORF41 overexpression significantly ameliorated hepatic inflammation and lipid accumulation in palmitic acid (PA)-treated hepatocytes, whereas C7ORF41 knockdown showed the opposite effects. Mechanistically, we found the anti-inflammatory role of C7ORF41 was attributed to the suppression of NF-κB p65-mediated induction of inflammatory cytokines. Moreover, we demonstrated that the suppression of C7ORF41 expression in hepatocytes is due to JNK activation, which promotes c-Jun-mediated transcriptional repression of C7ORF41. In conclusion, our findings suggested that a c-Jun/C7ORF41/NF-κB regulatory network controls the inflammatory response and lipid accumulation in NAFLD and may benefit the development of novel and promising therapeutic targets for NAFLD.