Liver X Receptor Alpha Activation Inhibits Autophagy and Lipophagy in Hepatocytes by Dysregulating Autophagy-Related 4B Cysteine Peptidase and Rab-8B, Reducing Mitochondrial Fuel Oxidation

Autophagy and hepatic lipid metabolism: mechanistic insight and therapeutic potential for MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) originates from a homeostatic imbalance in hepatic lipid metabolism. Increased fat deposition in the liver of people suffering from MASLD predisposes them to develop further metabolic derangements, including diabetes mellitus, metabolic dysfunction-associated steatohepatitis (MASH), and other end-stage liver diseases. Unfortunately, only limited pharmacological therapies exist for MASLD to date. Autophagy, a cellular catabolic process, has emerged as a primary mechanism of lipid metabolism in mammalian hepatocytes. Furthermore, preclinical studies with autophagy modulators have shown promising results in resolving MASLD and mitigating its progress into deleterious liver pathologies. In this review, we discuss our current understanding of autophagy-mediated hepatic lipid metabolism, its therapeutic modulation for MASLD treatment, and current limitations and scope for clinical translation.

Unveiling global research trends and hotspots on mitochondria in NAFLD from 2000 to 2023: A bibliometric analysis

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) has garnered significant attention in the past decade as a prevalent chronic liver condition. Despite a growing body of evidence implicating mitochondria in NAFLD development, comprehensive bibliometric analyses within this research domain are scarce. This study aims to provide a thorough overview of the knowledge framework and key research areas related to mitochondria in the context of NAFLD, utilizing bibliometric techniques.

METHODS

A comprehensive search of publications on mitochondria in NAFLD from 2000 to 2023 was conducted using the Web of Science Core Collection database. VOSviewers, CiteSpace, and the R package "bibliometrix" were employed for a precise assessment of the literature.

RESULTS

Examining 2530 articles from 77 countries, primarily led by the United States and China, revealed a consistent increase in publications on mitochondria's role in NAFLD. Leading research institutions include the University of Coimbra, the University of Missouri, the Chinese Academy of Sciences, Fudan University, and Shanghai Jiao Tong University. Notably, the International Journal of Molecular Sciences emerged as the most popular journal, and Hepatology was the most frequently cited. With contributions from 14,543 authors, Michael Roden published the highest number of papers, and A. J. Samyal was the most frequently cocited author. Key focus areas include investigating mitochondrial mechanisms impacting NAFLD and developing therapeutic strategies targeting mitochondria. Emerging research hotspots are associated with keywords such as "inflammation," "mitochondrial dysfunction," "autophagy," "obesity," and "insulin resistance."

CONCLUSION

This study, the first comprehensive bibliometric analysis, synthesizes research trends and advancements in the role of mitochondria in NAFLD. Insights derived from this analysis illuminate current frontiers and emerging areas of interest, providing a valuable reference for scholars dedicated to mitochondrial studies.

Dysfunction of autophagy in high-fat diet-induced non-alcoholic fatty liver disease

ABBREVIATIONS

ACOX1: acyl-CoA oxidase 1; ADH5: alcohol dehydrogenase 5 (class III), chi polypeptide; ADIPOQ: adiponectin, C1Q and collagen domain containing; ATG: autophagy related; BECN1: beclin 1; CRTC2: CREB regulated transcription coactivator 2; ER: endoplasmic reticulum; F2RL1: F2R like trypsin receptor 1; FA: fatty acid; FOXO1: forkhead box O1; GLP1R: glucagon like peptide 1 receptor; GRK2: G protein-coupled receptor kinase 2; GTPase: guanosine triphosphatase; HFD: high-fat diet; HSCs: hepatic stellate cells; HTRA2: HtrA serine peptidase 2; IRGM: immunity related GTPase M; KD: knockdown; KDM6B: lysine demethylase 6B; KO: knockout; LAMP2: lysosomal associated membrane protein 2; LAP: LC3-associated phagocytosis; LDs: lipid droplets; Li KO: liver-specific knockout; LSECs: liver sinusoidal endothelial cells; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAP3K5: mitogen-activated protein kinase kinase kinase 5; MED1: mediator complex subunit 1; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin complex 1; NAFLD: non-alcoholic fatty liver disease; NASH: non-alcoholic steatohepatitis; NFE2L2: NFE2 like bZIP transcription factor 2; NOS3: nitric oxide synthase 3; NR1H3: nuclear receptor subfamily 1 group H member 3; OA: oleic acid; OE: overexpression; OSBPL8: oxysterol binding protein like 8; PA: palmitic acid; RUBCNL: rubicon like autophagy enhancer; PLIN2: perilipin 2; PLIN3: perilipin 3; PPARA: peroxisome proliferator activated receptor alpha; PRKAA2/AMPK: protein kinase AMP-activated catalytic subunit alpha 2; RAB: member RAS oncogene family; RPTOR: regulatory associated protein of MTOR complex 1; SCD: stearoyl-CoA desaturase; SIRT1: sirtuin 1; SIRT3: sirtuin 3; SNARE: soluble N-ethylmaleimide-sensitive factor attachment protein receptor; SQSTM1/p62: sequestosome 1; SREBF1: sterol regulatory element binding transcription factor 1;SREBF2: sterol regulatory element binding transcription factor 2; STING1: stimulator of interferon response cGAMP interactor 1; STX17: syntaxin 17; TAGs: triacylglycerols; TFEB: transcription factor EB; TP53/p53: tumor protein p53; ULK1: unc-51 like autophagy activating kinase 1; VMP1: vacuole membrane protein 1.

Liraglutide ameliorates hepatic steatosis via retinoic acid receptor-related orphan receptor α-mediated autophagy pathway

Liraglutide, an analog of human glucagon-like peptide-1 (GLP-1), has been found to improve hepatic steatosis in clinical practice. However, the underlying mechanism remains to be fully defined. Increasing evidence suggests that retinoic acid receptor-related orphan receptor α (RORα) is involved in hepatic lipid accumulation. In the current study, we investigated whether the ameliorating impact of liraglutide on lipid-induced hepatic steatosis is dependent on RORα activity and examined the underlying mechanisms. Cre-loxP-mediated, liver-specific Rorα knockout (Rora LKO) mice, and littermate controls with a Roraloxp/loxp genotype were established. The effects of liraglutide on lipid accumulation were evaluated in mice challenged with a high-fat diet (HFD) for 12 weeks. Moreover, mouse AML12 hepatocytes expressing small interfering RNA (siRNA) of Rora were exposed to palmitic acid to explore the pharmacological mechanism of liraglutide. The results showed that liraglutide treatment significantly alleviated HFD-induced liver steatosis, marked by reduced liver weight and triglyceride accumulation, improved glucose tolerance and serum levels of lipid profiles and aminotransferase. Consistently, liraglutide also ameliorated lipid deposits in a steatotic hepatocyte model in vitro. In addition, liraglutide treatment reversed the HFD-induced downregulation of Rora expression and autophagic activity in mouse liver tissues. However, the beneficial effect of liraglutide on hepatic steatosis was not observed in Rora LKO mice. Mechanistically, the ablation of Rorα in hepatocytes diminished liraglutide-induced autophagosome formation and the fusion of autophagosomes and lysosomes, resulting in weakened autophagic flux activation. Thus, our findings suggest that RORα is essential for the beneficial impact of liraglutide on lipid deposition in hepatocytes and regulates autophagic activity in the underlying mechanism.

Recent insights into the pathogenesis and therapeutic targets of chronic liver diseases

Viral hepatitis, alcohol-associated liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD) are the three major causes of chronic liver diseases, which account for approximately 2 million deaths per year worldwide. The current direct-acting antiviral drugs and vaccinations have effectively reduced and ameliorated viral hepatitis infection, but there are still no effective drug treatments for ALD, NAFLD and liver cancer due to the poor understanding of their pathogenesis. To better understand the pathogenesis, the fifth Chinese American Liver Society/Society of Chinese Bioscientists in America Hepatology Division Annual Symposium, which was held virtually on 21-22 October 2022, focused on the topics related to ALD, NAFLD and liver cancer. Here, we briefly highlight the presentations that focus on the current progress in basic and translational research in ALD, NAFLD and liver cancer. The roles of non-coding RNA, autophagy, extrahepatic signalling, macrophages, etc in liver diseases are deliberated, and the application of single-cell RNA sequencing in the study of liver disease is also discussed.

Hypoxia-induced GPCPD1 depalmitoylation triggers mitophagy via regulating PRKN-mediated ubiquitination of VDAC1

Mitophagy, which selectively eliminates the dysfunctional and excess mitochondria by autophagy, is crucial for cellular homeostasis under stresses such as hypoxia. Dysregulation of mitophagy has been increasingly linked to many disorders including neurodegenerative disease and cancer. Triple-negative breast cancer (TNBC), a highly aggressive breast cancer subtype, is reported to be characterized by hypoxia. However, the role of mitophagy in hypoxic TNBC as well as the underlying molecular mechanism is largely unexplored. Here, we identified GPCPD1 (glycerophosphocholine phosphodiesterase 1), a key enzyme in choline metabolism, as an essential mediator in hypoxia-induced mitophagy. Under the hypoxic condition, we found that GPCPD1 was depalmitoylated by LYPLA1, which facilitated the relocating of GPCPD1 to the outer mitochondrial membrane (OMM). Mitochondria-localized GPCPD1 could bind to VDAC1, the substrate for PRKN/PARKIN-dependent ubiquitination, thus interfering with the oligomerization of VDAC1. The increased monomer of VDAC1 provided more anchor sites to recruit PRKN-mediated polyubiquitination, which consequently triggered mitophagy. In addition, we found that GPCPD1-mediated mitophagy exerted a promotive effect on tumor growth and metastasis in TNBC both in vitro and in vivo. We further determined that GPCPD1 could serve as an independent prognostic indicator in TNBC. In conclusion, our study provides important insights into a mechanistic understanding of hypoxia-induced mitophagy and elucidates that GPCPD1 could act as a potential target for the future development of novel therapy for TNBC patients.Abbreviations: ACTB: actin beta; 5-aza: 5-azacytidine; BNIP3: BCL2 interacting protein 3; BNIP3L: BCL2 interacting protein 3 like; CCCP: carbonyl cyanide m-chlorophenyl hydrazone; ChIP: chromatin immunoprecipitation; co-IP: co-immunoprecipitation; CQ: chloroquine; CsA: cyclosporine; DOX: doxorubicin; FIS1: fission, mitochondrial 1; FUNDC1: FUN14 domain containing 1; GPCPD1: glycerophosphocholine phosphodiesterase 1; HAM: hydroxylamine; HIF1A: hypoxia inducible factor 1 subunit alpha; HRE: hypoxia response element; IF: immunofluorescence; LB: lysis buffer; LC3B/MAP1LC3B: microtubule associated protein 1 light chain 3 beta; LC-MS: liquid chromatography-mass spectrometry; LYPLA1: lysophospholipase 1; LYPLA2: lysophospholipase 2; MDA231: MDA-MB-231; MDA468: MDA-MB-468; MFN1: mitofusin 1; MFN2: mitofusin 2; MKI67: marker of proliferation Ki-67; OCR: oxygen consumption rate; OMM: outer mitochondrial membrane; OS: overall survival; PalmB: palmostatin B; PBS: phosphate-buffered saline; PINK1: PTEN induced kinase 1; PRKN: parkin RBR E3 ubiquitin protein ligase; SDS: sodium dodecyl sulfate; TOMM20: translocase of outer mitochondrial membrane 20; TNBC: triple-negative breast cancer; VBIT-4: VDAC inhibitor; VDAC1: voltage dependent anion channel 1; WT: wild type.

Targeting Liver X Receptors for the Treatment of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) refers to a range of conditions in which excess lipids accumulate in the liver, possibly leading to serious hepatic manifestations such as steatohepatitis, fibrosis/cirrhosis and cancer. Despite its increasing prevalence and significant impact on liver disease-associated mortality worldwide, no medication has been approved for the treatment of NAFLD yet. Liver X receptors α/β (LXRα and LXRβ) are lipid-activated nuclear receptors that serve as master regulators of lipid homeostasis and play pivotal roles in controlling various metabolic processes, including lipid metabolism, inflammation and immune response. Of note, NAFLD progression is characterized by increased accumulation of triglycerides and cholesterol, hepatic de novo lipogenesis, mitochondrial dysfunction and augmented inflammation, all of which are highly attributed to dysregulated LXR signaling. Thus, targeting LXRs may provide promising strategies for the treatment of NAFLD. However, emerging evidence has revealed that modulating the activity of LXRs has various metabolic consequences, as the main functions of LXRs can distinctively vary in a cell type-dependent manner. Therefore, understanding how LXRs in the liver integrate various signaling pathways and regulate metabolic homeostasis from a cellular perspective using recent advances in research may provide new insights into therapeutic strategies for NAFLD and associated metabolic diseases.

Current, emerging, and potential therapies for non-alcoholic steatohepatitis

Non-alcoholic fatty liver disease (NAFLD) has been identified as the most common chronic liver disease worldwide, with a growing incidence. NAFLD is considered the hepatic manifestation of a metabolic syndrome that emerges from multiple factors (e.g., oxidative stress, metabolic disorders, endoplasmic reticulum stress, cell death, and inflammation). Non-alcoholic steatohepatitis (NASH), an advanced form of NAFLD, has been reported to be a leading cause of cirrhosis and hepatic carcinoma, and it is progressing rapidly. Since there is no approved pharmacotherapy for NASH, a considerable number of therapeutic targets have emerged with the deepening of the research on NASH pathogenesis. In this study, the therapeutic potential and properties of regulating metabolism, the gut microbiome, antioxidant, microRNA, inhibiting apoptosis, targeting ferroptosis, and stem cell-based therapy in NASH are reviewed and evaluated. Since the single-drug treatment of NASH is affected by individual heterogeneous responses and side effects, it is imperative to precisely carry out targeted therapy with low toxicity. Lastly, targeted therapeutic agent delivery based on exosomes is proposed in this study, such that drugs with different mechanisms can be incorporated to generate high-efficiency and low-toxicity individualized medicine.

Restoration of lipid homeostasis between TG and PE by the LXRα-ATGL/EPT1 axis ameliorates hepatosteatosis

Converting lipid disturbances in response to energy oversupply into healthy lipid homeostasis is a promising therapy to alleviate hepatosteatosis. Our clinical studies found that a further elevation of triglyceride (TG) in obese patients with the body mass index (BMI) greater than 28 was accompanied by a further reduction of phosphatidylethanolamine (PE). Shorter survival and poor prognosis were shown for the patients with high TG and low PE levels. Liver X receptor alpha (LXRα) knockout mice aggravated high-fat diet (HFD)-induced obesity and lipid disorders, making the TG enrichment and the PE decrease more pronounced according to the liver lipidomics analysis. The RNA-seq from mice liver exhibited that these metabolism disorders were attributed to the decline of Atgl (encoding the TG metabolism enzyme ATGL) and Ept1 (encoding the PE synthesis enzyme EPT1) expression. Mechanistic studies uncovered that LXRα activated the ATGL and EPT1 gene via direct binding to a LXR response element (LXRE) in the promoter. Moreover, both the supplement of PE in statin or fibrate therapy, and the LXRα inducer (oridonin) ameliorated cellular lipid deposition and lipotoxicity. Altogether, restoration of lipid homeostasis of TG and PE via the LXRα-ATGL/EPT1 axis may be a potential approach for the management of hepatosteatosis and metabolic syndrome.

Microsomal Prostaglandin E Synthase-1 and -2: Emerging Targets in Non-Alcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) affects a substantial proportion of the general population and is even more prevalent in obese and diabetic patients. NAFLD, and particularly the more advanced manifestation of the disease, nonalcoholic steatohepatitis (NASH), increases the risk for both liver-related and cardiovascular morbidity. The pathogenesis of NAFLD is complex and multifactorial, with many molecular pathways implicated. Emerging data suggest that microsomal prostaglandin E synthase-1 and -2 might participate in the development and progression of NAFLD. It also appears that targeting these enzymes might represent a novel therapeutic approach for NAFLD. In the present review, we discuss the association between microsomal prostaglandin E synthase-1 and -2 and NAFLD.

Increased Hepatic ATG7 mRNA and ATG7 Protein Expression in Nonalcoholic Steatohepatitis Associated with Obesity

The autophagy gene ATG7 has been shown to be essential for the induction of autophagy, a process that used to be suppressed in nonalcoholic fatty liver disease (NAFLD). However, the specific role of ATG7 in NAFLD remains unclear. The aim of this study was to analyze hepatic ATG7 mRNA and ATG7 protein expression regarding obesity-associated NAFLD. Patients included women classified into normal weight (NW, n = 6) and morbid obesity (MO, n = 72). The second group was subclassified into normal liver (NL, n = 11), simple steatosis (SS, n= 29), and nonalcoholic steatohepatitis (NASH, n = 32). mRNA expression was analyzed by RT-qPCR and protein expression was evaluated by Western blotting. Our results showed that NASH patients presented higher ATG7 mRNA and ATG7 protein levels. ATG7 mRNA expression was increased in NASH compared with SS, while ATG7 protein abundance was enhanced in NASH compared with NL. ATG7 mRNA correlated negatively with the expression of some hepatic lipid metabolism-related genes and positively with endocannabinoid receptors, adiponectin hepatic expression, and omentin levels. These results suggest that ATG7-mediated autophagy may play an important role in the pathogenesis of NAFLD, especially in NASH, perhaps playing a possible protective role. However, this is a preliminary study that needs to be further studied.

Induction of autophagy via the PI3K/Akt/mTOR signaling pathway by Pueraria flavonoids improves non-alcoholic fatty liver disease in obese mice

Non-alcoholic fatty liver disease (NAFLD) is the most common among lipid metabolism disorders. Autophagy plays an important role in lipid metabolism in NAFLD. Pueraria flavonoids, the main active ingredients of Pueraria lobata, exert antioxidant and anti-inflammatory effects. Herein, we report the potential lipid-lowering and anti-inflammatory effects of Pueraria flavonoids on NAFLD induced by a high-fat diet. In vivo and in vitro experiments showed that Pueraria flavonoids reduced intracellular lipid deposition by inhibiting lipid synthesis and the release of pro-inflammatory cytokines. We analyzed the autophagy flux by mRFP-GFP-LC3 plasmid transfection to assess the role of autophagy in intracellular scavenging. After treating mice fed on high fat and HepG2 cells with Pueraria flavonoids, the number of autophagosomes increased significantly, along with the level of autophagy. The autophagy loss after siRNA transfection aggravated lipid deposition and the release of inflammatory cytokines. Mechanistically, Pueraria flavonoids trigger autophagy through PI3K/Akt/mTOR signaling pathway to reduce lipid deposition and inflammation. In summary, our results showed that Pueraria flavonoids stimulated autophagy by inhibiting the PI3K/Akt/mTOR signaling pathway, thereby reducing intracellular lipid accumulation and inflammation levels and alleviating NAFLD.

Pathogenesis and treatment of non-alcoholic steatohepatitis and its fibrosis

The initial presentation of non-alcoholic steatohepatitis (NASH) is hepatic steatosis. The dysfunction of lipid metabolism within hepatocytes caused by genetic factors, diet, and insulin resistance causes lipid accumulation. Lipotoxicity, oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum stress would further contribute to hepatocyte injury and death, leading to inflammation and immune dysfunction in the liver. During the healing process, the accumulation of an excessive amount of fibrosis might occur while healing. During the development of NASH and liver fibrosis, the gut-liver axis, adipose-liver axis, and renin-angiotensin system (RAS) may be dysregulated and impaired. Translocation of bacteria or its end-products entering the liver could activate hepatocytes, Kupffer cells, and hepatic stellate cells, exacerbating hepatic steatosis, inflammation, and fibrosis. Bile acids regulate glucose and lipid metabolism through Farnesoid X receptors in the liver and intestine. Increased adipose tissue-derived non-esterified fatty acids would aggravate hepatic steatosis. Increased leptin also plays a role in hepatic fibrogenesis, and decreased adiponectin may contribute to hepatic insulin resistance. Moreover, dysregulation of peroxisome proliferator-activated receptors in the liver, adipose, and muscle tissues may impair lipid metabolism. In addition, the RAS may contribute to hepatic fatty acid metabolism, inflammation, and fibrosis. The treatment includes lifestyle modification, pharmacological therapy, and non-pharmacological therapy. Currently, weight reduction by lifestyle modification or surgery is the most effective therapy. However, vitamin E, pioglitazone, and obeticholic acid have also been suggested. In this review, we will introduce some new clinical trials and experimental therapies for the treatment of NASH and related fibrosis.

Induction of the hepatic aryl hydrocarbon receptor by alcohol dysregulates autophagy and phospholipid metabolism via PPP2R2D

Disturbed lipid metabolism precedes alcoholic liver injury. Whether and how AhR alters degradation of lipids, particularly phospho-/sphingo-lipids during alcohol exposure, was not explored. Here, we show that alcohol consumption in mice results in induction and activation of aryl hydrocarbon receptor (AhR) in the liver, and changes the hepatic phospho-/sphingo-lipids content. The levels of kynurenine, an endogenous AhR ligand, are elevated with increased hepatic tryptophan metabolic enzymes in alcohol-fed mice. Either alcohol or kynurenine treatment promotes AhR activation with autophagy dysregulation via AMPK. Protein Phosphatase 2 Regulatory Subunit-Bdelta (Ppp2r2d) is identified as a transcriptional target of AhR. Consequently, PPP2R2D-dependent AMPKα dephosphorylation causes autophagy inhibition and mitochondrial dysfunction. Hepatocyte-specific AhR ablation attenuates steatosis, which is associated with recovery of phospho-/sphingo-lipids content. Changes of AhR targets are corroborated using patient specimens. Overall, AhR induction by alcohol inhibits autophagy in hepatocytes through AMPKα, which is mediated by Ppp2r2d gene transactivation, revealing an AhR-dependent metabolism of phospho-/sphingo-lipids.

Antioxidative myricetin-enriched nanoparticles towards acute liver injury

Acute liver injury (ALI) could severely destroy the liver function and cause inevitable damage to human health. Studies have demonstrated that excessive reactive oxygen species (ROS) and accompanying inflammatory factors play vital roles in the ALI disease. Herein, we fabricated a kind of nature-inspired myricetin-enriched nanomaterial via Michael addition and Schiff base reaction, which possessed uniform morphology, tunable component ratios, great stabilities, promising free radical scavenging abilities, biocompatibility and protective effects towards cells under oxidative stress. Additionally, the therapeutic effects were demonstrated using an ALI model by down-regulating ROS and inflammatory levels and restoring the liver function. This study could provide a strategy to construct robust and antioxidative nanomaterials using naturally occurring molecules against intractable diseases.

Advances of microRNAs in regulating mitochondrial function: new potential application in NAFLD treatment

Nonalcoholic fatty liver disease (NAFLD) is one of the most common metabolic diseases and closely associated with lipid disorder. Mitochondrion has been recognized to play a key role in lipid metabolism as the main site of energy metabolism in cells, and its dysfunction is involved in the progression of NAFLD. MicroRNAs (miRNAs), one of regulators in the pathogenesis of NAFLD, are discovered to modulate mitochondrial function by targeting mitochondrial proteins or mitochondrial-related factors, thereby improving or deteriorating NAFLD-associated pathologies. This review summarizes the differentially expressed miRNAs from clinical and experimental models of NAFLD with abilities in regulating mitochondrial function, expounds their underlying molecular mechanism and discusses their prospect and future research direction.

Hepatic lipid accumulation induced by a high-fat diet is regulated by Nrf2 through multiple pathways

Nuclear factor erythroid 2-related factor 2 (Nrf2) is reportedly involved in hepatic lipid metabolism, but the results are contradictory, and the underlying mechanism remains unclear. Here, we focused on elucidating the effects of Nrf2 on hepatic adipogenesis and on determining the possible underlying mechanism. We established a non-alcoholic fatty liver disease (NAFLD) model in a high-fat diet (HFD)-fed Nrf2 knockout (Nrf2 KO) mice; further, a cell model of lipid accumulation was established using mouse primary hepatocytes (MPHs) treated with free fatty acids (FAs). Using these models, we investigated the relationship between Nrf2 and autophagy and its role in the development of NAFLD. We observed that Nrf2 expression levels were upregulated in patients with NAFLD and diet-induced obese mice. Nrf2 deficiency led to hepatic lipid accumulation in vivo and in vitro, in addition to, promoting lipogenesis mainly by increasing SREBP-1c activity. Moreover, Nrf2 deficiency attenuated autophagic flux and inhibited the fusion of autophagosomes and lysosomes in vivo and in vitro. Decreased autophagy caused reduced lipolysis in the liver. Importantly, chromatin immunoprecipitation-qPCR (ChIP-qPCR) and dual-luciferase assay results proved that Nrf2 bound to the LAMP1 promoter and regulated its transcriptional activity. Accordingly, we report that Nrf2-LAMP1 interaction plays an indispensable role in Nrf2-regulated hepatosteatosis. Our data collectively confirm that Nrf2 deficiency promotes hepatosteatosis by enhancing SREBP-1c activity and attenuating autophagy. Our findings provide a novel multi-pathway effect of Nrf2 on lipid metabolism in the liver. We believe that multi-target intervention of Nrf2 is a novel strategy for the treatment of NAFLD.

Scavenging ROS to Alleviate Acute Liver Injury by ZnO-NiO@COOH

Currently, the incidence of acute liver injury (ALI) is increasing year by year, and infection with coronavirus disease 2019 (COVID-19) can also induce ALI, but there are still no targeted therapeutic drugs. ZnO-NiO particles is mainly used to clean up reactive oxygen species (ROS) in industrial wastewater, and it is insoluble in water. Its excellent properties are discovered and improved by adding shuttle-based bonds to make it more water-soluble. ZnO-NiO@COOH particles are synthetically applied to treat ALI. The p-n junction in ZnO-NiO@COOH increases the surface area and active sites, thereby creating large numbers of oxygen vacancies, which can quickly adsorb ROS. The content in tissues and serum levels of L-glutathione (GSH) and the GSH/oxidized GSH ratio are measured to assess the capacity of ZnO-NiO@COOH particles to absorb ROS. The ZnO-NiO@COOH particles significantly reduce the expression levels of inflammatory factors (i.e., IL-1, IL-6, and TNF-α), macrophage infiltration, and granulocyte activation. ZnO-NiO@COOH rapidly adsorb ROS in a short period of time to block the generation of inflammatory storms and gain time for the follow-up treatment of ALI, which has important clinical significance.

Transcriptional Regulation of Hepatic Autophagy by Nuclear Receptors

Autophagy is an adaptive self-eating process involved in degradation of various cellular components such as carbohydrates, lipids, proteins, and organelles. Its activity plays an essential role in tissue homeostasis and systemic metabolism in response to diverse challenges, including nutrient depletion, pathogen invasion, and accumulations of toxic materials. Therefore, autophagy dysfunctions are intimately associated with many human diseases such as cancer, neurodegeneration, obesity, diabetes, infection, and aging. Although its acute post-translational regulation is well described, recent studies have also shown that autophagy can be controlled at the transcriptional and post-transcriptional levels. Nuclear receptors (NRs) are in general ligand-dependent transcription factors consisting of 48 members in humans. These receptors extensively control transcription of a variety of genes involved in development, metabolism, and inflammation. In this review, we discuss the roles and mechanisms of NRs in an aspect of transcriptional regulation of hepatic autophagy, and how the NR-driven autophagy pathway can be harnessed to treat various liver diseases.

RORα Enhances Lysosomal Acidification and Autophagic Flux in the Hepatocytes

Lysosomes are intracellular acidic organelles with catabolic functions that contribute to the activation of autophagy. Although autophagy abnormality is associated with defects in lysosomal acidification during the progression of nonalcoholic fatty liver disease (NAFLD), the mechanisms of control of lysosomal acidification are not well understood at the molecular level. Thus, we aimed to elucidate the role of the orphan nuclear receptor retinoic acid-related orphan receptor α (RORα) in lysosomal acidification and autophagic flux, particularly in nutrition-enriched hepatocytes. First, lysosomal acidity was much lower in the hepatocytes obtained from hepatocyte-specific RORα-deleted (RORα-LKO) mice, whereas the infusion of an adenovirus encoding RORα in wild-type hepatocytes increased lysosomal acidity, as determined by LysoSensor. Second, the lysosomal translocation of the mechanistic target of rapamycin was increased and immature cathepsin D was accumulated in the liver of RORα-LKO mice. Third, the accumulation of LC3-II, p62/sequestosome 1 (SQSTM1), and neighbor of BRCA1 gene 1 (NBR1) was increased in the livers of RORα-LKO mice, indicating an impaired autophagic flux in the livers. Consistently, the number of autolysosomes containing mitochondria and lipid droplets was dramatically reduced in the RORα-deleted hepatocytes. Finally, we found that RORα induced the transcription of genes involved in lysosomal function, such as Atp6v1g1, a vacuolar H+ -ATPase (v-ATPase) subunit, which were largely down-regulated in the livers of mice with high-fat diet-induced NAFLD and patients with hepatitis. Conclusion: Targeting RORα may be a potential therapeutic strategy to restore lysosomal acidification, which inhibits the progression of NAFLD.

Resolvin D1 Suppresses H2O2-Induced Senescence in Fibroblasts by Inducing Autophagy through the miR-1299/ARG2/ARL1 Axis

ARG2 has been reported to inhibit autophagy in vascular endothelial cells and keratinocytes. However, studies of its mechanism of action, its role in skin fibroblasts, and the possibility of promoting autophagy and inhibiting cellular senescence through ARG2 inhibition are lacking. We induced cellular senescence in dermal fibroblasts by using H2O2. H2O2-induced fibroblast senescence was inhibited upon ARG2 knockdown and promoted upon ARG2 overexpression. The microRNA miR-1299 suppressed ARG2 expression, thereby inhibiting fibroblast senescence, and miR-1299 inhibitors promoted dermal fibroblast senescence by upregulating ARG2. Using yeast two-hybrid assay, we found that ARG2 binds to ARL1. ARL1 knockdown inhibited autophagy and ARL1 overexpression promoted it. Resolvin D1 (RvD1) suppressed ARG2 expression and cellular senescence. These data indicate that ARG2 stimulates dermal fibroblast cell senescence by inhibiting autophagy after interacting with ARL1. In addition, RvD1 appears to promote autophagy and inhibit dermal fibroblast senescence by inhibiting ARG2 expression. Taken together, the miR-1299/ARG2/ARL1 axis emerges as a novel mechanism of the ARG2-induced inhibition of autophagy. Furthermore, these results indicate that miR-1299 and pro-resolving lipids, including RvD1, are likely involved in inhibiting cellular senescence by inducing autophagy.

The roles of autophagy and thyroid hormone in the pathogenesis and treatment of NAFLD

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disorder worldwide. It comprises simple steatosis and non-alcoholic steatohepatitis (NASH), which can further progress to cirrhosis and hepatocellular carcinoma. The pathogenesis of NAFLD involves genetic, environmental, and endocrine factors, and several molecular mechanisms have been identified. In this review, we discuss the recent findings on the role of autophagy, in particular lipophagy and mitophagy, in hepatic lipid oxidation. We discuss the pre-clinical and clinical evidence suggesting that impairment of autophagy exacerbates NAFLD progression and restoration of autophagy exerts beneficial effects on NAFLD. We discuss how thyroid hormone (TH) simultaneously regulates lipophagy, mitophagy, and mitochondrial biogenesis to increase β-oxidation of fatty acids and reduce steatosis in the liver. Lastly, we discuss the recent clinical progress in using TH or thyromimetics in treating NAFLD/NASH.

Non-Alcoholic Fatty Liver Disease: Metabolic, Genetic, Epigenetic and Environmental Risk Factors

Non-alcoholic fatty liver disease (NAFLD) is one of the most frequent causes of chronic liver disease in the Western world, probably due to the growing prevalence of obesity, metabolic diseases, and exposure to some environmental agents. In certain patients, simple hepatic steatosis can progress to non-alcoholic steatohepatitis (NASH), which can sometimes lead to liver cirrhosis and its complications including hepatocellular carcinoma. Understanding the mechanisms that cause the progression of NAFLD to NASH is crucial to be able to control the advancement of the disease. The main hypothesis considers that it is due to multiple factors that act together on genetically predisposed subjects to suffer from NAFLD including insulin resistance, nutritional factors, gut microbiota, and genetic and epigenetic factors. In this article, we will discuss the epidemiology of NAFLD, and we overview several topics that influence the development of the disease from simple steatosis to liver cirrhosis and its possible complications.

MicroRNAs in the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD), or, more accurately, metabolic associated fatty liver disease, accounts for a large proportion of chronic liver disorders worldwide and is closely associated with other conditions such as cardiovascular disease, obesity, and type 2 diabetes mellitus. NAFLD ranges from simple steatosis to nonalcoholic steatohepatitis (NASH) and can progress to cirrhosis and, eventually, also hepatocellular carcinoma. The morbidity and mortality associated with NAFLD are increasing rapidly year on year. Consequently, there is an urgent need to understand the etiology and pathogenesis of NAFLD and identify effective therapeutic targets. MicroRNAs (miRNAs), important epigenetic factors, have recently been proposed to participate in NAFLD pathogenesis. Here, we review the roles of miRNAs in lipid metabolism, inflammation, apoptosis, fibrosis, hepatic stellate cell activation, insulin resistance, and oxidative stress, key factors that contribute to the occurrence and progression of NAFLD. Additionally, we summarize the role of miRNA-enriched extracellular vesicles in NAFLD. These miRNAs may comprise suitable therapeutic targets for the treatment of this condition.

The interplay of microRNAs and transcription factors in autophagy regulation in nonalcoholic fatty liver disease

The autophagy-lysosomal degradation system has an important role in maintaining liver homeostasis by removing unnecessary intracellular components. Impaired autophagy has been linked to nonalcoholic fatty liver disease (NAFLD), which includes hepatitis, steatosis, fibrosis, and cirrhosis. Thus, gaining an understanding of the mechanisms that regulate autophagy and how autophagy contributes to the development and progression of NAFLD has become the focus of recent studies. Autophagy regulation has been thought to be primarily regulated by cytoplasmic processes; however, recent studies have shown that microRNAs (miRNAs) and transcription factors (TFs) also act as key regulators of autophagy by targeting autophagy-related genes. In this review, we summarize the miRNAs and TFs that regulate the autophagy pathway in NAFLD. We further focus on the transcriptional and posttranscriptional regulation of autophagy and discuss the complex regulatory networks involving these regulators in autophagy. Finally, we highlight the potential of targeting miRNAs and TFs involved in the regulation of autophagy for the treatment of NAFLD.

Genetic and epigenetic factors determining NAFLD risk

BACKGROUND

Hepatic steatosis is a common chronic liver disease that can progress into more severe stages of NAFLD or promote the development of life-threatening secondary diseases for some of those affected. These include the liver itself (nonalcoholic steatohepatitis or NASH; fibrosis and cirrhosis, and hepatocellular carcinoma) or other organs such as the vessels and the heart (cardiovascular disease) or the islets of Langerhans (type 2 diabetes). In addition to elevated caloric intake and a sedentary lifestyle, genetic and epigenetic predisposition contribute to the development of NAFLD and the secondary diseases.

SCOPE OF REVIEW

We present data from genome-wide association studies (GWAS) and functional studies in rodents which describe polymorphisms identified in genes relevant for the disease as well as changes caused by altered DNA methylation and gene regulation via specific miRNAs. The review also provides information on the current status of the use of genetic and epigenetic factors as risk markers.

MAJOR CONCLUSION

With our overview we provide an insight into the genetic and epigenetic landscape of NAFLD and argue about the applicability of currently defined risk scores for risk stratification and conclude that further efforts are needed to make the scores more usable and meaningful.

Endoplasmic reticulum stress and autophagy dysregulation in alcoholic and non-alcoholic liver diseases

Alcoholic and non-alcoholic liver diseases begin from an imbalance in lipid metabolism in hepatocytes as the earliest response. Both liver diseases share common disease features and stages (i.e., steatosis, hepatitis, cirrhosis, and hepatocellular carcinoma). However, the two diseases have differential pathogenesis and clinical symptoms. Studies have elucidated the molecular basis underlying similarities and differences in the pathogenesis of the diseases; the factors contributing to the progression of liver diseases include depletion of sulfhydryl pools, enhanced levels of reactive oxygen and nitrogen intermediates, increased sensitivity of hepatocytes to toxic cytokines, mitochondrial dysfunction, and insulin resistance. Endoplasmic reticulum (ER) stress, which is caused by the accumulation of misfolded proteins and calcium depletion, contributes to the pathogenesis, often causing catastrophic cell death. Several studies have demonstrated a mechanism by which ER stress triggers liver disease progression. Autophagy is an evolutionarily conserved process that regulates organelle turnover and cellular energy balance through decomposing damaged organelles including mitochondria, misfolded proteins, and lipid droplets. Autophagy dysregulation also exacerbates liver diseases. Thus, autophagy-related molecules can be potential therapeutic targets for liver diseases. Since ER stress and autophagy are closely linked to each other, an understanding of the molecules, gene clusters, and networks engaged in these processes would be of help to find new remedies for alcoholic and non-alcoholic liver diseases. In this review, we summarize the recent findings and perspectives in the context of the molecular pathogenesis of the liver diseases.

Association of Genetic Polymorphisms in MicroRNAs With Type 2 Diabetes Mellitus in a Chinese Population

INTRODUCTION

MicroRNAs (miRNA) involved in the insulin signaling pathways deeply affect the pathogenesis of T2DM. The aim of this study was to assess the association between single nucleotide polymorphisms (SNP) of the related miRNAs (let-7f rs10877887, let-7a-1 rs13293512, miR-133a-1 rs8089787, miR-133a-2 rs13040413, and miR-27a rs895819) and susceptibility to type 2 diabetes mellitus (T2DM), and its possible mechanisms.

METHODS

Five SNPs in miRNAs (let-7f rs10877887, let-7a-1 rs13293512, miR-133a-1 rs8089787, miR-133a-2 rs13040413, and miR-27a rs895819) involved in the insulin signaling pathways were selected and genotyped in a case-control study that enrolled 371 T2DM patients and 381 non-diabetic controls. The individual SNP association analyses, interaction analyses of SNP-SNP, SNP-environmental factors were performed. The effect the risk-associated polymorphism on regulating its mature miRNA expression was also evaluated.

RESULTS

In overall analyses, miR-133a-2 rs13040413 and let-7a-1 rs13293512 were related to the susceptibility to T2DM. In stratified analyses, miR-133a-2 rs13040413, let-7a-1 rs13293512 and miR-27a rs895819 showed associations with T2DM in the age ≥ 60 years subgroup. Moreover, let-7a-1 rs13293512 and miR-27a rs895819 showed associations with T2DM in male subgroup. In SNP-environmental factors interaction analyses, there were interaction effects of miR-133a-2 rs13040413 with dyslipidemia, let-7a-1 rs13293512 with smoking, and let-7a-1 rs13293512 with dyslipidemia on T2DM. In SNP-SNP interaction analyses, there were also interaction effects of miR-133a-1 rs8089787 with let-7a-1 rs13293512, and miR-133a-1 rs8089787 with let-7f rs10877887 on T2DM. Furthermore, for miR-133a-2 rs13040413, the variant T allele showed a trend toward decreased miR-133a expression in comparison with the wild C allele. For let-7a-1 rs13293512, the variant C allele expressed a lower let-7a compared to the wild T allele.

CONCLUSION

MiRNAs polymorphisms involved in the insulin signaling pathways and the interaction effects of SNP-SNP, SNP-environmental factors were related to T2DM susceptibility in a Chinese population.