Lipotoxicity-induced STING1 activation stimulates MTORC1 and restricts hepatic lipophagy

Morroniside delays the progression of non-alcoholic steatohepatitis by promoting AMPK-mediated lipophagy

BACKGROUND

Non-alcoholic steatohepatitis (NASH), the inflammatory subtype in the progression of non-alcoholic fatty liver disease, is becoming a serious burden threatening human health, but no approved medication is available to date. Mononoside is a natural active substance derived from Cornus officinalis and has been confirmed to have great potential in regulating lipid metabolism in our previous studies. However, its effect and mechanism to inhibit the progression of NASH remains unclear.

PURPOSE

Our work aimed to explore the action of mononoside in delaying the progression of NASH and its regulatory mechanisms from the perspective of regulating lipophagy.

METHODS AND RESULTS

Male C57BL/6 mice were fed with a high-fat and high-fructose diet for 16 weeks to establish a NASH mouse model. After 8 weeks of high-fat and high-fructose feeding, these mice were administrated with different doses of morroniside. H&E staining, ORO staining, Masson staining, RNA-seq, immunoblotting, and immunofluorescence were performed to determine the effects and molecular mechanisms of morroniside in delaying the progression of NASH. In this study, we found that morroniside is effective in attenuating hepatic lipid metabolism disorders and inflammatory response activation, thereby limiting the progression from simple fatty liver to NASH in high-fat and high-fructose diet-fed mice. Mechanistically, we identified AMPK signaling as the key molecular pathway for the positive efficacy of morroniside by transcriptome sequencing. Our results revealed that morroniside maintained hepatic lipid metabolism homeostasis and inhibited NLRP3 inflammasome activation by promoting AMPKα phosphorylation-mediated lipophagy and fatty acid oxidation. Consistent results were observed in palmitic acid-treated cell models. Of particular note, silencing AMPKα both in vivo and in vitro reversed morroniside-induced lipophagy flux enhancement and NLRP3 inflammasome inhibition, emphasizing the critical role of AMPKα activation in the effect of morroniside in inhibiting NASH progression.

CONCLUSION

In summary, the present study provides strong evidence for the first time that morroniside inhibits NASH progression by promoting AMPK-dependent lipophagy and inhibiting NLRP3 inflammasome activation, suggesting that morroniside is expected to be a potential molecular entity for the development of therapeutic drugs for NASH.

Inflammation-mediated metabolic regulation in adipose tissue

Chronic inflammation of adipose tissue is a prominent characteristic of many metabolic diseases. Lipid metabolism in adipose tissue is consistently dysregulated during inflammation, which is characterized by substantial infiltration by proinflammatory cells and high cytokine concentrations. Adipose tissue inflammation is caused by a variety of endogenous factors, such as mitochondrial dysfunction, reactive oxygen species (ROS) production, endoplasmic reticulum (ER) stress, cellular senescence, ceramides biosynthesis and mediators of lipopolysaccharides (LPS) signaling. Additionally, the gut microbiota also plays a crucial role in regulating adipose tissue inflammation. Essentially, adipose tissue inflammation arises from an imbalance in adipocyte metabolism and the regulation of immune cells. Specific inflammatory signals, including nuclear factor-κB (NF-κB) signaling, inflammasome signaling and inflammation-mediated autophagy, have been shown to be involved in the metabolic regulation. The pathogenesis of metabolic diseases characterized by chronic inflammation (obesity, insulin resistance, atherosclerosis and nonalcoholic fatty liver disease [NAFLD]) and recent research regarding potential therapeutic targets for these conditions are also discussed in this review.

Unveiling the Pharmacological Role of Human Deubiquitinating Enzymes in Temozolomide Response of Glioblastoma Cells

Temozolomide (TMZ) stands as the primary chemotherapeutic drug utilized in clinical glioma treatment, particularly for high-grade glioblastoma (GBM). However, the emergence of TMZ resistance in GBM poses a significant hurdle to its clinical efficacy. Our objective was to elucidate the role of deubiquitinating enzymes (DUBs) in GBM cell resistance to TMZ. We employed the broad-spectrum DUBs inhibitor G5 to investigate the function of DUBs in TMZ cytotoxicity against GBM cells. Eighty-two GBM cell lines with specified DUBs knockout were generated and subjected to CCK-8 assays to assess cell proliferation and TMZ resistance. Furthermore, the association between DUBs and TMZ resistance in GBM cells, along with the modulation of autophagic flux, was examined. The pan-DUBs inhibitor G5 demonstrated the ability to induce cell death and enhance TMZ toxicity in GBM cells. Subsequently, we identified potential DUBs involved in regulating GBM cell proliferation and TMZ resistance. The impact of DUBs knockout on TMZ cytotoxicity was found to be associated with their regulation of TMZ-induced autophagy. In summary, our study provides primary insights into the role of DUBs in GBM cell proliferation and TMZ resistance, and contributes to a deeper understanding of the complex function of DUBs genes underlying TMZ resistance in GBM cells.

Activation of lipophagy ameliorates cadmium-induced neural tube defects via reducing low density lipoprotein cholesterol levels in mouse placentas

Neural tube defects (NTDs) represent a prevalent and severe category of congenital anomalies in humans. Cadmium (Cd) is an environmental teratogen known to cause fetal NTDs. However, its underlying mechanisms remain elusive. This study aims to investigate the therapeutic potential of lipophagy in the treatment of NTDs, providing valuable insights for future strategies targeting lipophagy activation as a means to mitigate NTDs.We successfully modeled NTDs by Cd exposure during pregnancy. RNA sequencing was employed to investigate the transcriptomic alterations and functional enrichment of differentially expressed genes in NTD placental tissues. Subsequently, pharmacological/genetic (Atg5-/- placentas) experiments confirmed that inducing placental lipophagy can alleviate Cd induced-NTDs. We found that Cd exposure caused NTDs. Further analyzed transcriptomic data from the placentas with NTDs which revealed significant downregulation of low-density lipoprotein receptor associated protein 1(Lrp1) gene expression responsible for positive regulation of low-density lipoprotein cholesterol (LDL-C) transport. Correspondingly, there was an increase in maternal serum/placenta/amniotic fluid LDL-C content. Subsequently, we have discovered that Cd exposure activated placental lipophagy. Pharmacological/genetic (Atg5-/- placentas) experiments confirmed that inducing placental lipophagy can alleviate Cd induced-NTDs. Furthermore, our findings demonstrate that activation of placental lipophagy effectively counteracts the Cd-induced elevation in LDL-C levels. Lipophagy serves to mitigate Cd-induced NTDs by reducing LDL-C levels within mouse placentas.

The causal effect of mTORC1-dependent circulating protein levels on nonalcoholic fatty liver disease: A Mendelian randomization study

BACKGROUND

The mechanistic target of rapamycin (mTOR) signal pathway plays a crucial role in the development of nonalcoholic fatty liver disease (NAFLD). However, the causal effect of mTOR downstream proteins on NAFLD remains unknown.

AIMS

We conducted a two-sample Mendelian randomization (MR) study to investigate whether the mTOR-dependent circulating proteins, including Eukaryotic Initiation Factor 4E Binding Proteins (eIF4EBPs), Ribosomal Protein S6K kinase 1 (RP-S6K), Eukaryotic Initiation Factor 4E (eIF4E), Eukaryotic Initiation Factor 4A (eIF4A) and Eukaryotic Initiation Factor 4 G (eIF4G), have causal effects on the risk of NAFLD.

METHODS

The causal estimate was evaluated with the inverse-variance weighted (IVW) method in discovery stage and validation stage. The single-nucleotide polymorphisms (SNPs) were selected to genetically predict exposures from Genome-Wide Association Studies (GWAS). Exposures with statistically significant effects in the discovery dataset would be further validated in the validation dataset.

RESULTS

MR study revealed that eIF4E had a causal effect on NAFLD in both discovery stage (OR = 1.339, P = 0.037) and validation stage (OR = 1.0007, P = 0.022). Sensitivity analyses confirmed robustness of the results.

CONCLUSION

The genetically predicted higher level of mTOR-dependent eIF4E in plasma might have a causal effect on the occurrence of NAFLD.

Exploring the role of genetic variations in NAFLD: implications for disease pathogenesis and precision medicine approaches

Non-alcoholic fatty liver disease (NAFLD) is one of the leading causes of chronic liver diseases, affecting more than one-quarter of people worldwide. Hepatic steatosis can progress to more severe forms of NAFLD, including NASH and cirrhosis. It also may develop secondary diseases such as diabetes and cardiovascular disease. Genetic and environmental factors regulate NAFLD incidence and progression, making it a complex disease. The contribution of various environmental risk factors, such as type 2 diabetes, obesity, hyperlipidemia, diet, and sedentary lifestyle, to the exacerbation of liver injury is highly understood. Nevertheless, the underlying mechanisms of genetic variations in the NAFLD occurrence or its deterioration still need to be clarified. Hence, understanding the genetic susceptibility to NAFLD is essential for controlling the course of the disease. The current review discusses genetics' role in the pathological pathways of NAFLD, including lipid and glucose metabolism, insulin resistance, cellular stresses, and immune responses. Additionally, it explains the role of the genetic components in the induction and progression of NAFLD in lean individuals. Finally, it highlights the utility of genetic knowledge in precision medicine for the early diagnosis and treatment of NAFLD patients.

Co-methylation analyses identify CpGs associated with lipid traits in Chinese discordant monozygotic twins

To control genetic background and early life milieu in genome-wide DNA methylation analysis for blood lipids, we recruited Chinese discordant monozygotic twins to explore the relationships between DNA methylations and total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglycerides (TG). 132 monozygotic (MZ) twins were included with discordant lipid levels and completed data. A linear mixed model was conducted in Epigenome-wide association study (EWAS). Generalized estimating equation model was for gene expression analysis. We conducted Weighted correlation network analysis (WGCNA) to build co-methylated interconnected network. Additional Qingdao citizens were recruited for validation. Inference about Causation through Examination of Familial Confounding (ICE FALCON) was used to infer the possible direction of these relationships. A total of 476 top CpGs reached suggestively significant level (P < 10-4), of which, 192 CpGs were significantly associated with TG (FDR < 0.05). They were used to build interconnected network and highlight crucial genes from WGCNA. Finally, four CpGs in GATA4 were validated as risk factors for TC; six CpGs at ITFG2-AS1 were negatively associated with TG; two CpGs in PLXND1 played protective roles in HDL-C. ICE FALCON indicated abnormal TC was regarded as the consequence of DNA methylation in CpGs at GATA4, rather than vice versa. Four CpGs in ITFG2-AS1 were both causes and consequences of modified TG levels. Our results indicated that DNA methylation levels of 12 CpGs in GATA4, ITFG2-AS1, and PLXND1 were relevant to TC, TG, and HDL-C, respectively, which might provide new epigenetic insights into potential clinical treatment of dyslipidemia.

mTORC1 accelerates osteosarcoma progression via m6A-dependent stabilization of USP7 mRNA

Osteosarcoma (OS) is considered a sex steroid hormone-dependent bone tumor. The development and progression of OS are regulated by 17β-estradiol (E2). However, the detailed mechanisms of E2-modulated OS progression remained to be elucidated. Here, we found that E2-activated mammalian target of rapamycin (mTOR) signaling promoted N6-methyladenosine (m6A) modification through regulating WTAP. Inhibition of mTOR complex 1 (mTORC1) reversed E2-activated WTAP expression. Meanwhile, inhibition of mTORC1 suppressed OS cell proliferation and migration. Deficiency of TSC2 activated mTORC1 signaling and enhanced OS cell proliferation and migration, while abrogated by Rapamycin. Interestingly, mTOMC1 promoted mRNA stability of ubiquitin-specific protease 7 (USP7) through m6A modification. Loss of USP7 suppressed the proliferation, migration, and ASC specks, while promoted apoptosis of OS cells. USP7 interacted with NLRP3 and deubiquitinated NLRP3 through K48-ubiquitination. USP7 was upregulated and positive correlation with NLRP3 in OS patients with high level of E2. Loss of USP7 suppressed the progression of OS via inhibiting NLRP3 inflammasome signaling pathway. Our results demonstrated that E2-activtated mTORC1 promoted USP7 stability, which promoted OS cell proliferation and migration via upregulating NLRP3 expression and enhancing NLRP3 inflammasome signaling pathway. These results discover a novel mechanism of E2 regulating OS progression and provide a promising therapeutic target for OS progression.

Drug targets regulate systemic metabolism and provide new horizons to treat nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH), is the advanced stage of nonalcoholic fatty liver disease (NAFLD) with rapidly rising global prevalence. It is featured with severe hepatocyte apoptosis, inflammation and hepatic lipogenesis. The drugs directly targeting the processes of steatosis, inflammation and fibrosis are currently under clinical investigation. Nevertheless, the long-term ineffectiveness and remarkable adverse effects are well documented, and new concepts are required to tackle with the root causes of NASH progression. We critically assess the recently validated drug targets that regulate the systemic metabolism to ameliorate NASH. Thermogenesis promoted by mitochondrial uncouplers restores systemic energy expenditure. Furthermore, regulation of mitochondrial proteases and proteins that are pivotal for intracellular metabolic homeostasis normalize mitochondrial function. Secreted proteins also improve systemic metabolism, and NASH is ameliorated by agonizing receptors of secreted proteins with small molecules. We analyze the drug design, the advantages and shortcomings of these novel drug candidates. Meanwhile, the structural modification of current NASH therapeutics significantly increased their selectivity, efficacy and safety. Furthermore, the arising CRISPR-Cas9 screen strategy on liver organoids has enabled the identification of new genes that mediate lipid metabolism, which may serve as promising drug targets. In summary, this article discusses the in-depth novel mechanisms and the multidisciplinary approaches, and they provide new horizons to treat NASH.

Ubiquitination of cytoplasmic HMGB1 by RNF186 regulates hepatic lipophagy in non-alcoholic fatty liver disease

BACKGROUND

Lipophagy is a vital biological process that maintains the balance of intracellular lipid metabolism in nonalcoholic fatty liver disease (NAFLD). However, the precise regulatory mechanism of RNF186 in hepatic lipophagy is still unclear. This study investigates the roles and mechanisms of RNF186 in the regulation of lipophagy during the development of NAFLD.

METHODS

In this study, we employed RNF186 knockout mice as well as human liver cells and mouse primary hepatocytes (MPHs) to investigate the role and mechanisms of RNF186 in lipophagy during the progression of NAFLD. Additionally, liver specimens from individuals with NAFLD were examined to assess the expression of RNF186 and its associated factors.

RESULTS

Here, we provide evidence that depletion of RNF186 enhances lipophagy in hepatocytes of a NAFLD model. Mechanistically, RNF186 acts as an E3 ubiquitin ligase that targets cytoplasmic HMGB1 for lysine 48 (K48)- and K63-linked ubiquitination, leading to its subsequent proteasomal degradation. Importantly, the translocation of HMGB1 from the nucleus to the cytoplasm is responsible for inducing lipophagy in NAFLD samples. Knockdown of HMGB1 significantly reduces the activation of lipophagy and mediates the decrease in lipid accumulation caused by RNF186 depletion in hepatocytes. Furthermore, we find that maintaining the nuclear HMGB1 level and inhibiting its nuclear-cytoplasmic shuttling are critical for the proper function of RNF186 in NAFLD. Additionally, the expression of RNF186 and HMGB1 in human NAFLD samples, along with factors related to lipophagy, suggest that RNF186 may play a similar role in the pathogenesis of human fatty liver.

CONCLUSION

RNF186 deficiency accelerates hepatic lipophagy in NAFLD through the inhibition of ubiquitination and degradation of cytoplasmic HMGB1. Consequently, targeting the RNF186-HMGB1 axis may offer a promising strategy for the prevention and treatment of NAFLD.

TRAF2 decrease promotes the TGF-β-mTORC1 signal in MAFLD-HCC through enhancing AXIN1-mediated Smad7 degradation

According to recent research, metabolic-associated fatty liver disease (MAFLD) has emerged as an important underlying etiology of hepatocellular carcinoma (HCC). However, the molecular mechanism of MAFLD-HCC is still unclear. Tumor necrosis factor receptor-associated factor 2 (TRAF2) is the key molecule to mediate the signal of inflammatory NF-κB pathway. This study aims to investigate the potential dysregulation of TRAF2 and its biological function in MAFLD-HCC. Huh7 TRAF2-/- demonstrated increased tumor formation ability compared to huh7 TRAF2+/+ when stimulated with transforming growth factor-β (TGF-β). The decisive role of TGF-β in the development of MAFLD-HCC was confirmed through the specific depletion of TGF-β receptor II gene in the hepatocytes (Tgfbr2ΔHep) of mice. In TRAF2-/- cells treated with TGF-β, both the glycolysis rate and lipid synthesis were enhanced. We proved the signal of the mechanistic target of rapamycin complex 1 (mTORC1) could be activated in the presence of TGF-β, and was enhanced in TRAF2-/- cells. The coimmunoprecipitation (co-IP) experiments revealed that TRAF2 fortified the Smurf2-mediated ubiquitination degradation of AXIN1. Hence, TRAF2 depletion resulted in increased Smad7 degradation induced by AXIN1, thus promoting the TGF-β signal. We also discovered that PLX-4720 could bind with AXIN1 and restrained the tumor proliferation of TRAF2-/- in mice fed with high-fat diet (HFD). Our findings indicate that TRAF2 plays a significant role in the pathogenesis of MAFLD-HCC. The reduction of TRAF2 expression leads to the enhancement of the TGF-β-mTORC1 pathway by facilitating AXIN1-mediated Smad7 degradation.

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.

Update on the STING Signaling Pathway in Developing Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a prevalent chronic liver condition with limited treatment options. Inflammation caused by metabolic disturbances plays a significant role in NAFLD development. Stimulator of interferon gene (STING), a critical regulator of innate immunity, induces the production of interferons and other pro-inflammatory factors by recognizing cytoplasmic DNA to defend against pathogen infection. The STING-mediated signaling pathway appears to play a vital role in hepatic inflammation, metabolic disorders, and even carcinogenesis. Promisingly, pharmacological interventions targeting STING have shown improvements in the pathological state of NAFLD. Macrophages, dendritic cells, natural killer cells, and T cell pathways regulated by STING present potential novel druggable targets for NAFLD treatment. Further research and development in this area may offer new therapeutic options for managing NAFLD effectively.

Roles of immune dysregulation in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic liver disease worldwide. Its occurrence and progression involve the process from simple hepatic steatosis to metabolic dysfunction associated steatohepatitis (MASH), which could develop into advanced liver fibrosis, cirrhosis, or hepatocellular carcinoma (HCC). Growing evidences support that the pathogenesis and progression of MASLD are closely related to immune system dysfunction. This review aims to summarize the association of MASLD with immune disorders and the prospect of using immunotherapy for MASLD.

Cell-type specific role of autophagy in the liver and its implications in non-alcoholic fatty liver disease

Autophagy, a cellular degradative process, has emerged as a key regulator of cellular energy production and stress mitigation. Dysregulated autophagy is a common phenomenon observed in several human diseases, and its restoration offers curative advantage. Non-alcoholic fatty liver disease (NAFLD), more recently renamed metabolic dysfunction-associated steatotic liver disease, is a major metabolic liver disease affecting almost 30% of the world population. Unfortunately, NAFLD has no pharmacological therapies available to date. Autophagy regulates several hepatic processes including lipid metabolism, inflammation, cellular integrity and cellular plasticity in both parenchymal (hepatocytes) and non-parenchymal cells (Kupffer cells, hepatic stellate cells and sinusoidal endothelial cells) with a profound impact on NAFLD progression. Understanding cell type-specific autophagy in the liver is essential in order to develop targeted treatments for liver diseases such as NAFLD. Modulating autophagy in specific cell types can have varying effects on liver function and pathology, making it a promising area of research for liver-related disorders. This review aims to summarize our present understanding of cell-type specific effects of autophagy and their implications in developing autophagy centric therapies for NAFLD.

Didymin alleviates metabolic dysfunction-associated fatty liver disease (MAFLD) via the stimulation of Sirt1-mediated lipophagy and mitochondrial biogenesis

BACKGROUND

Metabolic dysfunction-associated fatty liver disease (MAFLD) is one of the most prevalent metabolic syndromes worldwide. However, no approved pharmacological treatments are available for MAFLD. Chenpi, one kind of dried peel of citrus fruits, has traditionally been utilized as a medicinal herb for liver diseases. Didymin is a newly identified oral bioactive dietary flavonoid glycoside derived from Chenpi. In this study, we investigated the therapeutic potential of Didymin as an anti-MAFLD drug and elucidated its underlying mechanisms.

METHODS

High-fat diet (HFD)-induced MAFLD mice and alpha mouse liver 12 (AML12) cells were utilized to evaluate the effects and mechanisms of Didymin in the treatment of MAFLD. Liver weight, serum biochemical parameters, and liver morphology were examined to demonstrate the therapeutic efficacy of Didymin in MAFLD treatment. RNA-seq analysis was performed to identify potential pathways that could be affected by Didymin. The impact of Didymin on Sirt1 was corroborated through western blot, molecular docking analysis, microscale thermophoresis (MST), and deacetylase activity assay. Then, a Sirt1 inhibitor (EX-527) was utilized to confirm that Didymin alleviates MAFLD via Sirt1. Western blot and additional assays were used to investigate the underlying mechanisms.

RESULTS

Our results suggested that Didymin may possess therapeutic potential against MAFLD in vitro and in vivo. By promoting Sirt1 expression as well as directly binding to and activating Sirt1, Didymin triggers downstream pathways that enhance mitochondrial biogenesis and function while reducing apoptosis and enhancing lipophagy.

CONCLUSIONS

These suggest that Didymin could be a promising medication for MAFLD treatment. Furthermore, its therapeutic effects are mediated by Sirt1.

Pharmacological effects of mTORC1/C2 inhibitor in a preclinical model of NASH progression

Knowledge of the benefits of mTOR inhibition concerning adipogenesis and inflammation has recently encouraged the investigation of a new generation of mTOR inhibitors for non-alcoholic steatohepatitis (NASH). We investigated whether treatment with a specific mTORC1/C2 inhibitor (Ku-0063794; KU) exerted any beneficial impacts on experimentally-induced NASH in vitro and in vivo. The results indicated that KU decreases palmitic acid-induced lipotoxicity in cultivated primary hepatocytes, thus emerging as a successful candidate for testing in an in vivo NASH dietary model, which adopted the intraperitoneal KU dosing route rather than oral application due to its significantly greater bioavailability in mice. The pharmacodynamics experiments commenced with the feeding of male C57BL/6 mice with a high-fat atherogenic western-type diet (WD) for differing intervals over several weeks aimed at inducing various phases of NASH. In addition to the WD, the mice were treated with KU for 3 weeks or 4 months. Acute and chronic KU treatments were observed to be safe at the given concentrations with no toxicity indications in the mice. KU was found to alleviate NASH-related hepatotoxicity, mitochondrial and oxidative stress, and decrease the liver triglyceride content and TNF-α mRNA in at least one set of in vivo experiments. The KU modulated liver expression of selected metabolic and oxidative stress-related genes depended upon the length and severity of the disease. Although KU failed to completely reverse the histological progression of NASH in the mice, we demonstrated the complexity of mTORC1/C2 signaling regulation and suggest a stratified therapeutic management approach throughout the disease course.

RING finger protein 13 protects against nonalcoholic steatohepatitis by targeting STING-relayed signaling pathways

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disorder worldwide. Recent studies show that innate immunity-related signaling pathways fuel NAFLD progression. This study aims to identify potent regulators of innate immunity during NAFLD progression. To this end, a phenotype-based high-content screening is performed, and RING finger protein 13 (RNF13) is identified as an effective inhibitor of lipid accumulation in vitro. In vivo gain- and loss-of-function assays are conducted to investigate the role of RNF13 in NAFLD. Transcriptome sequencing and immunoprecipitation-mass spectrometry are performed to explore the underlying mechanisms. We reveal that RNF13 protein is upregulated in the liver of individuals with NASH. Rnf13 knockout in hepatocytes exacerbate insulin resistance, steatosis, inflammation, cell injury and fibrosis in the liver of diet-induced mice, which can be alleviated by Rnf13 overexpression. Mechanically, RNF13 facilitates the proteasomal degradation of stimulator of interferon genes protein (STING) in a ubiquitination-dependent way. This study provides a promising innate immunity-related target for NAFLD treatment.

Long-term and liver-selected ginsenoside C-K nanoparticles retard NAFLD progression by restoring lipid homeostasis

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent hepatic disease characterized as lipid accumulation, yet without any approved drug. And development of therapeutic molecules is obstructed by low efficiency and organ toxicity. Herein, we develop a long-term, low-toxic and liver-selected nano candidate, nabCK, to alleviate NAFLD. NabCK is simply composed by natural compound ginsenoside compound K (CK) and albumin. As a major metabolite of ginseng, ginsenoside CK has excellently modulating functions for lipid metabolism, but accompanied by an extremely poor bioavailability <1%. Albumin is a key lipid carrier secreted and metabolized by livers. Thereby, it can improve solubility and liver-localization of CK. In adipocytes and hepatocytes, nabCK prevents lipid deposition and eliminates lipid droplets. Transcriptomic analysis reveals that nabCK rectifies various pathways that involved in steatosis development, including lipid absorption, lipid export, fatty acid biosynthesis, lipid storage and inflammation. All these pathways are modulated by mTOR, the pivotal feedback sensor that is hyperactive in NAFLD. NabCK suppresses mTOR activation to restores lipid homeostasis. In high-fat diet (HFD) induced NAFLD mice, nabCK retards development of steatosis and fibrosis, coupling a protective effect on cardiac tissues from lipotoxicity. Together, nabCK is a safe and potent candidate to offer benefits for NAFLD treatment.

Recent Insights into the Biomarkers, Molecular Targets and Mechanisms of Non-Alcoholic Steatohepatitis-Driven Hepatocarcinogenesis

Non-alcoholic fatty liver disease (NAFLD) or metabolic dysfunction-associated steatotic liver disease (MASLD) and steatohepatitis (NASH) are chronic hepatic conditions leading to hepatocellular carcinoma (HCC) development. According to the recent "multiple-parallel-hits hypothesis", NASH could be caused by abnormal metabolism, accumulation of lipids, mitochondrial dysfunction, and oxidative and endoplasmic reticulum stresses and is found in obese and non-obese patients. Recent translational research studies have discovered new proteins and signaling pathways that are involved not only in the development of NAFLD but also in its progression to NASH, cirrhosis, and HCC. Nevertheless, the mechanisms of HCC developing from precancerous lesions have not yet been fully elucidated. Now, it is of particular importance to start research focusing on the discovery of novel molecular pathways that mediate alterations in glucose and lipid metabolism, which leads to the development of liver steatosis. The role of mTOR signaling in NASH progression to HCC has recently attracted attention. The goals of this review are (1) to highlight recent research on novel genetic and protein contributions to NAFLD/NASH; (2) to investigate how recent scientific findings might outline the process that causes NASH-associated HCC; and (3) to explore the reliable biomarkers/targets of NAFLD/NASH-associated hepatocarcinogenesis.

The S100 calcium-binding protein A6 plays a crucial role in hepatic steatosis by mediating lipophagy

BACKGROUND

S100 calcium-binding protein A6 (S100A6) is a calcium-binding protein that is involved in a variety of cellular processes, such as proliferation, apoptosis, and the cellular response to various stress stimuli. However, its role in NAFLD and associated metabolic diseases remains uncertain.

METHODS AND RESULTS

In this study, we revealed a new function and mechanism of S100A6 in NAFLD. S100A6 expression was upregulated in human and mouse livers with hepatic steatosis, and the depletion of hepatic S100A6 remarkably inhibited lipid accumulation, insulin resistance, inflammation, and obesity in a high-fat, high-cholesterol (HFHC) diet-induced murine hepatic steatosis model. In vitro mechanistic investigations showed that the depletion of S100A6 in hepatocytes restored lipophagy, suggesting S100A6 inhibition could alleviate HFHC-induced NAFLD. Moreover, S100A6 liver-specific ablation mediated by AAV9 alleviated NAFLD in obese mice.

CONCLUSIONS

Our study demonstrates that S100A6 functions as a positive regulator of NAFLD, targeting the S100A6-lipophagy axis may be a promising treatment option for NAFLD and associated metabolic diseases.

Sertoli cell adaptation to glucose deprivation: Potential role of AMPK in the regulation of lipid metabolism

Sertoli cells (SCs) provide an adequate environment for germ cell development. SCs possess unique features that meet germ cells' metabolic demands: they produce lactate from glucose, which is delivered as energy substrate to germ cells. SCs store fatty acids (FAs) as triacylglycerols (TAGs) in lipid droplets (LDs) and can oxidize FAs to sustain their own energetic demands. They also produce ketone bodies from FAs. It has been shown that exposure of SCs to metabolic stresses, such as glucose deprivation, triggers specific adaptive responses that sustain cell survival and preserve lactate supply to germ cells. The aim of the present study was to investigate whether there are modifications in rat SCs lipid metabolism, including LD content, FA oxidation, and ketone bodies production, as part of their adaptive response to glucose deprivation. The present study was performed in 20-day-old rat SCs cultures. We determined LD content by Oil Red O staining, FA oxidation by measuring the release of ³ H₂ O from [³ H] palmitate, TAGs and 3-hydroxybutyrate levels by spectrophotometric methods, and mRNA levels by RT-qPCR. Results show that the absence of glucose in SC culture medium entails: (1) a decrease in LD content and TAGs levels that is accompanied by decreased perilipin 1 mRNA levels, (2) an increase in FA oxidation that is in part mediated by AMP kinase (AMPK) activation and (3) a decrease in 3-hydroxybutyrate production. Additionally, we studied whether sestrins (SESN1, 2 and 3), proteins involved in the cellular response to stress, are regulated in glucose deprivation conditions. We show that there is an increase in SESN2 mRNA levels in deprived conditions. In conclusion, glucose deprivation affects SC lipid metabolism promoting FA mobilization from LDs to be used as energy source.

Autophagy: A Cellular Guardian against Hepatic Lipotoxicity

Lipotoxicity is a phenomenon of lipid-induced cellular injury in nonadipose tissue. Excess of free saturated fatty acids (SFAs) contributes to hepatic injury in nonalcoholic fatty liver disease (NAFLD), which has been growing at an unprecedented rate in recent years. SFAs and their derivatives such as ceramides and membrane phospholipids have been shown to induce intrahepatic oxidative damage and ER stress. Autophagy represents a cellular housekeeping mechanism to counter the perturbation in organelle function and activation of stress signals within the cell. Several aspects of autophagy, including lipid droplet assembly, lipophagy, mitophagy, redox signaling and ER-phagy, play a critical role in mounting a strong defense against lipotoxic lipid species within the hepatic cells. This review provides a succinct overview of our current understanding of autophagy-lipotoxicity interaction and its pharmacological and nonpharmacological modulation in treating NAFLD.

RNA-Seq analysis of obese Pdha1fl/flLyz2-Cre mice induced by a high-fat diet

Pyruvate dehydrogenase complex (PDH) is an important complex of three enzymes that transforms pyruvate into acetyl-CoA, subsequently entering the tricarboxylic acid (TCA) cycle to produce ATP and electron donors. As a key regulator of energy and metabolic homeostasis, PDH is considered a potential therapeutic target of many diseases. On the other hand, the relationship between PDH and obesity is not clear. In this study, peripheral blood of Pdha1^fl/flLyz2-Cre and C57BL/6 mice fed a high-fat diet (HFD) was collected and subjected to extensive transcriptome sequencing. Differentially expressed genes (DEGs) were identified. Enrichment of functions and signaling pathways analyses were performed based on Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to verify the genes selected from RNA sequencing (RNA-seq). Eventually, we found that Pdha1^fl/flLyz2-Cre mice were more susceptible to HFD-induced obesity. A total of 302 up-regulated genes and 30 down-regulated genes were screened that were differentially expressed between Pdha1^fl/flLyz2-Cre mice fed the HFD and the control groups. Furthermore, we verified that significant transcriptional changes in the genes Sgstm1, Ncoa4, Rraga, Slc3a2, Usp15, Gabarapl2, Wipi1, Sh3glb1, Mtmr3, and Cd36 were consistent with the results obtained from RNA-seq analysis. In summary, this study preliminarily established that there is a close relationship between Pdha1 and obesity and revealed the possible downstream pathways and target genes involved, laying a good foundation for the further study of Pdha1 function in the future.

The essential effect of mTORC1-dependent lipophagy in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a chronic progressive liver disease with increasing prevalence. Lipophagy is a type of programmed cell death that plays an essential role in maintaining the body's balance of fatty acid metabolism. However, the livers of NAFLD patients are abnormally dysregulated in lipophagy. mTORC1 is a critical negative regulator of lipophagy, which has been confirmed to participate in the process of lipophagy through various complex mechanisms. Therefore, targeting mTORC1 to restore failed autophagy may be an effective therapeutic strategy for NAFLD. This article reviews the main pathways through which mTORC1 participates in the formation of lipophagy and the intervention effect of mTORC1-regulated lipophagy in NAFLD, providing new therapeutic strategies for the prevention and treatment of NAFLD in the future.

mTOR: A Potential New Target in Nonalcoholic Fatty Liver Disease

The global prevalence of nonalcoholic fatty liver disease (NAFLD) continues to rise, yet effective treatments are lacking due to the complex pathogenesis of this disease. Although recent research has provided evidence for the “multiple strikes” theory, the classic “two strikes” theory has not been overturned. Therefore, there is a crucial need to identify multiple targets in NAFLD pathogenesis for the development of diagnostic markers and targeted therapeutics. Since its discovery, the mechanistic target of rapamycin (mTOR) has been recognized as the central node of a network that regulates cell growth and development and is closely related to liver lipid metabolism and other processes. This paper will explore the mechanisms by which mTOR regulates lipid metabolism (SREBPs), insulin resistance (Foxo1, Lipin1), oxidative stress (PIG3, p53, JNK), intestinal microbiota (TLRs), autophagy, inflammation, genetic polymorphisms, and epigenetics in NAFLD. The specific influence of mTOR on NAFLD was hypothesized to be divided into micro regulation (the mechanism of mTOR’s influence on NAFLD factors) and macro mediation (the relationship between various influencing factors) to summarize the influence of mTOR on the developmental process of NAFLD, and prove the importance of mTOR as an influencing factor of NAFLD regarding multiple aspects. The effects of crosstalk between mTOR and its upstream regulators, Notch, Hedgehog, and Hippo, on the occurrence and development of NAFLD-associated hepatocellular carcinoma are also summarized. This analysis will hopefully support the development of diagnostic markers and new therapeutic targets in NAFLD.

RNA helicase DEAD-box protein 5 alleviates nonalcoholic steatohepatitis progression via tethering TSC complex and suppressing mTORC1 signaling

BACKGROUND AND AIMS

Nonalcoholic fatty liver disease and its progressive form, nonalcoholic steatohepatitis (NASH), are rapidly becoming the top causes of hepatocellular carcinoma (HCC). Currently, there are no approved therapies for the treatment of NASH. DEAD-box protein 5 (DDX5) plays important roles in different cellular processes. However, the precise role of DDX5 in NASH remains unclear.

APPROACH AND RESULTS

DDX5 expression was downregulated in patients with NASH, mouse models with diet-induced NASH (high-fat diet [HFD], methionine- and choline-deficient diet, and choline-deficient HFD), mouse models with NASH-HCC (diethylnitrosamine with HFD), and palmitic acid-stimulated hepatocytes. Adeno-associated virus-mediated DDX5 overexpression ameliorates hepatic steatosis and inflammation, whereas its deletion worsens such pathology. The untargeted metabolomics analysis was carried out to investigate the mechanism of DDX5 in NASH and NASH-HCC, which suggested the regulatory effect of DDX5 on lipid metabolism. DDX5 inhibits mechanistic target of rapamycin complex 1 (mTORC1) activation by recruiting the tuberous sclerosis complex (TSC)1/2 complex to mTORC1, thus improving lipid metabolism and attenuating the NACHT-, leucine-rich-repeat (LRR)-, and pyrin domain (PYD)-containing protein 3  inflammasome activation. We further identified that the phytochemical compound hyperforcinol K directly interacted with DDX5 and prevented its ubiquitinated degradation mediated by ubiquitin ligase (E3) tripartite motif protein 5, thereby significantly reducing lipid accumulation and inflammation in a NASH mouse model.

CONCLUSIONS

These findings provide mechanistic insight into the role of DDX5 in mTORC1 regulation and NASH progression, as well as suggest a number of targets and a promising lead compound for therapeutic interventions against NASH.