SEMA7AR148W mutation promotes lipid accumulation and NAFLD progression via increased localization on the hepatocyte surface

STING-mediated IL-6 Inhibits OATP1B1 Expression via the TCF4 Signaling Pathway in Cholestasis

Background and Aims

Organic anion-transporting polypeptides (OATPs) play a crucial role in the transport of bile acids and bilirubin. In our previous study, interleukin 6 (IL-6) reduced OATP1B3 levels in cholestatic disease. However, it remains unclear whether IL-6 inhibits OATP1B1 expression in cholestatic diseases. This study aimed to investigate whether IL-6 can inhibit OATP1B1 expression and explore the underlying mechanisms.

Methods

The effect of stimulator of interferon genes (STING) signaling on inflammatory factors was investigated in a cholestatic mouse model using RT-qPCR and enzyme-linked immunosorbent assay. To assess the impact of inflammatory factors on OATP1B1 expression in hepatocellular carcinoma, we analyzed OATP1B1 expression by RT-qPCR and Western Blot after treating PLC/PRF/5 cells with TNF-α, IL-1β, and IL-6. To elucidate the mechanism by which IL-6 inhibits OATP1B1 expression, we examined the expression of the OATP1B1 regulator TCF4 in PLC/PRF/5 and HepG2 cells using RT-qPCR and Western Blot. The interaction mechanism between β-catenin/TCF4 and OATP1B1 was investigated by knocking down β-catenin/TCF4 through siRNA transfection.

Results

The STING inhibitor decreased inflammatory factor levels in the cholestatic mouse model, with IL-6 exhibiting the most potent inhibitory effect on OATP1B1. IL-6 downregulated β-catenin/TCF4, leading to decreased OATP1B1 expression. Knocking-down β-catenin/TCF4 counteracted the β-catenin/TCF4-mediated repression of OATP1B1.

Conclusions

STING-mediated IL-6 up-regulation may inhibit OATP1B1, leading to reduced transport of bile acids and bilirubin by OATP1B1. This may contribute to altered pharmacokinetics in patients with diseases associated with increased IL-6 production.

Discovery of Anti-Hypercholesterolemia Agents Targeting LXRα from Marine Microorganism-Derived Natural Products

A strategy integrating in silico molecular docking with LXRα and phenotypic assays was adopted to discover anti-hypercholesterolemia agents in a small library containing 205 marine microorganism-derived natural products, collected by our group in recent years. Two fumitremorgin derivatives, 12R,13S-dihydroxyfumitremorgin C (1) and tryprostatin A (3), were identified as potential LXRα agonists, by real-time qPCR and Western blot (WB) analysis, together with a surface plasmon resonance (SPR) assay. The anti-hypercholesterolemic effects of 1 and 3, together with their mechanisms, were investigated in depth using different cell and mouse models, among which the study of LXRα is of crucial importance. Compound 1 or 3 exhibited the capacity to effectively reverse excessive lipid accumulation in a hepatic steatosis cell model and significantly reduce liver damage and blood cholesterol levels in high cholesterol diet (HCD)-fed wild-type mice, whereas those beneficial effects were completely nullified in HCD-fed LXRα-knockout mice. Furthermore, 1 and 3 outperformed common LXRα agonists by suppressing the expression of sterol regulatory element-binding protein 1 (SREBP1) in HCD-fed mice, mitigating lipotoxicity. Thus, this study highlights the discovery of two marine microorganism-derived anti-hypercholesterolemia agents targeting LXRα.

Phosphorylation: new star of pathogenesis and treatment in steatotic liver disease

Steatotic liver disease poses a serious threat to human health and has emerged as one of the most significant burdens of chronic liver disease worldwide. Currently, the research mechanism is not clear, and there is no specific targeted drug for direct treatment. Phosphorylation is widely regarded as the most common type of protein modification, closely linked to steatotic liver disease in previous studies. However, there is no systematic review to clarify the relationship and investigate from the perspective of phosphorylation. Phosphorylation has been found to mainly regulate molecule stability, affect localization, transform molecular function, and cooperate with other protein modifications. Among them, adenosine 5'-monophosphate-activated protein kinase (AMPK), serine/threonine kinase (AKT), and nuclear factor kappa-B (NF-kB) are considered the core mechanisms in steatotic liver disease. As to treatment, lifestyle changes, prescription drugs, and herbal ingredients can alleviate symptoms by influencing phosphorylation. It demonstrates the significant role of phosphorylation as a mechanism occurrence and a therapeutic target in steatotic liver disease, which could be a new star for future exploration.

Multi-omics analysis of a fatty liver model using human hepatocyte chimeric mice

We developed a fatty liver mouse model using human hepatocyte chimeric mice. As transplanted human hepatocytes do not respond to mouse growth hormone (GH) and tend to accumulate fat, we hypothesized that addition of human GH would alter lipid metabolism and reduce accumulation of fat in the liver even when fed a high-fat diet. Six uPA/SCID chimeric mice were fed a high-fat GAN diet to induce fatty liver while six were fed a normal CRF1 diet, and GH was administered to three mice in each group. The mice were euthanized at 8 weeks, and human hepatocytes were extracted for RNA-Seq, DIA proteomics, and metabolomics analysis. Abdominal echocardiography revealed that the degree of fatty liver increased significantly in mice fed GAN diet (p < 0.001) and decreased significantly in mice treated with GH (p = 0.026). Weighted gene correlation network analysis identified IGF1 and SEMA7A as eigengenes. Administration of GH significantly reduced triglyceride levels and was strongly associated with metabolism of amino acids. MiBiOmics analysis identified perilipin-2 as a co-inertia driver. Results from multi-omics analysis revealed distinct gene expression and protein/metabolite profiles in each treatment group when mice were fed a high-fat or normal diet with or without administration of GH.

Farnesoid X receptor overexpression prevents hepatic steatosis through inhibiting AIM2 inflammasome activation in nonalcoholic fatty liver disease

Oxidative stress-mediated activation of inflammasome has a significant effect on the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Farnesoid X receptor (NR1H4, FXR) has been implicated in biological function and many diseases, including NAFLD. The regulatory effect of FXR on oxidative stress and whether this process is related with the activation of absent melanoma 2 (AIM2) inflammasome in NAFLD remain unclear. In the present research, we confirmed that FXR in the livers of steatosis patients is significantly reduced compared with normal liver tissue by using the Gene Expression Omnibus (GEO) database and a palmitic acid (PA) - mediated steatosis model in AML-12 cells. Under the premise of ensuring the same food intake as the control group, overexpression of FXR in mice attenuated HFD-mediated weight gain and liver steatosis, facilitated lipid metabolism, improved fatty acid β-oxidation, lipolysis, and reduced fatty acid synthesis and intake, which also inhibited the activation of AIM2 inflammasome. Overexpression of FXR alleviated PA-induced triglyceride (TG) accumulation, imbalance of lipid homeostasis, and the activation of AIM2 inflammasome in hepatic steatosis cells, while FXR knockdown appeared the opposite effects. FXR overexpression suppressed PA- and HFD-induced oxidative stress, but FXR siRNA demonstrated the opposite influence. The decreased ROS generation may be the reason why FXR weakens AIM2 activation when a fatty acid overload occurs. In conclusion, our results confirm that other than regulating lipid homeostasis and blocking NLRP3 inflammasome activation, FXR improves hepatic steatosis by a novel mechanism that inhibits oxidative stress and AIM2 inflammasome activation.

Loss of LBP triggers lipid metabolic disorder through H3K27 acetylation-mediated C/EBPβ- SCD activation in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is associated with mutations in lipopolysaccharide-binding protein ( LBP), but the underlying epigenetic mechanisms remain understudied. Herein, LBP -/- rats with NAFLD were established and used to conduct integrative targeting-active enhancer histone H3 lysine 27 acetylation (H3K27ac) chromatin immunoprecipitation coupled with high-throughput and transcriptomic sequencing analysis to explore the potential epigenetic pathomechanisms of active enhancers of NAFLD exacerbation upon LBP deficiency. Notably, LBP -/- reduced the inflammatory response but markedly aggravated high-fat diet (HFD)-induced NAFLD in rats, with pronounced alterations in the histone acetylome and regulatory transcriptome. In total, 1 128 differential enhancer-target genes significantly enriched in cholesterol and fatty acid metabolism were identified between wild-type (WT) and LBP -/- NAFLD rats. Based on integrative analysis, CCAAT/enhancer-binding protein β (C/EBPβ) was identified as a pivotal transcription factor (TF) and contributor to dysregulated histone acetylome H3K27ac, and the lipid metabolism gene SCD was identified as a downstream effector exacerbating NAFLD. This study not only broadens our understanding of the essential role of LBP in the pathogenesis of NAFLD from an epigenetics perspective but also identifies key TF C/EBPβ and functional gene SCD as potential regulators and therapeutic targets.

A de novo missense mutation in MPP2 confers an increased risk of Vogt-Koyanagi-Harada disease as shown by trio-based whole-exome sequencing

Vogt-Koyanagi-Harada (VKH) disease is a leading cause of blindness in young and middle-aged people. However, the etiology of VKH disease remains unclear. Here, we performed the first trio-based whole-exome sequencing study, which enrolled 25 VKH patients and 50 controls, followed by a study of 2081 VKH patients from a Han Chinese population to uncover detrimental mutations. A total of 15 de novo mutations in VKH patients were identified, with one of the most important being the membrane palmitoylated protein 2 (MPP2) p.K315N (MPP2-N315) mutation. The MPP2-N315 mutation was highly deleterious according to bioinformatic predictions. Additionally, this mutation appears rare, being absent from the 1000 Genome Project and Genome Aggregation Database, and it is highly conserved in 10 species, including humans and mice. Subsequent studies showed that pathological phenotypes and retinal vascular leakage were aggravated in MPP2-N315 mutation knock-in or MPP2-N315 adeno-associated virus-treated mice with experimental autoimmune uveitis (EAU). In vitro, we used clustered regularly interspaced short palindromic repeats (CRISPR‒Cas9) gene editing technology to delete intrinsic MPP2 before overexpressing wild-type MPP2 or MPP2-N315. Levels of cytokines, such as IL-1β, IL-17E, and vascular endothelial growth factor A, were increased, and barrier function was destroyed in the MPP2-N315 mutant ARPE19 cells. Mechanistically, the MPP2-N315 mutation had a stronger ability to directly bind to ANXA2 than MPP2-K315, as shown by LC‒MS/MS and Co-IP, and resulted in activation of the ERK3/IL-17E pathway. Overall, our results demonstrated that the MPP2-K315N mutation may increase susceptibility to VKH disease.

Semaphorin 7A interacts with nuclear factor NF-kappa-B p105 via integrin β1 and mediates inflammation

Semaphorin7a (SEMA7A), a membrane-anchored member of the semaphorin protein family, could be involved in a diverse range of immune responses via its receptor integrin β1. Recently, we reported that the SEMA7A^R148W mutation (a gain-of-function mutation, Sema7a^R145W in mice) is a risk factor for progressive familial intrahepatic cholestasis and nonalcoholic fatty liver disease via upregulated membrane localization. In this study, we demonstrated that integrin β1 is a membrane receptor for nuclear factor NF-kappa-B p105 (NF-κB p105) and a critical mediator of inflammation. Integrin β1 could interact with the C-terminal domain of NF-κB p105 to promote p50 generation and stimulate the NF-κB p50/p65 signalling pathway, upregulate TNF-α and IL-1β levels, and subsequently render hepatocytes more susceptible to inflammation. The induction of integrin β1 depends on elevated Sema7a membrane localization. Moreover, we revealed elevated levels of Sema7a^WT (SEMA7A^WT) in hepatocellular carcinoma (HCC) patients and an HCC mouse model. In line with our findings, the NF-κB p50/p65 pathway could also be activated by high Sema7a expression and repressed by integrin β1 silencing. In conclusion, our findings suggest that the Sema7a^R145W (SEMA7A^R148W) mutation and high Sema7a^WT (SEMA7A^WT) expression both activate the NF-κB p50/p65 pathway via integrin β1 and play a crucial role in inflammatory responses. Video Abstract.

Do Semaphorins Play a Role in Development of Fibrosis in Patients with Nonalcoholic Fatty Liver Disease?

Nonalcoholic fatty liver disease (NAFLD) is associated with systemic changes in immune response linked with chronic low-grade inflammation and disease progression. Semaphorins, a large family of biological response modifiers, were recently recognized as one of the key regulators of immune responses, possibly also associated with chronic liver diseases. The aim of this study was to identify semaphorins associated with NAFLD and their relationship with steatosis and fibrosis stages. In this prospective, case-control study, serum semaphorin concentrations (SEMA3A, -3C, -4A, -4D, -5A and -7A) were measured in 95 NAFLD patients and 35 healthy controls. Significantly higher concentrations of SEMA3A, -3C and -4D and lower concentrations of SEAMA5A and -7A were found in NAFLD. While there was no difference according to steatosis grades, SEMA3C and SEMA4D significantly increased and SEMA3A significantly decreased with fibrosis stages and had better accuracy in predicting fibrosis compared to the FIB-4 score. Immunohistochemistry confirmed higher expression of SEMA4D in hepatocytes, endothelial cells and lymphocytes in NAFLD livers. The SEMA5A rs1319222 TT genotype was more frequent in the NAFLD group and was associated with higher liver stiffness measurements. In conclusion, we provide the first evidence of the association of semaphorins with fibrosis in patients with NAFLD.

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

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