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Background: Recent studies have suggested a relationship between gut microbiota and non-alcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH). However, the nature and direction of this potential causal relationship are still unclear. This study used two-sample Mendelian randomization (MR) to clarify the potential causal links., Methods: Summary-level Genome-Wide Association Studies (GWAS) statistical data for gut microbiota and NAFLD/NASH were obtained from MiBioGen and FinnGen respectively. The MR analyses were performed mainly using the inverse-variance weighted (IVW) method, with sensitivity analyses conducted to verify the robustness. Additionally, reverse MR analyses were performed to examine any potential reverse causal associations., Results: Our analysis, primarily based on the IVW method, strongly supports the existence of causal relationships between four microbial taxa and NAFLD, and four taxa with NASH. Specifically, associations were observed between Enterobacteriales ( P =0.04), Enterobacteriaceae ( P =0.04), Lachnospiraceae UCG-004 ( P =0.02), and Prevotella9 ( P =0.04) and increased risk of NAFLD. Dorea ( P =0.03) and Veillonella ( P =0.04) could increase the risks of NASH while Oscillospira ( P =0.04) and Ruminococcaceae UCG-013 ( P =0.005) could decrease them. We also identified that NAFLD was found to potentially cause an increased abundance in Holdemania ( P =0.007) and Ruminococcus2 ( P =0.002). However, we found no evidence of reverse causation in the microbial taxa associations with NASH., Conclusion: This study identified several specific gut microbiota that are causally related to NAFLD and NASH. Observations herein may provide promising theoretical groundwork for potential prevention and treatment strategies for NAFLD and its progression to NASH in future., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Zhai, Wu, Zheng, Zhong, Du, Yuan, Peng, Cai and Li.)

Non‑alcoholic fatty liver disease (NAFLD) is a manifestation of metabolic syndrome in the liver and is closely associated with diabetes; however, its pathogenesis remains to be elucidated. Carbohydrate responsive element binding protein (ChREBP), the hub of glucolipid metabolism, regulates the induction of fatty acid synthase (FASN), the key enzyme of de novo lipogenesis, by directly binding to carbohydrate response element (ChoRE) in its promoter. Investigations of histone modifications on NAFLD remain in their infancy. In the present study, by using ChIP, the association between histone modifications and FASN transcription was investigated and histone modifications in FASN modulated by ChREBP were measured. It was demonstrated that ChREBP induced FASN ChREBP‑ChoRE binding to accelerate the expression of FASN, leading to hepatocellular steatosis by facilitating H3 and H4 acetylation, H3K4 trimethylation and the phosphorylation of H3S10, but inhibiting the trimethylation of H3K9 and H4K20 in FASN promoter regions of HepG2 and L02 cells. It was also found that ChREBP‑ChoRE binding of FASN relied on histone acetylation and that the transcriptional activity of ChREBP on FASN is required, based on the premise that histone acetylation causes conformational changes in FASN chromatin. This indicated histone acetylation as a crucial mechanism involved in the transcription of FASN modulated by ChREBP. Consequently, the present study provides further insight into the pathophysiology and a novel therapeutic potential of NAFLD based on epigenetic mechanisms.

The cleavage and secretion of pro-inflammatory cytokines IL-1β and IL-18 is regulated by NLRP3 (NACHT, LRR, and PYD domain-containing protein 3) inflammasome activation. Kupffer cells (KCs) are implicated in the pathogenesis of various liver diseases, such as non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease, and liver fibrosis. However, the role of NLRP3 played in the non-alcoholic steatohepatitis (NASH) has yet to be evaluated. In the present study, methionine-choline-deficient (MCD) diet was used to establish the mice NASH model. The expression levels of F4/80 and NLRP3 in liver tissues were evaluated, and the IL-1β and IL-18 in serum were also evaluated. KCs were isolated from wild-type (WT) mice and NLRP3 knockout (NLRP3 -/- ) mice and then randomly divided into two groups: the control and palmitic acid (PA) groups. The expression levels of NLRP3, ASC, and caspase-1 in KCs were determined by RT-PCR, western blotting, and immunofluorescence. The levels of IL-1β and IL-18 in the supernatant (SN) of KCs were evaluated by enzyme-linked immunosorbent assay (ELISA). We found that KCs and NLRP3 play pro-inflammatory roles in the progression of NASH, probably through secretions of IL-1β and IL-18 by KCs induced by PA. PA could act as a kind of damage-associated molecular patterns to elevate the messenger RNA and protein expression levels of NLRP3, ASC, and caspase-1 in KCs from WT mice. In the contrast, NLRP3 deletion could inhibit the NLRP3 inflammasome upregulation and activation in KCs induced by PA. Furthermore, the levels of pro-inflammatory cytokines IL-1β and IL-18 in the SN of KCs from WT mice were all elevated with the stimulation of PA, and the increase of these cytokines in the SN was blocked by NLRP3 deletion. In conclusion, our novel findings demonstrate that NLRP3 plays a pivotal role in NASH development and pro-inflammatory cytokines IL-1β and IL-18 secretion induced by PA stimulation, and NLRP3 might be an effective potential target for the treatment of liver inflammatory diseases associated with NLRP3 inflammasome activation.

NOD-like receptor (NLR) NLRP3 inflammasome activation has been implicated in the progression of non-alcoholic fatty liver disease (NAFLD) from non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH). It has been also shown that palmitic acid (PA) activates NLRP3 inflammasome and promotes interleukin-1β (IL-1β) secretion in Kupffer cells (KCs). However, the specific mechanism of the NLRP3 inflammasome activation is unclear. We studies the molecular mechanisms by investigating the roles of Thioredoxin-interacting protein (TXNIP) and NLRP3 on NAFLD development in patients, high-fat diet (HFD)-induced NAFL and methionine choline deficient (MCD) diet-induced NASH in wild type (WT), TXNIP-/- (thioredoxin-interacting protein) and NLRP3-/- mice, and isolated KCs. We found that the expressions of NLRP3 and TXNIP in human liver tissues were higher in NASH group than in NAFL group. Furthermore, co-immunoprecipitation analyses show that activation of the TXNIP-NLRP3 inflammasome protein complex occurred in KCs of NASH WT mice rather than NAFL WT mice, thus suggesting that the formation and activation of this protein complex is mainly involved in the development of NASH. NLRP3-/- mice exhibited less severe NASH than WT mice in MCD diet model, whereas TXNIP deficiency enhanced NLRP3 inflammasome activation and exacerbated liver injury. PA triggered the activation and co-localization of the NLRP3 inflammasome protein complex in KCs isolated from WT and TXNIP-/- but not NLRP3-/- mice, and most of the complex co-localized with mitochondria of KCs following PA stimulation. Taken together, our novel findings indicate that TXNIP plays a protective and anti-inflammatory role in the development of NAFLD through binding and suppressing NLRP3.

Non-alcoholic fatty liver disease (NAFLD) and its causal factors of hepatic insulin resistance (IR) and type 2 diabetes are rapidly growing worldwide. Developing new therapeutic methods for these conditions requires a comprehensive understanding between hepatic lipid metabolism and IR. Sterol regulatory element-binding transcription factor 1c (SREBP-1c) and carbohydrate responsive-element binding protein (ChREBP) are the major regulators of fatty acid synthase (FASN), a key enzyme of de novo fatty acid synthesis. They are induced by insulin, which directly binds to the sterol regulatory elements (SRE) or carbohydrate-responsive elements (ChORE) of the FASN promoter to induce its expression. The insulin pathway involved in NAFLD has well studied, but the role of histone modification in NAFLD is just beginning to be investigated, and there is minimal data regarding its involvement. In the current study, we investigated histone modifications in FASN under insulin stimulation. H3K4 hypertrimethylation and H3, H4 hyperacetylation in the FASN promoter was found in HepG2 cells and primary hepatocytes following insulin stimulation. We also found that insulin treatment induced the transcription factor SREBP-1c, ChREBP and could accelerate FASN expression by enhancing SREBP-1c, SRE, and ChREBP ChORE binding and inducing H3, H4 hyperacetylation at SRE, ChORE, or transcription start site (TSS) regions of the FASN promoter in hepatocellular carcinoma cell line (HepG2) and primary hepatocytes. Finally, histone acetylation could influence FASN expression by impairing SREBP-1c SRE and ChREBP ChORE binding., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Abstract: Non-alcoholic fatty liver disease (NAFLD) has emerged as a common public health problem that can progress to end-stage liver disease. Although the function of aquaglyceroporin-9 (AQP9) as a glycerol channel has been proven, the mechanism of AQP9 in the development of NAFLD is poorly understood. To investigate the effect of hepatic glycerol uptake inhibition, we utilized a lentivirus-associated RNA interference technique to knock down the expression of hepatic AQP9 in high fat diet (HFD)-induced NAFLD in rodents. Male Sprague–Dawley rats were fed with a standard chow diet or HFD for 8weeks. Rats fed a HFD were separated into 3 groups: HFD, control and transfection group, which were injected with equivalent amounts of PBS, lentivirus-scramble and lentivirus-shRNA-AQP9 through the hepatic portal vein. The results showed a remarkable decrease in the expression of AQP9 mRNA and protein in liver for the transfection group. Furthermore, less hepatic steatosis occurred when compared to the HFD and control groups after 8weeks. Our results indicate a potential role for AQP9 in the pathogenesis of hepatic steatosis. [Copyright &y& Elsevier]