Project description:With the improvement of people's living standards and lifestyle changes, nonalcoholic fatty liver disease (NAFLD) has become one of the most common chronic liver diseases worldwide. However, few drugs are available for NAFLD, partly due to an incomplete understanding of its pathogenic mechanisms. Here, using in vivo and in vitro gain- and loss-of function approaches, we identified DKK1 as a pivotal mediator of the progression of NAFLD and its accompanying metabolic disorders in dietary obese mice. Mechanistic study reveals that DKK1 enhances the capacity of hepatocytes to uptake fatty acids through ERK-PPARγ-CD36 pathway. Moreover, DKK1 increased insulin resistance by activating the JNK signaling pathway, which in turn exacerbates disorders of hepatic lipid metabolism. These results suggest that DKK1 is a regulator of fatty acid uptake in lipid metabolism and insulin signaling, and may be a potential therapeutic candidate for NAFLD
Project description:Hepatic steatosis is a very common response to liver injury and often attributed to metabolic disorders. Prior studies have demonstrated the efficacy of a biotechnologically produced oyster mushroom (Pleurotus sajor-caju, PSC) in alleviating hepatic steatosis in obese Zucker rats. This study aims to elucidate molecular events underlying the anti-steatotic effects of PSC.
Project description:The impairment of the intestinal barrier will lead to the accumulation of fat and harmful substances in the liver, inducing hepatic steatosis or steatohepatitis. Zhang et al. identified NSD2 in the intestine as a novel and essential regulator of hepatic steatosis. NSD2 directly regulates transcriptional activation of ERN1 through the modification of H3 dimethylated on lysine 36 (H3K4me36), thereby activating the ERN1-JNK axis to induce inflammatory response, intestinal barrier impairment, and hepatic steatosis. This functional mechanism of NSD2 provides a potential therapeutic target for this disease.
Project description:The impairment of the intestinal barrier will lead to the accumulation of fat and harmful substances in the liver, inducing hepatic steatosis or steatohepatitis. Zhang et al. identified NSD2 in the intestine as a novel and essential regulator of hepatic steatosis. NSD2 directly regulates transcriptional activation of ERN1 through the modification of H3 dimethylated on lysine 36 (H3K4me36), thereby activating the ERN1-JNK axis to induce inflammatory response, intestinal barrier impairment, and hepatic steatosis. This functional mechanism of NSD2 provides a potential therapeutic target for this disease.
Project description:Individuals with hepatic steatosis often display several metabolic abnormalities including insulin resistance and muscle atrophy. Previously, we found that hepatic steatosis results in an altered hepatokine secretion profile, thereby inducing skeletal muscle insulin resistance via inter-organ crosstalk. In this study, we aimed to investigate whether the altered secretion profile in the state of hepatic steatosis also induces skeletal muscle atrophy via effects on muscle protein turnover. To investigate this, eight-week-old male C57BL/6J mice were fed a chow (4.5% fat) or a high-fat diet (HFD; 45% fat) for 12 weeks to induce hepatic steatosis, after which the livers were excised and cut into ~200 µm slices. Slices were cultured to collect secretion products (conditioned medium; CM). Differentiated L6-GLUT4myc myotubes were incubated with chow or HFD CM to measure glucose uptake. Differentiated C2C12 myotubes were incubated with chow or HFD CM to measure protein synthesis and breakdown, and gene expression via RNA sequencing. Furthermore, proteomics analysis was performed in chow and HFD CM. It was found that HFD CM caused insulin resistance in L6-GLUT4myc myotubes compared with chow CM, as indicated by a blunted insulin-stimulated increase in glucose uptake. Furthermore, protein breakdown was increased in C2C12 cells incubated with HFD CM, while there was no effect on protein synthesis. RNA profiling of C2C12 cells indicated that 197 genes were differentially expressed after incubation with HFD CM, compared with chow CM, and pathway analysis showed that pathways related to anatomical structure and function were enriched. Proteomic analysis of the CM showed that 32 proteins were differentially expressed in HFD CM compared with chow CM. Pathway enrichment analysis indicated that these proteins had important functions with respect to insulin-like Growth Factor transport and uptake, and affect post-translational processes, including protein folding, protein secretion and protein phosphorylation. In conclusion, the results of this study support the hypothesis that secretion products from the liver contribute to the development of muscle atrophy in individuals with hepatic steatosis.
Project description:We generated hepatocyte-specific CD36 knockout (CD36LKO) mice to study in vivo effects of CD36 on de novo lipogenesis (DNL) under high fat diet (HFD). Lipid deposition and DNL were analyzed in primary hepatocytes isolated from CD36LKO mice or HepG2 cells with CD36 overexpression. RNA-sequence, co-immunoprecipitation and proximity ligation assay were carried out to determine its role in regulating DNL. Results: Hepatic CD36 expression was upregulated in NAFLD mice and patients, and CD36LKO mice exhibited attenuated HFD-induced hepatic steatosis and insulin resistance. We identified hepatocyte CD36 as a key regulator for DNL in the liver. Sterol regulatory element-binding protein 1 (SREBP1) and its downstream lipogenic enzymes such as FASN, ACCα and ACLY were significantly downregulated in the liver of HFD-fed CD36LKO mice, whereas overexpression CD36 stimulated insulin-mediated DNL and lipid droplet formation in vitro. Mechanistically, CD36 was activated by insulin and formed a complex with insulin induced gene-2 (INSIG2), that disrupts the interaction between SREBP cleavage-activating protein (SCAP) and INSIG2, thereby leading to the translocation of SREBP1 from ER to Golgi for processing. Furthermore, treatment with 25-hydroxycholesterol or betulin, molecules shown to enhance SCAP/INSIG interaction, reversed the effects of CD36 on SREBP1 cleavage.
Project description:Pyrimidine catabolism is implicated in hepatic steatosis. Dihydropyrimidine Dehydrogenase (DPYD) is an enzyme responsible for uracil and thymine catabolism, and DPYD human genetic variability affects clinically observed toxicity following 5-Fluorouracil (5-FU) administration. In an in vitro model of diet-inducedfatty acid-induced steatosis, the pharmacologic inhibition of DPYD resulted in protection from lipid accumulation. Additionally, a gain-of-function mutation of DPYD, created through clustered regularly interspaced short palindromic repeats associated protein 9 (CRISPR-Cas9) engineering, led to an increased lipid burden, which was associated with altered mitochondrial functionality in a hepatocarcionma cell line. The studies presented herein describe a novel role for DPYD in hepatocyte metabolic regulation as a modulator of hepatic steatosis.
Project description:Limb expression 1-like protein (LIX1L) plays important role in various liver disorders, but its role and underlying mechanism in nonalcoholic hepatitis (NASH) and HCC progression remains obscure. Here, we report that LIX1L functions as a key integrative regulator linking lipid metabolism and inflammation, adipose tissue dysfunction and hepatic microenvironment reprogramming which promotes NASH progression. LIX1L significantly upregulated in NAFLD/NASH patients, mouse models and palmitic acid-stimulated hepatocytes. Lix1l deletion inhibits lipid deposition, inflammatory response and fibrosis in liver as well as adipocyte differentiation by downregulation of fatty acid translocase CD36 expression, alleviating NASH and associated HCC progression. In contrast, adeno-associated virus (AAV)-mediated LIX1L overexpression exacerbates NASH progression in mice. Mechanistically, metabolic stress promotes PARP1 mediated poly-ADP-ribosylation (PARylation) of LIX1L, subsequently increasing the stability and RNA binding ability of LIX1L protein. LIX1L binds to AU-rich element (ARE) in the 3’ untranslated region (UTR) of CD36 mRNA, thus attenuating CD36 mRNA decay. In NASH and associated HCC mouse models, LIX1L deficiency-mediated downregulation of CD36 suppresses adipogenesis, hepatic lipid uptake, and reprograms the tumor-prone liver microenvironment with increased cytotoxic T lymphocytes (CTLs), reduced immunosuppressive cell proportions. These data indicate a systematic function of LIX1L in the pathogenesis of NASH and underscore the PARP1/LIX1L/CD36 axis as a potential target for treatment of NASH and associated HCC.