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GPR40 agonist ameliorates liver X receptor-induced lipid accumulation in liver by activating AMPK pathway.

ABSTRACT: Hepatic steatosis is strongly linked to insulin resistance and type 2 diabetes. GPR40 is a G protein-coupled receptor mediating free fatty acid-induced insulin secretion and thus plays a beneficial role in the improvement of diabetes. However, the impact of GPR40 agonist on hepatic steatosis still remains to be elucidated. In the present study, we found that activation of GPR40 by its agonist GW9508 attenuated Liver X receptor (LXR)-induced hepatic lipid accumulation. Activation of LXR in the livers of C57BL/6 mice fed a high-cholesterol diet and in HepG2 cells stimulated by chemical agonist caused increased expression of its target lipogenic genes and subsequent lipid accumulation. All these effects of LXR were dramatically downregulated after GW9508 supplementation. Moreover, GPR40 activation was accompanied by upregulation of AMPK pathway, whereas the inhibitive effect of GPR40 on the lipogenic gene expression was largely abrogated by AMPK knockdown. Taken together, our results demonstrated that GW9508 exerts a beneficial effect to ameliorate LXR-induced hepatic steatosis through regulation of AMPK signaling pathway.

SUBMITTER: Li M

PROVIDER: S-EPMC4848522 | biostudies-other | 2016 Apr

REPOSITORIES: biostudies-other

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Project description:Recent studies have indicated that the Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) pathway is closely involved in liver fibrosis and other fibrotic diseases. However, whether targeting the AMPK pathway can rescue liver fibrosis and its complications, such as portal hypertension, is unknown. This study aimed to explore the therapeutic value of AICAR (5-aminoimidazole-4-carboxyamide ribonucleoside), an agonist of the AMPK pathway, on liver fibrosis and portal hypertension in bile duct ligation (BDL) rats. In vitro experiments showed that the gene expression levels of TGF-b, a-SMA, and collagen 1 in primary rat hepatic stellate cells (HSCs) were significantly decreased after AICAR treatment. The p-eNOS expression and nitric oxide (NO) production were increased by AICAR administration in sinusoidal endothelial cells (SECs). For in vivo animal studies, AICAR acutely decreased portal pressure in the BDL and CCL4 fibrotic rats, but not in the partial portal vein ligation (PVL) rats, without changes in systemic hemodynamics. It was also observed by using intravital fluorescence microscopy that AICAR led to sinusoidal vasodilation in situ experiment. We propose that the relevant mechanisms may be related to the activation of the AMPK/NO pathway in SECs and that this activation promoted NO production in the liver, thereby promoting hepatic sinusoid microcirculation and decreased intrahepatic resistance. The results were verified using the NO inhibitor L-NAME. Chronic AICAR treatment also showed profound beneficial effects on the BDL model rats. The hemodynamic condition was greatly improved, but the positive effect could be partially blocked by L-NAME. Moreover, AICAR also decreased hepatic fibrogenesis in the BDL rats. KEY MESSAGES: Acute and chronic use of AICAR could alleviate portal pressure without changing systemic hemodynamics. AICAR induced sinusoidal vasodilation by improving NO bioavailability and ameliorating endothelial dysfunction in vivo and in vitro. AICAR could alleviate liver cirrhosis in the BDL model rats.

Project description:Methods: We performed mRNA sequence analysis by deep sequencing, in triplicate, using Illumina HiSeq to assess the impact of PHLPP1 knockdown in regulating gene expression in RAW 264.7 cells treated with/without OxLDL. The transcriptome libraries were constructed using the NEB adapters and were sequenced on at 150 nucleotide read length using the paired-end chemistry. The raw reads were subjected to Adapter and low-quality reads removal by Trimmomatic -0.36v. The raw reads were subjected to contamination [structural RNA / low complexity sequences] removal by mapping with bowtie 2-2.2.1. The decontaminated data set was mapped to the mouse genome. Reads mapping to gene list were counted using feature count module of sub reads package. The read counts were normalized in DESeq2-3.5, and subject to differential expression analysis. Differentially expressed genes were selected based on log2-ratio change with p-value <0.05 (Student’s t-test, unpaired). Hierarchical clustering was performed with the programs Cluster (uncentered correlation; average linkage clustering) and Treeview. Results: To gain a deeper understanding of the role of PHLPP1 in lipid metabolism in macrophages, we performed mRNA Seq analysis to assess the gene expression changes in a mouse macrophage cell line. The experiment has been carried out in triplicates. Alignment of the reads showed 97% alignment to the reference mouse genome. Identification of the differentially expressed genes were then carried out by DESeq2 version 1.2.10 with stringent criteria (FDR <0.05% with 2 fold up and down regulation) which reveals in control treated vs. control (121-down, 396-Up), Test vs. Control - (326-down, 569 Up) and Test treated vs. control treated (1314-down, 1328 up) of DEG to be altered in expression respectively. Inference: RNA-seq analysis revealed that PHLPP1 knockdown parallel with OxLDL treatment resulted in diminished expression profile of cholesterol biosynthesis and lipid metabolism genes.

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GPR40 agonist ameliorates liver X receptor-induced lipid accumulation in liver by activating AMPK pathway.

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