Irisin Is Controlled by Farnesoid X Receptor and Regulates Cholesterol Homeostasis.
ABSTRACT: Objective:The aim of this study was to investigate whether the nuclear receptor farnesoid X receptor (FXR) could regulate FNDC5/Irisin expression and the role of Irisin in hyperlipidemia and atherosclerosis in ApoE-/- mice. Methods and Results:We treated primary human hepatocytes, HepG2 cells, and Rhesus macaques with FXR agonist (CDCA, GW4064, and ivermectin). FNDC5 expression was highly induced by CDCA and GW4064 in hepatocytes, HepG2 cells, and the circulating level of Irisin increased in Rhesus macaques. Luciferase reporter and CHIP assays were used to determine whether FXR could regulate FNDC5 promoter activity. Irisin-ApoE-/- and ApoE-/- mice were used to study the metabolic function of Irisin in dyslipidemia and atherosclerosis. Irisin-ApoE-/- mice showed improved hyperlipidemia and alleviated atherosclerosis as compared with ApoE-/- mice. Irisin upregulated the expression of Abcg5/Abcg8 in liver and intestine, which increased the transport of biliary cholesterol and fecal cholesterol output. Conclusion:Activation of FXR induces FNDC5 mRNA expression in human and increased the circulating level of Irisin in Rhesus macaques. FNDC5/Irisin is a direct transcriptional target of FXR. Irisin may be a novel therapeutic strategy for dyslipidemia and atherosclerosis.
Project description:<h4>Background and purpose</h4>Low doses of acetyl salicylic acid (ASA) and non-steroidal anti-inflammatory drugs (NSAIDs) cause gastrointestinal damage. The farnesoid X receptor (FXR) is a bile acid sensor essential for maintenance of intestinal homeostasis. Here, we have investigated whether FXR is required for mucosal protection in models of gastrointestinal injury caused by ASA and NSAIDs and if FXR activation has potential in the treatment or prevention of gastrointestinal injury caused by these agents.<h4>Experimental approach</h4>FXR(+/+) and FXR(-/-) mice were given ASA (10 to 100 mg·kg(-1) ) or NSAIDs. Gastric and intestinal mucosal damage assessed by measuring lesion scores. FXR were activated by giving mice natural (chenodeoxycholic acid; CDCA) or synthetic (GW4064) FXR agonists.<h4>Key results</h4>FXR, mRNA and protein, was detected in human and mouse stomach. FXR(-/-) mice were more prone to develop severe gastric and intestinal injury in response to ASA and NSAIDs and showed a severe reduction in the gastrointestinal expression of cystathionine-?-lyase (CSE), an enzyme required for generation of hydrogen sulphide. CSE expression was reduced by ?50% in wild-type mice challenged with ASA. Treating wild-type mice but not FXR(-/-) mice with CDCA or GW4064 protected against gastric injury caused by ASA and NSAIDs, by a CSE-dependent and cycloxygenase- and NO-independent, mechanism. FXR activation by GW4064 rescued mice from intestinal injury caused by naproxen.<h4>Conclusions and implications</h4>FXR was essential to maintain gastric and intestinal mucosal barriers. FXR agonists protected against gastric injury caused by ASA and NSAIDs by a CSE-mediated mechanism.
Project description:This study evaluated HIF-1? inhibitors under different hypoxic conditions, physiological hypoxia (5% O2) and severe hypoxia (0.1% O2). We found that chenodeoxy cholic acid (CDCA) reduced the amount of HIF-1? protein only under physiological hypoxia but not under severe hypoxia without decreasing its mRNA level. By using a proteasome inhibitor MG132 and a translation inhibitor cyclohexamide, we showed that CDCA reduced HIF-1? protein by decreasing its translation but not by enhancing its degradation. The following findings indicated that farnesoid X receptor (FXR), a CDCA receptor and its target gene, Small heterodimer partner (SHP) are not involved in this effect of CDCA. Distinctly from CDCA, MG132 prevented SHP and an exogenous FXR agonist, GW4064 from reducing HIF-1? protein. Furthermore a FXR antagonist, guggulsterone failed to prevent CDCA from decreasing HIF-1? protein. Furthermore, guggulsterone by itself reduced HIF-1? protein even in the presence of MG132. These findings suggested that CDCA and guggulsterone reduced the translation of HIF-1? in a mechanism which FXR and SHP are not involved. This study reveals novel therapeutic functions of traditional nontoxic drugs, CDCA and guggulsterone, as inhibitors of HIF-1? protein.
Project description:Global gene expression in primary cultured mouse kidney proximal tubule cells treated with either DMSO or 1uM GW4064 (an FXR agonist) was compared. Results provide insight into mechanisms underlying effects of FXR activation on gene expression in mouse kidney proximal tubule cells. Overall design: Male C57/BJ mice aged 6 weeks were sacrificed under anesthesia and kidney proximal tubule cells were cultured until confluent. Cells were treated with either GW4064 (1uM) or equal amount of DMSO and incubated for 24 hours. 4 total RNA samples per group were analyzed and gene expression was compared between the groups. GW4064 is a compound which activates FXR, a bile acid nuclear receptor. The natural FXR agonists are usually bile acids, such as cholic acid and CDCA. GW4064 is an artificial FXR agonist which is synthesized by Sigma-Aldrich.
Project description:<h4>Background</h4>Farnesoid X receptor/retinoid X receptor-alpha (FXR/RXR?) is the master transcriptional regulator of bile salt synthesis and transport in liver and intestine. FXR is activated by bile acids, RXR? by the vitamin A-derivative 9-cis retinoic acid (9cRA). Remarkably, 9cRA inhibits binding of FXR/RXR? to its response element, an inverted repeat-1 (IR-1). Still, most FXR/RXR? target genes are maximally expressed in the presence of both ligands, including the small heterodimer partner (SHP). Here, we revisited the FXR/RXR?-mediated regulation of human SHP.<h4>Methods</h4>A 579-bp hSHP promoter element was analyzed to locate FXR/chenodeoxycholic acid (CDCA)- and RXR?/9cRA-responsive elements. hSHP promoter constructs were analyzed in FXR/RXR?-transfected DLD-1, HEK293 and HepG2 cells exposed to CDCA, GW4064 (synthetic FXR ligand) and/or 9cRA. FXR-DNA interactions were analyzed by in vitro pull down assays.<h4>Results</h4>hSHP promoter elements lacking the previously identified IR-1 (-291/-279) largely maintained their activation by FXR/CDCA, but were unresponsive to 9cRA. FXR-mediated activation of the hSHP promoter was primarily dependent on the -122/-69 region. Pull down assays revealed a direct binding of FXR to the -122/-69 sequence, which was abrogated by site-specific mutations in a binding site for the liver receptor homolog-1 (LRH-1) at -78/-70. These mutations strongly impaired the FXR/CDCA-mediated activation, even in the context of a hSHP promoter containing the IR-1. LRH-1 did not increase FXR/RXR?-mediated activation of hSHP promoter activity.<h4>Conclusion</h4>FXR/CDCA-activated expression of SHP is primarily mediated through direct binding to an LRH-1 binding site, which is not modulated by LRH-1 and unresponsive to 9cRA. 9cRA-induced expression of SHP requires the IR-1 that overlaps with a direct repeat-2 (DR-2) and DR-4. This establishes for the first time a co-stimulatory, but independent, action of FXR and RXR? agonists.
Project description:BACKGROUND: Although human immunodeficiency virus (HIV)-related morbidity and mortality rates in patients treated with a combination of high active antiretroviral therapy (HAART) have declined, significant metabolic/vascular adverse effects associated with the long term use of HIV protease inhibitors (PIs) have emerged as a significant side effect. Here we illustrate that targeting the bile acid sensor farnesoid X receptor (FXR) protects against dyslipidemia and vascular injury induced HIV-PIs in rodents. METHODOLOGY/PRINCIPAL FINDINGS: Administration of the HIV PI ritonavir to wild type mice increased plasma triacylglycerols and cholesterol levels and this effect was exacerbated by dosing ritonavir to mice harbouring a disrupted FXR. Dyslipidemia induced by ritonavir associated with a shift in the liver expression of signature genes, Sterol Regulatory Element-Binding Protein (SREBP)-1 and fatty acid synthase. Treating wild type mice with the FXR agonist (chenodeoxycholic acid, CDCA) protected against development of dyslipidemia induced by ritonavir. Administration of ritonavir to ApoE(-/-) mice, a strain that develop spontaneously atherosclerosis, increased the extent of aortic plaques without worsening the dyslipidemia. Treating these mice with CDCA reduced the extent of aortic plaques by 70% without changing plasma lipoproteins or the liver expression of signature genes. A beneficial effect on aortic plaques was also obtained by treating ApoE(-/-) mice with gemfibrozil, a PPAR? agonist. FXR activation counter-regulated induction of expression/activity of CD36 caused by HIV-PIs in circulating monocytes and aortic plaques. In macrophages cell lines, CDCA attenuated CD36 induction and uptake of acetylated LDL caused by ritonavir. Natural and synthetic FXR ligands reduced the nuclear translocation of SREBP1c caused by ritonavir. CONCLUSIONS/SIGNIFICANCE: Activation of the bile acid sensor FXR protects against dyslipidemia and atherosclerotic caused by ritonavir, a widely used HIV PI. From a mechanistic stand point it appears that besides reducing the liver expression of genes involved in fatty acid synthesis, FXR activation counter-regulates the expression/activity of CD36 on monocytes. FXR ligands might hold promise in the treatment dyslipidemia induced by ritonavir.
Project description:Irisin is a product of fibronectin type III domain-containing protein (Fndc5) and is involved in the regulation of adipokine secretion and the differentiation of osteoblasts and osteoclasts. In this study, we aimed to determine whether irisin lacking affects glucose/lipid and bone metabolism. We knocked out the Fndc5 gene to generate irisin-lacking mice. Remarkable, irisin lacking was related to poor 'browning response', with a bigger size of the intraperitoneal white adipose cell and decreased a number of brown adipose cells in brown adipose of interscapular tissue. The irisin lacking mice had hyperlipidemia and insulin resistance, reduced HDL-cholesterol level, increased LDL-cholesterol level, and decreased insulin sensitivity. The lacking of irisin was associated with reduced bone strength and bone mass in mice. The increased number of osteoclasts and higher expression of RANKL indicated increased bone resorption in irisin lacking mice. The level of IL-6 and TNF-? also increased in irisin lacking mice. The results showed that irisin lacking was related to decreased 'browning response', glucose/lipid metabolic derangement, and reduced bone mass with increased bone resorption. Further studies are needed to confirm these initial observations and explore the mechanisms underlying the effects of irisin on glucose/lipid and bone metabolism.
Project description:Chemoresistance is common in patients with biliary tract cancer (BTC) including gallbladder cancer (GBC) and cholangiocarcinoma (CC). Therefore, it is necessary to identify effective chemotherapeutic agents for BTC. In the present study, we for the first time tested the effect of farnesoid X receptor (FXR) agonists GW4064 and CDCA (chenodeoxycholic acid) in combination with cisplatin (CDDP) on increasing the chemosensitivity in BTC. Our results show that co-treatment of CDDP with FXR agonists remarkably enhance chemosensitivity of BTC cells. Mechanistically, we found that activation of FXR induced expression of small heterodimer partner (SHP), which in turn inhibited signal transducer and activator of transcription 3 (STAT3) phosphorylation and resulted in down-regulation of Bcl-xL expression in BTC cells, leading to increased susceptibility to CDDP. Moreover, the experiments on tumor-bearing mice showed that GW4064/CDDP co-treatment inhibited the tumor growth in vivo by up-regulating SHP expression and down-regulating STAT3 phosphorylation. These results suggest CDDP in combination with FXR agonists could be a potential new therapeutic strategy for BTC.
Project description:To investigate the effects of abolished cholic acid (CA) synthesis in the ApoE knockout model [apolipoprotein E (apoE) KO],a double-knockout (DKO) mouse model was created by crossbreeding Cyp8b1 knockout mice (Cyp8b1 KO), unable to synthesize the primary bile acid CA, with apoE KO mice. After 5 months of cholesterol feeding, the development of atherosclerotic plaques in the proximal aorta was 50% less in the DKO mice compared with the apoE KO mice. This effect was associated with reduced intestinal cholesterol absorption, decreased levels of apoB-containing lipoproteins in the plasma, enhanced bile acid synthesis, reduced hepatic cholesteryl esters, and decreased hepatic activity of ACAT2. The upregulation of Cyp7a1 in DKO mice seemed primarily caused by reduced expression of the intestinal peptide FGF15. Treatment of DKO mice with the farnesoid X receptor (FXR) agonist GW4064 did not alter the intestinal cholesterol absorption, suggesting that the action of CA in this process is confined mainly to formation of intraluminal micelles and less to its ability to activate the nuclear receptor FXR. Inhibition of CA synthesis may offer a therapeutic strategy for the treatment of hyperlipidemic conditions that lead to atherosclerosis.
Project description:Defective brain hormonal signaling has been associated with Alzheimer's disease (AD), a disorder characterized by synapse and memory failure. Irisin is an exercise-induced myokine released on cleavage of the membrane-bound precursor protein fibronectin type III domain-containing protein 5 (FNDC5), also expressed in the hippocampus. Here we show that FNDC5/irisin levels are reduced in AD hippocampi and cerebrospinal fluid, and in experimental AD models. Knockdown of brain FNDC5/irisin impairs long-term potentiation and novel object recognition memory in mice. Conversely, boosting brain levels of FNDC5/irisin rescues synaptic plasticity and memory in AD mouse models. Peripheral overexpression of FNDC5/irisin rescues memory impairment, whereas blockade of either peripheral or brain FNDC5/irisin attenuates the neuroprotective actions of physical exercise on synaptic plasticity and memory in AD mice. By showing that FNDC5/irisin is an important mediator of the beneficial effects of exercise in AD models, our findings place FNDC5/irisin as a novel agent capable of opposing synapse failure and memory impairment in AD.