ABSTRACT
BACKGROUND AND AIMS: Obesity-driven lipotoxicity is a risk factors for cardiovascular disease. The Farnesoid X Receptor (FXR) is a bile acids sensor and member of the nuclear receptor superfamily. Activation of FXR lowers plasma triacylglycerols and glucose levels through a mechanism that involves both the repression of key regulatory genes in the liver and the modulation of insulin sensitivity in peripheral tissues. In the present study we have investigated whether administering obese (fa/fa) Zucker rats, a genetic model of obesity associated with dyslipidemia and insulin resistance, with an FXR ligand protects against lipid-induced cardiomyopathy. METHODS AND RESULTS: FXR is expressed in neonatal cardiomyocytes and the treatment with FXR agonists, chenodeoxycholic acid (CDCA), and GW4064, increased the mRNA expression of FXR and its canonical target gene, the small heterodimer partner (SHP), as well as proliferator-activated receptor alpha PPARα, acyl-CoA oxidase (AOX) and pyruvate dehydrogenase kinase (PDK-4). Feeding obese fa/fa rats with CDCA, 12 weeks, reduced hyperinsulinemia and hyperlipidaemia. The histological-pathological analysis of hearts demonstrated that treatment with the FXR ligand reduced lipid heart content decreased the rate of apoptosis, fibrosis scores and restored heart insulin signalling. Chronic CDCA administration, in the heart, induced PPARα and PPARα-regulated genes involved in ß-oxidation. CONCLUSION: FXR agonism exerts beneficial effects in a genetic model of lipid-induced cardiomyopathy. The striking benefit of this therapy on cardiac function in this model warrants an effort to determine whether a counterpart of this activity translates in human settings.
Subject(s)
Cardiovascular Diseases/physiopathology , Lipid Metabolism , Myocardium/metabolism , Obesity/physiopathology , Receptors, Cytoplasmic and Nuclear/genetics , Acyl-CoA Oxidase/genetics , Acyl-CoA Oxidase/metabolism , Animals , Apoptosis/drug effects , Bile Acids and Salts/metabolism , Blood Glucose/analysis , Cardiovascular Diseases/etiology , Chenodeoxycholic Acid/pharmacology , Dyslipidemias/metabolism , Dyslipidemias/pathology , Fibrosis/drug therapy , Hyperinsulinism/drug therapy , Hyperlipidemias/drug therapy , Insulin Resistance , Isoxazoles/pharmacology , Liver/metabolism , Obesity/complications , PPAR alpha/genetics , PPAR alpha/metabolism , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolism , Pyruvate Dehydrogenase Acetyl-Transferring Kinase , RNA, Messenger/genetics , RNA, Messenger/metabolism , Rats , Rats, Zucker , Receptors, Cytoplasmic and Nuclear/agonists , Receptors, Cytoplasmic and Nuclear/metabolism , Risk Factors , Triglycerides/bloodABSTRACT
In addition to their role in dietary lipid absorption bile acids are signaling modules activating nuclear receptors and at least one G-protein coupled receptors named the TGR5. With a different rank of potency primary and secondary bile acids activates a subset of nuclear receptors including the farnesoid-X-receptor (FXR, NR1H4); the constitutive androstane receptor (CAR, NR1H3), the pregnane-x- receptor (PXR, NR1H2), the vitamin D receptor (VDR, NR1H1). Originally, these receptors were characterized for their role as bile acid and xenobiotic sensors, emerging evidence, however, indicates that FXR, PXR and VDR and their ligands are important for the modulation of immune and inflammatory reactions in entero-hepatic tissues. The immune phenotype FXR deficient mice indicates that these receptors are essential for the maintenance of immune homeostasis. A common theme of all bile acid-activated receptor is their ability to counter-regulate effector activities of cells of innate immunity establishing that signals generated by these receptors and their ligands function as a braking signals for inflammation in entero-hepatic tissues. In this review, we will spotlight the molecular mechanisms of receptor/ligand function and how bile acid-activated receptors regulate the innate immunity in the gastrointestinal tract and liver. The ability of these receptors to integrate metabolic and inflammatory signaling makes them particularly attractive targets for intervention in immune-mediated diseases.
