RESUMEN
The nuclear bile acid receptor farnesoid X receptor (FXR) is an important transcriptional regulator of bile acid, lipid, and glucose metabolism. FXR is highly expressed in the liver and intestine and controls the synthesis and enterohepatic circulation of bile acids. However, little is known about FXR-associated proteins that contribute to metabolic regulation. Here, we performed a mass spectrometry-based search for FXR-interacting proteins in human hepatoma cells and identified AMPK as a coregulator of FXR. FXR interacted with the nutrient-sensitive kinase AMPK in the cytoplasm of target cells and was phosphorylated in its hinge domain. In cultured human and murine hepatocytes and enterocytes, pharmacological activation of AMPK inhibited FXR transcriptional activity and prevented FXR coactivator recruitment to promoters of FXR-regulated genes. Furthermore, treatment with AMPK activators, including the antidiabetic biguanide metformin, inhibited FXR agonist induction of FXR target genes in mouse liver and intestine. In a mouse model of intrahepatic cholestasis, metformin treatment induced FXR phosphorylation, perturbed bile acid homeostasis, and worsened liver injury. Together, our data indicate that AMPK directly phosphorylates and regulates FXR transcriptional activity to precipitate liver injury under conditions favoring cholestasis.
Asunto(s)
Adenilato Quinasa/metabolismo , Ácidos y Sales Biliares/biosíntesis , Homeostasis , Hipoglucemiantes/farmacología , Metformina/farmacología , Receptores Citoplasmáticos y Nucleares/metabolismo , Adenilato Quinasa/antagonistas & inhibidores , Secuencia de Aminoácidos , Aminoimidazol Carboxamida/análogos & derivados , Aminoimidazol Carboxamida/farmacología , Animales , Transporte Biológico , Células CACO-2 , Colestasis Intrahepática/metabolismo , Colestasis Intrahepática/patología , Células Hep G2 , Humanos , Mucosa Intestinal/metabolismo , Intestinos/efectos de los fármacos , Hígado/efectos de los fármacos , Hígado/metabolismo , Hígado/patología , Masculino , Ratones , Ratones Endogámicos C57BL , Datos de Secuencia Molecular , Fosforilación , Regiones Promotoras Genéticas , Unión Proteica , Procesamiento Proteico-Postraduccional , Receptores Citoplasmáticos y Nucleares/química , Ribonucleótidos/farmacología , Transducción de Señal , Transactivadores/metabolismo , Transcripción Genética , Activación Transcripcional/efectos de los fármacosRESUMEN
Common multi-allelic copy number variants (CNVs) appear enriched for phenotypic associations compared to their biallelic counterparts. Here we investigated the influence of gene dosage effects on adiposity through a CNV association study of gene expression levels in adipose tissue. We identified significant association of a multi-allelic CNV encompassing the salivary amylase gene (AMY1) with body mass index (BMI) and obesity, and we replicated this finding in 6,200 subjects. Increased AMY1 copy number was positively associated with both amylase gene expression (P = 2.31 × 10(-14)) and serum enzyme levels (P < 2.20 × 10(-16)), whereas reduced AMY1 copy number was associated with increased BMI (change in BMI per estimated copy = -0.15 (0.02) kg/m(2); P = 6.93 × 10(-10)) and obesity risk (odds ratio (OR) per estimated copy = 1.19, 95% confidence interval (CI) = 1.13-1.26; P = 1.46 × 10(-10)). The OR value of 1.19 per copy of AMY1 translates into about an eightfold difference in risk of obesity between subjects in the top (copy number > 9) and bottom (copy number < 4) 10% of the copy number distribution. Our study provides a first genetic link between carbohydrate metabolism and BMI and demonstrates the power of integrated genomic approaches beyond genome-wide association studies.
Asunto(s)
Metabolismo de los Hidratos de Carbono/genética , Dosificación de Gen/genética , Predisposición Genética a la Enfermedad/genética , Obesidad/genética , alfa-Amilasas Salivales/genética , Índice de Masa Corporal , Genómica/métodos , Humanos , Análisis por Micromatrices , Oportunidad Relativa , alfa-Amilasas Salivales/sangreRESUMEN
BACKGROUND: Liver biopsy is considered as the gold standard for assessing nonalcoholic fatty liver disease (NAFLD) histologic lesions in patients with morbid obesity. The aim of this study was to determine the diagnostic utility of noninvasive markers of fibrosis (FibroTest), steatosis (SteatoTest), and steatohepatitis (NashTest, ActiTest) in these patients. MATERIALS AND METHODS: Two hundred and eighty-eight patients presenting with interpretable baseline operative biopsy and biomarkers, in an ongoing prospective cohort of patients treated with bariatric surgery, were included. Histology (NAFLD activity score, or NAFLD scoring system) and biochemical measurements were centralized and blinded to other characteristics. The area under the receiver operating characteristic curves (AUROC), sensitivity, specificity, positive and negative predictive values were assessed. Weighted AUROC (Obuchowski method) was used to prevent multiple testings and a spectrum effect. RESULTS: The prevalence of advanced fibrosis (bridging) was 6.9%, advanced steatosis (>33%) was 48%, and steatohepatitis was 6.9% (NAFLD scoring system>4). Weighted AUROCs of the tests were as follows (mean, 95% confidence interval, significance): FibroTest for advanced fibrosis: 0.85, 0.83-0.87, P<0.0001; SteatoTest for advanced steatosis: 0.81, 0.79-0.83, P<0.0001; and ActiTest for steatohepatitis: 0.77, 0.73-0.81, P<0.0001. CONCLUSION: In patients with morbid obesity, the diagnostic performances of the FibroTest, SteatoTest, and ActiTest were statistically significant, thereby possibly reducing the need for biopsy in this population.