RESUMEN
Brown fat cells are specialized to dissipate energy and can counteract obesity; however, the transcriptional basis of their determination is largely unknown. We show here that the zinc-finger protein PRDM16 is highly enriched in brown fat cells compared to white fat cells. When expressed in white fat cell progenitors, PRDM16 activates a robust brown fat phenotype including induction of PGC-1alpha, UCP1, and type 2 deiodinase (Dio2) expression and a remarkable increase in uncoupled respiration. Transgenic expression of PRDM16 at physiological levels in white fat depots stimulates the formation of brown fat cells. Depletion of PRDM16 through shRNA expression in brown fat cells causes a near total loss of the brown characteristics. PRDM16 activates brown fat cell identity at least in part by simultaneously activating PGC-1alpha and PGC-1beta through direct protein binding. These data indicate that PRDM16 can control the determination of brown fat fate.
Asunto(s)
Tejido Adiposo Pardo/metabolismo , Proteínas de Unión al ADN/fisiología , Regulación de la Expresión Génica , Factores de Transcripción/fisiología , Transcripción Genética , Células 3T3-L1 , Adipocitos , Adipocitos Marrones/metabolismo , Adipocitos Blancos/metabolismo , Tejido Adiposo Blanco/metabolismo , Animales , Western Blotting , Células COS , Diferenciación Celular , Respiración de la Célula , Células Cultivadas , Chlorocebus aethiops , Ensayo de Cambio de Movilidad Electroforética , Fibroblastos , Genes Reporteros , Yoduro Peroxidasa/genética , Yoduro Peroxidasa/metabolismo , Canales Iónicos/genética , Canales Iónicos/metabolismo , Masculino , Ratones , Ratones Endogámicos C3H , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Transgénicos , Mitocondrias , Proteínas Mitocondriales/genética , Proteínas Mitocondriales/metabolismo , Consumo de Oxígeno , Coactivador 1-alfa del Receptor Activado por Proliferadores de Peroxisomas gamma , Fenotipo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transactivadores/genética , Transactivadores/metabolismo , Factores de Transcripción/genética , Proteína Desacopladora 1 , Yodotironina Deyodinasa Tipo IIRESUMEN
Maintenance of ATP levels is a critical feature of all cells. Mitochondria are responsible for most ATP synthesis in eukaryotes. We show here that mammalian cells respond to a partial chemical uncoupling of mitochondrial oxidative phosphorylation with a decrease in ATP levels, which recovers over several hours to control levels. This recovery occurs through an increased expression of the transcriptional coactivator peroxisome proliferator-activated receptor-coactivator 1alpha (PGC-1alpha) and mitochondrial genes. Cells and animals lacking PGC-1alpha lose this compensatory mechanism and cannot defend their ATP levels or increase mitochondrial gene expression in response to reduced oxidative phosphorylation. The induction of PGC-1alpha and its mitochondrial target genes is triggered by a burst of intracellular calcium, which causes an increase in cAMP-response-element-binding protein and transducer of regulated cAMP-response-element-binding proteins actions on the PGC-1alpha promoter. These data illustrate a fundamental transcriptional cycle that provides homeostatic control of cellular ATP. In light of this compensatory system that limits the toxicity of mild uncoupling, the use of chemical uncoupling of mitochondria as a means of treating obesity should be re-evaluated.
Asunto(s)
Metabolismo Energético , Mitocondrias/metabolismo , Transactivadores/fisiología , Proteínas Quinasas Activadas por AMP , Adenosina Trifosfato/análisis , Animales , Calcio/fisiología , Carbonil Cianuro p-Trifluorometoxifenil Hidrazona/farmacología , Supervivencia Celular , Células Cultivadas , Proteína de Unión a Elemento de Respuesta al AMP Cíclico/fisiología , Homeostasis , Ratones , Complejos Multienzimáticos/fisiología , Fosforilación Oxidativa , Coactivador 1-alfa del Receptor Activado por Proliferadores de Peroxisomas gamma , Regiones Promotoras Genéticas , Proteínas Serina-Treonina Quinasas/fisiología , Transactivadores/genética , Factores de TranscripciónRESUMEN
Leigh syndrome French Canadian variant (LSFC) is an autosomal recessive neurodegenerative disorder due to mutation in the LRP130 (leucine-rich protein 130 kDa) gene. Unlike classic Leigh syndrome, the French Canadian variant spares the heart, skeletal muscle, and kidneys, but severely affects the liver. The precise role of LRP130 in cytochrome c oxidase deficiency and hepatic lactic acidosis that accompanies this disorder is unknown. We show here that LRP130 is a component of the PGC-1alpha (peroxisome proliferator-activated receptor coactivator 1-alpha) transcriptional coactivator holocomplex and regulates expression of PEPCK (phosphoenolpyruvate carboxykinase), G6P (glucose-6-phosphatase), and certain mitochondrial genes through PGC-1alpha. Reduction of LRP130 in fasted mice via adenoviral RNA interference (RNAi) vector blocks the induction of PEPCK and G6P, and blunts hepatic glucose output. LRP130 is also necessary for PGC-1alpha-dependent transcription of several mitochondrial genes in vivo. These data link LRP130 and PGC-1alpha to defective hepatic energy homeostasis in LSFC, and reveal a novel regulatory mechanism of glucose homeostasis.
Asunto(s)
Regulación de la Expresión Génica , Gluconeogénesis/genética , Glucosa/metabolismo , Enfermedad de Leigh/metabolismo , Proteínas de Neoplasias/metabolismo , Transactivadores/metabolismo , Animales , Sitios de Unión , Inmunoprecipitación de Cromatina , Metabolismo Energético/genética , Proteína Forkhead Box O1 , Factores de Transcripción Forkhead/metabolismo , Genes Mitocondriales/genética , Glucosa-6-Fosfatasa/genética , Homeostasis/genética , Enfermedad de Leigh/genética , Hígado/metabolismo , Ratones , Coactivador 1-alfa del Receptor Activado por Proliferadores de Peroxisomas gamma , Fosfoenolpiruvato Carboxiquinasa (ATP)/genética , Factores de TranscripciónRESUMEN
PGC-1alpha is a coactivator of nuclear receptors and other transcription factors that regulates several metabolic processes, including mitochondrial biogenesis and respiration, hepatic gluconeogenesis, and muscle fiber-type switching. We show here that, while hepatocytes lacking PGC-1alpha are defective in the program of hormone-stimulated gluconeogenesis, the mice have constitutively activated gluconeogenic gene expression that is completely insensitive to normal feeding controls. C/EBPbeta is elevated in the livers of these mice and activates the gluconeogenic genes in a PGC-1alpha-independent manner. Despite having reduced mitochondrial function, PGC-1alpha null mice are paradoxically lean and resistant to diet-induced obesity. This is largely due to a profound hyperactivity displayed by the null animals and is associated with lesions in the striatal region of the brain that controls movement. These data illustrate a central role for PGC-1alpha in the control of energy metabolism but also reveal novel systemic compensatory mechanisms and pathogenic effects of impaired energy homeostasis.