RESUMO
Metabolic homeostasis and circadian rhythms are closely intertwined biological processes. Nuclear receptors, as sensors of hormonal and nutrient status, are actively implicated in maintaining this physiological relationship. Although the orphan nuclear receptor estrogen-related receptor α (ERRα, NR3B1) plays a central role in the control of energy metabolism and its expression is known to be cyclic in the liver, its role in temporal control of metabolic networks is unknown. Here we report that ERRα directly regulates all major components of the molecular clock. ERRα-null mice also display deregulated locomotor activity rhythms and circadian period lengths under free-running conditions, as well as altered circulating diurnal bile acid and lipid profiles. In addition, the ERRα-null mice exhibit time-dependent hypoglycemia and hypoinsulinemia, suggesting a role for ERRα in modulating insulin sensitivity and glucose handling during the 24-hour light/dark cycle. We also provide evidence that the newly identified ERRα corepressor PROX1 is implicated in rhythmic control of metabolic outputs. To help uncover the molecular basis of these phenotypes, we performed genome-wide location analyses of binding events by ERRα, PROX1, and BMAL1, an integral component of the molecular clock. These studies revealed the existence of transcriptional regulatory loops among ERRα, PROX1, and BMAL1, as well as extensive overlaps in their target genes, implicating these three factors in the control of clock and metabolic gene networks in the liver. Genomic convergence of ERRα, PROX1, and BMAL1 transcriptional activity thus identified a novel node in the molecular circuitry controlling the daily timing of metabolic processes.
Assuntos
Proteínas de Homeodomínio/metabolismo , Fígado/metabolismo , Receptores de Estrogênio/metabolismo , Proteínas Supressoras de Tumor/metabolismo , Fatores de Transcrição ARNTL/genética , Fatores de Transcrição ARNTL/metabolismo , Animais , Ácidos e Sais Biliares/sangue , Glicemia/análise , Western Blotting , Proteínas CLOCK/metabolismo , Células COS , Chlorocebus aethiops , Colesterol/sangue , Ritmo Circadiano , Perfilação da Expressão Gênica , Regulação da Expressão Gênica , Gluconeogênese , Glicólise , Células Hep G2 , Proteínas de Homeodomínio/genética , Homeostase , Humanos , Insulina/sangue , Fígado/citologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Atividade Motora , Fotoperíodo , Regiões Promotoras Genéticas , Ligação Proteica , Interferência de RNA , Receptores de Estrogênio/genética , Triglicerídeos/sangue , Proteínas Supressoras de Tumor/genética , Receptor ERRalfa Relacionado ao EstrogênioRESUMO
Erk4 and Erk3 are atypical members of the mitogen-activated protein (MAP) kinase family. The high sequence identity of Erk4 and Erk3 proteins and the similar organization of their genes imply that the two protein kinases are paralogs. Recently, we have shown that Erk3 function is essential for neonatal survival and critical for the establishment of fetal growth potential and pulmonary function. To investigate the specific functions of Erk4, we have generated mice with a targeted disruption of the Mapk4 gene. We show that Erk4-deficient mice are viable and fertile and exhibit no gross morphological or physiological anomalies. Loss of Erk4 is not compensated by changes in Erk3 expression or activity during embryogenesis or in adult tissues. We further demonstrate that additional loss of Erk4 does not exacerbate the fetal growth restriction and pulmonary immaturity phenotypes of Erk3(-/-) mice and does not compromise the viability of Erk3(+/-) neonates. Interestingly, behavioral phenotyping revealed that Erk4-deficient mice manifest depression-like behavior in the forced-swimming test. Our analysis indicates that the MAP kinase Erk4 is dispensable for mouse embryonic development and reveals that Erk3 and Erk4 have acquired specialized functions through evolutionary diversification.
