ABSTRACT
Glucocorticoids have various medical uses but are accompanied by side effects. The glucocorticoid receptor (GR) has been reported to regulate the clock genes, but the underlying mechanisms are incompletely understood. In this study, we focused on the suppressive effect of the GR on the expression of Rev-erbα (Nr1d1), an important component of the clock regulatory circuits. Here we show that the GR suppresses Rev-erbα expression via the formation of a complex with CLOCK and BMAL1, which binds to the E-boxes in the Nr1d1 promoter. In this GR-CLOCK-BMAL1 complex, the GR does not directly bind to DNA, which is referred to as tethering. These findings provide new insights into the role of the GR in the control of circadian rhythm.
Subject(s)
ARNTL Transcription Factors/metabolism , CLOCK Proteins/metabolism , Dexamethasone/administration & dosage , Nuclear Receptor Subfamily 1, Group D, Member 1/genetics , Receptors, Glucocorticoid/metabolism , Animals , Circadian Rhythm/drug effects , Dexamethasone/pharmacology , Gene Expression Regulation/drug effects , HEK293 Cells , Hep G2 Cells , Humans , Male , Mice , Nuclear Receptor Subfamily 1, Group D, Member 1/chemistry , Nuclear Receptor Subfamily 1, Group D, Member 1/metabolism , Promoter Regions, Genetic , Receptors, Glucocorticoid/agonistsABSTRACT
The SNP rs7903146 at the transcription factor 7-like 2 (TCF7L2) locus is established as the strongest known genetic marker for type 2 diabetes via genome-wide association studies. However, the functional SNPs regulating TCF7L2 expression remain unclear. Here, we show that the SNP rs7074440 is a candidate functional SNP highly linked with rs7903146. A reporter plasmid with rs7074440 normal allele sequence exhibited 15-fold higher luciferase activity compared with risk allele sequence in hepatocytes, demonstrating a strong enhancer activity at rs7074440. Additionally, we identified C-FOS as an activator binding to the rs7074440 enhancer using a TFEL genome-wide screen method. Consistently, knockdown of C-FOS significantly reduced TCF7L2 expression in hepatocytes. Collectively, a novel enhancer regulating TCF7L2 expression was revealed through searching for functional SNPs.
Subject(s)
Diabetes Mellitus, Type 2/genetics , Hepatocytes/metabolism , Polymorphism, Single Nucleotide , Proto-Oncogene Proteins c-fos/metabolism , Transcription Factor 7-Like 2 Protein/genetics , Animals , Cell Line , Female , Gene Expression , HEK293 Cells , Hep G2 Cells , Hepatocytes/cytology , Humans , Male , MiceABSTRACT
Sodium-glucose cotransporter 2 (SGLT2) inhibitors have both anti-diabetic and anti-obesity effects. However, the precise mechanism of the anti-obesity effect remains unclear. We previously demonstrated that the glycogen depletion signal triggers lipolysis in adipose tissue via liver-brain-adipose neurocircuitry. In this study, therefore, we investigated whether the anti-obesity mechanism of SGLT2 inhibitor is mediated by this mechanism. Diet-induced obese mice were subjected to hepatic vagotomy (HVx) or sham operation and loaded with high fat diet containing 0.015% tofogliflozin (TOFO), a highly selective SGLT2 inhibitor, for 3 weeks. TOFO-treated mice showed a decrease in fat mass and the effect of TOFO was attenuated in HVx group. Although both HVx and sham mice showed a similar level of reduction in hepatic glycogen by TOFO treatment, HVx mice exhibited an attenuated response in protein phosphorylation by protein kinase A (PKA) in white adipose tissue compared with the sham group. As PKA pathway is known to act as an effector of the liver-brain-adipose axis and activate triglyceride lipases in adipocytes, these results indicated that SGLT2 inhibition triggered glycogen depletion signal and actuated liver-brain-adipose axis, resulting in PKA activation in adipocytes. Taken together, it was concluded that the effect of SGLT2 inhibition on weight loss is in part mediated via the liver-brain-adipose neurocircuitry.
Subject(s)
Adipose Tissue/physiology , Benzhydryl Compounds/administration & dosage , Brain/physiology , Glucosides/administration & dosage , Liver/physiology , Sodium-Glucose Transporter 2 Inhibitors , Sodium-Glucose Transporter 2/metabolism , Weight Loss/physiology , Adipose Tissue/drug effects , Adipose Tissue/innervation , Animals , Anti-Obesity Agents/administration & dosage , Brain/drug effects , Liver/drug effects , Liver/innervation , Male , Mice , Mice, Inbred C57BL , Vagotomy , Vagus Nerve/drug effects , Vagus Nerve/physiology , Vagus Nerve/surgeryABSTRACT
Fatty acid synthase (Fasn) is a key component of energy metabolism that is dynamically induced by food intake. Although extensive studies have revealed a number of transcription factors involved in the fasting/refeeding transition of Fasn expression in hepatocytes, much less evidence is available for adipocytes. Using the in vivo Ad-luc analytical system, we identified the inverted CCAAT element (ICE) around -100 nucleotides in the Fasn promoter as a critical cis-element for the refeeding response in adipocytes. Electrophoretic mobility shift assays and chromatin immunoprecipitation show that nuclear factor Y (NF-Y) binds to ICE specifically in refeeding states. Notably, the NF-Y binding to ICE is differently regulated between adipocytes and hepatocytes. These findings provide insights into the specific mechanisms controlling energy metabolism in adipocytes.
