Project description:Identification and validation of the pathways and functions regulated by the orphan nuclear receptor, ROR alpha1, in skeletal muscle The retinoic acid receptor-related orphan receptor (ROR) alpha has been demonstrated to regulate lipid metabolism. We were interested in the physiologically relevant roles, and pathways regulated by RORalpha1 action in skeletal muscle. This major mass organ accounts for ~40% of the total body mass, and significant levels of lipid catabolism, glucose disposal and energy expenditure. We utilized the strategy of targeted muscle specific expression of a truncated (dominant negative) RORalphaâDE in transgenic mice, to investigate RORalpha1 signalling (and function) in this peripheral tissue. Expression profiling and pathway analysis indicated that RORalpha regulated genes involved in: (i) lipid and carbohydrate metabolism, cardiovascular and metabolic disease; and (ii) the LXR nuclear receptor signaling pathway and, (iii) the Akt and AMPK signaling cascades. This analysis was extensively validated by rigorous qPCR analysis using TaqMan Low Density Arrays, coupled to rigorous statistical analysis (with Empirical Bayes, and Benjamini-Hochberg). Moreover, westerns and metabolic profiling were utilized to validate the genes, proteins and pathways (lipogenic, Akt, AMPK and fatty acid oxidation) involved in the regulation of metabolism by RORalph1. The identified genes and pathways were in concordance with the demonstration of hyperglycemia, glucose intolerance, attenuated insulin stimulated phosphorylation of Akt, and impaired glucose uptake in the transgenic heterozygous Tg-RORalphaâDE animals. In conclusion, we propose that RORalpha1 is involved in regulating the Akt2-AMPK signalling pathways in the context of lipid homeostasis in skeletal muscle. Total RNA was compared from quadriceps femoris of both transgenic and wild type mice. Transgenic mice contained a truncated version of human RORalpha1 (RORalpha1delDE) where the entire E region and part of the hinge/D region have been removed. This transgene is driven by a skeletal muscle specific human skeletal alpha-actin (HSA) promoter.

Project description:This experiment was conducted to identify target genes of the peroxisome proliferator-activated receptor beta (PPARb) in skeletal muscle of transgenic mice that overexpressed PPARb. The following abstract from the submitted manuscript describes the major findings of this work. The Nuclear Receptor Transcription Factor PPARbeta/delta Programs Muscle Glucose Metabolism. Zhenji Gan, Eileen Burkart-Hartman, Dong-Ho Han, Brian Finck, Teresa C. Leone, John Holloszy, and Daniel P. Kelly. To identify new gene regulatory pathways controlling skeletal muscle energy metabolism, comparative studies were conducted on muscle-specific transgenic mouse lines expressing the nuclear receptors, PPARalpha (MCK-PPARalpha) or PPARbeta/delta (MCK-PPARbeta/delta). MCK-PPARbeta/delta mice are known to have enhanced exercise performance whereas MCK-PPARalpha mice perform at low levels. Transcriptional profiling revealed that the lactate dehydrogenase (Ldh)b/Ldha gene expression ratio is increased in MCK-PPARbeta/delta muscle, an isoenzyme shift that diverts pyruvate into the mitochondrion for the final steps of glucose oxidation. PPARbeta/delta gain- and loss-of-function studies in skeletal myotubes demonstrated that PPARbeta/delta, but not PPARalpha, interacts with the exercise inducible kinase, AMP-activated protein kinase (AMPK), to synergistically activate Ldhb gene transcription by cooperating with myocyte enhancer factor 2A (MEF2A), in a PPARbeta/delta ligand-independent manner. MCK-PPARbeta/delta muscle was shown to have high glycogen stores, increased levels of GLUT4, and augmented capacity for mitochondrial pyruvate oxidation suggesting a broad reprogramming of glucose utilization pathways. Lastly, exercise studies demonstrated that MCK-PPARbeta/delta mice had lower circulating levels of lactate compared to non-transgenic controls, while exhibiting supranormal performance on a high intensity exercise regimen. These results identify a transcriptional regulatory mechanism that increases capacity for muscle glucose utilization in a pattern that resembles the effects of exercise training. Keywords: muscle, exercise, nuclear receptors, glucose metabolism, gene regulation RNA from two wild-type (non-transgenic (NTG)) and two PPARbeta overexpressing (MCK-PPARb) mice was analyzed. Two replicates of each are provided.

Project description:This experiment was conducted to identify target genes of the peroxisome proliferator-activated receptor beta (PPARb) in skeletal muscle of transgenic mice that overexpressed PPARb. The following abstract from the submitted manuscript describes the major findings of this work. The Nuclear Receptor Transcription Factor PPARbeta/delta Programs Muscle Glucose Metabolism. Zhenji Gan, Eileen Burkart-Hartman, Dong-Ho Han, Brian Finck, Teresa C. Leone, John Holloszy, and Daniel P. Kelly. To identify new gene regulatory pathways controlling skeletal muscle energy metabolism, comparative studies were conducted on muscle-specific transgenic mouse lines expressing the nuclear receptors, PPARalpha (MCK-PPARalpha) or PPARbeta/delta (MCK-PPARbeta/delta). MCK-PPARbeta/delta mice are known to have enhanced exercise performance whereas MCK-PPARalpha mice perform at low levels. Transcriptional profiling revealed that the lactate dehydrogenase (Ldh)b/Ldha gene expression ratio is increased in MCK-PPARbeta/delta muscle, an isoenzyme shift that diverts pyruvate into the mitochondrion for the final steps of glucose oxidation. PPARbeta/delta gain- and loss-of-function studies in skeletal myotubes demonstrated that PPARbeta/delta, but not PPARalpha, interacts with the exercise inducible kinase, AMP-activated protein kinase (AMPK), to synergistically activate Ldhb gene transcription by cooperating with myocyte enhancer factor 2A (MEF2A), in a PPARbeta/delta ligand-independent manner. MCK-PPARbeta/delta muscle was shown to have high glycogen stores, increased levels of GLUT4, and augmented capacity for mitochondrial pyruvate oxidation suggesting a broad reprogramming of glucose utilization pathways. Lastly, exercise studies demonstrated that MCK-PPARbeta/delta mice had lower circulating levels of lactate compared to non-transgenic controls, while exhibiting supranormal performance on a high intensity exercise regimen. These results identify a transcriptional regulatory mechanism that increases capacity for muscle glucose utilization in a pattern that resembles the effects of exercise training. Keywords: muscle, exercise, nuclear receptors, glucose metabolism, gene regulation

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Identification and validation of the pathways and functions regulated by the ROR alpha1 in skeletal muscle

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