Showing papers by "Bruce M. Spiegelman published in 2007"

AMP-activated protein kinase (AMPK) action in skeletal muscle via direct phosphorylation of PGC-1α

Abstract: Activation of AMP-activated kinase (AMPK) in skeletal muscle increases glucose uptake, fatty acid oxidation, and mitochondrial biogenesis by increasing gene expression in these pathways. However, the transcriptional components that are directly targeted by AMPK are still elusive. The peroxisome-proliferator-activated receptor γ coactivator 1α (PGC-1α) has emerged as a master regulator of mitochondrial biogenesis; furthermore, it has been shown that PGC-1α gene expression is induced by exercise and by chemical activation of AMPK in skeletal muscle. Using primary muscle cells and mice deficient in PGC-1α, we found that the effects of AMPK on gene expression of glucose transporter 4, mitochondrial genes, and PGC-1α itself are almost entirely dependent on the function of PGC-1α protein. Furthermore, AMPK phosphorylates PGC-1α directly both in vitro and in cells. These direct phosphorylations of the PGC-1α protein at threonine-177 and serine-538 are required for the PGC-1α-dependent induction of the PGC-1α promoter. These data indicate that AMPK phosphorylation of PGC-1α initiates many of the important gene regulatory functions of AMPK in skeletal muscle.

PGC-1α regulates the neuromuscular junction program and ameliorates Duchenne muscular dystrophy

Abstract: The coactivator PGC-1α mediates key responses of skeletal muscle to motor nerve activity. We show here that neuregulin-stimulated phosphorylation of PGC-1α and GA-binding protein (GABP) allows recruitment of PGC-1α to the GABP complex and enhances transcription of a broad neuromuscular junction gene program. Since a subset of genes controlled by PGC-1α and GABP is dysregulated in Duchenne muscular dystrophy (DMD), we examined the effects of transgenic PGC-1α in muscle of mdx mice. These animals show improvement in parameters characteristic of DMD, including muscle histology, running performance, and plasma creatine kinase levels. Thus, control of PGC-1α levels in skeletal muscle could represent a novel avenue to prevent or treat DMD.

Abnormal glucose homeostasis in skeletal muscle–specific PGC-1α knockout mice reveals skeletal muscle–pancreatic β cell crosstalk

Abstract: The transcriptional coactivator PPARgamma coactivator 1alpha (PGC-1alpha) is a strong activator of mitochondrial biogenesis and oxidative metabolism. While expression of PGC-1alpha and many of its mitochondrial target genes are decreased in the skeletal muscle of patients with type 2 diabetes, no causal relationship between decreased PGC-1alpha expression and abnormal glucose metabolism has been established. To address this question, we generated skeletal muscle-specific PGC-1alpha knockout mice (MKOs), which developed significantly impaired glucose tolerance but showed normal peripheral insulin sensitivity. Surprisingly, MKOs had expanded pancreatic beta cell mass, but markedly reduced plasma insulin levels, in both fed and fasted conditions. Muscle tissue from MKOs showed increased expression of several proinflammatory genes, and these mice also had elevated levels of the circulating IL-6. We further demonstrated that IL-6 treatment of isolated mouse islets suppressed glucose-stimulated insulin secretion. These data clearly illustrate a causal role for muscle PGC-1alpha in maintenance of glucose homeostasis and highlight an unexpected cytokine-mediated crosstalk between skeletal muscle and pancreatic islets.

A fundamental system of cellular energy homeostasis regulated by PGC-1α

Abstract: 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 1α (PGC-1α) and mitochondrial genes Cells and animals lacking PGC-1α 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-1α 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-1α 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

Transcriptional Control of Mitochondrial Energy Metabolism through the PGC1 Coactivators

Abstract: The PGC1 transcriptional coactivators are major regulators of several crucial aspects of energy metabolism. PGC1alpha controls many aspects of oxidative metabolism, including mitochondrial biogenesis and respiration through the coactivation of many nuclear receptors, and factors outside the nuclear receptor family. ERRalpha, NRF1 and NRF2 are key targets of the PGC1s in mitochondrial biogenesis. We have recently addressed the question of the role of PGC1 coactivators in the metabolism of reactive oxygen species (ROS). We now show that PGC1alpha and beta are induced when cells are given an oxidative stressor, H2O2. In fact, experiments with either genetic knockouts or RNAi for the PGC1s show that the ability of ROS to induce a ROS scavenging programme depends entirely on the PGC1s. This includes genes encoding mitochondrial proteins like SOD2, but also includes cytoplasmic proteins such as catalase and GPX1. Cells lacking PGC1alpha are hypersensitive to death from oxidative stress caused by H2O2 or paraquat. Mice deficient in PGC1alpha get excessive neurodegeneration when given kainic acid-induced seizures or MPTP, which causes Parkinsonism. These data show that the PGC1s are key modulators of mitochondrial biology and important protective molecules against ROS generation and damage. The implications of this for diabetes and neurodegenerative diseases are discussed.

Transcriptional control of energy homeostasis through the PGC1 coactivators.

Abstract: The PGC1 transcriptional coactivators are major regulators of several crucial aspects of energy metabolism. PGC1alpha controls many aspects of oxidative metabolism, including mitochondrial biogenesis and respiration through the coactivation of many nuclear receptors, and factors outside the nuclear receptor family. ERRalpha, NRF1 and NRF2 are key targets of the PGC1s in mitochondrial biogenesis. We have recently addressed the question of the role of PGC1 coactivators in the metabolism of reactive oxygen species (ROS). We now show that PGC1alpha and beta are induced when cells are given an oxidative stressor, H2O2. In fact, experiments with RNAi for the PGC1s show that the ability of ROS to induce a ROS scavenging programme depends entirely on the PGC1s. This includes genes encoding mitochondrial proteins like SOD2, but also includes cytoplasmic proteins like catalase and GPX1. Cells lacking PGC1alpha are hypersensitive to death from oxidative stress caused by H2O2 or paraquat. Mice deficient in PGC1alpha get excessive neurodegeneration when given kainic acid-induced seizures or MPTP, which causes Parkinsonism. These data show that the PGC1s are important protective molecules against ROS generation and damage. The implications of this for diabetes and neurodegenerative diseases will be discussed.

Molecular control of brown fat differentiation and energy expenditure

Abstract: The invention provides methods and compositions for inducing brown fat cell differentiation through modulation of Prdm 16 activity or expression. Also provided are methods for preventing or treating obesity or an obesity related disorder in a subject through stimulation of Prdm 16 expression or activity. Further provided are methods for identifying compounds that are capable of modulating Prdm 16 expression or activity.