Showing papers by "Bruce M. Spiegelman published in 2009"
TL;DR: It is shown that PRDM16 forms a transcriptional complex with the active form of C/EBP-β (also known as LAP), acting as a critical molecular unit that controls the cell fate switch from myoblastic precursors to brown fat cells.
Abstract: Brown adipose cells are specialized to dissipate chemical energy in the form of heat, as a physiological defence against cold and obesity. PRDM16 (PR domain containing 16) is a 140 kDa zinc finger protein that robustly induces brown fat determination and differentiation. Recent data suggests that brown fat cells arise in vivo from a Myf5-positive, myoblastic lineage by the action of PRDM16 (ref. 3); however, the molecular mechanisms responsible for this developmental switch is unclear. Here we show that PRDM16 forms a transcriptional complex with the active form of C/EBP-beta (also known as LAP), acting as a critical molecular unit that controls the cell fate switch from myoblastic precursors to brown fat cells. Forced expression of PRDM16 and C/EBP-beta is sufficient to induce a fully functional brown fat program in naive fibroblastic cells, including skin fibroblasts from mouse and man. Transplantation of fibroblasts expressing these two factors into mice gives rise to an ectopic fat pad with the morphological and biochemical characteristics of brown fat. Like endogenous brown fat, this synthetic brown fat tissue acts as a sink for glucose uptake, as determined by positron emission tomography with fluorodeoxyglucose. These data indicate that the PRDM16-C/EBP-beta complex initiates brown fat formation from myoblastic precursors, and may provide opportunities for the development of new therapeutics for obesity and type-2 diabetes.
651 citations
TL;DR: The preservation of muscle integrity and function in MCK-PGC-1α animals resulted in significantly improved whole-body health; both the loss of bone mineral density and the increase of systemic chronic inflammation, observed during normal aging, were prevented.
Abstract: Aging is a major risk factor for metabolic disease and loss of skeletal muscle mass and strength, a condition known as sarcopenia. Both conditions present a major health burden to the elderly population. Here, we analyzed the effect of mildly increased PGC-1α expression in skeletal muscle during aging. We found that transgenic MCK-PGC-1α animals had preserved mitochondrial function, neuromuscular junctions, and muscle integrity during aging. Increased PGC-1α levels in skeletal muscle prevented muscle wasting by reducing apoptosis, autophagy, and proteasome degradation. The preservation of muscle integrity and function in MCK-PGC-1α animals resulted in significantly improved whole-body health; both the loss of bone mineral density and the increase of systemic chronic inflammation, observed during normal aging, were prevented. Importantly, MCK-PGC-1α animals also showed improved metabolic responses as evident by increased insulin sensitivity and insulin signaling in aged mice. Our results highlight the importance of intact muscle function and metabolism for whole-body homeostasis and indicate that modulation of PGC-1α levels in skeletal muscle presents an avenue for the prevention and treatment of a group of age-related disorders.
603 citations
TL;DR: The last several years have seen an explosion of information relating to the transcriptional control of brown fat cell development, and new data have emerged that clearly demonstrate that adult humans do indeed have substantial amounts of functioning brown adipose tissue.
Abstract: The last several years have seen an explosion of information relating to the transcriptional control of brown fat cell development. At the same time, new data have emerged that clearly demonstrate that adult humans do indeed have substantial amounts of functioning brown adipose tissue (BAT). Together, these advances are stimulating a reassessment of the role of brown adipose tissue in human physiology and pathophysiology. These data have also opened up exciting new opportunities for the development of entirely novel classes of therapeutics for metabolic diseases like obesity and type 2 diabetes.
290 citations
TL;DR: Hepatic gain of function and complete genetic ablation of PGC-1α show that this coactivator is important for activating the programs of gluconeogenesis, fatty acid oxidation, oxidative phosphorylation, and lipid secretion during times of nutrient deprivation.
Abstract: OBJECTIVE The peroxisome proliferator–activated receptor-γ coactivator (PGC)-1 family of transcriptional coactivators controls hepatic function by modulating the expression of key metabolic enzymes. Hepatic gain of function and complete genetic ablation of PGC-1α show that this coactivator is important for activating the programs of gluconeogenesis, fatty acid oxidation, oxidative phosphorylation, and lipid secretion during times of nutrient deprivation. However, how moderate changes in PGC-1α activity affect metabolism and energy homeostasis has yet to be determined. RESEARCH DESIGN AND METHODS To identify key metabolic pathways that may be physiologically relevant in the context of reduced hepatic PGC-1α levels, we used the Cre/Lox system to create mice heterozygous for PGC-1α specifically within the liver (LH mice). RESULTS These mice showed fasting hepatic steatosis and diminished ketogenesis associated with decreased expression of genes involved in mitochondrial β-oxidation. LH mice also exhibited high circulating levels of triglyceride that correlated with increased expression of genes involved in triglyceride-rich lipoprotein assembly. Concomitant with defects in lipid metabolism, hepatic insulin resistance was observed both in LH mice fed a high-fat diet as well as in primary hepatocytes. CONCLUSIONS These data highlight both the dose-dependent and long-term effects of reducing hepatic PGC-1α levels, underlining the importance of tightly regulated PGC-1α expression in the maintenance of lipid homeostasis and glucose metabolism.
132 citations
TL;DR: It is demonstrated that pharmacological activation of PPARδ induces FAO via PGC-1α, however, PPAR δ agonism does not induce mitochondrial gene expression and function.
128 citations
TL;DR: It is shown that obese mice with genetically reduced levels of a key hepatic transcriptional coactivator, PGC-1α, have improved whole-body insulin sensitivity with increased levels of hepatic and circulating FGF21.
Abstract: FGF21 is a hormone produced in liver and fat that dramatically improves peripheral insulin sensitivity and lipid metabolism. We show here that obese mice with genetically reduced levels of a key hepatic transcriptional coactivator, PGC-1α, have improved whole-body insulin sensitivity with increased levels of hepatic and circulating FGF21. Gain- and loss-of-function studies in primary mouse hepatocytes show that hepatic FGF21 levels are regulated by the expression of PGC-1α. Importantly, PGC-1α-mediated reduction of FGF21 expression is dependent on Rev-Erbα and the expression of ALAS-1. ALAS-1 is a PGC-1α target gene and the rate-limiting enzyme in the synthesis of heme, a ligand for Rev-Erbα. Modulation of intracellular heme levels mimics the effect of PGC-1α on FGF21 expression, and inhibition of heme biosynthesis completely abrogates the down-regulation of FGF21 in response to PGC-1α. Thus, PGC-1α can impact hepatic and systemic metabolism by regulating the levels of a nuclear receptor ligand.
114 citations