Table of Contents

Volume 1, Issue 1

  January/February/March 2012

  Pages 1 - 72

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LETTER FROM THE EDITOR

Open Access Article

Welcome to Adipocyte

Fahumiya Samad
Page 1
http://dx.doi.org/10.4161/adip.19455
Full Text | PDF




EDITOR'S PREVIEW

Open Access Article

In this issue of Adipocyte

Elaine Ellerton
Pages 2 - 3
http://dx.doi.org/10.4161/adip.19475
PDF




REVIEWS

Open Access Article

Adipose tissue signaling by nuclear receptors in metabolic complications of obesity

David Jacobi, Kristopher Stanya and Chih-Hao Lee
Pages 4 - 12
http://dx.doi.org/10.4161/adip.19036
Abstract | Full Text | PDF

In recent years white adipose tissue inflammation has been recognized to be associated with obesity. Adipocytes and adipose tissue associated macrophages (ATMs) secrete bioactive molecules, including adipokines, chemokines/cytokines and free fatty acids that modulate the development of low-grade inflammation and insulin resistance responsible for obesity-related metabolic and cardiovascular diseases. Nuclear receptors, notably peroxisome-proliferator-activated receptors, are sensors of dietary lipids and control transcriptional programs of key metabolic and inflammatory pathways in adipocytes and macrophages. This review focuses on mechanisms by which nuclear receptors maintain white adipose tissue homeostasis. The identification of ATMs as active players in the initiation of chronic inflammation and the links between inflammatory signaling and metabolic dysfunction will be presented, followed by discussion of recent evidence for nuclear receptors in ATM function, with an emphasis on the paracrine interaction between adipocytes and ATMs.

Open Access Article

Brown adipose tissue: Recent insights into development, metabolic function and therapeutic potential

Kristy Townsend and Yu-Hua Tseng
Pages 13 - 24
http://dx.doi.org/10.4161/adip.18951
Abstract | Full Text | PDF

Obesity is currently a global pandemic, and is associated with increased mortality and co-morbidities including many metabolic diseases. Obesity is characterized by an increase in adipose mass due to increased energy intake, decreased energy expenditure, or both. While white adipose tissue is specialized for energy storage, brown adipose tissue has a high concentration of mitochondria and uniquely expresses uncoupling protein 1, enabling it to be specialized for energy expenditure and thermogenesis. Although brown fat was once considered only necessary in babies, recent morphological and imaging studies have provided evidence that, contrary to prior belief, this tissue is present and active in adult humans. In recent years, the topic of brown adipose tissue has been reinvigorated with many new studies regarding brown adipose tissue differentiation, function and therapeutic promise. This review summarizes the recent advances, discusses the emerging questions and offers perspective on the potential therapeutic applications targeting this tissue.

Open Access Article

Proteomics in the characterization of adipose dysfunction in obesity

David Brockman and Xiaoli Chen
Pages 25 - 37
http://dx.doi.org/10.4161/adip.19129
Abstract | Full Text | PDF

Adipose tissue plays a central role in body weight homeostasis, inflammation, and insulin resistance via serving as a fat-buffering system, regulating lipid storage and mobilization and releasing a large range of adipokines and cytokines. Adipose tissue is also the major inflammation-initiated site in obesity. Adipose-derived adipokines and cytokines are known to be involved in the modulation of a wide range of important physiological processes, particularly immune response, glucose and lipid homeostasis and insulin resistance. Adipose tissue dysfunction, characterized by an imbalanced secretion of pro- and anti-inflammatory adipokines and cytokines, decreased insulin-stimulated glucose uptake, dysregulation of lipid storage and release and mitochondrial dysfunction, has been linked to obesity and its associated metabolic disorders. Proteomic technology has been a powerful tool for identifying key components of the adipose proteome, which may contribute to the pathogenesis of adipose tissue dysfunction in obesity. In this review, we summarized the recent advances in the proteomic characterization of adipose tissue and discussed the identified proteins that potentially play important roles in insulin resistance and lipid homeostasis.

Open Access Article

WAT is a functional adipocyte?

Christopher Church, Mark Horowitz and Matthew Rodeheffer
Pages 38 - 45
http://dx.doi.org/10.4161/adip.19132
Abstract | Full Text | PDF

In vertebrates, adipose tissue is the main storage site for lipids within specialized lipid-laden mature adipocytes. While many species have evolved cells capable of lipid storage, the adipocyte represents a unique specialized cell involved in fuel storage, endocrine, nervous and immune function. However, the adipocytes are not the only cell type in mammals that can accumulate lipid droplets. The ectopic accumulation of lipid in non-adipose tissues including the liver, skeletal muscle, bone, pancreas, and heart in combination with its excessive accumulation in adipose tissue contributes to metabolic disease. Determining the lipid processing components that are necessary and sufficiently for lipid accumulation in adipose and non-adipose tissues, in addition to endocrine function, will lead to a clearer definition of an adipocyte.




RESEARCH PAPER

Open Access Article

Effect of soluble Jagged1-mediated inhibition of Notch signaling on proliferation and differentiation of an adipocyte progenitor cell model

Sumithra Urs, Bryce Turner, Yuefeng Tang, Bahman Rostama, Deena Small and Lucy Liaw
Pages 46 - 57
http://dx.doi.org/10.4161/adip.19186
Abstract | Full Text | PDF

Adipose tissue development is dependent on multiple signaling mechanisms and cell-cell interactions that regulate adipogenesis, angiogenesis and extracellular remodeling. The Notch signaling pathway is an important cell-fate determinant whose role in adipogenesis is not clearly defined. To address this issue, we examined the effect of inhibition of Notch signaling by soluble-Jagged1 in the 3T3-L1 preadipocyte line. In vitro, soluble-Jagged1 expression in 3T3-L1 cells altered cell morphology, increased the rate of cell proliferation and induced an early transcriptional response to differentiation stimuli. However, these cells did not form mature adipocytes due to their inability to exit the cell-cycle in response to serum-starvation and glucocorticoid-induced cell-cycle arrest. In contrast, subcutaneous allografts of soluble-Jagged1 cells formed larger fat pads containing lipid-filled adipocytes with improved neovascularization compared with controls. Since adipogenesis is tightly associated with angiogenesis, we evaluated the influence of soluble-Jagged1 on endothelial cells by culturing them in cell-free conditioned media from preadipocytes. Soluble Jagged1-mediated inhibition of Notch signaling increased levels of secreted cytokines, potentially contributing to the improved cell growth and proliferation observed in these cultures. Our findings demonstrate an initial requirement of Notch signaling inactivation for preadipocyte cell commitment and support the hypothesis that cell-to-cell crosstalk between the preadipocytes and endothelial cells is required for neovascularization and remodeling of the tissue to promote hyperplasia and hypertrophy of differentiating adipocytes.




BRIEF REPORT

Open Access Article

Orexin receptor-1 mediates brown fat developmental differentiation

Dyan Sellayah and Devanjan Sikder
Pages 58 - 63
http://dx.doi.org/10.4161/adip.18965
Abstract | Full Text | PDF

Orexin A (OX) is a small excitatory neuropeptide hormone that stimulates feeding, wakefulness and energy expenditure via a pair of G-coupled protein receptors, namely orexin receptor-1 (OXR1) and orexin receptor-2 (OXR2). OX-deficient mice are sensitive to obesity despite being hypophagic. The obesogenic effect of OX-deletion is due to brown adipose tissue (BAT) dysfunction, a defect that originates during fetal growth. Brown preadipocytes in OX-null mice display undifferentiated histological appearance and fail to support both diet- and cold-induced thermogenesis. We show that the OXR1-null mice phenocopies the differentiation defect observed in the ligand-null mice indicating that OXR1 relays OX’s differentiation and thermogenic function. Consistent with this, OX fails to induce differentiation in cultured OXR1-null preadipocytes. Thus, OX signaling via OXR1 constitutes an important thermoregulatory mechanism that defends against cold and obesity.




COMMENTARIES

Open Access Article

Is the adipose tissue a key target of developmental programming of adult adiposity by maternal undernutrition?

Marie-Amélie Lukaszewski, Fabien Delahaye, Didier Vieau and Christophe Breton
Pages 64 - 67
http://dx.doi.org/10.4161/adip.18952
Abstract | Full Text | PDF

Epidemiological studies have shown that maternal undernutrition during pregnancy (MU) leads to intrauterine growth retardation and low birth weight, and may predispose individuals to the development of metabolic syndrome symptoms later in life such as overweight. Some clues from a model of prenatal maternal 70% food-restricted diet throughout gestation in pregnant female rats (FR30) suggest that the white adipose tissue (WAT) is a key target of MU fetal programming. Under standard diet, although showing a lean phenotype, adult FR30 male rats were predisposed to adiposity exhibiting higher serum leptin and corticosterone concentration, two hormones actively involved in WAT regulation. Although FR30 procedure does not worsen the metabolic syndrome features induced by HF diet, FR30HF rats gained more weight and showed hyperleptinemia suggesting increased adiposity. WAT FR30 adult rats revealed marked changes in transcript levels of several genes. In particular, leptin and Ob-Rb, many peptide precursors and receptors, factors involved in lipogenesis and glucocorticoid sensitivity mRNA expression levels as well as mechanisms involved in leptin sensitivity, were modified in FR30 offspring in depot-specific and diet-specific manners. These modifications might predispose for altered fat accumulation in adult male rat offspring.

Open Access Article

Imaging the neuroendocrinology of appetite

Victoria Salem, Akila De Silva, Paul M. Matthews and Waljit S. Dhillo
Pages 68 - 72
http://dx.doi.org/10.4161/adip.19021
Abstract | Full Text | PDF

Functional magnetic resonance imaging has become a powerful tool to investigate the neuroendocrinology of appetite. In a recent study, we demonstrated that the brain activation pattern seen following the infusion of the anorectic gut hormones PYY_3–36 and GLP-1_{7–36 amide} to fasted individuals resembles the brain activation pattern seen in the physiological satiated state. This commentary discusses the significance of these findings and compares them with other landmark studies in the field, with specific reference to the brain areas involved in appetite regulation. We highlight the importance of this type of research in order to pave the way for the development of efficacious and safe anti-obesity therapies.