Obesity is characterized by adipose tissue expansion as well as macrophage infiltration of adipose tissue. This results in an increase in circulating inflammatory cytokines and nonesterified fatty acids, factors that cause skeletal muscle insulin resistance. Whether obesity also results in skeletal muscle inflammation is not known. In this study, we quantified macrophages immunohistochemically in vastus lateralis biopsies from eight obese and eight lean subjects. Our study demonstrates that macrophages infiltrate skeletal muscle in obesity, and we developed an in vitro system to study this mechanistically. Myoblasts were isolated from vastus lateralis biopsies and differentiated in culture. Coculture of differentiated human myotubes with macrophages in the presence of palmitic acid, to mimic an obese environment, revealed that macrophages in the presence of palmitic acid synergistically augment cytokine and chemokine expression in myotubes, decrease IkappaB-alpha protein expression, increase phosphorylated JNK, decrease phosphorylated Akt, and increase markers of muscle atrophy. These results suggest that macrophages alter the inflammatory state of muscle cells in an obese milieu, inhibiting insulin signaling. Thus in obesity both adipose tissue and skeletal muscle inflammation may contribute to insulin resistance.

OBJECTIVE-We examined the relationship between the expression of thrombospondin (TSP)1, an antiangiogenic factor and regulator of transforming growth factor-␤ activity, obesity, adipose inflammation, and insulin resistance.RESEARCH DESIGN AND METHODS-TSP1 gene expression was quantified in subcutaneous adipose tissue (SAT) of 86 nondiabetic subjects covering a wide range of BMI and insulin sensitivity, from visceral adipose (VAT) and SAT from 14 surgical patients and from 38 subjects with impaired glucose tolerance randomized to receive either pioglitazone or metformin for 10 weeks. An adipocyte culture system was also used to assess the effects of pioglitazone and coculture with macrophages on TSP1 gene expression. RESULTS-TSP1mRNA was significantly associated with obesity (BMI) and insulin resistance (low insulin sensitivity index). Relatively strong positive associations were seen with markers of inflammation, including CD68, macrophage chemoattractant protein-1, and plasminogen activator inhibitor (PAI)-1 mRNA (r Ն 0.46, P ϭ 0.001 for each), that remained significant after controlling for BMI and S i . However, TSP1 mRNA was preferentially expressed in adipocyte fraction, whereas inflammatory markers predominated in stromal vascular fraction. Coculture of adipocytes and macrophages augmented TSP1 gene expression and secretion from both cell types. Pioglitazone (not metformin) treatment resulted in a 54% decrease (P Ͻ 0.04) in adipose TSP gene expression, as did in vitro pioglitazone treatment of adipocytes.CONCLUSIONS-TSP1 is a true adipokine that is highly expressed in obese, insulin-resistant subjects; is highly correlated with adipose inflammation; and is decreased by pioglitazone. TSP1 is an important link between adipocytes and macrophagedriven adipose tissue inflammation and may mediate the elevation of PAI-1 that promotes a prothrombotic state. Diabetes 57: 432-439, 2008

SummaryMyogenic progenitors in adult muscle are necessary for the repair, maintenance and hypertrophy of post-mitotic muscle fibers. With age, fat deposition and fibrosis contribute to the decline in the integrity and functional capacity of muscles. In a previous study we reported increased accumulation of lipid in myogenic progenitors obtained from aged mice, accompanied by an up-regulation of genes involved in adipogenic differentiation. The present study was designed to extend our understanding of how aging affects the fate and gene expression profile of myogenic progenitors. Affymetrix murine U74 Genechip analysis was performed using RNA extracted from myogenic progenitors isolated from adult (8-month-old) and aged (24-month-old) DBA/2JNIA mice. The cells from the aged animals exhibited major alterations in the expression level of many genes directly or indirectly involved with the TGFβ β β β signaling pathway. Our data indicate that with age, myogenic progenitors acquire the paradoxical phenotype of being both TGFβ β β β activated based on overexpression of TGFβ β β β -inducible genes, but resistant to the differentiation-inhibiting effects of exogenous TGFβ β β β . The overexpression of TGFβ β β β -regulated genes, such as connective tissue growth factor, may play a role in increasing fibrosis in aging muscle.

The development of obesity is becoming an international problem and the role of fructose is unclear. Studies using liver tissue and hepatocytes have contributed to the understanding of fructose metabolism. Excess fructose consumption also affects extra hepatic tissues including adipose tissue. The effects of fructose on human adipocytes are not yet fully characterized, although in vivo studies have noted increased adiposity and weight gain in response to fructose sweetened-beverages. In order to understand and predict the metabolic responses of adipocytes to fructose, this study examined differentiating and differentiated human adipocytes in culture, exposed to a range of fructose concentrations equivalent to that reported in blood after consuming fructose. A stable isotope based dynamic profiling method using [U-13C6]-d-fructose tracer was used to examine the metabolism and fate of fructose. A targeted stable isotope tracer fate association method was used to analyze metabolic fluxes and flux surrogates with exposure to escalating fructose concentration. This study demonstrated that fructose stimulates anabolic processes in adipocytes robustly, including glutamate and de novo fatty acid synthesis. Furthermore, fructose also augments the release of free palmitate from fully differentiated adipocytes. These results imply that in the presence of fructose, the metabolic response of adipocytes in culture is altered in a dose dependent manner, particularly favoring increased glutamate and fatty acid synthesis and release, warranting further in vivo studies.Electronic supplementary materialThe online version of this article (doi:10.1007/s11306-014-0716-0) contains supplementary material, which is available to authorized users.

Rhabdomyosarcoma is a primitive neoplasm with a poorly understood etiology that exhibits features of fetal skeletal muscle. It represents the most frequent malignant soft tissue sarcoma affecting the pediatric population and is often treated very aggressively. Embryonal rhabdomyosarcoma (ERMS) and alveolar rhabdomyosarcoma constitute the two major subtypes and exhibit different molecular features. We investigated one potential molecular basis for ERMS by using cells derived from tumors produced in p53 Efforts to unravel the molecular events underlying the origin of different types of cancer have contributed to finding treatments for these diseases. However, largely left behind in this effort are tumors with poorly understood etiologies like rhabdomyosarcoma (RMS). RMS describes a heterogeneous group of poorly differentiated pediatric sarcomas that display features of developing muscle.1 Representing 60% of all pediatric sarcomas and accounting for 5% to 10% of all childhood malignancies, treatment is often very aggressive, involving local irradiation, lengthy rounds of combination chemotherapy, and tumor resection.2 RMS is broadly categorized into two subtypes, embryonal (ERMS) and alveolar (ARMS), that possess distinctive clinical, pathological, and biological properties. 3ARMS portends a poor prognosis and predominantly occurs in the extremities.1 Cytogenetically, most ARMS harbor one or both of two distinct chromosomal translocations: t(2;13)(q35;q14) or t(1;13)(p36;q14), resulting in the formation of the fusion genes PAX3-FOXO1 or PAX7-FOXO1 that contribute to pathogenesis. 4 Conversely, ERMS represents 75% of all cases of RMS, most frequently occurs in the orbit, head and neck, and genitourinary tract, 3 and lacks any of the signature chromosomal rearrangements identified in ARMS.