In contrast to the earlier contention, adult humans have been shown recently to possess active brown adipose tissue with a potential of being of metabolic significance. Up to now, brown fat precursor cells have not been available for human studies. We have shown previously that human multipotent adipose-derived stem (hMADS) cells exhibit a normal karyotype and high self-renewal ability; they are known to differentiate into cells that exhibit the key properties of human white adipocytes, that is, uncoupling protein two expression, insulin-stimulated glucose uptake, lipolysis in response to b-agonists and atrial natriuretic peptide, and release of adiponectin and leptin. Herein, we show that, upon chronic exposure to a specific PPARc but not to a PPARb/d or a PPARa agonist, hMADS cell-derived white adipocytes are able to switch to a brown phenotype by expressing both uncoupling protein one (UCP1) and CIDEA mRNA. This switch is accompanied by an increase in oxygen consumption and uncoupling. The expression of UCP1 protein is associated to stimulation of respiration by b-AR agonists, including b3-AR agonist. Thus, hMADS cells represent an invaluable cell model to screen for drugs stimulating the formation and/or the uncoupling capacity of human brown adipocytes that could help to dissipate excess caloric intake of individuals.

OBJECTIVE -The purpose of this study was to clarify the effects of maternal obesity on insulin sensitivity and secretion in offspring.RESEARCH DESIGN AND METHODS -Fifty-one offspring of both sexes of obese (Ob group) and 15 offspring of normal-weight (control group) mothers were studied. Plasma glucose, insulin, and C-peptide were measured during an oral glucose tolerance test (OGTT). Insulin sensitivity was calculated using the oral glucose insulin sensitivity index, and insulin secretion and ␤-cell glucose sensitivity were computed by a mathematical model. Fasting leptin and adiponectin were also measured. Body composition was assessed by dual-X-ray absorptiometry. , P Ͻ 0.01) but did not differ significantly in women. ␤-Cell glucose sensitivity was not statistically different between groups. A multivariate analysis of variance showed that maternal obesity and offspring sex concurred together with BMI and ␤-cell glucose sensitivity to determine the differences in insulin sensitivity and secretion observed in offspring. RESULTSCONCLUSIONS -Obese mothers can give birth to normal birth weight babies who later develop obesity and insulin resistance. The maternal genetic/epigenetic transmission shows a clear sexual dimorphism, with male offspring having a higher value of insulin sensitivity (although not statistically significant) associated with significantly higher insulin secretion than female offspring.

OBJECTIVEType 2 diabetes is associated with insulin resistance and skeletal muscle mitochondrial dysfunction. We have found that subjects with early-onset type 2 diabetes show incapacity to increase Vo2max in response to chronic exercise. This suggests a defect in muscle mitochondrial response to exercise. Here, we have explored the nature of the mechanisms involved.RESEARCH DESIGN AND METHODSMuscle biopsies were collected from young type 2 diabetic subjects and obese control subjects before and after acute or chronic exercise protocols, and the expression of genes and/or proteins relevant to mitochondrial function was measured. In particular, the regulatory pathway peroxisome proliferator–activated receptor γ coactivator (PGC)-1α/mitofusin-2 (Mfn2) was analyzed.RESULTSAt baseline, subjects with diabetes showed reduced expression (by 26%) of the mitochondrial fusion protein Mfn2 and a 39% reduction of the α-subunit of ATP synthase. Porin expression was unchanged, consistent with normal mitochondrial mass. Chronic exercise led to a 2.8-fold increase in Mfn2, as well as increases in porin, and the α-subunit of ATP synthase in muscle from control subjects. However, Mfn2 was unchanged after chronic exercise in individuals with diabetes, whereas porin and α-subunit of ATP synthase were increased. Acute exercise caused a fourfold increase in PGC-1α expression in muscle from control subjects but not in subjects with diabetes.CONCLUSIONSOur results demonstrate alterations in the regulatory pathway that controls PGC-1α expression and induction of Mfn2 in muscle from patients with early-onset type 2 diabetes. Patients with early-onset type 2 diabetes display abnormalities in the exercise-dependent pathway that regulates the expression of PGC-1α and Mfn2.

BackgroundIt is well established that adipose tissue plays a key role in energy storage and release but is also a secretory organ and a source of stem cells. Among different lineages, stem cells are able to differentiate into adipocytes and osteoblasts. As secreted proteins could regulate the balance between both lineages, we aimed at characterizing the secretome of human multipotent adipose-derived stem cell (hMADS) at an early step of commitment to adipocytes and osteoblasts.ResultsA proteomic approach, using mono-dimensional electrophoresis and tandem mass spectrometry, allowed us to identify a total of 73 proteins at day 0 and day 3 of adipocyte and osteoblast differentiation. Analysis of identified proteins showed that 52 % corresponded to classical secreted proteins characterized by a signal peptide, that 37 % previously described in the extracellular compartment were devoid of signal peptide and that 11 % neither exhibited a signal peptide nor had been previously described extracellularly. These proteins were classified into 8 clusters according to their function. Quantitative analysis has been performed for 8 candidates: PAI-1, PEDF, BIGH3, PTX3, SPARC, ENO1, GRP78 and MMP2. Among them, PAI-1 was detected at day 0 and day 3 of osteoblast differentiation but never in adipocyte secretome. Furthermore we showed that PAI-1 mRNA was down-regulated in the bone of ovariectomized mice.ConclusionGiven its regulation during the early events of hMADS cell differentiation and its status in ovariectomized mice, PAI-1 could play a role in the adipocyte/osteoblast balance and thus in bone diseases such as osteoporosis.

Exposure of preadipocytes to long-chain fatty acids induces the expression of several markers of adipocyte differentiation. In an attempt to identify novel genes and proteins that are regulated by fatty acids in preadipocytes, we performed a substractive hybridization screening and identified PTX3, a protein of the pentraxin family. PTX3 mRNA expression is transient during adipocyte differentiation of clonal cell lines and is absent in fully differentiated cells. Stable overexpression of PTX3 in preadipocytes has no effect on adipocyte differentiation. In line with this, PTX3 mRNA is expressed in the stromal-vascular fraction of adipose tissue, but not in the adipocyte fraction; however, in 3T3-F442A adipocytes, the PTX3 gene can be reinduced by tumor necrosis factor ␣ (TNF ␣ ) in a dose-dependent manner. This effect is accompanied by PTX3 protein secretion from both 3T3-F442A adipocytes and explants of mouse adipose tissue. PTX3 mRNA levels are found to be higher in adipose tissue of genetically obese mice versus control mice, consistent with their increased TNF ␣ levels. In conclusion, PTX3 appears as a TNF ␣ -induced protein that provides a new link between chronic low-level inflammatory state and obesity. -Abderrahim-Ferkoune, A., O.

BackgroundA reciprocal relationship between bone and fat development in osteoporosis is clinically well established. Some of the key molecular regulators involved in this tissue replacement process have been identified. The detailed mechanisms governing the differentiation of mesenchymal stem cells (MSC) – the key cells involved – are however only now beginning to emerge. In an attempt to address the regulation of the adipocyte/osteoblast balance at the level of gene transcription in a comprehensive and unbiased manner, we performed a large-scale gene expression profiling study using a unique cellular model, human multipotent adipose tissue-derived stem cells (hMADS).ResultsThe analysis of 1606 genes that were found to be differentially expressed between adipogenesis and osteoblastogenesis revealed gene repression to be most prevalent prior to commitment in both lineages. Computational analyses suggested that this gene repression is mediated by miRNAs. The transcriptional activation of lineage-specific molecular processes in both cases occurred predominantly after commitment. Analyses of the gene expression data and promoter sequences produced a set of 65 genes that are candidates for genes involved in the process of adipocyte/osteoblast commitment. Four of these genes were studied in more detail: LXRα and phospholipid transfer protein (PLTP) for adipogenesis, the nuclear receptor COUP-TF1 and one uncharacterized gene, TMEM135 for osteoblastogenesis. PLTP was secreted during both early and late time points of hMADS adipocyte differentiation. LXRα, COUP-TF1, and the transmembrane protein TMEM135 were studied in primary cultures of differentiating bone marrow stromal cells from healthy donors and were found to be transcriptionally activated in the corresponding lineages.ConclusionOur results reveal gene repression as a predominant early mechanism before final cell commitment. We were moreover able to identify 65 genes as candidates for genes controlling the adipocyte/osteoblast balance and to further evaluate four of these. Additional studies will explore the precise role of these candidate genes in regulating the adipogenesis/osteoblastogenesis switch.

Haptoglobin (Hp) is a glycoprotein involved in the acute phase response to inflammation. Our previous findings indicate that Hp mRNA and protein are present in the adipose tissue of rodents and that Hp gene expression is up-regulated in obese models. The aim of the present study was to establish whether Hp could be considered a marker of obesity in humans. In 312 subjects, serum Hp was correlated directly with body mass index (BMI), leptin, C-reactive protein (CRP), and age. In a multivariate stepwise regression analysis, BMI and CRP were independent determinants of serum Hp in females, with BMI having the strongest effect. CRP and age were independent determinants of serum Hp in males, although explaining only a modest percentage of the total variability. Serum Hp was positively associated with body fat, as assessed by dual-energy x-ray absorptiometry, both in female and in male groups. The level of significance improved when serum Hp was analyzed against fat mass adjusted for lean mass. Finally, Northern and Western blot analyses performed in biopsies of sc abdominal fat from 20 obese individuals showed the presence of Hp mRNA and protein in the human adipose tissue. In conclusion, serum Hp constitutes a novel marker of adiposity in humans, and the adipose tissue likely contributes to determine its levels.

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