The current study was done to assess if heterogeneity existed in the degree of adipogenesis in stromal cells (preadipocytes) from multiple donors. In addition to conventional lipid-based methods, we have employed a novel signal amplification technology, known as branched DNA, to monitor expression of an adipocyte specific gene product aP2. The fatty acid binding protein aP2 increases during adipocyte differentiation and is induced by thiazolidinediones and other peroxisome proliferator activated receptor gamma ligands. The current work examined the adipogenic induction of aP2 mRNA levels in human adipose tissue stromal cells derived from 12 patients (mean age +/- SEM, 38.9 +/- 3.1) with mild to moderate obesity (mean body mass index +/- SEM, 27.8 +/- 2.4). Based on branched DNA technology, a rapid and sensitive measure of specific RNAs, the relative aP2 level in adipocytes increased by 679 +/- 93-fold (mean +/- SEM, n=12) compared to preadipocytes. Normalization of the aP2 mRNA levels to the housekeeping gene, glyceraldehyde phosphate dehydrogenase, did not significantly alter the fold induction in a subset of 4 patients (803.6 +/- 197.5 vs 1118.5 +/- 308.1). Independent adipocyte differentiation markers were compared between adipocytes and preadipocytes in parallel studies. Leptin secretion increased by up to three-orders of magnitude while measurements of neutral lipid accumulation by Oil Red O and Nile Red staining increased by 8.5-fold and 8.3-fold, respectively. These results indicate that preadipocytes isolated from multiple donors displayed varying degrees of differentiation in response to an optimal adipogenic stimulus in vitro. This work also demonstrates that branched DNA measurement of aP2 is a rapid and sensitive measure of adipogenesis in human stromal cells. The linear range of this assay extends up to three-orders of magnitude and correlates directly with independent measures of cellular differentiation.

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We have previously shown that both a commercially available mixture of conjugated linoleic acid (CLA) isomers and the trans-10, cis-12 isomer of CLA reduced the triglyceride (TG) content and induced apoptosis in differentiating cultures of murine 3T3-L1 preadipocytes. However, the influence of CLA isomers on differentiating human (pre)adipocytes is unknown. Therefore, we conducted a series of studies using primary cultures of stromal vascular cells isolated from human adipose tissue to determine: 1) the influence of seeding density and thiazolidinedione (TZD) concentration on TG content; 2) the chronic dose response of cis-9, trans-11 CLA vs. trans-10, cis-12 CLA on TG content; 3) whether chronic linoleic acid supplementation could rescue the TG content of CLA-treated cultures; and 4) whether trans-10, cis-12-mediated reduction in cellular TG was due to decreased lipogenesis and/or increased lipolysis. In expt. 1, the TG content [micromol/(L x 10(6) cells)] increased as both seeding density and TZD concentration increased. For example, cultures seeded at 4 x 10(4) cells/cm(2) and supplemented with 10 micromol/L BRL 49653 had 10-fold more TG than similarly seeded cultures without BRL 49653. In expt. 2, TG content decreased as the level of trans-10, cis-12 CLA increased from 1 to 10 micromol/L, whereas the TG content increased with increasing concentrations of either linoleic acid or cis-9, trans-11 CLA. In expt. 3, linoleic acid supplementation restored the TG content of cultures treated with trans-10, cis-12 CLA compared with cultures treated with CLA alone, suggesting that attenuation of TG content by CLA is reversible. In expt. 4, glucose incorporation into total lipid decreased with increasing levels of trans-10, cis-12 CLA, whereas neither CLA isomer acutely affected lipolysis. These data suggest that the reported antiobesity actions of a supplement containing a crude mixture of CLA isomers given to humans may be due to inhibition of lipogenesis by the trans-10, cis-12 isomer.

OBJECTIVEAdipocyte infiltration of the musculoskeletal system is well recognized as a hallmark of aging, obesity, and type 2 diabetes. Intermuscular adipocytes might serve as a benign storage site for surplus lipid or play a role in disrupting energy homeostasis as a result of dysregulated lipolysis or secretion of proinflammatory cytokines. This investigation sought to understand the net impact of local adipocytes on skeletal myocyte metabolism.RESEARCH DESIGN AND METHODSInteractions between these two tissues were modeled using a coculture system composed of primary human adipocytes and human skeletal myotubes derived from lean or obese donors. Metabolic analysis of myocytes was performed after coculture with lipolytically silent or activated adipocytes and included transcript and metabolite profiling along with assessment of substrate selection and insulin action.RESULTSCocultured adipocytes increased myotube mRNA expression of genes involved in oxidative metabolism, regardless of the donor and degree of lipolytic activity. Adipocytes in the basal state sequestered free fatty acids, thereby forcing neighboring myotubes to rely more heavily on glucose fuel. Under this condition, insulin action was enhanced in myotubes from lean but not obese donors. In contrast, when exposed to lipolytically active adipocytes, cocultured myotubes shifted substrate use in favor of fatty acids, which was accompanied by intracellular accumulation of triacylglycerol and even-chain acylcarnitines, decreased glucose oxidation, and modest attenuation of insulin signaling.CONCLUSIONSThe effects of cocultured adipocytes on myocyte substrate selection and insulin action depended on the metabolic state of the system. These findings are relevant to understanding the metabolic consequences of intermuscular adipogenesis.

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OBJECTIVE: The purpose of this study was to determine if the antiobesity actions of dehydroepiandrosterone (DHEA) observed in vivo are due to an in¯uence on the proliferation and differentiation of primary cultures of stromal-vascular (SV) cells isolated from human adipose tissue. DESIGN: SV cells were isolated from subcutaneous adipose tissue obtained from a young adult female undergoing elective liposuction. For the proliferation assay (Experiment 1), cultures were fed proliferation media containing 0, 5, 25 or 100 mM DHEA for 3 d. At the end of this treatment period, cultures were either prepared for counting or for determining their metabolic activity using the Alamar Blue staining procedure. For the differentiation assays (Experiment 2), cultures were fed differentiation media containing 0, 25 or 50 mM DHEA for 20 d. At the end of this treatment period, cultures were either prepared for lipid staining using Oil Red O or for marker enzyme analysis (glycerol-3-phosphate dehydrogenase activity; GPDH). To determine if the stimulatory effects of DHEA on SV cell differentiation were dependent on the presence of thiazolidinediones (Experiment 3), cultures of differentiating SV cells were incubated in the presence and absence of BRL 49653 and either 0, 25 or 50 mM DHEA. RESULTS: In Experiment 1, cultures treated with 25 and 100 mM DHEA had fewer cells than cultures treated with either 0 or 5 mM DHEA. Alamar Blue staining decreased as the level of DHEA in the cultures increased. In Experiment 2, cultures treated with DHEA had more lipid and GPDH activity than control cultures. In Experiment 3, cultures treated with BRL 49653 had more triglyceride than cultures treated without BRL 49653. Likewise, cultures treated with DHEA had more triglyceride than their non-DHEA controls. Regardless of the BRL status, cultures supplemented with DHEA had more triglyceride than control cultures. CONCLUSION: These data suggest that in cultures of SV cells from human adipose tissue, DHEA supplementation attenuates proliferation and enhances differentiation. These data support the hypothesis that DHEA directly attenuates preadipocyte proliferation in humans as we previously demonstrated in primary cultures of pig and rat SV cells and in cultures of 3T3-L1 preadipocytes. In contrast, DHEA stimulated the differentiation of human preadipocytes, which is contrary to its actions in differentiating cultures of preadipocytes from animals.