The principal soy phytoestrogen genistein has an array of biological actions. It binds to estrogen receptor (ER) ␣ and ␤ and has ER-mediated estrogenic effects. In addition, it has antiestrogenic effects as well as non-ERmediated effects such as inhibition of tyrosine kinase. Because of its complex biological actions, the molecular mechanisms of action of genistein are poorly understood. Here we show that genistein dose-dependently increases estrogenic transcriptional activity in mesenchymal progenitor cells, but its biological effects on osteogenesis and adipogenesis are different. At low concentrations (<1 M), genistein acts as estrogen, stimulating osteogenesis and inhibiting adipogenesis. At high concentrations (>1 M), however, genistein acts as a ligand of PPAR␥, leading to up-regulation of adipogenesis and down-regulation of osteogenesis.Transfection experiments show that activation of PPAR␥ by genistein at the micromolar concentrations down-regulates its estrogenic transcriptional activity, while activation of ER␣ or ER␤ by genistein downregulates PPAR␥ transcriptional activity. Genistein concurrently activates two different transcriptional factors, ERs and PPAR␥, which have opposite effects on osteogenesis or adipogenesis. As a result, the balance between activated ERs and PPAR␥ determines the biological effects of genistein on osteogenesis and adipogenesis. Our findings may explain distinct effects of genistein in different tissues.

Aims/hypothesis Changes in cardiac substrate utilisation leading to altered energy metabolism may underlie the development of diabetic cardiomyopathy. We studied cardiomyocyte substrate uptake and utilisation and the role of the fatty acid translocase CD36 in relation to in vivo cardiac function in rats fed a high-fat diet (HFD). Methods Rats were exposed to an HFD or a low-fat diet (LFD). In vivo cardiac function was monitored by echocardiography. Substrate uptake and utilisation were determined in isolated cardiomyocytes.Results Feeding an HFD for 8 weeks induced left ventricular dilation in the systolic phase and decreased fractional shortening and the ejection fraction. Insulin-stimulated glucose uptake and proline-rich Akt substrate 40 phosphorylation were 41% (p<0.001) and 45% (p<0.05) lower, respectively, in cardiomyocytes from rats on the HFD. However, long-chain fatty acid (LCFA) uptake was 1.4-fold increased (p<0.001) and LCFA esterification into triacylglycerols and phospholipids was increased 1.4-and 1.5-fold, respectively (both p<0.05), in cardiomyocytes from HFD compared with LFD hearts. In the presence of the CD36 inhibitor sulfo-N-succinimidyloleate, LCFA uptake and esterification were similar in LFD and HFD cardiomyocytes. In HFD hearts CD36 was relocated to the sarcolemma, and basal phosphorylation of a mediator of CD36-trafficking, i.e. protein kinase B (PKB/Akt), was increased. Diabetologia (2007) 50:1938-1948 DOI 10.1007 Electronic supplementary material The online version of this article (doi:10.1007/s00125-007-0735-8) contains supplementary material, which is available to authorised users. Conclusions/interpretation Feeding rats an HFD induced cardiac contractile dysfunction, which was accompanied by the relocation of CD36 to the sarcolemma, and elevated basal levels of phosphorylated PKB/Akt. The permanent presence of CD36 at the sarcolemma resulted in enhanced rates of LCFA uptake and myocardial triacylglycerol accumulation, and may contribute to the development of insulin resistance and diabetic cardiomyopathy.

Osteoblasts and adipocytes arise from a common progenitor cell in bone marrow. Whether estrogen directly regulates the progenitor cells differentiating into osteoblasts or adipocytes remains unknown. Using a mouse clonal cell line KS483 cultured in charcoal-stripped fetal bovine serum (FBS), we showed that 17␤-estradiol (E 2 ) stimulates the differentiation of progenitor cells into osteoblasts and concurrently inhibits adipocyte formation in an estrogen receptor (ER)-dependent way. E 2 increased alkaline phosphate (ALP) activity and nodule formation and stimulated messenger RNA (mRNA) expression of core-binding factor ␣-1 (Cbfa1), parathyroid hormone/parathyroid hormone-related protein receptors (PTH/PTHrP-Rs), and osteocalcin. In contrast, E 2 decreased adipocyte numbers and down-regulated mRNA expression of peroxisome proliferatoractivated receptor-␥ (PPAR␥)2, adipocyte protein 2 (aP2), and lipoprotein lipase (LPL). Furthermore, the reciprocal control of osteoblast and adipocyte differentiation by E 2 was observed also in the presence of the adipogenic mixture of isobutylmethylxanthine, dexamethasone, and insulin. Immunohistochemical staining showed that ER␣ and ER␤ were present in osteoblasts and adipocytes. A new mouse splice variant ER␤2 was identified, which differed in two amino acid residues from the rat isoform.

Fasting readily induces hepatic steatosis. Hepatic steatosis is associated with hepatic insulin resistance. The purpose of the present study was to document the effects of 16 h of fasting in wild-type mice on insulin sensitivity in liver and skeletal muscle in relation to 1 ) tissue accumulation of triglycerides (TGs) and 2 ) changes in mRNA expression of metabolically relevant genes. Sixteen hours of fasting did not show an effect on hepatic insulin sensitivity in terms of glucose production in the presence of increased hepatic TG content. In muscle, however, fasting resulted in increased insulin sensitivity, with increased muscle glucose uptake without changes in muscle TG content. In liver, fasting resulted in increased mRNA expression of genes promoting gluconeogenesis and TG synthesis but in decreased mRNA expression of genes involved in glycogenolysis and fatty acid synthesis. In muscle, increased mRNA expression of genes promoting glucose uptake, as well as lipogenesis and ␤ -oxidation, was found. In conclusion, 16 h of fasting does not induce hepatic insulin resistance, although it causes liver steatosis, whereas muscle insulin sensitivity increases without changes in muscle TG content. Therefore, fasting induces differential changes in tissue-specific insulin sensitivity, and liver and muscle TG contents are unlikely to be involved in these changes. -Heijboer, A. C., E. Donga, P. J. Fasting increases hepatic triglycerides (TGs) in rodents (1). This fasting-induced hepatic steatosis results from repartitioning of FFAs, released from adipose tissue, to the liver. In the liver, FFAs can either be used for ␤ -oxidation in mitochondria or reesterified into TG. TG can be stored or secreted as VLDL. In turn, TG-rich VLDL particles are lipolyzed by LPL and deliver FFAs to other tissues, such as skeletal muscle (2), where FFAs are used for ␤ -oxidation. If muscle FFA uptake exceeds ␤ -oxidation, excessive TG storage will be the consequence (3).Evidence is accumulating indicating that accumulation of TG is involved in tissue-specific insulin resistance. For instance, studies in transgenic mice with targeted disturbances in peripheral fatty acid/TG partitioning showed that there is an inverse relationship between hepatic TG stores and hepatic insulin sensitivity (4, 5). In muscle, TG accumulation is also associated with insulin resistance, characterized by a decrease in insulin-stimulated glucose uptake (6). There is a lot of evidence on the action of fatty acid derivatives as agonists and antagonists for nuclear transcription factors, such as peroxisome proliferator-activated receptors (PPARs) and sterol-regulatory element binding proteins (SREBPs) (7,8). These transcription factors profoundly alter the expression of enzymes/proteins involved in glucose and lipid metabolism (8-13) and have interactions with hormones such as insulin (14,15). Therefore, these transcription factors could be molecular links between intracellular fatty acid/TG accumulation and insulin resistance. Because hepatic steatosis is ...

Materials and Methods:Mouse bone marrow cells and mouse osteoprogenitor KS483 cells that concurrently differentiate into osteoblasts and adipocytes were cultured. Biochemical measurement of alkaline phosphatase (ALP) activity, RT-PCR, and gene reporter assays were used in this study. Results: Daidzein, one of the major soy phytoestrogens, had biphasic effects on osteogenesis and adipogenesis. Daidzein stimulated osteogenesis (ALP activity and nodule formation) and decreased adipogenesis (the number of adipocytes) at concentrations below 20 M, whereas it inhibited osteogenesis and stimulated adipogenesis at concentrations higher than 30 M. When estrogen receptors (ERs) were blocked by ICI182,780, daidzein-induced effects were not biphasic. A decrease in osteogenesis and an increase in adipogenesis were observed at the concentrations higher than 20 and 10 M, respectively. In addition to ERs, daidzein transactivated not only peroxisome proliferator-activate receptor ␥ (PPAR␥), but also PPAR␣ and PPAR␦ at micromolar concentrations. Activation of PPAR␣ had no direct effects on osteogenesis and adipogenesis. In contrast, activation of PPAR␦ stimulated osteogenesis but had no effects on adipogenesis, whereas PPAR␥ inhibited osteogenesis and stimulated adipogenesis. Transfection experiments show that an activation of PPAR␣ or PPAR␥ by daidzein downregulated its estrogenic transcriptional activity, whereas activation of PPAR␦ upregulated its estrogenic transcriptional activity. Activation of ER␣ or ER␤ by daidzein downregulated PPAR␥ transcriptional activity but had no influence on PPAR␣ or PPAR␦ transcriptional activity. Conclusions: Daidzein at micromolar concentrations concurrently activates different amounts of ERs and PPARs, and the balance of the divergent actions of ERs and PPARs determines daidzein-induced osteogenesis and adipogenesis.