High fat intake is associated with fat mass gain through fatty acid activation of peroxisome proliferator-activated receptors ␦ and ␥ , which promote adipogenesis. We show herein that, compared to a combination of specific agonists to both receptors or to saturated, monounsaturated, and -3 polyunsaturated fatty acids, arachidonic acid (C20:4, -6) promoted substantially the differentiation of clonal preadipocytes. This effect was blocked by cyclooxygenase inhibitors and mimicked by carbacyclin, suggesting a role for the prostacyclin receptor and activation of the cyclic AMPdependent pathways that regulate the expression of the CCAAT enhancer binding proteins ␤ and ␦ implicated in adipogenesis. During the pregnancy-lactation period, mother mice were fed either a high-fat diet rich in linoleic acid, a precursor of arachidonic acid (LO diet), or the same isocaloric diet enriched in linoleic acid and ␣ -linolenic acid (LO/ LL diet). Body weight from weaning onwards, fat mass, epididymal fat pad weight, and adipocyte size at 8 weeks of age were higher with LO diet than with LO/LL diet. In contrast, prostacyclin receptor-deficient mice fed either diet were similar in this respect, indicating that the prostacyclin signaling contributes to adipose tissue development. These results raise the issue of the high content of linoleic acid of i ) ingested lipids during pregnancy and lactation, and ii ) formula milk and infant foods in relation to the epidemic of childhood obesity. -Massiera, F., P. Saint-Marc, J. Seydoux, T. Murata, T. Kobayashi, S. Narumiya, P. Guesnet, E-Z. Amri, R. Negrel, and G, Ailhaud. Obesity is associated with metabolic disorders such as dyslipidemia, diabetes, and hypertension, and fat mass excess in severe obesities is typically due to an increase in adipocyte size and number. The formation of adipocytes is a critical event, as mature adipocytes do not divide in vivo and do not undergo significant turnover under physiological conditions. The capacity for proliferation of precursor cells and their differentiation into adipocytes is highest at early age and decrease thereafter in humans and rodents. A limited number of hormones can affect the adipose tissue mass and possibly its distribution (1). High dietary fat intake is now recognized to be associated with a gain of fat mass in animals and humans at all ages (2-5). However, the lack of evidence of a general increase in energy intake as fat among youths, despite a striking increase in the prevalence of obesity in industrial and developing countries, may be due in part to decreased physical activity and nonexercise activity thermogenesis (6), but also to the composition of food intake in early life. The long-term relationship between the fatty acid composition of dietary fats and the development of adipose tissue in humans is difficult to assess in contrast to animals. When mother rats were fed a high-fat diet rich in linoleic acid (C18:2, -6) or saturated fatty acids, suckling pups at 17 days of age exhibited hyperplasia or hypertrophy of whi...

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White adipose tissue is known to contain the components of the renin-angiotensin system, which gives rise to angiotensin II from angiotensinogen (AGT). Recent evidence obtained in vitro and ex vivo is in favor of angiotensin II acting as a trophic factor of adipose tissue development. To determine whether AGT plays a role in vivo in this process, comparative studies were performed in AGT-deficient (agt(-/-)) mice and control wild-type mice. The results showed that agt(-/-) mice gain less weight than wild-type mice in response to a chow or high fat diet. Adipose tissue mass from weaning to adulthood appeared altered rather specifically, as both the size and the weight of other organs were almost unchanged. Food intake was similar for both genotypes, suggesting a decreased metabolic efficiency in agt(-/-) mice. Consistent with this hypothesis, cellularity measurement indicated hypotrophy of adipocytes in agt(-/-) mice with a parallel decrease in the fatty acid synthase activity. Moreover, AGT-deficient mice exhibited a significantly increased locomotor activity, whereas metabolic rate and mRNA levels of uncoupling proteins remained similar in both genotypes. Thus, AGT appears to be involved in the regulation of fat mass through a combination of decreased lipogenesis and increased locomotor activity that may be centrally mediated.

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Adipose tissue is an important source of angiotensinogen (AGT). Recent evidence shows that a local renin ± angiotensinogen system (RAS) is present in human adipose tissue and may act as a distinct system from plasma RAS. In obese patients, the involvement of angiotensin II (angII) as a consequence of increased plasma AGT secreted from adipose tissue has been proposed in the development of hypertension. Another role of AGT via angII in the development of adipose tissue is supported by the following: (i) in vitro, angII stimulates the production and release of prostacyclin from adipocytes, which in turn promotes the differentiation of precursor cells into adipocytes; (ii) ex vivo and in vivo, both angII and (carba)prostacyclin promote the formation of new fat cells; and (iii) AGT 7a7 mice exhibit a slowing down of adipose tissue development, as compared to wild-type mice. Altogether the data are consistent with an autocrineaparacrine mechanism implicating AGT, angII and prostacyclin in adipose tissue development.

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The essential role of CCAAT/enhancer binding proteins (C/EBPs) beta and delta for adipocyte differentiation has been clearly established. In preadipocytes, their expression is up-regulated by the activation of leukemia inhibitory factor receptor (LIF-R) and prostacyclin receptor (IP-R) via the extracellular signal-regulated kinase (ERK) pathway and cAMP production, respectively. However, the molecular mechanisms by which LIF and prostacyclin-induced signals are propagated to the nucleus and the transcription factors mediating ERK and cAMP-induced C/EBP gene expression were unknown. Here we report that both pathways share cAMP responsive element binding protein/activation transcription factor 1 (CREB/ATF-1) as common downstream effectors. LIF-R and IP-R activation induced binding of CREB and/or ATF-1 to C/EBP promoters and CREB-dependent transcription. Expression of dominant negative forms of CREB dramatically reduced the LIF- and prostacyclin-stimulated C/EBP beta and C/EBP delta expression. Upon stimulation of the IP-R, the ERK pathway was activated in a PKA-dependent manner. ERK activation by the PKA pathway was not required for CREB/ATF-1 phosphorylation but rather was necessary for CREB-dependent up-regulation of C/EBPs expression. Our findings suggest that ERK activation is required for CREB transcriptional activity, possibly by recruitment of a coactivator.