Our longterm goal is to elucidate how maternal obesity alters the intrauterine metabolic environment and programs offspring obesity. Adiponectin is an adipocyte-secreted hormone with a predominant function in maintaining energy homeostasis. During late pregnancy, maternal adiponectin levels decrease steadily, while fetal adiponectin levels increase rapidly. Adiponectin cannot pass through the placenta barrier. At delivery, a huge difference (~4-7-fold) in blood adiponectin levels between fetal and maternal blood exists. We call this difference the maternal-fetal adiponectin differential (MFAD). In contrast to adults, neonatal blood adiponectin levels are positively correlated with anthropometric parameters of adiposity. Adiponectin enhances lipid accumulation in adipocytes and increase fat tissue mass in mice. Our preliminary study showed that maternal obesity increases fetal mouse fat tissue mass with a significant elevation of adiponectin in fetal blood. However, in adiponectin gene knockout (Adipoq-/-) mice, maternal obesity failed to increase fetal body weight and fat tissue mass, which suggests that adiponectin plays an important role in fetal fat deposition. Using another fetal mouse model with controlled maternal adiponectin levels, we further studied the regulatory effects of adiponectin on fetal lipid metabolism. We found that Adipoq-/+ fetuses have significantly higher levels of: 1) body fat; 2) liver triglycerid content and expression of de novo lipogenic genes and 3) lipoprotein lipase (LPL) in fat tissue, compared with Adipoq-/- fetuses. Therefore, we hypothesize that during late gestation; the MFAD coordinates both maternal and fetal lipid metabolism, and enhances fetal fat deposition by increasing fetal hepatic de novo lipogenesis and lipid accumulation. Maternal obesity further increases the MFAD, which induces more fetal fat deposition. A series of in vivo studies will be carried out using mouse models with various levels of the MFAD. Specific aim 1 will compare the adiposity of offspring from infancy to adulthood who are either exposed in utero or not to the MFAD. The role of increased MFAD in maternal obesity-enhanced fetal fat deposition will also be studied. Specific Aim 2 is designed to determine whether maternal obesity induces fetal liver de novo lipogenesis, and to examine the regulatory effects of adiponectin on fetal liver de novo lipogenesis. Two studies will be carried out in Specific Aim 3 to investigate if elevated fetal adiponectin stimulates triglyceride hydrolysis and fatty acid uptake in fetal fat tissues. The role of LPL in these processes will be studied using inducible adipocyte-specific LPL knockout mice. The findings of this project should identify adiponectin as a key hormone that regulates the intrauterine metabolic environment favoring fetal fat deposition via opposite changes of adiponectin levels in maternal and fetal circulation. Importantly, this project will significantly improve our understanding of maternal obesity-induced offspring adiposity.