LIPOGENIC PATHWAYS IN ADIPOSE TISSUE DEVELOPMENT AND METABOLISM

描述(由申请人提供)：这份职业发展计划将为Irfan Lodhi博士过渡到代谢研究领域的独立学术研究员的职位做好准备。这个5年项目的指导阶段(K99)将在华盛顿大学医学院Clay Semenkovich博士的实验室完成。这个项目的总体目标是了解成脂途径在PPARg激活中的作用，PPARg是脂肪组织发育和代谢的关键调节因子。PPARG属于过氧化物酶体增殖物激活受体(PPAR)家族的配体激活的核受体，最初识别的基础是它们被促进过氧化物酶体增殖的试剂激活的能力。PPARg激活的内源性途径尚不清楚。以往的工作表明，脂肪酸合成酶(Fas)介导的从头脂肪生成对脂肪细胞中PPARg的内源性激活具有重要作用。一种基于质谱学的方法确定了几种依赖于Fas的复合脂类作为PPARg的内源性配体。这些脂质是在过氧化体中产生的，需要一种以前未知的名为PexRAP的过氧化物体酶来合成。在培养细胞中敲除PexRAP会损害PPARg的激活和脂肪生成，这两者都可以被PPARg的药理激活剂罗格列酮所拯救。在小鼠中，反义寡核苷酸介导的PexRAP基因敲除减少了PPARg依赖基因的表达，减少了脂肪质量，增加了苗条，并改善了胰岛素敏感性。更多的研究表明，在脂肪形成过程中，参与过氧化体生物发生的基因增加，并受PPARg调控。总而言之，这些研究导致了这样的假设，即过氧化体衍生的脂类激活了PPARg，反过来，PPARg促进了过氧化体的生物发生，导致了驱动脂肪细胞分化的前馈循环。为了检验这一假设，我们设计了以下具体目标。目的1将确定PexRAP脂肪特异性缺失的小鼠是否受到保护，使其免受饮食诱导和遗传形式的肥胖和糖尿病的影响。目的2研究PexRAP在脂肪细胞中作用的分子机制。最后，目标3将确定过氧化体生物发生在脂肪细胞分化中的作用。

DESCRIPTION (provided by applicant): This career development plan will prepare Dr. Irfan Lodhi to transition to a position as an independent academic investigator in metabolic research. The mentored phase (K99) of this 5 year project will be completed in the laboratory of Dr. Clay Semenkovich at Washington University School of Medicine. The overall objective of this project is to understand the role of lipogenic pathways in the activation of PPARg, a key regulator of adipose tissue development and metabolism. PPARg belongs to the peroxisome proliferator- activated receptor (PPAR) family of ligand-activated nuclear receptors, originally identified based on their ability to be activated by agents that promote peroxisome proliferation. Endogenous pathways of PPARg activation have remained unclear. Previous work suggests that de novo lipogenesis mediated by fatty acid synthase (FAS) is important for endogenous activation of PPARg in adipocytes. A mass spectrometry-based approach identified several FAS-dependent complex lipids as putative endogenous ligands for PPARg. These lipids are made in peroxisomes and require a previously unidentified peroxisomal enzyme named PexRAP for their synthesis. Knockdown of PexRAP in cultured cells impaired PPARg activation and adipogenesis, both of which could be rescued with rosiglitazone, a pharmacological activator of PPARg. Antisense oligonucleotide- mediated knockdown of PexRAP in mice decreased expression of PPARg-dependent genes, reduced fat mass, increased leanness, and improved insulin sensitivity. Additional studies suggested that genes involved in peroxisomal biogenesis increase during adipogenesis and are regulated by PPARg. Together, these studies led to the hypothesis that peroxisome-derived lipids activate PPARg and, reciprocally, PPARg promotes peroxisomal biogenesis, resulting in a feed-forward cycle that drives adipocyte differentiation. The following specific aims are designed to test this hypothesis. Aim 1 will determine if mice with adipose-specific deletion of PexRAP are protected from diet-induced and genetic forms of obesity and diabetes. Aim 2 will characterize the molecular mechanism of PexRAP function in adipocytes. Finally, Aim 3 will determine the role of peroxisomal biogenesis in adipocyte differentiation.