LIPOGENIC PATHWAYS IN ADIPOSE TISSUE DEVELOPMENT AND METABOLISM

描述（由申请人提供）：这个职业发展计划将准备博士Irfan Lodhi过渡到一个位置作为一个独立的学术研究代谢研究。这个5年项目的指导阶段（K99）将在华盛顿大学医学院的Clay Semenkovich博士的实验室完成。该项目的总体目标是了解脂肪生成途径在激活PPARg中的作用，PPARg是脂肪组织发育和代谢的关键调节因子。PPARg属于配体激活的核受体的过氧化物酶体增殖物激活受体（PPAR）家族，最初基于其被促进过氧化物酶体增殖的试剂激活的能力而鉴定。PPARg激活的内源性途径仍不清楚。以前的工作表明，从头脂肪酸合成酶（FAS）介导的脂肪生成是重要的内源性激活的PPARg在脂肪细胞。基于质谱的方法确定了几种FAS依赖性复合脂质作为PPARg的假定内源性配体。这些脂质是在过氧化物酶体中产生的，需要一种以前未鉴定的过氧化物酶体酶PexRAP来合成。在培养的细胞中PexRAP的敲除损害了PPARg的活化和脂肪形成，这两者都可以用PPARg的药理学活化剂罗格列酮来挽救。反义寡核苷酸介导的小鼠PexRAP敲低降低了PPARg依赖性基因的表达，减少了脂肪量，增加了瘦度，并改善了胰岛素敏感性。另外的研究表明，在脂肪形成过程中，参与过氧化物酶体生物发生的基因增加，并受到PPARg的调节。总之，这些研究导致了过氧化物酶体衍生的脂质激活PPARg的假设，并且PPARg促进过氧化物酶体生物合成，导致驱动脂肪细胞分化的前馈循环。以下具体目标旨在检验这一假设。目的1将确定脂肪特异性缺失PexRAP的小鼠是否受到饮食诱导和遗传形式的肥胖和糖尿病的保护。目的2研究PexRAP在脂肪细胞中的作用机制。最后，目标3将确定过氧化物酶体生物合成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.