The Role of eIF4G1 and eIF4G2 in Translational Control of Adipogenesis and Obesity

项目摘要 肥胖症是一种由脂肪量升高引起的疾病，在过去几十年中流行率有所增加。 超过30%的人口患有肥胖症，随着时间的推移，它会导致生命的发病率增加- 威胁性疾病，包括II型糖尿病、心脏病和癌症。许多研究都致力于 找到新的治疗方法，这些方法仍然无效，因为1）肥胖是高度多基因的，2）它们可以改善 而不是针对疾病的源头。迫切需要确定肥胖症中中断的途径， 更好的治疗方法，更精确地治疗脂肪量扩张的病例特异性来源。 我的实验室通过对调节脂肪量的GPCR进行全基因组筛选， 发现FFAR 4，一种纤毛GPCR，结合ω-3脂肪酸，促进前脂肪细胞分化为新的 脂肪细胞（脂肪生成），而不是在现有组织中沉积脂质，引起炎症（肥大）。 这一发现对人类健康特别有用，因为即使脂肪形成和肥大都 导致体重增加，肥大最终是更有害的，因为慢性炎症导致 并发症，包括高血压和糖尿病。因此，了解FFAR 4如何驱动前脂肪细胞 分化可以帮助我们规避肥大性肥胖和下游病理。的机制 FFAR 4驱动脂肪形成的机制尚未阐明。为此，杰克逊实验室进行了第一次 使用前脂肪细胞的全基因组CRISPR敲除筛选FFAR 4途径脂肪生成调节因子 在分化后的不同时间点收获。本实验室发现翻译起始因子eIF 4G 1 和eIF 4G 2，高度同源的蛋白质，竞争相同的核糖体结合位点以驱动转录 募集，对FFAR 4下游的脂肪形成具有相反的作用：eIF 4G 2是最强的抑制剂 而eIF 4G 1是脂肪形成的最强驱动因素之一。我将检验我的中心假设， 从eIF 4G 2依赖性翻译到eIF 4G 1依赖性翻译（通过eIF 4G 2的降解和eIF 4G 1的活化）， 在FFAR 4诱导的cAMP信号传导的下游，通过转化为 特别是促进脂肪生成的转录物。我将使用3 T3-L1前脂肪细胞和小鼠 遗传模型，以获得对eIF 4G 1/2在细胞和系统水平上的功能的机制性洞察。在目标1中， 将确定eIF 4G 1/2在体外前脂肪细胞分化中的作用机制。我会把 eIF 4G 1和eIF 4G 2通过探测机制起作用的途径，跟踪它们在脂肪形成中的动力学， 确定它们是否是驱动脂肪生成所必需/足够的，并鉴定它们各自的转录物。 规范。在目的2中，我将使用小鼠模型来确定eIF 4G 1/2在体内脂肪扩张和代谢中的作用。 模型系统，以了解eIF 4G 1和eIF 4G 2功能如何与多细胞系统相关。总的来说，我的 这项工作将为探索驱动脂肪细胞下游脂肪形成的信号事件网络铺平道路。 纤毛，并可能为治疗肥胖症的单基因来源铺平道路。

PROJECT SUMMARY Obesity, a disease caused by elevated fat mass, has increased in prevalence over the past few decades. Over 30% of the population suffers from obesity, and over time it can lead to increased incidence of life- threatening pathologies, including Type II Diabetes, heart disease, and cancer. Much study has been devoted to finding new treatments, which remain ineffective because 1) obesity is highly polygenic, and 2) they ameliorate symptoms rather than target the disease source. It is urgent to identify pathways disrupted in obesity to develop better therapeutics that more precisely treat the case-specific source of fat mass expansion. My lab contributed to this effort by performing a genome-wide screen for fat mass-regulating GPCRs and discovered FFAR4, a ciliary GPCR that binds ω-3 fatty acids to promote preadipocyte differentiation into new adipocytes (adipogenesis) instead of depositing lipids in existing tissue, causing inflammation (hypertrophy). This discovery is especially useful to human health because even though adipogenesis and hypertrophy both cause weight gain, hypertrophy is ultimately much more pernicious because the chronic inflammation leads to complications, including hypertension and diabetes. Therefore, understanding how FFAR4 drives preadipocyte differentiation may help us circumvent hypertrophic obesity and downstream pathology. The mechanism by which FFAR4 drives adipogenesis has yet to be elucidated. To do so, the Jackson lab performed the first genome-wide CRISPR knockout screen for FFAR4-pathway adipogenesis regulators using preadipocytes harvested at different time points post-differentiation. Our lab discovered that translation initiation factors eIF4G1 and eIF4G2, highly homologous proteins that compete for the same ribosomal binding site to drive transcript recruitment, have opposite effects on adipogenesis downstream of FFAR4: eIF4G2 was the strongest inhibitor and eIF4G1 was one of the strongest drivers of adipogenesis. I will test my central hypothesis that the switch from eIF4G2-dependent to eIF4G1-dependent translation (by degradation of eIF4G2 and activation of eIF4G1), downstream of FFAR4-induced cAMP signaling, drives fate change through converting to the translation of transcripts that specifically promote adipogenesis. I will use a combination of 3T3-L1 preadipocytes and mouse genetic models to gain mechanistic insight into eIF4G1/2 functions on a cellular and systemic level. In Aim 1, I will determine the mechanism of eIF4G1/2 function in preadipocyte differentiation in vitro. I will tease apart the pathway(s) through which eIF4G1 and eIF4G2 act by probing mechanism, tracking their kinetics in adipogenesis, determining if they are necessary/sufficient to drive adipogenesis, and identifying the transcripts they each regulate. In Aim 2, I will determine the role of eIF4G1/2 in fat expansion and metabolism in vivo using mouse model systems to see how eIF4G1 and eIF4G2 function relates to multicellular systems. Taken together, my work will pave the way for exploring the network of signaling events that drive adipogenesis downstream of the cilium and may pave the way for therapeutics targeting monogenic sources of obesity.