Regulation of adipose lipid metabolism by new lipid droplet protein

我们最近鉴定了一种以前未表征的 38 kD 蛋白质，它含有载脂蛋白样结构域，并且在脂肪组织中特异性表达。然而，由于缺乏信号序列，该蛋白质不被分泌。相反，我们发现它定位于脂滴 (LD)，使该蛋白成为新发现的脂肪特异性 LD 相关蛋白。我们发现这种新的 LD 相关蛋白存在于 LD 接触位点并促进脂质转移。此外，我们检测到与 Fsp27（也称为 CideC）的直接相互作用。此外，编码这种载脂蛋白样蛋白的基因的表达在禁食小鼠的脂肪组织中非常低，但在进食后增加，尤其是在喂食高脂肪饮食时。我们还发现它在遗传和饮食引起的肥胖中过度表达，表明它对肥胖有贡献。我们已经利用 CRISPR-Cas9 系统生成了在脂肪组织中过度表达的转基因小鼠，以及全局 KO 小鼠。我们的转基因小鼠表现出白色脂肪组织（WAT）质量大大增加，WAT中的脂肪细胞增大，脂肪分解减少，但脂肪生成没有显着变化。相反，我们的全球 KO 小鼠表现出脂肪组织质量大幅减少，脂肪细胞尺寸更小，脂肪分解更高，从而保护小鼠免受饮食引起的肥胖。我们的长期目标是了解该蛋白作为 LD 相关蛋白的功能的分子细节和生理意义，以促进 LD 生长/脂质转移和 WAT 中的 TAG 存储。目标 1 是检查 ApoL6 对脂质转运的调节。目标 2 是检查该蛋白质对脂肪分解的调节。最后，目标 3 是通过在小鼠中进行功能丧失和获得的研究来检查其在体内的作用。总体而言，拟议的研究将确定这种新发现的 LD 蛋白对 WAT 中 LD 生长/脂质转移和脂肪分解的作用。这项研究不仅有助于更好地了解脂肪 LD 的生理学，还可以为肥胖/糖尿病提供未来的治疗靶点。

We recently identified a previously uncharacterized 38 kD protein, which contains an apolipoprotein-like domain and is specifically expressed in adipose tissue. Due to lack of signal sequence, however, the protein is not secreted. Rather, we found that it is localized to lipid droplets (LD), making this protein a newly discovered adipose-specific LD-associated protein. We found that this new LD-associated protein is found at the LD contact site and promotes lipid transfer. In addition, we detected direct interaction with Fsp27 (also called CideC). Furthermore, expression of the gene coding for this apolipoprotein-like protein is very low in adipose tissue of fasted mice, but is increased upon feeding, especially when fed a high fat diet. We also found it to be overexpressed in both genetic and diet induced obesity, suggesting its contribution to adiposity. We have generated transgenic mice for overexpression in adipose tissue, as well as global KO mice by using CRISPR-Cas9 system. Our transgenic mice showed a greatly increased white adipose tissue (WAT) mass with enlarged adipocytes in WAT, having decreased lipolysis without significant changes in lipogenesis. Conversely, our global KO mice showed a substantially diminished adipose tissue mass with smaller adipocyte size with higher lipolysis that protected mice from diet induced obesity. Our long-term goal is to understand the molecular details and physiological significance of the function of this protein as a LD-associated protein to promote LD growth/lipid transfer and TAG storage in WAT. Aim 1 is to examine regulation of lipid transfer by ApoL6. Aim 2 is to examine regulation of lipolysis by this protein. Finally, Aim 3 is to examine its role in vivo by performing loss- and gain-of function studies in mice. Overall, the proposed research will define the role of this newly discovered LD protein on LD growth/lipid transfer and lipolysis in WAT. This research may not only help to better understand adipose LD physiology but also provide future therapeutic targets for obesity/diabetes.