白色脂肪米色化关键基因的鉴定及其功能研究

Obesity results from a chronic imbalance between energy intake and energy expenditure, which is closely associated with many diseases, including cardiovascular diseases, type 2 diabetes and nonalcoholic fatty liver disease. White adipose tissue (WAT) is essential for triglyceride storage and endocrine signaling, while brown adipose tissue (BAT) dissipates energy to generate heat through uncoupled respiration mediated by UCP1. BAT is specialized in energy expenditure and counteracts obesity. Recent studies have identified a subset of cells in WAT that could be converted into brown-like adipocyte (also called beige, or brite cells). In response to environmental or hormonal stimuli (such as cold exposure or β-adrenergic receptor agonists), these beige cells undergo a browning process and possess brown feature, including multilocular lipid droplets and high UCP1 protein levels. This browning process has been suggested to have strong anti-obesity and anti-diabetic benefits. Although beige cells are functionally similar to brown adipocytes, they are developmentally of different origins. The classical brown adipocytes have a common ancestor with myocytes that express Myf5 and Pax7, while beige cells originate from a Pax7- Myf5- lineage. .To identify genes involved in development of beige fat, we first injectedβ-adrenergic receptor agonist into mice and harvested inguinal fat for microarray analysis of differentially expressed genes. Our microarray data identified several candidate genes, including SIRT6 and KLF9. Moreover, Western blot analysis indicates that the protein levels of SIRT6 and KLF9 in inguinal fat tissue of mice are increased in response to cold exposure or β-adrenergic receptor agonist treatment. We have generated fat-specific SIRT6-deficient mice. These SIRT6-mutant mice displayed obesity and cold intolerance. Furthermore, SIRT6-deficient mice exhibited impaired browning of white adipose tissue induced by cold exposure orβ-adrenergic receptor agonist treatment. Likewise, the global KLF9 deficient mice also displayed obesity and these mutant mice showed impaired beiging of white fat stimulated by cold exposure orβ-adrenergic receptor agonist treatment. .These data obtained from SIRT6 or KLF9-mutant mice suggest that both SIRT6 and KLF9 are involved in beige fat development. However, how these genes regulate beige fat development and activation remains unclear. .We will perform the following studies:.1, We will study the mechanism of SIRT6 and KLF9 action in beige fat using primary adipocyte; .2, We need generate SIRT6-transgenic mice and KLF9-trangenic mice. We will also generate fat-specific KLF9-deficient mice since we just have global KLF9-mutant mice in hand. .3, In addition to SIRT6 and KLF9, we have also identified the other genes and signaling pathway possibly involved in beige fat development. We will also study these genes using different cell and mouse models. .Notably, recent studies have revealed that adult humans also have functional UCP1+ brown adipocytes. Human adipose depots are highly heterogeneous, and brown adipocytes coexist with beige and white adipocytes. Thus, promoting development and function of brown and beige fat may represent an attractive treatment for obesity.

现有证据表明哺乳动物存在第三种脂肪细胞，即米色脂肪细胞。米色脂肪细胞在寒冷等条件下被激活而发挥产热功能，但其发育和激活过程分子机制尚不清楚。本申请拟从表观遗传和基因转录调控着手研究米色脂肪的发育和激活。我们前期工作表明，寒冷或去甲肾上腺素处理小鼠，发现其皮下白色脂肪组蛋白去乙酰化酶SIRT6和转录因子KLF9表达增加；脂肪组织特异敲除SIRT6的小鼠表现出肥胖，体温下降，寒冷诱发的白色脂肪米色化受损；同样，KLF9基因全身敲除小鼠也有类似的表型；这些结果表明SIRT6和KLF9参与了米色脂肪细胞发育。本申请拟开展以下工作：1，从分子水平和细胞水平深入研究SIRT6和KLF9调节米色脂肪细胞发育机制；2，构建SIRT6和KLF9脂肪特异转基因小鼠以及KLF9脂肪特异敲除动物模型，确定这些基因对米色脂肪发育及对机体代谢的影响。研究米色脂肪细胞发育具有重要生理意义，可为治疗肥胖提供潜在靶点。

现有证据表明哺乳动物存在第三种脂肪细胞，即米色脂肪细胞。米色脂肪细胞在寒冷等条.件下被激活而发挥产热功能，但其发育和激活过程分子机制尚不清楚。我们前期工作表明，寒冷或去甲肾上腺素处理小鼠，发现其皮下白色脂肪组蛋白去乙酰化酶SIRT6和转录因子KLF9表达增加；提示SIRT6和KLF9可能参与了米色脂肪细胞发育。本项目主要从分子水平、细胞水平和动物整体水平研究SIRT6和KLF9调节米色脂肪细胞发育机制。在该项目的支持下，我们发现Sirt6基因敲除损害了棕色脂肪的产热功能，抑制了白色脂肪棕色化，所以脂肪组织特异性敲除Sirt6的小鼠表现出肥胖，胰岛素抵抗以及肝脏脂质沉积的表型。该研究发表在Cell Reports（2017），其意义在于，SIRT6作为去乙酰化酶，适合作为药物靶点，其激动剂有可能用于治疗肥胖等代谢性疾病。我们也发现脂肪中Klf9的表达受到肾上腺素激动剂和其他生理刺激的调节， 脂肪组织中Klf9转基因促进了棕色脂肪产热和白色脂肪棕色化，相反Klf9的小鼠表现出肥胖以及氧耗降低，脂肪产热功能减弱的表型。该研究发表在Diabetes（2020），其意义在于，脂肪组织特异性激活Klf9将促进米色脂肪发育，具有治疗肥胖的潜力。有意思的是，我们还发现，在肝脏组织中，klf9介导了糖皮质激素诱发肝脏糖异生及高血糖症。糖皮质激素诱导肝脏Klf9的表达，Klf9刺激肝脏的糖异生，在肝脏组织激活Klf9表达能升高小鼠血糖水平，相反，肝脏Klf9特异敲除小鼠表现出饥饿后低血糖。该研究发表在JCI（2019），其研究意义在于，糖皮质激素在临床使用广泛，但其诱发糖尿病的机理不清，我们阐明了这一科学问题，为治疗糖皮质激素诱发的糖尿病打下基础。另外，我们还研究了Foxi2通过调控AgRP表达和分泌，影响脂肪产热和食欲；以及Klf9家族其他成员，包括Klf10和Klf16分别调控肝脏的糖异生和脂肪酸氧化，这些研究分别发表在Diabetes（2022），Gut（2021）以及Diabetologia（2017），这些研究揭示了体内糖脂代谢调控网络。

内容获取失败，请点击重试