TRIB2 缺乏減少MYCBP2 E3 連接酶的招募與UCP1降解進而增強了產熱作用並防止肥胖

Abstract

過多的脂肪堆積於體內導致肥胖，增加多種慢性疾病的風險，包括糖尿病、心血管疾病和肝脂肪變性。 Tribble 同系物 (Tribs) 是一種參與呼吸鏈耗竭、粒線體疾病和脂肪組織脂質代謝的假激酶。 全基因組關聯研究 (GWAS) 已鑑定出Tribble 同源物 2 (Trib2) 遺傳變異(variants)與內臟脂肪積累、脂肪細胞發育和分化有關。 過去研究已發現TRIB2參與了3T3-L1白色前脂肪細胞的脂肪形成，但TRIB2 在棕色脂肪組織 (BAT) 中的作用目前仍不清楚。 我們先前的研究發現，剔除Trib2基因可以防止小鼠體重和脂肪的增加。 在高脂肪高蔗糖飲食下，與野生型小鼠相比，Trib2 剔除(Trib2-KO)的小鼠表現出較好的葡萄糖耐受性和胰島素敏感性。相較與於Trib2 野生型小鼠 (Trib2-Wt)，Trib2-KO 小鼠表現出更高的能量消耗和生熱作用且 TRIB2蛋白主要表現多集中於在產熱的調節器--棕色脂肪。 此外，我們也觀察到 Trib2-KO 小鼠的棕色脂肪組織中 UCP1 的表現高於 Trib2-Wt 小鼠。 我們使用下拉測定(Pulldown assay)和質譜分析 UCP1為TRIB2 相互作用的蛋白質之一。 在本研究中，我們觀察到 WT1 棕色前脂肪細胞在脂肪生成過程中 TRIB2 和 UCP1 的蛋白呈相反的表現量。 我們證明了 TRIB2 和 UCP1 之間有直接結合。 UCP1 與 TRIB2 的結合促進 UCP1 的泛素化。 在WT1 細胞中減少TRIB2 的表現會下調 UCP1 的泛素化。 我們發現 MYCBP2 E3 連接酶會直接與 TRIB2 和 UCP1 結合。 當存在TRIB2時，促進 MYCBP2 E3 連接酶降解 UCP1 蛋白。 我們認為 TRIB2 招募 MYCBP2 E3 連接酶，導致 UCP1被降解。缺少TRIB2 的會減弱 UCP1 的降解，增強生熱作用並減少肥胖。

Obesity, characterized by excessive fat accumulation, increases the risk of several chronic diseases, including diabetes, cardiovascular disease, and hepatic steatosis. Tribble homologs (Tribs) are pseudokinases involved in respiratory chain depletion, mitochondrial disorders, and lipid metabolism in adipose tissues. Genome-wide association studies (GWAS) have identified Tribble homolog 2 (Trib2) genetic variants associated with visceral fat accumulation, adipocyte development, and differentiation. It has been reported that TRIB2 is involved in the adipogenesis of 3T3-L1 preadipocytes. However, the role of TRIB2 in brown adipose tissue (BAT) remains unclear. Our previous study found that the loss of Trib2 prevents the increase of body weight and fat in mice. Trib2 knockout (Trib2-KO) mice exhibited improved glucose tolerance and insulin sensitivity compared to the wild-type littermates on a high-fat, high-sucrose diet. Additionally, Trib2-KO mice showed increased energy expenditure and thermogenesis compared to the Trib2 wild-type mice (Trib2-Wt). TRIB2 is primarily expressed in brown adipose tissue, a major modulator of thermogenesis. Moreover, we observed higher expression of UCP1 in the brown adipose tissue of Trib2-KO mice than in Trib2-Wt mice. Using pull-down assays and mass spectrometry, we identified UCP1 as one of the proteins interacting with TRIB2. In this study, we observed reversed protein expression levels of TRIB2 and UCP1 during WT1 brown preadipocyte adipogenesis. We demonstrated a direct interaction between TRIB2 and UCP1. UCP1 interaction with TRIB2 may facilitate the ubiquitination of UCP1. Knockdown of TRIB2 in WT1 cells downregulates the ubiquitination of UCP1. We observed that the MYCBP2 E3 ligase directly interacts with both TRIB2 and UCP1. The presence of TRIB2 facilitated the MYCBP2 E3 ligase-mediated degradation of UCP1 protein. We propose that TRIB2 recruits MYCBP2 E3 ligase, leading to the downregulation of UCP1 expression. The deficiency of TRIB2 attenuates the ubiquitination of UCP1, leading to enhanced thermogenesis and reduced adiposity.