Department of Biological Sciences, School of Life Sciences, Ulsan National Institute of Science and Technology, Ulsan 44919, Republic of Korea.
Department of Convergence Medicine, University of Ulsan College of Medicine, Seoul 05505, Republic of Korea; Convergence Medicine Research Center, Asan Institute for Life Sciences, Asan Medical Center, Seoul 05505, Republic of Korea.
Metabolism. 2021 Jan;114:154430. doi: 10.1016/j.metabol.2020.154430. Epub 2020 Nov 12.
Obesity-induced adipose tissue remodeling is closely associated with systemic insulin resistance. However, the mechanistic involvement of adipocyte-derived extracellular matrix proteins under pathophysiological conditions remains unclear. Our aim was to investigate the distinctive contributions of each chain of type VI collagens (Col6) and its cleavage protein endotrophin to adipocyte functions and insulin sensitivity.
Col6 comprises three alpha chains: Col6a1, Col6a2, and Col6a3. We generated Col6a1-, Col6a2-, and Col6a3-deficient 3T3-L1 adipocytes using the CRISPR-Cas9 system as well as a novel Col6a3-deficient (Col6a3KO) mouse model for loss-of-function studies. Adenoviral-endotrophin and adipocyte-specific doxycycline-inducible endotrophin transgenic mice were utilized for the gain-of-function analysis.
The holo-Col6 fibrils were found to be required for mature adipocyte differentiation. Only Col6a3-deficient 3T3-L1 adipocytes showed decreased inflammation and basal adipocyte lipolysis and prevented ER-stress-induced insulin resistance. Consistently, Col6a3KO mice showed decreased adipocyte size and fat mass of epididymal adipose tissues due to a defect in adipogenic and lipolytic capacity of adipocytes. Beyond the structural role of Col6a3, overexpression of endotrophin in obese mice further augmented insulin resistance, which was tightly associated with a significant increase in lipolysis, inflammation, and cellular apoptosis in adipose tissues, whereas this showed a limited effect on adipogenesis.
These novel findings corroborate our previous observations suggesting that adipose tissue extracellular matrix regulates adipocyte function and insulin sensitivity in pathophysiological conditions. Mechanistically, holo-Col6 fibrils and their signaling derivative endotrophin govern adipocyte function independently of their role as structural supports via MAPK signaling pathways, and the latter could be an important metabolic effector in obesity-related metabolic diseases.
肥胖诱导的脂肪组织重塑与全身胰岛素抵抗密切相关。然而，在病理生理条件下，脂肪细胞衍生细胞外基质蛋白的机制参与仍不清楚。我们的目的是研究 VI 型胶原（Col6）各链及其裂解蛋白内毒素在脂肪细胞功能和胰岛素敏感性中的独特作用。
Col6 由三条α链组成：Col6a1、Col6a2 和 Col6a3。我们使用 CRISPR-Cas9 系统生成 Col6a1、Col6a2 和 Col6a3 缺陷型 3T3-L1 脂肪细胞，以及用于功能丧失研究的新型 Col6a3 缺陷型（Col6a3KO）小鼠模型。使用腺病毒-内毒素和脂肪细胞特异性强力霉素诱导的内毒素转基因小鼠进行功能获得分析。
发现完整的 Col6 原纤维对于成熟脂肪细胞分化是必需的。只有 Col6a3 缺陷型 3T3-L1 脂肪细胞显示出炎症和基础脂肪细胞脂解减少，并预防内质网应激诱导的胰岛素抵抗。一致地，Col6a3KO 小鼠由于脂肪细胞的成脂和脂解能力缺陷而导致脂肪细胞大小和附睾脂肪组织中脂肪质量减少。除了 Col6a3 的结构作用外，肥胖小鼠中内毒素的过表达进一步加剧了胰岛素抵抗，这与脂肪组织中脂解、炎症和细胞凋亡的显著增加密切相关，而这对内生作用的影响有限。
这些新发现证实了我们之前的观察结果，即脂肪组织细胞外基质在病理生理条件下调节脂肪细胞功能和胰岛素敏感性。从机制上讲，完整的 Col6 原纤维及其信号衍生物内毒素通过 MAPK 信号通路独立于其作为结构支持的作用来控制脂肪细胞功能，后者可能是肥胖相关代谢疾病中的重要代谢效应物。
