Department of Medical Biochemistry, Amsterdam UMC, Amsterdam Cardiovascular Sciences and Gastroenterology and Metabolism, University of Amsterdam, Meibergdreef 9, 1105AZ, Amsterdam, the Netherlands.
Department of Medical Biochemistry, Amsterdam UMC, Amsterdam Cardiovascular Sciences and Gastroenterology and Metabolism, University of Amsterdam, Meibergdreef 9, 1105AZ, Amsterdam, the Netherlands.
Atherosclerosis. 2020 Dec;315:1-9. doi: 10.1016/j.atherosclerosis.2020.10.898. Epub 2020 Nov 9.
Cholesterol metabolism is tightly regulated by transcriptional and post-transcriptional mechanisms. Accordingly, dysregulation of cholesterol metabolism is a major risk factor for the development of coronary artery disease and associated complications. In recent years, it has become apparent that next to the liver, the intestine plays a key role in systemic cholesterol metabolism by governing cholesterol absorption, secretion, and incorporation into lipoprotein particles. We have previously demonstrated that the Liver X receptor (LXR)-regulated E3 ubiquitin ligase inducible degrader of LDLR (IDOL) is a regulator of cholesterol uptake owing to its ability to promote the ubiquitylation of the low-density lipoprotein receptor (LDLR). However, whether the LXR-IDOL-LDLR axis regulates the LDLR in the intestine and whether this influences intestinal cholesterol homeostasis is not known.
In this study, we evaluated the role of the LXR-IDOL-LDLR axis in enterocyte cell models and in primary enterocytes isolated from Idol and wild type mice. Furthermore, we studied the regulation of intestinal LDLR in Idol and in wild type mice treated with the LXR agonist GW3965. Finally, we assessed ezetimibe-induced trans-intestinal cholesterol efflux in Idol mice.
We show that in a wide range of intestinal cell lines LXR activation decreases LDLR protein abundance, cell surface occupancy, and LDL uptake in an IDOL-dependent manner. Similarly, we find that pharmacological dosing of C57BL6/N mice with the LXR agonist GW3965 increases Idol expression across the intestine with a concomitant reduction in Ldlr protein. Conversely, primary enterocytes isolated from Idol mice have elevated Ldlr. To test whether these changes contribute to trans-intestinal cholesterol efflux, we measured fecal cholesterol in mice following ezetimibe dosing, but found no differences between Idol and control mice in this setting.
In conclusion, our study establishes that the LXR-IDOL-LDLR axis is active in the intestine and is part of the molecular circuitry that maintains cholesterol homeostasis in enterocytes.
胆固醇代谢受转录和转录后机制的严格调控。因此，胆固醇代谢失调是导致冠状动脉疾病及相关并发症发展的主要危险因素。近年来，人们已经意识到，除了肝脏，肠道在调节胆固醇吸收、分泌和纳入脂蛋白颗粒方面对全身胆固醇代谢起着关键作用。我们之前已经证明，肝 X 受体 (LXR) 调节的 LDLR 降解酶诱导物 (IDOL) 是胆固醇摄取的调节剂，因为它能够促进 LDLR 的泛素化。然而，LXR-IDOL-LDLR 轴是否调节肠道中的 LDLR，以及这是否影响肠道胆固醇稳态尚不清楚。
在这项研究中，我们评估了 LXR-IDOL-LDLR 轴在肠上皮细胞模型和从 Idol 和野生型小鼠分离的原代肠细胞中的作用。此外，我们研究了在 Idol 和野生型小鼠中用 LXR 激动剂 GW3965 处理时，肠道 LDLR 的调节情况。最后，我们评估了 ezetimibe 诱导的 Idol 小鼠跨肠胆固醇外排。
我们发现，在广泛的肠细胞系中，LXR 激活以 IDOL 依赖的方式降低 LDLR 蛋白丰度、细胞表面占有率和 LDL 摄取。同样，我们发现用 LXR 激动剂 GW3965 对 C57BL6/N 小鼠进行药物治疗会导致整个肠道中 Idol 的表达增加，同时 LDLR 蛋白减少。相反，从 Idol 小鼠分离的原代肠细胞具有升高的 Ldlr。为了测试这些变化是否有助于跨肠胆固醇外排，我们在 ezetimibe 给药后测量了小鼠粪便中的胆固醇，但在这种情况下，未发现 Idol 和对照小鼠之间有差异。
总之，我们的研究表明，LXR-IDOL-LDLR 轴在肠道中活跃，并构成维持肠上皮细胞胆固醇稳态的分子电路的一部分。
