Department of Endocrinology and Metabolism, Faculty of Medicine, Kagawa University, Miki-cho, Kita-gun, Kagawa, Japan.
J Mol Endocrinol. 2022 Jan 10;68(2):89-98. doi: 10.1530/JME-20-0211.
Adiponectin (APN) is an adipokine that protects against diabetes and atherosclerosis. High-density lipoprotein (HDL) mediates reverse cholesterol transport, which also protects against atherosclerosis. In this process, the human homolog of the B class type I scavenger receptor (SR-BI/CLA-1) facilitates the cellular uptake of cholesterol from HDL. The level of circulating APN is positively correlated with the serum level of HDL-cholesterol. In this study, we investigated whether HDL stimulates the gene expression of APN through the Ca2+/calmodulin (CaM)-dependent protein kinase IV (CaMKIV) cascade. APN expression was examined using real-time PCR and western blot analysis in 3T3-L1 cells incubated with HDL. CaMKIV activity was assessed by the detection of activation loop phosphorylation (at Thr196 residue), and the effect of the constitutively active form, CaMKIVc, on APN promoter activity was investigated. Our results showed that HDL stimulated APN gene expression via hSR-BI/CLA-1. Furthermore, we explored the signaling pathways by which HDL stimulated APN expression in 3T3-L1 cells. The stimulation of APN gene expression by HDL appears to be mediated by CaMKK, as STO-609, a specific inhibitor of CaMKK2, prevents this effect. We revealed that CaMKIVc increased APN gene transcriptional activity, and the CaMKIV-dominant negative mutant blocked the effect of HDL on APN promoter activity. Finally, knockdown of hSR-BI/CLA-1 also canceled the effect of HDL on APN gene expression. These results suggest that HDL has an important role to improve the function of adipocytes by activating hSR-BI/CLA-1, and CaMKK/CaMKIV pathway is conceivable as one of the signaling pathways of this activation mechanism.
脂联素（APN）是一种脂肪因子，可预防糖尿病和动脉粥样硬化。高密度脂蛋白（HDL）介导胆固醇的逆向转运，也可预防动脉粥样硬化。在此过程中，B 类 I 型清道夫受体（SR-BI/CLA-1）的人类同源物促进胆固醇从 HDL 摄取到细胞内。循环 APN 水平与血清 HDL-胆固醇水平呈正相关。在这项研究中，我们研究了 HDL 是否通过 Ca2+/钙调蛋白（CaM）依赖性蛋白激酶 IV（CaMKIV）级联反应刺激 APN 的基因表达。通过实时 PCR 和 Western blot 分析在孵育有 HDL 的 3T3-L1 细胞中检查 APN 表达。通过检测激活环磷酸化（在 Thr196 残基）来评估 CaMKIV 活性，并研究了组成激活形式 CaMKIVc 对 APN 启动子活性的影响。我们的结果表明，HDL 通过 hSR-BI/CLA-1 刺激 APN 基因表达。此外，我们还探索了 HDL 在 3T3-L1 细胞中刺激 APN 表达的信号通路。STO-609（CaMKK2 的特异性抑制剂）可防止 HDL 刺激 APN 基因表达，表明 CaMKK 介导了 APN 基因表达的刺激。我们揭示了 CaMKIVc 增加了 APN 基因转录活性，并且 CaMKIV 显性失活突变体阻断了 HDL 对 APN 启动子活性的影响。最后，hSR-BI/CLA-1 的敲低也取消了 HDL 对 APN 基因表达的影响。这些结果表明，HDL 通过激活 hSR-BI/CLA-1 对脂肪细胞的功能具有重要作用，而 CaMKK/CaMKIV 途径可以作为这种激活机制的信号通路之一。
