Department of Cardiology, Zhongnan hospital, Wuhan University.
Department of Obstetrics and Gynecology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology.
J Atheroscler Thromb. 2021 Apr 1;28(4):375-384. doi: 10.5551/jat.54445. Epub 2020 Jul 9.
Activin receptor-like kinase 7 (ALK7) acts as a key receptor for TGF-β family members, which play important roles in regulating cardiovascular activity. However, ALK7's potential role, and underlying mechanism, in the macrophage activation involved in atherogenesis remain unexplored.
ALK7 expression in macrophages was tested by RT-PCR, western blot, and immunofluorescence co-staining. The loss-of-function strategy using AdshALK7 was performed for functional study. Oil Red O staining was used to observe the foam cell formation, while inflammatory mediators and genes related to cholesterol efflux and influx were determined by RT-PCR and western blot. A PPARγ inhibitor (G3335) was used to reveal whether PPARγ was required for ALK7 to affect macrophage activation.
The results exhibited upregulated ALK7 expression in oxidized low-density lipoprotein (Ox-LDL) induced bone marrow derived macrophages (BMDMs) and mouse peritoneal macrophages (MPMs), isolated from ApoE-deficient mice, while ALK7's strong immunoreactivity in BMDMs was observed. ALK7 knockdown significantly attenuated pro-inflammatory, but promoted anti-inflammatory, macrophage markers expression. Additionally, ALK7 silencing decreased foam cell formation, accompanied by the up-regulation of ABCA1 and ABCG1 involved in cholesterol efflux but the down-regulation of CD36 and SR-A implicated in cholesterol influx. Mechanistically, ALK7 knockdown upregulated PPARγ expression, which was required for the ameliorated effect of ALK7 silencing macrophage activation.
Our study demonstrated that ALK7 was a positive regulator for macrophage activation, partially through down-regulation of PPARγ expression, which suggested that neutralizing ALK7 might be promising therapeutic strategy for treating atherosclerosis.
激活素受体样激酶 7（ALK7）作为 TGF-β家族成员的关键受体发挥作用，这些成员在调节心血管活动方面发挥着重要作用。然而，ALK7 在动脉粥样硬化形成中涉及的巨噬细胞激活中的潜在作用及其潜在机制仍未被探索。
通过 RT-PCR、western blot 和免疫荧光共染色检测巨噬细胞中 ALK7 的表达。使用 AdshALK7 进行功能丧失策略以进行功能研究。油红 O 染色用于观察泡沫细胞形成，同时通过 RT-PCR 和 western blot 测定与胆固醇流出和流入相关的炎症介质和基因。使用过氧化物酶体增殖物激活受体γ（PPARγ）抑制剂（G3335）来揭示 PPARγ 是否是 ALK7 影响巨噬细胞激活所必需的。
结果显示，氧化型低密度脂蛋白（Ox-LDL）诱导的骨髓来源巨噬细胞（BMDMs）和来自载脂蛋白 E 缺陷小鼠的小鼠腹腔巨噬细胞（MPMs）中 ALK7 表达上调，而 BMDMs 中 ALK7 的强免疫反应性被观察到。ALK7 敲低显著减弱了促炎，但促进了抗炎，巨噬细胞标志物的表达。此外，ALK7 沉默减少了泡沫细胞形成，伴随着胆固醇流出所涉及的 ABCA1 和 ABCG1 的上调，但胆固醇流入所涉及的 CD36 和 SR-A 的下调。在机制上，ALK7 敲低上调了 PPARγ 的表达，这是 ALK7 沉默改善巨噬细胞激活作用所必需的。
我们的研究表明，ALK7 是巨噬细胞激活的正调节剂，部分通过下调 PPARγ 的表达，这表明中和 ALK7 可能是治疗动脉粥样硬化的有前途的治疗策略。
