Department of Surgery, 987690 University of Nebraska Medical Center, Omaha, NE, USA.
Department of Cardiothoracic Surgery, The First Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, PR China.
Cardiovasc Res. 2019 Mar 15;115(4):807-818. doi: 10.1093/cvr/cvy264.
Abdominal aortic aneurysm (AAA) is one of the number of diseases associated with a prominent inflammatory cell infiltration, matrix protein degradation, and smooth muscle cell apoptosis. CD95 is an inflammatory mediator and an apoptosis inducer. Previous studies have shown elevated expression of CD95 or CD95L in the aortic tissue of AAA patients. However, how the CD95L/CD95 contributes to aneurysm degeneration and whether blocking its signalling would be beneficial to disease progression remains largely unknown. In the present study, we sought to determine the role of CD95L and its downstream target, caspase 8, in AAA progression.
By using the CaCl2 murine model of AAA, abdominal aortic aneurysms were induced in C57BL/6 mice. We found that both mRNA and protein levels of CD95L were increased in aneurysm tissue compared with NaCl-treated normal aortic tissue. To determine whether CD95L contributes directly to aneurysm formation, we used CD95L null (CD95L-/-) mice to examine their response to CaCl2 aneurysm induction. Six weeks after periaortic application of CaCl2, aortic diameters of CD95L-/- mice were significantly smaller compared to CaCl2-treated wild-type controls. Connective tissue staining of aortic sections from CaCl2-treated CD95L-/- mice showed minimal damage of medial elastic lamellae which was indistinguishable from the NaCl-treated sham control. Furthermore, CD95L deficiency attenuates macrophage and T cell infiltration into the aortic tissue. To study the role of CD95L in the myelogeous cells in AAA formation, we created chimaeric mice by infusing CD95L-/- bone marrow into sub-leathally irradiated wild-type mice (WT/CD95L-/-BM). As controls, wild-type bone marrow were infused into sub-leathally irradiated CD95L-/- mice (CD95L-/-/WTBM). WT/CD95L-/-BM mice were resistant to aneurysm formation compared to their controls. Inflammatory cell infiltration was blocked by the deletion of CD95L on myeloid cells. Western blot analysis showed the levels of caspase 8 in the aortas of CaCl2-treated wild-type mice were increased compared to NaCl-treated controls. CD95L deletion inhibited caspase 8 expression. Furthermore, a caspase 8-specific inhibitor was able to partially block aneurysm development in CaCl2-treated aneurysm models.
These studies demonstrated that inflammatory cell infiltration during AAA formation is dependent on CD95L from myelogeous cells. Aneurysm inhibition by deletion of CD95L is mediated in part by down-regulation of caspase 8.
腹主动脉瘤（AAA）是与炎症细胞浸润、基质蛋白降解和平滑肌细胞凋亡密切相关的疾病之一。CD95 是一种炎症介质和凋亡诱导剂。先前的研究表明，AAA 患者的主动脉组织中 CD95 或 CD95L 的表达升高。然而，CD95L/CD95 如何导致动脉瘤退化，以及阻断其信号是否有利于疾病进展，在很大程度上仍然未知。在本研究中，我们试图确定 CD95L 及其下游靶标 caspase 8 在 AAA 进展中的作用。
通过使用 CaCl2 诱导的小鼠 AAA 模型，在 C57BL/6 小鼠中诱导腹主动脉瘤。我们发现，与用 NaCl 处理的正常主动脉组织相比，AAA 组织中 CD95L 的 mRNA 和蛋白水平均升高。为了确定 CD95L 是否直接促进动脉瘤形成，我们使用 CD95L 敲除（CD95L-/-）小鼠来检测它们对 CaCl2 诱导的动脉瘤形成的反应。用 CaCl2 处理后 6 周，CD95L-/- 小鼠的主动脉直径明显小于用 CaCl2 处理的野生型对照。用 CaCl2 处理的 CD95L-/- 小鼠主动脉切片的结缔组织染色显示，中膜弹性板的损伤最小，与用 NaCl 处理的假对照无区别。此外，CD95L 缺乏可减轻巨噬细胞和 T 细胞浸润到主动脉组织中。为了研究 CD95L 在 AAA 形成中的髓样细胞中的作用，我们将 CD95L-/- 骨髓注入亚致死剂量照射的野生型小鼠（WT/CD95L-/-BM）中，以创建嵌合小鼠。作为对照，将野生型骨髓注入亚致死剂量照射的 CD95L-/- 小鼠（CD95L-/-/WTBM）中。与对照相比，WT/CD95L-/-BM 小鼠对动脉瘤形成有抗性。髓样细胞上 CD95L 的缺失阻断了炎症细胞浸润。Western blot 分析显示，与用 NaCl 处理的对照组相比，用 CaCl2 处理的野生型小鼠主动脉中 caspase 8 的水平升高。CD95L 缺失抑制 caspase 8 的表达。此外，caspase 8 特异性抑制剂能够部分阻断 CaCl2 处理的动脉瘤模型中的动脉瘤形成。
这些研究表明，AAA 形成过程中的炎症细胞浸润依赖于髓样细胞中的 CD95L。CD95L 的缺失通过下调 caspase 8 部分抑制动脉瘤。
