Burzynski Laura C, Humphry Melanie, Bennett Martin R, Clarke Murray C H
From the Division of Cardiovascular Medicine, University of Cambridge, Level 6, Box 110, Addenbrooke's Hospital, Cambridge CB2 0QQ, United Kingdom.
From the Division of Cardiovascular Medicine, University of Cambridge, Level 6, Box 110, Addenbrooke's Hospital, Cambridge CB2 0QQ, United Kingdom
J Biol Chem. 2015 Oct 9;290(41):25188-96. doi: 10.1074/jbc.M115.667915. Epub 2015 Aug 31.
Inflammation is a key instigator of the immune responses that drive atherosclerosis and allograft rejection. IL-1α, a powerful cytokine that activates both innate and adaptive immunity, induces vessel inflammation after release from necrotic vascular smooth muscle cells (VSMCs). Similarly, IL-1α released from endothelial cells (ECs) damaged during transplant drives allograft rejection. However, IL-1α requires cleavage for full cytokine activity, and what controls cleavage in necrotic ECs is currently unknown. We find that ECs have very low levels of IL-1α activity upon necrosis. However, TNFα or IL-1 induces significant levels of active IL-1α in EC necrotic lysates without alteration in protein levels. Increased activity requires cleavage of IL-1α by calpain to the more active mature form. Immunofluorescence and proximity ligation assays show that IL-1α associates with interleukin-1 receptor-2, and this association is decreased by TNFα or IL-1 and requires caspase activity. Thus, TNFα or IL-1 treatment of ECs leads to caspase proteolytic activity that cleaves interleukin-1 receptor-2, allowing IL-1α dissociation and subsequent processing by calpain. Importantly, ECs could be primed by IL-1α from adjacent damaged VSMCs, and necrotic ECs could activate neighboring normal ECs and VSMCs, causing them to release inflammatory cytokines and up-regulate adhesion molecules, thus amplifying inflammation. These data unravel the molecular mechanisms and interplay between damaged ECs and VSMCs that lead to activation of IL-1α and, thus, initiation of adaptive responses that cause graft rejection.
炎症是驱动动脉粥样硬化和同种异体移植排斥反应的免疫反应的关键诱因。白细胞介素-1α（IL-1α）是一种激活固有免疫和适应性免疫的强效细胞因子，从坏死的血管平滑肌细胞（VSMC）释放后可诱导血管炎症。同样，移植过程中受损的内皮细胞（EC）释放的IL-1α会引发同种异体移植排斥反应。然而，IL-1α需要经过切割才能具备完整的细胞因子活性，而目前尚不清楚是什么控制着坏死EC中的切割过程。我们发现，EC在坏死后IL-1α活性水平非常低。然而，肿瘤坏死因子α（TNFα）或IL-1可在EC坏死裂解物中诱导产生显著水平的活性IL-1α，而蛋白质水平并无改变。活性增加需要钙蛋白酶将IL-1α切割为活性更高的成熟形式。免疫荧光和邻近连接分析表明，IL-1α与白细胞介素-1受体-2相关联，TNFα或IL-1可降低这种关联，且这一过程需要半胱天冬酶活性。因此，用TNFα或IL-1处理EC会导致半胱天冬酶蛋白水解活性，从而切割白细胞介素-1受体-2，使IL-1α解离并随后被钙蛋白酶加工处理。重要的是，EC可被相邻受损VSMC释放的IL-1α启动，坏死的EC可激活邻近的正常EC和VSMC，促使它们释放炎性细胞因子并上调黏附分子，从而放大炎症反应。这些数据揭示了受损EC与VSMC之间导致IL-1α激活的分子机制及相互作用，进而引发导致移植排斥的适应性反应。
