Jiang Chunling, Liu Zheng, Hu Rong, Bo Lulong, Minshall Richard D, Malik Asrar B, Hu Guochang
Department of Anesthesiology, University of Illinois College of Medicine, Chicago, IL 60612.
Department of Anesthesiology, West China Hospital, Sichuan University, Chengdu, Sichuan 610041, China.
J Immunol. 2017 Feb 15;198(4):1660-1672. doi: 10.4049/jimmunol.1601495. Epub 2017 Jan 4.
The timely and efficient clearance of apoptotic neutrophils by macrophages (efferocytosis) is required for the resolution of inflammation and tissue repair, but the regulatory mechanisms remain unclear. In this study, we investigated the role of the small GTPase Ras-related protein in brain (Rab)11a in regulating efferocytosis, and on this basis the resolution of inflammatory lung injury. We observed that apoptotic neutrophil feeding induced a rapid loss of Rab11a activity in bone marrow-derived macrophages and found that depletion of Rab11a in macrophages by small interfering RNA dramatically increased the phagocytosis of apoptotic neutrophils compared with control cells. Additionally, overexpression of wild-type Rab11a inhibited macrophage efferocytosis, whereas overexpression of dominant-negative Rab11a (Rab11a S25N) increased the clearance of apoptotic neutrophils. Rab11a knockdown also increased the surface level of CD36 in macrophages, but it reduced cell surface expression of a disintegrin and metalloproteinase (ADAM) 17. Depletion of ADAM17 rescued the decreased surface CD36 expression found in macrophages overexpressing wild-type Rab11a. Also, blockade of CD36 abolished the augmented efferocytosis seen in Rab11a-depleted macrophages. In mice challenged with endotoxin, intratracheal instillation of Rab11a-depleted macrophages reduced neutrophil count in bronchoalveolar lavage fluid, increased the number of macrophages containing apoptotic neutrophils, and prevented inflammatory lung injury. Thus, Rab11a inactivation in macrophages as a result of apoptotic cell binding initiates phagocytosis of apoptotic neutrophils via the modulation of ADAM17-mediated CD36 cell surface expression. Our results raise the possibility that inhibition of Rab11a activity in macrophages is a promising strategy for activating the resolution of inflammatory lung injury.
巨噬细胞及时有效地清除凋亡中性粒细胞（胞葬作用）是炎症消退和组织修复所必需的，但调节机制仍不清楚。在本研究中，我们调查了脑内小GTP酶Ras相关蛋白11a（Rab11a）在调节胞葬作用以及在此基础上炎症性肺损伤消退中的作用。我们观察到凋亡中性粒细胞吞噬诱导骨髓来源巨噬细胞中Rab11a活性迅速丧失，并发现与对照细胞相比，小干扰RNA使巨噬细胞中Rab11a缺失显著增加了对凋亡中性粒细胞的吞噬作用。此外，野生型Rab11a的过表达抑制巨噬细胞胞葬作用，而显性负性Rab11a（Rab11a S25N）的过表达增加了对凋亡中性粒细胞的清除。Rab11a基因敲低也增加了巨噬细胞中CD36的表面水平，但降低了去整合素和金属蛋白酶（ADAM）17的细胞表面表达。ADAM17的缺失挽救了过表达野生型Rab11a的巨噬细胞中CD36表面表达的降低。同样，CD36的阻断消除了Rab11a缺失的巨噬细胞中增强的胞葬作用。在内毒素攻击的小鼠中，气管内注入Rab11a缺失的巨噬细胞可降低支气管肺泡灌洗液中的中性粒细胞计数，增加含有凋亡中性粒细胞的巨噬细胞数量，并预防炎症性肺损伤。因此，凋亡细胞结合导致巨噬细胞中Rab11a失活，通过调节ADAM17介导的CD36细胞表面表达启动对凋亡中性粒细胞的吞噬作用。我们的结果提示，抑制巨噬细胞中Rab11a活性可能是激活炎症性肺损伤消退途径的一种有前景的策略。
