Barzilai Sagi, Yadav Sandeep Kumar, Morrell Steven, Roncato Francesco, Klein Eugenia, Stoler-Barak Liat, Golani Ofra, Feigelson Sara W, Zemel Assaf, Nourshargh Sussan, Alon Ronen
Department of Immunology, The Weizmann Institute of Science, Rehovot 7610001, Israel.
William Harvey Research Institute, Barts and The London School of Medicine and Dentistry, Queen Mary University of London, London EC1M 6BQ, UK.
Cell Rep. 2017 Jan 17;18(3):685-699. doi: 10.1016/j.celrep.2016.12.076.
The endothelial cytoskeleton is a barrier for leukocyte transendothelial migration (TEM). Mononuclear and polymorphonuclear leukocytes generate gaps of similar micron-scale size when squeezing through inflamed endothelial barriers in vitro and in vivo. To elucidate how leukocytes squeeze through these barriers, we co-tracked the endothelial actin filaments and leukocyte nuclei in real time. Nuclear squeezing involved either preexistent or de novo-generated lobes inserted into the leukocyte lamellipodia. Leukocyte nuclei reversibly bent the endothelial actin stress fibers. Surprisingly, formation of both paracellular gaps and transcellular pores by squeezing leukocytes did not require Rho kinase or myosin II-mediated endothelial contractility. Electron-microscopic analysis suggested that nuclear squeezing displaced without condensing the endothelial actin filaments. Blocking endothelial actin turnover abolished leukocyte nuclear squeezing, whereas increasing actin filament density did not. We propose that leukocyte nuclei must disassemble the thin endothelial actin filaments interlaced between endothelial stress fibers in order to complete TEM.
内皮细胞骨架是白细胞跨内皮迁移（TEM）的一个屏障。单核细胞和多形核白细胞在体外和体内挤过炎症性内皮屏障时会产生类似微米级大小的间隙。为了阐明白细胞如何挤过这些屏障，我们实时共同追踪了内皮肌动蛋白丝和白细胞细胞核。核挤压涉及插入白细胞片状伪足中的预先存在的或新生的叶状结构。白细胞核可逆地弯曲内皮肌动蛋白应力纤维。令人惊讶的是，挤压白细胞形成细胞旁间隙和跨细胞孔并不需要Rho激酶或肌球蛋白II介导的内皮收缩性。电子显微镜分析表明，核挤压使内皮肌动蛋白丝移位而不使其凝聚。阻断内皮肌动蛋白周转可消除白细胞核挤压，而增加肌动蛋白丝密度则不会。我们提出，白细胞核必须拆解交织在内皮应力纤维之间的薄内皮肌动蛋白丝，以便完成跨内皮迁移。
