Aix Marseille Université, CNRS, Centre Interdisciplinaire de Nanoscience de Marseille, Turing Centre for Living Systems, Marseille 13009, France.
Richard and Loan Hill Department of Biomedical Engineering, University of Illinois, Chicago, IL 60612.
Proc Natl Acad Sci U S A. 2023 Oct 31;120(44):e2300095120. doi: 10.1073/pnas.2300095120. Epub 2023 Oct 24.
The splenic interendothelial slits fulfill the essential function of continuously filtering red blood cells (RBCs) from the bloodstream to eliminate abnormal and aged cells. To date, the process by which 8 [Formula: see text]m RBCs pass through 0.3 [Formula: see text]m-wide slits remains enigmatic. Does the slit caliber increase during RBC passage as sometimes suggested? Here, we elucidated the mechanisms that govern the RBC retention or passage dynamics in slits by combining multiscale modeling, live imaging, and microfluidic experiments on an original device with submicron-wide physiologically calibrated slits. We observed that healthy RBCs pass through 0.28 [Formula: see text]m-wide rigid slits at 37 °C. To achieve this feat, they must meet two requirements. Geometrically, their surface area-to-volume ratio must be compatible with a shape in two tether-connected equal spheres. Mechanically, the cells with a low surface area-to-volume ratio (28% of RBCs in a 0.4 [Formula: see text]m-wide slit) must locally unfold their spectrin cytoskeleton inside the slit. In contrast, activation of the mechanosensitive PIEZO1 channel is not required. The RBC transit time through the slits follows a [Formula: see text]1 and [Formula: see text]3 power law with in-slit pressure drop and slip width, respectively. This law is similar to that of a Newtonian fluid in a two-dimensional Poiseuille flow, showing that the dynamics of RBCs is controlled by their cytoplasmic viscosity. Altogether, our results show that filtration through submicron-wide slits is possible without further slit opening. Furthermore, our approach addresses the critical need for in vitro evaluation of splenic clearance of diseased or engineered RBCs for transfusion and drug delivery.
脾内内皮细胞裂孔的基本功能是不断从血流中过滤红细胞（RBC）以清除异常和衰老的细胞。迄今为止，8μm RBC 通过 0.3μm 宽的裂孔的过程仍然是一个谜。裂孔口径是否会在 RBC 通过时像有时建议的那样增加？在这里，我们通过结合多尺度建模、活体成像和微流控实验，在具有亚微米宽生理校准裂孔的原始设备上，阐明了控制 RBC 在裂孔中保留或通过动力学的机制。我们观察到健康的 RBC 在 37°C 下通过 0.28μm 宽的刚性裂孔。为了实现这一壮举，它们必须满足两个要求。从几何形状上看，它们的表面积与体积比必须与两个连接的等球体的形状兼容。从力学上讲，表面积与体积比低的细胞（0.4μm 宽的裂孔中 28%的 RBC）必须在裂孔内局部展开它们的血影蛋白细胞骨架。相比之下，不需要激活机械敏感的 PIEZO1 通道。RBC 通过裂孔的传输时间遵循与内裂孔压降和滑移宽度分别为[Formula: see text]1 和 [Formula: see text]3 的幂律关系。该定律类似于二维泊肃叶流动中的牛顿流体，表明 RBC 动力学受其细胞质粘度控制。总之，我们的结果表明，在没有进一步裂孔开口的情况下，通过亚微米宽的裂孔进行过滤是可行的。此外，我们的方法解决了体外评估脾脏清除患病或工程 RBC 以用于输血和药物输送的关键需求。
