Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139.
Université Paris Cité, INSERM, Biologie Intégrée du Globule Rouge, 75015 Paris, France.
Proc Natl Acad Sci U S A. 2023 Feb 7;120(6):e2217607120. doi: 10.1073/pnas.2217607120. Epub 2023 Feb 2.
The spleen clears altered red blood cells (RBCs) from circulation, contributing to the balance between RBC formation (erythropoiesis) and removal. The splenic RBC retention and elimination occur predominantly in open circulation where RBCs flow through macrophages and inter-endothelial slits (IESs). The mechanisms underlying and interconnecting these processes significantly impact clinical outcomes. In sickle cell disease (SCD), blockage of intrasplenic sickled RBCs is observed in infants splenectomized due to acute splenic sequestration crisis (ASSC). This life-threatening RBC pooling and organ swelling event is plausibly triggered or enhanced by intra-tissular hypoxia. We present an oxygen-mediated spleen-on-a-chip platform for in vitro investigations of the homeostatic balance in the spleen. To demonstrate and validate the benefits of this general microfluidic platform, we focus on SCD and study the effects of hypoxia on splenic RBC retention and elimination. We observe that RBC retention by IESs and RBC-macrophage adhesion are faster in blood samples from SCD patients than those from healthy subjects. This difference is markedly exacerbated under hypoxia. Moreover, the sickled RBCs under hypoxia show distinctly different phagocytosis processes from those non-sickled RBCs under hypoxia or normoxia. We find that reoxygenation significantly alleviates RBC retention at IESs, and leads to rapid unsickling and fragmentation of the ingested sickled RBCs inside macrophages. These results provide unique mechanistic insights into how the spleen maintains its homeostatic balance between splenic RBC retention and elimination, and shed light on how disruptions in this balance could lead to anemia, splenomegaly, and ASSC in SCD and possible clinical manifestations in other hematologic diseases.
脾脏清除循环中异常的红细胞（RBC），有助于维持 RBC 生成（红细胞生成）和清除之间的平衡。脾脏 RBC 的保留和消除主要发生在开放循环中，其中 RBC 流经巨噬细胞和内皮细胞间隙（IES）。这些过程的潜在机制及其相互联系对临床结果有重大影响。在镰状细胞病（SCD）中，由于急性脾扣押危机（ASSC），婴儿脾切除术时观察到脾内镰状 RBC 阻塞。这种危及生命的 RBC 聚集和器官肿胀事件可能由组织内缺氧引发或增强。我们提出了一种基于氧的脾脏芯片平台，用于体外研究脾脏的动态平衡。为了展示和验证这个通用微流控平台的优势，我们专注于 SCD，并研究了缺氧对脾脏 RBC 保留和消除的影响。我们观察到，来自 SCD 患者的血液样本中，IES 处的 RBC 保留和 RBC-巨噬细胞黏附比健康受试者更快。在缺氧条件下，这种差异明显加剧。此外，缺氧下的镰状 RBC 表现出与非镰状 RBC 在缺氧或常氧下不同的吞噬过程。我们发现再氧化显著缓解了 IES 处的 RBC 保留，并导致巨噬细胞内摄取的镰状 RBC 迅速去镰状化和碎片化。这些结果提供了有关脾脏如何在 RBC 保留和消除之间维持其动态平衡的独特机制见解，并阐明了这种平衡的破坏如何导致 SCD 中的贫血、脾肿大和 ASSC 以及其他血液疾病中的可能临床表现。
