Restoring Dysfunctional Bone Marrow Endothelial Cell Alleviates Aplastic Anemia
Authors: Tang Shu-Qian , Yao Wei-Li , Zhao Hong-Yan , Wen Qi , Zhang Yuan-Yuan , Lyu Zhong-Shi , Xing Tong , Wang Yu , Xu Lan-Ping , Zhang Xiao-Hui , Huang Xiao-Jun , Kong Yuan 
Published: November 2021

Abstract
Background
Aplastic anemia (AA) is a life-threatening disease characterized by bone marrow (BM) failure and pancytopenia. Immunosuppressive therapy can rescue most patients with AA. However, the pathogenesis of AA is still not well elucidated and the new strategies need to be developed for AA patients. Increasing evidences suggested the dysfunctional BM microenvironment may be involved in the pathogenesis of AA. As important components of the BM microenvironment, endothelial cells (ECs) play a crucial role in supporting hematopoiesis and regulating immune. However, whether BM ECs are involved in the occurrence of AA and whether repairing BM ECs could improve the hematopoietic and immune status of AA patients remain to be elucidated.
Aims
To evaluate the quantity and function of BM ECs from AA patients. Moreover, to determine whether the dysfunctional BM ECs are involved in the occurrence of AA by affecting hematopoiesis and regulating immunity in vitro and in vivo. Finally, to uncover the therapeutic potential of repairing dysfunctional BM ECs to alter the hematopoietic and immunological status in AA patients.
Methods
This study enrolled 30 patients with AA and 30 healthy donors(HD). Flow cytometry and BM in situ immunofluorescence staining were used to analyze the proportion of ECs in BM of the two groups. The level of intracellular reactive oxygen species(ROS) and the proportion of apoptosis were detected by flow cytometry. The functions of BM ECs were evaluated by double-positive staining, migration and tube formation assays. To determine the effect of BM ECs on hematopoiesis and immunity, primary human BM ECs were separately cocultured with CD34 + and CD3 + cells. To further validate the role of BM ECs in the occurrence of AA, a classical AA mice model and VE-cadherin blocking antibody that could antagonize the function of BM ECs were used. Moreover, to explore potential approach of targeting the dysfunctional BM ECs, the exogenous EC infusion or N-acetyl-L-cysteine (NAC, a ROS scavenger) for repairing BM ECs were administrated to the AA mice. To further explore the repairing effect of NAC on BM ECs, the primary BM ECs from AA patients were treated by NAC in vitroand then the functions of BM ECs were evaluated.
Results
Compared with HD, BM ECs in AA patients were decreased and dysfunctional, which characterized by higher levels of ROS and apoptosis, impaired abilities of migration and angiogenesis. Furthermore, dysfunctional BM ECs from AA patients not only impaired their hematopoiesis-supporting ability but also promoted co-cultured T cells to polarize towards pro-inflammatory T cells in vitro, which resulted in an unbalanced T cell subsets. Consistently, AA mice demonstrated decreased BM ECs with increased level of intracellular ROS. Moreover, hematopoietic failure and immune imbalance in AA mice became more severe when the function of BM ECs was antagonized, whereas the administration of NAC or infusion of exogenous EC improved the hematopoietic and immunological status of AA mice via repairing BM ECs in vivo. In addition, we found the NAC treatment also restored the hematopoiesis-supporting ability and immunity-regulating ability of the primary ECs derived from AA patients in vitro.
Summary/Conclusion
Our study demonstrates for the first time that dysfunctional BM ECs with impaired hematopoiesis-supporting ability and abnormal immunomodulatory ability are involved in the pathogenesis of AA. Although further validation is required, restoring dysfunctional BM ECs via EC infusion or administration of ROS scavenger NAC might be a potential therapeutic approach for AA patients.

Disclosures
No relevant conflicts of interest to declare.