Bone Marrow Failure (BMF) Model Mimics Aplastic Anemia (AA) Patients: Single-Cell Landscape of Immune Response Reveals Novel Mechanisms of Immune Imbalance in AA

Background: the pathogenesis of HSPCs impairment in aplastic anemia (AA) remains unclear.We focused on CD8+ T cells, and investigated platelets, CD4+ T cells, macrophages, and mitochondrial energy metabolism, aiming to elucidate the cellular atlas changes associated with bone marrow failure (BMF). Methods: We have successfully established a mouse model of bone marrow failure and analyzed the immune response at the single-cell level. Results: platelets regulate CD4+/CD8+ T cells, and macrophages by releasing PF4. CXCR3/CXCR5 bind to PF4, activating mitochondrial signaling pathways. The decrease of Treg, weakening immunosuppression. Additionally, there is a significant increase in CD8+ effector T cells. Increased energy metabolism was observed in CD8+ stress T cells. It should be noted that, platelet reduction itself in AA weakens energy metabolism, subsequently impairing the hemostatic and thrombotic functions. However, platelets' regulatory function in immune cells remains significant. An imbalance in M1 and M2 macrophage polarization is observed. While a phenotype macrophage and CD8+ naive T cells are important cell phenotypes in marrow aging, not contribute to pathology failure. Conclusion: the possible mechanisms of BMF in AA: based on PF4, platelet-T cell/macrophage crosstalk leads to immune overactivation and the release of cytokines such as IFN-? and TNF-a, which attack the marrow. Therefore, transforming imbalanced CD8+ effector T cells, stress T cells, Treg cells, and M1/M2 macrophages into CD8+ naive T cells and a phenotype of macrophages via inhibiting platelet immune regulatory function, may provide a promising strategy to reverse BMF. Overall design: The mice were divided into four groups: The BMF group (experimental group), the total-body irradiation (TBI) group (control group), the normal young mouse group (wild type, WT), and the normal aged mouse group (Aged). Bone marrow samples were collected from all four groups, with one sample from each group, for a Single Cell RNA-seq Workflow (WTA for whole-transcriptome amplification and ABseq for antibody sequencing) (Fig 1A). The study was approved by the Experimental Animal Welfare Ethics Committee of Xuanwu Hospital, Capital Medical University (approval number: XW-20210531-1). The more details were in "Supplementary materials-METHODS", and the Fig 1A for the experimental design.