ADAP-STAT1 module maintains platelet homeostasis via restraint of macrophage phagocytic in ITP. ADAP-STAT1 module maintains platelet homeostasis via restraint of macrophage phagocytic in ITP

Heightened platelet phagocytosis by macrophages accompanied with an increase in IFN-γ is often attributed to the etiology of immune thrombocytopenia (ITP), an autoimmune disease characterized by low platelet counts. While deletion of the hematopoietic cell adaptor protein ADAP predisposes to ITP in mice, the mechanisms that underlie the functional role of ADAP during ITP remains largely unknown. Here we report that ADAP restrains platelet clearance by macrophages via modulation of STAT1-FcγR signaling axis. We show that under-expression of ADAP in splenic macrophage was associated with low platelet counts in patients with ITP. Further, macrophages from Adap−/− mice had an elevated phagocytosis capacity and exhibited upregulated pro-inflammatory signaling, and the thrombocytopenia in Adap−/− mice was mitigated in vivo by depletion of macrophages. Mechanically, ADAP interacted and competed with STAT1 binding to importin a5, a nuclear shuttling receptor for activated STAT1. While having no effect on STAT1 tyrosine phosphorylation, loss of ADAP increased the assembly of STAT1-importin a5 complex and facilitated STAT1 nuclear entry, leading to a selective enhancement of transcription of FcγRI/IV in macrophages. Moreover, pharmacological inhibition of STAT1 or disruption of STAT1-importin a5 interaction relieved the thrombocytopenia in Adap−/− mice. Thus, our findings reveal a critical role for ADAP as an intracellular immune checkpoint for shaping macrophage phagocytic ability in homeostatic maintenance of platelets. Overall design: RNA profiles of splenic macrophages from wild-type and Adap-KO mice

巨噬细胞介导的血小板吞噬作用增强，伴随γ干扰素（interferon-γ, IFN-γ）水平升高，这一表现常与免疫性血小板减少症（immune thrombocytopenia, ITP）的发病机制相关——该疾病是一类以血小板计数降低为特征的自身免疫性疾病。尽管造血细胞衔接蛋白ADAP（hematopoietic cell adaptor protein ADAP）的缺失会使小鼠易感免疫性血小板减少症，但ADAP在该疾病进程中发挥功能的具体分子机制目前仍不甚明确。
本研究证实，ADAP可通过调控信号转导与转录激活因子1-Fcγ受体（STAT1-FcγR）信号轴，抑制巨噬细胞对血小板的清除过程。研究团队观察到，免疫性血小板减少症患者脾脏巨噬细胞中ADAP的低表达，与患者的血小板计数降低存在显著相关性。
进一步实验显示，Adap基因敲除（Adap−/−）小鼠的巨噬细胞吞噬能力显著增强，且促炎信号通路出现上调；通过体内巨噬细胞清除策略，可有效缓解Adap−/−小鼠的血小板减少症表型。机制层面研究表明，ADAP可与激活的STAT1的核穿梭受体——输入蛋白α5（importin α5）结合，并竞争性抑制STAT1与该受体的结合。ADAP缺失虽不影响STAT1的酪氨酸磷酸化修饰，但可增强STAT1-importin α5复合物的组装效率，促进STAT1的核转位过程，进而选择性上调巨噬细胞中Fcγ受体I/IV（FcγRI/IV）的转录水平。
此外，通过药物抑制STAT1活性或破坏STAT1与importin α5的相互作用，可减轻Adap−/−小鼠的血小板减少症。
综上，本研究揭示了ADAP作为胞内免疫检查点的关键作用：其可通过调控巨噬细胞的吞噬能力，参与维持血小板的稳态平衡。
整体实验设计：野生型与Adap基因敲除（Adap-KO）小鼠的脾脏巨噬细胞RNA表达谱分析。