ESTABLISHING THE ROLE OF BONE MARROW STROMAL ANTIGEN 2 IN HEMATOPOIETIC STEM CELL NICHE INTERACTIONS AND ACTIVATION

摘要 干扰素γ（IFNγ）是一种促炎细胞因子，在慢性感染期间上调， 造血干细胞（HSC）的活化、分化和最终丧失。我们之前已经证明， 这些效应可能导致慢性感染期间骨髓（BM）功能不全和血细胞减少。 IFNγ激活和耗竭HSC的机制尚不清楚。由于HSC 受到与BM微环境相互作用的严重影响2，我们以前研究了 IFNγ对HSC-小生境相互作用的影响。我们的初步数据显示，IFNγ激活的HSC重新定位于骨髓， 远离静止促进CXCL 12丰富的网状（CAR）细胞。我们用转录组分析 鉴定骨髓基质抗原2（BST 2）是IFNγ刺激后唯一上调的表面蛋白 在HSC迁移的早期阶段。我们迄今为止的工作表明，BST 2缺陷小鼠具有更多的HSC， 存在于BM中，它们的HSC比野生型（WT）HSC增殖性更低，并且BST 2 KO HSC不重新表达。 在IFNγ诱导期间，BST 2从CAR细胞定位，表明BST 2可以在调节活化中起作用。 以前的报道表明，BST 2可以作为一种粘附蛋白，以促进在其他细胞中的迁移。 细胞类型，我们怀疑它可能在HSC中执行类似的功能。本提案的总体目标是 目的是通过确定BST 2-蛋白质相互作用及其对HSC活化的影响来阐明BST 2在HSC活化中的作用。 HSC在生态位内的相互作用。我们假设BST 2表达的增加促进HSC 通过促进与替代小生境细胞类型的结合，在炎症应激期间激活。测试 假设，在目的1中，我们将使用交联辅助的方法在HSC中建立BST 2-表面蛋白的相互作用， 亲和纯化质谱。我们将进一步确定阻止这些相互作用是否会影响 通过测量HSC数量、增殖和细胞周期状态来激活HSC。在目标2中，我们将确定BM 通过使用各种BM进行活体成像来促进BST 2介导的HSC活化的小生境细胞 报告小鼠来鉴定HSC相对于其他小生境细胞的空间位置。之间的直接互动 还将测试BST 2阳性HSC和小生境细胞。总的来说，这里提出的实验旨在 扩大我们对BST 2改变HSC-生态位相互作用的机制的理解。阐明如何 HSC在IFNγ刺激过程中被激活，这将有助于深入了解炎症反应的机制。 驱动HSC衰竭，并可能导致骨髓衰竭综合征的新治疗策略 与过度炎症有关。

Abstract Interferon gamma (IFNγ) is a pro-inflammatory cytokine that is upregulated during chronic infections and leads to activation, differentiation, and eventual loss of hematopoietic stem cells (HSCs). We previously showed that these effects may contribute to bone marrow (BM) insufficiency and cytopenias during chronic infection.1 Despite its clinical significance, the mechanism by which IFNγ activates and depletes HSCs is unknown. Since HSCs are heavily influenced by their interaction with the BM microenvironment2, we previously studied the impact of IFNγ on HSC-niche interactions. Our preliminary data show that HSCs activated by IFNγ re-localize in the BM away from quiescent-promoting CXCL12-abundant reticular (CAR) cells. We used transcriptomic analysis to identify Bone Marrow Stromal Antigen 2 (BST2) as the only surface protein upregulated upon IFNγ stimulation during the early stages of HSC migration. Our work to date shows that BST2-deficient mice have more HSCs present in the BM, their HSCs are less proliferative than wild type (WT) HSCs, and BST2 KO HSCs do not re- localize from CAR cells during IFNγ induction suggesting that BST2 could play a role in regulating activation. Previous reports have suggested that BST2 could serve as an adhesion protein to facilitate migration in other cell types, and we suspect that it may perform a similar function in HSCs. The overarching goal of this proposal is to elucidate the role of BST2 in HSC activation by determining BST2-protein interactions and its impact on HSC interactions within the niche. We hypothesize that increased expression of BST2 promotes HSC activation during inflammatory stress by facilitating binding to alternative niche cell types. To test the hypothesis, in Aim 1, we will establish BST2-surface protein interactions in HSCs using cross-linking aided affinity purification mass spectrometry. We will further determine whether blocking these interactions will affect HSC activation by measuring HSC numbers, proliferation and cell cycle status. In Aim 2, we will identify the BM niche cells that facilitate BST2-mediated HSC activation by performing intravital imaging using a variety of BM reporter mice to identify the spatial location of HSCs relative to the other niche cells. Direct interaction between BST2-positive HSCs and niche cells will also be tested. Collectively, the experiments proposed here aim to expand our understanding of the mechanism by which BST2 alters HSC-niche interactions. Elucidating how HSCs become activated during IFNγ stimulation will provide insight into the mechanisms by which inflammation drives HSC exhaustion and will potentially lead to novel therapeutic strategies for bone marrow failure syndromes associated with excessive inflammation.