ADAM17/Hedgehog介导MSC衰老导致骨髓血管微环境失稳态在ITP发病机制中的作用

Immune thrombocytopenia (ITP) is a common hematologic disorder characterized by isolated thrombocytopenia which is mainly caused by reduced thrombopoiesis. Bone marrow microvascular niche is the main site for megakaryocytopoiesis and thrombocytopoiesis. Our previous works had revealed that more bone marrow mesenchymal stem cells and endothelial cells undergone apoptosis and senescence in ITP patients. Mesenchymal stem cells are critical perivascular cells, which play a role in sustaining vessel stability and promoting angiogenesis. And perivascular mesenchymal stem cells can induce migration of megakaryocyte to the bone marrow microvessels through secreting chemokines, and promote its survival, mature and platelets release. So, it is very meaningful to reveal the mechanism of MSC senesence which has a close relationship with microvessels and megakaryopoiesis. Through mRNA microarray analysis, we discovered a powerful gene ADAM17 whose expression level is dramatically downregulated. In this research, we aim to explore the molecular mechanism of MSCs senescence mediated by ADAM17/Hedgehog signaling pathway, and to reveal possible molecular targets to reverse MSC senesence. In addition, we plan to clarify the effect of MSCs senescence on microvessel formation and stability whose deregulation finally resulted in reduced platelet product. In-depth reserch of ITP MSCs is in favor of uncovering the cellular and molecular mechnism of blocked megakayocyte mature and reduced proplate formation, which will provid a new treatment strategy for ITP patients.

免疫性血小板减少症（ITP）是一种获得性血小板减少性疾病，巨核细胞发育成熟障碍是其重要发病机制。骨髓血管微环境是巨核细胞成熟分化、血小板生成的主要场所。课题组前期研究发现，ITP患者骨髓MSC和血管内皮细胞衰老凋亡增加。MSC是维持微血管稳定，参与血管再生修复的重要血管周细胞。因此，揭示MSC衰老机制对阐明ITP巨核细胞成熟障碍至关重要。课题前期通过基因表达谱芯片及大样本分析证实ADAM17低表达是ITP患者MSC的特征性改变，这一发现国内外尚未见报道；进一步研究意外发现，ADAM17酶切底物Shh分泌显著减少。本课题拟通过体内外实验，深入研究ADAM17/Hedgehog信号通路介导MSC衰老的机制，寻找可能逆转MSC衰老的分子靶点；探索MSC衰老及分泌谱改变对内皮细胞凋亡、微血管结构密度及巨核细胞成熟分化的影响，进一步阐明MSC衰老在ITP发病机制中的作用，为ITP临床防治提供新思路。

骨髓间充质干细胞作为微血管周细胞，具有维持血管稳定性以及调节周围免疫反应的重要功能。近年来多项研究证实ITP来源BMSCs活性及免疫调节功能异常。在本研究中我们发现ITP骨髓CD271+CD45-BMSCs数量减少。我们在前期工作中发现部分ITP患者BMSCs表达ADAM17水平减低。为阐明ADAM17低表达对BMSCs功能活性的影响。我们利用慢病毒干扰技术在体外抑制ADAM17在BMSCs中的表达，结果显示抑制ADAM17表达促进BMSCs增殖迁移，减缓细胞衰老，抑制向成骨细胞分化。为探索BMSCs低表达ADAM17对骨髓血管微环境的影响，我们以外周血来源的血管内皮克隆形成细胞为模型，结果发现BMSCs低表达ADAM17 导致血管内皮细胞炎症反应增加，通透性增加，炎症细胞跨内皮迁移增加。综合以上实验结果，我们推断ITP来源的BMSCs低表达ADAM17 导致骨髓微血管炎症反应增强，加速外周血炎症细胞向骨髓内迁移，导致ITP骨髓免疫稳态失衡。