Contribution of the vascular niche to the hematopoietic reconstitution.

描述（由申请人提供）：我们小组和其他研究人员积累的证据表明，骨髓（BM）窦状内皮细胞（SECs）代表一个动态的“血管生态位”，它可能为骨髓抑制后的造血重建提供细胞平台。利用骨髓（BM）制备技术的进步，我们最近建立了稳态和血管再生过程中BM SECs的综合表型和功能特征。我们最近的研究表明，在中度至重度骨髓抑制后，退化的SECs的快速再生对于移植的长期造血干细胞（lt - hsc）的移植和补充以及造血功能的重建至关重要。最有可能的是，移植的HSC及其造血祖细胞（HPCs）通过释放新血管生成因子促进SEC的再生。然而，促血管生成造血细胞（如CXCR4+VEGFR1+髓细胞和巨核细胞祖细胞）释放的血管生成因子支持SEC重建的确切机制尚不清楚。本研究的长期目标是确定分子途径并确定血管生成因子（特别是VEGF-A亚型、PlGF和SDF1）支持骨髓“血管生态位”组装和重塑的机制，从而支持造血干细胞的重建和骨髓抑制后的造血功能。因此，我们假设在BM内，VE- cadherin+VEGFR2+VEGFR3+Sca1- SECs建立了一个血管生态位，这是一个动态的细胞微环境，对于HSC的重建和骨髓抑制后的造血至关重要。通过释放VEGF-A - SDF-1再生促血管生成的CXCR4+VEGFR1+造血细胞，以及尚未被识别的血管生成因子加速了SECs的再生，从而加速了LT- hsc的重建和造血。这一假设将通过以下方式得到验证：1)确定促血管生成造血细胞通过生成VEGF-A和SDF-1支持退化的SECs再生从而重建lt - hsc和造血的机制；2)评估预先存在的CXCR4+内皮细胞与移植的CXCR4+VEGFR1+造血细胞对缺血肢体血运重建的相对贡献；3)评估血管生成因子的强制表达在加速骨髓内皮细胞再生和造血重建中的生理意义。我们预计，了解血管生成因子调节造血和HSC自我更新的机制将为治疗骨髓衰竭状态（包括再生障碍性贫血、骨髓增生异常综合征）提供新的策略，并加速化疗、放疗和移植后的骨髓重建。

DESCRIPTION (provided by applicant): Accumulating evidence from our group and others suggest that bone marrow (BM) sinusoidal endothelial cells (SECs) represent a dynamic "vascular niche", which may provide the cellular platform for the reconstitution of hematopoiesis after myelosuppression. Using technical advances in bone marrow (BM) preparation, we have recently established a comprehensive phenotypic and functional signature of BM SECs at steady state and during hemangiogenic regeneration. We have recently shown that, after moderate to severe myelosuppression rapid regeneration of the regressed SECs is essential for engraftment and replenishment of the transplanted long-term hematopoietic stem cells (LT-HSCs) and reconstitution of hematopoiesis. Most likely, transplanted HSC and their lineage committed hematopoietic progenitor cells (HPCs) by releasing of neo- angiogenic factors contribute to the regeneration of SEC. However, the precise mechanism by which angiogenic factors released by the pro-angiogenic hematopoietic cells, such as CXCR4+VEGFR1+ myeloid and megakaryocytic progenitors cells support reconstruction of the SECs is not known. The broad long-term objective of this proposal is to identify the molecular pathways and to define the mechanism whereby angiogenic factors, specifically the VEGF-A isoforms, PlGF and SDF1 elaborated by specific subsets of the hematopoietic cells support assembly and remodeling of BM's "Vascular Niche", thereby supporting reconstitution of HSCs and hematopoiesis after myelosuppression. Therefore, we hypothesize that within BM, the VE- cadherin+VEGFR2+VEGFR3+Sca1- SECs establish a vascular niche, which is a dynamic cellular microenvironment essential for the reconstitution of HSC, and hematopoiesis after myelosuppression. Regenerating pro-angiogenic CXCR4+VEGFR1+ hematopoietic cells through release of VEGF-A SDF-1, and as yet unrecognized angiogenic factors accelerate regeneration of the SECs thereby accelerating the reconstitution of the LT- HSCs and hematopoiesis. This hypothesis will be tested through: 1) determining the mechanism by which pro-angiogenic hematopoietic cells by elaborating VEGF-A and SDF-1 support the regeneration of regressed SECs thereby reconstituting LT-HSCs and hematopoiesis: 2) assessing the relative contribution of preexisting CXCR4+ endothelial cells versus transplanted CXCR4+VEGFR1+ hematopoietic cells to the revascularization of the ischemic limbs and 3) evaluating the physiological significance of enforced expression of angiogenic factors in accelerating the regeneration of BM SECs and reconstitution of hematopoiesis. We anticipate that understanding the mechanism by which angiogenic factors regulate hematopoiesis and HSC self-renewal will offer new strategies to treat BM failure states, including aplastic anemia, myelodysplastic syndromes and accelerate BM reconstitution after chemotherapy, irradiation and transplantation. PUBLIC HEALTH RELEVANCE: We hypothesize that bone marrow's vascular niche is a dynamic cellular microenvironment that is essential for the maintenance and reconstitution of hematopoiesis after myelosuppression. Regenerating CXCR4+VEGFR1+ hematopoietic cells through release of angiogenic factors, including VEGF-A, PlGF, SDF-1 and FGF-2 support regeneration of the sinusoidal endothelial cells into functional vascular niche thereby accelerating the restoration of hematopoietic stem cells and reconstitution of hematopoiesis. We anticipate that understanding the mechanism by which angiogenic factors regulate the reconstruction of the vascular niche in the bone marrow will offer new strategies to treat hematopoietic failure states, including aplastic anemia, myelodysplastic syndromes and accelerate BM reconstitution after chemotherapy, irradiation and bone marrow transplantation.