Contribution of the vascular niche to the hematopoietic reconstitution.

描述（由申请人提供）：本研究组和其他研究组的累积证据表明，骨髓（BM）窦状内皮细胞（SEC）代表一种动态“血管生态位”，可为骨髓抑制后造血重建提供细胞平台。利用骨髓（BM）制备技术的进步，我们最近建立了一个全面的表型和功能签名的BM SEC在稳态和血管生成再生。我们最近发现，在中度至重度骨髓抑制后，消退的SEC的快速再生对于移植的长期造血干细胞（LT-HSC）的植入和补充以及造血重建是必不可少的。最有可能的是，移植的HSC及其谱系定向造血祖细胞（HPC）通过释放新血管生成因子而有助于SEC的再生。然而，由促血管生成造血细胞释放的血管生成因子（如CXCR 4 + VEGFR 1+骨髓和巨核细胞祖细胞）支持SEC重建的确切机制尚不清楚。该提议的广泛的长期目标是鉴定分子途径并定义血管生成因子，特别是由造血细胞的特定亚群精心制作的VEGF-A同种型、PlGF和SDF 1支持BM的“血管龛”的组装和重塑的机制，从而支持造血干细胞的重建和骨髓抑制后的造血。因此，我们假设在BM内，VE-钙粘蛋白+VEGFR 2 + VEGFR 3 + Sca 1-SEC建立了血管生态位，这是造血干细胞重建和骨髓抑制后造血所必需的动态细胞微环境。通过释放VEGF-A SDF-1和尚未识别的血管生成因子再生促血管生成CXCR 4 + VEGFR 1+造血细胞加速SEC的再生，从而加速LT-HSC的重建和造血。1）确定促血管生成造血细胞通过阐述VEGF-A和SDF-1支持退化SEC再生从而重建LT-HSC和造血的机制：2）评估预先存在的CXCR 4+内皮细胞相对于移植的CXCR 4 + VEGF 1+造血细胞对缺血肢体的血管再生的相对贡献，以及3）评估血管生成因子的增强表达在加速BM SEC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自我更新的机制将提供新的策略来治疗BM衰竭状态，包括再生障碍性贫血，骨髓增生异常综合征和加速化疗，放疗和移植后的BM重建。 公共卫生相关性：我们假设骨髓的血管龛是一个动态的细胞微环境，对骨髓抑制后造血的维持和重建至关重要。通过释放血管生成因子（包括VEGF-A、PlGF、SDF-1和FGF-2）再生CXCR 4 + VEGFR 1+造血细胞支持窦状隙内皮细胞再生为功能性血管龛，从而加速造血干细胞的恢复和造血重建。我们预期，了解血管生成因子调节骨髓血管生态位重建的机制将为治疗造血功能衰竭状态提供新的策略，包括再生障碍性贫血，骨髓增生异常综合征和加速化疗，放疗和骨髓移植后的BM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.