Contribution of the vascular niche to the hematopoietic reconstitution.

描述(申请人提供)：来自我们团队和其他人的越来越多的证据表明，骨髓(BM)窦状内皮细胞(SECs)代表着一个动态的“血管生态位”，这可能为骨髓抑制后重建造血提供细胞平台。利用骨髓(BM)制备技术的进步，我们最近建立了BM Secs在稳定状态和血管再生过程中的全面表型和功能特征。我们最近发现，在中度到重度骨髓抑制后，退化的SECs的快速再生对于移植的长期造血干细胞(LT-HSCs)的植入和补充以及重建造血是必不可少的。最有可能的是，移植的HSC及其谱系通过释放新的血管生成因子而承诺的造血祖细胞(HPC)有助于SEC的再生。然而，促血管生成的造血细胞，如CXCR4+VEGFR1+髓系细胞和巨核系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。这一建议的长期目标是确定分子途径，并确定血管生成因子，特别是由特定的造血细胞亚群所阐述的血管生成因子，尤其是血管生成因子、PlGF和SDF1，以支持骨髓抑制后HSCs的重建和造血。因此，我们推测，在骨髓中，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是必不可少的。促血管生成的CXCR4+VEGFR1+造血细胞通过释放VEGF-A SDF-1来再生，而未知的血管生成因子可以加速SEC的再生，从而加速LT-HSCs的重建和造血。该假说将通过以下方面得到验证：1)确定促血管生成的造血细胞通过表达VEGF-A和SDF-1支持退化的SEC再生，从而重建LT-HSCs和造血的机制：2)评估预先存在的CXCR4+内皮细胞和移植的CXCR4+VEGFR1+造血细胞在缺血肢体血运重建中的相对贡献；3)评估血管生成因子增强表达在加速BM SEC再生和重建造血中的生理学意义。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包括再生障碍性贫血、骨髓增生异常综合征在内的骨髓衰竭状态提供新的策略，并加速化疗、放疗和移植后的骨髓重建。 公共卫生相关性：我们假设骨髓的血管生态位是一个动态的细胞微环境，对于骨髓抑制后造血的维持和重建是必不可少的。CXCR4+VEGFR1+造血细胞通过释放血管生成因子，包括VEGF-A、PlGF、SDF-1和FGF-2，支持肝窦内皮细胞向功能性血管内皮细胞的再生，从而加速造血干细胞的恢复和造血的重建。我们预计，了解血管生成因子调节骨髓中血管生态位重建的机制将为治疗包括再生障碍性贫血、骨髓增生异常综合征在内的造血衰竭状态提供新的策略，并加速化疗、放疗和骨髓移植后的骨髓重建。

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.