Reconstitution of thrombopoiesis by angiogenic factors

描述(申请人提供)：谱系特异性细胞因子，包括血小板生成素(TPO)，不能重建辐射引起的骨髓抑制的早期阶段，导致长期威胁生命的血小板减少和出血并发症。这项建议的长期目标是证明具有趋化活性的促血管生成因子，包括基质衍生因子-1(SDF-1)、SDF-1类似物(CTCE-0214，趋化因子治疗)、成纤维细胞生长因子-4和成纤维细胞生长因子-20(CG53135，CuraGen)、Kit-Ligand(Amgen)、血管内皮生长因子-A和血管生成素-1，通过快速再生骨髓(BM)血管壁龛和募集干细胞和祖细胞，可以在高剂量辐射暴露后恢复血小板生成，促进移植骨髓的植入。在骨髓中，造血干细胞和祖细胞存在于特定的“小生境”中，在那里它们接受增殖和分化的分子和细胞指令。我们已经证明，将巨核祖细胞招募到骨髓的血管壁龛，支持它们分化为功能性血小板。骨髓照射不仅能诱导造血干细胞的快速凋亡，而且还会破坏骨髓的血管微环境。这会导致骨髓移植后长期的危及生命的血小板减少和植入失败。在这些研究的基础上，我们假设具有干细胞和祖细胞趋化因子活性的血管生成因子，如SDF-1，FGF-4及其类似物，通过血管壁龛的快速重建，加速了血小板的生成，从而防止了威胁生命的辐射诱导的血小板减少。此外，血管生成因子，包括血管内皮生长因子-A、Kit-Ligand和Angiopoietin-1，通过促进血管壁龛的再生和稳定，不仅有助于迅速恢复血栓生成，而且支持移植的干细胞植入，从而促进照射后的血栓生成恢复。这些目标将通过执行下列临床前机制研究来实现：1)评估促血管生成趋化因子在促进辐射诱导的骨髓抑制后的血小板生成中的潜力：2)确定血管生成因子VEGF-A、可溶性Kit-L和Angiopoietin-1在BM的血管生态位再生中的作用，以恢复照射后的血小板恢复3)评估FGFs、VEGF-A和Kit-Land对BM微环境的预适应对促进BM移植到照射后的BM内的干细胞植入的有效性。我们预计SDF-1类似物、CTCE-0214(趋化因子治疗)、成纤维细胞生长因子-20(CuraGen，CG53135)、Kit-Ligand和即将到来的临床级别促血管生成因子将提供平台，用于评估这些药物在改善和快速恢复放射引起的血小板减少方面的作用，因为它可能是由于核坠落造成的。暴露在辐射下会对骨髓造成重大损害，从而导致血液生产的失败。这会导致严重的危及生命的出血和感染。目前，可以促进血液生成的因素，特别是血小板，在恢复骨髓功能方面并不有效。我们发现了特定的“血管生成”因子，通过激活骨髓中血管的形成，也会诱导血小板的快速生成，从而改善与高剂量辐射暴露相关的致命出血并发症。此外，通过促进血管的快速组装，这些血管生成因子为移植的干细胞植入骨髓微环境提供了肥沃的土壤。这将促进血液生产和血小板恢复。总而言之，我们预测，我们的研究将确定传递这些血管生成因子的最佳方法，以恢复血液生产、血小板恢复和增加干细胞植入，从而减少与核脱落相关的并发症。

DESCRIPTION (provided by applicant): Lineage-specific cytokines, including thrombopoietin (TPO), fail to reconstitute early phases of myelosuppression induced by irradiation, leading to prolonged life-threatening thrombocytopenia and bleeding complications. The long-term objective of this proposal is to demonstrate that pro- angiogenic factors with chemotactic activity, including Stromal Derived Factor-1 (SDF-1), SDF-1 analogue (CTCE-0214, Chemokine Therapeutics), FGF-4 and FGF-20 (CG53135, CuraGen), Kit-ligand (Amgen), VEGF-A and angiopoietin-1 by rapid regeneration of the bone marrow's (BM) vascular niche and recruitment of stem and progenitor cells could restore thrombopoiesis and facilitate engraftment of transplanted BM, after high dose radiation exposure. Within the BM, hematopoietic stem and progenitor cells reside in defined "niches", where they receive molecular and cellular instructions for proliferation, and differentiation. We have shown that recruitment of the megakaryocytic progenitors to the BM's vascular niche, supports their differentiation into functional platelets. Irradiation exposure to the BM not only induces rapid apoptosis of hematopoietic stem cells, but also damages the BM's vascular microenvironment. This leads to long-lasting life-threatening thrombocytopenia and engraftment failure after BM transplantation. Based on these studies, we hypothesize that angiogenic factors with stem and progenitor chemokine activity, such as SDF-1, FGF-4 and their analogues by rapid reconstitution of the vascular niche accelerates thrombopoiesis thereby protecting against life-threatening radiation-induced thrombocytopenia. In addition, angiogenic factors, including VEGF-A, Kit-ligand and angiopoietin-1 by enhancing the regeneration and stabilization of the vascular niche not only contribute to rapid restoration of thrombopoiesis, but also support engraftment of transplanted stem cells thereby augmenting restoration of thrombopoiesis after irradiation. These goals will be achieved through executing the following pre-clinical mechanistic studies: 1) Assess the potential of pro-angiogenic chemokines in accelerating thrombopoiesis after radiation-induced myelosuppression: 2) Determine the role of the angiogenic factors, VEGF-A, soluble Kit-ligand and angiopoietin-1, in regeneration of the BM's vascular niche to restore platelet recovery after irradiation 3) Evaluate the effectiveness of pre-conditioning of the BM microenvironment with FGFs, VEGF-A and Kit-ligand to accelerate regeneration of the vascular niche to enhance engraftment of stem cells after BM transplantation into the irradiated BM. We anticipate that clinical availability of the SDF-1 analogue, CTCE-0214 (Chemokine Therapeutics), FGF-20 (CuraGen, CG53135), Kit-ligand and upcoming clinical grade pro-angiogenic factors that are currently being evaluated in phase I clinical trials, would provide the platform for assessing the role of these agents in amelioration and rapid restoration of thrombocytopenia induced by irradiation as it might occur as a consequence of a nuclear fall out. Exposure to irradiation results in major damage to the bone marrow resulting in failure in blood production. This leads to development of major life-threatening bleeding and infection. Currently, the factors that could promote blood production, specifically platelets, are not effective in restoring bone marrow's function. We have discovered specific "angiogenic" factors that by activating the formation of the blood vessels in the bone marrow will also induce rapid generation of platelets thereby ameliorating fatal bleeding complications associated with high doses of radiation exposure. Furthermore, these angiogenic factors by facilitating rapid assembly of the blood vessels provide for a fertile ground for the engraftment of transplanted stem cells into the bone marrow's microenvironment. This will result in enhanced restoration of blood production and platelet recovery. Collectively, we predict that our studies will determine the optimal means to deliver these angiogenic factors to restore blood production, platelet recovery and augment stem cell engraftment thereby diminishing complications associated with a nuclear fall out.