调控骨髓微环境的活性材料构建及其促进造血发生的机制研究

Hematopoietic stem cells (HSCs) play a crucial role in the generation of the body’s blood and immune cells. How to obtain more HSCs is a hot topic in the field of tissue regeneration and stem cell. Unfortunately, owing to the extremely complicated haematopoietic microenvironment which is difficult for simulating, conventional in vitro cell proliferation method is usually unsatisfied. Aiming at this bottleneck problems, we raise the academic hypothesis of in vivo constructing the hematopoietic microenvironment by means of biomaterials. In this project, two strategies are formulated for regulating the vascular niche and hematopoietic signaling molecules in order to construct the bone marrow microenvironment which can supports hematopoietic stem cells and promote hematopoiesis. The heterotopic bone induced by the growth factor-loaded biomaterials will be generated and studied as model. The effects of molecular parameters of sulfonated polysaccharide on hematopoiesis in the ectopic bone marrow will be systematically studied, as well as their structure-function relevance relations. Moreover, research will focus on the vascularization effect of biomaterials, and the synergistic effect between materials and hematopoietic cytokines to explore the regulation rule of biomaterials on the heterotopic bone marrow microenvironment, and the molecular mechanism of promotion of hematopoietic stem cells in heterotopic bone. Through the study of this project, the regulation mechanism of biomaterials on the hematopoietic microenvironment will be revealed, and the design criteria for in vivo construction of bone marrow microenvironment for hematopoietic stem cells will be established. Furthermore, the work will provide a fresh thought of facilitating hematopoietic stem cells, and supply experimental basis and theoretic reference for the design of novel materials which can promote hematopoiesis.

造血干细胞在生物体中承担重要作用，如何获取更多的造血干细胞是组织再生及干细胞领域关注的热点问题。但目前常规的体外扩增方法因无法很好模拟体内复杂的造血微环境，难以取得令人满意的效果。本项目针对上述瓶颈问题，提出借助生物材料体内构建造血微环境的学术思想。围绕体内构建支持造血干细胞的骨髓微环境并促进造血发生这一目标，设计了针对血管周龛和造血相关信号分子的两种调控策略，通过材料负载生长因子体内诱导产生的异位骨为模型，深入研究磺化多糖分子参数对异位骨中造血发生的影响规律及构效关系，并进一步从材料的血管化效应、材料与造血相关因子的协同作用等角度探索材料对异位骨骨髓微环境的调控作用及促进异位骨中造血干细胞发生的分子机制。通过本项目研究，揭示生物材料对造血微环境的调控机制，建立体内构建造血干细胞骨髓微环境的设计准则，为促进造血干细胞发生提供研究思路，并为设计制备新型促进造血发生的材料提供理论和实验依据。

干细胞在组织再生中承担重要作用。本项目针对临床上干细胞难以大规模获取的困境，提出利用负载rhBMP-2的活性材料构建体内干细胞发生器（BiG），原位获得功能性干细胞群的设计思路。.研究发现，通过活性材料诱导产生的骨髓微环境中BiG中具有丰富的血管网络，富含H型血管。BiG中富集了包括MSCs与HSCs在内的多种干细胞，其中的MSCs能够形成CFU，且具有完整的成骨、成脂和成软骨分化能力；其中的HSCs能够形成多种CFU，且移植的HSCs能够重建受致死剂量辐照小鼠的造血系统，包括T、B及髓系造血。.通过对BiG不同发生阶段所含细胞分析，证实BiG发生初期含有极高比例的Mφ，特别发现有一类细胞亚群VCAM-1的表达显著高于其他亚群，且呈现出与BiG中HSCs一致的变化趋势，能够促进BiG中HSCs的归巢。生物信息学分析筛选到143个在BiG发生过程中与原位骨髓中具有差异表达蛋白因子，主要集中在细胞趋化与炎症相关通路，表明炎症微环境在BiG的发生过程中至关重要。.单独使用BMP-2诱导产生的BiG中所富集的HSCs的数量与功能仍需要进一步提高和增强。本项目进一步通过在支架材料上引入磺化多糖SCS或SCOS改善BiG中HSCs的数量与功能。研究证实低分子量SCOS能提高BiG中的HSCs含量与自我更新能力，而高分子量的SCS不具备此特性。SCOS处理的BiG中HSCs比例最高，且具有最强的集落形成能力以及最高的长期竞争性重建嵌合率。SCOS一方面能够提高HSCs上EPCR的表达从而增强HSCs在BiG中定植的能力，另一方面能够特异性地提高CD11bhiF4/80hiMφ上VCAM-1的表达从而增强CD11bhiF4/80hiMφ引导HSCs归巢至BiG中的能力。.本研究揭示了生物材料对骨髓微环境的调控机制，为促进造血发生和干细胞治疗提供研究思路，也为设计新型活性材料提供理论和实验依据。