Mechanically controlled release of hematopoietic factors from mesenchymal stromal cells for blood regeneration

造血干细胞（Hematopoietic stem cell， HSC）移植已被用作许多造血疾病和恶性肿瘤的标准治疗方法，以实现许多患者的血液再生。然而，为需要同种异体移植的患者获得足够数量的相容HSC来源仍然具有挑战性，因此只有一小部分患者接受了移植。因此，在体外扩增造血干细胞或在体内再生造血干细胞的策略上需要新的进展。多能骨髓间充质基质细胞（MSCs）是骨髓中造血干细胞生态位的主要组成部分，为程序化造血提供关键的调控信号。如何利用间充质干细胞仍然是实现血液再生临床效益的重要目标。生物力学领域的进展表明，天然骨髓环境所表现出的一系列基质刚度在间充质干细胞中引起了深刻的收缩力依赖的生物反应。因此，本提案的目标是评估具有可调基质刚度的生物材料在控制间充质干细胞以促进血液再生中的潜力。总体假设是基质硬度控制MSCs中蛋白质的分泌，进而以旁分泌方式影响造血。具体目标包括：(1)阐明基质刚度依赖性造血因子从间充质干细胞释放的机制。(2)设计可注射的水凝胶微滴，可以封装具有可调基质刚度的单个MSCs。(3)评估水凝胶微滴中MSCs对人体内血液再生的治疗效果。在K99培训期间，该奖项将用于候选人在干细胞力学生物学方面的进一步培训，并使他能够胜任生物材料设计和先进微技术的物理方法。这项研究将在哈佛大学的一个主要生物工程实验室进行，该实验室专注于组织工程的生物材料技术开发和机械转导研究，并与麻省总医院的临床联系密切。这一经历将确保候选人顺利过渡到R00阶段，成为机械生物学和生物工程之间的独立转化研究者，开发新的造血疾病治疗策略。

DESCRIPTION (provided by applicant): Project Summary Hematopoietic stem cell (HSC) transplantation has been used as a standard treatment for a number of hematopoietic disorders and malignancies to achieve blood regeneration in many patients. However, procuring a sufficient number of compatible HSC sources for patients who need allogeneic transplantation remains challenging, and thus only a fraction of the patients undergo transplantation. Therefore, new advances are needed to develop strategies to either expand HSCs ex vivo or regenerate HSCs in vivo. Multipotent bone marrow (BM) mesenchymal stromal cells (MSCs) are the major constituents of the HSC niche in the bone marrow, providing key regulatory signals to program hematopoiesis. How MSCs can be harnessed remains an important goal to achieve clinical benefits for blood regeneration. Advances in the field of biomechanics have revealed that a range of matrix stiffness exhibited by the native BM milieu elicits profound contractile force- dependent biological responses in MSCs. The goal of this proposal is thus to evaluate the potential of biomaterials with tunable matrix stiffness for use in controlling MSCs to facilitate blood regeneration. The overall hypothesis is that matrix stiffness controls secretion of proteins from MSCs, and in turn, influences hematopoiesis in a paracrine manner. The specific aims include: (1) Elucidate mechanisms behind matrix stiffness-dependent release of hematopoietic factors from MSCs. (2) Engineer injectable hydrogel microdroplets that can encapsulate single MSCs with tunable matrix stiffness. (3) Assess the therapeutic effect of MSCs in hydrogel microdroplets on human blood regeneration in vivo. During the K99 training period, this award will be used to further the candidate's training in stem cell mechanobiology, and for him to become competent in physical approaches to biomaterial design and advanced microtechnologies. This research will be conducted in a major bioengineering laboratory at Harvard University that focus on biomaterial-based technology development for tissue engineering and studying mechanotransduction, with close clinical connections at Massachusetts General Hospital. This experience will ensure a smooth transition into the R00 phase for the candidate to become an independent translational investigator at the interface between mechanobiology and bioengineering to develop novel therapeutic strategies for hematopoietic disorders.