Semaphorin signaling regulates vascular and hematopoietic regeneration

项目摘要 造血干细胞（HSC）具有自我更新和维持整个造血系统的能力。 血液和免疫系统在一个人的一生中。HSC维护取决于信号 以及由骨髓（BM）微环境或“生态位”产生的旁分泌因子。HSC再生 在骨髓毒性之后，需要小生境内血管EC的再生。然而，精确 BM EC调节HSC再生的机制仍不完全清楚。阐发 控制HSC再生的机制可能具有重大的医学影响，因为大量的 癌症患者接受HSC消耗高剂量化疗，放疗或 清髓性造血细胞移植治疗其疾病。造血毒性， 这种疗法通常会导致住院、感染并发症和治愈性治疗的延迟。我们 已经确定了一种自分泌机制，其中BM EC分泌一种蛋白质，semaphorin 3A（SEMA 3A）， 这种蛋白质与EC受体NRP 1结合，导致BM EC增加， 死亡和延迟的BM血管再生。我们假设靶向抑制SEMA 3A或其 BM EC上的受体NRP 1将阻断损伤后BM EC中的SEMA 3A-NRP 1信号传导，从而促进 骨髓内皮细胞的再生和造血干细胞所在的骨髓血管生态位。为此，我们建议， 骨髓血管系统的早期恢复将促进HSC再生和早期造血重建 在骨髓抑制之后事实上，我们的初步结果表明，抗体介导的NRP 1抑制 减少照射后骨髓细胞凋亡并加速照射小鼠骨髓血管再生。 重要的是，全身性抗NRP 1治疗还促进白色血细胞、中性粒细胞、 骨髓祖细胞，具有长期再生能力的HSC，并增加受辐射小鼠的存活率。 我们建议利用药理学和细胞特异性遗传模型来表征SEMA 3A的功能 和NRP 1在调节骨髓血管再生和造血再生中的作用。我们还将审问 整合素功能在介导SEMA 3A对BM EC功能的影响中的作用，并将评估 SEMA 3A-NRP 1信号传导对人BM EC功能和人造血再生的调节。 我们广泛的、长期的目标是确定SEMA 3A-NRP 1通路在调节BM血管生成中的作用。 再生作为治疗性人类造血再生的新平台。

Project Summary Hematopoietic stem cells (HSCs) possess the remarkable capacity to self-renew and sustain the entirety of the blood and immune system throughout the lifetime of an individual. HSC maintenance depends upon signals and paracrine factors produced by the bone marrow (BM) microenvironment or “niche.” HSC regeneration following myelotoxicity requires regeneration of vascular ECs within the niche. However, the precise mechanisms through which BM ECs regulate HSC regeneration remain incompletely understood. Elucidation of the mechanisms that govern HSC regeneration could have significant medical impact since a substantial percentage of cancer patients receive HSC-depleting high dose chemotherapy, radiation therapy or myeloablative hematopoietic cell transplantation in the treatment of their disease. Hematopoietic toxicities from such regimens commonly cause hospitalizations, infectious complications and delays in curative therapy. We have identified an autocrine mechanism in which BM ECs secrete a protein, semaphorin 3A (SEMA3A), in response to myelotoxic irradiation, and this protein binds to an EC receptor, NRP1, causing increased BM EC death and delayed BM vascular regeneration. We hypothesize that targeted inhibition of SEMA3A or its receptor, NRP1, on BM ECs will block SEMA3A-NRP1 signaling in BM ECs following injury, thereby facilitating the regeneration of BM ECs and the BM vascular niche wherein HSCs reside. In so doing, we propose that early restoration of the BM vasculature will promote HSC regeneration and early hematopoietic reconstitution after myelosuppression. Indeed, our preliminary results suggest that antibody-mediated inhibition of NRP1 decreases BM apoptosis following irradiation and accelerates BM vascular regeneration in irradiated mice. Importantly, systemic anti-NRP1 treatment also promotes the early recovery of white blood cells, neutrophils, myeloid progenitor cells, HSCs with long-term repopulating capacity, and increases survival of irradiated mice. We propose to utilize pharmacologic and cell-specific genetic models to characterize the functions of SEMA3A and NRP1 in regulating BM vascular regeneration and hematopoietic regeneration. We will also interrogate the role of integrin function in mediating SEMA3A effects on BM EC function and will evaluate the effects of modulation of SEMA3A-NRP1 signaling on human BM EC function and human hematopoietic regeneration. Our broad, long-term objective is to define the role of the SEMA3A-NRP1 pathway in regulating BM vascular regeneration as a novel platform for therapeutic human hematopoietic regeneration.