Modulating signaling pathways in endothelial cells to abate leukemic progression

 描述(申请人提供)：本研究项目的总体目标是确定骨髓(BM)血管壁龛的生理性老化如何导致信号通路的失调，从而导致骨髓血管壁龛和造血干细胞(HSC)之间的细胞串扰中断。在这项建议中，我们的目标是确定与年龄相关的BM血管壁龛改变可以促进血液系统恶性肿瘤进展的机制。我们已经证明，BM内皮细胞(BMECs)中的Akt信号支持HSCs的维持，而与年龄相关的MAPK和NF-kB信号的增加促进HSCs分化为谱系承诺的后代。我们的初步数据表明，MAPK信号在内皮细胞中的过度表达导致HSC过早老化(表型和功能)，而抑制Akt激活的ECs中的NF-kB信号会导致功能性HSC在体内的强劲扩张，从而促进骨髓抑制后的造血恢复。此外，我们还发现，Akt、MAPK和NF-kB信号在体内的BMECs中与AML细胞接触时上调，并且在ECs中Akt的激活可以扩大表型白血病起始细胞，导致侵袭性疾病。基于这一证据，我们假设，老年BMEC中关键信号通路的破坏剥夺了造血系统从EC衍生的指令信号中获得的指令信号，而EC是维持和再生非恶性造血细胞所必需的。为了正式解决这一假说，我们的实验室设计了新的体内和体外模型，使我们能够确定血管内皮细胞特异性信号通路的调节是否可以安全地保护正常的HSC，同时增加白血病细胞对化疗方案的敏感性，有效地为非恶性造血系统提供竞争优势。利用我们的体内小鼠模型和体外指导性小鼠EC/HSC共培养系统，我们将能够测试1)老化的BMEC和异常激活的(MAPK)BMECs是否能够支持侵袭性白血病克隆的生长，2)Akt/NF-kB信号轴的调节是否能够逆转年龄相关的造血缺陷，并为稳定状态和化疗干预后的非恶性造血细胞提供竞争优势，以及3)使用AML体内遗传模型，BM内皮的激活状态是否推动AML的发病。这些研究将开始揭示在老化的骨髓微环境中，骨髓微环境中BMECs的调节失调可能会失去其支持HSC自我更新和分化之间的适当平衡的指导能力的机制。这些研究的成功可能为开发广泛的治疗策略开辟新的途径，这些治疗策略旨在通过增强白血病细胞对化疗方案的敏感性来减少白血病负担和最小残留疾病的有效手段。

 DESCRIPTION (provided by applicant): The overall goal of this research project is to determine how physiological aging of the bone marrow (BM) vascular niche results in a dysregulation of signaling pathways which leads to the disruption of the cellular cross talk between the BM vascular niche and the hematopoietic stem cell (HSC). In this proposal, we aim to define the mechanisms by which age-related alterations to the BM vascular niche can enhance the progression of hematopoietic malignancies. We have demonstrated that Akt signaling in BM endothelial cells (BMECs) supports the maintenance of the HSCs, whereas age-related increases in Mapk and NF-kB signaling promote the differentiation of HSCs into lineage-committed progeny. Our preliminary data demonstrates that the overexpression of Mapk signaling specifically in ECs leads to premature aging (phenotypic and functional) of the HSC and that inhibiting NF-kB signaling in Akt-activated ECs results in a robust in vivo expansion of functional HSCs thereby enhancing hematopoietic recovery following myelosuppression. Additionally, we have found that Akt, Mapk, and NF-kB signaling are upregulated in in vivo BMECs when in contact with AML cells and that Akt-activation in ECs can expand phenotypic leukemia initiating cells leading to aggressive disease. Based on this evidence, we hypothesize that disruption of key signaling pathways in aged BMECs deprive the hematopoietic system from EC-derived instructive signals that are essential for the maintenance and regeneration of non-malignant hematopoietic cells. To formally address this hypothesis, our laboratory has devised novel in vivo and in vitro models that will allow us to determine if modulation of endothelial-specific signaling pathways can "safe guard" normal HSCs while increasing the susceptibility of the leukemic cells to chemotherapeutic regimens, effectively giving a competitive advantage to the non-malignant hematopoietic system. Utilizing our in vivo mouse models and ex vivo instructive mouse EC/HSC co-culture system that can be utilized to assess the growth potential and aggressiveness of leukemic cells grown on various BMEC lines, we will be able to test 1) if aged BMECs and aberrantly activated (Mapk) BMECs can support the outgrowth of aggressive leukemic clones, 2) if modulation of the Akt/NF-kB signaling axis can reverse age-related hematopoietic defects and give a competitive advantage to non-malignant hematopoietic cells at steady state and following chemotherapeutic intervention, and 3) whether the activation state of the BM endothelium drive the onset of AML using an in vivo genetic mouse model of AML. These studies will begin to unravel the mechanisms by which dysregulation of BMECs in an aged BM microenvironment can lose their instructive capacity to support the proper balance between HSC self-renewal and differentiation. The success of these studies may potentially open up new avenues for the development of a wide array of therapeutic strategies designed as an effective means to diminish leukemic burden and minimal residual disease by augmenting the sensitivity of leukemic cells to chemotherapeutic regimens.