Constrained Fetal Hematopoiesis and Clonal Restriction in Fanconi Anemia

总结 本研究基于Fanconi贫血（FA）的发病机制， 蛋白质保护造血干细胞（HSC）在快速发育过程中免受复制应激 胎儿肝脏（FL）扩张。FA是一种遗传性DNA修复障碍，具有癌症易感性 和几乎一致的骨髓（BM）衰竭。虽然大多数FA患者在早期出现症状性失败， 在学龄期，骨髓造血干细胞（HSC）数量在生命的早期就已经受到损害。我们 最近报道，FA基因敲除小鼠HSC缺陷的生理发作发生在子宫内。我们现在 显示FA缺陷首先出现在FL中，由复制应激相关Atr/Chk 1检查点引起 参与免疫表型定义的HSC。因为HSC池通常在出生时就已经完成， 这些限制不仅构成了以前未认识到的FA中HSC池形成的瓶颈， 也是造成出生后HSC快速衰竭的主要危险因素。为了理解夸张的 我们已经对FL进行了额外的初步研究 这些微环境涉及形成HSC小生境的支持细胞的子集。委员会共 假设FA蛋白的生理作用是保护HSC库的克隆性和基因组 在复制应力条件下的完整性。这些观察使我们能够测试 FA对HSC自我更新和造血储备的胎儿缺陷。 具体目标1：确定绝对HSC池大小和克隆多样性作为以下疾病的驱动风险因素： FA中HSC耗竭 具体目标2：分析检查点激活对基因组稳定性的长期影响， 胎儿FA HSC功能 具体目标3：识别导致造血缺陷的FL特异性生态位异常 在FA中，并揭示了功能性限制HSC扩增的关键信号通路 总而言之，该项目提出了一个新的范式，即FA蛋白使发育扩展 自我更新分裂对HSC库中的克隆多样性和基因组稳定性至关重要。这确定 FA患者的发育缺陷是HSC衰竭的驱动风险因素，也是 发病率和死亡率。结果将为开发安全有效的新疗法提供见解 减轻FA中造血功能的丧失。

Summary This proposal explores a new model of Fanconi Anemia (FA) pathogenesis based on our findings that FA proteins protect hematopoietic stem cells (HSCs) from replication stress during the rapid developmental expansion in the fetal liver (FL). FA is a recessively inherited DNA repair disorder with cancer predisposition and near uniform bone marrow (BM) failure. While most FA patients experience symptomatic failure in early school age, BM hematopoietic stem cell (HSC) numbers are already compromised much earlier in life. We recently reported that the physiologic onset of HSC deficits in FA knockout mice occurs in utero. We now show that deficits in FA first emerge in the FL, caused by replication stress-associated Atr/Chk1 checkpoint engagement in immunophenotypically defined HSC. Because the HSC pool is typically complete at birth, these constraints constitute not only a previously unrecognized bottleneck for HSC pool formation in FA, but also pose a principal risk factor for rapid postnatal HSC exhaustion. To understand the exaggerated developmental vulnerability in the FA FL we have conducted additional preliminary studies of the FL microenvironment that implicate a subset of supportive cells forming the HSC niche. Altogether, we hypothesize that the physiological role of FA proteins is to safeguard in HSC pool clonality and genome integrity under conditions of replication stress. These observations lead us to test the long-term impact of fetal deficits in FA on HSC self-renewal and hematopoietic reserve. Specific Aim 1 ïDetermine absolute HSC pool size and clonal diversity as driving risk factors for HSC exhaustion in FA Specific Aim 2 ïDissect the long-term impact of checkpoint activation on genome stability and function in fetal FA HSC Specific Aim 3 ïIdentify the FL specific niche abnormalities that contribute to hematopoietic deficits in FA, and reveal the key signaling pathways that functionally limit HSC expansion Altogether, this project advances a new paradigm, whereby FA proteins enable developmental expansion and self-renewal divisions critical to clonal diversity and genome stability in the HSC pool. This positions developmental deficits in FA patients as a driving risk factor for HSC exhaustion and a critical cause for morbidity and mortality. Results will provide insight for the development of safe and effective new therapies that mitigate loss of hematopoietic function in FA.