Embryonic origin and self-renewal of B-1a cells

项目摘要/摘要 B-1细胞是小鼠的先天免疫B细胞，优先定位于腹膜腔，分泌 天然抗体以T细胞不依赖的方式，在对抗病毒的第一道防线中发挥重要作用 细菌或病毒感染、败血症和动脉粥样硬化。尽管B-1细胞在宿主防御中的重要性 和动态平衡，它们的发育起源尚不清楚。驻留在腹膜腔内的CD5+B-1a细胞 通过移植胎肝(FL)祖细胞而不是成人骨髓(BM)重建 造血干细胞(HSC)。因此，B-1a细胞被认为是胎儿起源的，其机制是 在成人生活中维持B-1a细胞而不被成人HSCs补充尚未被阐明。整体而言 该项目的目标是确定不依赖于HSC的胚胎B-1祖细胞对 成人腹膜B-1a细胞，并确定在成人一生中维持B-1a细胞的机制。 我们已报道存在来源于血源性内皮细胞的B-1祖细胞 (HECS)在HSC缺陷小鼠模型的卵黄囊(YS)。我们最近的初步数据表明， 胎肝HSCs移植后B-1a细胞重组不良。因此，我们假设腹膜B- 1细胞来源于HECs，在发育的任何阶段完全独立于HSCs的贡献 或者成年后的生活。在目标1中，我们将利用一种血统追踪小鼠模型，在该模型中，人们可以标记HEC及其 在HSC出现之前的特定胚胎时间点通过他莫昔芬诱导子代，我们将 补充这一方法，从胎儿到新生儿和成人期的HSC移植测试证明 B-1a细胞池中没有HSCs的贡献。在AIM2中，我们将询问分子机制 在一生中维持胚胎来源的B-1a细胞的自我补充能力。BMI1是一个多梳的 对造血干细胞自我更新至关重要的组蛋白。我们现在报告说， Bmi1-/-和CD19Cre：Bmi1flx/Flox B-1a细胞受损，提出了Bmi1发挥重要作用的假设 在B-1a细胞自我更新中。由于Bmi1-/-小鼠表现出明显更严重的B-1a细胞减少 与CD19Cre：Bmi1flx/FLOX小鼠相比，我们假设B-1a细胞微环境可能是 在Bmi1-/-小鼠身上发生了改变。我们将研究B-1细胞的利基，B-1细胞是最近报道的脂肪相关淋巴样细胞 在Bmi1-/-小鼠中，大网膜和肠系膜中有簇状细胞(FALC)。我们还将追求下游的目标 BMI1在B-1a自我更新中发挥作用。这些实验考虑了细胞的内在和外在角色 BMI1以确定其在B-1a细胞维护和自我更新中的关键作用。我们的结果将建立一个新的 为了解B-1细胞在小鼠体内的发育和维持提供了新的工具 转化为人类对B-1样细胞的研究。 1

PROJECT SUMMARY/ABSTRACT B-1 cells are murine innate immune B cells that preferentially localize in the peritoneal cavity, secrete natural antibodies in a T cell independent manner, and play important roles in the first line of defense against bacterial or viral infections, sepsis, and atherosclerosis. Despite the importance of B-1 cells in host defense and homeostasis, their developmental origin is not clear. CD5+B-1a cells residing in the peritoneal cavity can be reconstituted by transplantation of fetal liver (FL) progenitors, but not by adult bone marrow (BM) hematopoietic stem cells (HSCs). Thus B-1a cells are considered to be of fetal origin and the mechanisms that maintain B-1a cells in adult life without being replenished by adult HSCs have yet to be elucidated. The overall goal of the project is to determine the contribution of HSC-independent embryonic B-1 progenitor cells into the adult peritoneal B-1a cells and define the mechanisms that maintain B-1a cells throughout adult life. We have reported the presence of B-1 progenitor cells originated from hemogenic endothelial cells (HECs) in the yolk sac (YS) in an HSC-deficient mouse model. Our recent preliminary data demonstrated that fetal liver HSCs poorly reconstituted B-1a cells upon transplantation. Thus, we hypothesize that peritoneal B- 1a cells are derived from HECs and are totally independent of HSCs contributions at any stage of development or adult life. In Aim 1, we will utilize a lineage tracing mouse model where one can mark HECs and their progeny at a specific embryonic time point before HSC emergence by tamoxifen induction and we will supplement this approach with HSC transplantation assays from fetus to neonatal and adult stages to prove there is no contribution of HSCs into the B-1a cell pool. In Aim2, we will interrogate the molecular mechanisms that maintain the self-replenishing ability of embryonic derived B-1a cells throughout life. Bmi1 is a polycomb group protein that is critical for self-renewal of HSCs. We now report that the self-replenishing capacity of Bmi1-/- and CD19Cre:Bmi1flox/flox B-1a cells is impaired, raising the hypothesis that Bmi1 plays an important role in B-1a cell self-renewal. Since Bmi1-/- mice displayed a significantly more severe reduction in B-1a cell number compared to CD19Cre:Bmi1flox/flox mice, we hypothesize that the B-1a cell microenvironment may be altered in Bmi1-/- mice. We will examine a niche for B-1 cells, the recently reported fat-associated lymphoid clusters (FALCs) in the omentum and mesentery, in Bmi1-/- mice. We will also pursue a downstream target of Bmi1 as playing a role in B-1a self-renewal. These experiments consider cell intrinsic and extrinsic roles of Bmi1 to define its critical role in B-1a cell maintenance and self-renewal. Our results will establish a new paradigm for understanding B-1 cell development and maintenance in mice and will provide new tools to translate to human investigation of B-1 like cells. 1