Regulation of Myeloid Development and Function by II-4

描述（由申请人提供）：细胞因子IL-4由TH 2淋巴细胞、NKT细胞和先天免疫系统的细胞（包括肥大细胞和嗜酸性粒细胞）产生。它最初被鉴定为B细胞增殖的刺激物，但现在清楚的是，IL-4可以调节许多细胞类型中的增殖、凋亡、基因表达和分化。特别是对于该提议，IL-4可以在调节单核细胞-巨噬细胞谱系的细胞的分化和功能活性中发挥关键作用。这些细胞来源于常见的造血祖细胞，并且可以根据细胞外环境分化成具有明显不同特征的几种细胞类型。这些细胞类型中的一些是单核细胞，如树突状细胞和巨噬细胞，而其他细胞类型则属于多核类别，包括多核巨细胞（MNG）和破骨细胞。这些细胞可以在肉芽肿形成和骨稳态中发挥关键作用。 已经有许多报道描述了IL-4对骨生物学的影响。以前的研究，使用共培养系统进行，已经证明了IL-4对成骨细胞和髓源性破骨细胞的复杂作用。我们利用重组RANKL的简化系统直接测试IL-4对破骨细胞的作用。我们已经表明，IL-4直接阻止RANKL诱导的骨髓前体细胞向破骨细胞的分化，同时促进巨细胞的形成。此外，我们发现IL-4抑制成熟破骨细胞的骨吸收，这些反应是STAT 6依赖性的。我们发现IL-4对祖细胞的抑制作用是不可逆的，并且与基因表达模式的变化有关。基于这些研究，我们的具体目标是了解IL-4调节髓样前体细胞远离破骨细胞命运的发展和抑制成熟破骨细胞的功能活性的分子机制。我们假设IL-4通过在该过程中的3个不同步骤起作用来抑制破骨细胞的发育和功能，即（1）调节发育中的祖细胞中的基因表达谱，改变多能前体的分化命运，（2）影响定向祖细胞中RANK启动的反应，以及（3）抑制成熟破骨细胞的骨吸收活性。旨在检验这一假设的具体目的是（1）表征负责IL-4介导的骨髓祖细胞命运控制的STAT 6调节基因，（2）确定IL-4激活的STAT 6途径调节定向祖细胞中RANK诱导反应的机制，以及（3）分析IL-4调节成熟破骨细胞功能的机制。这些目标的完成将增强我们对IL-4调节骨髓细胞发育和功能的机制的理解。

DESCRIPTION (provided by applicant): The cytokine IL-4 is produced by TH2 lymphocytes, NKT cells, and by cells of the innate immune system including mast cells, and eosinophils. It was originally identified as a stimulator of B cell proliferation, but it is now clear that IL-4 can regulate proliferation, apoptosis, gene expression, and differentiation in many cell types. In particular for this proposal, IL-4 can play a critical role in regulating the differentiation and functional activity of cells of the monocyte-macrophage lineage. Such cells are derived from common hematopoietic progenitors and can differentiate into several cell types with markedly distinct characteristics depending on the extracellular environment. Some of these cell types are mononuclear, such as dendritic cells and macrophages, while others fall into the multinucleated category including multinucleated-giant cells (MNG), and osteoclasts. These cells can play critical roles in granuloma formation and in bone homeostasis. There have been numerous reports describing effects of IL-4 on bone biology. Previous studies, performed using co-culture systems, have demonstrated complex effects of IL-4 on both osteoblasts and myeloid-derived osteoclasts. We took advantage of a simplified system using recombinant RANKL to directly test the effect of IL-4 on osteoclasts. We have shown that IL-4 directly prevents the RANKL-induced differentiation of myeloid precursors to osteoclasts while promoting the formation of giant cells. Furthermore, we found that IL-4 inhibits bone resorption by mature osteoclasts; these responses were STAT6-dependent. We found that the inhibitory effect of IL-4 on progenitors is irreversible and is associated with changes in gene expression patterns. Based on these studies, our specific goal is to understand the molecular mechanisms by which IL-4 regulates the development of myeloid precursors away from the osteoclast fate and suppresses the functional activity of mature osteoclasts. We hypothesize that IL-4 inhibits osteoclast development and function by acting at 3 different steps in the process by (1) regulating gene expression profiles in the developing progenitors altering the differentiation fate of a multipotential precursor, (2) influencing RANK-initiated responses in committed progenitors, and (3) suppressing the bone resorbing activity of mature osteoclasts. The specific aims designed to test this hypothesis are (1) to characterize the STAT6-regulated genes responsible for the IL-4-mediated control of myeloid progenitor fate, (2) to determine the mechanism by which the IL-4-activated STAT6 pathway regulates RANK-induced responses in committed progenitors, and (3) to analyze the mechanism by which IL-4 regulates mature osteoclast function. Completion of these aims will enhance our understanding of the mechanisms by which IL-4 regulates myeloid cell development and function.