Regulation of Myeloid Development and Function by II-4

说明(申请人提供)：细胞因子IL-4由TH2淋巴细胞、NKT细胞以及包括肥大细胞和嗜酸性粒细胞在内的天然免疫系统的细胞产生。它最初被认为是B细胞增殖的刺激因子，但现在清楚地表明，IL-4可以调节许多类型细胞的增殖、凋亡、基因表达和分化。尤其是对于这一建议，IL-4可以在调节单核巨噬细胞系细胞的分化和功能活性方面发挥关键作用。这类细胞来源于普通的造血祖细胞，可以根据细胞外环境分化为几种具有明显不同特征的细胞类型。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，而另一些属于多核类型，包括多核巨细胞(MNG)和破骨细胞。这些细胞在肉芽肿的形成和骨内环境的稳定中起着关键作用。 已有大量报道描述了IL-4对骨生物学的影响。以前使用共培养系统进行的研究表明，IL-4对成骨细胞和髓系来源的破骨细胞都有复杂的影响。我们利用简化的重组RANKL系统直接检测IL-4对破骨细胞的作用。我们已经证明，IL-4直接阻止RANKL诱导的髓系前体细胞向破骨细胞分化，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STAT6依赖的。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改变有关。在这些研究的基础上，我们的具体目标是了解IL-4调节髓系前体细胞发育远离破骨细胞命运并抑制成熟破骨细胞功能活性的分子机制。我们推测，IL-4通过以下3个不同的步骤抑制破骨细胞的发育和功能：(1)调节发育中的前体细胞的基因表达谱，改变多潜能前体细胞的分化命运；(2)影响承诺前体细胞的RANK启动反应；(3)抑制成熟破骨细胞的骨吸收活性。验证这一假说的具体目的是：(1)确定负责IL-4介导的髓系祖细胞命运的STAT6调节基因的特征；(2)确定IL-4激活的STAT6通路调节承诺祖细胞RANK诱导反应的机制；(3)分析IL-4调节成熟破骨细胞功能的机制。这些目标的完成将加深我们对IL-4调节髓系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.