Effect of NFATs on Chondrocytes

描述（由申请人提供）：软骨发生是间充质细胞有序和同步分化为软骨细胞的过程。软骨内骨化是决定骨骼生长的软骨细胞分化过程。我们的目标是更好地了解控制（i）间充质细胞向软骨细胞谱系的定向分化和（ii）软骨内骨化过程中软骨细胞分化的信号传导和转录途径。在追求这一目标，我们已经确定了一种新的途径，诱导软骨形成和软骨细胞基因表达。在该途径中，细胞内钙的升高引起（i）钙调磷酸酶和（ii）转录因子、活化T细胞核因子4（NFAT 4）的顺序活化。然后NFAT 4进入细胞核并直接诱导BMP-2基因表达。反过来，BMP-2充当分化的自分泌/旁分泌诱导剂。由于钙依赖性信号传导由许多生长因子/激素和基本细胞生物学过程诱导，我们假设NFAT的钙依赖性活化和BMP表达的诱导是调节软骨形成和软骨细胞分化的中心途径。为了验证这一假设并进一步了解软骨细胞分化，我们将追求以下具体目标：（1）确定NFAT 1、2和3对软骨形成和BMP表达的作用，（2）阐明钙调神经磷酸酶和NFAT 4对体内软骨形成和软骨细胞分化的作用，（3）研究软骨形成/软骨细胞基因表达期间NFAT的激酶控制，和（4）分析NFAT和转录的协同调节物对BMP-2基因的转录控制。这些研究将利用我们在初步研究期间创建的许多试剂，并将从根本上推进我们对软骨形成和软骨细胞分化的理解。我们预计这些研究将提出促进软骨再生或抑制软骨退化的新方法。

DESCRIPTION (provided by applicant): Chondrogenesis is a process of ordered and synchronous differentiation of mesenchymal cells into chondrocytes. Endochondral ossification is a process of chondrocyte differentiation that determines skeletal growth. Our goal is to better understand the signaling and transcriptional pathways that control (i) commitment of mesenchymal cells to the chondrocyte cell lineage and (ii) the differentiation of chondrocytes during endochondral ossification. In the pursuit of this goal, we have identified a novel pathway that induces chondrogenesis and chondrocyte gene expression. In this pathway, elevation of intracellular calcium causes sequential activation of (i) calcineurin and (ii) the transcription factor, nuclear factor of activated T-cell 4 (NFAT4). NFAT4 then enters the nucleus and directly induces BMP-2 gene expression. In turn, BMP-2 acts as an autocrine/paracrine inducer of differentiation. Because calcium-dependent signaling is induced by many growth factors/hormones and basic cell biological processes, we hypothesize that calcium-dependent activation of NFATs and induction of BMP expression is a central pathway regulating chondrogenesis and chondrocyte differentiation. To test this hypothesis and further our understanding of chondrocyte differentiation we will pursue the following Specific Aims: (1) determine the effects of NFAT1, 2, and 3 on chondrogenesis and BMP expression, (2) elucidate the effect of calcineurin and NFAT4 on chondrogenesis and chondrocyte differentiation in vivo, (3) investigate the kinase control of NFATs during chondrogenesis/chondrocyte gene expression, and (4) analyze the transcriptional control of the BMP-2 gene by NFATs and cooperating regulators of transcription. These studies will utilize many reagents created during our preliminary studies and will fundamentally advance our understanding of chondrogenesis and chondrocyte differentiation. We anticipate that these studies will suggest novel ways to promote cartilage regeneration or suppress cartilage degeneration.