Effect of NFATs on Chondrocytes

描述（申请人提供）：软骨形成是间充质细胞有序、同步分化为软骨细胞的过程。软骨内成骨是一个决定骨骼生长的软骨细胞分化过程。我们的目标是更好地理解控制(i)间充质细胞对软骨细胞谱系的承诺和（ii）软骨内成骨过程中软骨细胞分化的信号传导和转录途径。为了实现这一目标，我们已经确定了一种诱导软骨形成和软骨细胞基因表达的新途径。在这一途径中，细胞内钙的升高导致(i)钙调磷酸酶和（ii）转录因子，活化t细胞4的核因子（NFAT4）的顺序激活。然后NFAT4进入细胞核，直接诱导BMP-2基因表达。反过来，BMP-2作为自分泌/旁分泌诱导分化。由于钙依赖性信号是由许多生长因子/激素和基本细胞生物学过程诱导的，我们假设钙依赖性激活nfat和诱导BMP表达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NFAT1、2和3对软骨形成和BMP表达的影响；(2)阐明钙调磷酸酶和NFAT4对体内软骨形成和软骨细胞分化的影响；(3)研究NFAT1在软骨形成/软骨细胞基因表达过程中的激酶调控；(4)分析NFAT1和协同转录调控因子对BMP-2基因的转录调控。这些研究将利用我们在初步研究中创建的许多试剂，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变性的新方法。

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.