The mechanobiology of TGF-beta signaling in chondrocytes

描述(申请人提供)：软骨细胞对从压缩到细胞外基质硬度等多个长度尺度的物理信号非常敏感。然而，在骨关节炎中，关节软骨的物理和生物学特性是通过耦合但不清楚的机制被破坏的。尽管细胞外基质硬度的变化是骨关节炎最早可检测到的迹象之一，但软骨细胞微环境中的这些物理变化在多大程度上导致软骨细胞内稳态的丧失尚不完全清楚。细胞通过富含整合素的局部粘连和肌动蛋白产生的细胞骨架张力来感知和响应微环境中的物理提示。细胞骨架张力的变化影响细胞信号和基因表达，进而调节基本的细胞过程，如增殖和分化。例如，细胞骨架张力的变化驱动了转化生长因子引起的Smad3的磷酸化和易位，以控制成软骨基因的表达。虽然细胞骨架张力通过几个生长因子信号通路改变细胞对信号的反应，但导致这种敏感性的分子机制尚不清楚。因此，本项目的目标是确定新的分子机制，通过细胞骨架张力调节转化生长因子ç信号，以及这些机制在软骨对多尺度物理提示的反应中所扮演的角色。为了实现这一目标，拟议的研究将检验这样一种假设，即物理提示通过诱导细胞骨架张力的变化来调节软骨细胞的行为，而细胞骨架张力的变化反过来又影响生长因子受体的定位和功能。目标1将确定细胞骨架张力改变细胞对生长因子的反应的机制。初步数据表明，细胞骨架张力在细胞膜水平上调节转化生长因子？信号，调节转化生长因子？受体、整合素及其效应物之间的物理和功能相互作用。新的分子工具、超分辨率定量成像和生化方法将被用于探索这一可能性。目的2将确定细胞骨架张力是软骨细胞对不同生理信号做出反应的常见机制的程度。利用细胞播种的3D结构，AIM 2扩展了AIM 1中确定的机制，以了解它们在通过转化生长因子？信号维持或丧失软骨细胞内稳中的作用。这项研究的完成将产生新的分子机制，细胞通过这些机制整合物理和生化线索。这一贡献意义重大，因为它将促进分子靶点的识别，使因损伤或疾病而导致的软骨物理退化与软骨细胞内稳态的丧失相分离，以预防或阻止骨关节炎。

DESCRIPTION (provided by applicant): Chondrocytes are acutely sensitive to physical cues across multiple length scales ranging from compression to extracellular matrix stiffness. However, in osteoarthritis, the physical and biological properties of articular cartilage are disrupted through mechanisms that are coupled but unclear. Although changes in extracellular matrix stiffness are among the earliest detectable signs of osteoarthritis, the extent to which these physical changes in the chondrocyte microenvironment contribute to the loss of chondrocyte homeostasis is not fully understood. Cells sense and respond to physical cues in their microenvironment through integrin-rich focal adhesions and actomyosin-generated cytoskeletal tension. Changes in cytoskeletal tension affect cell signaling and gene expression, which in turn, regulate basic cellular processes such as proliferation and differentiation. For example, changes in cytoskeletal tension drive TGFß-induced Smad3 phosphorylation and translocation to control chondrogenic gene expression. Although cytoskeletal tension modifies the cellular response to signaling by several growth factor signaling pathways, the molecular mechanisms responsible for this sensitivity remain unclear. Therefore, the goal of this project is to identify novel molecular mechanisms by which cytoskeletal tension regulates TGFß signaling and the role of these mechanisms in the well-documented response of cartilage to multi-scale physical cues. To achieve this goal, the proposed research will test the hypothesis that physical cues regulate chondrocyte behavior by inducing changes in cytoskeletal tension, which, in turn, influences growth factor receptor localization and function. Aim 1 will identify mechanisms by which cytoskeletal tension alters the cellular response to growth factors. Preliminary data suggest that cytoskeletal tension regulates TGFß signaling at the level of the cell membrane, regulating physical and functional interactions among TGFß receptors, integrins, and their effectors. New molecular tools, super-resolution quantitative imaging, and biochemical approaches will be employed to pursue this possibility. Aim 2 will determine the extent to which cytoskeletal tension is a common mechanism by which chondrocytes respond to diverse physical cues. Using cell-seeded 3D constructs, Aim 2 extends mechanisms identified in Aim 1 to understand their role in the maintenance or loss of chondrocyte homeostasis by TGFß signaling. The completion of this research will yield new molecular mechanisms by which cells integrate physical and biochemical cues. This contribution is significant because it will advance the identification of molecular targets that uncouple the physical degeneration of cartilage, due to injury or disease, from the loss of chondrocyte homeostasis, to prevent or block osteoarthritis.