Substrate stiffness and the role of actin in regulating chondrocyte dedifferentiation

关节软骨覆盖在骨骼的末端，便于关节的运动和力的传递。骨性关节炎是一种以软骨丧失为特征的关节疾病，表现为疼痛、僵硬和活动范围丧失，大约每6名加拿大人中就有1人在15岁以上致残。软骨受损时几乎没有修复能力。目前的治疗方法只是缓解症状，并不能阻止疾病的发展，因此最终受损的关节将需要用假肢进行关节置换。这些都是由金属和塑料制成的，最终都会失败。显然，非常需要新的生物细胞疗法来修复/替换受损的软骨，使关节功能和健康完全恢复正常。 这些治疗所需的细胞可以从多种来源获得，例如关节软骨本身或干细胞。干细胞不适合，因为到目前为止，还不可能将这些细胞分化为关节软骨细胞，以形成合适的软骨。关节软骨是最理想的细胞来源，但软骨细胞数量太少，无法使用。当它们在培养中生长以增加细胞数量时，它们失去了形成软骨的能力，因为有利于增殖的条件会导致软骨细胞去分化(丧失关节软骨细胞的特征)。这可能是因为培养皿比天然软骨更硬。因此，我们研究计划的长期目标是了解在培养中生长的细胞如何调节关节软骨细胞的表型。我们有证据表明，肌动蛋白，细胞的骨架，调节细胞表型。这项拟议的研究将探讨肌动蛋白细胞骨架的聚合是否通过激活调节软骨细胞去分化的特定信号转导通路来转换外源性底物刚性的影响。了解软骨细胞去分化的调控机制将有助于材料的设计和/或新药的开发，以确保有可能增加关节软骨细胞的数量，并仍然拥有能够修复软骨缺陷的细胞和合适的关节软骨组织。这将促进我们对软骨细胞表型的理解，以及将再生医学方法应用于软骨修复和恢复关节健康的临床翻译。此外，这些研究还可能导致开发治疗骨性关节炎的新疗法。

Articular cartilage covers the ends of bone facilitating joint movement and transfer of forces. Osteoarthritis is a disease of joints characterized by loss of the cartilage, and manifests as pain, stiffness and loss of range of motion disabling approximately 1 in 6 Canadians over the age of 15. Cartilage has little ability to repair when damaged. Current treatments alleviate symptoms only and do not stop disease progression so ultimately the damaged joint will require joint replacement with a prosthesis. These are made from metals and plastic and will ultimately fail. Clearly there is a great need for novel biological cell therapies to repair/replace the damaged cartilage that will fully restore joint function and health to normal. The cells required for these treatments can be obtained from a number of sources, such as articular cartilage itself or from stem cells. Stem cells are not suitable as differentiation of these cells to articular chondrocytes that make proper cartilage has not been possible to date. Articular cartilage is the optimal source of cells but chondrocytes, the cells of cartilage, are too few in number to use. When they are grown in culture to increase cell number they lose their ability to make cartilage as conditions that favour proliferation results in chondrocyte dedifferentiation (loss of articular chondrocyte characteristics). This may be due to the fact that the culture dish is more stiff than native cartilage. Thus the long term goal of our research program is to understand how growing cells in culture modulates the articular chondrocyte phenotype. We have evidence that actin, the skeleton of the cell, regulates cell phenotype. The proposed studies will examine whether polymerization of the actin cytoskeleton is responsible for translating the effects of the extrinsic substrate stiffness by activating specific signal transduction pathways that modulate chondrocyte dedifferentiation. Understanding the mechanisms regulating chondrocyte dedifferentiation will facilitate design of materials and/or the development of novel drugs that will ensure that it will be possible to increase articular chondrocyte numbers and still have cells that can repair cartilage defects with proper articular cartilage tissue. Accomplishing this will advance our understanding of chondrocyte phenotype as well as the clinical translation of regenerative medicine approaches to cartilage repair and restoration of joint health. Also these studies could lead to the development of novel therapeutics to treat osteoarthritis.