Zone of Calcified Cartilage – a Natural Boarder in the Osteochondral Unit to Control Diffusion of Molecules between Articular Cartilage and Subchondral Bone

骨关节炎(OA)是世界上最常见的关节疾病，超过20%的德国社会患有这种疼痛和致残的疾病。骨性关节炎期间的生理和病理变化包括软骨组织的退化和侵蚀，直到下面的骨暴露。为了干预本病的进展，迫切需要在分子、细胞和组织水平上更好地了解骨软骨单位，特别是钙化层(ZCC)的机制。ZCC正在将未钙化的关节软骨深层连接到软骨下骨。然而，对ZCC在软骨内稳态中的作用知之甚少，ZCC是健康组织的稳定状态。我假设ZCC是一个自然边界，控制着软骨和骨组织之间的分子扩散，并调节细胞与细胞之间的通讯。这种通透性在骨性关节炎发作时发生改变，导致细胞外基质中细胞因子和形态原的改变，导致软骨细胞的表型改变。我将从两个角度来探讨这个话题：宏观组织层面和微观细胞层面。第一个目标包括使用先进的3D成像技术和分光光度技术来量化可以在体外通过人类ZCC的分子从骨到软骨，反之亦然。通过ZCC的分子的大小和它们在这个薄组织层中的位置将与OA患者骨软骨组织的结构变化相关。第二个目标是利用下一代测序技术识别钙化软骨中肥大软骨细胞的特异性基因表达模式。该文库将被用来比较特定的分子(形态原和生长因子)如何在体外刺激从深部未钙化的软骨中分离出来的软骨细胞向肥大的软骨细胞分化，以及这些变化与肥大的骨性关节炎软骨细胞的表型有多接近。我将与主宾研究小组密切合作，就ZCC在软骨内稳态和骨性关节炎进展中的调控作用产生新的知识和见解。通过ZCC在人体外植体中扩散特性的表征，以及深区软骨细胞对环境因素的体外反应，将为深入了解与骨关节炎肥大分化相关的机制提供独特的途径。这些知识将导致新的方法来阻碍或延缓骨性关节炎的进展和软骨退变。

Osteoarthritis (OA) is the commonest joint disease worldwide with more than 20% of the German society suffering from this painful and disabling disease. Physiological and pathological changes during OA include the degeneration and erosion of cartilage tissue up to the exposure of the underlying bone. To intervene the progression of this disease, there is urgent need to better understand the mechanisms at molecular, cell and tissue level of the osteochondral unit, especially the zone of calcified layer (ZCC). The ZCC is connecting the deep zone of non-calcified articular cartilage to the subchondral bone. However, little is known about the role of the ZCC in cartilage homeostasis, the steady state condition of healthy tissue.I hypothesize that the ZCC serves as a natural border that controls the diffusion of molecules between cartilage and bone tissue and regulates cell-cell communication. This permeability is altered upon onset of OA leading to changes in cytokines and morphogens in the extracellular matrix inducing phenotypic changes in chondrocytes. I will approach this topic from two perspectives: the macroscopic tissue-level and the microscopic cellular-level. The first objective covers the quantification of molecules that can pass through human ZCC ex vivo from bone to cartilage and vice versa using advanced 3D imaging techniques and spectrophotometry. The size of molecules passing the ZCC and their location in this thin tissue layer will be correlated to the structural changes in the osteochondral tissue of OA patients. The second objective focuses on the identification of gene expression patterns specific for hypertrophic chondrocytes residing in the calcified cartilage using next generation sequencing technique. This library will be used to compare how specific molecules (morphogens and growth factors) can stimulate chondrocytes isolated from non-calcified cartilage of the deep zone to undergo differentiation towards hypertrophic chondrocytes in vitro and how close these changes match with the phenotype of hypertrophic OA chondrocytes.In close collaboration with the host and guest research groups, I will generate new knowledge and insights on the regulatory role of the ZCC in cartilage homeostasis and OA progression. The characterization of diffusion properties through the ZCC in human explants, together with the response of deep zone chondrocyte to environmental factors in vitro will provide a unique approach to deeper understand the mechanism related to hypertrophic differentiation during OA. This knowledge will result in novel approaches to impede or delay OA progression and cartilage degeneration.