The role of PEDF (SERPINF1) for terminal chondrocyte differentiation in osteoarthritis and cartilage repair

在生理条件下，关节软骨细胞永久保持其稳定的表型数十年。相比之下，骨关节炎以及软骨修复过程面临着软骨细胞的不稳定终末分化，这与细胞肥大、细胞凋亡和基质钙化有关。虽然终末软骨细胞分化是一个生理序列endochondrialossification过程中，这一过程显着阻碍了成人关节软骨的完整性，我们以前的全基因组表达分析表明，色素上皮衍生因子（PEDF/SERPINF 1）是一个因素，这是显着更高的表达在修复软骨相比，健康的关节软骨。在这种情况下，PEDF主要在前肥大软骨细胞中检测到，这基本上反映了胎儿生长板内的表达模式。在多种其他细胞类型中，PEDF被认为是一种有效的抗血管生成和抗肿瘤生成因子，主要通过促凋亡机制介导其作用。因此，本项目基于PEDF负责终末软骨细胞分化和PEDF决定暂时而不是永久的软骨细胞表型的假设，为了分析PEDF与软骨细胞表型的关联，将研究其在胎儿骨骺和成人关节结构中的空间表达模式。将在使用重组PEDF的刺激实验和使用siRNA转染或中和抗体的功能丧失实验中研究PEDF在软骨细胞中的作用机制。读数将主要集中在对前体细胞以及健康和骨关节炎软骨细胞的细胞肥大和凋亡的影响上。此外，将研究PEDF活性的抑制是否会阻止软骨细胞在不同培养系统中经历终末分化和凋亡。本项目的目的是通过调节PEDF途径来稳定骨关节软骨中的软骨细胞表型并修复软骨。

Under physiological conditions, articular chondrocytes permanently retain their stable phenotype for many decades. By contrast, osteoarthritis as well as cartilage repair processes are confronted with inadvertant terminal differentiation of chondrocytes, which is associated with cellular hypertrophy, apoptosis and calcification of the matrix. While terminal chondrocyte differentiation is a physiological sequence during endochondral ossification, this process significantly hampers the integrity of adult articular cartilage.Our previous genome-wide expression analyses demonstrated that Pigment Epithelium-Derived Factor (PEDF/ SERPINF1) was a factor that was strikingly higher expressed in repair cartilage compared with healthy articular cartilage. In this context, PEDF was detected most predominantly in areas of prehypertrophic chondrocytes, which basically reflects the expression pattern within the fetal growth plate. In a variety of other cell types, PEDF is known as a potent anti-angiogenic and anti-tumorigenic factor mediating its effects predominantly via pro-apoptotic mechanisms. Therefore, this project is based on the hypothesis that PEDF is responsible for terminal chondrocyte differentiation and that PEDF determines the transient instead of the permanent chondrocyte phenotype.In order to analyse the association of PEDF with the chondrocyte phenotype, its spatial expression pattern will be investigated in fetal epiphyses and adult joint structures. The mechanism of action of PEDF in chondrocytes will be investigated in stimulation experiments using recombinant PEDF and in loss-of-function experiments using siRNA-transfection or neutralizing antibodies. The readout will predominantly focus on effects on cellular hypertrophy and apoptosis of precursor cells as well as healthy and osteoarthritic chondrocytes. Furthermore, it will be investigated if the inhibition of the PEDF-activity will prevent chondrocytes from undergoing terminal differentiation and apoptosis in different culture systems. The aim of this project is to stabilize the chondrocyte phenotype in osteoarthric cartilage and repair cartilage by modulating the PEDF pathway.