Aigner Thomas, Gebhard Pia Margarethe, Schmid Erik, Bau Brigitte, Harley Vincent, Pöschl Ernst
Cartilage Research, Department of Pathology, University of Erlangen-Nürnberg, Krankenhausstrasse 8-10, Erlangen 91504, Germany.
Matrix Biol. 2003 Jun;22(4):363-72. doi: 10.1016/s0945-053x(03)00049-0.
Anabolic activity is a crucial activity of articular chondrocytes and its failure is one major reason of osteoarthritic cartilage degeneration. The intracellular factors responsible for the increase or decrease of anabolic activity of articular chondrocytes remain largely unknown. A recent candidate, the transcription factor SOX9, has elicited much interest as it is suggested to be a central factor in chondrocytic differentiation during development, including collagen type II (COL2A1) expression, the major anabolic gene product of chondrocytes. Here we show that normal adult human articular chondrocytes in vivo contain high SOX9 mRNA levels, which are decreased in osteoarthritic cartilage. Surprisingly, no positive correlation between SOX9 and COL2A1 expression was observed--to the contrary, the expression of COL2A1 was significantly increased in the diseased cells. Immunolocalization confirmed the presence of SOX9 protein in normal and osteoarthritic chondrocytes without showing significant differences in both SOX9 quantity and subcellular localization in osteoarthritic compared to normal cartilage tissue. Interestingly, laser scanning confocal microscopy showed that the subcellular distribution of SOX9 in adult chondrocytes was not restricted to the nucleus as observed in fetal chondrocytes, but was also detected within the cytoplasm, with no differences in subcellular SOX9 distribution between normal and OA cartilage. This is consistent with the lack of positive correlation between SOX9 and COL2A1 expression in adult articular chondrocytes. Also, no positive correlation between SOX9 and COL2A1 expression was observed in vitro after challenge of chondrocytes with Il-1beta, which is a strong (negative) regulator of COL2A1 expression, or with IGF-I, which stimulates COL2A1 expression. These results suggest that SOX9 is not the key regulator of COL2A1 promoter activity in human adult articular chondrocytes. However, SOX9 might still be involved in maintaining the chondrocytic phenotype in normal and osteoarthritic cartilage.
合成代谢活性是关节软骨细胞的一项关键活动，其功能失调是骨关节炎软骨退变的一个主要原因。导致关节软骨细胞合成代谢活性增减的细胞内因子在很大程度上仍不为人知。最近的一个候选因子，即转录因子SOX9，引发了诸多关注，因为它被认为是发育过程中软骨细胞分化的核心因子，包括II型胶原（COL2A1）的表达，而COL2A1是软骨细胞主要的合成代谢基因产物。在此我们表明，正常成年人体关节软骨细胞在体内含有高水平的SOX9 mRNA，而在骨关节炎软骨中其水平降低。令人惊讶的是，未观察到SOX9与COL2A1表达之间存在正相关——相反，在病变细胞中COL2A1的表达显著增加。免疫定位证实正常和骨关节炎软骨细胞中均存在SOX9蛋白，与正常软骨组织相比，骨关节炎软骨中SOX9的数量和亚细胞定位均未显示出显著差异。有趣的是，激光扫描共聚焦显微镜显示，成年软骨细胞中SOX9的亚细胞分布并不局限于细胞核（如在胎儿软骨细胞中观察到的那样），在细胞质中也能检测到，正常软骨和骨关节炎软骨之间SOX9的亚细胞分布没有差异。这与成年关节软骨细胞中SOX9和COL2A1表达缺乏正相关是一致的。此外，在用白细胞介素-1β（COL2A1表达的强（负）调节因子）或胰岛素样生长因子-I（刺激COL2A1表达）刺激软骨细胞后，在体外也未观察到SOX9与COL2A1表达之间存在正相关。这些结果表明，SOX9不是人类成年关节软骨细胞中COL2A1启动子活性的关键调节因子。然而，SOX9可能仍参与维持正常和骨关节炎软骨中的软骨细胞表型。
