THE ROLE OF BCL2 PROTEINS IN CHONDROCYTE BIOLOGY

退行性软骨疾病（骨关节炎，OA）是老年人发病的主要原因。一些证据支持这一概念，即软骨细胞活力下降和基质合成减少或改变（特别是）对生长因子的反应导致OA发病率随着年龄的增长而增加。Bcl-2家族含有促凋亡和抗凋亡的蛋白。最近的研究表明Bcl-2蛋白在调节软骨细胞凋亡中的作用。然而，Bcl-2在体内调节关节软骨细胞凋亡的作用尚未得到直接证明，Bcl-2家族主要成员在关节软骨中的表达也未得到系统的研究。除了Bcl-2在调节细胞凋亡中的传统作用外，现在已经清楚的是，Bcl-2还参与调节非凋亡途径，控制轴突再生和上皮细胞分化等事件。现在有证据表明，这种途径在软骨细胞中起作用，并可能与聚集蛋白的表达有关。通过bcl -2依赖性途径调节聚集蛋白的机制尚未确定，也未确定该途径在多大程度上调节其他软骨基质基因。因此，Bcl-2蛋白在调节软骨细胞凋亡和基质基因表达中发挥双重作用的一般假设将通过以下具体目的进行探讨：1)通过测量II、IX、XI、link蛋白等编码mRNA的水平，确定血清戒断或反义Bcl-2表达对聚集蛋白表达的抑制是否参与了软骨细胞特异性基因表达的协同下调；2)建立聚集蛋白（及其他基质基因）表达降低的机制，探讨特异性转录因子（NFkappaB）在软骨细胞对血清戒断或反义Bcl-2的反应中的作用；3)通过大鼠和人关节软骨中Bcl-2主要成员蛋白的表达模式与衰老、细胞凋亡和软骨退行性变的相关性，确定Bcl-2主要成员在体内的相关性；在转基因小鼠模型中降低Bcl-2表达对软骨细胞凋亡和基质基因表达的影响也将被确定。这项多方面的实验方法旨在探讨Bcl-2蛋白在软骨细胞生物学中的基本作用，并确定软骨维持和OA发病机制的重要机制。

Degenerative cartilage disease (osteoarthritis, OA) is a major contributor to morbidity in the elderly population. Several lines of evidence support the concept that decreased chondrocyte viability and diminished or altered matrix synthesis (especially) in response to growth factors contribute to the increased incidence of OA with aging. The Bcl-2 family contains proteins that are both pro-apoptotic and anti-apoptotic. Recent studies have demonstrated a role for Bcl-2 proteins in regulating chondrocyte apoptosis. However it has not been shown directly that Bcl-2 plays a role in regulating articular chondrocyte apoptosis in vivo, nor has the expression of the major members of the Bcl-2 family been systematically examined in articular cartilage. In addition to the traditional role of Bcl-2 in regulating apoptosis, it is now clear that Bcl-2 is involved in the regulation of non-apoptotic pathways that control events such as axonal regeneration and epithelial cell differentiation. Evidence now exists that this type of pathway is operating in the chondrocyte and may be linked to the expression of aggrecan. The mechanisms that regulate aggrecan through a Bcl-2-dependent pathway have not been determined nor has it been established to what extent this pathway may regulate other cartilage matrix genes. Therefore, the general hypothesis that Bcl-2 proteins play a dual role in regulating both chondrocyte apoptosis and matrix gene expression will be explored through the following specific aims: 1) Determine if the inhibition of aggrecan expression in response to serum withdrawal or anti-sense Bcl-2 expression is part of a coordinate down-regulation of chondrocyte-specific gene expression by measuring mRNA levels coding for collagen II, IX, XI, link protein and others; 2) Establish the mechanism for decreased aggrecan (and other matrix gene) expression and probe the role of a specific transcription factor (NFkappaB) in the chondrocyte response to serum withdrawal or anti-sense Bcl-2; 3) Determine the relevance of the major members of the Bcl-2 in vivo by correlating the expression pattern of these proteins in the articular cartilage of rats and humans with aging, apoptosis and cartilage degeneration; also the effect of reduced Bcl-2 expression in a transgenic mouse model on chondrocyte apoptosis and matrix gene expression will be determined. This multifaceted experimental approach is intended to probe the basic role of Bcl-2 proteins in chondrocyte biology and to identify mechanisms that are important for cartilage maintenance and the pathogenesis of OA.