Analysis of signal transduction and role of intracellular calcium in proliferation and differentiation of chondrocytes

为了比较成年动物和胚胎动物修复关节软骨的潜力，我们用大鼠模型研究了股骨膝关节软骨表面缺陷后的早期过程。胎龄19d的胎儿，表面缺损人工损伤后48h，软骨细胞和细胞外基质均有显著反应。藏红花素O染色显示，伤后1h，创面周围细胞外基质的部分成分发生改变，并在24小时内从有限的区域扩散到整个膝关节软骨。伤后1~6h，创面周围软骨细胞c-fos表达呈一过性升高。创面在出生后1天，即伤后72小时仍然存在，但在出生后10天完全修复。相比之下，12周龄的成年关节软骨在损伤后48小时既没有观察到明显的反应，也没有观察到一过性的c-fos表达。然后，我们研究了细胞内钙离子浓度([Ca^&lt；2+&gt；]i)与诱导软骨中c-fos表达的关系。应用三磷酸腺苷或钙离子载体A23187增加软骨细胞c-fos的表达。1μMATP可使胎儿软骨细胞[Ca~(2+)]_i升高，而成人软骨切片则需1 mM。我们的发现表明，有一条明显活跃于胎儿关节软骨修复而不是成人关节软骨修复的信号通路，涉及细胞间ATP的转移，[Ca~(2+)&gt；]_i的升高，以及软骨中c-fos的表达。

To compare the potential of adult and fetal animals to repair articular cartilage, we investigated the early process after creating superficial defects in the femoral knee cartilage using rat models. In fetuses at 19 days of gestation, both chondrocytes and the extracellular matrix responded remarkably by 48 hours after artificial injury of superficial defect. Staining patterns with safranin O revealed that by 1 hour after injury, some components of the extracellular matrix around the wound were modified, and the change spread from the limited region to the entire knee cartilage in 24 hours. The chondrocytes in the area surrounding the wound transiently expressed increased level of c fos from 1 to 6 hours. The wound remained 1 day after birth, i.e., 72 hours after injury, but was completely repaired 10 days after birth. In contrast, neither visible responses nor transient c fos expression was observed in 12-week-old adult articular cartilage 48 hours after injury. Then, we examined the relationships between intracellular Ca^<2+> concentration ([Ca^<2+>]_i and the induction of c-fos expression in the cartilage. Applications of ATP or Ca^<2+> ionophore A23187 that increase [Ca^<2+>]_i induced immediate expression of c-fos in primary cultured chondrocytes. One μM ATP elicited the increase of [Ca^<2+>]_i in chondrocytes in fetal but 1 mM was required in adult cartilage slices. Our findings showed that there is a signaling pathway, apparently active in the repair of fetal but not adult articular cartilage, that involves intercellular transfer of ATP, increase of [Ca^<2+>]_i, and expression of c-fos in the cartilage.