Activation of Transforming Growth Factor β in Chondrocytes Undergoing Endochondral Ossification
作者:Marina D'Angelo、David P. Sarment、Paul C. Billings、Maurizio Pacifici
DOI:10.1359/jbmr.2001.16.12.2339
日期:——
Transforming growth factor β (TGF‐β) has well‐documented roles in chondrocyte maturation and endochondral ossification, but the mechanisms of TGF‐β activation during these processes remain unclear. In this study, we analyzed TGF‐β activation in chick embryo resting, proliferating, and hypertrophic chondrocytes in culture. We found that both levels and activation of TGF‐β increased substantially with maturation. The majority of TGF‐β produced by resting cells over culture time remained latent, but a larger portion produced by proliferating and hypertrophic cells was activated with increasing maturation. Zymography of gelatin gels revealed that matrix metalloprotease 2 (MMP‐2) and MMP‐9 were expressed by each population and that MMP‐13 characterized hypertrophic chondrocytes and to a lesser extent proliferating chondrocytes in late cultures. Treatment with pharmacologic agents revealed that both MMPs and serine proteases are involved in activation. However, because inhibition of MMPs almost completely prevented TGF‐β activation, MMPs appear crucial for activation. During culture, inclusion of the tetracycline‐derived, collagenase/gelatinase inhibitor chemically modified nonantimicrobial tetracycline (CMT‐8) at concentrations specific for MMP‐13 inhibition resulted in complete inhibition of TGF‐β activation by proliferating and hypertrophic chondrocytes. These results show that TGF‐β production, release, and activation are regulated developmentally in chondrocytes. Our findings point to a strict mode of regulation of this potent factor to elicit diverse and highly specific effects during chondrocyte maturation and ossification.
转化生长因子 β(TGF-β)在软骨细胞成熟和软骨内骨化过程中的作用已被充分证明,但这些过程中 TGF-β 的激活机制仍不清楚。在这项研究中,我们分析了小鸡胚胎静止、增殖和肥大软骨细胞在培养过程中的 TGF-β 激活情况。我们发现,随着细胞的成熟,TGF-β的水平和活化程度都大幅增加。静止细胞在培养过程中产生的大部分 TGF-β 仍处于潜伏状态,但增殖和肥大细胞产生的大部分 TGF-β 随着成熟度的增加而被激活。明胶凝胶的酶谱分析显示,基质金属蛋白酶2(MMP-2)和MMP-9在每个细胞群中都有表达,MMP-13是肥大软骨细胞的特征,增殖软骨细胞在晚期培养中表达较少。用药剂处理后发现,MMPs 和丝氨酸蛋白酶都参与了活化。然而,由于抑制 MMPs 几乎完全阻止了 TGF-β 的活化,因此 MMPs 似乎对活化至关重要。在培养过程中,以抑制 MMP-13 的特异浓度加入四环素衍生的胶原酶/明胶酶抑制剂化学修饰非抗菌四环素(CMT-8),可完全抑制增殖和肥大软骨细胞的 TGF-β 激活。这些结果表明,软骨细胞中 TGF-β 的产生、释放和活化是受发育调控的。我们的研究结果表明,在软骨细胞成熟和骨化过程中,这种强效因子具有严格的调节模式,可产生多种高度特异性的效应。