Sakou T, Onishi T, Yamamoto T, Nagamine T, Sampath T k, Ten Dijke P
Department of Orthopaedic Surgery, Faculty of Medicine, Kagoshima University, Kagoshima, Japan.
J Bone Miner Res. 1999 Jul;14(7):1145-52. doi: 10.1359/jbmr.1999.14.7.1145.
Members of the transforming growth factor-beta (TGF-beta) family transduce signals from the cell membrane to the nucleus via specific type I and type II receptors and Smad proteins. Smad1 and Smad5 mediate intracellular signaling of bone morphogenetic protein (BMP), whereas Smad2 and Smad3 transduce TGF-beta signaling. Smad4 is a common mediator required for both pathways. Smad6 and Smad7 inhibit signaling by members of the TGF-beta superfamily. Here, we examined the expression of Smad1 to Smad7 proteins during endochondral ossification of epiphyseal plate of growing rats using immunohistochemical techniques. The expression of Smad proteins was correlated with the expression of TGF-beta1 and its receptors, and BMP-2/4 and BMP receptors. The results show that TGF-beta1 and BMP-2/4 were actively expressed in chondrocytes that are undergoing proliferation and maturation, which overlaps with expression of their corresponding type I and type II receptors. The Smads, however, exhibited a distinct expression pattern, respectively. For example, Smad1 and Smad5 were highly expressed in proliferating chondrocytes and in those chondrocytes that are undergoing maturation. The TGF-beta/activin-restricted Smads were also expressed in a nearly complementary fashion; Smad2 was strongly expressed in proliferating chondrocytes, whereas Smad3 was strongly observed in maturing chondrocytes. Smad4 was broadly expressed in all zones of epiphyseal plate. Inhibitory Smads, Smad6 and Smad7, were strongly expressed in the zone of cartilage that contained mature chondrocytes. Our findings show a colocalization of the pathway-restricted and inhibitory Smads with activating ligands or ligands whose action they antagonize and their receptors in various zones of epiphyseal growth plate, suggesting that TGF-beta superfamily Smad signaling pathways plays a morphogenic role during endochondral bone formation.
转化生长因子-β（TGF-β）家族成员通过特定的I型和II型受体以及Smad蛋白将信号从细胞膜传导至细胞核。Smad1和Smad5介导骨形态发生蛋白（BMP）的细胞内信号传导，而Smad2和Smad3传导TGF-β信号。Smad4是这两条通路所需的共同介质。Smad6和Smad7抑制TGF-β超家族成员的信号传导。在此，我们使用免疫组织化学技术检测了生长中大鼠骨骺板软骨内成骨过程中Smad1至Smad7蛋白的表达。Smad蛋白的表达与TGF-β1及其受体以及BMP-2/4和BMP受体的表达相关。结果显示，TGF-β1和BMP-2/4在正在增殖和成熟的软骨细胞中活跃表达，这与它们相应的I型和II型受体的表达重叠。然而，Smad蛋白呈现出不同的表达模式。例如，Smad1和Smad5在增殖的软骨细胞以及正在成熟的软骨细胞中高表达。TGF-β/激活素限制的Smad蛋白也以几乎互补的方式表达；Smad2在增殖的软骨细胞中强烈表达，而Smad3在成熟的软骨细胞中强烈表达。Smad4在骨骺板的所有区域广泛表达。抑制性Smad蛋白Smad6和Smad7在含有成熟软骨细胞的软骨区域强烈表达。我们的研究结果表明，在骨骺生长板的各个区域，通路限制型和抑制性Smad蛋白与激活配体或其作用被它们拮抗的配体及其受体共定位，这表明TGF-β超家族Smad信号通路在软骨内骨形成过程中发挥形态发生作用。
