Ishikawa Y, Genge B R, Wuthier R E, Wu L N
Department of Chemistry and Biochemistry, and School of Medicine, University of South Carolina, Columbia 29208, USA.
J Bone Miner Res. 1998 Sep;13(9):1398-411. doi: 10.1359/jbmr.1998.13.9.1398.
As a continuation of our studies on mineralization in epiphyseal growth plate (GP) chondrocyte cultures, the effects of tri-iodothyronine (T3) in both beta-glycerophosphate-containing, serum-free (HL-1) and beta-glycerophosphate-free, serum-containing medium (DATP5) were studied. The GP cells responded to T3 in a serum-, stage-, and dosage-dependent manner. Added at graded levels (0.1-10.0 nM) to preconfluent cultures (from day 7) in both HL-1 and DATP5, T3 caused progressive decreases in protein, collagen, and DNA synthesis but increased mineral deposition. In postconfluent cultures, these effects of T3 were generally muted. In preconfluent cultures, proteoglycan (PG) levels were not significantly affected in DATP5, although in HL-1 they were decreased by approximately 50%. In postconfluent cultures, T3 increased PG levels in DATP5 but had no effect in HL-1. In HL-1, alkaline phosphatase (ALP) activity was progressively increased by 200-500% in both pre- and postconfluent cultures. In DATP5 in preconfluent cultures, T3 initially stimulated but later suppressed ALP; in postconfluent cultures, T3 also transiently increased ALP but did not suppress activity upon longer exposure. The inhibitory effects of T3 on protein, PG, and DNA levels of GP chondrocytes suggest that in vivo its effects on bone growth must occur primarily after cellular proliferation. Apparently by binding to the 50 kDa thyroxine-binding globulin, which cannot penetrate the PG barrier, accessibility of T3 to GP chondrocytes is limited until the time of vascular penetration when its stimulatory effects on ALP and mineral deposition become critical for continued bone development.
作为我们对骨骺生长板（GP）软骨细胞培养矿化研究的延续，我们研究了三碘甲状腺原氨酸（T3）在含β - 甘油磷酸的无血清培养基（HL - 1）和不含β - 甘油磷酸的含血清培养基（DATP5）中的作用。GP细胞对T3的反应呈血清、阶段和剂量依赖性。在HL - 1和DATP5中，以分级水平（0.1 - 10.0 nM）添加到预汇合培养物（第7天开始）中，T3导致蛋白质、胶原蛋白和DNA合成逐渐减少，但增加了矿物质沉积。在汇合后培养物中，T3的这些作用通常减弱。在预汇合培养物中，DATP5中的蛋白聚糖（PG）水平没有受到显著影响，尽管在HL - 1中它们下降了约50%。在汇合后培养物中，T3增加了DATP5中的PG水平，但对HL - 1没有影响。在HL - 1中，预汇合和汇合后培养物中的碱性磷酸酶（ALP）活性均逐渐增加200 - 500%。在预汇合培养物的DATP5中，T3最初刺激但后来抑制ALP；在汇合后培养物中，T3也短暂增加ALP，但长时间暴露后不抑制活性。T3对GP软骨细胞蛋白质含量、PG和DNA水平的抑制作用表明，在体内其对骨骼生长的影响主要发生在细胞增殖之后。显然，通过与50 kDa的甲状腺素结合球蛋白结合，该球蛋白无法穿透PG屏障，T3对GP软骨细胞的可及性受到限制，直到血管穿透时，其对ALP和矿物质沉积的刺激作用对骨骼持续发育变得至关重要。
