Farquharson C, Berry J L, Mawer E B, Seawright E, Whitehead C C
Roslin Institute (Edinburgh), Midlothian, Scotland, UK.
Eur J Cell Biol. 1998 Jun;76(2):110-8. doi: 10.1016/s0171-9335(98)80023-x.
Chondrocyte terminal differentiation is associated with cellular hypertrophy increased activity of plasma membrane alkaline phosphatase and the synthesis of collagen type X. The hypertrophic phenotype of cultured chondrocytes can be stimulated by ascorbic acid but the underlying mechanisms for this phenotypic change are unclear. As ascorbic acid is central to many hydroxylation reactions, the possibility was examined that its pro-differentiating effects are mediated by its effects on collagen and vitamin D metabolite formation. In vitro studies indicated that ascorbic acid-induced chondrocyte alkaline phosphatase activity was inhibited by the addition of both collagen and proteoglycan synthesis inhibitors. The addition of arginine-glycine-aspartic acid (RGD)-containing peptides also resulted in lower alkaline phosphatase activity. Chicks supplemented with dietary ascorbic acid had higher concentrations of both collagen and proteoglycans within their growth plates but the chondrocyte maturation rate was unaltered. No evidence was obtained to suggest that ascorbic acid-induced collagen production was mediated by lipid peroxidation. In addition, supplementation with dietary ascorbic acid resulted in higher serum 1,25-dihydroxyvitamin D3 concentrations and increased chondrocyte vitamin D receptor number. Ascorbic acid-treated chondrocytes maintained in vitro also had increased vitamin D receptor numbers but chondrocyte receptor affinity for 1,25-dihydroxyvitamin D3 was unaltered. These results indicate that ascorbic acid promotes both chondrocyte matrix production and 1,25-dihydroxyvitamin D3 synthesis, accompanied by upregulation of the vitamin D receptor. Thus, ascorbic acid may be causing amplification of the vitamin D receptor-dependent genomic response to 1,25-dihydroxyvitamin D, resulting in promotion of terminal differentiation. Strong evidence is provided to support the hypothesis that ascorbic acid-induced chondrocyte terminal differentiation is mediated by interactions between integrins and RGD-containing cartilage matrix proteins.
软骨细胞终末分化与细胞肥大、质膜碱性磷酸酶活性增加以及X型胶原蛋白的合成有关。培养的软骨细胞的肥大表型可被抗坏血酸刺激，但这种表型变化的潜在机制尚不清楚。由于抗坏血酸在许多羟基化反应中起核心作用，因此研究了其促分化作用是否通过对胶原蛋白和维生素D代谢产物形成的影响来介导。体外研究表明，添加胶原蛋白和蛋白聚糖合成抑制剂可抑制抗坏血酸诱导的软骨细胞碱性磷酸酶活性。添加含精氨酸-甘氨酸-天冬氨酸（RGD）的肽也会导致碱性磷酸酶活性降低。日粮中添加抗坏血酸的雏鸡生长板内胶原蛋白和蛋白聚糖的浓度较高，但软骨细胞成熟率未改变。没有证据表明抗坏血酸诱导的胶原蛋白产生是由脂质过氧化介导的。此外，日粮中添加抗坏血酸会导致血清1,25-二羟维生素D3浓度升高和软骨细胞维生素D受体数量增加。体外培养的经抗坏血酸处理的软骨细胞维生素D受体数量也增加，但软骨细胞受体对1,25-二羟维生素D3的亲和力未改变。这些结果表明，抗坏血酸促进软骨细胞基质产生和1,25-二羟维生素D3合成，同时伴随着维生素D受体的上调。因此，抗坏血酸可能导致对1,25-二羟维生素D的维生素D受体依赖性基因组反应放大，从而促进终末分化。有力证据支持了抗坏血酸诱导的软骨细胞终末分化是由整合素与含RGD的软骨基质蛋白之间的相互作用介导的这一假说。
