Research for effect of irradiation on growth plate chondrocytes

辐照引起的骨生长迟缓可能与生长板软骨内成骨功能受损密切相关，但其机制尚不清楚。本研究采用兔生长板软骨细胞培养系统，观察x射线照射对生长板软骨细胞分化的直接影响。1 ~ 10Gy剂量的X射线对早期软骨细胞抑制蛋白多糖（PG）合成，诱导PG降解。10Gy剂量的X射线抑制X型胶原合成和含量，但不改变II型胶原的表达，降低碱性磷酸酶（ALPase）活性。10Gy辐照培养细胞外基质中钙沉积量为对照的40%。2.对成熟软骨细胞进行10Gy剂量的x射线照射未改变PG合成。辐照后，PG的降解增强。虽然1 ~ 10Gy剂量的X射线不影响X型胶原合成，但抑制了ALPase活性和钙沉积。3.在肥厚期，1 ~ 10Gy剂量的辐照对PG、X型胶原和ALPase活性的影响微乎其微。然而，[^<45>Ca]掺入细胞层和钙沉积减少。4.随着软骨细胞分化程度的加深，其对辐照的敏感性逐渐降低。在本研究中，我们阐明了1 ~ 10Gy剂量的辐照抑制生长板软骨细胞的基质形成、终末分化和诱导细胞外基质钙化。然而，一旦软骨细胞受到照射，它们就不能表达进一步分化的表型，并且照射的抑制作用永远不会恢复。这些结果表明，辐照对软骨内成骨的干扰源于辐照对生长板软骨细胞基质合成和基质钙化的直接抑制作用。

The retardation of bone growth caused by irradiation suggested to be closely related to the impairment of endochondral ossification in growth plate, but its mechanism remains unclear. In this study the direct effect of X-ray irradiation cytodifferentiation of the growth plate chondrocytes was examined using a rabbit growth plate chondrocyte culture system.1.One to 10Gy doses of X-ray to the chondrocytes in premature stage inhibited proteoglycan (PG) synthesis, and induced degradation of PG.A 10Gy dose of X-ray suppressed type X collagen synthesis and content without changing type II collagen expression, and decreased alkaline phosphatase (ALPase) activity. Calcium deposition in the extracellular matrix of 10Gy dose irradiated culture was 40% of the control. 2.A 10Gy dose of X-ray to the mature chondrocytes did not change PG synthesis. PG degradation, however, was enhanced after irradiation. Although 1 to 10Gy doses of X-ray did not affect type X collagen synthesis, suppressed ALPase activity and calcium deposition. 3.In the hypertrophic stage, 1 to 10Gy doses of irradiation had marginal effect on PG,type X collagen, and ALPase activity. However, [^<45>Ca] incorporation into the cell layr and calcium deposition were decreased. 4.The sensitivity of the cytodifferentiation of the chondrocytes to irradiation became less as their differentiation advanced.In this study we clarified that 1 to 10Gy doses of irradiation inhibited matrix formation, terminal differentiation and induction of extracellular matrix calcification of growth plate chondrocytes. However, once the chondrocytes were irradiated, they could not express the further differentiated phenotypes and the inhibitory effects of irradiation were never restored. These findings indicate that the disturbance of endochondral ossification by irradiation originate in the direct inhibitory effects of irradiation on the matrix synthesis and matrix calcification in growth plate chondrocytes.