Basic study on the risk factors of osteoporosis.

我们将骨质疏松症称为钙代谢异常的全身性疾病，并探讨了肠道钙吸收的调节机制和促骨因子在骨形成和骨吸收中的作用。1.通过比较鸡肠刷缘和基侧膜组分的钙吸收，发现1α，25-二羟基维生素D_3[1α，25(OH)_2D_3]对鸡肠道钙吸收的增加主要归因于基侧膜钙的外流，而非基侧膜钙的内流。研究结果表明：1.有证据表明，肠上皮细胞基侧膜上存在的钙泵为Ca~(2+)、Mg~(2+)~(2+)-ATPase，它们通过磷酸化-去磷酸化的形式参与肠道钙转运。从小鼠骨髓基质细胞(ST2)和经1α，25(OH)2D_3处理的原代成骨细胞培养上清液中纯化出190 kDa的蛋白质，鉴定为补体(C3)的第三组分。1α，25(OH)2D3对C3的调节处于转录水平下，并且似乎是组织特异性的。C3的产生不仅增加了1α、25(OH)2D3，而且局部骨吸收药物如IL-1、TNFα和脂多糖也增加了C3的产生。在骨髓培养中加入1α，25(OH)2D3和抗C3抗体可显著抑制TPAP阳性破骨细胞样多核细胞的形成。巨噬细胞在1α，25(OH)2D3和地塞米松存在下与ST2细胞共同培养，可向破骨细胞样细胞分化。通过对破骨细胞形成因子(S)的研究发现，M-CSF是促使破骨祖细胞分化为成熟破骨细胞的重要因子。

We referred osteoporosis to a general disease in abnormal calcium metabolism, and approached to clarify the regulation mechanism of calcium absorption in the intestine and the functions of osteotropic factors in bone formation and resorption. Results obtained in this study could be summarized as follows :1. By comparing chick intestinal calcium absorption between brush border and basolateral membrane fractions which were purified by saccharide gradient centrifugation, the increased calcium absorption by 1alpha, 25-dihydroxyvitamin D_3 [1alpha, 25(OH)_2D_3] was much attributive to efflux of calcium from basolateral membranes than influx of calcium from brush border membranes. Several pieces of evidence supported that calcium pump present in the basolateral membranes was Ca^<2+>, Mg^<2+>-ATPase, which contributed to the intestinal calcium transport depending upon the phosphorylation-dephosphorylation forms.2. A 190 kDa protein was purified from conditioned media of mouse bone marrow-derived stromal cell(ST2)and primary osteoblastic cell cultures treated with 1alpha, 25(OH)_2D_3 and identified as the third component of complement(C3). The regulation of C3 by 1alpha, 25(OH)_2D_3 was under a transcriptional level, and appeared to occur tissue-specifically. The production of C3 was increased by not only 1alpha, 25(OH)_2D_3, but also local bone-resorbing agents such as IL-1, TNFalpha, and LPS. Adding 1alpha, 25(OH)_2D_3 together with antibody against C3 to bone marrow cultures greatly inhibited the formation of TPAP-positive osteoclast-like multinucleated cells.3. Macrophages were able to differentiate into osteoclast-like cells by culturing macrophages with ST2 cells in the presence of 1alpha, 25(OH)_2D_3 and dexamethasone. When the factor(s)committing osteoclast formation was examined, it was found that M-CSF is an important factor, which commits osteoclast progenitors differentiating into mature osteoclast cells.