Metabolism of vitamin D3 in human osteoblasts:: Evidence for autocrine and paracrine activities of 1α,25-dihydroxyvitamin D3
Metabolism of vitamin D3 in human osteoblasts:: Evidence for autocrine and paracrine activities of 1α,25-dihydroxyvitamin D3
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DOI：
10.1016/j.bone.2007.02.024
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发表时间：
2007-06-01
期刊：
影响因子：
4.1
通讯作者：
Morris, Howard A.
中科院分区：
文献类型：
--
作者：
Atkins, Gerald J.;Anderson, Paul H.;Morris, Howard A.
循环1 α，25-二羟基维生素D-3（1，25 D）来源于25-羟基维生素D-3（25 D）通过25 D 1 α-羟化酶（CYP 27 B1）的肾脏转化。血液中的25 D水平，而不是1，25 D水平，是维生素D状态的最佳指标，并预测老年人骨折的风险。我们研究了成骨细胞代谢25 D的程度。采用实时PCR技术，对人原代成骨细胞和骨肉瘤（OS）细胞系中与维生素D代谢相关基因的表达和调控进行了研究。发现原代成骨细胞和OS细胞系表达CYP 27 B1 mRNA，并响应于25 D分泌可检测的1，25 D。在检测的OS细胞系中，HOS表达最多的CYP 27 B1 mRNA，分泌最高水平的1，25 D。当与1，25 D或25 D孵育时，所有成骨细胞检测到1，25 D的分解代谢调节剂25-羟基维生素D-24-羟化酶（CYP 24）的表达上调。暴露于生理水平的25 D导致1，25 D应答基因骨钙素（OCN）、骨桥蛋白（OPN）和RANKL的转录上调。使用siRNA特异性敲低HOS细胞中的CYP 27 B1导致1，25 D分泌以及OCN和CYP 24的转录减少高达80%，强烈暗示成骨细胞中的25 D效应之前是转化为1，25 D。与1，251一样，与25 D孵育抑制原代成骨细胞增殖并促进体外矿化。最后，我们检测成骨细胞的维生素D结合蛋白（DBP），cubilin和megalin受体的表达，表明成骨细胞能够在体内内化DBP-25 D复合物。总之，我们的研究结果表明，自分泌，也许旁分泌，维生素D-3代谢途径可能调节关键成骨细胞功能独立于循环，肾源性1，25 D。因此，我们的研究结果与报道的老年人保持健康的维生素D状态以降低骨折风险的益处一致。(c)2007年爱思唯尔公司All rights reserved.
Circulating 1 alpha,25-dihydroxyvitamin D-3 (1,25D) derives from renal conversion of 25-hydroxyvitamin D-3 (25D), by the 25D 1 alpha-hydroxylase (CYP27B1). Blood 25D levels, but not 1,25D levels, are the best indicator of vitamin D status and predict fracture risk in the elderly. We examined the extent to which osteoblasts can metabolize 25D. Well-characterized human primary osteoblasts and osteosarcoma (OS) cell lines were examined for the expression and regulation of genes associated with vitamin D metabolism, using real-time PCR. Primary osteoblasts and OS cell lines were found to express CYP27B1 mRNA and secreted detectable 1,25D in response to 25D. Of the OS cell lines tested, HOS expressed the most CYP27B1 mRNA and secreted the highest levels of 1,25D. All osteoblastic cells examined up-regulated expression of the catabolic regulator of 1,25D, the 25-hydroxyvitamin D-24-hydroxylase (CYP24), when incubated with either 1,25D or 25D. Exposure to physiological levels of 25D resulted in up-regulated transcription of the 1,25D responsive genes, osteocalcin (OCN), osteopontin (OPN) and RANKL. Specific knockdown of CYP27B1 in HOS cells using siRNA resulted in up to 80% reduction in both 1,25D secretion and the transcription of OCN and CYP24, strongly implying that the 25D effect in osteoblasts is preceded by conversion to 1,25D. Incubation with 25D, like 1,251), inhibited primary osteoblast proliferation and promoted in vitro mineralization. Finally, we detected expression by osteoblasts of receptors for vitamin D binding protein (DBP), cubilin and megalin, suggesting that osteoblasts are able to internalize DBP-25D complexes in vivo. Together, our results suggest that autocrine, and perhaps paracrine, pathways of vitamin D-3 metabolism may regulate key osteoblast functions independently of circulating, kidney derived 1,25D. Our results are therefore consistent with the reported benefits of maintaining a healthy vitamin D status in the elderly to reduce the risk of fractures. (c) 2007 Elsevier Inc. All rights reserved.