Atkins Gerald J, Welldon Katie J, Wijenayaka Asiri R, Bonewald Lynda F, Findlay David M
Univ. of Adelaide, Hanson Institute, SA, Australia.
Am J Physiol Cell Physiol. 2009 Dec;297(6):C1358-67. doi: 10.1152/ajpcell.00216.2009. Epub 2009 Aug 12.
The vitamin K family members phylloquinone (vitamin K1) and the menaquinones (vitamin K2) are under study for their roles in bone metabolism and as potential therapeutic agents for skeletal diseases. We have investigated the effects of two naturally occurring homologs, phytonadione (vitamin K1) and menatetrenone (vitamin K2), and those of the synthetic vitamin K, menadione (vitamin K3), on human primary osteoblasts. All homologs promoted in vitro mineralization by these cells. Vitamin K1-induced mineralization was highly sensitive to warfarin, whereas that induced by vitamins K2 and K3 was less sensitive, implying that gamma-carboxylation and other mechanisms, possibly genomic actions through activation of the steroid xenobiotic receptor, are involved in the effect. The positive effect on mineralization was associated with decreased matrix synthesis, evidenced by a decrease from control in expression of type I collagen mRNA, implying a maturational effect. Incubation in the presence of vitamin K2 or K3 in a three-dimensional type I collagen gel culture system resulted in increased numbers of cells with elongated cytoplasmic processes resembling osteocytes. This effect was not warfarin sensitive. Addition of calcein to vitamin K-treated cells revealed vitamin K-dependent deposition of mineral associated with cell processes. These effects are consistent with vitamin K promoting the osteoblast-to-osteocyte transition in humans. To test whether vitamin K may also act on mature osteocytes, we tested the effects of vitamin K on MLO-Y4 cells. Vitamin K reduced receptor activator of NF-kappaB ligand expression relative to osteoprotegerin by MLO-Y4 cells, an effect also seen in human cultures. Together, our findings suggest that vitamin K promotes the osteoblast-to-osteocyte transition, at the same time decreasing the osteoclastogenic potential of these cells. These may be mechanisms by which vitamin K optimizes bone formation and integrity in vivo and may help explain the net positive effect of vitamin K on bone formation.
维生素K家族成员叶绿醌（维生素K1）和甲萘醌（维生素K2）在骨代谢中的作用以及作为骨骼疾病潜在治疗药物的研究正在进行中。我们研究了两种天然存在的同系物，维生素K1（叶绿醌）和维生素K2（四烯甲萘醌）以及合成维生素K（甲萘醌，维生素K3）对人原代成骨细胞的影响。所有同系物均促进了这些细胞的体外矿化。维生素K1诱导的矿化对华法林高度敏感，而维生素K2和K3诱导的矿化则不太敏感，这意味着γ-羧化和其他机制，可能是通过激活类固醇外源性受体的基因组作用，参与了这一效应。对矿化的积极作用与基质合成减少有关，I型胶原mRNA表达相对于对照的降低证明了这一点，这意味着有成熟作用。在三维I型胶原凝胶培养系统中，在维生素K2或K3存在下孵育导致具有类似骨细胞的细长细胞质突起的细胞数量增加。这种效应对华法林不敏感。向维生素K处理的细胞中添加钙黄绿素显示与细胞突起相关的维生素K依赖性矿物质沉积。这些效应与维生素K促进人类成骨细胞向骨细胞转变一致。为了测试维生素K是否也作用于成熟骨细胞，我们测试了维生素K对MLO-Y4细胞的影响。相对于骨保护素，维生素K降低了MLO-Y4细胞中核因子κB受体激活剂配体的表达，在人类培养物中也观察到了这种效应。总之，我们的研究结果表明，维生素K促进成骨细胞向骨细胞转变，同时降低这些细胞的破骨细胞生成潜能。这些可能是维生素K在体内优化骨形成和完整性的机制，可能有助于解释维生素K对骨形成的净积极作用。
