Gowen Lori C, Petersen Donna N, Mansolf Amy L, Qi Hong, Stock Jeffrey L, Tkalcevic George T, Simmons Hollis A, Crawford David T, Chidsey-Frink Kristen L, Ke Hua Zhu, McNeish John D, Brown Thomas A
Department of Cardiovascular and Metabolic Diseases, Pfizer Global Research and Development, Groton, Connecticut 06340, USA.
J Biol Chem. 2003 Jan 17;278(3):1998-2007. doi: 10.1074/jbc.M203250200. Epub 2002 Nov 5.
We have previously described osteoblast/osteocyte factor 45 (OF45), a novel bone-specific extracellular matrix protein, and demonstrated that its expression is tightly linked to mineralization and bone formation. In this report, we have cloned and characterized the mouse OF45 cDNA and genomic region. Mouse OF45 (also called MEPE) was similar to its rat orthologue in that its expression was increased during mineralization in osteoblast cultures and the protein was highly expressed within the osteocytes that are imbedded within bone. To further determine the role of OF45 in bone metabolism, we generated a targeted mouse line deficient in this protein. Ablation of OF45 resulted in increased bone mass. In fact, disruption of only a single allele of OF45 caused significantly increased bone mass. In addition, knockout mice were resistant to aging-associated trabecular bone loss. Cancellous bone histomorphometry revealed that the increased bone mass was the result of increased osteoblast number and osteoblast activity with unaltered osteoclast number and osteoclast surface in knockout animals. Consistent with the bone histomorphometric results, we also determined that OF45 knockout osteoblasts produced significantly more mineralized nodules in ex vivo cell cultures than did wild type osteoblasts. Osteoclastogenesis and bone resorption in ex vivo cultures was unaffected by OF45 mutation. We conclude that OF45 plays an inhibitory role in bone formation in mouse.
我们之前曾描述过成骨细胞/骨细胞因子45(OF45),一种新型的骨特异性细胞外基质蛋白,并证明其表达与矿化和骨形成紧密相关。在本报告中,我们克隆并鉴定了小鼠OF45的cDNA和基因组区域。小鼠OF45(也称为MEPE)与其大鼠同源物相似,其表达在成骨细胞培养矿化过程中增加,且该蛋白在嵌入骨内的骨细胞中高度表达。为了进一步确定OF45在骨代谢中的作用,我们构建了该蛋白缺失的靶向小鼠品系。OF45的缺失导致骨量增加。事实上,仅破坏OF45的一个等位基因就会导致骨量显著增加。此外,基因敲除小鼠对与衰老相关的小梁骨丢失具有抗性。松质骨组织形态计量学显示,骨量增加是由于基因敲除动物中成骨细胞数量和活性增加,而破骨细胞数量和破骨细胞表面积未改变。与骨组织形态计量学结果一致,我们还确定,在体外细胞培养中,OF45基因敲除的成骨细胞比野生型成骨细胞产生的矿化结节明显更多。体外培养中的破骨细胞生成和骨吸收不受OF45突变的影响。我们得出结论,OF45在小鼠骨形成中起抑制作用。