Transcription profiling of juvenile and adult calvarial bone

Background: It has widely been observed that young children are capable of reossifying large calvarial defects, while adults lack this endogenous tissue-engineering capacity. The ability of juvenile animals to regenerate calvarial defects has been investigated in multiple animal models, including mice. In this study, the authors used cDNA microarrays to investigate the expression of osteogenesis-associated genes upstream and downstream of Runx2 in juvenile and adult mouse calvaria. Methods: Nonsuture-associated parietal bone discs were harvested from 6-day-old (n = 50) and 60-day-old (n = 35) male CD-1 mice. After separation of the underlying dura mater and overlying pericranium, the calvarial discs were snap-frozen and RNA was extracted from pooled samples of calvaria for microarray analysis. Genes analyzed included cytokines, receptors, and cell-surface and matrix proteins both upstream and downstream of Runx2. Results: Genes associated with the Runx2 pathway had notably higher levels in the juvenile versus adult calvaria. All genes except for osteocalcin were expressed at least twofold higher in the juvenile calvaria. This pattern was validated with quantitative real-time polymerase chain reaction. In addition, mRNA for potent osteoinductive growth factors was present at higher levels in the juvenile compared with the adult calvaria. Conclusions: These findings reflect a genomic environment of active osteoblast differentia-tion and ossification in the juvenile calvaria compared with the adult aquiescent calvarial tissue. These data suggest that a decreased osteogenic potential of adult calvarial osteoblasts may, in part, explain the inability of adult animals to heal calvarial defects.背景：学界已广泛观察到，幼儿可实现大型颅骨缺损（calvarial defects）的再骨化（reossify），而成人则缺乏此类内源性组织工程能力（endogenous tissue-engineering capacity）。幼年动物再生颅骨缺损的能力已在包括小鼠在内的多种动物模型中得到研究。本研究采用cDNA微阵列（cDNA microarrays），探究了幼年与成年小鼠颅骨中Runt相关转录因子2（Runx2）上下游成骨相关基因的表达情况。 方法：从6日龄（n=50）及60日龄（n=35）雄性CD-1小鼠体内获取无缝线附着的顶骨骨盘。分离下方硬脑膜（dura mater）与上方骨膜（pericranium）后，将颅骨骨盘快速冷冻，并从混合的颅骨样本中提取RNA用于微阵列分析。本次分析涵盖Runx2上下游的细胞因子、受体、细胞表面蛋白及基质蛋白相关基因。 结果：与成年小鼠颅骨相比，Runx2通路相关基因在幼年小鼠颅骨中的表达水平显著更高。除骨钙蛋白（osteocalcin）外，其余所有基因在幼年颅骨中的表达量均至少高出两倍。该表达模式通过实时定量聚合酶链反应（quantitative real-time polymerase chain reaction）得到验证。此外，相较于成年颅骨，幼年颅骨中强效骨诱导生长因子（osteoinductive growth factors）的mRNA水平更高。 结论：上述结果表明，相较于成年小鼠处于静止状态的颅骨组织，幼年小鼠颅骨所处的基因组环境更利于成骨细胞分化与骨化过程。本研究数据提示，成年小鼠颅骨成骨细胞的成骨潜能下降，可部分解释成年动物无法修复颅骨缺损的原因。