Bronckers Antonius L J J, Sasaguri Kenichi, Engelse Marten A
Department of Oral Cell Biology, ACTA, 1081 BT Amsterdam, The Netherlands.
Microsc Res Tech. 2003 Aug 15;61(6):540-8. doi: 10.1002/jemt.10377.
Runx2/Cbfa1 is a transcription factor, essential for the osteogenic/chondrogenic and odontogenic lineage. Three isoforms of Cbfa1 have been identified, type I (Pebp2alphaA isoform), type II (til-1 isoform), and type III (Osf2 isoform). Here we examined the expression of the Runx2/Cbfa1 during intramembranous and enchondral bone formation in the craniofacial tissues of neonatal rodents (hamster, rat, mouse) and the human fetus. We used a monoclonal antibody raised against the Pebp2alphaA portion and thus potentially recognizing all three isoforms of Runx2/Cbaf1. We report Cbfa1 at the mRNA and protein level in periosteum, preosteoblasts, osteoblasts, young osteocytes, perichondrium, resting and hypertrophic chondrocytes. During active bone remodeling, almost one third of tartrate resistant acid phosphatase (TRAP) positive multinuclear cells identified as osteoclasts were also stained with anti-Pebp2alphaA antibodies. Osteoclasts, however, did not express mRNA transcripts of the Pebp2alphaA gene. Some of the immunopositive structures within these osteoclasts resembled (ingested) cells. TRAP-positive mononuclear cells not attached to bone surfaces did not stain with anti-Pebp2alphaA antibodies. We concluded that the tissue distribution of Runx2/Cbaf1/Pebp2alphaA in ossifying bones of the human fetus is similar to that in neonatal rodent tissues. Osteoclasts do not transcribe the Runx2/Cbfa1 gene but become immunostained by phagocytosing and digesting osteocytes/hypertrophic chondrocytes. The substantial number of osteoclasts involved in phagocytosis of Runx2/Cbfa1 immunopositive cells suggests that phagocytosis is a major way of removing osteocytes/hypertrophic chondrocytes during resorption of bone and cartilage. Finally, the data indicate that positive immunostaining of osteoclasts for typical osteogenic/chondrogenic markers has to be interpreted with caution due to the phagocytosing capacity of these cells.
Runx2/Cbfa1是一种转录因子，对成骨/软骨生成和牙源性谱系至关重要。已鉴定出Cbfa1的三种亚型，即I型（Pebp2alphaA亚型）、II型（til-1亚型）和III型（Osf2亚型）。在此，我们研究了Runx2/Cbfa1在新生啮齿动物（仓鼠、大鼠、小鼠）和人类胎儿颅面组织的膜内和软骨内骨形成过程中的表达。我们使用了一种针对Pebp2alphaA部分产生的单克隆抗体，因此可能识别Runx2/Cbaf1的所有三种亚型。我们报告了Cbfa1在骨膜、前成骨细胞、成骨细胞、年轻骨细胞、软骨膜、静止和肥大软骨细胞中的mRNA和蛋白质水平。在活跃的骨重塑过程中，几乎三分之一被鉴定为破骨细胞的抗酒石酸酸性磷酸酶（TRAP）阳性多核细胞也被抗Pebp2alphaA抗体染色。然而，破骨细胞不表达Pebp2alphaA基因的mRNA转录本。这些破骨细胞内的一些免疫阳性结构类似于（摄取的）细胞。未附着于骨表面的TRAP阳性单核细胞未被抗Pebp2alphaA抗体染色。我们得出结论，Runx2/Cbaf1/Pebp2alphaA在人类胎儿骨化骨中的组织分布与新生啮齿动物组织中的相似。破骨细胞不转录Runx2/Cbfa1基因，但通过吞噬和消化骨细胞/肥大软骨细胞而被免疫染色。大量参与吞噬Runx2/Cbfa1免疫阳性细胞的破骨细胞表明，吞噬作用是在骨和软骨吸收过程中清除骨细胞/肥大软骨细胞的主要方式。最后，数据表明，由于这些细胞的吞噬能力，破骨细胞对典型成骨/软骨生成标志物的阳性免疫染色必须谨慎解释。
