Manolson Morris F, Yu Hesheng, Chen Weimin, Yao Yeqi, Li Keying, Lees Rita L, Heersche Johan N M
Faculty of Dentistry, University of Toronto, Toronto, Ontario M5G 1G6, Canada.
J Biol Chem. 2003 Dec 5;278(49):49271-8. doi: 10.1074/jbc.M309914200. Epub 2003 Sep 22.
Osteoclasts dissolve bone through acidification of an extracellular compartment by means of a multimeric vacuolar type H+-ATPase (V-ATPase). In mammals, there are four isoforms of the 100-kDa V-ATPase "a" subunit. Mutations in the a3 isoform result in deficient bone resorption and osteopetrosis, suggesting that a3 has a unique function in osteoclasts. It is thus surprising that several studies show a basal level of a3 expression in most tissues. To address this issue, we have compared a3 expression in bone with expression in other tissues. RNA blots revealed that the a3 isoform was expressed highest in bone and confirmed its expression (in decreasing order) in liver, kidney, brain, lung, spleen, and muscle. In situ hybridization on bone tissue sections revealed that the a3 isoform was highly expressed in multinucleated osteoclasts but not in mononuclear stromal cells, whereas the a1 isoform was expressed in both cell types at about the same level. We also found that a3 expression was greater in osteoclasts with 10 or more nuclei as compared with osteoclasts with five or fewer nuclei. We hypothesize that these differences in a3 expression may be associated with previously demonstrated differences between large and small osteoclasts with reference to their resorptive activity.
破骨细胞通过多聚体空泡型H⁺-ATP酶（V-ATP酶）酸化细胞外区室来溶解骨质。在哺乳动物中，100-kDa V-ATP酶“a”亚基有四种同工型。a3同工型的突变会导致骨吸收不足和骨质石化，这表明a3在破骨细胞中具有独特功能。因此，令人惊讶的是，多项研究表明大多数组织中a3表达处于基础水平。为解决这一问题，我们比较了骨组织中a3的表达与其他组织中的表达情况。RNA印迹显示a3同工型在骨组织中表达最高，并证实其在肝脏、肾脏、脑、肺、脾脏和肌肉中的表达（按降序排列）。骨组织切片的原位杂交显示，a3同工型在多核破骨细胞中高表达，而在单核基质细胞中不表达，而a1同工型在这两种细胞类型中的表达水平大致相同。我们还发现，与具有5个或更少细胞核的破骨细胞相比，具有10个或更多细胞核的破骨细胞中a3表达更高。我们推测，a3表达的这些差异可能与之前所证实的大小破骨细胞在吸收活性方面的差异有关。
