Bone Biology Research Consortium, Department of Cell Biology and Anatomy, Institute of Biomedicine, University of Turku, FIN-20520 Turku, Finland.
Matrix Biol. 2010 May;29(4):287-94. doi: 10.1016/j.matbio.2010.01.003. Epub 2010 Jan 15.
Dissolution of the inorganic bone matrix releases not only calcium and phosphate ions, but also bicarbonate. Electroneutral sodium-bicarbonate co-transporter (NBCn1) is expressed in inactive osteoclasts, but its physiological role in bone resorption has remained unknown. We show here that NBCn1, encoded by the SLC4A7 gene, is directly involved in bone resorption. NBCn1 protein was specifically found at the bone-facing ruffled border areas, and metabolic acidosis increased NBCn1 expression in rats in vivo. In human hematopoietic stem cell cultures, NBCn1 mRNA expression was observed only after formation of resorbing osteoclasts. To further confirm the critical role of NBCn1 during bone resorption, human hematopoietic stem cells were transduced with SLC4A7 shRNA lentiviral particles. Downregulation of NBCn1 both on mRNA and protein level by lentiviral shRNAs significantly inhibited bone resorption and increased intracellular acidification in osteoclasts. The lentiviral particles did not impair osteoclast survival, or differentiation of the hematopoietic or mesenchymal precursor cells into osteoclasts or osteoblasts in vitro. Inhibition of NBCn1 activity may thus provide a new way to regulate osteoclast activity during pathological bone resorption.
无机骨基质的溶解不仅释放钙和磷酸盐离子，还释放碳酸氢盐。电中性的钠离子-碳酸氢盐协同转运蛋白（NBCn1）在不活跃的破骨细胞中表达，但它在骨吸收中的生理作用仍不清楚。我们在这里表明，由 SLC4A7 基因编码的 NBCn1 直接参与骨吸收。NBCn1 蛋白特异性地存在于面向骨的皱褶边缘区域，体内代谢性酸中毒增加了大鼠的 NBCn1 表达。在人类造血干细胞培养物中，只有在形成破骨细胞后才观察到 NBCn1 mRNA 表达。为了进一步证实 NBCn1 在骨吸收过程中的关键作用，用 SLC4A7 shRNA 慢病毒颗粒转导人类造血干细胞。慢病毒 shRNA 对 NBCn1 的 mRNA 和蛋白水平的下调显著抑制了破骨细胞的骨吸收，并增加了破骨细胞内的酸化。这些慢病毒颗粒在体外不会损害破骨细胞的存活，也不会损害造血或间充质前体细胞向破骨细胞或成骨细胞的分化。因此，抑制 NBCn1 活性可能为调节病理性骨吸收期间破骨细胞活性提供一种新方法。
