INSERM U1059/LBTO, Université de Lyon - Université Jean Monnet, Saint-Etienne, France.
J Cell Physiol. 2015 Mar;230(3):568-77. doi: 10.1002/jcp.24772.
Osteopontin (OPN) and bone sialoprotein (BSP) are coexpressed in osteoblasts and osteoclasts, and display overlapping properties. We used daily injection of parathyroid hormone 1-84 (iPTH) over the calvaria of BSP knockout (-/-) mice to investigate further their functional specificity and redundancy. iPTH stimulated bone formation in both +/+ and -/- mice, increasing to the same degree periosteum, osteoid and total bone thickness. Expression of OPN, osterix, osteocalcin (OCN) and DMP1 was also increased by iPTH in both genotypes. In contrast to +/+, calvaria cell cultures from -/- mice revealed few osteoblast colonies, no mineralization and little expression of OCN, MEPE or DMP1. In contrast, OPN levels were 5× higher in -/- versus +/+ cultures. iPTH increased alkaline phosphatase (ALP) activity in cell cultures of both genotypes, with higher OCN and the induction of mineralization in -/- cultures. siRNA blocking of OPN expression did not alter the anabolic action of the hormone in BSP +/+ calvaria, while it blunted iPTH effects in -/- mice, reduced to a modest increase in periosteum thickness. In -/- (not +/+) cell cultures, siOPN blocked the stimulation by iPTH of ALP activity and OCN expression, as well as the induction of mineralization. Thus, full expression of either OPN or BSP is necessary for the anabolic effect of PTH at least in the ectopic calvaria injection model. This suggests that OPN may compensate for the lack of BSP in the response to this hormonal challenge, and provides evidence of functional overlap between these cognate proteins.
骨桥蛋白 (OPN) 和骨唾液蛋白 (BSP) 在成骨细胞和破骨细胞中共同表达，并表现出重叠的特性。我们使用甲状旁腺激素 1-84（iPTH）每天注射到 BSP 敲除（-/-）小鼠的颅骨上来进一步研究它们的功能特异性和冗余性。iPTH 刺激 +/+ 和 -/- 小鼠的骨形成，使骨膜、类骨质和总骨厚度增加到相同程度。两种基因型中，iPTH 还增加了 OPN、osterix、骨钙素 (OCN) 和 DMP1 的表达。与 +/+ 相比，-/- 小鼠的颅骨细胞培养物中形成的成骨细胞菌落较少，没有矿化，OCN、MEPE 或 DMP1 的表达也很少。相比之下，-/- 培养物中的 OPN 水平比 +/+ 培养物高 5 倍。iPTH 增加了两种基因型细胞培养物中的碱性磷酸酶（ALP）活性，-/- 培养物中的 OCN 水平更高，诱导矿化。siRNA 阻断 OPN 表达不会改变激素在 BSP+/+ 颅骨中的合成代谢作用，而在 -/- 小鼠中则减弱了 iPTH 的作用，使骨膜厚度适度增加。在 -/-（而非 +/+）细胞培养物中，siOPN 阻断了 iPTH 对 ALP 活性和 OCN 表达的刺激作用，以及矿化的诱导作用。因此，至少在异位颅骨注射模型中，OPN 或 BSP 的完全表达是 PTH 合成代谢作用所必需的。这表明 OPN 可能在对这种激素挑战的反应中弥补 BSP 的缺乏，并为这些同源蛋白之间的功能重叠提供了证据。
