There is now conclusive evidence that extracellular nucleotides acting via cell surface P2 receptors are important local modulators of bone cell function. Multiple subtypes of P2 receptors have been localized to bone, where their activation modulates multiple processes including osteoblast proliferation, osteoblast‐mediated bone formation, and osteoclast formation and resorptive capacity. Locally released nucleotides also have been shown to sensitize surrounding cells to the action of systemic factors such as parathyroid hormone (PTH). In nonskeletal tissue recent attention has focused on one particular P2 receptor, the P2X7 receptor (previously termed P2Z), and its ability to form nonselective aqueous pores in the plasma membrane on prolonged stimulation. Expression of this receptor originally was thought to be restricted to cells of hemopoietic origin, in which it has been implicated in cell fusion, apoptosis, and release of proinflammatory cytokines. However, recent reports have indicated expression of this receptor in cells of stromal origin. In this study, we investigated the expression of the P2X7 receptor in two human osteosarcoma cell lines, as well as several populations of primary human bone‐derived cells (HBDCs) at the levels of messenger RNA (mRNA) and protein. We found that there is a subpopulation of osteoblasts that expresses the P2X7 receptor and that these receptors are functional as assessed by monitoring ethidium bromide uptake following pore formation. Inhibition of delayed lactate dehydrogenase (LDH) release in response to the specific agonist 2′,3′‐(4‐benzoyl)‐benzoyl‐adenosine triphosphate (BzATP) by the nonspecific P2X receptor antagonist PPADS confirmed a receptor‐mediated event. After treatment with BzATP SaOS‐2 cells exhibited dramatic morphological changes consistent with those observed after P2X7‐mediated apoptosis in hemopoietic cells. Dual staining with terminal deoxynucleotidyl transferase‐mediated deoxyuridine triphosphate‐biotin nick end labeling (TUNEL) and a P2X7‐specific monoclonal antibody confirmed the induction of apoptosis in osteoblasts expressing the P2X7 receptor. These data show for the first time the expression of functional P2X7 receptors in a subpopulation of osteoblasts, activation of which can result in ATP‐mediated apoptosis.
现在有确凿证据表明,通过细胞表面 P2 受体起作用的细胞外核苷酸是骨细胞功能的重要局部调节剂。多种亚型的 P2 受体已被定位到骨骼中,它们的激活可调节多种过程,包括成骨细胞增殖、成骨细胞介导的骨形成、破骨细胞形成和吸收能力。局部释放的核苷酸还被证明能使周围细胞对
甲状旁腺激素(
PTH)等全身因子的作用敏感。 在非骨骼组织中,最近的研究重点是一种特殊的 P2 受体,即 P2X7 受体(以前称为 P2Z),以及它在长期刺激下在质膜上形成非选择性
水孔的能力。这种受体的表达最初被认为仅限于造血细胞,它与细胞融合、细胞凋亡和促炎细胞因子的释放有关。然而,最近的报道表明,这种受体在基质来源的细胞中也有表达。在这项研究中,我们调查了 P2X7 受体在两种人骨肉瘤
细胞系以及几种原代人骨源性细胞(HBDCs)中信使 RNA(mRNA)和蛋白质
水平的表达情况。我们发现,成骨细胞中有一个亚群表达 P2X7 受体,通过监测孔形成后
溴化乙锭的摄取情况,可以评估这些受体的功能。非特异性 P2X 受体拮抗剂 P
PADS 可抑制特异性激动剂 2′,3′-(4-苯甲酰基)-苯甲酰基
腺苷三磷酸酯(Bz
ATP)引起的延迟
乳酸脱氢酶(LDH)释放,这证实了受体介导的事件。经 Bz
ATP 处理后,SaOS-2 细胞表现出与 P2X7 介导的造血细胞凋亡后观察到的形态学变化一致的巨大变化。末端脱氧核苷酸转移酶介导的脱氧
尿苷三磷酸-
生物素缺口末端标记(TUNEL)和 P2X7 特异性单克隆
抗体的双重染色证实了表达 P2X7 受体的成骨细胞诱导了细胞凋亡。这些数据首次表明在成骨细胞的一个亚群中表达了功能性 P2X7 受体,激活该受体可导致
ATP 介导的细胞凋亡。