Effects of mechanical strain on the function of gap junctions in osteocytes are mediated through the prostaglandin EP2 receptor
Effects of mechanical strain on the function of gap junctions in osteocytes are mediated through the prostaglandin EP2 receptor
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DOI：
10.1074/jbc.m302993200
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发表时间：
2003-10-31
影响因子：
4.8
通讯作者：
Jiang, JX
中科院分区：
文献类型：
--
作者：
Cherian, PP;Cheng, BX;Jiang, JX
嵌入骨基质中的骨细胞被认为是机械感觉细胞，可将机械应变转化为调节骨建模和重塑的生化信号。我们之前已经证明，流体流动剪切应力显着诱导骨细胞样 MLO-Y4 细胞中前列腺素释放和 COX-2 mRNA 表达，并且这些细胞释放的前列腺素 E-2 (PGE(2)) 以自分泌方式发挥作用，调节间隙连接功能和连接蛋白 43 (Cx43) 表达。在这里，我们证明流体流动通过 PGE(2) 受体 EP2 激活 cAMP 依赖性蛋白激酶 A (PKA) 信号来调节间隙连接。 EP2 受体的表达随流体流动而增加，但 EP1、EP3 和 EP4 亚型则不然。将 PGE(2) 或来自流体流处理的细胞的条件培养基应用到未应激的 MLO-Y4 细胞中会增加 EP2 受体的表达。 EP2 受体拮抗剂 AH6809 抑制 PGE(2) 和流体流动调节培养基对 EP2 受体表达、Cx43 蛋白表达和间隙连接介导的细胞间偶联的刺激作用。相反，EP2受体激动剂布他前列素，而不是E-1/E-3受体激动剂磺前列酮，刺激Cx43的表达和间隙连接功能。流体流动条件培养基和PGE(2)刺激cAMP产生和PKA活性，表明机械刺激的细胞释放的PGE(2)负责cAMP和PKA的激活。腺苷酸环化酶激活剂毛喉素和 8-溴-cAMP 可增强细胞间连接性、功能性间隙连接的数量和 Cx43 蛋白表达，而 PKA 抑制剂 H89 则抑制 PGE(2) 对间隙连接的刺激作用。这些研究表明，EP2 受体介导自分泌 PGE(2) 对骨细胞间隙连接的影响，以响应流体流动引起的剪切应力。这些数据支持这样的假设：EP2 受体、cAMP 和 PKA 是机械应变和骨细胞之间缝隙连接介导的通讯之间信号级联的关键组成部分。
Osteocytes embedded in the matrix of bone are thought to be mechanosensory cells that translate mechanical strain into biochemical signals that regulate bone modeling and remodeling. We have shown previously that fluid flow shear stress dramatically induces prostaglandin release and COX-2 mRNA expression in osteocyte-like MLO-Y4 cells, and that prostaglandin E-2 (PGE(2)) released by these cells functions in an autocrine manner to regulate gap junction function and connexin 43 (Cx43) expression. Here we show that fluid flow regulates gap junctions through the PGE(2) receptor EP2 activation of cAMP-dependent protein kinase A (PKA) signaling. The expression of the EP2 receptor, but not the subtypes EP1, EP3, and EP4, increased in response to fluid flow. Application of PGE(2) or conditioned medium from fluid flow-treated cells to non-stressed MLO-Y4 cells increased expression of the EP2 receptor. The EP2 receptor antagonist, AH6809, suppressed the stimulatory effects of PGE(2) and fluid flow-conditioned medium on the expression of the EP2 receptor, on Cx43 protein expression, and on gap junction-mediated intercellular coupling. In contrast, the EP2 receptor agonist butaprost, not the E-1/E-3 receptor agonist sulprostone, stimulated the expression of Cx43 and gap junction function. Fluid flow conditioned medium and PGE(2) stimulated cAMP production and PKA activity suggesting that PGE(2) released by mechanically stimulated cells is responsible for the activation of cAMP and PKA. The adenylate cyclase activators, forskolin and 8-bromo-cAMP, enhanced intercellular connectivity, the number of functional gap junctions, and Cx43 protein expression, whereas the PKA inhibitor, H89, inhibited the stimulatory effect of PGE(2) on gap junctions. These studies suggest that the EP2 receptor mediates the effects of autocrine PGE(2) on the osteocyte gap junction in response to fluid flow-induced shear stress. These data support the hypothesis that the EP2 receptor, cAMP, and PKA are critical components of the signaling cascade between mechanical strain and gap junction-mediated communication between osteocytes.