Effects of mechanical strain on the function of gap junctions in osteocytes are mediated through the prostaglandin EP2 receptor

被引:143
作者
Cherian, PP
Cheng, BX
Gu, SM
Sprague, E
Bonewald, LF
Jiang, JX
机构
[1] Univ Texas, Hlth Sci Ctr, Dept Biochem, MSC 7760, San Antonio, TX 78229 USA
[2] Univ Texas, Hlth Sci Ctr, Dept Radiol, San Antonio, TX 78229 USA
[3] Univ Missouri, Sch Dent, Dept Oral Biol, Kansas City, MO 64108 USA
关键词
D O I
10.1074/jbc.M302993200
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
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.
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页码:43146 / 43156
页数:11
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