Signal transduction pathways involved in fluid flow-induced PGE(2) production by cultured osteocytes

To maintain its structural competence, the skeleton adapts to changes in it s mechanical environment. Osteocytes are generally considered the bone mech anosensory cells that translate mechanical signals into biochemical, bone m etabolism-regulating stimuli necessary for the adaptive process. Prostaglan dins are an important part of this mechanobiochemical signaling. We investi gated the signal transduction pathways in osteocytes through which mechanic al stress generates an acute release of prostaglandin E-2 (PGE(2)). Isolate d chicken osteocytes were subjected to 10 min of pulsating fluid flow (PFF; 0.7 +/- 0.03 Pa at 5 Hz), and PGE(2) release was measured. Blockers of Ca2 + entry into the cell or Ca2+ release from internal stores markedly inhibit ed the PFF-induced PGE(2) release, as did disruption of the actin cytoskele ton by cytochalasin B. Specific inhibitors of Ca2+-activated phospholipase C, protein kinase C, and phospholipase A(2) also decreased PFF-induced PGE( 2) release. These results are consistent with the hypothesis that PFF raise s intracellular Ca2+ by an enhanced entry through mechanosensitive ion chan nels in combination with Ca2+- and inositol trisphosphate (the product of p hospholipase C)-induced Ca2+ release from intracellular stores. Ca2+ and pr otein kinase C then stimulate phospholipase A(2) activity, arachidonic acid production, and ultimately PGE(2) release.