Low-Intensity Pulsed Ultrasound Modulates Shear Stress Induced PGHS-2 Expression and PGE2 Synthesis in MLO-Y4 Osteocyte- Like Cells

Fluid shear stress (SS) has been shown to be a prevailing physiological stimulus in the regulation of bone cell metabolism and so are the exogenous biomechanical forces, like ultrasound (US) and vibration. The purpose of this study is to elaborate the interplay of laminar fluid SS with low-intensity pulsed US in the regulation of prostaglandin H synthase 2 (PGHS-2) and prostaglandin E-2 (PGE(2)). Murine long bone osteocyte-like (MLO-Y4) cells were exposed to various regimes of US (1.5 Hz, 30 mW/cm(2)) and SS (19 dyn/cm(2)) alone and sequentially. Changes in PGHS-2 gene expression levels were quantified at 3 and 24 h using real-time RT-PCR. PGE(2) levels in the culture media were measured using enzyme immunoassay at 3 and 24 h. PGE(2) levels significantly increased after exposure to SS for 3 and 24 h by 2.17 +/- 0.02 and 5.47 +/- 0.42-fold, respectively, compared to control cells. A 20 min US treatment prior to SS significantly increased SS PGE(2) levels 2.95 +/- 0.18 and 2.90 +/- 0.50-fold at 3 and 24 h, respectively. US also significantly increased PGHS-2 mRNA levels in cells exposed to SS. SS caused a 2.74 +/- 0.49-fold increase in PGHS-2 mRNA levels at 3 h and a significant 3.70 +/- 0.25-fold increase at 24 h relative to control. A 20 min US treatment caused 1.35 +/- 0.49 and 2.44 +/- 0.82-fold increase in PGHS-2 mRNA levels in cells exposed to SS at 3 and 24 h, respectively. These results indicate that combining US with SS may have a more anabolic benefit for bone tissue than either stimulus alone.