AMP-activated protein kinase is involved in COX-2 expression in response to ultrasound in cultured osteoblasts

It has been shown that ultrasound (US) stimulation accelerates fracture healing in the animal models and in clinical studies. Cyclooxygenase-2 (COX-2) is a crucial mediator in mechanically induced bone formation. AMP-activated protein kinase (AMPK) has reported to sense and regulate the cellular energy status in various cell types. Here we found that US-mediated COX-2 expression was attenuated by LKB1 and AMPK alpha 1 small interference RNA (siRNA) in human osteoblasts. Pretreatment of osteoblasts with AMPK inhibitor (araA and compound C), p38 inhibitor (SB203580), NF-kappa B inhibitor (PDTC), I kappa B protease inhibitor (TPCK) and NF-kappa B inhibitor peptide also inhibited the potentiating action of US. US increased the kinase activity and phosphorylation of LKB1, AMPK and p38. Stimulation of osteoblasts with US activated I kappa B kinase alpha/beta (IKK alpha/beta), I kappa B alpha phosphorylation, I kappa B alpha degradation, p65 phosphorylation at Ser(276), p65 and p50 translocation from the cytosol to the nucleus, and kappa B-luciferase activity. US-mediated an increase of IK kappa alpha/beta activity, kappa B-luciferase activity and p65 and p50 binding to the NF-kappa B element was inhibited by araA, SB203580 and LKB1 siRNA. Our results suggest that US increased COX-2 expression in osteoblasts via the LKB1/AMPK alpha 1/ p38/IKK alpha beta and NF-kappa B signaling pathway. (C) 2008 Elsevier Inc. All rights reserved.