Stretch-Induced Inhibition of Wnt/beta-Catenin Signaling in Mineralizing Osteoblasts

Writ signaling is important for bone formation and osteoblastic differentiation Recent findings indicate a stimulating role of Writ signaling in bone mechanotransduction However, negative effects of Wnt signaling on osteoblast differentiation and mineralization have been described as well We conducted in vitro stretch experiments using human pre-osteoblasts to study short- and long-term effects of mechanical loading on Wnt/beta-catenin signaling As the extracellular regulated kinase (ERK) pathway is known to be involved in mechanotransduction in osteoblasts. we also evaluated its role in Wnt/beta-catenin Signaling Stretch experiments up to 21 days (using stretch episodes of 15 min, alternated with 90 min rest) resulted in higher mineralization compared to static control cultures We found that 15 min of stretch initially increased nuclear beta-catenin, but ultimately resulted in significant. decrease at 12 anti 40 h after stretch Downregulation of Wnt-responsive element activity 16 h after stretch, using a luciferase construct, further supported these findings The presence of the ERK inhibitor U0126 did not alter the stretch-induced decrease: of beta-catenin levels Our data indicate a biphasic effect of mechanical loading on beta-catenin in mineralizing human differentiating osteoblasts, which is independent of the ERK pathway The osteogenic potential of our loading regime was confirmed by an increase in osteogenic differentiation markers such as alkaline phosphatase activity anti calcium deposition after 3 weeks of culture We conjecture that the biphasic aspect of Wnt/beta-catenin signaling with a strong decrease up to 40 h after the stretch induction, is important for the anabolic effects of mechanical stretch on bone (C) 2009 Orthopaedic Research Society Published by Wiley Periodicals, Inc J Orthop Res 28 390-396, 2010