Stretch-induced inhibition of Wnt/beta-catenin signaling in mineralizing osteoblasts.
Wnt signaling is important for bone formation and osteoblastic differentiation. Recent findings indicate a stimulating role of Wnt 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 and 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 and 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.
Department of Orthopaedics, Erasmus University Medical Centre, Room Ee 1614, P.O. Box 2040, 3000 CA Rotterdam, the Netherlands.
Justus H W
JH
Jansen
Marco
M
Eijken
Holger
H
Jahr
Hideki
H
Chiba
Jan A N
JA
Verhaar
Johannes P T M
JP
van Leeuwen
Harrie
H
Weinans
D002070:Butadienes / Q000494:pharmacology; D002113:Calcification, Physiologic / Q000502:physiology*; D002454:Cell Differentiation; D002461:Cell Line, Transformed; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017930:Genes, Reporter; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D018021:Lithium Chloride / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D010957:Plasmids; D020218:Response Elements / Q000187:drug effects / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects; D013314:Stress, Mechanical; D013997:Time Factors; D014018:Tissue Distribution / Q000187:drug effects; D015854:Up-Regulation; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism*
D002070:Butadienes; D004791:Enzyme Inhibitors; D009570:Nitriles; C113580:U 0126; D051153:Wnt Proteins; D051176:beta Catenin; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; D018021:Lithium Chloride