Affiliations: Department of Orthopaedic Surgery, University of Regensburg, Bad Abbach, Germany | Biomechanics and Tissue Engineering Laboratory, The Ohio State University, Columbus, OH, USA | Clinical Research Unit 208, Center of Dento-Maxillo-Facial Medicine, University of Bonn, Germany | Department of Orthopaedic Surgery, University of Aachen, Aachen, Germany | Department of Experimental Orthopaedics, University of Regensburg, ZMB/Biopark, Regensburg, Germany
Note: [] Address for correspondence: Dr. Björn Rath, University of Regensburg, Kaiser-Karl V.-Allee 3, 93077 Bad Abbach, Germany. Tel.: +49 241 803 6286; Fax: +1 614 247 7475; E-mail: brath27@gmail.com.
Note: [] Both first authors contributed equally to this study.
Abstract: Osteoblasts are mechanosensitive cells, which respond to biomechanical stimuli to regulate the bone structure through anabolic and catabolic gene regulation. To examine the effects of mechanical forces on the osteogenic responses through the SMAD signaling in osteoblasts, the cells were cultured in well-characterized mechanoresponsive 3-D scaffolds and exposed to 10% dynamic compressive strain (Cmp) at 1 Hz. Subsequently, SMAD phosphorylation and osteogenic gene induction was examined. Osteoblasts cultured in 3-D scaffolds exhibited increased constitutive SMAD 1/5/8 phosphorylation, as compared to monolayers cultures. This SMAD 1/5/8 phosphorylation was further upregulated after 10, 30 and 60 min in response to Cmp, exhibiting a peak activation at 30 min. No significant changes in SMAD2 phosphorylation were observed, suggesting signals generated by Cmp may not activate the Transforming Growth Factor-β signaling cascade. Subsequently, biomechanical stimulation-induced SMAD 1/5/8 phosphorylation upregulated the expression of osteogenic genes such as Osteoprotegrin, Msx2 and Runx2. Dorsomorphin, a selective inhibitor of the bone morphogenetic protein (BMP) receptor type 1 (BMPR1), blocked Cmp-induced SMAD 1/5/8 phosphorylation, as well as Osteoprotegrin, Msx2 and Runx2 gene expression. Collectively, the present findings demonstrate that biomechanical stimulation of osteoblasts activates SMAD 1/5/8 in the BMP signaling pathway through BMPR1 and may enhance osteogenesis by upregulating SMAD-dependent osteogenic genes.
