Focal Adhesion Kinase Is Important for Fluid Shear Stress‐Induced Mechanotransduction in Osteoblasts

• Published in: Journal of bone and mineral research Vol. 24; no. 3; pp. 411 - 424
• Main Authors: Young, Suzanne RL, Gerard‐O'Riley, Rita, Kim, Jae‐Beom, Pavalko, Fredrick M
• Format: Journal Article
• Language: English
• Published: Washington, DC John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR) 01.03.2009; Wiley; Amer Soc Bone & Mineral Res
• Subjects: Animals; Biological and medical sciences; Cyclooxygenase 2 - biosynthesis; Dinoprostone - metabolism; Enzyme Activation - drug effects; Enzyme Induction - drug effects; Extracellular Signal-Regulated MAP Kinases - metabolism; Focal Adhesion Protein-Tyrosine Kinases - antagonists & inhibitors; Focal Adhesion Protein-Tyrosine Kinases - deficiency; Focal Adhesion Protein-Tyrosine Kinases - metabolism; Fundamental and applied biological sciences. Psychology; integrins; mechanical loading; Mechanotransduction, Cellular - drug effects; Mice; Original; osteoblasts; Osteoblasts - cytology; Osteoblasts - drug effects; Osteoblasts - enzymology; osteopontin; Osteopontin - metabolism; Phosphorylation - drug effects; Protein Kinase Inhibitors - pharmacology; Proto-Oncogene Proteins c-fos - metabolism; Rats; Rheology; RNA, Small Interfering - metabolism; Skeleton and joints; Stress, Mechanical; stress/strain; Time Factors; Transfection; Up-Regulation - drug effects; Vertebrates: osteoarticular system, musculoskeletal system; Enzyme; Transferases; Osteopontin; Adhesion; Stress; Osteoarticular system; mechanical loading; Vertebrata; integrins; Integrin; Mammalia; Kinase; Osteoblast; Bone; osteoblasts; stress/strain
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1359/jbmr.081102

Mechanical loading of bone is important for maintenance of bone mass and structural stability of the skeleton. When bone is mechanically loaded, movement of fluid within the spaces surrounding bone cells generates fluid shear stress (FSS) that stimulates osteoblasts, resulting in enhanced anabolic activity. The mechanisms by which osteoblasts convert the external stimulation of FSS into biochemical changes, a process known as mechanotransduction, remain poorly understood. Focal adhesions are prime candidates for transducing external stimuli. Focal adhesion kinase (FAK), a nonreceptor tyrosine kinase found in focal adhesions, may play a key role in mechanotransduction, although its function has not been directly examined in osteoblasts. We examined the role of FAK in osteoblast mechanotransduction using short interfering RNA (siRNA), overexpression of a dominant negative FAK, and FAK−/− osteoblasts to disrupt FAK function in calvarial osteoblasts. Osteoblasts were subjected to varying periods oscillatory fluid flow (OFF) from 5 min to 4 h, and several physiologically important readouts of mechanotransduction were analyzed including: extracellular signal‐related kinase 1/2 phosphorylation, upregulation of c‐fos, cyclooxygenase‐2, and osteopontin, and release of prostaglandin E2. Osteoblasts with disrupted FAK signaling exhibited severely impaired mechanical responses in all endpoints examined. These data indicate the importance of FAK for both short and long periods of FSS‐induced mechanotransduction in osteoblasts.