title: GRK2 desensitizes flow-induced responses in osteoblasts.
abstract: Bone desensitization after mechanical loading is essential for bone to adapt to its mechanical environment. However, the desensitization mechanism is unknown. Previous studies suggest that G protein-coupled receptors (GPCRs), including P2Y and parathyroid hormone receptors, play important roles in osteoblast mechanobiology. Thus, for the present research, we examined the role of G protein-coupled receptor kinase 2 (GRK2) in osteoblast desensitization after exposure to mechanical stimulation. We first showed the existence of osteoblast desensitization after mechanical stimulation based on cytosol Ca2+and phosphorylated ERK1/2 activities, detected using a fluorescent Ca2+-sensitive dye and western blotting, respectively. We then demonstrated that GRK2 overexpression in MC3T3-E1 cells inhibits flow-induced ERK1/2 phosphorylation, while siRNA knockdown of GRK2 enhances ERK1/2 phosphorylation. Additionally, we found that GRK2 overexpression in MC3T3-E1 cells inhibits cyclooxygenase-2 mRNA expression in the short term and alkaline phosphatase activity in the long term. More importantly, we discovered that GRK2 translocated to the cell membrane shortly after flow stimulation - a step necessary for GPCR desensitization. Previously, we have demonstrated that P2Y2 purinergic receptors, one type of GPCRs, are involved in various flow-induced osteoblastic responses. In this research, we also showed that GRK2 overexpression does not affect ATP release. Accordingly, GRK2 is able to inhibit flow-induced osteoblast responses possibly through desensitizing P2Y2 receptors.
authors.affiliation: Beijing Key Laboratory of Rehabilitation Technical Aids for Old-Age Disability, National Research Center for Rehabilitation Technical Aids, Beijing, China Department of Orthopaedics and Rehabilitation, The Pennsylvania State University College of Medicine, Hershey, PA, USA xingyanghui@hotmail.com.
authors.forename: Y
authors.initials: Y
authors.lastname: Xing
authors.forename: Y
authors.initials: Y
authors.lastname: Gu
authors.affiliation: Beijing Key Laboratory of Rehabilitation Technical Aids for Old-Age Disability, National Research Center for Rehabilitation Technical Aids, Beijing, China Department of Orthopaedics and Rehabilitation, The Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: X
authors.initials: X
authors.lastname: Shan
authors.affiliation: Beijing Key Laboratory of Rehabilitation Technical Aids for Old-Age Disability, National Research Center for Rehabilitation Technical Aids, Beijing, China Department of Orthopaedics and Rehabilitation, The Pennsylvania State University College of Medicine, Hershey, PA, USA.
authors.forename: L
authors.initials: L
authors.lastname: Wang
authors.forename: J
authors.initials: J
authors.lastname: You
mesh_terms: D000818:Animals; D015415:Biomarkers; D002460:Cell Line; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D055595:Mechanical Phenomena; D051379:Mice; D010006:Osteoblasts / Q000502:physiology*; D010766:Phosphorylation; D058473:Receptors, Purinergic P2Y2 / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D015415:Biomarkers; D058473:Receptors, Purinergic P2Y2; D054769:G-Protein-Coupled Receptor Kinase 2