Pertussis toxin-sensitive Galphai protein and ERK-dependent pathways mediate ultrasound promotion of osteogenic transcription in human osteoblasts.
Bone cells respond to mechanical stimulation via mechanoreceptors and convert biophysical stimulation into biochemical signals that alter gene expression and cellular adaptation. Pulsed acoustic energy treatment raises membrane potential and induces osteogenic activity. How membrane-bound osteoblast mechanoreceptors convert physical ultrasound (US) stimuli into osteogenic responses is not fully understood. We demonstrated that low-intensity pulsed US treatment (200-micros pulse, 1 kHz, 30 mW/cm2) elevated Cbfa1/Runx2 mRNA expression and progressively promoted osteocalcin mRNA expression in human osteoblasts. Pretreatment with pertussis toxin (PTX), but not with cholera toxin, suppressed US-augmented osteogenic transcription. This indicated that Gi proteins, but not Gs proteins, were involved in US promotion of osteogenic transcription. Further studies demonstrated US treatment could rapidly increase PTX-sensitive Galphai protein levels and subsequently enhanced phosphorylation of extracellular signal-regulated kinase (ERK). PTX pretreatment significantly reduced US promotion of ERK activation. Moreover, inhibition of ERK activity by PD98059 suppressed US augmentation of Cbfa1/Runx2 and osteocalcin mRNA expression. Membranous Galphai proteins and cytosolic ERK pathways acted as potent mechanosensitive signals in the response of osteoblasts to pulsed US stimulation.
Department of Orthopedic Surgery, Chang Gung University, Linkou, Taiwan.
Yeung-Jen
YJ
Chen
Ching-Jen
CJ
Wang
Kuender D
KD
Yang
Per-Rong
PR
Chang
Hui-Chen
HC
Huang
Yu-Ting
YT
Huang
Yi-Chih
YC
Sun
Feng-Sheng
FS
Wang
D002460:Cell Line; D050659:Core Binding Factor Alpha 1 Subunit; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009363:Neoplasm Proteins; D010006:Osteoblasts / Q000378:metabolism* / Q000528:radiation effects; D015675:Osteocalcin / Q000235:genetics; D010012:Osteogenesis / Q000235:genetics / Q000528:radiation effects; D012333:RNA, Messenger / Q000096:biosynthesis; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects / Q000528:radiation effects*; D014465:Ultrasonics; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D050659:Core Binding Factor Alpha 1 Subunit; D008070:Lipopolysaccharides; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D010566:Virulence Factors, Bordetella; C084764:pertussis endotoxin; D015675:Osteocalcin; D020928:Mitogen-Activated Protein Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go