Pertussis toxin‐sensitive Gαi protein and ERK‐dependent pathways mediate ultrasound promotion of osteogenic transcription in human osteoblasts¹

Abstract

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-W Ws pulse, 1 kHz, 30 mW/cm 2 ) 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 GK Ki protein levels and subsequently enhanced phosphorylation of extracellular signal-regulated kinase (ERK). PTX pretreatment signi¢cantly reduced US promotion of ERK activation. Moreover, inhibition of ERK activity by PD98059 suppressed US augmentation of Cbfa1/Runx2 and osteocalcin mRNA expression. Membranous GK Ki proteins and cytosolic ERK pathways acted as potent mechanosensitive signals in the response of osteoblasts to pulsed US stimulation.

Low intensity pulsed ultrasound accelerated bone remodeling during consolidation stage of distraction osteogenesis

“…30 In addition, LIPUS was reported to increase osteocalcin mRNA expression in preosteoblastic cell line. 31 All these studies implied that ultrasound stimulated osteoblast, activated bone matrix formation and, finally, facilitated intramembranous ossification. Moreover, high cellularity and less mineralization at the early stage of consolidation might be in favor of LIPUS treatment.…”

Tenocyte responses to mechanical loading in vivo: A role for local insulin‐like growth factor 1 signaling in early tendinosis in rats

“…In cultured human osteoblasts, ERK-1/2 blockade prevented shear-induced proliferation and matrix synthesis (43). Tenocytes appear to share elements of a load-sensing mechanism similar to osteoblasts and osteocytes; stretch-activated potassium and calcium channels, internal calcium release, interstitial ATP release, and gap junction signaling all play a role in the proliferative response to membrane deformation, substrate deformation, or fluid shear (43)(44)(45)(46)(47). In elongated tenocytes, proliferation and collagen synthesis in response to ex vivo loading of chicken flexor tendon could be blocked by a gap junction inhibitor (48).…”

Optimal Intensity Shock Wave Promotes the Adhesion and Migration of Rat Osteoblasts via Integrin β1-mediated Expression of Phosphorylated Focal Adhesion Kinase

“…Many studies have shown that effective physical stimulation could induce a series of biological changes in osteoblasts, such as osteogenic effect (58,59), alteration of gene expression (44,60), and related signal pathway changes (44,61). The beneficial effects for enhanced osteoblast adhesion and migration may result from reorganization of actin cytoskeleton to a certain degree (23).…”