Low-intensity pulsed ultrasound stimulates matrix metabolism of human annulus fibrosus cells mediated by transforming growth factor β1 and extracellular signal-regulated kinase pathway

Purpose: There are limited strategies to restore the damaged annulus fibrosus (AF) of the intervertebral disc. Low-intensity pulsed ultrasound (LIPUS) has positive effects on the proliferation of several types of cells and the repair of damage tissue in vivo. However, scientific evidence of therapeutic effects of LIPUS on AF cells remains limited. The purpose of this study is to evaluate the feasibility of applying LIPUS to the repair of the AF. Materials and methods: We used an in vitro model of human AF cells subjected to LIPUS stimulation to examine its effects on cell proliferation and matrix metabolism. Cell viability, synthesis of collagen and glycosaminoglycan (GAG), expression of matrix metalloproteinases (MMPs) and transforming growth factor beta 1 and pathways involving mitogen-activated protein kinases (MAPKs) were investigated. Results: LIPUS significantly enhanced proliferation of AF cells after 5 days of treatment. LIPUS with an intensity of 0.5 W/cm(2) increased the collagen and GAG synthesis and decreased the expressions of MMP-1 and -3 of human AF cells. Real-time polymerase chain reactions and western blotting analysis revealed that LIPUS could increase transforming growth factor beta 1 (TGF-beta 1) and activate extracellular signal-regulated kinase (ERK) pathway. In addition, TGF-beta receptor kinase inhibitor could suppress the ultrasound-induced alterations in cell viability and matrix metabolism. Conclusions: The findings suggested that LIPUS could be useful as a physical stimulation of cell metabolism for the repair of the AF.