Study design: In vitro experimental study.
Objective: To investigate the effect of low-intensity pulsed ultrasound (LIPUS) on the extracellular matrix (ECM) synthesis of degenerative human nucleus pulposus cells and explore the molecular mechanism.
Summary of background data: LIPUS has been used successfully for bone fracture healing and been proved to be effective in stimulating ECM metabolism in animal intervertebral disc cells. However, whether LIPUS also exerts an anabolic effect on degenerative human nucleus pulposus cells and the possible molecular mechanism is still unclear.
Methods: The degenerative human nucleus pulposus cells were cultured in calcium alginate beads. In the LIPUS group, cells were exposed to an average temporal intensity of 30 mW/cm2 and a frequency of 1.5 MHz of LIPUS 20 minutes daily for 1 week. The control group was cultured in the same way but without LIPUS stimulation. The LY294002 group was stimulated by LIPUS and treated with LY294002 simultaneously. The expression of aggrecan, collagen-II, Sox9, tissue inhibitor of metalloproteinase-,1 and matrix metalloproteinase-3 were evaluated by Enzyme-Linked Immunosorbent Assay, Western blot or RT-PCR. Expression of signaling proteins involved in FAK/PI3K/Akt pathway was studied by Western blot analysis.
Results: LIPUS significantly upregulated expression of aggrecan, collagen-II, Sox9, and tissue inhibitor of metalloproteinase-1 compared with control group, but inhibited secretion of matrix metalloproteinase-3. The study further demonstrated that the upregulation of aggrecan, collagen-II, and Sox9 was related to the activation of focal adhesion kinase (FAK)//PI3K/Akt pathway caused by LIPUS. Moreover, inhibition of PI3K/Akt significantly suppressed the special biological effect activated by LIPUS.
Conclusion: LIPUS promotes the ECM synthesis of degenerative human nucleus pulposus cells through activation of FAK/PI3K/Akt pathway.
Level of evidence: N/A.