Low‐intensity pulsed ultrasound stimulation enhances TIMP‐1 in nucleus pulposus cells and MCP‐1 in macrophages in the rat

Abstract

Recent studies have reported that low-intensity pulsed ultrasound (LIPUS) stimulates cell proliferation and proteoglycan production in rabbit intervertebral disc cells, and moreover promotes the secretion of MCP-1 (monocyte chemotaxis protein-1) from macrophages in a disc organ culture model. These findings suggest the possible application of LIPUS for biological repair of disc degeneration and herniation. Although the mechanisms involved are not well understood, several cytokine pathways may play a role. Therefore, in order to evaluate the effect of LIPUS stimulation on cytokine production by nucleus pulposus cells and macrophages, in vitro culture studies were designed. Nucleus pulposus cells and macrophages were collected from Sprague-Dawley rats, cultured separately in a monolayer, and stimulated with LIPUS for 7 days. After culture, the culture medium and the cells were analyzed by cytokine array, RT-PCR, and ELISA. Cytokine array showed that LIPUS stimulation significantly upregulated TIMP-1 (tissue inhibitor of metalloproteinase-1) in the nucleus pulposus and MCP-1 in macrophages in comparison with the control. This was confirmed at the gene level by RT-PCR in nucleus pulposus cells and macrophages after stimulation with LIPUS. Quantitative evaluation of these proteins by ELISA showed higher levels in nucleus pulposus cells and macrophages stimulated by LIPUS than in controls. These results showed that LIPUS stimulation significantly activated TIMP-1 and MCP-1 in nucleus pulposus cells and macrophages at both the protein and gene levels, suggesting that LIPUS may be a promising supplemental treatment for intervertebral disc herniation.