Effects of cyclic tensile strain on actin cytoskeleton rearrangement in annulus fibrosus cells / 中国组织工程研究

ABSTRACT

BACKGROUND:When the intervertebral disc is under stress, the hydraulic pressure generated inside the nucleus pulposus makes the annulus fibrosus extend outward and expand, and the annulus colagen fibers are stretched so that the extracelular matrix of annulus fibrosus cels is also under the pressure. In the intervertebral disc, aggrecan is the main component of proteoglycans, matrix metaloproteinase-2 is a major enzyme for extracelular matrix degradation, and tissue inhibitor of metaloproteinase is a multifunctional specific inhibition factor for matrix metaloproteinase activity. There is a mutual regulation between the latter two to keep the homeostasis between them. OBJECTIVE: To investigate the mechanism of cyclic tensile strain in the metabolism of intervertebral disc annulus matrix. METHODS:Rat anulus fibrosus cels were subjected to 2% or 10% cyclic tensile strain at 1.0 Hz for 2 and 12 hours using Flexcel4000 tension system. Then cels were colected and cultured in conditioned medium for gene and protein detection. Real-time quantitative PCR was used to detect mRNA expression of aggrecan, matrix metaloproteinases-2 and tissue inhibitor of metaloproteinase-2. Gelatin zymography was used to detect matrix metaloproteinases-2 activity. RESULTS AND CONCLUSION:The use of 2% cyclic tensile strain had no obvious effect on the stress fiber of actin cytoskeleton, whereas actin cytoskeleton was depolymerized in response to 10% cyclic tensile strain. The 2% cyclic tensile strain raised the expression of Aggrecan at 12 hours; whereas raised the matrix metaloproteinases-2 and tissue inhibitor of metaloproteinase-2 at 2 hours, both of which were in homeostasis; matrix metaloproteinases-2 activity had no significant changes. 10% cyclic tensile strain had no effect on the mRNA expression of Aggrecan. No matter stretching 2 or 12 hours, the matrix metaloproteinases-2 was up-regulated, and the tissue inhibitor of metaloproteinase-2 was down-regulated, both of which were not in balance. Moreover, the matrix metaloproteinases-2 activity was not significantly changed. These findings indicate that the mRNA expressions of Aggrecan, matrix metaloproteinases-2 and tissue inhibitor of metaloproteinase-2 alter in response to cyclic tensile strain in rat anulus fibrosus cels, and the tensile strain induces different mechano-responses in the actin cytoskeleton.