Abstract
Introduction
Low back pain is a major public health problem in our society. Degeneration of intervertebral disc (IVD) appears to be the leading cause of chronic low-back pain [1]. Mechanical stimulations including compressive and tensional forces are directly implicated in IVD degeneration. Several studies have implicated the cytoskeleton in mechanotransduction [2, 3], which is important for communication and transport between the cells and extracellular matrix (ECM). However, the potential roles of the cytoskeletal elements in the mechanotransduction pathways in IVD are largely unknown.
Methods
Outer annulus fibrosus (OAF) and nucleus pulposus (NP) cells from skeletally mature bovine IVD were either seeded onto Flexcell¯ type I collagen coated plates or seeded in 3% agarose gels, respectively. OAF cells were subjected to cyclic tensile strain (10%, 1Hz) and NP cells to cyclic compressive strain (10%, 1Hz) for 60 minutes. Post-loading, cells were processed for immunofluorescence microscopy and RNA extracted for quantitative PCR analysis.
Results
F-actin reorganisation was evident in OAF and NP cells subjected to tensile and compressive strain respectively and is likely due to load-induced differential mRNA expression of actin-binding proteins. The vimentin network was also more intricately organised in loaded NP cells. Compressive strain increased type II collagen and aggrecan transcription in NP cells, whereas levels decreased in OAF cells under tension. mRNA levels of ECM-degrading enzymes were significantly reduced in both cell populations after loading.
Conclusion
Tensile and compressive strains induce different mechano-responses in the organisation/expression of cytoskeletal elements and on markers of IVD metabolism. Differential mechano-regulation of anabolic and catabolic ECM components in the OAF and NP populations reflects their respective mechanical environments in situ.
