A fibronectin fragment alters the metabolism by rabbit intervertebral disc cells in vitro

Study Design. A biochemical and gene expression study was conducted to determine the effects of the 30-kDa N-terminal fibronectin fragment (Fn-f) on the glycosaminoglycan content of nucleus pulposus (NP) explant cultures, and on the gene expression profile of NP cells in alginate culture. Objective. To determine the effects of Fn-f on NP cells in alginate culture and disc explant cultures. Summary of Background Data. The macroscopic and histologic features of disc degeneration have been well described, but the molecular biology of disc degeneration remains poorly understood. Although fibronectin and fibronectin fragments are known to accumulate in degenerative discs, the role of fibronectin fragments on the degenerative process has not been elucidated. This study sought to define the effects of Fn-f on the expression of key matrix and degradative genes and on disc matrix proteins. Methods. New Zealand white rabbits discs were harvested. NP cells were either isolated and grown in alginate culture or cultured as explanted tissue. The cultured cells were exposed to 10 nmol/L, 100 nmol/L, and 1 mu mol/L concentrations of 30-kDa N-terminal Fn-f or a control substance and then analyzed histologically, biochemically, and with gene expression studies. Results. Alginate-cultured NP cells maintained a histologic appearance and phenotypic expression pattern similar to disc cells in vivo. Exposure of these cells to Fn-f led to the up-regulation of the MMP-9, MMP-13, and Fas genes and the down-regulation of the Type II collagen and aggrecan genes. In explant culture, Fn-f exposure led to a 60% reduction in glycosaminoglycan content compared with controls. Conclusion. Treatment of NP cells in vitro with Fn-f led to changes in matrix proteins and gene expression similar to those seen during disc degeneration in vivo. This supports a possible detrimental role of the N-terminal fibronectin fragment in degenerative disc disease.