Comparative Gene Expression Profiling of Normal and Degenerative Discs

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Abstract
A rabbit annular laceration model was used to investigate intervertebral disc gene expression in normal and lacerated discs. To determine and compare the pattern of expression of potentially important genes in normal and lacerated discs and to determine if the changes in gene expression were similar to human degenerative discs. Little is known regarding gene expression in normal or degenerating disc tissue. Eighteen rabbits were subjected to annular laceration of the L1-L2 and L2-L3 discs while two rabbits served as sham controls. Control and lacerated discs were harvested 1 week, 3 weeks, and 6 weeks following surgery and subjected to histologic examination and gene expression analysis using the reverse transcription-polymerase chain reaction (RT-PCR). The genes studied included collagen Type I (Col I), collagen Type II (Col II), decorin, fibronectin (FN), interleukin-1a (IL-1alpha), bone morphogenetic protein 2 (BMP-2), Fas, matrix metalloproteinase 1 (MMP-1), matrix metalloproteinase 9 (MMP-9), matrix metalloproteinase 13 (MMP-13), and tumor necrosis factor (TNF). Expression levels of each gene were normalized to that of glyceraldehyde-3-phosphate dehydrogenase (GADPH), a constitutively expressed gene. Histology confirmed progressive degeneration of the discs over the 6-week study period. Different patterns of gene expression were observed in control and lesioned discs. Annular laceration caused a marked upregulation (two- to eightfold) of the expression of Col I, Col II, FN, MMP-1, MMP-9, MMP-13, and Fas genes, whereas that of BMP-2, IL-1alpha, and TNF genes was unaffected. Expression of the decorin gene was downregulated approximately sixfold after annular laceration. Annular laceration in this animal model resulted in marked changes in gene expression. Upregulation of gene expression was observed for some molecules found at high concentration in human degenerated discs, suggesting similarities to human disc degeneration at the molecular level. This supports the need for further study of the genes found to be activated by annular laceration.