Snapshot of degenerative aging of porcine intervertebral disc: a model to unravel the molecular mechanisms.

Larger animal models, such as porcine, have been validated as appropriate models of the human disc with respect to biomechanics and biochemistry. They are advantageous for research as the models are relatively straightforward to prepare and easily obtainable for research to perform surgical techniques. The intention of this study was to quantitatively analyze gene expression for collagen and proteoglycan components of the extracellular matrix and for collagenase (MMP-1) in porcine discs of varying ages (Newborn; 2-3weeks, Mature; 6-9 month, Older; 2-3 years). In this study, we observed that the cell number and GAG (glycosaminoglycan) formation dramatically decreased with aging. Also, gene expression in the annulus fibrosus (AF) and nucleus pulposus (NP) cells changed with aging. The level of MMP-1 mRNA increased with age and both type I, II collagens decreased with age. The level of aggrecan mRNA was highest in the mature group and decreased significantly with aging. In the mature group, MMP-1 expression was minimal compared to the newborn group. In AF cells, type II collagen was expressed at a high level in the mature group with a higher level of aggrecan, when aged NP showed a decrease in type II collagen. The model of IVD degeneration in the porcine disc shows many changes in gene expression with age that have been previously documented for human and may serve as a model for studying changes in IVD metabolism with age. We concluded that the porcine model is excellent to test hypotheses related to disc degeneration while permitting time-course study in biologically active systems.