Osteogenic protein-1 enhances matrix replenishment by intervertebral disc cells previously exposed to interleukin-1.

Abstract

A study of the mechanisms involved in matrix repair by intervertebral disc cells cultured in alginate gel was performed. To determine the effects of osteogenic protein-1 on the extracellular matrix of intervertebral disc cells previously exposed to interleukin-1, which is an in vitro model for degraded extracellular matrix. Disc degeneration is accompanied by a decrease in the content of negatively charged proteoglycans in the matrix. No previous attempt has been made to repair the degraded matrix of the disc. Nucleus pulposus and anulus fibrosus cells were isolated from the lumbar discs of New Zealand white rabbits and were separately encapsulated in alginate beads. The alginate beads were cultured with or without osteogenic protein-1 after previous exposure to interleukin-1alpha in the presence of 10% fetal bovine serum. The total contents of proteoglycan, collagen, and DNA in the alginate beads were measured. The rate of proteoglycan synthesis by the encapsulated cells was also determined. Treatment with interleukin-1alpha resulted in a significant decrease in proteoglycan and collagen contents in the matrix formed by both the nucleus pulposus and anulus fibrosus. However, subsequent treatment with osteogenic protein-1 led in both cases to rapid recovery of proteoglycans and collagens, whose contents returned to the levels seen in cells not previously exposed to interleukin-1alpha. By the end of the culture period (day 21), those values reached levels higher than those found in beads containing cells never exposed to interleukin-1alpha. Further, the rate of proteoglycan synthesis by both cell types in beads treated with osteogenic protein-1 after previous exposure to interleukin-1alpha was significantly higher than in beads whose cells were not treated with osteogenic protein-1 after previous exposure to interleukin-1alpha. Disc cells that have been previously exposed to interleukin-1alpha have lost none of their potential to upregulate proteoglycan synthesis in response to stimulation with osteogenic protein-1. On stimulation with osteogenic protein-1, these disc cells not only replenished the matrix with proteoglycans that had been lost during interleukin-1alpha treatment but proceeded to reform a matrix that was richer in these resilient molecules than that formed by disc cells never exposed to interleukin-1alpha.