Sensitivity of Anulus Fibrosus Cells to Interleukin 1β

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Abstract
Anulus fibrosus cells from rabbits were grown in primary culture 1) to study their ability to produce prostaglandin E2 and Type II phospholipase A2, and to express stromelysin-1 messenger ribonucleic acid; and 2) to study the effect of interleukin 1β on this production and on proteoglycan aggregation. To investigate the potency of anulus fibrosus cells to respond to interleukin 1β by producing degradative and inflammatory agents as compared with the potency of articular chondrocytes in the same animal. Interleukin 1β has been implicated in the degradation of intervertebral discs. The way anulus fibrosus cells differ from articular chondrocytes in their responses to interleukin 1β remains to be established. Anulus fibrosus cells and articular chondrocytes were obtained from young rabbits, grown in primary culture, and incubated with interleukin 1β. The newly synthesized proteoglycan was measured by labeling with [35S]-sulfate. Proteoglycan aggregation was analyzed by the elution profile on Sepharose 2B columns. The contents of collagen Type II and stromelysin-1 messenger ribonucleic acid were assessed by Northern blot analysis. The Type II phospholipase A2 activity was measured using a fluorometric substrate. Prostaglandin E2 production was evaluated by radioimmunoassay. Anulus fibrosus cells had 2.5-fold less Type II collagen messenger ribonucleic acid than articular chondrocytes, and interleukin 1β had no significant effect on this. Anulus fibrosus cells synthesized and secreted fourfold less proteoglycan than articular chondrocytes. Interleukin 1β reduced the anulus fibrosus content of total [35S]-sulfated proteoglycan by 35% (P < 0.01), and that of articular cells by 41% and decreased proteoglycan aggregation. Interleukin 1β induced the production of stromelysin-1 messenger ribonucleic acid in both cell types. The stromelysin-1 messenger ribonucleic acid content of anulus fibrosus cells was one half that of articular cells. Interleukin 1β increased the production of prostaglandin E2 and caused a dose-dependent secretion of Type II phospholipase A2 activity in both cell types. Its effect was 2.5-fold lower in anulus fibrosus cells than in articular chondrocytes. Anulus fibrosus cells can be stimulated by interleukin 1β to produce factors implicated in local degradative and inflammatory processes. This production is associated with decreased proteoglycan aggregation. Anulus fibrosus cells respond slightly less well to interleukin 1βin vitro than do articular cells.

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