Retinoic acid attenuates cytokine-driven fibroblast degradation of extracellular matrix in three-dimensional culture

Proteolytic degradation of extracellular matrix is thought to play an important role both in emphysema and in tissue development and repair. Retinoic acid has been suggested to modify tissue injury, and in an animal model of emphysema may induce alveolar repair. Since cytokines can induce matrix metalloproteinase (MMP) production in fibroblasts and neutrophil elastase (NE) can activate MMPs, we hypothesized that retinoic acid could attenuate collagen degradation by modifying MMP production and activation. To evaluate this, human lung fibroblasts were cast into native type I collagen gels and floated in medium containing cytomix (TNF-alpha, IL-1 beta, and IFN-gamma) alone or in combination with NE in the presence and absence of retinoic acid (1 muM). After 5 d, cytomix with elastase induced significant degradation of the collagen gels assessed by quantifying total hydroxyproline (41.6 +/- 1.6 mug versus 3.3 +/- 1.5 mug, P < 0.01). Retinoic acid significantly inhibited this degradation (23.3 +/- 1.5 mug versus 3.3 +/- 1.5 mug, P < 0.01). Gelatin zymography and Western blot revealed that MMP-1, MMP-3, and MMP-9 were induced by cytomix and that co-exposure to NE resulted in increased production of activated forms of these enzymes. Retinoic acid attenuated the induction and activation of MMP-1 and MMP-3. The current study, therefore, suggests that in addition to stimulating anabolic effects, retinoic acid may modulate proteolytic processes thought to contribute to tissue destruction in emphysema.