Suppression by an RAR-c Agonist of Collagen Degradation Mediated by Corneal Fibroblasts

METHODS. Primary rabbit corneal fibroblasts embedded in a three-dimensional collagen gel were incubated with or without all-trans retinoic acid (ATRA), the RAR-a agonist Am580, the RAR-b agonist AC55649, or the RAR-c agonist R667. Collagen degradation was determined by measurement of hydroxyproline produced in acid hydrolysates of culture supernatants. Matrix metalloproteinase (MMP) expression was evaluated by immunoblot analysis and gelatin zymography. The phosphorylation of mitogen-activated protein kinases (MAPKs) and the endogenous nuclear factor (NF)–jB inhibitor IjB-a was examined by immunoblot analysis. Cell proliferation was measured with a bromodeoxyuridine incorporation assay, and cell viability was determined by measurement of the release of lactate dehydrogenase.