RETINOIC ACID TREATMENT ELEVATES MATRIX METALLOPROTEINASE-2 PROTEIN AND MESSENGER-RNA LEVELS IN AVIAN GROWTH-PLATE CHONDROCYTE CULTURES

Matrix metalloproteinases (MMPs) play a crucial role in tissue remodel ing, in growth plate (CP) cartilage, extensive remodeling occurs at th e calcification front. To study the potential involvement of MMPs in r etinoic acid (RA) regulation of skeletal development, we studied the e ffect of all-trans-RA on MMPs levels in mineralizing chicken epiphysea l chondrocyte primary cultures. When treated for 4 day periods on days 10 and 17, RA increased levels of an similar to 70 kDa gelatinase act ivity. The N-terminal sequence of the first 20 amino acid residues of the purified enzyme was identical to that deduced from chicken MMP-2 c DNA. Time-course studies indicated that RA elevated MMP-2 activity lev els in the cultures within 16 h. This increase was inhibited by cycloh eximide and was enhanced by forskolin. The increase in MMP-2 activity induced by RA was accompanied by an increase in MMP-2 mRNA levels and was abolished by treatment with cycloheximide. This upregulation of MM P levels by RA in CP chondrocytes is consistent with its effects on os teoblasts and osteosarcoma cells and opposite its inhibitory effects o n fibroblasts and endothelial cells. it may well be related to the bre akdown of the extracellular matrix in the CP and would be governed by the availability of RA at the calcification front where extensive vasc ularization also occurs. (C) 1998 Wiley-Liss, Inc.