Abstract
Expression of matrix metalloproteinase‐9 mRNA in osteoarthritic and normal cartilage was analyzed using reverse transcription polymerase chain reaction and in situ hybridization. Fifty‐four osteoarthritic cartilage samples were obtained from 24 patients undergoing total knee arthroplasty. Sixteen normal cartilage samples were obtained from non‐osteoarthritic knees of four autopsy cases. With normal cartilage, reverse transcription‐polymerase chain reaction analysis for matrix metalloproteinase‐9 mRNA showed that chondrocytes exhibited only a trace signal. In analysis of osteoarthritic cartilage, chondrocytes of moderately and severely fibrillated cartilage exhibited a 73‐fold and 110‐fold increase in matrix metalloproteinase‐9 mRNA signal, respectively, relative to normal cartilage. Chondrocytes of nonfibrillated osteoarthritic cartilage exhibited a 6‐fold increase (p < 0.02) in matrix metalloproteinase‐9 mRNA signal relative to normal cartilage. Analysis of matrix metalloproteinase‐9 mRNA expression in fresh‐frozen sections of normal and osteoarthritic cartilage by in situ hybridization confirmed these results. This study showed that reverse transcriptionpolymerase chain reaction provides a sensitive index of mRNA levels in normal and osteoarthritic cartilage samples and suggests that increased expression of matrix metalloproteinase‐9 precedes fibrillation of cartilage in the development of osteoarthritis.