DNA cytofluorometric analysis of chondrocytes in human articular cartilages under normal aging or arthritic conditions

Objective: Since most chondrocytes in articular cartilage are in the restin g phase (G0) of the cell cycle, it has been difficult to investigate their cell kinetics using 3H-thymidine autoradiography, or immunohistochemistry. In the present study, DNA cytofluorometry, which is useful to analyse the c ell kinetics even for such inactive cell populations as in the G0 phase, wa s applied to human chondrocytes of the articular cartilages under normal ag ing and pathologic conditions such as osteoarthritis (OA), rheumatoid arthr itis (RA), and aseptic necrosis (AN). Design: The human articular cartilages for the study were obtained from aut opsy and surgical materials. Fifty joints were used for the study of aging, 54 for the study of OA, 20 for studying RA, and 10 for AN study. The isola ted chondrocytes were quickly prepared from fresh articular cartilages, usi ng a combination method of enzymatic digestion with papain and collagenase, followed by mechanical cell separation by churning and homogenization. Results: The DNA histograms obtained by cytofluorometry with propidium-iodi de staining showed that most chondrocytes had diploid DNA content (2c) in a ll cartilages studied, suggesting that they were in the G0 phase. However, there were a few chondrocytes having tetraploid DNA content (4c) in the nor mally aged articular cartilages, and there were some cells having DNA conte nt between 2c and 4c in the diseased cartilages. The former cells were cons idered to be G0-phase cells of the 4c chondrocytes, while the latter cells were considered to be in the DNA synthetic (S) phase or G2-phase of the 2c chondrocytes. The frequency of 4c chondrocytes in aged cartilage was signif icantly increased, compared to that in the young cartilage. In contrast to the normal cartilage, the frequency of S- and G2-phase cells, which was exp ressed as the S-G2 index, in diseased cartilages (OA, RA and AN) was signif icantly high (P <0.0001). In OA cartilage, the S-G2 index was much higher i n the severe or moderate stage than in the mild stage, suggesting that the chondrocytes in clusters may actively proliferate. Conclusion: These results showed that in normal articular cartilages most c hondrocytes are in the G0-phase, while some became 4c polyploid cells, and that these G0-phase chondrocytes had a potential to proliferate under disea sed conditions. (C) 2001 OsteoArthritis Research Society International.