Heterogenous response of knee cartilage to pregnancy in the rabbit: assessment of specific mRNA levels

Objective: The purpose of this study was to evaluate the effect of pregnancy on mRNA levels for several relevant molecules between five articular cartilage surfaces of the rabbit knee joint. Design: Total RNA was extracted from the following five knee joint articular surfaces: the lateral and medial femoral condyles (LFC and MFC); the lateral and medial tibial plateau (LTP and MTP); and the femoral groove (G) from pregnant and age-matched non-pregnant skeletally immature New Zealand White rabbits. The RNA was analysed by the sensitive molecular technique of semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) using rabbit specific primer sets. Two types of comparisons were performed: (i) comparison of mRNA levels between cartilage surfaces and (ii) comparison of mRNA levels between pregnant and non-pregnant rabbits within the same articular surfaces. Results: (i) Total RNA yield from the MFC and G represented 53 and 58% of the total RNA amount from the five cartilage surfaces in both non-pregnant and pregnant rabbits, respectively. Transcript levels for progesterone receptor (PR), aggrecan and biglycan were similar in all of the cartilage surfaces. In contrast, the cartilage surfaces exhibited significantly different transcript levels with a similar pattern for the estrogen receptor (ER), collagenase and urokinase (i.e., MTP<LTP<MFC=G<LFC). In addition, mRNA levels were significantly different for type II collagen (COL 2) between the LFC and MTP, for decorin between the LTP and both LFC and G, for TIMP-1 between the MFC and both the LTP and the G, as well as for PAI-1 between the LTP and MTP. (ii) Total RNA concentration from pregnant animals were significantly decreased in the MFC and the G. For all molecules studied except PR, there was a general tendency for decreased mRNA levels during pregnancy. Compared to non-pregnant rabbits, mRNA levels were significantly decreased in pregnant rabbits for ER in the LFC, LTP and MTP; for COL2 in both LTP and MTP; for aggrecan in the MTP, for biglycan in both LTP and MTP, for decorin in the MTP and G; for collagenase in the LFC, LTP, MTP and G, for urokinase in the LFC, MFC and LTP; for TIMP-1 in the MFC, LTP and MTP. In contrast, PAI-1 exhibited increased mRNA levels during pregnancy in the LFC and LTP. (iii) Comparison of results between the present and the previous study demonstrates that subtle changes in one or more of the cartilage surfaces may be obscured if cartilage is pooled. Conclusion: The present study demonstrates that regulation of RNA levels in articular cartilage during pregnancy is complex and variable between cartilage surfaces. (C) 2000 OsteoArthritis Research Society International.