Influence of pregnancy on gene expression in rabbit articular cartilage

Objective: Articular cartilage is known to be influenced by estrogen and the pregnancy-associated hormone, relaxin, in vitro. Such observations have raised the possibility that articular cartilage in females may be subjected to unique regulatory influences by such hormones in vivo. The purpose of this study was to evaluate mRNA levels for several relevant molecules in the articular cartilage of pregnant and non-pregnant rabbits. Design: Total RNA was extracted from New Zealand White rabbit knee articular cartilage using the TRIspin method. The total RNA was reverse transcribed and analysed by the sensitive molecular technique of semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) using rabbit specific primer sets. Results: Total RNA yield from articular cartilage from primigravida rabbits was reduced to 65% of age-matched control values (P=0.0003); however the yield from multiparous animals was not significantly depressed. In both cases, DNA yields were not affected by pregnancy. There was a general tendency for depressed mRNA levels for most genes investigated in cartilage from pregnant animals. Articular cartilage from multiparous rabbits showed a significant decrease in mRNA levels for relevant molecules such as type II collagen, biglycan, collagenase and tissue inhibitors of metalloproteinases (TIMP)-1, as well as necrosis factor-alpha (TNF-alpha, inducible nitric oxide synthase (iNOS) and cyclo-oxygenase 2 (COX-2). Transcripts for collagenase and lumican were significantly lower in cartilage from primigravida rabbits. Transforming growth factor beta 1 (TGF-beta 1) transcript levels were significantly decreased in both pregnant groups. In contrast, basic fibroblast growth factor (bFGF) and insulin-like growth factor-2 (IGF-2) mRNA levels were significantly decreased in cartilage from primigravida rabbits, whereas transcripts for these molecules were upregulated in the cartilage of multiparous rabbits. Conclusions: The present study demonstrates that regulation of RNA levels in articular cartilage during pregnancy is complex and is influenced by the parity and/or the skeletal maturity of the animals.