Pregnancy induces complex changes in the the pattern of mRNA expression in knee ligaments of the adolescent rabbit

Knee laxity has been shown to increase during human pregnancy, and the laxity of the rabbit medial collateral ligament also increases during pregnancy. To determine whether the changes in tissue function could be related to alterations in the regulation of gene expression for a subset of relevant molecules in ligaments, RNA was isolated from the medial collateral(MCL) and anterior cruciate(ACL) ligaments of first time pregnant adolescent rabbits. Levels of mRNA for matrix molecules (collagen types I and III and the proteoglycans biglycan, decorin, versican and lumican), proteinases and inhibitors (collagenase, urokinase, PAI-1 and TIMP-1, -2 and -3), growth factors (bFGF, IGF-I, TGF-beta1 and ET-1), cytokines (IL-1beta and TNF) and enzymes responsible for important tissue mediators (COX-2 and iNOS) were assessed by semi-quantitative RT-PCR. In the MCL, levels of transcripts for all of the matrix molecules, growth factors and TIMPs 1 and 2 were significantly depressed at 29 days of pregnancy compared to age-matched non-pregnant controls. In contrast, transcripts for PAI-1 were elevated during pregnancy, while those for collagenase (MMP-1), urokinase, TIMP-3, IL-1beta, TNF, COX-2 and iNOS were not statistically altered. mRNA transcript levels rebounded by 7 days post-partum for most genes studied, indicating that the changes were rapidly reversible. For some molecules, transcript levels were again depressed at 18 days post-partum, indicating that regulatory mechanisms were still not stabilized. Analysis of mRNA from the ACL also revealed changes in the pattern of gene expression, with some similarities and differences from the MCL noted. These results indicate that pregnancy induces reversible changes in mRNA for matrix molecules in ligaments, but differences in responsiveness exist between different ligaments. The complexity of the changes observed indicates that there is probably no simple cause and effect relationship between laxity changes and the molecular alterations during pregnancy.