PREGNANCY INDUCES COMPLEX CHANGES IN THE PATTERN OF MESSENGER-RNA 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 s ubset of relevant molecules in ligaments, RNA was isolated from the me dial collateral(MCL) and anterior cruciate(ACL) ligaments of first tim e pregnant adolescent rabbits. Levels of mRNA for matrix molecules (co llagen types I and III and the proteoglycans biglycan, decorin, versic an and lumican), proteinases and inhibitors (collagenase, urokinase, P AI-1 and TIMP-1, -2 and -3), growth factors (bFGF, TGF-T, TGF-beta 1 a nd ET-1), cytokines (IL-1 beta and TNF) and enzymes responsible for im portant tissue mediators (COX-2 and iNOS) were assessed by semi-quanti tative RT-PCR. In the MCL, levels of transcripts for all of the matrix molecules, growth factors and TIMPs 1 and 2 were significantly depres sed at 29 days of pregnancy compared to age-matched non-pregnant contr ols. Tn contrast, transcripts for PAI-1 were elevated during pregnancy , while those for collagenase (MMP-1), urokinase, TIMP-3, IL-1 beta, T NF, COX-2 and iNOS were not statistically altered, mRNA transcript lev els rebounded by 7 days post-partum for most genes studied, indicating that the changes were rapidly reversible. For some molecules, transcr ipt levels were again depressed at 18 days post-partum, indicating tha t regulatory mechanisms were still not stabilized. Analysis of mRNA fr om the ACL also revealed changes in the pattern of gene expression, wi th some similarilties and differences from the MCL noted. These result s indicate that pregnancy induces reversible changes in mRNA for matri x molecules in ligaments, hut differences in responsiveness exist betw een different ligaments. The complexity of the changes observed indica tes that there is probably no simple cause and effect relationship bet ween laxity changes and the molecular alterations during pregnancy.