Early changes in lapine menisci during osteoarthritis development - Part II: Molecular alterations

Objective: Osteoarthritis (OA) is the most common form of arthritis and pat ients with meniscal and ligament injuries of the knee are at high risk to d evelop the disease. The purpose of this study was to evaluate changes occur ring in both medial and lateral menisci from the knees of anterior cruciate ligament (ACL) transected rabbits at 3 and 8 weeks post-surgery. This stud y describes both molecular and cellular alterations in menisci during the e arly stages of OA development. Design: Rabbit meniscal tissues were processed for molecular analysis: DNA and RNA concentrations were assessed, as well as semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for a subset of r elevant molecules was performed. In situ DNA fragmentation was evaluated us ing the TUNEL assay. Results: Total RNA yields from the medial meniscus were significantly eleva ted at both 3 and 8 weeks post-ACL transection, while in the lateral menisc us total RNA levels were unchanged following ACL transection. DNA concentra tions were significantly decreased in the medial menisci only at 8 weeks po st-ACL transection. Following ACL transection, analysis of in situ DNA frag mentation using the TUNEL assay demonstrated an increase in the number of a poptotic cells in the medial meniscus only, in particular at 3 weeks post-A CL transection, a finding which correlates with declines in DNA content. An alysis of specific mRNA levels by RT-PCR demonstrated complex changes in bo th menisci following ACL transection. At 3 and 8 weeks post-ACL transection , in both medial and lateral menisci, mRNA levels for type I collagen and T IMP-1 were significantly increased, while mRNA levels for decorin, TNF-alph a and IGF-2 were significantly depressed. In the medial meniscus, significa nt increases in mRNA levels for type I) collagen, biglycan as well as iNOS and PAI-I were detected at both time periods, while mRNA levels for aggreca n, type III collagen and COX-2 were significantly elevated at 3 weeks post- ACL transection and mRNA levels for MMP-1 were significantly elevated at 8 weeks post-ACL transection. In contrast, mRNA levels for COL2 and aggrecan were unchanged in the lateral meniscus following ACL transection. In the la teral meniscus, at 3 weeks post-ACL transection, type III collagen mRNA lev els were dramatically increased while fibromodulin mRNA levels were signifi cantly depressed. In the lateral meniscus? significant increases in mRNA le vels for biglycan were detected at 8 weeks post-ACL transection. Conclusion: These results show that after ACL transection complex molecular changes, as well as apoptosis, occur early, particularly in the medial men iscus. (C) 2001 OsteoArthritis Research Society International.