Osteoarthritis (OA) is the most common form of arthritis and patients with meniscal and ligament injuries of the knee are at high risk to develop the disease. The purpose of this study was to evaluate changes occurring in both medial and lateral menisci from the knees of anterior cruciate ligament (ACL) transected rabbits at 3 and 8 weeks post-surgery. This study describes both molecular and cellular alterations in menisci during the early stages of OA development.
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 relevant molecules was performed. In situ DNA fragmentation was evaluated using the TUNEL assay.
Total RNA yields from the medial meniscus were significantly elevated at both 3 and 8 weeks post-ACL transection, while in the lateral meniscus total RNA levels were unchanged following ACL transection. DNA concentrations were significantly decreased in the medial menisci only at 8 weeks post-ACL transection. Following ACL transection, analysis of in situ DNA fragmentation using the TUNEL assay demonstrated an increase in the number of apoptotic cells in the medial meniscus only, in particular at 3 weeks post-ACL transection, a finding which correlates with declines in DNA content. Analysis of specific mRNA levels by RT-PCR demonstrated complex changes in both 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 TIMP-1 were significantly increased, while mRNA levels for decorin, TNF-alpha and IGF-2 were significantly depressed. In the medial meniscus, significant increases in mRNA levels for type II collagen, biglycan as well as iNOS and PAI-1 were detected at both time periods, while mRNA levels for aggrecan, 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 lateral meniscus, at 3 weeks post-ACL transection, type III collagen mRNA levels were dramatically increased while fibromodulin mRNA levels were significantly depressed. In the lateral meniscus, significant increases in mRNA levels for biglycan were detected at 8 weeks post-ACL transection.
These results show that after ACL transection complex molecular changes, as well as apoptosis, occur early, particularly in the medial meniscus.