035 DESTABILIZATION OF THE MEDIAL MENISCUS AS A MODEL FOR THE STUDY OF PAIN PATHWAYS ASSOCIATED WITH DEVELOPMENT OF MURINE OSTEOARTHRITIS

Abstract

Purpose: Pain is the major symptom in osteoarthritis (OA) and one of the leading causes of impaired mobility in the elderly. There is no simple correlation between pathological changes in the joint and pain severity. No animal models adequately describe the correlation between joint structure and symptoms, and very few have properly examined mechanisms of OA pain generation. We recently reported that, following DMM in the right knee, C57BL/6 mice develop rapid-onset progressive mechanical allodynia in the ipsilateral hindpaw only, as early as 2 weeks and developing over 8 weeks post DMM surgery. Adamts5 knockout (KO) mice, which do not develop OA-like structural changes after DMM, did not develop allodynia. Our long-term goal is to quantitatively measure pain and dissect molecular pathways involved in pain generation in a mouse model of OA. We chose destabilization of the medial meniscus (DMM) in C57BL/6 mice because, unlike other rodent OA models, the joint pathology in this model is slowly progressive over 16 weeks and thus optimally suited for studying pain at different stages of disease. Methods: DMM surgery was performed in the right knee of 10-week old male C57BL/6 mice. At different time points after surgery (2, 4, 8, 12 and 16 weeks), pain was assessed in DMM operated mice, in sham controls and in age-matched naive controls. Pain-dependent measures included 1) von Frey analysis to measure mechanical allodynia; and 2) behavioral monitoring with LaborasTM equipment, which quantifies activity using pattern recognition software, including total distance traveled over a specified time period. Concurrently, innervating dorsal root ganglia (DRG) L2-L5 were harvested from both the operated and the non-operated side at different time points after surgery for RT-PCR analysis. Knee joints were collected for histopathology or India ink staining. Results: In the current studies, we found that the unilateral mechanical allodynia subsided 8-16 weeks after DMM surgery. Total distance traveled over a specified period was relatively constant over the first 8 weeks after surgery, but decreased from 12 weeks after surgery. RT-PCR analysis of innervating DRG at different time points (4, 8, 16 weeks) following DMM revealed significantly increased levels of mRNA (compared to naive agematched controls) for the neurotrophic factors, NGF (nerve growth factor) and GDNF (glial cell-derived neurotrophic factor), and for the chemokine, MCP-1 at the 8-week time point. mRNA levels were elevated in both the ipsiand in the contralateral DRG (but more so in the ipsilateral DRG). mRNA levels for substance P or for the NGF receptor, TrkA, were not elevated (Figure 1). mRNA levels for the genes studied were not elevated in Adamts5 KO mice.