Enhanced Extracellular Matrix Breakdown Characterizes the Early Distraction Phase of Canine Knee Joint Distraction

Abstract

Objective Joint distraction triggers intrinsic cartilage repair in animal models of osteoarthritis (OA), corroborating observations in human OA patients treated with joint distraction. The present study explores the still largely elusive mechanism initiating this repair process. Design Unilateral OA was induced in the knee joint of 8 dogs using the groove model; the contralateral joint served as a control. After 10 weeks, 4 animals received joint distraction, the other 4 serving as OA controls. Halfway the distraction period (after 4 weeks of a standard 8-week distraction treatment), all animals were euthanized, and joint tissues were collected. A targeted quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis was performed of commonly involved processes including matrix catabolism/anabolism, inflammation, and known signaling pathways in OA. In addition, cartilage changes were determined on tissue sections using the canine OARSI (Osteoarthritis Research Society International) histopathology score and collagen type II (COL2A1) immunostaining. Results Midway distraction, the distracted OA joint showed an upregulation of proteolytic genes, for example, ADAMTS5, MMP9, MMP13, compared to OA alone and the healthy joints, which correlated with an increased OARSI score. Additionally, genes of the transforming growth factor (TGF)-β and Notch pathway, and markers associated with progenitor cells were increased. Conclusions Joint distraction initiates both catabolic and anabolic transcriptional responses. The enhanced turnover, and thereby renewal of the matrix, could be the key to the cartilage repair observed in the months after joint distraction.

The catabolic-to-anabolic shift seen in the canine osteoarthritic cartilage treated with knee joint distraction occurs after the distraction period

“…Extensive information about the animal husbandry and experimental procedures is described in supplementary file 1.1 and 1.2. Sample size calculation used the size effects obtained in the previous KJD study [ 13 ].…”

“…A mikro-dismembrator (B. Braun Biotech International) was used to reduce snap-frozen cartilage samples and subchondral bone plugs to powder (two cycles; 2000 ​rpm). After lysis with QIAzol Lysis Reagent (79,306, Qiagen) total RNA was extracted and quantified as described previously [ 13 ] (Supplementary file 1.3.3).…”

“…Therefore, in the present study, a bilateral OA groove was employed to investigated joint tissues directly after 8 weeks of unilateral KJD, and at 10 weeks of follow-up after KJD. Combined with the studies performed in the same canine groove model of OA at an earlier and later timepoint of follow up [ 12 , 13 ], this explorative study provides complementary insights into the regenerative mechanisms behind KJD.…”

“…It was therefore hypothesized that tissue structure modification is initiated during distraction and proceeds in the post-distraction period, resulting in the tissue repair seen in human clinical studies. However, a recent study, employing KJD 10 weeks after OA was induced with the groove model, showed that midway KJD treatment (after 4 weeks of KJD), cartilage integrity decreased [ 13 ]. This was reflected by increased histological OARSI score and upregulation of catabolic genes in the distracted joint as compared to OA joint [ 13 ].…”

“…However, a recent study, employing KJD 10 weeks after OA was induced with the groove model, showed that midway KJD treatment (after 4 weeks of KJD), cartilage integrity decreased [ 13 ]. This was reflected by increased histological OARSI score and upregulation of catabolic genes in the distracted joint as compared to OA joint [ 13 ].…”