Inflammatory and degenerative phases resulting from anterior cruciate rupture in a non‐invasive murine model of post‐traumatic osteoarthritis

Abstract

Joint injury is the predominant risk factor for post‐traumatic osteoarthritis development (PTOA). Several non‐invasive mouse models mimicking human PTOA investigate molecular mechanisms of disease development; none have characterized the inflammatory response to this acute traumatic injury. Our aim was to characterize the early inflammatory phase and later degenerative component in our in vivo non‐invasive murine model of PTOA induced by anterior cruciate ligament (ACL) rupture. Right knees of 12‐week‐old C57Bl6 mice were placed in flexion at a 30° offset position and subjected to a single compressive load (12N, 1.4 mm/s) to induce ACL rupture with no obvious damage to surrounding tissues. Tissue was harvested 4 h post‐injury and on days 3, 14, and 21; contralateral left knees served as controls. Histological, immunohistochemical, and gene analyzes were performed to evaluate inflammatory and degenerative changes. Immunohistochemistry revealed time‐dependent expression of mature (F4/80 positive) and inflammatory (CD11b positive) macrophage populations within the sub‐synovial infiltrate, developing osteophytes, and inflammation surrounding the ACL in response to injury. Up‐regulation of genes encoding acute pro‐inflammatory markers, inducible nitric oxide synthase, interleukin‐6 and interleukin‐17, and the matrix degrading enzymes, ADAMTS‐4 and MMP3 was detected in femoral cartilage, concomitant with extensive cartilage damage and bone remodelling over 21‐days post‐injury. Our non‐invasive model describes pathologically distinct phases of the disease, increasing our understanding of inflammatory episodes, the tissues/cells producing inflammatory mediators and the early molecular changes in the joint, thereby defining the early phenotype of PTOA. This knowledge will guide appropriate interventions to delay or arrest disease progression following joint injury. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. J Orthop Res 36:2118–2127, 2018.

Characterization of Post‐Traumatic Osteoarthritis in Rats Following Anterior Cruciate Ligament Rupture by Non‐Invasive Knee Injury (NIKI)

“…All of these cytokines were found at higher levels in the synovial fluid of injured knees compared with uninjured knees, suggesting that inflammation is a contributing factor to PTOA development in this model. This finding is supported by a recent study that found increased IL‐6 in the extracellular matrices of the ACL, synovium, and cartilage following non‐invasive injury in mice, as the cytokines found in the synovial fluid originate from the cells within these tissues . We also assessed levels of CTX‐II, a widely studied biomarker of collagen fragmentation that has been shown to increase following traumatic joint injury in humans .…”

“…In the last 10 years, multiple non‐invasive ACL rupture models have been developed. These models have primarily used mice and rabbits, with a limited number of studies involving rats . Despite being relatively understudied, there are advantages to establishing this injury model in rats, such as their amenability to behavioral tests and their larger size, which can accommodate certain imaging modalities and therapeutic interventions .…”

“…Even within the few studies using rats, different structural outcomes have been observed following ACL rupture, ranging from cartilage degeneration to cartilage thickening . Additionally, the characterization of the inflammatory response to this injury has been scarcely studied, with only one recent evaluation of immune cell involvement and cytokine profile following injury in mice reported . Considering the important role of inflammation in PTOA development and the conflicting findings between early studies in rats, additional characterization of this model is merited.…”

Regulation of microRNA‐221, ‐222, ‐21 and ‐27 in articular cartilage subjected to abnormal compressive forces

“…A single 12 N load at a velocity of 1.4 mm s −1 was then applied resulting in anterior cruciate ligament (ACL) rupture as described previously (Gilbert et al . 2018); mechanical loading was always conducted in the morning. Buprenorphine (0.05 mg kg −1 ) was administered s.c. to mice at the start of the experiment; animals were able to move freely and were monitored for welfare and lameness until termination of the experiment.…”

Potential of zebrafish as a model to characterise MicroRNA profiles in mechanically mediated joint degeneration

“…Utilisation of a single compressive load (12 N) has been previously demonstrated to rupture the ACL initiating pathological changes in murine articular cartilage and underlying subchondral bone (Christiansen et al 2012 ). Pathologically distinct phases with an early inflammatory phase and a later degenerative component are evident in the non-invasive murine PTOA model (Gilbert et al 2018 ); this proves advantageous as a model system as it provides a ‘therapeutic window’ following mechanical insult in which to assess treatments to delay or halt joint degeneration.…”