Articular cartilage degeneration following anterior cruciate ligament injury: a comparison of surgical transection and noninvasive rupture as preclinical models of post-traumatic osteoarthritis

A standardized, open-source, portable model for noninvasive joint injury in mice

Preclinical models of osteoarthritis (OA) are crucial for the study of disease mechanisms and for the development of critically-needed disease-modifying therapeutics. While surgical OA models, such as the destabilization of the medial meniscus (DMM), have been the gold standard in the field for decades, noninvasive joint loading-based models have increased in popularity and utility. To facilitate standardization of the noninvasive anterior cruciate ligament rupture (ACLR) model in mice, we present the Mo bile J oint-Injury O perator (MoJO) - an open-source protocol with accompanying fixtures and data, designed for a low-cost, commercially-available, portable uniaxial testing system with a small footprint. We provide 3d-printable fixture designs and a rapid, highly-repeatable ACLR-mediated joint injury protocol that results in the expected post-traumatic osteoarthritis phenotype in male and female C56Bl/6 mice. We then describe the expected mechanical data from the injury procedure and offer various troubleshooting strategies. Finally, we summarize the resultant PTOA phenotype by knee hyperalgesia testing, µCT imaging, flow cytometry, and histological assessment. Increased standardization of this model is a critical aspect of the overall refinement of animal models of OA.

The active ingredient of Evodia rutaecarpa reduces inflammation in knee osteoarthritis rats through blocking calcium influx and NF-κB pathway

Chronic inflammation significantly contributes to the progression of osteoarthritis (OA), and an anti-inflammatory small molecule derived from medicinal herbs could be a potential drug candidate for OA. Herein, we investigated the function and mechanism of Evodiamine (EAE), the active ingredient from Evodia rutaecarpa, in chondrocytes and macrophages in vitro and in vivo. The cytotoxicity of EAE was determined using an MTT assay. And the anti-inflammatory and anti-extracellular matrix (ECM) degradation effects of EAE were investigated using qRT-PCR, western blot (WB), immunofluorescence (IF). Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), Fluo-4 AM, IF and AutoDock were used to elucidate the molecular mechanisms and signalling pathways of the reducing-inflammatory properties of EAE on chondrocytes in vitro. Moreover, the effect of EAE on macrophage polarization was detected by IF and flow cytometry (FC). Ultimately, we explored the in vivo therapeutic efficacy of EAE in an anterior cruciate ligament transection (ACLT)-induced OA model. The finding demonstrated that EAE blocked the phosphorylation of IKBα and Ca2+ influx, thereby curbing inflammation and ECM degradation. Additionally, EAE can prevent the polarization towards the M1 phenotype. Thus, our findings suggest that EAE has great potential as a therapeutic drug for the treatment of OA.

Concurrent Joint Contact in Anterior Cruciate Ligament Injury induces cartilage micro-injury and subchondral bone sclerosis, resulting in knee osteoarthritis

Objective

Anterior Cruciate Ligament (ACL) injury initiates post-traumatic osteoarthritis (PTOA) via two distinct processes: initial direct contact injury of the cartilage surface during ACL injury, and secondary joint instability due to the ACL deficiency. Using the well-established Compression-induced ACL rupture method (ACL-R) and a novel Non-Compression ACL-R model, we aimed to reveal the individual effects of cartilage compression and joint instability on PTOA progression after ACL injury in mice.

Design

Twelve-week-old C57BL/6J male were randomly divided to three experimental groups: Compression ACL-R, Non-Compression ACL-R, and Intact. Following ACL injury, we performed joint laxity testing and microscopic analysis of the articular cartilage surface at 0 days, in vivo optical imaging of matrix-metalloproteinase (MMP) activity at 3 and 7 days, and histological and microCT analysis at 0, 7, 14, and 28 days.

Results

The Compression ACL-R group exhibited a significant increase of cartilage roughness immediately after injury compared with the Non-Compression group. At 7 days, the Compression group exhibited increased MMP-induced fluorescence intensity and MMP-13 positive cell ratio of chondrocytes. Moreover, histological cartilage degeneration was observable in the Compression group at the same time point. Sclerosis of tibial subchondral bone in the Compression group was more significantly developed than in the Non-Compression group at 28 days.

Conclusions

Both Compression and Non-Compression ACL injury initiated PTOA progression due to joint instability. However, joint contact during ACL rupture also caused initial micro-damage on the cartilage surface and initiated early MMP activity, which could accelerate PTOA progression compared to ACL injury without concurrent joint contact.

Effects of risk factors on evoked pain patterns in rat models of experimental knee osteoarthritis

Pain experiences in patients with knee osteoarthritis (OA) may be influenced differently by OA risk factors, reducing the translatability of preclinical research into the clinic. Our objective was to contrast evoked pain patterns after exposure to different OA risk factors including acute joint trauma, chronic instability, or obesity/metabolic syndrome using rat models of experimental knee OA. We tested longitudinal patterns of evoked pain behaviors (knee pressure pain threshold and hindpaw withdrawal threshold) in young male rats exposed to different OA-inducing risk factors including (1) nonsurgical joint trauma (impact-induced anterior cruciate ligament (ACL) rupture); (2) surgical joint destabilization (ACL + medial meniscotibial ligament transection); and (3) high fat/sucrose (HFS) diet-induced obesity. Histopathology for synovitis, cartilage damage, and subchondral bone morphology was performed. Pressure pain threshold was reduced (more pain) most, and earlier by joint trauma (Week 4-12) and HFS (Week 8-28) than by joint destabilization (Week 12). Hindpaw withdrawal threshold was reduced transiently after joint trauma (Week 4), with smaller and later reductions after joint destabilization (Week 12), but not with HFS. Synovial inflammation occurred at Week 4 after joint trauma and instability but only coincided with pain behaviors after joint trauma. Cartilage and bone histopathology were most severe after joint destabilization and least severe with HFS. The pattern, intensity, and timing of evoked pain behaviors varied due to OA risk factor exposure and were inconsistently associated with histopathological OA features. These findings may help to explain the challenges with translating preclinical OA pain research to multimorbid clinical OA contexts.

Mesenchymal stem cells in synovial fluid increase in number in response to synovitis and display more tissue-reparative phenotypes in osteoarthritis

BACKGROUND

Synovial fluid mesenchymal stem cells (SF-MSCs) originate in the synovium and contribute to the endogenous repair of damaged intra-articular tissues. Here, we clarified the relationship between their numbers and joint structural changes during osteoarthritis (OA) progression and investigated whether SF-MSCs had phenotypes favorable for tissue repair, even in an OA environment.

METHODS

Partial medial meniscectomy (pMx) and sham surgery were performed on both knees of rats. SF and knee joints were collected from intact rats and from rats at 2, 4, and 6 weeks after surgery. SF was cultured for 1 week to calculate the numbers of colony-forming cells and colony areas. Joint structural changes were evaluated histologically to investigate their correlation with the numbers and areas of colonies. RNA sequencing was performed for SF-MSCs from intact knees and knees 4 weeks after the pMx and sham surgery.

RESULTS

Colony-forming cell numbers and colony areas were greater in the pMx group than in the intact and sham groups and peaked at 2 and 4 weeks, respectively. Synovitis scores showed the strongest correlation with colony numbers (R = 0.583) and areas (R = 0.456). RNA sequencing revealed higher expression of genes related to extracellular matrix binding, TGF-β signaling, and superoxide dismutase activity in SF-MSCs in the pMx group than in the sham group.

CONCLUSION

The number of SF-MSCs was most closely correlated with the severity of synovitis in this rat OA model. Tissue-reparative gene expression patterns were observed in SF-MSCs from OA knees, but not from knees without intra-articular tissue damage.

Acute Bone Loss and Infrapatellar Fat Pad Fibrosis in the Knee After an In Vivo ACL Injury in Adolescent Mice

BACKGROUND

Young patients are 6 times more likely than adults to have a primary anterior cruciate ligament (ACL) graft failure. Biological factors (ie, tunnel osteolysis) may account for up to a third of these failures. Previous evaluations of patient ACL explants indicated significant bone loss within the entheseal regions. However, it remains unknown if the degree of bone loss within the ACL insertion regions, wherein ACL grafts are fixated, exceeds that of the femoral and tibial condylar bone.

HYPOTHESIS

Bone loss in the mineralized matrices of the femoral and tibial ACL entheses is distinct from that clinically reported across the whole knee after injury.

STUDY DESIGN

Controlled laboratory study.

METHODS

We developed a clinically relevant in vivo mouse ACL injury model to cross-sectionally track the morphological and physiological postinjury changes within the ACL, femoral and tibial entheses, synovial joint space, and load-bearing epiphyseal cortical and trabecular bone components of the knee joint. Right ACLs of 10-week-old C57BL/6J female mice (N = 75) were injured in vivo with the contralateral ACLs serving as controls. Mice were euthanized at 1, 3, 7, 14, or 28 days after injury (n = 12/cohort). Downstream analyses included volumetric cortical and trabecular bone analyses and histopathologic assessments of the knee joint after injury. Gait analyses across all time points were also performed (n = 15 mice).

RESULTS

The majority of the ACL injuries in mice were partial tears. The femoral and tibial cortical bone volumes were 39% and 32% lower, respectively, at 28 days after injury than those of the uninjured contralateral knees (P < .01). Trabecular bone measures demonstrated little difference between injured and control knees after injury. Across all bone measures, bone loss was similar between the injured knee condyles and ACL entheses. There was also significant inflammatory activity within the knee after injury. By 7 days after injury, synovitis and fibrosis were sigificantly elevated in the injured knee compared with the controls (P < .01), which corresponded with significantly higher osteoclast activity in bone at this time point compared with the controls. This inflammatory response signficantly persisted throughout the duration of the study (P < .01). The hindlimb gait after injury deviated from normal, but mice habitually loaded their injured knee throughout the study.

CONCLUSION

Bone loss was acute and persisted for 4 weeks after injury in mice. However, the authors' hypothesis was not confirmed, as bone quality was not significantly lower in the entheses compared with the condylar bone regions after injury. With relatively normal hindlimb loading but a significant physiological response after injury, bone loss in this model may be driven by inflammation.

CLINICAL RELEVANCE

There is persistent bone resorption and fibrotic tissue development after injury that is not resolved. Inflammatory and catabolic activity may have a significant role in the postinjury decline of bone quality in the knee.

Early patellofemoral cartilage and bone pathology in a rat model of noninvasive anterior cruciate ligament rupture

OBJECTIVE

Anterior cruciate ligament rupture (ACLR) is a risk factor for the development of post-traumatic osteoarthritis (PTOA). While PTOA in the tibiofemoral joint compartment is well-characterized, very little is known about pathology in the patellofemoral compartment after ACL injury. Here, we evaluated the extent to which ACLR induces early patellofemoral joint damage in a rat model.

METHODS

Adult female Lewis rats were randomized to noninvasive ACLR or Sham. Two weeks post-injury, contrast-enhanced micro-computed tomography (µCT) of femoral and patellar cartilage was performed using 20% v/v ioxaglate. Morphometric parameters of femoral trochlear and patellar cartilage, subchondral bone, and trabecular bone were derived from µCT. Sagittal Safranin-O/Fast-Green-stained histologic sections were graded using the OARSI score in a blinded fashion.

RESULTS

Cartilage and bone remodelling consistent with an early PTOA phenotype were observed in both femoral trochleas and patellae. ACLR caused osteophyte formation of the patella and pathology in the superficial zone of articular cartilage, including surface fibrillation, fissures, increased cellularity, and abnormal chondrocyte clustering. There were significant increases in thickness of patellar and trochlear cartilage. Loss of subchondral bone thickness, bone volume fraction, and tissue mineral density, as well as changes to patellar and trochlear trabecular microarchitecture, were indicative of catabolic bone remodelling. Several injury-induced changes, including increased cartilage thickness and trabecular spacing and decreased trabecular number were more severe in the patella compared to the trochlea.

CONCLUSION

The patellofemoral joint develops mild but evident pathology in the early period following ACL rupture, extending the utility of this model to the study of patellofemoral PTOA.

Induced Models of Osteoarthritis in Animal Models: A Systematic Review

The most common induction methods for OA are mechanical, surgical and chemical. However, there is not a gold standard in the choice of OA animal models, as different animals and induction methods are helpful in different contexts. Reporting the latest evidence and results in the literature could help researchers worldwide to define the most appropriate indication for OA animal-model development. This review aims to better define the most appropriate animal model for various OA conditions. The research was conducted on the following literature databases: Medline, Embase, Cinahl, Scopus, Web of Science and Google Scholar. Studies reporting cases of OA in animal models and their induction from January 2010 to July 2021 were included in the study and reviewed by two authors. The literature search retrieved 1621 articles, of which 36 met the selection criteria and were included in this review. The selected studies included 1472 animals. Of all the studies selected, 8 included information about the chemical induction of OA, 19 were focused on mechanical induction, and 9 on surgical induction. Nevertheless, it is noteworthy that several induction models, mechanical, surgical and chemical, have been proven suitable for the induction of OA in animals.

Synovial fibroblasts assume distinct functional identities and secrete R-spondin 2 in osteoarthritis

OBJECTIVES

Synovium is acutely affected following joint trauma and contributes to post-traumatic osteoarthritis (PTOA) progression. Little is known about discrete cell types and molecular mechanisms in PTOA synovium. We aimed to describe synovial cell populations and their dynamics in PTOA, with a focus on fibroblasts. We also sought to define mechanisms of synovial Wnt/β-catenin signalling, given its emerging importance in arthritis.

METHODS

We subjected mice to non-invasive anterior cruciate ligament rupture as a model of human joint injury. We performed single-cell RNA-sequencing to assess synovial cell populations, subjected Wnt-GFP reporter mice to joint injury to study Wnt-active cells, and performed intra-articular injections of the Wnt agonist R-spondin 2 (Rspo2) to assess whether gain of function induced pathologies characteristic of PTOA. Lastly, we used cultured fibroblasts, macrophages and chondrocytes to study how Rspo2 orchestrates crosstalk between joint cell types.

RESULTS

We uncovered seven distinct functional subsets of synovial fibroblasts in healthy and injured synovium, and defined their temporal dynamics in early and established PTOA. Wnt/β-catenin signalling was overactive in PTOA synovium, and Rspo2 was strongly induced after injury and secreted exclusively by Prg4^hi lining fibroblasts. Trajectory analyses predicted that Prg4^hi lining fibroblasts arise from a pool of Dpp4+ mesenchymal progenitors in synovium, with SOX5 identified as a potential regulator of this emergence. We also showed that Rspo2 orchestrated pathological crosstalk between synovial fibroblasts, macrophages and chondrocytes.

CONCLUSIONS

Synovial fibroblasts assume distinct functional identities during PTOA in mice, and Prg4^hi lining fibroblasts secrete Rspo2 that may drive pathological joint crosstalk after injury.

Small-Animal Compression Models of Osteoarthritis

The utility of nonsurgical, mechanical compression-based joint injury models to study osteoarthritis pathogenesis and treatments is increasing. Joint injury may be induced via cyclic compression loading or acute overloading to induce anterior cruciate ligament rupture. Models utilizing mechanical testing systems are highly repeatable, require little expertise, and result in a predictable onset of osteoarthritis-like pathology on a rapidly progressing timeline. In this chapter, we describe the procedures and equipment needed to perform mechanical compression-induced initiation of osteoarthritis in mice and rats.

Joint instability causes catabolic enzyme production in chondrocytes prior to synovial cells in novel non-invasive ACL ruptured mouse model

OBJECTIVE

The Anterior Cruciate Ligament (ACL)-deficient model helps to clarify the mechanism of knee osteoarthritis (OA); however, the conventional ACL injury model could have included concurrent onset factors such as direct compression stress to cartilage and subchondral bone. In this study, we established a novel Non-invasive ACL-Ruptured mouse model without concurrent injuries and elucidated the relationship between OA progression and joint instability.

DESIGN

We induced the ACL-Rupture non-invasively in twelve-week-old C57BL/6 male mice and evaluated histological, macroscopical, and morphological analysis at 0 days. Next, we created the ACL-R, controlled abnormal tibial translation (CATT), and Sham groups. Then, the joint stability and OA pathophysiology were analyzed at 2, 4, and 8 weeks.

RESULTS

No intra-articular injuries, except for ACL rupture, were observed in the ACL-R model. ACL-R mice increased anterior tibial displacement compared to the Sham group (P < 0.001, 95% CI [-1.509 to -0.966]) and CATT group (P < 0.001, 95% CI [-0.841 to -0.298]) at 8 weeks. All mice in the ACL-R group caused cartilage degeneration. The degree of cartilage degeneration in the ACL-R group was higher than in the CATT group (P = 0.006) at 8 weeks. The MMP-3-positive cell rate of chondrocytes increased in the ACL-R group than CATT group from 4 weeks (P = 0.043; 95% CI [-28.32 to -0.364]) while that of synovial cells increased at 8 weeks (P = 0.031; 95% CI [-23.398 to -1.021]).

CONCLUSION

We successfully established a Non-invasive ACL-R model without intra-articular damage. Our model revealed that chondrocytes might react to abnormal mechanical stress prior to synovial cells while the knee OA onset.

One session of 20 ​N cyclic compression induces chronic knee osteoarthritis in rats: A long-term study

Objective

Mechanical stimulation is a risk factor for knee osteoarthritis. Non-surgical compression has been used to study the effects of mechanical stimulation in vivo. However, the long-term effects of low-force compression on knee joint had not been studied. Therefore, we sought to identify the long-term effects of low-force cyclic compression on the rat knee joint.

Design

In this study, we applied one session cyclic compression with a peak load of 20 ​N for 60 cycles to the rat knee joint in an approximately 140-degree flexion position (Wistar, male, 12 weeks old), followed by 1 year of observation (including data from 1 week, 2 weeks, 4 weeks, 8 weeks, 6 months, and 1 year after compression), and then performed a sub-regional analysis with hematoxylin-eosin, Safranin O and Fast Green, and MMP13 immunohistochemical staining.

Results

We observed osteoarthritis-like cartilage damage, synovial inflammation, and high expression of MMP13 within 1 year after compression. However, these changes progressed slowly, with obvious matrix cracks that did not appear until 1 year after compression. In the regional analysis, we found that low-force compression caused a much slower development of injury at the compression contact site, and no significant structural cartilage damage was observed after 1 year of compression. In contrast, the non-contact site during compression at tibial cartilage in the same joint was the first to show significant structural damage.

Conclusion

This study demonstrates that one session of 20 ​N cyclic compression induces a chronic osteoarthritis-like phenotype in the rat knee in the long term.

OA foundations - experimental models of osteoarthritis

Osteoarthritis (OA) is increasingly recognised as a disease of diverse phenotypes with variable clinical presentation, progression, and response to therapeutic intervention. This same diversity is readily apparent in the many animal models of OA. However, model selection, study design, and interpretation of resultant findings, are not routinely done in the context of the target human (or veterinary) patient OA sub-population or phenotype. This review discusses the selection and use of animal models of OA in discovery and therapeutic-development research. Beyond evaluation of the different animal models on offer, this review suggests focussing the approach to OA-animal model selection on study objective(s), alignment of available models with OA-patient sub-types, and the resources available to achieve valid and translatable results. How this approach impacts model selection is discussed and an experimental design checklist for selecting the optimal model(s) is proposed. This approach should act as a guide to new researchers and a reminder to those already in the field, as to issues that need to be considered before embarking on in vivo pre-clinical research. The ultimate purpose of using an OA animal model is to provide the best possible evidence if, how, when and where a molecule, pathway, cell or process is important in clinical disease. By definition this requires both model and study outcomes to align with and be predictive of outcomes in patients. Keeping this at the forefront of research using pre-clinical OA models, will go a long way to improving the quality of evidence and its translational value.

Self-Healing of Hyaluronic Acid to Improve In Vivo Retention and Function

Convergent advances in the field of soft matter, macromolecular chemistry, and engineering have led to the development of biomaterials that possess autonomous, adaptive, and self-healing characteristics similar to living systems. These rationally designed biomaterials can surpass the capabilities of their parent material. Herein, the modification of hyaluronic acid (HA) to exhibit self-healing properties is described, and its physical and biological function both in vitro and in vivo is studied. The in vitro findings showed that self-healing HA designed to undergo self-repair improves lubrication, enhances free radical scavenging, and attenuates enzymatic degradation compared to unmodified HA. Longitudinal imaging following intraarticular injection of self-healing HA shows improved in vivo retention despite its low molecular weight. Concomitant with these functions, intraarticular injection of self-healing HA mitigates anterior cruciate ligament injury-mediated cartilage degeneration in rodents. This proof-of-concept study shows how incorporation of functional properties such as self-healing can be used to surpass the existing capabilities of biolubricants.

Impact of Controlling Abnormal Joint Movement on the Effectiveness of Subsequent Exercise Intervention in Mouse Models of Early Knee Osteoarthritis

OBJECTIVE

Moderate mechanical stress is necessary for preserving the cartilage. The clinician empirically understands that prescribing only exercise will progress osteoarthritis (OA) for knee OA patients with abnormal joint movement. When prescribing exercise for OA, we hypothesized that degeneration of articular cartilage could be further prevented by combining interventions with the viewpoint of normalizing joint movement.

DESIGN

Twelve-week-old ICR mice underwent anterior cruciate ligament transection (ACL-T) surgery in their right knee and divided into 4 groups: ACL-T, controlled abnormal joint movement (CAJM), ACL-T with exercise (ACL-T/Ex), CAJM with exercise (CAJM/Ex). Animals in the walking group were subjected to treadmill exercise 6 weeks after surgery, which included walking for 18 m/min, 30 min/d, 3 d/wk for 4 weeks. Joint instability was measured by anterior drawer test, and safranin-O staining and immunohistochemical staining were performed.

RESULTS

OARSI (Osteoarthritis Research Society International) score of ACL-T/Ex group showed highest among 4 groups (P < 0.001). And CAJM/Ex group was lower than ACL-T/Ex group. Positive cell ratio of IL-1β and MMP-13 in CAJM/Ex group was lower than ACL-T/Ex group (P < 0.05).

CONCLUSIONS

We found that the state of the intra-articular environment can greatly influence the effect of exercise on cartilage degeneration, even if exercise is performed under the same conditions. In the CAJM/Ex group where joint movement was normalized, abnormal mechanical stress such as shear force and compression force accompanying ACL cutting was alleviated. These findings may highlight the need to consider an intervention to correct abnormal joint movement before prescribing physical exercise in the treatment of OA.

Traumatic joint injury induces acute catabolic bone turnover concurrent with articular cartilage damage in a rat model of posttraumatic osteoarthritis

Assess acute alterations in bone turnover, microstructure, and histomorphometry following noninvasive anterior cruciate ligament rupture (ACLR). Twelve female Lewis rats were randomized to receive noninvasive ACLR or Sham loading (n = 6/group). In vivo μCT was performed at 3, 7, 10, and 14 days postinjury to quantify compartment-dependent subchondral (SCB) and epiphyseal trabecular bone remodeling. Near-infrared (NIR) molecular imaging was used to measure in vivo bone anabolism (800 CW BoneTag) and catabolism (Cat K 680 FAST). Metaphyseal bone remodeling and articular cartilage morphology was quantified using ex vivo μCT and contrast-enhanced µCT, respectively. Calcein-based dynamic histomorphometry was used to quantify bone formation. OARSI scoring was used to assess joint degeneration, and osteoclast number was quantified on TRAP stained-sections. ACLR induced acute catabolic bone remodeling in subchondral, epiphyseal, and metaphyseal compartments. Thinning of medial femoral condyle (MFC) SCB was observed as early as 7 days postinjury, while lateral femoral condyles (LFCs) exhibited SCB gains. Trabecular thinning was observed in MFC epiphyseal bone, with minimal changes to LFC. NIR imaging demonstrated immediate and sustained reduction of bone anabolism (~15%-20%), and a ~32% increase in bone catabolism at 14 days, compared to contralateral limbs. These findings were corroborated by reduced bone formation rate and increased osteoclast numbers, observed histologically. ACLR-injured femora had significantly elevated OARSI score, cartilage thickness, and cartilage surface deviation. ACL rupture induces immediate and sustained reduction of bone anabolism and overactivation of bone catabolism, with mild-to-moderate articular cartilage damage at 14 days postinjury.

Sex- and injury-based differences in knee biomechanics in mouse models of post-traumatic osteoarthritis

Sex and joint injury are risk factors implicated in the onset and progression of osteoarthritis (OA). In mouse models of post-traumatic OA (ptOA), the pathogenesis of disease is notably impacted by sex (often worse in males) and injury model (e.g. meniscal versus ligament injury). Increasing ptOA progression and severity is often associated with greater relative instability of the joint but few studies have directly quantified changes in joint mechanics after injury and compared outcomes across multiple models in both male and female mice. Passive anterior-posterior knee biomechanics were evaluated in 10-week-old, male and female C57BL/6J mice. PtOA injury models included destabilisation of the medial meniscus (DMM), anterior cruciate ligament transection (ACLT) or mechanical rupture (ACLR), and combined DMM and ACLT (DMM + ACLT). Sham operated and non-operated controls (NOC) were included for baseline comparisons. The test apparatus loaded hindlimbs at 60° flexion between ± 1 N at 0.5 mm/s (build specifications available for download: https://doi.org/10.17632/z754455x3c.1). Measures of joint laxity (range of motion, neutral zone) and stiffness were calculated. Joint laxity was comparable between male and female mice while joint stiffness was greater in females (P ≤ 0.002, correcting for body-mass and injury-model). Anterior-posterior joint mechanics were minimally altered by DMM but significantly affected by loss of the ACL (P < 0.001), with equivalent changes between ACL-injury models despite different injury mechanisms and adjacent meniscal damage. These findings suggest that despite the important role of joint injury; sex- and model-specific differences in ptOA progression and severity are not primarily driven by altered anterior-posterior knee biomechanics.

[Histological diagnostics in joint pathology due to increasing regenerative therapeutic strategies - special consideration for cartilage damage]

Orthopedic and trauma surgery are currently confronted with significant changes in their interventional and therapeutic strategies, especially in knee surgery. Minimally invasive and reconstructive techniques lead not only to modifications of the repertoire of interventional methods but also of the indications and questions for histopathological diagnostics. The classical problems in knee surgery remain important issues, which are traumatic, degenerative, and infectious lesions. In addition, questions regarding regeneration and integration of cell-material constructs will become more and more important in the future. Furthermore, questions regarding the regenerative potential of an implantation site for such constructs and the morphological quality of harvested tissue for the in vitro cell expansion of autologous cells are becoming increasingly important. The autologous chondrocyte transplantation is a good example of the relevance of the histopathological re-evaluation of the regenerated tissue for a better understanding of the pathophysiology of reconstructive therapies. It becomes clear that for specific aims based on reconstructive therapies, new scoring systems should be established for the histopathological routine diagnostic service. Furthermore, there is need for the definition of further histopathological criteria, which will help to optimize the differential application of reconstructive strategies via tissue engineering. The present report gives a short overview of the modifying requirements on the histopathological diagnostics in specimens from knee-surgery but does not claim to be exhaustive.

Automated MicroCT-based bone and articular cartilage analysis using iterative shape averaging and atlas-based registration

Micro-computed tomography (μCT) and contrast-enhanced μCT are important tools for preclinical analysis of bone and articular cartilage (AC). Quantitative data from these modalities is highly dependent on the accuracy of tissue segmentations, which are often obtained via time-consuming manual contouring and are prone to inter- and intra-observer variability. Automated segmentation strategies could mitigate these issues, but few such approaches have been described in the context of μCT. Here, we validated a fully-automated strategy for bone and AC segmentation based on registration of an average tissue atlas. Femora from healthy and arthritic rats underwent μCT scanning, and epiphyseal trabecular bone and AC volumes were manually contoured by an expert. Average tissue atlases composed of 1, 3, 5, 10 and 20 pre-contoured training images (n = 10 atlases/group) were generated using iterative shape averaging and registered onto unknown images via affine and non-rigid registration. Atlas-based and expert-defined volumes for bone and AC were compared in terms of shape-based similarity metrics, as well as morphometric and densitometric parameters. Our results demonstrate that atlas-based registrations were capable of highly accurate and consistent segmentation. Atlases built from as few as 3 training images had no incidence of mal-registration and exhibited improved incidence of accurate registration, and higher sensitivity and specificity compared to atlases built from only one training image. Atlas-based segmentation of bone and AC from μCT images is a robust and accurate alternative to manual tissue segmentation, enabling faster, more consistent segmentation of pre-clinical datasets.

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

Small animal models are essential for studying anterior cruciate ligament (ACL) injury, one of the leading risk factors for post-traumatic osteoarthritis (PTOA). Non-surgical models of ACL rupture have recently surged as a new tool to study PTOA, as they circumvent the confounding effects of surgical disruption of the joint. These models primarily have been explored in mice and rabbits, but are relatively understudied in rats. The purpose of this work was to establish a non-invasive, mechanical overload model of ACL rupture in the rat and to study the disease pathogenesis following the injury. ACL rupture was induced via non-invasive tibial compression in Lewis rats. Disease state was characterized for 4 months after ACL rupture via histology, computed tomography, and biomarker capture from the synovial fluid. The non-invasive knee injury (NIKI) model created consistent ACL ruptures without direct damage to other tissues and resulted in conventional OA pathology. NIKI knees exhibited structural changes as early as 4 weeks post-injury, including regional structural changes to cartilage, chondrocyte and cartilage disorganization, changes to the bone architecture, synovial hyperplasia, and the increased presence of biomarkers of cartilage fragmentation and pro-inflammatory cytokines. These results suggest that this model can be a valuable tool to study PTOA. By establishing the fundamental pathogenesis of this injury, additional opportunities are created to evaluate unique contributing factors and potential therapeutic interventions for this disease. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:356-367, 2020.

Articular cartilage gene expression patterns in the tissue surrounding the impact site following applications of shear and axial loads

BACKGROUND

Osteoarthritis is a degradative joint disease found in humans and commercial swine which can develop from a number of factors, including prior joint trauma. An impact injury model was developed to deliver in vitro loads to disease-free porcine patellae in a model of OA.

METHODS

Axial impactions (2000 N normal) and shear impactions (500 N normal with induced shear forces) were delivered to 48 randomly assigned patellae. The patellae were then cultured for 0, 3, 7, or 14 days following the impact. Specimens in the tissue surrounding the loading site were harvested and expression of 18 OA related genes was studied via quantitative PCR. The selected genes were previously identified from published work and fell into four categories: cartilage matrix, degradative enzymes, inflammatory response, and apoptosis.

RESULTS

Type II collagen (Col2a1) showed significantly lower expression in shear vs. axial adjacent tissue at day 0 and 7 (fold changes of 0.40 & 0.19, respectively). In addition, higher expression of degradative enzymes and Fas, an apoptosis gene, was observed in the shear specimens.

CONCLUSIONS

The results suggest that a more physiologically valid shear load may induce more damage to surrounding articular cartilage than a normal load alone.

Controlled release of celecoxib inhibits inflammation, bone cysts and osteophyte formation in a preclinical model of osteoarthritis

Major hallmarks of osteoarthritis (OA) are cartilage degeneration, inflammation and osteophyte formation. COX-2 inhibitors counteract inflammation-related pain, but their prolonged oral use entails the risk for side effects. Local and prolonged administration in biocompatible and degradable drug delivery biomaterials could offer an efficient and safe treatment for the long-term management of OA symptoms. Therefore, we evaluated the disease-modifying effects and the optimal dose of polyesteramide microspheres delivering the COX-2 inhibitor celecoxib in a rat OA model. Four weeks after OA induction by anterior cruciate ligament transection and partial medial meniscectomy, 8-week-old female rats (n = 6/group) were injected intra-articular with celecoxib-loaded microspheres at three dosages (0.03, 0.23 or 0.39 mg). Unloaded microspheres served as control. During the 16-week follow-up, static weight bearing and plasma celecoxib concentrations were monitored. Post-mortem, micro-computed tomography and knee joint histology determined progression of synovitis, osteophyte formation, subchondral bone changes, and cartilage integrity. Systemic celecoxib levels were below the detection limit 6 days upon delivery. Systemic and local adverse effects were absent. Local delivery of celecoxib reduced the formation of osteophytes, subchondral sclerosis, bone cysts and calcified loose bodies, and reduced synovial inflammation, while cartilage histology was unaffected. Even though the effects on pain could not be evualated directly in the current model, our results suggest the application of celecoxib-loaded microspheres holds promise as novel, safe and effective treatment for inflammation and pain in OA.

Metabolomic serum profiling after ACL injury in rats: A pilot study implicating inflammation and immune dysregulation in post-traumatic osteoarthritis

ACL rupture is a major risk factor for post-traumatic osteoarthritis (PTOA) development. Little information exists on acute systemic metabolic indicators of disease development. Thirty-six female Lewis rats were randomized to Control or noninvasive anterior cruciate ligament rupture (ACLR) and to three post-injury time points: 72 h, 4 weeks, 10 weeks (n = 6). Serum was collected and analyzed by ¹ H nuclear magnetic resonance (NMR) spectroscopy and combined direct injection and liquid chromatography (LC)-mass spectrometry (MS)/MS (DI-MS). Univariate and multivariate statistics were used to analyze metabolomic data, and predictive biomarker models were analyzed by receiver operating characteristic (ROC) analysis. Topological pathway analysis was used to identify perturbed pathways. Two hundred twenty-two metabolites were identified by ¹ H NMR and DI-MS. Differences in the serum metabolome between ACLR and Control were dominated by medium- and long-chain acylcarnitine species. Further, decreases in several tryptophan metabolites were either found to be significantly different in univariate analysis or to play important contributory roles to multivariate model separation. In addition to acylcarnitines and tryptophan metabolites, glycine, carnosine, and D-mannose were found to differentiate ACLR from Control. Glycine, 9-hexadecenoylcarnitine, trans-2-Dodecenoylcarnitine, linoelaidyl carnitine, hydroxypropionylcarnitine, and D-Mannose were identified as biomarkers with high area under ROC curve values and high predictive accuracies. Our analysis provides new information regarding the potential contribution of inflammatory processes and immune dysregulation to the onset and progression of PTOA following ACL injury. As these processes have most commonly been associated with inflammatory arthropathies, larger-scale studies elucidating their involvement in PTOA development and progression are necessary. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1969-1979, 2018.

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

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 9999:1-10, 2018.

Chondroitin sulfate from Scophthalmus maximus for treating osteoarthritis

Osteoarthritis (OA) is a common joint disease characterized by cartilage degradation. Chondroitin sulfate from shark (CS-S) has a good effect on OA in clinical, but due to source limited of CS from shark. Therefore, it is important to find a novel CS source with similar efficacy to CS-S in the treatment of OA. Herein, we reported a therapeutic effect of CS from scophthalmus maximus (CS-SM) for treating OA in rats. The OA model was established. After intervention with CS-SM by intragastric administration. Our results showed that CS-SM could protect articular cartilage in OA, inhibit the degradation of cartilage, decrease the apoptosis of chondrocytes, decline the content of interleukin-1, tumor necrosis factor-α and Prostaglandins E₂ in synovial fluid, down-regulate the protein expression of matrix metalloproteinase-1 and up-regulate the protein expression of tissue inhibitor of metalloproteinase-1. Our results suggest that oral CS from SM is a new potential therapy for OA.

Acute mobilization and migration of bone marrow-derived stem cells following anterior cruciate ligament rupture

OBJECTIVE

Little is known regarding acute local and systemic processes following anterior cruciate ligament (ACL) rupture. No study has elucidated whether bone marrow-derived mesenchymal stem cells (MSCs) are mobilized into circulation and recruited to the injured joint.

METHODS

In Part 1, Lewis rats were randomized to noninvasive ACL rupture (Rupture) or non-injured (Control) (n = 6/group). After 72 h, whole blood MSC concentration was assessed using flow cytometry. Synovial fluid and serum were assayed for stromal cell-derived factor (SDF)-1α and cartilage degeneration biomarkers, respectively. In Part 2, 12 additional rats were randomized and intravenously-injected with fluorescently-labeled allogenic MSCs. Cell tracking was performed using longitudinal, in vivo and ex vivo near-infrared (NIR) imaging and histology. Synovium SDF-1α and interleukin (IL)-17A immunostaining was performed. Serum was assayed for SDF-1α and 29 other cytokines.

RESULTS

In Part 1, there was a significant increase in MSC concentration and synovial fluid SDF-1α in Rupture. No differences in cartilage biomarkers were observed. In Part 2, Rupture had significantly higher NIR signal at 24, 48, and 72 h, indicating active recruitment of MSCs to the injured joint. Ex vivo cell tracking demonstrated MSC localization in the synovium and myotendinous junction (MTJ) of the quadriceps. Injured synovia exhibited increased synovitis grade and higher degree of IL-17A and SDF-1α immunostaining.

CONCLUSION

ACL rupture induced peripheral blood mobilization of MSCs and migration of intravenously-injected allogenic MSCs to the injured joint, where they localized in the synovium and quadriceps MTJ.

PDK2 promotes chondrogenic differentiation of mesenchymal stem cells by upregulation of Sox6 and activation of JNK/MAPK/ERK pathway

This study was undertaken to clarify the role and mechanism of pyruvate dehydrogenase kinase isoform 2 (PDK2) in chondrogenic differentiation of mesenchymal stem cells (MSCs). MSCs were isolated from femurs and tibias of Sprague-Dawley rats, weighing 300-400 g (5 females and 5 males). Overexpression and knockdown of PDK2 were transfected into MSCs and then cell viability, adhesion and migration were assessed. Additionally, the roles of aberrant PDK2 in chondrogenesis markers SRY-related high mobility group-box 6 (Sox6), type ΙΙ procollagen gene (COL2A1), cartilage oligomeric matrix protein (COMP), aggrecan (AGC1), type ΙX procollagen gene (COL9A2) and collagen type 1 alpha 1 (COL1A1) were measured by quantitative reverse-transcription polymerase chain reaction (qRT-PCR). The expressions of c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK) and extracellular regulated protein kinase (ERK) were measured. Overexpressing PDK2 promoted cell viability, adhesion and inhibited cell migration in MSCs (all P<0.05). qRT-PCR assay showed a potent increase in the mRNA expressions of all chondrogenesis markers in response to overexpressing PDK2 (P<0.01 or P<0.05). PDK2 overexpression also induced a significant accumulation in mRNA and protein expressions of JNK, p38MAPK and ERK in MSCs compared to the control (P<0.01 or P<0.05). Meanwhile, silencing PDK2 exerted the opposite effects on MSCs. This study shows a preliminary positive role and potential mechanisms of PDK2 in chondrogenic differentiation of MSCs. It lays the theoretical groundwork for uncovering the functions of PDK2 and provides a promising basis for repairing cartilage lesions in osteoarthritis.