Objective The current study was undertaken to adapt Equilibrium Partitioning of an Ionic Contrast agent via microcomputed tomography (EPIC-µCT) to mouse articular cartilage, which presents a particular challenge because it is thin (~30 µm) and has a small volume (0.2 – 0.4 mm3), meaning there is only approximately 2 – 4 µg of chondroitin sulfate glycosaminoglycan per joint surface cartilage. Design Using 6 µm isotropic voxels and the negatively charged contrast agent ioxaglate (Hexabrix), we optimized contrast agent concentration and incubation time, assessed two methods of tissue preservation (formalin fixation and freezing), examined the effect of ex vivo chondroitinase ABC digestion on x-ray attenuation, assessed accuracy and precision, compared young and skeletally mature cartilage, and determined patterns of degradation in a murine cartilage damage model induced by treadmill running. Results The optimal concentration of the contrast agent was 15%, formalin fixation was preferred to freezing, and 2 hours of incubation was needed to reach contrast agent equilibrium with formalin fixed specimens. There was good agreement with histologic measurements of cartilage thickness, although µCT overestimated thickness by 13% (~5 µm) in 6 week old mice. Enzymatic release of 0.8 µg of choindrotin sulfate (about 40% of the total) increased x-ray attenuation by ~17%. There was a 15% increase in x-ray attenuation in 14 week old mice compared to 6 week old mice (p < 0.001) and this corresponded to ~65% decrease in chondroitin sulfate content at 14 weeks. The older mice also had reductions of 33% in cartilage thickness and 44% in cartilage volume (p < 0.001). Treadmill running induced a 16% decrease in cartilage thickness (p = 0.012) and a 12% increase in x-ray attenuation (p = 0.006) in 14 week old mice. Conclusion This technique enables non-destructive visualization and quantification of murine femoral articular cartilage in three dimensions with anatomic specificity and should prove to be a useful new tool in studying degeneration of cartilage in mouse models.

Objective Articular cartilage defects commonly result from traumatic injury and predispose to degenerative joint diseases. To test the hypothesis that aberrant healing responses and chronic inflammation lead to osteoarthritis, we examined spatiotemporal changes in joint tissues after cartilage injury in murine knees. Since intra-articular injection of hyaluronan (HA) can attenuate injury-induced osteoarthritis in wild-type (WT) mice, we investigated a role for HA in the response to cartilage injury in mice lacking HA synthase 1 (Has1−/−). Design Femoral groove cartilage of WT and Has1−/− mice was debrided to generate a non-bleeding wound. Macroscopic imaging, histology, and gene expression were used to evaluate naïve, sham-operated, and injured joints. Results Acute responses (1–2 weeks) in injured joints from WT mice included synovial hyperplasia with HA deposition and joint-wide increases in expression of genes associated with inflammation, fibrosis, and extracellular matrix (ECM) production. By 4 weeks, some resurfacing of damaged cartilage occurred, and early cell responses were normalized. Cartilage damage in Has1−/− mice also induced early responses; however, at 4 weeks, inflammation and fibrosis genes remained elevated with widespread cartilage degeneration and fibrotic scarring in the synovium and joint capsule. Conclusions We conclude that the ineffective repair of injured cartilage in Has1−/− joints can be at least partly explained by the markedly enhanced expression of particular genes in pathways linked to ECM turnover, IL-17/IL-6 cytokine signaling, and apoptosis. Notably, Has1 ablation does not alter gross HA content in the ECM, suggesting that HAS1 has a unique function in the metabolism of inflammatory HA matrices.

We conclude that progressive articular CA damage in post-injury OA results primarily from biomechanical, cell biologic and mediator changes that promote a fibroblastic phenotype in joint cells. Since ADAMTS5 and TGFβ1 appear to control this process, agents which interfere with their activities may not only enhance endogenous CA repair in vivo, but also improve the properties of tissue-engineered CA for implantation.

The present study is the first study for the efficacy of DEI for cartilage lesions in an animal joint, from very early signs through erosion down to subchondral bone, representing the spectrum of cartilage changes occurring in human osteoarthritis (OA). Here we show that DEI allows the visualization of cartilage lesions in intact canine knee joints with good accuracy. Hence, DEI may be applicable for following joint degeneration in animal models of OA.

No abstract

Diffraction-enhanced imaging (DEI) is a radiographic technology that harnesses the X-ray refraction and scatter rejection properties that are not available with conventional radiography. Here, we test the efficacy of planar DEI to render images from which cartilage degeneration, characteristic of osteoarthritis, can be detected. DEI was carried out on human cadaveric intact knee joints at the X-15 beamline at the National Synchrotron Light Source. The gross specimens and the DEI images were graded separately for levels of cartilage degeneration on six individual surfaces: anterior and posterior femoral and tibial on both medial and lateral sides. There was a significant correlation between the actual levels of cartilage degeneration and what was observed in their respective DEI images (P < 0.05) for all six articular surfaces. Some articular surfaces (patellar surfaces, in particular) could not be visualized because of overlap with superimposed bone. Sensitivity for the graded articular surfaces was 0.73 and specificity was 0.92 (Grade 0 being no lesion and Grades 1-6 being increasing gradations of lesions). Chondrocalcinosis was also observed in DEI images to a far greater extent compared with the conventional radiographs. DEI renders images that are significantly correlated with their actual gross morphology. Detection of lesions was better for more severe grades of degeneration than for partial focal lesions. Although some articular surfaces could not be visualized because of superimposed bone, we feel that DEI has potential for the diagnosis of cartilage lesions and chondrocalcinosis.

Osteoarthritis (OA) is an aging-related degenerative joint disease, which has no cure partly due to limited understanding of its pathological mechanism(s). Here we report that the focal adhesion protein Kindlin-2, but not Kindlin-1 or -3, is highly expressed in articular chondrocytes of the hyaline cartilage, which is dramatically decreased in the degenerated articular cartilage of aged mice and patients with OA. Inducible deletion of Kindlin-2 in chondrocytes at adult stage leads to spontaneous OA and much severe OA lesions in the mice receiving the surgery of destabilization of the medial meniscus. Mechanistically, Kindlin-2 deficiency promotes mitochondrial oxidative stress and activates Stat3 in articular chondrocytes, leading to Runx2-mediated chondrocyte hypertrophic differentiation and catabolism. In vivo, systemic pharmacological blockade of Stat3 activation or genetic ablation of Stat3 in chondrocytes reverses aberrant accumulation of Runx2 and ECM-degrading enzymes and limits OA deteriorations caused by Kindlin-2 deficiency. Furthermore, genetic inactivation of Runx2 in chondrocytes reverses structural changes and OA lesions caused by Kindlin-2 deletion without down-regulating p-Stat3 in articular chondrocytes. Of translational significance, intraarticular injection of Kindlin-2-expressing adeno-associated virus decelerates progression of aging- and instability-induced knee joint OA in mice. Collectively, we identify a novel pathway comprising of Kindlin-2, Stat3 and Runx2 in articular chondrocytes responsible for maintaining integrity of the articular cartilage and define a potential therapeutic target for OA.

The authors regret that references 137e180 were missing from the original article published. This caused citations within Table I to not be referenced and so Table I has been corrected and appears below, along with the missing references. The authors would like to apologise for any inconvenience caused.