A Mouse Model of Acute Cartilage Injury and Repair

Chondral defects are common and disabling. The development of pharmacological approaches for cartilage repair requires the availability of in vivo models which are amenable for gain and loss of function and ideally to genetic modification. In this chapter, we describe a method to induce full-thickness cartilage defects which, in young DBA/1 mice, heal spontaneously, but fail to heal in C57BL/6 mice of the same age or in aged DBA/1 mice. This model (or variants) has been used for genetic screenings to identify genes associated to repair capacity, to study stem cells involved in cartilage repair, and to study the function of molecules involved in repair mechanisms.

Disease modification and symptom relief in osteoarthritis using a mutated GCP-2/CXCL6 chemokine

We showed that the chemokine receptor C-X-C Motif Chemokine Receptor 2 (CXCR2) is essential for cartilage homeostasis. Here, we reveal that the CXCR2 ligand granulocyte chemotactic protein 2 (GCP-2) was expressed, during embryonic development, within the prospective permanent articular cartilage, but not in the epiphyseal cartilage destined to be replaced by bone. GCP-2 expression was retained in adult articular cartilage. GCP-2 loss-of-function inhibited extracellular matrix production. GCP-2 treatment promoted chondrogenesis in vitro and in human cartilage organoids implanted in nude mice in vivo. To exploit the chondrogenic activity of GCP-2, we disrupted its chemotactic activity, by mutagenizing a glycosaminoglycan binding sequence, which we hypothesized to be required for the formation of a GCP-2 haptotactic gradient on endothelia. This mutated version (GCP-2-T) had reduced capacity to induce transendothelial migration in vitro and in vivo, without affecting downstream receptor signaling through AKT, and chondrogenic activity. Intra-articular adenoviral overexpression of GCP-2-T, but not wild-type GCP-2, reduced pain and cartilage loss in instability-induced osteoarthritis in mice. We suggest that GCP-2-T may be used for disease modification in osteoarthritis.

In vivo potency assay for the screening of bioactive molecules on cartilage formation

Cartilage regeneration is a priority in medicine for the treatment of osteoarthritis and isolated cartilage defects. Several molecules with potential for cartilage regeneration are under investigation. Unfortunately, in vitro chondrogenesis assays do not always predict the stability of the newly formed cartilage in vivo. Therefore, there is a need for a stringent, quantifiable assay to assess in vivo the capacity of molecules to promote the stable formation of cartilage that is resistant to calcification and endochondral bone formation. We developed an ectopic cartilage formation assay (ECFA) that enables one to assess the capacity of bioactive molecules to support cartilage formation in vivo using cartilage organoids. The ECFA predicted good clinical outcomes when used as a quality control for efficacy of chondrocyte preparations before implantation in patients with cartilage defects. In this assay, articular chondrocytes from human donors or animals are injected either intramuscularly or subcutaneously in nude mice. As early as 2 weeks later, cartilage organoids can be retrieved. The size of the implants and their degree of differentiation can be assessed by histomorphometry, immunostainings of molecular markers and real-time PCR. Mineralization can be assessed by micro-computed tomography or by staining. The effects of molecules on cartilage formation can be tested following the systemic administration of the molecule in mice previously injected with chondrocytes, or after co-injection of chondrocytes with cell lines overexpressing and secreting the protein of interest. Here we describe the ECFA procedure, including steps for harvesting human and bovine articular cartilage, isolating primary chondrocytes, preparing overexpression cell lines, injecting the cells intramuscularly and retrieving the implants. This assay can be performed by technicians and researchers with appropriate animal training within 3 weeks.

ROR2 blockade as a therapy for osteoarthritis

Osteoarthritis is characterized by the loss of the articular cartilage, bone remodeling, pain, and disability. No pharmacological intervention can currently halt progression of osteoarthritis. Here, we show that blocking receptor tyrosine kinase-like orphan receptor 2 (ROR2) improves cartilage integrity and pain in osteoarthritis models by inhibiting yes-associated protein (YAP) signaling. ROR2 was up-regulated in the cartilage in response to inflammatory cytokines and mechanical stress. The main ligand for ROR2, WNT5A, and the targets YAP and connective tissue growth factor were up-regulated in osteoarthritis in humans. In vitro, ROR2 overexpression inhibited chondrocytic differentiation. Conversely, ROR2 blockade triggered chondrogenic differentiation of C3H10T¹/₂ cells and suppressed the expression of the cartilage-degrading enzymes a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4 and ADAMTS-5. The chondrogenic effect of ROR2 blockade in the cartilage was independent of WNT signaling and was mediated by down-regulation of YAP signaling. ROR2 signaling induced G protein and Rho-dependent nuclear accumulation of YAP, and YAP inhibition was required but not sufficient for ROR2 blockade-induced chondrogenesis. ROR2 silencing protected mice from instability-induced osteoarthritis with improved structural outcomes, sustained pain relief, and without apparent side effects or organ toxicity. Last, ROR2 silencing in human articular chondrocytes transplanted in nude mice led to the formation of cartilage organoids with more and better differentiated extracellular matrix, suggesting that the anabolic effect of ROR2 blockade is conserved in humans. Thus, ROR2 blockade is efficacious and well tolerated in preclinical animal models of osteoarthritis.

WNT3A-loaded exosomes enable cartilage repair

Cartilage defects repair poorly. Recent genetic studies suggest that WNT3a may contribute to cartilage regeneration, however the dense, avascular cartilage extracellular matrix limits its penetration and signalling to chondrocytes. Extracellular vesicles actively penetrate intact cartilage. This study investigates the effect of delivering WNT3a into large cartilage defects in vivo using exosomes as a delivery vehicle. Exosomes were purified by ultracentrifugation from conditioned medium of either L-cells overexpressing WNT3a or control un-transduced L-cells, and characterized by electron microscopy, nanoparticle tracking analysis and marker profiling. WNT3a loaded on exosomes was quantified by western blotting and functionally characterized in vitro using the SUPER8TOPFlash reporter assay and other established readouts including proliferation and proteoglycan content. In vivo pathway activation was assessed using TCF/Lef:H2B-GFP reporter mice. Wnt3a loaded exosomes were injected into the knees of mice, in which large osteochondral defects were surgically generated. The degree of repair was histologically scored after 8 weeks. WNT3a was successfully loaded on exosomes and resulted in activation of WNT signalling in vitro. In vivo, recombinant WNT3a failed to activate WNT signalling in cartilage, whereas a single administration of WNT3a loaded exosomes activated canonical WNT signalling for at least one week, and eight weeks later, improved the repair of osteochondral defects. WNT3a assembled on exosomes, is efficiently delivered into cartilage and contributes to the healing of osteochondral defects.

Agrin induces long-term osteochondral regeneration by supporting repair morphogenesis

Cartilage loss leads to osteoarthritis, the most common cause of disability for which there is no cure. Cartilage regeneration, therefore, is a priority in medicine. We report that agrin is a potent chondrogenic factor and that a single intraarticular administration of agrin induced long-lasting regeneration of critical-size osteochondral defects in mice, with restoration of tissue architecture and bone-cartilage interface. Agrin attracted joint resident progenitor cells to the site of injury and, through simultaneous activation of CREB and suppression of canonical WNT signaling downstream of β-catenin, induced expression of the chondrogenic stem cell marker GDF5 and differentiation into stable articular chondrocytes, forming stable articular cartilage. In sheep, an agrin-containing collagen gel resulted in long-lasting regeneration of bone and cartilage, which promoted increased ambulatory activity. Our findings support the therapeutic use of agrin for joint surface regeneration.

Lessons from joint development for cartilage repair in the clinic

More than 250 years ago, William Hunter stated that when cartilage is destroyed it never recovers. In the last 20 years, the understanding of the mechanisms that lead to joint formation and the knowledge that some of these mechanisms are reactivated in the homeostatic responses of cartilage to injury has offered an unprecedented therapeutic opportunity to achieve cartilage regeneration. Very large investments in ambitious clinical trials are finally revealing that, although we do not have perfect medicines yet, disease modification is a feasible possibility for human osteoarthritis.

Cellular and molecular mechanisms of cartilage damage and repair

Cartilage breakdown is the disabling outcome of rheumatic diseases, whether prevalently inflammatory such as rheumatoid arthritis or prevalently mechanical such as osteoarthritis (OA). Despite the differences between immune-mediated arthritides and OA, common mechanisms drive cartilage breakdown. Inflammation, chondrocyte phenotype and homeostatic mechanisms have recently been the focus of research and will be summarised in this review.

Self-management education programmes by lay leaders for people with chronic conditions

BACKGROUND

Lay-led self-management programmes are becoming widespread in the attempt to promote self-care for people with chronic conditions.

OBJECTIVES

To assess systematically the effectiveness of lay-led self-management programmes for people with chronic conditions.

SEARCH STRATEGY

We searched: the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library 2005, Issue 1), MEDLINE (January 1986 to May 2006), EMBASE (January 1986 to June 2006), AMED (January 1986 to June 2006), CINAHL (January 1986 to June 2006), DARE (1994 to July 2006, National Research Register (2000 to July 2006), NHS Economic Evaluations Database (1994 to July 2006), PsycINFO (January 1986 to June 2006), Science Citation Index (January 1986 to July 2006), reference lists and forward citation tracking of included studies. We contacted principal investigators and experts in the field. There were no language restrictions.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing structured lay-led self-management education programmes for chronic conditions against no intervention or clinician-led programmes.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. We contacted study authors for additional information. Results of RCTs were pooled using a random-effects model with standardised mean differences (SMDs) or weighted mean differences (WMDs) for continuous outcomes.

MAIN RESULTS

We included seventeen trials involving 7442 participants. The interventions shared similar structures and components but studies showed heterogeneity in conditions studied, outcomes collected and effects. There were no studies of children and adolescents, only one study provided data on outcomes beyond six months, and only two studies reported clinical outcomes.

PRIMARY OUTCOMES

Health status: There was a small, statistically-significant reduction in: pain (11 studies, SMD -0.10 (95% confidence interval (CI) -0.17 to -0.04)); disability (8 studies, SMD -0.15 (95% CI -0.25 to -0.05); and fatigue (7 studies, SMD -0.16 (95% CI -0.23 to -0.09); and small, statistically-significant improvement in depression (6 studies, SMD -0.16 95% CI -0.24 to -0.07). There was a small (but not statistically- or clinically-significant) improvement in psychological well-being (5 studies; SMD -0.12 (95% CI -0.33 to 0.09)); but no difference between groups for health-related quality of life (3 studies; WMD -0.03 (95% CI -0.09 to 0.02). Six studies showed a statistically-significant improvement in self-rated general health (WMD -0.20 (95% CI -0.31 to -0.10). Health behaviours: 7 studies showed a small, statistically-significant increase in self-reported aerobic exercise (SMD -0.20 (95% CI -0.27 to -0.12)) and a moderate increase in cognitive symptom management (4 studies, WMD -0.55 ( 95% CI -0.85 to -0.26)). Healthcare use: There were no statistically-significant differences between groups in physician or general practitioner attendance (9 studies; SMD -0.03 (95% CI -0.09 to 0.04)). There were also no statistically-significant differences between groups for days/nights spent in hospital (6 studies; WMD -0.32 (95% CI -0.71 to 0.07)). Self-efficacy: (confidence to manage condition) showed a small statistically-significant improvement (10 studies): SMD -0.30, 95% CI -0.41 to -0.19. No adverse events were reported in any of the studies.

AUTHORS' CONCLUSIONS

Lay-led self-management education programmes may lead to small, short-term improvements in participants' self-efficacy, self-rated health, cognitive symptom management, and frequency of aerobic exercise. There is currently no evidence to suggest that such programmes improve psychological health, symptoms or health-related quality of life, or that they significantly alter healthcare use. Future research on such interventions should explore longer term outcomes, their effect on clinical measures of disease and their potential role in children and adolescents.