Osteoarthritis (OA) is a degenerative joint disease that involves the destruction of articular cartilage and eventually leads to disability. Molecules that promote the selective differentiation of multipotent mesenchymal stem cells (MSCs) into chondrocytes may stimulate the repair of damaged cartilage. Using an image-based high-throughput screen, we identified the small molecule kartogenin, which promotes chondrocyte differentiation (median effective concentration = 100 nM), shows chondroprotective effects in vitro, and is efficacious in two OA animal models. Kartogenin binds filamin A, disrupts its interaction with the transcription factor core-binding factor β subunit (CBFβ), and induces chondrogenesis by regulating the CBFβ-RUNX1 transcriptional program. This work provides new insights into the control of chondrogenesis that may ultimately lead to a stem cell—based therapy for osteoarthritis.

http://science.sciencemag.org/content/sci/336/6082/717.full.pdf

A Stem Cell–Based Approach to Cartilage Repair

Background
Full-thickness chondral defects and early osteoarthritis continue to present major challenges for the patient and the orthopaedic surgeon as a result of the limited healing potential of articular cartilage. The use of bioactive growth factors is under consideration as a potential therapy to enhance healing of chondral injuries and modify the arthritic disease process.

The Role of Growth Factors in Cartilage Repair

Osteoarthritis (OA) is one of the most commonly occurring forms of arthritis in the world today. It is a debilitating chronic illness causing pain and immense discomfort to the affected individual. Significant research is currently ongoing to understand its pathophysiology and develop successful treatment regimens based on this knowledge. Animal models have played a key role in achieving this goal. Animal models currently used to study osteoarthritis can be classified based on the etiology under investigation, primary osteoarthritis, and post-traumatic osteoarthritis, to better clarify the relationship between these models and the pathogenesis of the disease. Non-invasive animal models have shown significant promise in understanding early osteoarthritic changes. Imaging modalities play a pivotal role in understanding the pathogenesis of OA and the correlation with pain. These imaging studies would also allow in vivo surveillance of the disease as a function of time in the animal model. This review summarizes the current understanding of the disease pathogenesis, invasive and non-invasive animal models, imaging modalities, and pain assessment techniques in the animals.

/pdf/animal-models-of-osteoarthritis-classification-update-and-2wgv2mx17k.pdf

Animal models of osteoarthritis: classification, update, and measurement of outcomes.

Stem cell behaviors are regulated by multiple microenvironmental cues. As an external signal, mechanical stiffness of the extracellular matrix is capable of governing stem cell fate determination, but how this biophysical cue is translated into intracellular signaling remains elusive. Here, we elucidate mechanisms by which stem cells respond to microenvironmental stiffness through the dynamics of the cytoskeletal network, leading to changes in gene expression via biophysical transduction signaling pathways in two-dimensional culture. Furthermore, a putative rapid shift from original mechanosensing to de novo cell-derived matrix sensing in more physiologically relevant three-dimensional culture is pointed out. A comprehensive understanding of stem cell responses to this stimulus is essential for designing biomaterials that mimic the physiological environment and advancing stem cell-based clinical applications for tissue engineering.

/pdf/mechanism-of-regulation-of-stem-cell-differentiation-by-3f9iptcl2h.pdf

Mechanism of regulation of stem cell differentiation by matrix stiffness

Painful degeneration of soft tissues accounts for high socioeconomic costs Tissue engineering aims to provide biomimetics recapitulating native tissues Biocompatible thermoplastics for 3D printing can generate high-resolution structures resembling tissue extracellular matrix Large-pore 3D-printed acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) scaffolds were compared for cell ingrowth, viability, and tissue generation Primary articular chondrocytes and nucleus pulposus (NP) cells were cultured on ABS and PLA scaffolds for three weeks Both cell types proliferated well, showed high viability, and produced ample amounts of proteoglycan and collagen type II on both scaffolds NP generated more matrix than chondrocytes; however, no difference was observed between scaffold types Mechanical testing revealed sustained scaffold stability This study demonstrates that chondrocytes and NP cells can proliferate on both ABS and PLA scaffolds printed with a simplistic, inexpensive desktop 3D printer Moreover, NP cells produced more proteoglycan than chondrocytes, irrespective of thermoplastic type, indicating that cells maintain individual phenotype over the three-week culture period Future scaffold designs covering larger pore sizes and better mimicking native tissue structure combined with more flexible or resorbable materials may provide implantable constructs with the proper structure, function, and cellularity necessary for potential cartilage and disc tissue repair in vivo

https://www.mdpi.com/1422-0067/16/7/15118/pdf

3D-Printed ABS and PLA Scaffolds for Cartilage and Nucleus Pulposus Tissue Regeneration.

https://www.oarsijournal.com/article/S1063-4584(09)00222-2/pdf

Evaluation of histological scoring systems for tissue-engineered, repaired and osteoarthritic cartilage

Intraarticular administration of autologous conditioned serum (ACS) recently demonstrated some clinical effectiveness in treatment of osteoarthritis (OA). The current study aims to evaluate the in vitro effects of ACS on cartilage proteoglycan (PG) metabolism, its composition and the effects on synovial fluid (SF) cytokine levels following intraarticular ACS administration. The effect of conditioned serum on PG metabolism of cultured OA cartilage explants was compared to unconditioned serum. The effect of serum conditioning on levels of interleukin-1beta (IL-1β), IL-4, IL-6, IL-10, IL-13, interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), osteoprotegerin (OPG), oncostatin M (OSM), interleukin-1 receptor (IL-1ra) and transforming growth factor beta (TGF-β) were measured by multiplex ELISA. As TNF-α levels were found to be increased in conditioned serum, the effect of TNF-α inhibition by etanercept on PG metabolism was studied in cartilage explants cultured in the presence of conditioned serum. Furthermore, cytokine levels in SF were measured three days after intraarticular ACS injection in OA patients to verify their retention time in the joint space. PG metabolism was not different in the presence of conditioned serum compared to unconditioned serum. Levels of the anti-inflammatory cytokines IL-1ra, TGF-β, IL-10 as well as of pro-inflammatory cytokines IL-1β, IL-6, TNF-α and OSM were increased. IL-4, IL-13 and IFN-γ levels remained similar, while OPG levels decreased. TNF-α inhibition did not influence PG metabolism in cartilage explant culture in the presence of condtioned serum. Although OPG levels were higher and TGF-β levels were clearly lower in ACS than in SF, intraarticular ACS injection in OA patients did not result in significant changes in these cytokine levels. ACS for treatment of osteoarthritis contains increased levels of anti-inflammatory as well as pro-inflammatory cytokines, in particular TNF-α, but conditioned serum does not seem to have a net direct effect on cartilage metabolism, even upon inhibition of TNF-α. The fast intraarticular clearance of cytokines in the injected ACS may explain the limited effects found previously in vivo.

/pdf/cytokine-profile-of-autologous-conditioned-serum-for-2qs580o8qd.pdf

Cytokine profile of autologous conditioned serum for treatment of osteoarthritis, in vitro effects on cartilage metabolism and intra-articular levels after injection

This study aimed to determine whether, as in osteoarthritis, increased levels of interleukin-6 (IL-6) are present in the synovial fluid of patients with symptomatic cartilage defects and whether this IL-6 affects cartilage regeneration as well as the cartilage in the degenerated knee. IL-6 concentrations were determined by ELISA in synovial fluid and in conditioned media of chondrocytes regenerating cartilage. Chondrocytes were obtained from donors with symptomatic cartilage defects, healthy and osteoarthritic donors. The effect of IL-6 on cartilage regeneration and on metabolism of the resident cartilage in the knee was studied by both inhibition of endogenous IL-6 and addition of IL-6, in a regeneration model and in osteoarthritic explants in the presence of synovial fluid, respectively. Readout parameters were DNA and glycosaminoglycan (GAG) content and release. Differences between controls and IL-6 blocked or supplemented samples were determined by univariate analysis of variance using a randomized block design. Synovial fluid of patients with symptomatic cartilage defects contained more IL-6 than synovial fluid of healthy donors (P = 0.001) and did not differ from osteoarthritic donors. IL-6 production of osteoarthritic chondrocytes during cartilage regeneration was higher than that of healthy and defect chondrocytes (P < 0.001). Adding IL-6 increased GAG production by healthy chondrocytes and decreased GAG release by osteoarthritic chondrocytes (P < 0.05). Inhibition of IL-6 present in osteoarthritic synovial fluid showed a trend towards decreased GAG content of the explants (P = 0.06). Our results support a modest anabolic role for IL-6 in cartilage matrix production. Targeting multiple cytokines, including IL-6, may be effective in improving cartilage repair in symptomatic cartilage defects and osteoarthritis.

/pdf/interleukin-6-is-elevated-in-synovial-fluid-of-patients-with-4kvrbff861.pdf

Interleukin-6 is elevated in synovial fluid of patients with focal cartilage defects and stimulates cartilage matrix production in an in vitro regeneration model.

Introduction: Current cartilage repair procedures using autologous chondrocytes rely on a variety of carriers for implantation. Collagen types I and II are frequently used and valuable properties of both were shown earlier in vitro, although a preference for either was not demonstrated. Recently, however, fibrillar collagens were shown to promote cartilage degradation. The goal of this study was to evaluate the effects of collagen type I and type II coating on chondrogenic properties of in vitro cultured human chondrocytes, and to investigate if collagen-mediated cartilage degradation occurs.

Methods: Human chondrocytes of eight healthy cartilage donors were isolated, expanded, and cultured on culture well inserts coated with either collagen type I, type II, or no coating (control). After 28 days of redifferentiation culture, safranin O and immunohistochemical staining for collagen types I, II, X, and Runx2/Cbfa1 were performed and glycosaminoglycan (GAG) and DNA content and release were examined. Further, expression of collagen type I, type II, type X, MMP13, Runx2/Cbfa1, DDR2, α2 and β1 integrin were examined by reverse transcriptase-polymerase chain reaction.

Results: The matrix, created by chondrocytes grown on collagen type I- and II-coated membranes, resembled cartilage more than when grown on noncoated membranes as reflected by histological scoring. Immunohistochemical staining did not differ between the conditions. GAG content as well as GAG/DNA were higher for collagen type II-coated cartilage constructs than control. GAG release was also higher on collagen type I- and II-coated constructs. Expression of collagen type X was higher of chondrocytes grown on collagen type II compared to controls, but no collagen X protein could be demonstrated by immunohistochemistry. No effects of collagen coating on DDR2 nor MMP-13 gene expression were found. No differences were observed between collagen types I and II.

Conclusion: Chondrocyte culture on collagen type I or II promotes more active matrix production and turnover. No significant differences between collagen types I and II were observed, nor were hypertrophic changes more evident in either condition. The use of collagen type I or II coating for in vitro models, thus, seems a sound basis for in vivo repair procedures.

Effect of collagen type I or type II on chondrogenesis by cultured human articular chondrocytes

https://www.oarsijournal.com/article/S1063-4584(12)00874-6/pdf

Marijn Rutgers

Papers

Evaluation of histological scoring systems for tissue-engineered, repaired and osteoarthritic cartilage

Cytokine profile of autologous conditioned serum for treatment of osteoarthritis, in vitro effects on cartilage metabolism and intra-articular levels after injection

Interleukin-6 is elevated in synovial fluid of patients with focal cartilage defects and stimulates cartilage matrix production in an in vitro regeneration model.

Effect of collagen type I or type II on chondrogenesis by cultured human articular chondrocytes

dGEMRIC as a tool for measuring changes in cartilage quality following high tibial osteotomy: a feasibility study