Plasticity of clonal populations of dedifferentiated adult human articular chondrocytes

Deciphering cartilage neuro-immune interactions and innervation profile through 3D engineered osteoarthritic micropathophysiological system

Osteoarthritis (OA) is an inflammatory musculoskeletal disorder that results in cartilage breakdown and alterations in the surrounding tissue microenvironment. Imbalances caused by inflammation and catabolic processes potentiate pathological nerves and blood vessels outgrowth toward damaged areas leading to pain in the patients. Yet, the precise mechanisms leading the nerve sprouting into the aneural cartilaginous tissue remain elusive. In this work, we aim to recapitulate in vitro the hallmarks of OA pathophysiology, including the sensory innervation profile, and provide a sensitive and reliable analytical tool to monitor the in vitro disease progression at microscale. Leveraging the use of patient-derived cells and bioengineering cutting-edge technologies, we engineered cartilage-like microtissues composed of primary human chondrocytes encapsulated in gelatin methacrylate hydrogel. Engineered constructs patterned inside microfluidic devices show the expression of cartilage markers, namely collagen type II, aggrecan, SOX-9 and glycosaminoglycans. Upon pro-inflammatory triggering, using primary human pro-inflammatory macrophage secretome, hallmarks of OA are recapitulated namely catabolic processes of human chondrocytes and the sensory innervation profile, supported by gene expression and functional assays. To monitor the OA micropathological system, a highly sensitive technology - EliChip™ - is presented to quantitively assess the molecular signature of cytokines and growth factors (interleukin 6 and nerve growth factor) produced from a single microfluidic chip. Herein, we report a miniaturized pathophysiological model and analytical tool to foster the neuro-immune interactions playing a role in cartilage-related disorders.

Targeting Chondrocyte Hypertrophy as Strategies for the Treatment of Osteoarthritis

Osteoarthritis (OA) is a common joint disease characterized by pain and functional impairment, which severely impacts the quality of life of middle-aged and elderly individuals. During normal bone development, chondrocyte hypertrophy is a natural physiological process. However, in the progression of OA, chondrocyte hypertrophy becomes one of its key pathological features. Although there is no definitive evidence to date confirming that chondrocyte hypertrophy is the direct cause of OA, substantial experimental data indicate that it plays an important role in the disease's pathogenesis. In this review, we first explore the mechanisms underlying chondrocyte hypertrophy in OA and offer new insights. We then propose strategies for inhibiting chondrocyte hypertrophy from the perspectives of targeting signaling pathways and tissue engineering, ultimately envisioning the future prospects of OA treatment.

An Advanced Mechanically Active Osteoarthritis-on-Chip Model to Test Injectable Therapeutic Formulations: The SYN321 Case Study

Current treatments for osteoarthritis (OA) often fail to address the underlying pathophysiology and may have systemic side effects, particularly associated with long-term use of non-steroidal anti-inflammatory drugs (NSAIDs). Thus, researchers are currently directing their efforts toward innovative polymer-drug combinations, such as mixtures of hyaluronic acid viscoelastic hydrogels and NSAIDs like diclofenac, to ensure sustained release of the NSAID within the joint following intra-articular injection. However, the progress of novel injectable therapies for OA is hindered by the absence of preclinical models that accurately represent the pathology of the disease. The uBeat® MultiCompress platform is here presented as a novel approach for studying anti-OA injectable therapeutics on human mechanically-damaged OA cartilage microtissues, in a physiologically relevant environment. This platform can accommodate injectable therapeutic formulations and is successfully tested with SYN321, a novel diclofenac-sodium hyaluronate conjugate under development as a treatment for knee OA. Results indicate the platform's effectiveness in evaluating therapeutic potential, showing downregulation of inflammatory markers and reduction in matrix degradation in OA cartilage micro-tissues treated with SYN321. The uBeat® MultiCompress platform thus represents a valuable tool for OA research, offering a bridge between traditional in vitro studies and potential clinical applications, with implications for future drug discovery.

The iPSC secretome is beneficial for in vitro propagation of primary osteoarthritic chondrocytes cell lines

BACKGROUND

One of the obstacles to autologous chondrocyte implantation (ACI) is obtaining a large quantity of chondrocytes without depletion of their properties. The conditioned medium (CM) from different subpopulations of stem cells (mesenchymal stromal cells (MSC) or induced pluripotent stem cells (iPSC)) could be a gamechanger. MSCs' potential is related to the donor's health and age, which could be omitted when, as a source, iPSCs are used. There is a lack of data regarding their use in the chondrocyte culture expansion. Thus, we wanted to verify whether iPSC-CM could be beneficial for the cell culture of primary chondrocyte cells.

METHODS

We added the iPSC-CMs from GPCCi001-A and ND 41658*H cells to the culture of primary chondrocyte cell lines isolated from OA patients (n = 6) for other two passages. The composition of the CM was evaluated using Luminex technology. Then, we analysed the senescence, proliferation rate and using flow cytometry: viability, distribution of cell cycle phases, production of reactive oxygen species (ROS) and double-strand breaks. The cartilage-related markers were evaluated using Western blot and immunofluorescence. Additionally, a three-dimensional cell culture was used to determine the potential to form cartilage particles.

RESULTS

iPSC-CM increased proliferation and diminished cell ROS production and senescence. CM influenced the cartilage-related protein expression and promoted the growth of cartilage particles. The cell exposed to CM did not lose the ECM proteins, suggesting the chondroprotective effect for prolonged culture time.

CONCLUSION

Our preliminary results suggest a beneficial effect on maintaining chondrocyte biology during in vitro expansion.

Engineered human osteoarthritic cartilage organoids

The availability of human cell-based models capturing molecular processes of cartilage degeneration can facilitate development of disease-modifying therapies for osteoarthritis [1], a currently unmet clinical need. Here, by imposing specific inflammatory challenges upon mesenchymal stromal cells at a defined stage of chondrogenesis, we engineered a human organotypic model which recapitulates main OA pathological traits such as chondrocyte hypertrophy, cartilage matrix mineralization, enhanced catabolism and mechanical stiffening. To exemplify the utility of the model, we exposed the engineered OA cartilage organoids to factors known to attenuate pathological features, including IL-1Ra, and carried out mass spectrometry-based proteomics. We identified that IL-1Ra strongly reduced production of the transcription factor CCAAT/enhancer-binding protein beta [2] and demonstrated that inhibition of the C/EBPβ-activating kinases could revert the degradative processes. Human OA cartilage organoids thus represent a relevant tool towards the discovery of new molecular drivers of cartilage degeneration and the assessment of therapeutics targeting associated pathways.

BMP9 is a potent inducer of chondrogenesis, volumetric expansion and collagen type II accumulation in bovine auricular cartilage chondroprogenitors

Reconstruction of the outer ear currently requires harvesting of cartilage from the posterior of the auricle or ribs leading to pain and donor site morbidity. An alternative source for auricular reconstruction is in vitro tissue engineered cartilage using stem/progenitor cells. Several candidate cell-types have been studied with tissue-specific auricular cartilage progenitor cells (AuCPC) of particular interest. Whilst chondrogenic differentiation of competent stem cells using growth factor TGFβ1 produces cartilage this tissue is frequently fibrocartilaginous and lacks the morphological features of hyaline cartilage. Recent work has shown that growth factor BMP9 is a potent chondrogenic and morphogenetic factor for articular cartilage progenitor cells, and we hypothesised that this property extends to cartilage-derived progenitors from other tissues. In this study we show monoclonal populations of AuCPCs from immature and mature bovine cartilage cultured with BMP9 produced cartilage pellets have 3-5-fold greater surface area in sections than those grown with TGFβ1. Increased volumetric growth using BMP9 was due to greater sGAG deposition in immature pellets and significantly greater collagen accumulation in both immature and mature progenitor pellets. Polarised light microscopy and immunohistochemical analyses revealed that the organisation of collagen fibrils within pellets is an important factor in the growth of pellets. Additionally, chondrocytes in BMP9 stimulated cell pellets had larger lacunae and were more evenly dispersed throughout the extracellular matrix. Interestingly, BMP9 tended to normalise the response of immature AuCPC monoclonal cell lines to differentiation cues whereas cells exhibited more variation under TGFβ1. In conclusion, BMP9 appears to be a potent inducer of chondrogenesis and volumetric growth for AuCPCs a property that can be exploited for tissue engineering strategies for reconstructive surgery though with the caveat of negligible elastin production following 21-day treatment with either growth factor.

Increase of cell surface vimentin is associated with vimentin network disruption and subsequent stress-induced premature senescence in human chondrocytes

Accumulation of dysfunctional chondrocytes has detrimental consequences on the cartilagehomeostasis and is thus thought to play a crucial role during the pathogenesis of osteoarthritis(OA). However, the underlying mechanisms of phenotypical alteration in chondrocytes areincompletely understood. Here, we provide evidence that disruption of the intracellularvimentin network and consequent phenotypical alteration in human chondrocytes results in anexternalization of the intermediate filament. The presence of the so-called cell surfacevimentin (CSV) on chondrocytes was associated with the severity of tissue degeneration inclinical OA samples and was enhanced after mechanical injury of cartilage tissue. By meansof a doxorubicine-based in vitro model of stress-induced premature senescence (SIPS), wecould confirm the connection between cellular senescence and amount of CSV. AlthoughsiRNA-mediated silencing of CDKN2A clearly reduced the senescent phenotype as well asCSV levels of human chondrocytes, cellular senescence could not be completely reversed.Interestingly, knockdown of vimentin resulted in a SIPS-like phenotype and consequentlyincreased CSV. Therefore, we concluded that the integrity of the intracellular vimentinnetwork is crucial to maintain cellular function in chondrocytes. This assumption could beconfirmed by chemically- induced collapse of the vimentin network, which resulted in cellularstress and enhanced CSV expression. Regarding its biological function, CSV was found to beassociated with enhanced chondrocyte adhesion and plasticity. While osteogenic capacitiesseemed to be enhanced in chondrocytes expressing high levels of CSV, the chondrogenicpotential was clearly compromised. Overall, our study reinforces the importance of thevimentin network in maintenance of the chondrogenic phenotype and introduces CSV as anovel membrane-bound marker of dysfunctional chondrocytes.

Achieving Nasal Septal Cartilage In Situ Regeneration: Focus on Cartilage Progenitor Cells

The nasal septal cartilage plays an important role in preventing the collapse of the nasal bones and maintaining the appearance of the nose. In the context of inherent difficulties regarding septal cartilage repair and the shortage of cartilage graft resources for regeneration, tissue engineering, especially the in situ strategy based on scaffolds, has become a new prospect and become one of the most promising approaches. Given that it is difficult for chondrocytes to achieve directional migration and secrete matrix components to participate in tissue repair after cartilage injury, cartilage progenitor cells (CPCs), with great migratory ability and stem cell characteristics, have caught the attention of researchers and brought hope for nasal septal cartilage in situ regeneration. In this review, we first summarized the distribution, characteristics, isolation, and culture methods of nasal septal CPCs. Subsequently, we described the roles of migratory CPCs in cartilage regeneration. Finally, we reviewed the existing studies on CPCs-based cartilage tissue engineering and summarized the strategies for promoting the migration and chondrogenesis of CPCs so as to provide ideas for achieving nasal septal cartilage in situ regeneration.

Failure of cartilage regeneration: emerging hypotheses and related therapeutic strategies

Osteoarthritis (OA) is a disabling condition that affects billions of people worldwide and places a considerable burden on patients and on society owing to its prevalence and economic cost. As cartilage injuries are generally associated with the progressive onset of OA, robustly effective approaches for cartilage regeneration are necessary. Despite extensive research, technical development and clinical experimentation, no current surgery-based, material-based, cell-based or drug-based treatment can reliably restore the structure and function of hyaline cartilage. This paucity of effective treatment is partly caused by a lack of fundamental understanding of why articular cartilage fails to spontaneously regenerate. Thus, research studies that investigate the mechanisms behind the cartilage regeneration processes and the failure of these processes are critical to instruct decisions about patient treatment or to support the development of next-generation therapies for cartilage repair and OA prevention. This Review provides a synoptic and structured analysis of the current hypotheses about failure in cartilage regeneration, and the accompanying therapeutic strategies to overcome these hurdles, including some current or potential approaches to OA therapy.

YY1/miR-140-5p/Jagged1/Notch axis mediates cartilage progenitor/stem cells fate reprogramming in knee osteoarthritis

Osteoarthritis is a multifactorial disease characterized by cartilage degeneration, while cartilage progenitor/stem cells (CPCs) are responsible for endogenous cartilage repair. However, the relevant regulatory mechanisms of CPCs fate reprogramming in OA are rarely reported. Recently, we observed fate disorders in OA CPCs and found that microRNA-140-5p (miR-140-5p) protects CPCs from fate changes in OA. This study further mechanistically investigated the upstream regulator and downstream effectors of miR-140-5p in OA CPCs fate reprogramming. As a result, luciferase reporter assay and validation assays revealed that miR-140-5p targets Jagged1 and inhibits Notch signaling in human CPCs, and the loss-/gain-of-function experiments and rescue assays discovered that miR-140-5p improves OA CPCs fate, but this effect can be counteracted by Jagged1. Moreover, increased transcription factor Ying Yang 1 (YY1) was associated with OA progression, and YY1 could disturb CPCs fate via transcriptionally repressing miR-140-5p and enhancing the Jagged1/Notch signaling. Finally, the relevant changes and mechanisms of YY1, miR-140-5p, and Jagged1/Notch signaling in OA CPCs fate reprogramming were validated in rats. Conclusively, this study identified a novel YY1/miR-140-5p/Jagged1/Notch signaling axis that mediates OA CPCs fate reprogramming, wherein YY1 and Jagged1/Notch signaling exhibits an OA-stimulative role, and miR-140-5p plays an OA-protective effect, providing attractive targets for OA therapeutics.

miR-140-5p protects cartilage progenitor/stem cells from fate changes in knee osteoarthritis

Cartilage progenitor/stem cells (CPCs) are promising seed cells for cartilage regeneration, but their fate changes and regulatory mechanisms in osteoarthritis (OA) pathogenesis remain unclear. This study aimed to investigate the role and potential mechanism of the microRNA-140-5p (miR-140-5p), whose protective role in knee OA has been confirmed by our previous studies, in OA CPCs fate reprogramming. Firstly, the normal and OA CPCs were isolated, and the fate indicators, miR-140-5p, Jagged1, and Notch signals were detected and analyzed. Then, the effect of miR-140-5p and the Notch pathway on CPCs fate reprogramming and miR-140-5p on Jagged1/Notch signaling was investigated in IL-1β-induced chondrocytes in vitro. Finally, the effect of miR-140-5p on OA CPCs fate reprogramming and the potential mechanisms were validated in OA rats. As a result, CPCs percentage was increased in the mild OA cartilage-derived total chondrocytes while decreased in the advanced OA group. Significant fate changes (including reduced cell viability, migration, chondrogenesis, and increased apoptosis), increased Jagged1 and Notch signals, and reduced miR-140-5p were observed in OA CPCs and associated with OA progression. IL-1β induced OA-like changes in CPCs fate, which could be exacerbated by miR-140-5p inhibitor while alleviated by DAPT (a specific Notch inhibitor) and miR-140-5p mimic. Finally, the in vitro phenomenal and mechanistic findings were validated in OA rats. Overall, miR-140-5p protects CPCs from fate changes via inhibiting Jagged1/Notch signaling in knee OA, providing attractive targets for OA therapeutics.

Chondrocyte Hypertrophy in Osteoarthritis: Mechanistic Studies and Models for the Identification of New Therapeutic Strategies

Articular cartilage shows limited self-healing ability owing to its low cellularity and avascularity. Untreated cartilage defects display an increased propensity to degenerate, leading to osteoarthritis (OA). During OA progression, articular chondrocytes are subjected to significant alterations in gene expression and phenotype, including a shift towards a hypertrophic-like state (with the expression of collagen type X, matrix metalloproteinases-13, and alkaline phosphatase) analogous to what eventuates during endochondral ossification. Present OA management strategies focus, however, exclusively on cartilage inflammation and degradation. A better understanding of the hypertrophic chondrocyte phenotype in OA might give new insights into its pathogenesis, suggesting potential disease-modifying therapeutic approaches. Recent developments in the field of cellular/molecular biology and tissue engineering proceeded in the direction of contrasting the onset of this hypertrophic phenotype, but knowledge gaps in the cause-effect of these processes are still present. In this review we will highlight the possible advantages and drawbacks of using this approach as a therapeutic strategy while focusing on the experimental models necessary for a better understanding of the phenomenon. Specifically, we will discuss in brief the cellular signaling pathways associated with the onset of a hypertrophic phenotype in chondrocytes during the progression of OA and will analyze in depth the advantages and disadvantages of various models that have been used to mimic it. Afterwards, we will present the strategies developed and proposed to impede chondrocyte hypertrophy and cartilage matrix mineralization/calcification. Finally, we will examine the future perspectives of OA therapeutic strategies.

Biomolecules-releasing click chemistry-based bioadhesives for repairing acetabular labrum tears

Currently, there are no effective clinical or experimental treatments to fully restore the function of the torn acetabular labrum. To fill the gap, here, we report the finding of progenitor cells in labral tissue, which can be recruited and stimulated to repair torn acetabular labral tissue. This study aimed to develop a biomolecule releasing bioadhesive which can speed up labral tissue healing by eliciting autologous labral progenitor cellular responses. A click chemistry-based bioadhesive, capable of releasing biomolecules, was synthesized to exert ~3× adhesion strength compared with fibrin glue. Via the release of platelet-derived growth factor (PDGF), the adhesive was shown to actively recruit and stimulate the proliferation of labral progenitor cells to the tear sites and within the adhesive. Finally, the ability of this biomolecules-releasing adhesive designed to promote labral tissue regeneration was evaluated using discarded human acetabular labrum tissue compared with surgical suture ex vivo. Histological analysis shows that PDGF-releasing bioadhesive yielded significantly more labrum cell responses and extracellular matrix protein (proteoglycan and collagen) production at the tear tissue site than surgical suture controls. The results confirm that the new PDGF-releasing bioadhesive can activate the responses of autologous labral progenitor cells to significantly improve labral tissue regeneration. Clinical significance: These PDGF-releasing bioadhesives may serve as a new and effective tool for repairing and regenerating acetabular labrum tears.

Schwann cells in the subcutaneous adipose tissue have neurogenic potential and can be used for regenerative therapies

Stem cell therapies for nervous system disorders are hindered by a lack of accessible autologous sources of neural stem cells (NSCs). In this study, neural crest-derived Schwann cells are found to populate nerve fiber bundles (NFBs) residing in mouse and human subcutaneous adipose tissue (SAT). NFBs containing Schwann cells were harvested from mouse and human SAT and cultured in vitro. During in vitro culture, SAT-derived Schwann cells remodeled NFBs to form neurospheres and exhibited neurogenic differentiation potential. Transcriptional profiling determined that the acquisition of these NSC properties can be attributed to dedifferentiation processes in cultured Schwann cells. The emerging population of cells were termed SAT-NSCs because of their considerably distinct gene expression profile, cell markers, and differentiation potential compared to endogenous Schwann cells existing in vivo. SAT-NSCs successfully engrafted to the gastrointestinal tract of mice, migrated longitudinally and circumferentially within the muscularis, differentiated into neurons and glia, and exhibited neurochemical coding and calcium signaling properties consistent with an enteric neuronal phenotype. These cells rescued functional deficits associated with colonic aganglionosis and gastroparesis, indicating their therapeutic potential as a cell therapy for gastrointestinal dysmotility. SAT can be harvested easily and offers unprecedented accessibility for the derivation of autologous NSCs from adult tissues. Evidence from this study indicates that SAT-NSCs are not derived from mesenchymal stem cells and instead originate from Schwann cells within NFBs. Our data describe efficient isolation procedures for mouse and human SAT-NSCs and suggest that these cells have potential for therapeutic applications in gastrointestinal motility disorders.

In vitro maturation and in vivo stability of bioprinted human nasal cartilage

The removal of skin cancer lesions on the nose often results in the loss of nasal cartilage. The cartilage loss is either surgically replaced with autologous cartilage or synthetic grafts. However, these replacement options come with donor-site morbidity and resorption issues. 3-dimensional (3D) bioprinting technology offers the opportunity to engineer anatomical-shaped autologous nasal cartilage grafts. The 3D bioprinted cartilage grafts need to embody a mechanically competent extracellular matrix (ECM) to allow for surgical suturing and resistance to contraction during scar tissue formation. We investigated the effect of culture period on ECM formation and mechanical properties of 3D bioprinted constructs of human nasal chondrocytes (hNC)-laden type I collagen hydrogel in vitro and in vivo. Tissue-engineered nasal cartilage constructs developed from hNC culture in clinically approved collagen type I and type III semi-permeable membrane scaffold served as control. The resulting 3D bioprinted engineered nasal cartilage constructs were comparable or better than the controls both in vitro and in vivo. This study demonstrates that 3D bioprinted constructs of engineered nasal cartilage are feasible options in nasal cartilage reconstructive surgeries.

Genipin-crosslinked collagen scaffolds inducing chondrogenesis: a mechanical and biological characterization

Articular cartilage degeneration is still an unsolved issue owing to its weak repairing capabilities, which usually result in fibrocartilage tissue formation. This fibrous tissue lacks of structural and bio-mechanical properties, degrading over time. Currently, arthroscopic techniques and autologous transplantation are the most used clinical procedures. However, rather than restoring cartilage integrity, these methods only postpone further cartilage deterioration. Therefore, tissue engineering strategies aimed at selecting scaffolds that remarkably support the chondrogenic differentiation of human mesenchymal stem cells (hMSCs) could represent a promising solution, but they are still challenging for researchers. In this study, the influence of two different genipin (Gp) crosslinking routes on collagen (Coll)-based scaffolds in terms of hMSCs chondrogenic differentiation and biomechanical performances was investigated. Three-dimensional (3D) porous Coll scaffolds were fabricated by freeze-drying techniques and were crosslinked with Gp following a "two-step" and an in "bulk" procedure, in order to increase the physico-mechanical stability of the structure. Chondrogenic differentiation efficacy of hMSCs and biomechanical behavior under compression forces through unconfined stress-strain tests were assessed. Coll/Gp scaffolds revealed an isotropic and highly homogeneous pore distribution along with an increase in the stiffness, also supported by the increase in the Coll denaturation temperature (T_d  = 57-63°C) and a significant amount of Coll and GAG deposition during the 3 weeks of chondrogenic culture. In particular, the presence of Gp in "bulk" led to a more uniform and homogenous chondral-like matrix deposition by hMSCs if compared to the results obtained from the Gp "two-step" functionalization procedure.

The clinical potential of articular cartilage-derived progenitor cells: a systematic review

Over the past two decades, evidence has emerged for the existence of a distinct population of endogenous progenitor cells in adult articular cartilage, predominantly referred to as articular cartilage-derived progenitor cells (ACPCs). This progenitor population can be isolated from articular cartilage of a broad range of species, including human, equine, and bovine cartilage. In vitro, ACPCs possess mesenchymal stromal cell (MSC)-like characteristics, such as colony forming potential, extensive proliferation, and multilineage potential. Contrary to bone marrow-derived MSCs, ACPCs exhibit no signs of hypertrophic differentiation and therefore hold potential for cartilage repair. As no unique cell marker or marker set has been established to specifically identify ACPCs, isolation and characterization protocols vary greatly. This systematic review summarizes the state-of-the-art research on this promising cell type for use in cartilage repair therapies. It provides an overview of the available literature on endogenous progenitor cells in adult articular cartilage and specifically compares identification of these cell populations in healthy and osteoarthritic (OA) cartilage, isolation procedures, in vitro characterization, and advantages over other cell types used for cartilage repair. The methods for the systematic review were prospectively registered in PROSPERO (CRD42020184775).

OUP accepted manuscript

Cells of the stromal vascular fraction (SVF) of human adipose tissue have the capacity to generate osteogenic grafts with intrinsic vasculogenic properties. However, cultured adipose-derived stromal cells (ASCs), even after minimal monolayer expansion, lose osteogenic capacity in vivo. Communication between endothelial and stromal/mesenchymal cell lineages has been suggested to improve bone formation and vascularization by engineered tissues. Here, we investigated the specific role of a subpopulation of SVF cells positive for T-cadherin (T-cad), a putative endothelial marker. We found that maintenance during monolayer expansion of a T-cad-positive cell population, composed of endothelial lineage cells (ECs), is mandatory to preserve the osteogenic capacity of SVF cells in vivo and strongly supports their vasculogenic properties. Depletion of T-cad-positive cells from the SVF totally impaired bone formation in vivo and strongly reduced vascularization by SVF cells in association with decreased VEGF and Adiponectin expression. The osteogenic potential of T-cad-depleted SVF cells was fully rescued by co-culture with ECs from a human umbilical vein (HUVECs), constitutively expressing T-cad. Ectopic expression of T-cad in ASCs stimulated mineralization in vitro but failed to rescue osteogenic potential in vivo, indicating that the endothelial nature of the T-cad-positive cells is the key factor for induction of osteogenesis in engineered grafts based on SVF cells. This study demonstrates that crosstalk between stromal and T-cad expressing endothelial cells within adipose tissue critically regulates osteogenesis, with VEGF and adiponectin as associated molecular mediators.

Endogenous repair theory enriches construction strategies for orthopaedic biomaterials: a narrative review

The development of tissue engineering has led to new strategies for mitigating clinical problems; however, the design of the tissue engineering materials remains a challenge. The limited sources and inadequate function, potential risk of microbial or pathogen contamination, and high cost of cell expansion impair the efficacy and limit the application of exogenous cells in tissue engineering. However, endogenous cells in native tissues have been reported to be capable of spontaneous repair of the damaged tissue. These cells exhibit remarkable plasticity, and thus can differentiate or be reprogrammed to alter their phenotype and function after stimulation. After a comprehensive review, we found that the plasticity of these cells plays a major role in establishing the cell source in the mechanism involved in tissue regeneration. Tissue engineering materials that focus on assisting and promoting the natural self-repair function of endogenous cells may break through the limitations of exogenous seed cells and further expand the applications of tissue engineering materials in tissue repair. This review discusses the effects of endogenous cells, especially stem cells, on injured tissue repairing, and highlights the potential utilisation of endogenous repair in orthopaedic biomaterial constructions for bone, cartilage, and intervertebral disc regeneration.

Comparison of Human Articular Cartilage Tissue and Chondrocytes Isolated from Peripheral versus Central Regions of Traumatic Lesions

OBJECTIVE

Cellular and molecular events occurring in cartilage regions close to injury are poorly investigated, but can possibly compromise the outcome of cell-based cartilage repair. In this study, key functional properties were assessed for cartilage biopsies collected from the central part of traumatic joint lesions (central) and from regions surrounding the defect (peripheral). These properties were then correlated with the quality of the initial cartilage biopsy and the inflammatory state of the joint.

DESIGN

Cartilage samples were collected from knee joints of 42 patients with traumatic knee injuries and analyzed for cell phenotype (by reverse transcriptas-polymerase chain reaction), histological quality, cellularity, cell viability, proliferation capacity, and post-expansion chondrogenic capacity of chondrocytes (in pellet culture). Synovium was also harvested and analyzed for the expression of inflammatory cytokines.

RESULTS

Cartilage quality and post-expansion chondrogenic capacity were higher in peripheral versus central samples. Differences between these 2 parameters were more pronounced in joints with high inflammatory features characterized by >100-fold difference in the mRNA levels of IL6 and IL8 in the corresponding synovium. Peripheral chondrocytes isolated from good- versus bad-quality biopsies expressed higher levels of collagen II/I and aggrecan/versican and lower levels of MMP13 and ADAMTS5. They also exhibited reduced proliferation and enhanced cartilage-forming capacity.

CONCLUSIONS

Chondrocytes at the periphery of traumatic lesions better maintain properties of healthy cartilage compared to those isolated from the center, even when derived from bad-quality tissues harvested from highly inflamed joints. Future studies are necessary to investigate the change of functional properties of peripheral chondrocytes over time.

Human Platelet Lysate as an Alternative to Autologous Serum for Human Chondrocyte Clinical Use

OBJECTIVE

A pivotal aspect of cartilage tissue engineering resides in cell culture medium supplementation, in view of maximizing in vitro cell proliferation and preserving cellular functionality. Autologous human serum (aHS) is commonly used as an inducive supplement for safe human articular chondrocyte (HAC) proliferation prior to clinical implantation. However, practical clinical use of aHS is hindered by constraining manufacturing requirements and quality assurance-driven downstream processing. The present study investigated potential alternative use of commercial human platelet lysate (hPL) supplements in HAC manufacturing workflows related to clinical therapeutic pathways.

DESIGN

Differential effects of hPL, aHS, and fetal bovine serum were assessed on primary cultured HAC parameters (viability, proliferative rates, and morphology) in 2-dimensional in vitro systems. A 3-dimensional HAC pellet model served for postexpansion assessment of cellular functionality, by visualizing proteoglycan production (Alcian blue staining), and by using qRT-PCR relative quantification of chondrogenic marker (SOX9, COL2-A1, and ACAN) genetic expression.

RESULTS

We found that monolayer HAC culture with hPL or aHS supplements presented similar characteristics (elongated cell morphology and nearly identical growth kinetics). Chondrogenic activity appeared as conserved in HACs expanded with human or bovine supplements, wherein histologic analysis indicated a progressive sGAG accumulation and SOX9, COL2-A1, ACAN gene expression was upregulated in 3-dimensional HAC pellet models.

CONCLUSION

This study therefore supports the use of hPL as a functional equivalent and alternative to aHS for cultured HAC batch preparation, with the potential to effectively alleviate pressure on clinical and manufacturing bottlenecks in cell therapy approaches for cartilage regeneration.

Progenitor Cells in Healthy and Osteoarthritic Human Cartilage Have Extensive Culture Expansion Capacity while Retaining Chondrogenic Properties

OBJECTIVE

Articular cartilage-derived progenitor cells (ACPCs) are a potential new cell source for cartilage repair. This study aims to characterize endogenous ACPCs from healthy and osteoarthritic (OA) cartilage, evaluate their potential for cartilage regeneration, and compare this to cartilage formation by chondrocytes.

DESIGN

ACPCs were isolated from full-thickness healthy and OA human cartilage and separated from the total cell population by clonal growth after differential adhesion to fibronectin. ACPCs were characterized by growth kinetics, multilineage differentiation, and surface marker expression. Chondrogenic redifferentiation of ACPCs was compared with chondrocytes in pellet cultures. Pellets were assessed for cartilage-like matrix production by (immuno)histochemistry, quantitative analyses for glycosaminoglycans and DNA content, and expression of chondrogenic and hypertrophic genes.

RESULTS

Healthy and OA ACPCs were successfully differentiated toward the adipogenic and chondrogenic lineage, but failed to produce calcified matrix when exposed to osteogenic induction media. Both ACPC populations met the criteria for cell surface marker expression of mesenchymal stromal cells (MSCs). Healthy ACPCs cultured in pellets deposited extracellular matrix containing proteoglycans and type II collagen, devoid of type I collagen. Gene expression of hypertrophic marker type X collagen was lower in healthy ACPC pellets compared with OA pellets.

CONCLUSIONS

This study provides further insight into the ACPC population in healthy and OA human articular cartilage. ACPCs show similarities to MSCs, yet do not produce calcified matrix under well-established osteogenic culture conditions. Due to extensive proliferative potential and chondrogenic capacity, ACPCs show potential for cartilage regeneration and possibly for clinical application, as a promising alternative to MSCs or chondrocytes.

Probing Multicellular Tissue Fusion of Cocultured Spheroids-A 3D-Bioassembly Model

While decades of research have enriched the knowledge of how to grow cells into mature tissues, little is yet known about the next phase: fusing of these engineered tissues into larger functional structures. The specific effect of multicellular interfaces on tissue fusion remains largely unexplored. Here, a facile 3D-bioassembly platform is introduced to primarily study fusion of cartilage-cartilage interfaces using spheroids formed from human mesenchymal stromal cells (hMSCs) and articular chondrocytes (hACs). 3D-bioassembly of two adjacent hMSCs spheroids displays coordinated migration and noteworthy matrix deposition while the interface between two hAC tissues lacks both cells and type-II collagen. Cocultures contribute to increased phenotypic stability in the fusion region while close initial contact between hMSCs and hACs (mixed) yields superior hyaline differentiation over more distant, indirect cocultures. This reduced ability of potent hMSCs to fuse with mature hAC tissue further underlines the major clinical challenge that is integration. Together, this data offer the first proof of an in vitro 3D-model to reliably study lateral fusion mechanisms between multicellular spheroids and mature cartilage tissues. Ultimately, this high-throughput 3D-bioassembly model provides a bridge between understanding cellular differentiation and tissue fusion and offers the potential to probe fundamental biological mechanisms that underpin organogenesis.

Adult ovine connective tissue cells resemble mesenchymal stromal cells in their propensity for extensive ex vivo expansion

Purpose/Aim: Expanded, human connective tissue cells can adopt mesenchymal stromal cell (MSC) properties that are favorable for applications in regenerative medicine. Sheep are used as a large animal model for cell therapies, although for preclinical testing it is important to establish whether ovine cells resemble humans in their tendency to adopt MSC properties. The objective of this study was to investigate whether cells from five ovine connective tissues are MSC-like in their propensity for extensive expansion and immunophenotype.Materials and Methods: Monolayer cultures were established with cells from annulus fibrosus, cartilage, meniscus, tendon, and nucleus pulposus. Bone marrow MSCs were evaluated as a control. Cultures were seeded at 500 cells/cm², and subcultured every 5 days up to day 20. Flow cytometry was used to evaluate expression of cluster of differentiation (CD) molecules associated with MSCs (29, 44, 166). Colony formation was evaluated using time-lapse imaging of individual cells.Results: By day 20, cumulative population doublings ranged between 22 (chondrocytes) and 27 (MSCs). All cells uniformly expressed CD44 and 73. Expression of CD166 for MSCs was 98-99%, and ranged between 64 and 97% for the other cell types. Time-lapse imaging demonstrated that 58-94% of the cells colonized as indicated by 3 population doublings within 52 hours.Conclusions: Cells from ovine connective tissues resembled MSCs in their propensity for sustained, colony-forming growth and expression of CD molecules. These data supports the potential for preclinical testing of MSC-like connective tissue cells in sheep.

The effect of neonatal, juvenile, and adult donors on rejuvenated neocartilage functional properties

Cartilage does not naturally heal, and cartilage lesions from trauma and wear-and-tear can lead to eventual osteoarthritis. To address long-term repair, tissue engineering of functional biologic implants to treat cartilage lesions is desirable, but the development of such implants is hindered by several limitations including 1) donor tissue scarcity due to the presence of diseased tissues in joints, 2) dedifferentiation of chondrocytes during expansion, and 3) differences in functional output of cells dependent on donor age. Toward overcoming these challenges, 1) costal cartilage has been explored as a donor tissue, and 2) methods have been developed to rejuvenate the chondrogenic phenotype of passaged chondrocytes for generating self-assembled neocartilage. However, it remains unclear how the rejuvenation processes are influenced by donor age, and, thus, how to develop strategies that specifically target age-related differences. Using histological, biochemical, proteomic, and mechanical assays, this study sought to determine the differences among neocartilage generated from neonatal, juvenile, and adult donors using the Yucatan minipig, a clinically relevant large animal model. Based on the literature, a relatively young adult population of animals was chosen due to a reduction in functional output of human articular chondrocytes after 40 years of age. After isolation, costal chondrocytes were expanded, rejuvenated, and self-assembled, and the neocartilages were assessed. The aggregate modulus values of neonatal constructs were at least 1.65-fold of those from the juvenile or adult constructs. Poisson's ratio also significantly differed among all groups, with neonatal constructs exhibiting values 49% higher than adult constructs. Surprisingly, other functional properties such as tensile modulus and GAG content did not significantly differ among groups. Total collagen content was slightly elevated in the adult constructs when compared to neonatal and juvenile constructs. A more nuanced view via bottom-up mass spectrometry showed that Col2a1 protein was not significantly different among groups, but content of several other collagen subtypes (i.e., Col1a1, Col9a1, Col11a2, and Col12a1) was modulated by donor age. For example, Col12a1 in adult constructs was found to be 102.9% higher than neonatal-derived constructs. Despite these differences, this study shows that different aged donors can be used to generate neocartilages of similar functional properties.

Cell Sources for Cartilage Repair-Biological and Clinical Perspective

Cell-based therapy represents a promising treatment strategy for cartilage defects. Alone or in combination with scaffolds/biological signals, these strategies open many new avenues for cartilage tissue engineering. However, the choice of the optimal cell source is not that straightforward. Currently, various types of differentiated cells (articular and nasal chondrocytes) and stem cells (mesenchymal stem cells, induced pluripotent stem cells) are being researched to objectively assess their merits and disadvantages with respect to the ability to repair damaged articular cartilage. In this paper, we focus on the different cell types used in cartilage treatment, first from a biological scientist’s perspective and then from a clinician’s standpoint. We compare and analyze the advantages and disadvantages of these cell types and offer a potential outlook for future research and clinical application.

Engineered nasal cartilage for the repair of osteoarthritic knee cartilage defects

[Figure: see text].

Selection of Highly Proliferative and Multipotent Meniscus Progenitors through Differential Adhesion to Fibronectin: A Novel Approach in Meniscus Tissue Engineering

Meniscus injuries can be highly debilitating and lead to knee osteoarthritis. Progenitor cells from the meniscus could be a superior cell type for meniscus repair and tissue-engineering. The purpose of this study is to characterize meniscus progenitor cells isolated by differential adhesion to fibronectin (FN-prog). Human osteoarthritic menisci were digested, and FN-prog were selected by differential adhesion to fibronectin. Multilineage differentiation, population doubling time, colony formation, and MSC surface markers were assessed in the FN-prog and the total meniscus population (Men). Colony formation was compared between outer and inner zone meniscus digest. Chondrogenic pellet cultures were performed for redifferentiation. FN-prog demonstrated multipotency. The outer zone FN-prog formed more colonies than the inner zone FN-prog. FN-prog displayed more colony formation and a higher proliferation rate than Men. FN-prog redifferentiated in pellet culture and mostly adhered to the MSC surface marker profile, except for HLA-DR receptor expression. This is the first study that demonstrates differential adhesion to fibronectin for the isolation of a progenitor-like population from the meniscus. The high proliferation rates and ability to form meniscus extracellular matrix upon redifferentiation, together with the broad availability of osteoarthritis meniscus tissue, make FN-prog a promising cell type for clinical translation in meniscus tissue-engineering.

Crosstalk Between Mesenchymal Stromal Cells and Chondrocytes: The Hidden Therapeutic Potential for Cartilage Regeneration

Cartilage injuries following trauma create a puzzling clinical scenario. The finite reparative potential of articular cartilage is well known, and injuries are associated with an increased risk of osteoarthritis. Cell-based therapies have spotlighted chondrocytes and mesenchymal stromal cells (MSCs) as the functional unit of articular cartilage and the progenitor cells, respectively. The available clinical treatments cannot reproduce the biomechanical properties of articular cartilage and call for continuous investigations into alternative approaches. Co-cultures of chondrocytes and MSCs are an attractive in vitro system to step closer to the in vivo multicellular environment's complexity. Research on the mechanisms of interaction between both cell types will reveal essential cues to understand cartilage regeneration. This review describes the latest discoveries on these interactions, along with advantages and main challenges in vitro and in vivo. The successful clinical translation of in vitro studies requires establishing rigorous standards and clinically relevant research models and an organ-targeting therapeutic strategy.

Sterile Tissue Ablation Using Laser Light—System Design, Experimental Validation, and Outlook on Clinical Applicability

Preparation of biological samples for further processing or analysis is generally performed manually by means of standard mechanical tools such as scalpels or biopsy punches. While this approach is uncomplicated and swift, it entails constraints such as low, operator-dependent cutting accuracy and reproducibility. Tissue segments surrounding the cut may further suffer mechanical and thermal damage due to shear forces and friction between tool and sample. These hindrances affect procedures both in the laboratory environment as well as within clinical settings. A system has been developed leveraging robotic positioning and laser light for precise, controlled, and contactless tissue ablation, and providing a concise and intuitive graphical user interface. Additionally, sterility of the process is demonstrated, a paramount element for clinical application. The proposed process does not require sterilization of the robotic components or the lasers, easing a prospective integration into existing workflows. In the context of this work, mainly cartilage repair surgery is targeted. The proposed system allows for highly accurate and reproducible shaping of the cartilage lesion area as well as its corresponding engineered cartilage graft, possibly leading to better and faster integration at the defect site. Promising results could be obtained in a first test series with human cartilage samples, validating the functionality of the preparation system and the feasibility of the sterility concept.

Endoglin Level Is Critical for Cartilage Tissue Formation In Vitro by Passaged Human Chondrocytes

Transforming growth factor beta (TGFβ) signaling is required for in vitro chondrogenesis. In animal models of osteoarthritis (OA), TGFβ receptor alterations are detected in chondrocytes in severe OA cartilage. It is not known whether such changes are dependent on the grade of human OA and if they affect chondrogenesis. Thus, the purpose of this study was to determine if human OA chondrocytes obtained from low-grade or high-grade disease could form cartilage tissue and to assess the role of the co-receptors, endoglin (ENG) and TGFβ receptor 3 (TGFBRIII), in the regulation of this tissue generation in vitro. We hypothesized that the grade of OA disease would not affect the ability of cells to form cartilage tissue and that the TGFβ co-receptor, ENG, would be critical to regulating tissue formation. Chondrocytes isolated from low-grade OA or high-grade OA human articular cartilage (AC) were analyzed directly (P0) or passaged in monolayer to P2. Expression of the primary TGFβ receptor ALK5, and the co-receptors ENG and TGFβRIII, was assessed by image flow cytometry. To assess the ability to form cartilaginous tissue, cells were placed in three-dimensional culture at high density and cultured in chondrogenic media containing TGFβ3. ENG knockdown was used to determine its role in regulating tissue formation. Overall, grade-specific differences in expression of ALK5, ENG, and TGFβRIII in primary or passaged chondrocytes were not detected; however, ENG expression increased significantly after passaging. Despite the presence of ALK5, P0 cells did not form cartilaginous tissue. In contrast, P2 cells derived from low-grade and high-grade OA AC formed hyaline-like cartilaginous tissues of similar quality. Knockdown of ENG in P2 cells inhibited cartilaginous tissue formation compared to controls indicating that the level of ENG protein expression is critical for in vitro chondrogenesis by passaged articular chondrocytes. This study demonstrates that it is not the grade of OA, but the levels of ENG in the presence of ALK5 that influences the ability of human passaged articular chondrocytes to form cartilaginous tissue in vitro in 3D culture. This has implications for cartilage repair therapies. Impact statement These findings are important clinically, given the limited availability of osteoarthritis (OA) cartilage tissue. Being able to use cells from all grades of OA will increase our ability to obtain sufficient cells for cartilage repair. In addition, it is possible that endoglin (ENG) levels, in the presence of ALK5 expression, may be suitable to use as biomarkers to identify cells able to produce cartilage.

Research advances in cartilage stem cells markers and induced differentiation

Cartilage stem cells (CSCs) are cells that self-proliferate, have surface antigen expression, and have multidirectional differentiation potential in the articular cartilage. CSCs, as an ideal source of stem cells, has a good application prospect in stem cell therapy. This article reviews the CSCs markers, cartilage differentiation signaling pathway, and clinical treatment of osteoarthritis.

Rejuvenation of extensively passaged human chondrocytes to engineer functional articular cartilage

Human articular chondrocytes (hACs) are scarce and lose their chondrogenic potential during monolayer passaging, impeding their therapeutic use. This study investigated i) the translatability of conservative chondrogenic passaging and aggregate rejuvenation on restoring chondrogenic properties of hACs passaged up to P9; and ii) the efficacy of a combined treatment of TGF-β1 (T), chondroitinase-ABC (C), and lysyl oxidase-like 2 (L), collectively termed TCL, on engineering functional human neocartilage via the self-assembling process, as a function of passage number up to P11. Here, we show that aggregate rejuvenation enhanced glycosaminoglycan (GAG) content and type II collagen staining at all passages and yielded human neocartilage with chondrogenic phenotype present up to P7. Addition of TCL extended the chondrogenic phenotype to P11 and significantly enhanced GAG content and type II collagen staining at all passages. Human neocartilage derived from high passages, treated with TCL, displayed mechanical properties that were on par with or greater than those derived from low passages. Conservative chondrogenic passaging and aggregate rejuvenation may be a viable new strategy 1) to address the perennial problem of chondrocyte scarcity and 2) to successfully rejuvenate the chondrogenic phenotype of extensively passaged cells (up to P11). Furthermore, tissue engineering human neocartilage via self-assembly in conjunction with TCL treatment advances the clinical use of extensively passaged human chondrocytes for cartilage repair.

Establishment of a New Device for Electrical Stimulation of Non-Degenerative Cartilage Cells In Vitro

In cell-based therapies for cartilage lesions, the main problem is still the formation of fibrous cartilage, caused by underlying de-differentiation processes ex vivo. Biophysical stimulation is a promising approach to optimize cell-based procedures and to adapt them more closely to physiological conditions. The occurrence of mechano-electrical transduction phenomena within cartilage tissue is physiological and based on streaming and diffusion potentials. The application of exogenous electric fields can be used to mimic endogenous fields and, thus, support the differentiation of chondrocytes in vitro. For this purpose, we have developed a new device for electrical stimulation of chondrocytes, which operates on the basis of capacitive coupling of alternating electric fields. The reusable and sterilizable stimulation device allows the simultaneous use of 12 cavities with independently applicable fields using only one main supply. The first parameter settings for the stimulation of human non-degenerative chondrocytes, seeded on collagen type I elastin-based scaffolds, were derived from numerical electric field simulations. Our first results suggest that applied alternating electric fields induce chondrogenic re-differentiation at the gene and especially at the protein level of human de-differentiated chondrocytes in a frequency-dependent manner. In future studies, further parameter optimizations will be performed to improve the differentiation capacity of human cartilage cells.

Characterization and Chondroprotective Effects of Extracellular Vesicles From Plasma- and Serum-Based Autologous Blood-Derived Products for Osteoarthritis Therapy

Autologous blood products gain increasing interest in the field of regenerative medicine as well as in orthopedics, aesthetic surgery, and cosmetics. Currently, citrate-anticoagulated platelet-rich plasma (CPRP) preparations are often applied in osteoarthritis (OA), but more physiological and cell-free alternatives such as hyperacute serum (hypACT) are under development. Besides growth factors, blood products also bring along extracellular vesicles (EVs) packed with signal molecules, which open up a new level of complexity at evaluating the functional spectrum of blood products. Large proportions of EVs originated from platelets in CPRP and hypACT, whereas very low erythrocyte and monocyte-derived EVs were detected via flow cytometry. EV treatment of chondrocytes enhanced the expression of anabolic markers type II collagen, SRY-box transcription factor 9 (SOX9), and aggrecan compared to full blood products, but also the catabolic marker and tissue remodeling factor matrix metalloproteinase 3, whereas hypACT EVs prevented type I collagen expression. CPRP blood product increased SOX9 protein expression, in contrast to hypACT blood product. However, hypACT EVs induced SOX9 protein expression while preventing interleukin-6 secretion. The results indicate that blood EVs are sufficient to induce chondrogenic gene expression changes in OA chondrocytes, while preventing proinflammatory cytokine release compared to full blood product. This highlights the potential of autologous blood-derived EVs as regulators of cartilage extracellular matrix metabolism and inflammation, as well as candidates for new cell-free therapeutic approaches for OA.

Adult ovine chondrocytes in expansion culture adopt progenitor cell properties that are favorable for cartilage tissue engineering

Human chondrocytes in expansion culture can become progenitor-like in their ability to proliferate extensively and secrete neocartilage in chondrogenic culture. Sheep are used as a large animal model for cartilage tissue engineering, although for testing progenitor-like chondrocytes it is important that ovine chondrocytes resemble human in the ability to adopt progenitor properties. Here, we investigate whether ovine chondrocytes can adopt progenitor properties as indicated by rapid proliferation in a colony-forming fashion, and high levels of neocartilage secretion in chondrogenic culture. In conditions known to promote expansion of mesenchymal stromal cells, ovine chondrocytes proliferated through approximately 12 population doublings in 10 days. Time-lapse imaging indicated rapid proliferation in a colony-forming pattern. Expanded ovine chondrocytes that were seeded into agarose and cultured in chondrogenic medium accumulated neocartilage over 2 weeks, to a greater extent than primary chondrocytes. These data confirm that ovine chondrocytes resemble human chondrocytes in their ability to acquire progenitor properties that are important for cartilage tissue engineering. Given the broad interest in using progenitor cells to heal connective tissues, next we compared proliferation and trilineage differentiation of ovine chondrocytes, meniscus cells, and tenocytes. Meniscus cells and tenocytes experienced more than 13 population doublings in 10 days. In chondrogenic culture, cartilage matrix accumulation, and gene expression were largely similar among the cell types. All cell types resisted osteogenesis, while expanded tenocytes and meniscal cells were capable of adipogenesis. While ovine connective tissue cells demonstrated limited lineage plasticity, these data support the potential to promote certain progenitor properties with expansion.

Influence of Conditioned Media on the Re-Differentiation Capacity of Human Chondrocytes in 3D Spheroid Cultures

A major challenge of cell-based therapy for cartilage lesions is the preservation of the chondrogenic phenotype during ex vivo cell cultivation. In this in vitro study, the chondro-inductive capacity of two different hyaline cartilage-conditioned cell culture media on human chondrocytes in 3D spheroids was determined. Media were conditioned by incubation of 200 mg/mL vital or devitalized cartilage matrix in growth media over 35 days. The media were analyzed for the content of soluble procollagen type (Col) II and glycosaminoglycans (GAGs) as well as released TGF-β1, IGF-1 and IGFBP3. Unconditioned medium served as a negative control while the positive medium control was supplemented with TGF-β1 and IGF-1. Spheroid cultures prepared from human chondrocytes were cultivated at 37 °C, 5% CO₂ and 21% O₂ in the respective media and controls. After 14 and 35 days, the deposition of ECM components was evaluated by histological analysis. Vital cartilage-conditioned medium contained significantly higher levels of Col II and active TGF-β1 compared to medium conditioned with the devitalized cartilage matrix. Despite these differences, the incubation with vital as well as devitalized cartilage conditioned medium led to similar results in terms of deposition of proteoglycans and collagen type II, which was used as an indicator of re-differentiation of human chondrocytes in spheroid cultures. However, high density 3D cell cultivation showed a positive influence on re-differentiation.

Osteochondritis dissecans (OCD) in Horses - Molecular Background of its Pathogenesis and Perspectives for Progenitor Stem Cell Therapy

Osteochondrosis (osteochondrosis dissecans; OCD) is a disease syndrome of growing cartilage related to different clinical entities such as epiphysitis, subchondral cysts and angular carpal deformities, which occurs in growing animals of all species, including horses. Nowadays, these disorders are affecting increasing numbers of young horses worldwide. As a complex multifactorial disease, OCD is initiated when failure in cartilage canals because of existing ischemia, chondrocyte biogenesis impairment as well as biochemical and genetic disruptions occur. Recently, particular attention have been accorded to the definition of possible relations between OCD and some metabolic disorders; in this way, implication of mitochondrial dysfunctions, endoplasmic reticulum disruptions, oxidative stress or endocrinological affections are among the most considered axes for future researches. As one of the most frequent cause of impaired orthopaedic potential, which may result in a sharp decrease in athletic performances of the affected animals, and lead to the occurrence of complications such as joint fragility and laminitis, OCD remains as one of the primary causes of considerable economic losses in all sections of the equine industry. It would therefore be important to provide more information on the exact pathophysiological mechanism(s) underlying early OC(D) lesions, in order to implement innovative strategies involving the use of progenitor stem cells, which are considered nowadays as a promising approach to regenerative medicine, with the potential to treat numerous orthopaedic disorders, including osteo-degenerative diseases, for prevention and reduction of incidence of the disease, not only in horses, but also in human medicine, as the equine model is already widely accepted by the scientific community and approved by the FDA, for the research and application of cellular therapies in the treatment of human conditions.

Human pluripotent stem cell-derived chondroprogenitors for cartilage tissue engineering

The cartilage of joints, such as meniscus and articular cartilage, is normally long lasting (i.e., permanent). However, once damaged, especially in large animals and humans, joint cartilage is not spontaneously repaired. Compensating the lack of repair activity by supplying cartilage-(re)forming cells, such as chondrocytes or mesenchymal stromal cells, or by transplanting a piece of normal cartilage, has been the basis of therapy for biological restoration of damaged joint cartilage. Unfortunately, current biological therapies face problems on a number of fronts. The joint cartilage is generated de novo from a specialized cell type, termed a 'joint progenitor' or 'interzone cell' during embryogenesis. Therefore, embryonic chondroprogenitors that mimic the property of joint progenitors might be the best type of cell for regenerating joint cartilage in the adult. Pluripotent stem cells (PSCs) are expected to differentiate in culture into any somatic cell type through processes that mimic embryogenesis, making human (h)PSCs a promising source of embryonic chondroprogenitors. The major research goals toward the clinical application of PSCs in joint cartilage regeneration are to (1) efficiently generate lineage-specific chondroprogenitors from hPSCs, (2) expand the chondroprogenitors to the number needed for therapy without loss of their chondrogenic activity, and (3) direct the in vivo or in vitro differentiation of the chondroprogenitors to articular or meniscal (i.e., permanent) chondrocytes rather than growth plate (i.e., transient) chondrocytes. This review is aimed at providing the current state of research toward meeting these goals. We also include our recent achievement of successful generation of "permanent-like" cartilage from long-term expandable, hPSC-derived ectomesenchymal chondroprogenitors.

Intra-individual comparison of human nasal chondrocytes and debrided knee chondrocytes: Relevance for engineering autologous cartilage grafts

OBJECTIVE

Implantation of autologous chondrocytes for cartilage repair requires harvesting of undamaged cartilage, implying an additional joint arthroscopy surgery and further damage to the articular surface. As alternative possible cell sources, in this study we assessed the proliferation and chondrogenic capacity of debrided Knee Chondrocytes (dKC) and Nasal Chondrocytes (NC) collected from the same patients.

METHODS

Matched NC and dKC pairs from 13 patients enrolled in two clinical studies (NCT01605201 and NCT026739059) were expanded in monolayer and then chondro-differentiated in 3D collagenous scaffolds in medium with or without Transforming Growth Factor beta 1 (TGFβ1). Cell proliferation and amount of cartilage matrix production by these two cell types were assessed.

RESULTS

dKC exhibited an inferior proliferation rate than NC, and a lower capacity to chondro-differentiate. Resulting dKC-grafts contained lower amounts of cartilage specific matrix components glycosaminoglycans and type II collagen. The cartilage forming capacity of dKC did not significantly correlate with specific clinical parameters and was only partially improved by medium supplemention with TGFβ1.

CONCLUSIONS

dKC exhibit a reproducibly poor capacity to engineer cartilage grafts. Our in vitro data suggest that NC would be a better suitable cell source for the generation of autologous cartilage grafts.

Identification of human temporomandibular joint fibrocartilage stem cells with distinct chondrogenic capacity

OBJECTIVE

This study was aimed to identify the residence of human fibrocartilage stem cells (hFCSCs), characterize their stem cell properties and investigate the functional mechanisms which regulate fibrocartilage stem cells (FCSCs) toward chondrogenic differentiation during cartilage homeostasis and repairing.

METHODS

Cytological characteristics of hFCSCs and human orofacial mesenchymal stem cells (hOFMSCs) were analyzed. Chondrogenic potential of hFCSCs was compared with hOFMSCs both in vitro and in vivo. Regulatory role of SOX9 during FCSCs chondrogenesis was studied by shRNA interference in vitro, and by GFP⁺ FCSCs treatment in rat condylar cartilage defect model. SOX9 expression was also examined in temporomandibular joint osteoarthritis (TMJOA) patients' cartilage surface.

RESULTS

hFCSCs exhibited typical mesenchymal stem cell characteristics, with significantly stronger chondrogenic capability compared to hOFMSCs. Moreover, hFCSCs showed remarkably increased expression of SOX9. During cartilage pellet culture, there was stronger SOX9 expression in hFCSCs than hOFMSCs. SOX9 shRNA interference downregulated chondrogenic capability of hFCSCs in vitro, as well as disrupting migration and chondrogenic differentiation of GFP⁺ FCSCs toward mature chondrocytes in rat condylar cartilage defect. Of note, SOX9 expression was also found suppressed in the condylar superficial zone of TMJOA patients.

CONCLUSION

We found the existence of FCSCs in human TMJ cartilage, and characterized their distinct stem cell features. SOX9 is essential for hFCSCs chondrogenic differentiation, and a comprehensive understanding of the regulatory role of SOX9 in hFCSCs would be important for exploring potential intervention strategy of condylar cartilage degradation during TMJ disorders.

Single-cell mass cytometry reveals cross-talk between inflammation-dampening and inflammation-amplifying cells in osteoarthritic cartilage

Aging or injury leads to degradation of the cartilage matrix and the development of osteoarthritis (OA). Because of a paucity of single-cell studies of OA cartilage, little is known about the interpatient variability in its cellular composition and, more importantly, about the cell subpopulations that drive the disease. Here, we profiled healthy and OA cartilage samples using mass cytometry to establish a single-cell atlas, revealing distinct chondrocyte progenitor and inflammation-modulating subpopulations. These rare populations include an inflammation-amplifying (Inf-A) population, marked by interleukin-1 receptor 1 and tumor necrosis factor receptor II, whose inhibition decreased inflammation, and an inflammation-dampening (Inf-D) population, marked by CD24, which is resistant to inflammation. We devised a pharmacological strategy targeting Inf-A and Inf-D cells that significantly decreased inflammation in OA chondrocytes. Using our atlas, we stratified patients with OA in three groups that are distinguished by the relative proportions of inflammatory to regenerative cells, making it possible to devise precision therapeutic approaches.

Engineered Cartilage from Human Chondrocytes with Homozygous Knockout of Cell Cycle Inhibitor p21

Osteoarthritis (OA) is a highly prevalent disease with limited treatment options. The search for disease-modifying OA therapies would benefit from a more comprehensive knowledge of the genetic variants that contribute to chondrocyte dysfunction and the barriers to cartilage regeneration. One goal of this study was to establish a system for producing engineered cartilage tissue from genetically defined primary human chondrocytes through genome editing and single-cell expansion. This process was utilized to investigate the functional effect of biallelic knockout of the cell cycle inhibitor p21. The use of ribonucleoprotein (RNP) CRISPR/Cas9 complexes targeting two sites in the coding region of p21 resulted in a high frequency (16%) of colonies with homozygous p21 knockout. Chondrogenic pellet cultures from expanded chondrocytes with complete loss of p21 produced more glycosaminoglycans (GAG) and maintained a higher cell number. Single-cell-derived colonies retained the potential for robust matrix production after expansion, allowing for analysis of colony variability from the same population of targeted cells. The effect of enhanced cartilage matrix production in p21 knockout chondrocytes persisted when matrix production from individual colonies was analyzed. Chondrocytes had lower levels of p21 protein with further expansion, and the difference in GAG production with p21 knockout was strongest at early passages. These results support previous findings that implicate p21 as a barrier to cartilage matrix production and regenerative capacity. Furthermore, this work establishes the use of genome-edited human chondrocytes as a promising approach for engineered tissue models containing user-defined gene knockouts and other genetic variants for investigation of OA pathogenesis. Impact Statement This work provides two important advances to the field of tissue engineering. One is the demonstration that engineered cartilage tissue can be produced from genetically defined populations of primary human chondrocytes. While CRISPR/Cas-9 genome editing has been extensively used in cell lines that divide indefinitely, this work extends the technique to an engineered tissue model system to support investigation of genetic changes that affect cartilage production. A second contribution is the finding that chondrocytes with p21 knockout synthesized more cartilage matrix tissue than unedited controls. This supports the continued investigation of p21 as a potential barrier to effective cartilage regeneration.

MicroRNA-181a/b-1 over-expression enhances osteogenesis by modulating PTEN/PI3K/AKT signaling and mitochondrial metabolism

MicroRNAs are small non-coding RNAs that play important roles in many cellular processes including proliferation, metabolism and differentiation. They function by binding to specific regions within the 3'UTR of target mRNAs resulting in suppression of protein synthesis and modulation of potentially many cellular pathways. We previously showed that miRNA expression levels differed between cells from distinct regions of developing human embryonic long bones. Specifically, we found that miR-181a-1 was significantly more highly expressed in hypertrophic chondrocytes compared to proliferating differentiated or progenitor chondrocytes, suggesting a potential role in regulating chondrocyte hypertrophy and/or endochondral bone formation. The goal of this study was to determine how miR-181a-1 together with its clustered miRNA, miR-181b-1, regulates osteogenesis. We show that over-expression of the miR-181a/b-1 cluster enhanced osteogenesis and that cellular pathways associated with protein synthesis and mitochondrial metabolism were significantly up-regulated. Metabolic assays revealed that the oxygen consumption rate and ATP-linked respiration were increased by miR-181a/b-1. To further decipher a potential mechanism causing these metabolic changes, we showed that PTEN (phosphatase and tensin homolog) levels were suppressed following miR-181a/b-1 over-expression, and that PI3K/AKT signaling was subsequently increased. Over-expression of PTEN was found to attenuate the enhancing effects of miR-181a/b-1, providing further evidence that miR-181a/b-1 regulates the PTEN/PI3K/AKT axis to enhance osteogenic differentiation and mitochondrial metabolism. These findings have important implications for the design of miR-181a/b targeting strategies to treat bone conditions such as fractures or heterotopic ossification.

[Effects of cartilage progenitor cells and microRNA-140 on repair of osteoarthritic cartilage injury]

OBJECTIVE

To summarize the effect of cartilage progenitor cells (CPCs) and microRNA-140 (miR-140) on the repair of osteoarthritic cartilage injury, and analyze their clinical prospects.

METHODS

The recent researches regarding the CPCs, miR-140, and repair of cartilage in osteoarthritis (OA) disease were extensively reviewed and summarized.

RESULTS

CPCs possess the characteristics of self-proliferation, expression of stem cell markers, and multi-lineage differentiation potential, and their chondrogenic ability is superior to other tissues-derived mesenchymal stem cells. CPCs are closely related to the development of OA, but the autonomic activation and chondrogenic ability of CPCs around the osteoarthritic cartilage lesion cannot meet the requirements of complete cartilage repair. miR-140 specifically express in cartilage, and has the potential to activate CPCs by inhibiting key molecules of Notch signaling pathway and enhance its chondrogenic ability, thus promoting the repair of osteoarthritic cartilage injury. Intra-articular delivery of drugs is one of the main methods of OA treatment, although intra-articular injection of miR-140 has a significant inhibitory effect on cartilage degeneration in rats, it also exhibit some limitations such as non-targeted aggregation, low bioavailability, and rapid clearance. So it is a good application prospect to construct a carrier with good safety, cartilage targeting, and high-efficiency for miR-140 based on articular cartilage characteristics. In addition, CPCs are mainly dispersed in the cartilage surface, while OA cartilage injury also begins from this layer, it is therefore essential to emphasize early intervention of OA.

CONCLUSION

miR-140 has the potential to activate CPCs and promote the repair of cartilage injury in early OA, and it is of great clinical significance to further explore the role of miR-140 in OA etiology and to develop new OA treatment strategies based on miR-140.

Human Diseased Articular Cartilage Contains a Mesenchymal Stem Cell-Like Population of Chondroprogenitors with Strong Immunomodulatory Responses

Background: osteoarthritic human articular cartilage (AC)-derived cartilage cells (CCs) with same-donor bone marrow (BMSCs) and adipose tissue (ASCs)-derived mesenchymal stem cells were compared, in terms of stemness features, and secretory and immunomodulatory responses to inflammation. Methods: proteoglycan 4 (PRG4) presence was evaluated in AC and CCs. MSCs and CCs (n = 8) were cultured (P1 to P4) and characterized for clonogenicity, nanog homeobox (NANOG), and POU class 5 homeobox 1 (POU5F1) expression, immunotypification, and tri-lineage differentiation. Their basal and interleukin-1β (IL-1β)-stimulated expression of matrix metalloproteases (MMPs), tissue inhibitors (TIMPs), release of growth factors, and cytokines were analyzed, along with the immunomodulatory ability of CCs. Results: PRG4 was mainly expressed in the intact AC surface, whereas shifted to the intermediate zone in damaged cartilage and increased its expression in CCs upon culture. All cells exhibited a similar phenotype and stemness maintenance over passages. CCs showed highest chondrogenic ability, no adipogenic potential, a superior basal secretion of growth factors and cytokines, the latter further increased after inflammatory stimulation, and an immunomodulatory behavior. All stimulated cells shared an increased MMP expression without a corresponding TIMP production. Conclusion: based on the observed features, CCs obtained from pathological joints may constitute a potential tissue-specific therapeutic target or agent to improve damaged cartilage healing, especially damage caused by inflammatory/immune mediated conditions.

Tissue on the Transferred Coracoid Graft After Latarjet Procedure: Histological and Morphological Findings

BACKGROUND

Anterior shoulder instability is a debilitating condition that can require stabilization via a Latarjet procedure.

PURPOSE

The aim of this study was to characterize the histological composition of the articular-sided surface of the coracoid bone graft after Latarjet procedure. Specific features of cells isolated from the coracoid and graft tissues were assessed.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Tissue samples were harvested from 9 consecutive patients undergoing arthroscopic debridement and screw removal after arthroscopic or open Latarjet procedure. Tissues were processed histologically. In 2 patients, the samples were analyzed to assess specific cellular properties.

RESULTS

Safranin O staining indicated that glenoid tissues contained variable amounts of glycosaminoglycan (GAG) and round chondrocytic cells mainly organized in clusters. Graft tissues contained less GAG and were more cellular but were not organized in clusters and had variable morphological features. An association appeared to exist between the cartilage quality of glenoid tissues and that of the graft tissues. Cells isolated from glenoid and graft tissues exhibited similar proliferation capacity.

CONCLUSION

The results of our analysis show that cells located at the articular-sided surface of transferred coracoid grafts demonstrate fibrocartilaginous properties and may have the capacity for chondral proliferation. Further studies are needed to confirm this observation and future application.

In vitro chondrogenic potency of surplus chondrocytes from autologous transplantation procedures does not predict short-term clinical outcomes

BACKGROUND

Autologous chondrocyte implantation (ACI) has been used over the last two decades to treat focal cartilage lesions aiming to delay or prevent the onset of osteoarthritis; however, some patients do not respond adequately to the procedure. A number of biomarkers that can forecast the clinical potency of the cells have been proposed, but evidence for the relationship between in vitro chondrogenic potential and clinical outcomes is missing. In this study, we explored if the ability of cells to make cartilage in vitro correlates with ACI clinical outcomes. Additionally, we evaluated previously proposed chondrogenic biomarkers and searched for new biomarkers in the chondrocyte proteome capable of predicting clinical success or failure after ACI.

METHODS

The chondrogenic capacity of chondrocytes derived from 14 different donors was defined based on proteoglycans staining and visual histological grading of tissues generated using the pellet culture system. A Lysholm score of 65 two years post-ACI was used as a cut-off to categorise "success" and "failure" clinical groups. A set of predefined biomarkers were investigated in the chondrogenic and clinical outcomes groups using flow cytometry and qPCR. High-throughput proteomics of cell lysates was used to search for putative biomarkers to predict chondrogenesis and clinical outcomes.

RESULTS

Visual histological grading of pellets categorised donors into "high" and "low" chondrogenic groups. Direct comparison between donor-matched in vitro chondrogenic potential and clinical outcomes revealed no significant associations. Comparative analyses of selected biomarkers revealed that expression of CD106 and TGF-β-receptor-3 was enhanced in the low chondrogenic group, while expression of integrin-α1 and integrin-β1 was significantly upregulated in the high chondrogenic group. Additionally, increased surface expression of CD166 was observed in the clinical success group, while the gene expression of cartilage oligomeric matrix protein was downregulated. High throughput proteomics revealed no differentially expressed proteins from success and failure clinical groups, whereas seven proteins including prolyl-4-hydroxylase 1 were differentially expressed when comparing chondrogenic groups.

CONCLUSION

In our limited material, we found no correlation between in vitro cartilage-forming capacity and clinical outcomes, and argue on the limitations of using the chondrogenic potential of cells or markers for chondrogenesis as predictors of clinical outcomes.