Chondrogenic cells respond to partial-thickness defects of articular cartilage in adult rats: an in vivo study

Expression and diagnostic significance of integrin beta-2 in synovial fluid of patients with osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is characterized by synovial cartilage degeneration and is the leading cause of disability and pain worldwide. This study sought to investigate the expression of integrin beta-2 (ITGB2) in synovial fluid of OA patients and its clinical significance.

METHODS

A total of 110 OA patients were enrolled, who were classified into grade I (N = 35), II (N = 42), and III (N = 33) according to the Kellgren-Lawrence classification, with 110 healthy subjects as controls, and their clinical data were compared. ITGB2 level was detected by RT-qPCR. The receiver operating characteristic curve was used to analyze the predictive value of ITGB2 on OA occurrence. The correlation between ITGB2 and bone metabolism indexes procollagen type I N-terminal peptide (PINP), bone glaprotein (BGP), bone alkaline phosphatase (BALP), and β-collagen I telopeptide (β-CTX) was analyzed by the Pearson method. Logistic regression model was performed to analyze the influencing factors of OA.

RESULTS

The content of red blood cells, white blood cells, PINP, BGP, and BALP was lowered in OA patients, while β-CTX was elevated. ITGB2 was highly-expressed in OA patients, negatively-correlated with PINP, BGP, and BALP, but positively-correlated with β-CTX. ITGB2 level increased with the elevation of OA grade. The ITGB2 level >1.375 had certain diagnostic values for OA. ITGB2 level is related to OA severity and may be a biomarker for OA classification. ITGB2 was an independent risk factor for OA.

CONCLUSION

High expression of ITGB2 in synovial fluid can assist OA diagnosis and may be a biomarker for OA grade.

Advances in the Treatment of Partial-Thickness Cartilage Defect

Partial-thickness cartilage defects (PTCDs) of the articular surface is the most common problem in cartilage degeneration, and also one of the main pathogenesis of osteoarthritis (OA). Due to the lack of a clear diagnosis, the symptoms are often more severe when full-thickness cartilage defect (FTCDs) is present. In contrast to FTCDs and osteochondral defects (OCDs), PTCDs does not injure the subchondral bone, there is no blood supply and bone marrow exudation, and the nearby microenvironment is unsuitable for stem cells adhesion, which completely loses the ability of self-repair. Some clinical studies have shown that partial-thickness cartilage defects is as harmful as full-thickness cartilage defects. Due to the poor effect of conservative treatment, the destructive surgical treatment is not suitable for the treatment of partial-thickness cartilage defects, and the current tissue engineering strategies are not effective, so it is urgent to develop novel strategies or treatment methods to repair PTCDs. In recent years, with the interdisciplinary development of bioscience, mechanics, material science and engineering, many discoveries have been made in the repair of PTCDs. This article reviews the current status and research progress in the treatment of PTCDs from the aspects of diagnosis and modeling of PTCDs, drug therapy, tissue transplantation repair technology and tissue engineering ("bottom-up").

Assessment of functional roles and therapeutic potential of integrin receptors in osteoarthritis: A systematic review and meta-analysis of preclinical studies

BACKGROUND

Integrins are heterodimeric transmembrane receptors that mediate a variety of biological function and plays a critical role in osteoarthritis (OA) pathogenesis, which may provide new targets for the development of OA therapies. However, the roles of integrins in different stages of OA remain elusive.

OBJECTIVES

This study aimed to synthesize all published preclinical evidence on the roles of integrin receptors in different stages of OA to identify the potential target for drug development in alleviating OA pathogenesis.

METHODS

Major electronic databases were used to identify related original articles. The methodological quality of all included studies was appraised using the SYRCLE risk of bias tool. We used the generic inverse variance with random effects model to calculate standardized mean differences (SMDs) and 95% confidence interval (CI).

RESULTS

Seventeen studies were included in this systematic review. Integrin α5β1 activation increases the histopathological score both in early [SMD, 6.39; 95%CI (2.90, 9.87); p = 0.0003] and late [SMD, 3.41; 95%CI (2.44, 4.38); p < 0.00001] stage of OA. Integrin α5β1 also increased the core catabolic factors like MMP-3, IL-1β, and TNF-α. Interestingly, the inactivation of α5β1 integrin did not change the histopathological score (p = 0.84). Similarly, β1 integrin notably increased histopathological score at both stages of OA [early; SMD, 7.13; 95%CI (2.01, 12.24); p = 0.006]; [late; SMD, 10.25; 95%CI (5.11, 15.39); p < 0.0001], and increased the MMP-13 levels. However, integrin β1 was upregulated at the early stage and downregulated at the late stage of OA. Furthermore, α2β1 integrin significantly increased histopathological score [SMD, 3.14; 95%CI (2.18, 4.10); p < 0.00001] and MMP-13 [SMD, 2.24; 95%CI (0.07, 4.41); p = 0.04]. Deactivating integrin α1β1 increased histopathological score in late [SMD, 1.53; 95%CI (0.80, 2.26); p < 0.0001], but not in early [SMD, 0.90; 95%CI (-1.65, 3.45); p = 0.49] stage of OA.

CONCLUSION

This study provides evidence that α5β1, α2β1, and α1β1 integrin might be the potential target for future drug development in alleviating OA pathogenesis. Further work is required to establish our findings through activating/deactivating these receptors in different stages of OA.

From regeneration to osteoarthritis in the knee joint: The role shift of cartilage-derived progenitor cells

A mount of growing evidence has proven that cartilage-derived progenitor cells (CPCs) harbor strong proliferation, migration, andmultiple differentiation potentials over the past 2 decades. CPCs in the stage of immature tissue play an important role in cartilage development process and injured cartilage repair in the young and active people. However, during maturation and aging, cartilage defects cannot be completely repaired by CPCs in vivo. Recently, tissue engineering has revealed that repaired cartilage defects with sufficient stem cell resources under good condition and bioactive scaffolds in vitro and in vivo. Chronic inflammation in the knee joint limit the proliferation and chondrogenesis abilities of CPCs, which further hampered cartilage healing and regeneration. Neocartilage formation was observed in the varus deformity of osteoarthritis (OA) patients treated with offloading technologies, which raises the possibility that organisms could rebuild cartilage structures spontaneously. In addition, nutritionmetabolismdysregulation, including glucose and free fatty acid dysregulation, could influence both chondrogenesis and cartilage formation. There are a few reviews about the advantages of CPCs for cartilage repair, but few focused on the reasons why CPCs could not repair the cartilage as they do in immature status. A wide spectrum of CPCs was generated by different techniques and exhibited substantial differences. We recently reported that CPCs maybe are as internal inflammation sources during cartilage inflammaging. In this review, we further streamlined the changes of CPCs from immature development to maturation and from healthy status to OA advancement. The key words including “cartilage derived stem cells”, “cartilage progenitor cells”, “chondroprogenitor cells”, “chondroprogenitors” were set for latest literature searching in PubMed and Web of Science. The articles were then screened through titles, abstracts, and the full texts in sequence. The internal environment including long-term inflammation, extendedmechanical loading, and nutritional elements intake and external deleterious factors were summarized. Taken together, these results provide a comprehensive understanding of the underlying mechanism of CPC proliferation and differentiation during development, maturation, aging, injury, and cartilage regeneration in vivo.

Roles of Cartilage-Resident Stem/Progenitor Cells in Cartilage Physiology, Development, Repair and Osteoarthritis

Osteoarthritis (OA) is a degenerative disease that causes irreversible destruction of articular cartilage for which there is no effective treatment at present. Although articular cartilage lacks intrinsic reparative capacity, numerous studies have confirmed the existence of cartilage-resident stem/progenitor cells (CSPCs) in the superficial zone (SFZ) of articular cartilage. CSPCs are characterized by the expression of mesenchymal stromal cell (MSC)-related surface markers, multilineage differentiation ability, colony formation ability, and migration ability in response to injury. In contrast to MSCs and chondrocytes, CSPCs exhibit extensive proliferative and chondrogenic potential with no signs of hypertrophic differentiation, highlighting them as suitable cell sources for cartilage repair. In this review, we focus on the organizational distribution, markers, cytological features and roles of CSPCs in cartilage development, homeostasis and repair, and the application potential of CSPCs in cartilage repair and OA therapies.

The Hunt Is On! In Pursuit of the Ideal Stem Cell Population for Cartilage Regeneration

Cartilage injury and degeneration are hallmarks of osteoarthritis (OA), the most common joint disease. OA is a major contributor to pain, loss of function, and reduced quality of life. Over the last decade, considerable research efforts have focused on cell-based therapies, including several stem cell-derived approaches to reverse the cartilage alterations associated with OA. Although several tissue sources for deriving cell-based therapies have been identified, none of the resident stem cell populations have adequately fulfilled the promise of curing OA. Indeed, many cell products do not contain true stem cells. As well, issues with aggressive marketing efforts, combined with a lack of evidence regarding efficacy, lead the several national regulatory bodies to discontinue the use of stem cell therapy for OA until more robust evidence becomes available. A review of the evidence is timely to address the status of cell-based cartilage regeneration. The promise of stem cell therapy is not new and has been used successfully to treat non-arthritic diseases, such as hematopoietic and muscle disorders. These fields of regenerative therapy have the advantage of a considerable foundation of knowledge in the area of stem cell repair mechanisms, the role of the stem cell niche, and niche-supporting cells. This foundation is lacking in the field of cartilage repair. So, where should we look for the ideal stem cell to regenerate cartilage? It has recently been discovered that cartilage itself may contain a population of SC-like progenitors. Other potential tissues include stem cell-rich dental pulp and the adolescent growth plate, the latter of which contains chondrocyte progenitors essential for producing the cartilage scaffold needed for bone growth. In this article, we review the progress on stem cell therapies for arthritic disorders, focusing on the various stem cell populations previously used for cartilage regeneration, successful cases of stem cell therapies in muscle and hemopoietic disorders, some of the reasons why these other fields have been successful (i.e., “lessons learned” to be applied to OA stem cell therapy), and finally, novel potential sources of stem cells for regenerating damaged cartilage in vivo.

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).

Biomimetic Joint Paint for Efficient Cartilage Repair by Simultaneously Regulating Cartilage Degeneration and Regeneration in Pigs

Irregular partial-thickness cartilage defect is a common pathogenesis of osteoarthritis (OA) with no available treatment in clinical practice. Currently, cartilage tissue engineering is only suitable for a limited area of full-thickness cartilage defect. Here, we design a biomimetic joint paint for the intractable partial-thickness cartilage defect repair. The joint paint, composed of a bridging layer of chondroitin sulfate and a surface layer of gelatin methacrylate with hyaluronic acid, can quickly and tightly adhere to the cartilage defect by light activation. Being treated by the joint paint, the group of rabbit and pig models with partial-thickness cartilage defects showed a restoration of a smooth cartilage surface and the preservation of normal glycosaminoglycan content, whereas the untreated control group exhibited serious progressive OA development. This paint treatment functions by prohibiting chondrocyte apoptosis, maintaining chondrocyte phenotype, and preserving the content of glycosaminoglycan in the partial-thickness cartilage defects. These findings illustrated that the biomimetic joint paint is an effective and revolutionary therapeutics for the patients with noncurable partial-thickness cartilage defects.

Endogenous Repair and Regeneration of Injured Articular Cartilage: A Challenging but Promising Therapeutic Strategy

Articular cartilage (AC) has a very limited intrinsic repair capacity after injury or disease. Although exogenous cell-based regenerative approaches have obtained acceptable outcomes, they are usually associated with complicated procedures, donor-site morbidities and cell differentiation during ex vivo expansion. In recent years, endogenous regenerative strategy by recruiting resident mesenchymal stem/progenitor cells (MSPCs) into the injured sites, as a promising alternative, has gained considerable attention. It takes full advantage of body's own regenerative potential to repair and regenerate injured tissue while avoiding exogenous regenerative approach-associated limitations. Like most tissues, there are also multiple stem-cell niches in AC and its surrounding tissues. These MSPCs have the potential to migrate into injured sites to produce replacement cells under appropriate stimuli. Traditional microfracture procedure employs the concept of MSPCs recruitment usually fails to regenerate normal hyaline cartilage. The reasons for this failure might be attributed to an inadequate number of recruiting cells and adverse local tissue microenvironment after cartilage injury. A strategy that effectively improves local matrix microenvironment and recruits resident MSPCs may enhance the success of endogenous AC regeneration (EACR). In this review, we focused on the reasons why AC cannot regenerate itself in spite of potential self-repair capacity and summarized the latest developments of the three key components in the field of EACR. In addition, we discussed the challenges facing in the present EACR strategy. This review will provide an increasing understanding of EACR and attract more researchers to participate in this promising research arena.

Endogenous cell recruitment strategy for articular cartilage regeneration

In the absence of timely and proper treatments, injuries to articular cartilage (AC) can lead to cartilage degeneration and ultimately result in osteoarthritis. Regenerative medicine and tissue engineering techniques are emerging as promising approaches for AC regeneration and repair. Although the use of cell-seeded scaffolds prior to implantation can regenerate and repair cartilage lesions to some extent, these approaches are still restricted by limited cell sources, excessive costs, risks of disease transmission and complex manufacturing practices. Recently developed acellular scaffold approaches that rely on the recruitment of endogenous cells to the injured sites avoid these drawbacks and offer great promise for in situ AC regeneration. Multiple endogenous stem/progenitor cells (ESPCs) are found in joint-resident niches and have the capability to migrate to sites of injury to participate in AC regeneration. However, the natural recruitment of ESPCs is insufficient, and the local microenvironment is hostile after injury. Hence, an endogenous cell recruitment strategy based on the combination of chemoattractants and acellular scaffolds to effectively and specifically recruit ESPCs and improve local microenvironment may provide new insights into in situ AC regeneration. This review provides a brief overview of: (1) the status of endogenous cell recruitment strategy; (2) the subpopulations, potential migration routes (PMRs) of joint-resident ESPCs and their immunomodulatory and reparative effects; (3) chemoattractants and their potential adverse effects; (4) scaffold-based drug delivery systems (SDDSs) that are utilized for in situ AC regeneration; and (5) the challenges and future perspectives of endogenous cell recruitment strategy for AC regeneration. STATEMENT OF SIGNIFICANCE: Although the endogenous cell recruitment strategy for articular cartilage (AC) regeneration has been investigated for several decades, much work remains to be performed in this field. Future studies should have the following aims: (1) reporting the up-to-date progress in the endogenous cell recruitment strategies; (2) determining the subpopulations of ESPCs, the cellular and molecular mechanisms underlying the migration of these cells and their anti-inflammatory, immunomodulatory and reparative effects; (3) elucidating the chemoattractants that enhance ESPC recruitment and their potential adverse effects; and (4) developing advanced SDDSs for chemoattractant dispatch. Herein, we present a systematic overview of the aforementioned issues to provide a better understanding of endogenous cell recruitment strategies for AC regeneration and repair.

Tissue-Adhesive Paint of Silk Microparticles for Articular Surface Cartilage Regeneration

Current biomaterials and tissue engineering techniques have shown a promising efficacy on full-thickness articular cartilage defect repair in clinical practice. However, due to the difficulty of implanting biomaterials or tissue engineering constructs into a partial-thickness cartilage defect, it remains a challenge to provide a satisfactory cure in joint surface regeneration in the early and middle stages of osteoarthritis. In this study, we focused on a ready-to-use tissue-adhesive joint surface paint (JS-Paint) capable of promoting and enhancing articular surface cartilage regeneration. The JS-Paint is mainly composed of N-(2-aminoethyl)-4-(4-(hydroxymethyl)-2-methoxy-5-nitrosophenoxy) butanamide (NB)-coated silk fibroin microparticles and possess optimal cell adhesion, migration, and proliferation properties. NB-modified silk fibroin microparticles can directly adhere to the cartilage and form a smooth layer on the surface via the photogenerated aldehyde group of NB reacting with the -NH₂ groups of the cartilage tissue. JS-Paint treatment showed a significant promotion of cartilage regeneration and restored the smooth joint surface at 6 weeks postsurgery in a rabbit model of a partial-thickness cartilage defect. These findings revealed that silk fibroin can be utilized to bring about a tissue-adhesive paint. Thus, the JS-Paint strategy has some great potential to enhance joint surface regeneration and revolutionize future therapeutics of early and middle stages of osteoarthritis joint ailments.

Timing of Intra-Articular Injection of Synovial Mesenchymal Stem Cells Affects Cartilage Restoration in a Partial Thickness Cartilage Defect Model in Rats

OBJECTIVE

We investigated the effect of administration of intra-articular mesenchymal stem cells (MSCs) on cartilage repair at different timings, and the distribution of MSCs in the knee.

DESIGN

A partial thickness cartilage defect (PTCD) was created on the medial femoral condyle in 14-week-old Sprague-Dawley rats. Intra-articular injection of 1 × 10⁶ MSCs was performed at 3 time points, namely at the time of surgery (0w group), at 1 week after surgery (1w group), and at 2 weeks after surgery (2w group). For the control, 50 μL phosphate-buffered saline was injected at the time of surgery. The femoral condyles were collected at 6 weeks after creation of PTCD and assessed histologically. To investigate the distribution of MSCs, fluorescent-labeled MSCs were injected into the knee joint.

RESULTS

In the control group, the cartilage lesion was distinguishable from surrounding cartilage. In the 0w group, hypocellularity and a slight decrease in safranin O stainability were observed around the injured area, but cartilage was restored to a nearly normal condition. In contrast, in the 1w and 2w groups, the cartilage surface was irregular and safranin O stainability in the injured and surrounding areas was poor. Histological score in the 0w group was significantly better than in the control, 1w, and 2w groups. At 1 day postinjection, fluorescent-labeled MSCs were mostly distributed in synovium. However, no migration into the PTCD was observed.

CONCLUSIONS

Early intra-articular injection of MSCs was effective in enhancing cartilage healing in a rat PTCD model. Injected MSCs were distributed in synovium, not in cartilage surrounding the PTCD.

Articular cartilage regeneration: The role of endogenous mesenchymal stem/progenitor cell recruitment and migration

BACKGROUND

Trauma- or osteoarthritis-related cartilage damage resulted in functional decline of joints and heavy burden of public health. Recently, the reparative role of mesenchymal stem/progenitor cells (MSCs) in articular cartilage (AC) reconstruction is drawing more and more attention.

OBJECTIVE

To provide a review on (1) the locations and categories of joint-resident MSCs, (2) the regulation of chondrogenic capacities of MSCs, (3) the migratory approaches of MSCs to diseased AC and regulatory mechanisms.

METHODS

PubMed and Web of Science were searched for English-language articles related to MSC recruitment and migration for AC repair until June 2019. The presence of various MSCs in or around joints, the potential approaches to diseased AC` and the regenerative capacities of MSCs were reviewed.

RESULTS

Various intra- and peri-articular MSCs, with inherent migratory potentials, are present in multiple stem cell niches in or around joints. The recruitment and migration of joint-resident MSCs play crucial roles in endogenous AC repair. Multiple recruiting signals, such as chemokines, growth factors, etc., emerge during the development of AC diseases and participate in the regulation of MSC mobilization. Motivated MSCs could migrate into cartilage lesions and then exert multiple reparative potentials, including extracellular matrix (ECM) reconstruction and microenvironment modulation.

CONCLUSION

In general, AC repair based on endogenous MSC recruitment and migration is a feasible strategy, and a promising research field. Furthermore, endogenous AC repair mediated by native MSCs would provide new opportunities to efficient preventative or therapeutic options for AC diseases.

Age-dependent differences in response to partial-thickness cartilage defects in a rat model as a measure to evaluate the efficacy of interventions for cartilage repair

The objectives of this study are (1) to examine age-dependent longitudinal differences in histological responses after creation of partial-thickness articular cartilage defects (PTCDs) in rats and to use this model (2) to objectively evaluate the effectiveness of interventions for cartilage repair. Linear PTCDs were created at a depth of 100 μm in the weight-bearing region of the medial femoral condyle in rats of different ages (3 weeks, 6 weeks, 10 weeks and 14 weeks). One day, one week, two weeks, four weeks and twelve weeks after PTCD generation, spontaneous healing was evaluated histologically and immunohistochemically. Effects of interventions comprising mesenchymal stem cells (MSCs) or platelet-rich plasma (PRP) or both on 14-week-old PTCD rats were evaluated and compared with natural courses in rats of other ages. Younger rats exhibited better cartilage repair. Cartilage in 3-week-old and 6-week-old rats exhibited nearly normal restoration after 4-12 weeks. Cartilage in 14-week-old rats deteriorated over time and early signs of cartilage degeneration were observed. With injection of MCSs alone or MSCs + PRP, 14-week-old PTCD rats showed almost the same reparative cartilage as 6-week-old rats. With injection of PRP, 14-week-old PTCD rats showed almost the same reparative cartilage as 10-week-old rats. This model will be of great use to objectively compare the effects of interventions for small cartilage lesions and may help to advance the development of disease-modifying osteoarthritis drugs.

Mesenchymal Stem/Progenitor Cells Derived from Articular Cartilage, Synovial Membrane and Synovial Fluid for Cartilage Regeneration: Current Status and Future Perspectives

Large articular cartilage defects remain an immense challenge in the field of regenerative medicine because of their poor intrinsic repair capacity. Currently, the available medical interventions can relieve clinical symptoms to some extent, but fail to repair the cartilaginous injuries with authentic hyaline cartilage. There has been a surge of interest in developing cell-based therapies, focused particularly on the use of mesenchymal stem/progenitor cells with or without scaffolds. Mesenchymal stem/progenitor cells are promising graft cells for tissue regeneration, but the most suitable source of cells for cartilage repair remains controversial. The tissue origin of mesenchymal stem/progenitor cells notably influences the biological properties and therapeutic potential. It is well known that mesenchymal stem/progenitor cells derived from synovial joint tissues exhibit superior chondrogenic ability compared with those derived from non-joint tissues; thus, these cell populations are considered ideal sources for cartilage regeneration. In addition to the progress in research and promising preclinical results, many important research questions must be answered before widespread success in cartilage regeneration is achieved. This review outlines the biology of stem/progenitor cells derived from the articular cartilage, the synovial membrane, and the synovial fluid, including their tissue distribution, function and biological characteristics. Furthermore, preclinical and clinical trials focusing on their applications for cartilage regeneration are summarized, and future research perspectives are discussed.

Fibronectin Enhances Cartilage Repair by Activating Progenitor Cells Through Integrin α5β1 Receptor

This study aimed to determine the effect of fibronectin (FN) on cartilage regeneration through the activation of chondrogenic progenitor cells (CPCs). Cells were isolated from the knee cartilage of mice and cultured in the presence of various concentrations of FN. Proliferation, migration, and chondrogenic differentiation assays were performed in vitro. In some experiments, CPCs were preincubated with anti-integrin α5β1 antibody for 60 min before FN treatment to block the integrin α5β1 receptor. Soluble FN was mixed with Pluronic F-127 and injected into the joint cavity in an early-stage osteoarthritis model. Cartilage repair was evaluated histologically, biochemically, and biomechanically. In vitro, we observed that the isolated CPCs, which exhibited stem cell-relevant markers, proliferated most at a concentration of 20 μg/mL FN (p < 0.05). In addition, FN enhanced the proliferation, migration, and chondrogenic differentiation capacity of CPCs, and the enhancement was significantly decreased by blockade of the integrin α5β1 receptor (p < 0.05). In vivo, FN also significantly promoted cartilage repair along with increased CPC activation and integrin α5β1 expression (p < 0.05). These findings suggest that FN enhances CPC proliferation, migration, and chondrogenic differentiation through the integrin α5β1-dependent signaling pathway. Based on these results, a novel and promising therapy focused on targeted activation of CPCs by FN could be developed for the treatment of cartilage injuries in a clinical setting.

Osteoprotegerin deficiency leads to deformation of the articular cartilage in femoral head

Osteoarthritis (OA) was a degenerative joint disease characterized by articular cartilage degradation and extensive remodeling of the subchondral bone. Multiple lines of evidence indicated that Osteoprotegerin (OPG), a member of TNF receptor superfamily that was expressed in the chondrocytes of articular cartilage and adjacent locations in the physiological setting, was involved in maintaining integrity of articular cartilage. OPG could prevent subchondral bone from resorption, and also protect cartilage from degradation. In this study, we used Osteoprotegerin-knockout mice (Opg-KO mice) to find out the role of OPG in articular cartilage. We examined articular cartilage in the femoral head of Opg-KO mice began in early adulthood using modern molecular and imaging methods. We found cartilage changes starting from adulthood and progressively with age, reminiscent of pathological changes in OA. Deficiency of OPG caused thinned articular cartilage and extensive remodeling of the subchondral bone in femoral head in comparison with wild-type mice (WT mice). Also, the articular cartilage of femoral head expressed significantly less of Aggrecan, Col-II and Col-X, but more Col-I and Matrix Metalloproteinases-13 (Mmp-13) than WT mice both at gene and protein level. Moreover, increased chondrocyte apoptosis and decreased chondrocyte proliferation were observed in femoral head of Opg-KO mice compared to WT mice. These data suggested that OPG played an important role in maintaining the homeostasis of articular cartilage of femoral head.