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Osteoarthritis (OA) is a degenerative joint disease characterized by progressive cartilage degradation but also synovial membrane inflammation, osteophyte formation and subchondral ...bone sclerosis. Medical care is mainly based on alleviating pain symptoms, but to date, no effective drug can stop the disease progression. Cartilage is a tissue composed of only one cell type, chondrocytes, wrapped in a collagen rich extracellular matrix they synthesize. Chondrocytes can adopt different phenotypes in vivo and in vitro, defined by the collagen type they produce. Isolated from their matrix, chondrocytes present the particularity to dedifferentiate, producing fibroblastic type I and III collagens. With OA onset, chondrocytes undergo multiple changes, in terms of proliferation, viability, but also secretory profile. The acquisition of a hypertrophic phenotype (producing aberrant type X collagen and catabolic MMP-13 protease) by chondrocytes is well documented and contributes to OA development. However, it is increasingly believed that chondrocytes rather acquire a variety of degenerated phenotypes at the onset of OA, including a “dedifferentiated-like” phenotype that might also contribute to OA progression. In this review, we will (i) present molecular knowledge underlying dedifferentiation process, (ii) emphasize connections between dedifferentiation and OA and (iii) consider OA therapeutic strategies aiming at the maintenance of chondrogenic phenotype.
ROS/oxidative stress signaling in osteoarthritis Lepetsos, Panagiotis; Papavassiliou, Athanasios G.
Biochimica et biophysica acta,
April 2016, 2016-04-00, Volume:
1862, Issue:
4
Journal Article
Peer reviewed
Open access
Osteoarthritis is the most common joint disorder with increasing prevalence due to aging of the population. Its multi-factorial etiology includes oxidative stress and the overproduction of reactive ...oxygen species, which regulate intracellular signaling processes, chondrocyte senescence and apoptosis, extracellular matrix synthesis and degradation along with synovial inflammation and dysfunction of the subchondral bone. As disease-modifying drugs for osteoarthritis are rare, targeting the complex oxidative stress signaling pathways would offer a valuable perspective for exploration of potential therapeutic strategies in the treatment of this devastating disease.
•Osteoarthritis (OA) is a whole-joint degenerative multifactorial disease.•OA pathogenesis is influenced by oxidative stress, aging, hormones, and lifestyle habits.•Disease-modifying regimens are yet not available for OA.•Understanding OA pathobiology should lead to the discovery of more effective treatments.•Unraveling deregulated signaling cascades in OA will aid the development of novel therapies.
Fractures heal predominantly through the process of endochondral ossification. The classic model of endochondral ossification holds that chondrocytes mature to hypertrophy, undergo apoptosis and new ...bone forms by invading osteoprogenitors. However, recent data demonstrate that chondrocytes transdifferentiate to osteoblasts in the growth plate and during regeneration, yet the mechanism(s) regulating this process remain unknown. Here, we show a spatially-dependent phenotypic overlap between hypertrophic chondrocytes and osteoblasts at the chondro-osseous border in the fracture callus, in a region we define as the transition zone (TZ). Hypertrophic chondrocytes in the TZ activate expression of the pluripotency factors Sox2, Oct4 (Pou5f1), Nanog, and conditional knock-out of Sox2 during fracture healing results in reduction of the fracture callus and a delay in conversion of cartilage to bone. The signal(s) triggering expression of the pluripotency genes are unknown, but we demonstrate that endothelial cell conditioned medium upregulates these genes in ex vivo fracture cultures, supporting histological evidence that transdifferentiation occurs adjacent to the vasculature. Elucidating the cellular and molecular mechanisms underlying fracture repair is important for understanding why some fractures fail to heal and for developing novel therapeutic interventions.
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Clinical success on cartilage regeneration could be achieved by using available biomaterials and cell-based approaches. In this study, we have developed a composite gel based on ...collagen/hyaluronic acid (Coll-HA) as ideal, physiologically representative 3D support for in vitro chondrogenesis of human adipose-derived mesenchymal stem cells (hAMSCs) co-cultured with human articular chondrocytes (hAC). The incorporation of hyaluronic acid (HA) attempted to provide an additional stimulus to the hAMSCs for chondrogenesis and extracellular matrix deposition. Coll-HA gels were fabricated by directly mixing different amounts of HA (0–5%) into collagen solution before gelation. hACs and hAMSCs were co-cultured at different ratios from 100% to 0% in steps of 25%. Thus, five different co-culture groups were tested in the various Coll-HA 3D matrices. HA greatly impacted the cell viability and proliferation as well as the mechanical properties of the Coll-HA gel. The effective Young’s modulus changed from 5.8 to 9.0kPa with increasing concentrations of HA in the gel. In addition, significantly higher amounts of glycosaminoglycan (GAG) were detected that seemed to be dependent on HA content. The highest HA concentration used (5%) resulted in the lowest Collagen type X (Col10) expression for most of the cell culture groups. Unexpectedly, culturing in these gels was also associated with decreased SOX9 and Collagen type II (Col2) expression, while Collagen type III (Col3) and metalloproteinase 13 notably increased. By using 1% HA, a positive effect on SOX9 expression was observed in the co-culture groups. In addition, a significant increase in GAGs production was also detected. Regarding co-culturing, the group with 25% hAMSCs+75% hACs was the most chondrogenic one considering SOX9 and Col2 expression as well as GAGs production. This group showed negligible Col10 expression after 35days of culture independently of the gel used. It also featured the highest effective Young’s modulus (9.9kPa) when cultivated in the 1% HA matrix. Concerning the level of dissolved oxygen in situ, the groups with a higher amount of hAMSCs showed lower oxygen levels (40–58% O2) compared to hACs (63–74% O2). This might be attributed to the higher cellular metabolism and proliferation rate of the hAMSCs. Interestingly, lower oxygen was detected in the HA-containing gels when compared to plain collagen. This may contribute to the better chondrogenesis observed in these groups. Altogether, our results indicated that HA may favor chondrogenesis, but its effect highly depends on the concentration used. Additionally, co-culture of hACs with hAMSCs also favors chondrogenesis and especially increases extracellular matrix production and decreases hypertrophy.
In the clinical situation, large cartilage defects can be treated with MACT. However, this is a two-stage procedure, which increases the risk for the patient. Moreover, culturing chondrocytes leads to dedifferentiation. The matrix used for MACT is a collagen-based scaffold. In this study, it was demonstrated that hyaluronic acid, a natural component of the extracellular matrix, supplementation to a collagen hydrogel stimulates chondrogenic differentiation in a dose dependent manner. 1% HA showed the best overall results. Furthermore, exchanging 25% of human articular chondrocytes with adipose-derived mesenchymal stem cells didn’t change the chondrogenic potential, but reduced going in unwanted pathways and improved biomechanical properties. This could translate to a one-step procedure and shows the potential of inducing differentiation by natural biomaterials.
Background: Donor-site morbidity, limited numbers of cells, loss of phenotype during ex vivo expansion, and age-related decline in chondrogenic activity present critical obstacles to the use of ...autologous chondrocyte implantation for cartilage repair. Chondrocytes from juvenile cadaveric donors may represent an alternative to autologous cells.
Hypothesis/Purpose: The authors hypothesized that juvenile chondrocyte would show stronger and more stable chondrogenic activity than adult cells in vitro and that juvenile cells pose little risk of immunologic incompatibility in adult hosts.
Study Design: Controlled laboratory study.
Methods: Cartilage samples were from juvenile (<13 years old) and adult (>13 years old) donors. The chondrogenic activity of freshly isolated human articular chondrocytes and of expanded cells after monolayer culture was measured by proteoglycan assay, gene expression analysis, and histology. Lymphocyte proliferation assays were used to assess immunogenic activity.
Results: Proteoglycan content in neocartilage produced by juvenile chondrocytes was 100-fold higher than in neocartilage produced by adult cells. Collagen type II and type IX mRNA in fresh juvenile chondrocytes were 100- and 700-fold higher, respectively, than in adult chondrocytes. The distributions of collagens II and IX were similar in native juvenile cartilage and in neocartilage made by juvenile cells. Juvenile cells grew significantly faster in monolayer cultures than adult cells (P = .002) and proteoglycan levels produced in agarose culture was significantly higher in juvenile cells than in adult cells after multiple passages (P < .001). Juvenile chondrocytes did not stimulate lymphocyte proliferation.
Conclusion: These results document a dramatic age-related decline in human chondrocyte chondrogenic potential and show that allogeneic juvenile chondrocytes do not stimulate an immunologic response in vivo.
Clinical Relevance: Juvenile human chondrocytes have greater potential to restore articular cartilage than adult cells, and may be transplanted without the fear of rejection, suggesting a new allogeneic approach to restoring articular cartilage in older individuals.
According to current dogma, chondrocytes and osteoblasts are considered independent lineages derived from a common osteochondroprogenitor. In endochondral bone formation, chondrocytes undergo a ...series of differentiation steps to form the growth plate, and it generally is accepted that death is the ultimate fate of terminally differentiated hypertrophic chondrocytes (HCs). Osteoblasts, accompanying vascular invasion, lay down endochondral bone to replace cartilage. However, whether an HC can become an osteoblast and contribute to the full osteogenic lineage has been the subject of a century-long debate. Here we use a cell-specific tamoxifen-inducible genetic recombination approach to track the fate of murine HCs and show that they can survive the cartilage-to-bone transition and become osteogenic cells in fetal and postnatal endochondral bones and persist into adulthood. This discovery of a chondrocyte-to-osteoblast lineage continuum revises concepts of the ontogeny of osteoblasts, with implications for the control of bone homeostasis and the interpretation of the underlying pathological bases of bone disorders.
Osteoarthritis (OA) is a chronic degenerative disease that affects the whole joint, especially the knee joint. Its main features include articular cartilage defects and osteophyte formation, and it ...is common in middle-aged and elderly people. Although the pathogenesis of OA is not fully understood, mechanical factors, inflammation and immune abnormalities can affect joint tissue metabolism and destroy cartilage and bone homeostasis. Cartilage calcification is closely related to chondrocyte hypertrophy, differentiation and bone sclerosis in OA, which is manifested as pathological calcification of cartilage matrix. Chondrocytes in OA may change from a state of maintaining cartilage matrix balance to a state of promoting cartilage destruction and calcification. Inflammatory factors such as TNF-α and IL-1β promote this phenotypic shift, accelerating matrix degradation and calcium salt deposition. The change of calcium signal and an important factor of angiogenesis and promote cartilage calcification. Chondrocyte hypertrophy plays a crucial role in the pathogenesis and progression of OA, characterized by complex interactions with cartilage calcification, subchondral bone sclerosis, as well as chondrocyte proliferation, apoptosis, matrix remodeling, and signaling cascades. The degree of chondrocyte hypertrophy exhibits a positive correlation with the severity of OA. Furthermore, structural changes in the articular cartilage are associated with factors including reduced cartilage collagen synthesis or the activation by degradative enzymes. Regulatory mechanisms governing chondrocyte hypertrophy and cartilage calcification, alongside the identification of pertinent genes, represent pivotal areas for future investigation. This research will further elucidate the pathogenesis of OA and lay the groundwork for devising therapeutic strategies.
The story of hyaluronan in articular cartilage, pericellular hyaluronan in particular, essentially is also the story of aggrecan. Without properly tethered aggrecan, the load bearing function of ...cartilage is compromised. The anchorage of aggrecan to the cell surface only occurs due to the binding of aggrecan to hyaluronan—with hyaluronan tethered either to a hyaluronan synthase or by multivalent binding to CD44. In this review, details of hyaluronan synthesis are discussed including how HAS2 production of hyaluronan is necessary for normal chondrocyte development and matrix assembly, how an abundance or deficit of pericellular hyaluronan alters chondrocyte metabolism, and whether hyaluronan size matters or changes with aging or disease. The biomechanical role and matrix assembly function of hyaluronan in addition to the functions of hyaluronidases are discussed. The turnover of hyaluronan is considered including mechanisms by which its turnover, at least in part, is mediated by endocytosis by chondrocytes and regulated by aggrecan degradation. Differences between turnover and clearance of newly synthesized hyaluronan and aggrecan versus the half-life of hyaluronan remaining within the inter-territorial matrix of cartilage are discussed. The release of neutral pH-acting hyaluronidase activity remains one unanswered question concerning the loss of cartilage hyaluronan in osteoarthritis. Signaling events driven by changes in hyaluronan-chondrocyte interactions may involve a chaperone function of CD44 with other receptors/cofactors as well as the changes in hyaluronan production functioning as a metabolic rheostat.
•Hyaluronan is synthesized in cartilage by hyaluronan synthase-2 (HAS2).•Hyaluronan and aggrecan contribute to cell-cell spacing in cartilage.•Hyaluronan functions to anchor aggrecan to the surface of chondrocytes.•Hyaluronan turnover involves chondrocyte-mediated endocytosis.•Turnover of hyaluronan may differ in the pericellular and inter-territorial matrices and during disease or steady state.
Synovitis, a common clinical symptom for osteoarthritis (OA) patients, is highly related to OA pathological progression and pain manifestation. The activated synovial macrophages have been ...demonstrated to play an important role in synovitis, but the mechanisms about macrophage activation are still not clear. In this study, we found that the exosome-like vesicles from osteoarthritic chondrocytes could be a new biological factor to stimulate inflammasome activation and increase mature IL-1β production in macrophages. The degraded cartilage explants produced more exosome-like vesicles than the nondegraded ones, while the exosome-like vesicles from chondrocytes could enter into joint synovium tissue and macrophages. Moreover, the exosome-like vesicles from osteoarthritic chondrocytes enhanced the production of mature IL-1β in macrophages. These vesicles could inhibit ATG4B expression via miR-449a-5p, leading to inhibition of autophagy in LPS-primed macrophages. The decreased autophagy promoted the production of mitoROS, which further enhanced the inflammasome activation and subsequent IL-1β processing. Ultimately, the increase of mature IL-1β may aggravate synovial inflammation and promote the progression of OA disease. Our study provides a new perspective to understand the activation of synovial macrophages and synovitis in OA patients, which may be beneficial for therapeutic intervention in synovitis-related OA patients.
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