Chondroadherin (CHAD), a class IV small leucine rich proteoglycan/protein (SLRP), was hypothesized to play important roles in regulating chondrocyte signaling and cartilage homeostasis. However, its roles in cartilage development and function are not well understood, and no major osteoarthritis-like phenotype was found in the murine model with CHAD genetically deleted (CHAD(-/-)). In this study, we used atomic force microscopy (AFM)-based nanoindentation to quantify the effects of CHAD deletion on changes in the biomechanical function of murine cartilage. In comparison to wild-type (WT) mice, CHAD-deletion resulted in a significant ≈70-80% reduction in the indentation modulus, Eind, of the superficial zone knee cartilage of 11 weeks, 4 months and 1 year old animals. This mechanical phenotype correlates well with observed increases in the heterogeneity collagen fibril diameters in the surface zone. The results suggest that CHAD mainly plays a major role in regulating the formation of the collagen fibrillar network during the early skeletal development. In contrast, CHAD-deletion had no appreciable effects on the indentation mechanics of middle/deep zone cartilage, likely due to the dominating role of aggrecan in the middle/deep zone. The presence of significant rate dependence of the indentation stiffness in both WT and CHAD(-/-) knee cartilage suggested the importance of both fluid flow induced poroelasticity and intrinsic viscoelasticity in murine cartilage biomechanical properties. Furthermore, the marked differences in the nanomechanical behavior of WT versus CHAD(-/-) cartilage contrasted sharply with the relative absence of overt differences in histological appearance. These observations highlight the sensitivity of nanomechanical tools in evaluating structural and mechanical phenotypes in transgenic mice.

An early detection of Osteoarthritis is urgently needed and still not possible until today. The aim of the study was to assess whether molecular biomarkers of cartilage turnover are associated with longitudinal change in knee cartilage thickness during a 2 year period in individuals with increased risk of developing knee osteoarthritis. A secondary aim was to assess whether prior knee injury or subjective patient-reported outcomes at baseline (BL) were associated with articular cartilage changes. Nineteen volleyball players (mean age 46.5 ± 4.9 years, 47% male) with a 30-year history of regular high impact training were recruited. The serum biomarkers Cpropeptide of type II procollagen (CPII), cartilage oligomeric matrix protein (COMP), collagenase generated carboxy-terminal neoepitope of type II collagen (sC2C), cartilage intermediate layer protein 2 (CILP-2), and the urine biomarkers C-telopeptide of type II collagen (CTX-II) and collagenase-generated peptide(s) of type II collagen (C2C-HUSA) were assessed at BL and at 2 year follow up (FU). Femorotibial cartilage thinning, thickening and absolute thickness change between BL and FU was evaluated from magnetic resonance imaging. Subjective clinical status at BL was evaluated by the International Knee Documentation Committee Subjective Knee Form and the Short-Form 36 Physical Component Score.

Osteoarthritis (OA) is a progressive, chronic disease characterized by articular cartilage destruction. The pro-inflammatory cytokine IL-17 levels have been reported elevated in serum and synovial fluid of OA patients and correlated with increased cartilage defects and bone remodeling. The aim of this study was to characterize an IL-17-mediated articular cartilage degradation ex-vivo model and to investigate IL-17 effect on cartilage extracellular matrix protein turnover.

Proteomics is an emerging field in the study of joint disease. Our two aims with this pilot analysis were to compare healthy human knee articular cartilage with meniscus, two tissues both known to become affected in the osteoarthritic disease process, and to compare two mass spectrometry (MS)-based methods: data-dependent acquisition (DDA) and data-independent acquisition (DIA).

Most in vitro studies of potential osteoarthritis (OA) therapies have used cartilage monocultures, even though synovium is a key player in mediating joint inflammation and, thereby, cartilage degeneration. In the case of interleukin-1 (IL-1) inhibition using its receptor antagonist (IL-1Ra), like chondrocytes, synoviocytes also express IL-1 receptors that influence intra-articular IL-1 signaling and IL-1Ra efficacy. The short residence time of IL-1Ra after intra-articular injection requires the application of frequent dosing, which is clinically impractical and comes with increased risk of infection; these limitations motivate the development of effective drug delivery strategies that can maintain sustained intra-articular IL-1Ra concentrations with only a single injection. The goals of this study were to assess how the presence of synovium in IL-1-challenged cartilage-synovium co-culture impacts the time-dependent biological response of single and sustained doses of IL-1Ra, and to understand the mechanisms underlying any co-culture effects.

Unlike highly regenerative animals, such as axolotls, humans are believed to be unable to counteract cumulative damage, such as repetitive joint use and injury that lead to the breakdown of cartilage and the development of osteoarthritis. Turnover of insoluble collagen has been suggested to be very limited in human adult cartilage. The goal of this study was to explore protein turnover in articular cartilage from human lower limb joints. Analyzing molecular clocks in the form of nonenzymatically deamidated proteins, we unmasked a position-dependent gradient (distal high, proximal low) of protein turnover, indicative of a gradient of tissue anabolism reflecting innate tissue repair capacity in human lower limb cartilages that is associated with expression of limb-regenerative microRNAs. This association shows a potential link to a capacity, albeit limited, for regeneration that might be exploited to enhance joint repair and establish a basis for human limb regeneration.

Osteoarthritis (OA) is the most common joint disease, where articular cartilage degradation is often accompanied with sclerosis of the subchondral bone. However, the association between OA and tissue mineralization at the nanostructural level is currently not understood. In particular, it is technically challenging to study calcified cartilage, where relevant but poorly understood pathological processes such as tidemark multiplication and advancement occur. Here, we used state-of-the-art microfocus small-angle X-ray scattering with a 5-μm spatial resolution to determine the size and organization of the mineral crystals at the nanostructural level in human subchondral bone and calcified cartilage. Specimens with a wide spectrum of OA severities were acquired from both medial and lateral compartments of medial compartment knee OA patients (n = 15) and cadaver knees (n = 10). Opposing the common notion, we found that calcified cartilage has thicker and more mutually aligned mineral crystals than adjoining bone. In addition, we, for the first time, identified a well-defined layer of calcified cartilage associated with pathological tidemark multiplication, containing 0.32 nm thicker crystals compared to the rest of calcified cartilage. Finally, we found 0.2 nm thicker mineral crystals in both tissues of the lateral compartment in OA compared with healthy knees, indicating a loading-related disease process because the lateral compartment is typically less loaded in medial compartment knee OA. In summary, we report novel changes in mineral crystal thickness during OA. Our data suggest that unloading in the knee might be involved with the growth of mineral crystals, which is especially evident in the calcified cartilage. © 2022 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

In this exploratory study, we used discovery proteomics to follow the release of proteins from bovine knee articular cartilage in response to mechanical injury and cytokine treatment. We also studied the effect of the glucocorticoid Dexamethasone (Dex) on these responses.

Articular cartilage is a dense extracellular matrix-rich tissue that degrades following chronic mechanical stress, resulting in osteoarthritis (OA). The tissue has low intrinsic repair especially in aged and osteoarthritic joints. Here, we describe three pro-regenerative factors; fibroblast growth factor 2 (FGF2), connective tissue growth factor, bound to transforming growth factor-beta (CTGF-TGFβ), and hepatoma-derived growth factor (HDGF), that are rapidly released from the pericellular matrix (PCM) of articular cartilage upon mechanical injury. All three growth factors bound heparan sulfate, and were displaced by exogenous NaCl. We hypothesised that sodium, sequestered within the aggrecan-rich matrix, was freed by injurious compression, thereby enhancing the bioavailability of pericellular growth factors. Indeed, growth factor release was abrogated when cartilage aggrecan was depleted by IL-1 treatment, and in severely damaged human osteoarthritic cartilage. A flux in free matrix sodium upon mechanical compression of cartilage was visualised by 23Na -MRI just below the articular surface. This corresponded to a region of reduced tissue stiffness, measured by scanning acoustic microscopy and second harmonic generation microscopy, and where Smad2/3 was phosphorylated upon cyclic compression. Our results describe a novel intrinsic repair mechanism, controlled by matrix stiffness and mediated by the free sodium concentration, in which heparan sulfate-bound growth factors are released from cartilage upon injurious load. They identify aggrecan as a depot for sequestered sodium, explaining why osteoarthritic tissue loses its ability to repair. Treatments that restore matrix sodium to allow appropriate release of growth factors upon load are predicted to enable intrinsic cartilage repair in OA.

The cartilage aggrecan proteoglycan is crucial for both skeletal growth and articular cartilage function. A number of aggrecan (ACAN) gene variants have been linked to skeletal disorders, ranging from short stature to severe chondrodyplasias. Osteochondritis dissecans is a disorder where articular cartilage and subchondral bone fragments come loose from the articular surface. We previously reported a missense ACAN variant linked to familial osteochondritis dissecans, with short stature and early onset osteoarthritis, and now describe three novel ACAN gene variants from additional families with this disorder. Like the previously described variant, these are autosomal dominant missense variants, resulting in single amino acid residue substitutions in the C-type lectin repeat of the aggrecan G3 domain. Functional studies showed that neither recombinant variant proteins, nor full-length variant aggrecan proteoglycan from heterozygous patient cartilage, were secreted to the same level as wild-type aggrecan. The variant proteins also showed decreased binding to known cartilage extracellular matrix ligands. Mapping these and other ACAN variants linked to hereditary skeletal disorders showed a clustering of osteochondritis dissecans-linked variants to the G3 domain. Taken together, this supports a link between missense ACAN variants affecting the aggrecan G3 domain and hereditary osteochondritis dissecans.

Chondroadherin, a leucine rich repeat extracellular matrix protein with functions in cell to matrix interactions, binds cells via their α2β1 integrin as well as via cell surface proteoglycans, providing for different sets of signals to the cell. Additionally, the protein acts as an anchor to the matrix by binding tightly to collagens type I and II as well as type VI. We generated mice with inactivated chondroadherin gene to provide integrated studies of the role of the protein. The null mice presented distinct phenotypes with affected cartilage as well as bone. At 3-6 weeks of age the epiphyseal growth plate was widened most pronounced in the proliferative zone. The proteome of the femoral head articular cartilage at 4 months of age showed some distinct differences, with increased deposition of cartilage intermediate layer protein 1 and fibronectin in the chondroadherin deficient mice, more pronounced in the female. Other proteins show decreased levels in the deficient mice, particularly pronounced for matrilin-1, thrombospondin-1 and notably the members of the α1-antitrypsin family of proteinase inhibitors as well as for a member of the bone morphogenetic protein growth factor family. Thus, cartilage homeostasis is distinctly altered. The bone phenotype was expressed in several ways. The number of bone sialoprotein mRNA expressing cells in the proximal tibial metaphysic was decreased and the osteoid surface was increased possibly indicating a change in mineral metabolism. Micro-CT revealed lower cortical thickness and increased structure model index, i.e. the amount of plates and rods composing the bone trabeculas. The structural changes were paralleled by loss of function, where the null mice showed lower femoral neck failure load and tibial strength during mechanical testing at 4 months of age. The skeletal phenotype points at a role for chondroadherin in both bone and cartilage homeostasis, however, without leading to altered longitudinal growth.

Psoriatic arthritis (PsA) is a chronic musculoskeletal inflammatory disease found in up to 30% of psoriasis patients. Prolargin-an extracellular matrix (ECM) protein present in cartilage and tendon-has been previously shown elevated in serum of patients with psoriasis. ECM protein fragments can reflect tissue turnover and pathological changes; thus, this study aimed to develop, validate and characterize a novel biomarker PROM targeting a matrix metalloproteinase (MMP)-cleaved prolargin neo-epitope, and to evaluate it as a biomarker for PsA. A competitive ELISA was developed with a monoclonal mouse antibody; dilution- and spiking-recovery, inter- and intra-variation, and accuracy were evaluated. Serum levels were evaluated in 55 healthy individuals and 111 patients diagnosed with PsA by the CASPAR criteria. Results indicated that the PROM assay was specific for the neo-epitope. Inter- and intra- assay variations were 11% and 4%, respectively. PROM was elevated (p = 0.0003) in patients with PsA (median: 0.24, IQR: 0.19-0.31) compared to healthy controls (0.18; 0.14-0.23) at baseline. AUROC for separation of healthy controls from PsA patients was 0.674 (95% CI 0.597-0.744, P < 0.001). In conclusion, MMP-cleaved prolargin can be quantified in serum by the PROM assay and has the potential to separate patients with PsA from healthy controls.