Chondrocyte clusters adjacent to sites of cartilage degeneration have characteristics of progenitor cells

Histological analysis of nucleus pulposus tissue from patients with lumbar disc herniation after condoliase administration

Background

Condoliase is an enzyme used as a treatment for lumbar disc herniation (LDH). This enzyme degrades chondroitin sulfate (CS) in the nucleus pulposus of the intervertebral disc (IVD). However, there are cases in which symptoms do not improve, despite condoliase administration. This study reports histological analysis of lumbar disc tissue of LDH patients who underwent surgery because condoliase had no therapeutic effect.

Methods

Between March 2019 and August 2019, 12 LDH patients who underwent full endoscopic spine surgery (FESS) discectomy at the Dezawa Akira PED Clinic were the subjects of the study. There are two study groups: six cases underwent FESS after condoliase administration, while six underwent FESS without condoliase administration. The average duration from drug administration to surgery was 152 days. Herniated disc removed at surgery was evaluated by histological staining including immunohistochemistry by anti-CS antibodies.

Results

Multiple large clusters (40-120 μm in diameter) were observed in the nucleus pulposus of those who received condoliase, but no clusters were observed in those who did not. The lumbar disc tissues, including the nucleus pulposus of recipients, were stained with anti-CS antibodies that recognize the CS unsaturated disaccharide, but non-administration tissue was not stained. These findings suggest that the enzyme acted on the nucleus pulposus, even in cases where symptoms were not improved by condoliase administration. Furthermore, there was no histological difference between stained images of the extracellular matrix in those who did or did not receive condoliase, suggesting that condoliase acted specifically on CS in the nucleus pulposus.

Conclusions

We demonstrated that CS in the nucleus pulposus was degraded in patients in whom condoliase did not have a therapeutic effect. Moreover, condoliase acts in human IVD without causing necrosis of chondrocytes and surrounding tissues.

Effect of cells on spatial quantification of proteoglycans in articular cartilage of small animals

OBJECTIVE

Histochemical characterization of proteoglycan content in articular cartilage is important for the understanding of osteoarthritis pathogenesis. However, cartilage cells may interfere with the measurement of matrix proteoglycan content in small animal models (e.g. mice and rats) due to the high cell volume fraction (38%) in mice compared to human tissue (~1%). We investigated whether excluding the cells from image analysis affects the histochemically measured proteoglycan content of rat knee joint cartilage and assessed the effectiveness of a deep learning algorithm-based tool named U-Net in cell segmentation.

DESIGN

Histological sections were stained with Safranin-O, after which optical densities were measured using digital densitometry to estimate proteoglycan content. U-Net was trained with 600 annotated Safranin-O cartilage images for exclusion of cells from the cartilage extracellular matrix. Optical densities of the ECM with and without cells were compared as a function of normalized tissue depth.

RESULTS

U-Net cell segmentation was accurate, with the measured cell area fraction following largely that of ground-truth images (average difference: 4.3%). Cell area fraction varied as a function of tissue depth and took up 8-21% of the tissue area. The exclusion of cells from the analysis led to an increase in the analyzed depth-dependent optical density of cartilage by approximately 0.6-1.8% (p < 0.01).

CONCLUSIONS

Although the effect of cells on the analyzed proteoglycan content is small, it should be considered for improved sensitivity, especially at the onset of the disease during which cells may proliferate in small animals.

The catabolic-to-anabolic shift seen in the canine osteoarthritic cartilage treated with knee joint distraction occurs after the distraction period

Background

Methods

Results

Conclusion

The Translational Potential of this Article

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.

Knee Cartilage and Subchondral Bone Evaluations by Magnetic Resonance Imaging Correlate with Histological Biomarkers in an Osteoarthritis Rabbit Model

OBJECTIVE

To evaluate pathological changes in cartilage and subchondral bone MRI biomarkers in a rabbit model of osteoarthritis (OA) and correlate these with histological variations.

DESIGN

Transection of the anterior cruciate ligament was performed on the right knee of eighteen 12-week-old New Zealand white rabbits to induce OA. 3-Tesla MR images were obtained from 18 healthy control knees (left) and 18 knees with OA (right). Imaging biomarkers included volume, thickness, T1 and T2* cartilage parametric maps, and several subchondral bone features: bone volume to total volume ratio, trabecular thickness, trabecular spacing, trabecular number (TbN), 2D and 3D fractal dimensions, and quality of trabecular score (QTS). Microscopic analysis of the lateral femoral condyles was set as the ground truth.

RESULTS

When healthy and osteoarthritic knees were compared, significant differences were seen in the T1 and T2* values of the femur and tibia cartilage and in the subchondral bone volume to total volume, TbN, and QTS of both the lateral and medial aspects of the femur and tibia. Histological findings revealed significant osteoarthritic changes between healthy and osteoarthritic knees in stain, structure, chondrocyte density, total score, and subchondral bone biomarker levels. A positive correlation was found between histological staining, structure, chondrocyte density, and total score variables in T1 and T2* cartilage biomarkers. A negative correlation was observed between histological subchondral bone variables and magnetic resonance D2D and QTS biomarkers.

CONCLUSION

Quantification of several cartilage and subchondral bone imaging biomarkers in a rabbit model of OA allows the detection of significant changes, which are correlated with histological findings.

Synovial fluid from end-stage osteoarthritis induces proliferation and fibrosis of articular chondrocytes via MAPK and RhoGTPase signaling

OBJECTIVES

Alterations in the composition of synovial fluid have been associated with adverse effects on cartilage integrity and function. Here, we examined the phenotypic and proliferative behavior of human articular chondrocytes when cultured in vitro for 13 days with synovial fluid derived from end-stage osteoarthritis patients.

MATERIALS AND METHODS

Chondrocyte proliferation and phenotypical changes induced by osteoarthritic synovial fluid were analyzed using DNA staining, RT-qPCR, immunostainings, and immunoblotting. The molecular mechanisms by which osteoarthritic synovial fluid induced fibrosis and proliferation were studied using a phospho-protein antibody array and luciferase-based transcription factor activity assays. Specific pathway inhibitors were used to probe the involvement of pathways in fibrosis and proliferation.

RESULTS

Prolonged stimulation with osteoarthritic synovial fluid sustained chondrocyte proliferation and induced profound phenotypic changes, favoring a fibrotic over a chondrogenic or hypertrophic phenotype. A clear loss of chondrogenic markers at both the transcriptional and protein level was observed, while expression of several fibrosis-associated markers were upregulated over time. Phospho-kinase analysis revealed activation of MAPK and RhoGTPase signaling pathways by osteoarthritic synovial fluid, which was confirmed by elevated transcriptional activity of Elk-1 and SRF. Inhibitor studies revealed that ERK played a central role in the loss of chondrocyte phenotype, while EGFR and downstream mediators p38, JNK and Rac/Cdc42 were essential for fibrosis-associated collagen expression. Finally, we identified EGF signaling as a key activator of chondrocyte proliferation.

CONCLUSIONS

Osteoarthritic synovial fluid promoted chondrocyte fibrosis and proliferation through EGF receptor activation and downstream MAPK and RhoGTPase signaling.

EGFR Signaling Is Required for Maintaining Adult Cartilage Homeostasis and Attenuating Osteoarthritis Progression

The uppermost superficial zone of articular cartilage is the first line of defense against the initiation of osteoarthritis (OA). We previously used Col2-Cre to demonstrate that epidermal growth factor receptor (EGFR), a tyrosine kinase receptor, plays an essential role in maintaining superficial chondrocytes during articular cartilage development. Here, we showed that EGFR activity in the articular cartilage decreased as mice age. In mouse and human OA samples, EGFR activity was initially reduced at the superficial layer and then resurged in cell clusters within the middle and deep zone in late OA. To investigate the role of EGFR signaling in postnatal and adult cartilage, we constructed an inducible mouse model with cartilage-specific EGFR inactivation (Aggrecan-CreER Egfr^Wa5/flox , Egfr iCKO). EdU incorporation revealed that postnatal Egfr iCKO mice contained fewer slow-cycling cells than controls. EGFR deficiency induced at 3 months of age reduced cartilage thickness and diminished superficial chondrocytes, in parallel to alterations in lubricin production, cell proliferation, and survival. Furthermore, male Egfr iCKO mice developed much more severe OA phenotypes, including cartilage erosion, subchondral bone plate thickening, cartilage degeneration at the lateral site, and mechanical allodynia, after receiving destabilization of the medial meniscus (DMM) surgery. Similar OA phenotypes were also observed in female iCKO mice. Moreover, tamoxifen injections of iCKO mice at 1 month post-surgery accelerated OA development 2 months later. In summary, our data demonstrated that chondrogenic EGFR signaling maintains postnatal slow-cycling cells and plays a critical role in adult cartilage homeostasis and OA progression. © 2022 American Society for Bone and Mineral Research (ASBMR).

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).

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.

Peripheral shift in the viable chondrocyte population of the medial femoral condyle after anterior cruciate ligament injury in the porcine knee

Anterior cruciate ligament injuries result in posttraumatic osteoarthritis in the medial compartment of the knee, even after surgical treatment. How the chondrocyte distribution within the articular cartilage changes early in this process is currently unknown. The study objective was to investigate the chondrocyte distribution within the medial femoral condyle after an anterior cruciate ligament transection in a preclinical model. Forty-two adolescent Yucatan minipigs were allocated to receive unilateral anterior cruciate ligament surgery (n = 36) or no surgery (n = 6). Central coronal sections of the medial femoral condyle were obtained at 1- and 4 weeks after surgery, and the chondrocyte distribution was measured via whole slide imaging and a cell counting batch processing tool utilized in ImageJ. Ki-67 immunohistochemistry was performed to identify proliferating cells. Empty lacunae, karyolysis, karyorrhexis, and pyknosis were used to identify areas of irreversible cell injury. The mean area of irreversible cell injury was 0% in the intact controls, 13.4% (95% confidence interval: 6.4, 20.3) at 1-week post-injury and 19.3% (9.7, 28.9) at 4 weeks post-injury (p < .015). These areas occurred closest to the femoral intra-articular notch. The remaining areas containing viable chondrocytes had Ki-67-positive cells (p < .02) and increased cell density in the middle (p < .03) and deep zones (p = .001). For the entire section, the total chondrocyte number did not change significantly post-operatively; however, the density of cells in the peripheral regions of the medial femoral condyle increased significantly at 1- and 4 weeks post-injury relative to the intact control groups (p = .032 and .004, respectively). These data demonstrate a peripheral shift in the viable chondrocyte population of the medial femoral condyle after anterior cruciate ligament injury and further suggest that chondrocytes with the capacity to proliferate are not confined to one particular cartilage layer.

Lycium barbarum polysaccharides in ageing and its potential use for prevention and treatment of osteoarthritis: a systematic review

BACKGROUND

Lycium barbarum polysaccharide (LBP), the most abundant functional component of wolfberry, is considered a potent antioxidant and an anti-ageing substance. This review aims to outline the hallmarks of ageing in the pathogenesis of osteoarthritis (OA), followed by the current understanding of the senolytic effect of LBP and its potential use in the prevention and treatment of OA. This will be discussed through the lens of molecular biology and herbal medicine.

METHODS

A literature search was performed from inception to March 2020 using following keywords: "Lycium barbarum polysaccharide", "DNA damage", antioxidant, anti-apoptosis, anti-inflammation, anti-ageing, osteoarthritis, chondrocytes, fibroblasts, osteoblasts, osteoclasts, and "bone mesenchymal stem cell". The initial search yielded 2287 papers, from which 35 studies were selected for final analysis after screening for topic relevancy by the authors.

RESULTS

In literature different in vitro and in vivo ageing models are used to demonstrate LBP's ability to reduce oxidative stress, restore mitochondrial function, mitigate DNA damage, and prevent cellular senescence. All the evidence hints that LBP theoretically attenuates senescent cell accumulation and suppresses the senescence-associated secretory phenotype as observed by the reduction in pro-inflammatory cytokines, like interleukin-1beta, and matrix-degrading enzymes, such as MMP-1 and MMP-13. However, there remains a lack of evidence on the disease-modifying effect of LBP in OA, although its chondroprotective, osteoprotective and anti-inflammatory effects were reported.

CONCLUSION

Our findings strongly support further investigations into the senolytic effect of LBP in the context of age-related OA.

Statistical image analysis and escort histograms in characterization of articular cartilage repair in a skeleton animal model

Statistical image analysis of an ensemble of digital images of histological samples is performed as an auxiliary investigation a result of the recently proposed method of articular cartilage repair utilizing growth plate chondrocytes in a skeleton animal model. A fixed–shift model of maximal likelihood estimates of image histograms applied for monochromatic (grayscale) images or their RGB components confirms the statistically significant effect of the previously proposed medical treatment. The type of staining used to prepare images of histological samples is related to the visibility of the effectiveness of medical treatment. Hellinger distance of escort distributions for maximal likelihood estimates of image histograms of medically treated and control samples is investigated to identify grayscale (or RGB) intensities responsible for statistically significant difference of the estimates. A difference of Shannon entropy quantifying informational content of the histograms allows one to identify staining and image colors which are most suitable to visualize cluster formation typical for articular cartilage repair processes.

Determination of correlation of proximal sesamoid bone osteoarthritis with high-speed furlong exercise and catastrophic sesamoid bone fracture in Thoroughbred racehorses

OBJECTIVE

To examine whether proximal sesamoid bone (PSB) articular cartilage and bone osteoarthritic changes or palmar osteochondral disease (POD) scores were associated with exercise history and catastrophic PSB fracture in Thoroughbred racehorses.

SAMPLES

PSBs from 16 Thoroughbred racehorses (8 with and 8 without PSB fracture).

PROCEDURES

Exercise history was collected, and total career high-speed furlongs was used as the measure of total exercise per horse. At necropsy, medial and lateral condyles of the third metacarpus from each forelimb were assigned a POD score, followed by imaging with micro-CT for evaluation of osteophyte size. Three investigators that were blinded to the type of PSB (fracture or no fracture) used the Osteoarthritis Research Society International (OARSI) scoring system to evaluate acellularity, chondrocyte necrosis, cartilage fibrillation, chondrone formation, safranin O stain uptake, and tidemark advancement of 1 central sagittal tissue section/PSB (4 PSBs/horse). Cartilage thickness and bone necrosis were scored on the basis of histologic examination.

RESULTS

POD score, osteophyte size score, percentage of bone necrosis, tidemark advancement, chondrone formation, and total OARSI score were greater in horses with more accrued total career high-speed furlongs. Scores for POD, osteophyte size, fibrillation, acellularity, chondrone formation, and total OARSI were greater for horses with PSB fracture.

CONCLUSIONS AND CLINICAL REVELANCE

OARSI scoring revealed that more advanced osteoarthritic changes strongly correlated with total career high-speed furlongs and PSB fracture. However, the effect of exercise was dominant, suggesting that exercise history will be important to include in future models that aim to assess risk factors for catastrophic PSB fracture.

Magnesium in joint health and osteoarthritis

Osteoarthritis (OA) is a prevalent debilitating age-related skeletal disease. The hallmark of OA is the degradation of articular cartilage that cushions the joint during movement. It is characterized by chronic pain and disability. Magnesium, a critical trace element in the human body, plays a pivotal role in metabolism homeostasis and the energy balance. Humans obtain magnesium mainly from the diet. However, inadequate magnesium intake is not uncommon. Moreover, the magnesium status deteriorates with ageing. There has been a growing body of clinical studies pointing to an intimate relationship between dietary magnesium and OA although the conclusion remains controversial. As reported, the magnesium ion concentration is essential to determine cell fate. Firstly, the low-concentration magnesium ions induced human fibroblasts senescence. Magnesium supplementation was also able to mitigate chondrocyte apoptosis, and to facilitate chondrocyte proliferation and differentiation. In this literature review, we will outline the existing evidence in animals and humans. We will also discuss the controversies on plasma or intracellular level of magnesium as the indicator of magnesium status. In addition, we put forward the interplay between dietary magnesium intake and intestinal microbiome to modulate the inflammatory milieu in the conjecture of OA pathogenesis. This leads to an emerging hypothesis that the synergistic effect of magnesium and probiotics may open a new avenue for the prevention and treatment of OA.

p66shc siRNA Nanoparticles Ameliorate Chondrocytic Mitochondrial Dysfunction in Osteoarthritis

Background

Osteoarthritis (OA) is the most common type of joint disease associated with cartilage breakdown. However, the role played by mitochondrial dysfunction in OA remains inadequately understood. Therefore, we investigated the role played by p66shc during oxidative damage and mitochondrial dysfunction in OA and the effects of p66shc downregulation on OA progression.

Methods

Monosodium iodoacetate (MIA), which is commonly used to generate OA animal models, inhibits glycolysis and biosynthetic processes in chondrocytes, eventually causing cell death. To observe the effects of MIA and poly(lactic-co-glycolic acid) (PLGA)-based nanoparticles, histological analysis, immunohistochemistry, micro-CT, mechanical paw withdrawal thresholds, quantitative PCR, and measurement of oxygen consumption rate and extracellular acidification rate were conducted.

Results

p-p66shc was highly expressed in cartilage from OA patients and rats with MIA-induced OA. MIA caused mitochondrial dysfunction and reactive oxygen species (ROS) production, and the inhibition of p66shc phosphorylation attenuated MIA-induced ROS production in human chondrocytes. Inhibition of p66shc by PLGA-based nanoparticles-delivered siRNA ameliorated pain behavior, cartilage damage, and inflammatory cytokine production in the knee joints of MIA-induced OA rats.

Conclusion

p66shc is involved in cartilage degeneration in OA. By delivering p66shc-siRNA-loaded nanoparticles into the knee joints with OA, mitochondrial dysfunction-induced cartilage damage can be significantly decreased. Thus, p66shc siRNA PLGA nanoparticles may be a promising option for the treatment of OA.

Pathomechanisms of Posttraumatic Osteoarthritis: Chondrocyte Behavior and Fate in a Precarious Environment

Traumatic injuries of the knee joint result in a wide variety of pathomechanisms, which contribute to the development of so-called posttraumatic osteoarthritis (PTOA). These pathogenetic processes include oxidative stress, excessive expression of catabolic enzymes, release of damage-associated molecular patterns (DAMPs), and synovial inflammation. The present review focuses on the underlying pathomechanisms of PTOA and in particular the behavior and fate of the surviving chondrocytes, comprising chondrocyte metabolism, regulated cell death, and phenotypical changes comprising hypertrophy and senescence. Moreover, possible therapeutic strategies, such as chondroanabolic stimulation, anti-oxidative and anti-inflammatory treatment, as well as novel therapeutic targets are discussed.

p47phox siRNA-Loaded PLGA Nanoparticles Suppress ROS/Oxidative Stress-Induced Chondrocyte Damage in Osteoarthritis

Osteoarthritis (OA) is the most common joint disorder that has had an increasing prevalence due to the aging of the population. Recent studies have concluded that OA progression is related to oxidative stress and reactive oxygen species (ROS). ROS are produced at low levels in articular chondrocytes, mainly by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and ROS production and oxidative stress have been found to be elevated in patients with OA. The cartilage of OA-affected rat exhibits a significant induction of p47phox, a cytosolic subunit of the NADPH oxidase, similarly to human osteoarthritis cartilage. Therefore, this study tested whether siRNA p47phox that is introduced with poly (D,L-lactic-co-glycolic acid) (PLGA) nanoparticles (p47phox si_NPs) can alleviate chondrocyte cell death by reducing ROS production. Here, we confirm that p47phox si_NPs significantly attenuated oxidative stress and decreased cartilage damage in mono-iodoacetate (MIA)-induced OA. In conclusion, these data suggest that p47phox si_NPs may be of therapeutic value in the treatment of osteoarthritis.

Histologic Analysis of 2 Alternative Donor Sites of the Ipsilateral Elbow in the Treatment of Capitellar Osteochondritis Dissecans

PURPOSE

To compare the histologic features of the cartilage from the capitellum with 2 proposed alternative donor sites from the ipsilateral elbow in the treatment of capitellar osteochondritis dissecans (OCD): the nonarticulating part of the radial head and the nonarticulating lateral side of the olecranon tip.

METHODS

Ten human cadaveric elbow specimens with macroscopically normal articular surfaces were used to obtain 5-mm osteochondral grafts: 10 from the capitellum (60° anteriorly relative to the humeral shaft), 10 from the radial head (nonarticulating part at 80°), and 4 from the olecranon (lateral side of the olecranon tip). Grafts were fixated in formalin (4% formaldehyde), decalcified, and processed into standard 8-μm-thick hematoxylin and eosin-and Toluidine Blue-stained sections. These were assessed for cartilage thickness, shape of articular surface, and 13 histologic parameters of the International Cartilage Repair Society II. Olecranon scores were excluded from statistical analysis.

RESULTS

Mean cartilage thickness was 1.5 ± 0.22 mm at the capitellum; 1.3 ± 0.34 mm at the radial head; and 1.9 ± 1.0 mm at the olecranon. There was no difference in cartilage thickness between the capitellum and radial head (P = .062). All grafts demonstrated a convex articular surface. International Cartilage Repair Society II scores ranged from 82 to 100 for the capitellum, from 81 to 100 for the radial head, and from 67 to 87 for the olecranon tip. There was less chondrocyte clustering at the capitellum (84 ± 14) than in the radial head (94 ± 3.2; P = .019). Mid/deep zone assessment of the capitellum scored higher (97 ± 6.7) than the radial head (91 ± 4.6; P = .038).

CONCLUSIONS

This study demonstrates appropriate histologic similarities between the cartilage from the capitellum and 2 alternative donor sites of the ipsilateral elbow in the treatment of capitellar OCD: the nonarticulating part of the radial head and the nonarticulating lateral side of the olecranon tip.

CLINICAL RELEVANCE

From an histologic point of view, there seem to be no obstacles to use grafts from these alternative donor sites for reconstruction of the capitellum when performing osteochondral autologous transplantation.

Ultrastructural morphology is distinct among primary progenitor cell isolates from normal, inflamed, and cryopreserved equine hoof tissue and CD105+K14+ progenitor cells

The equine hoof dermal-epidermal interface requires progenitor cells with distinct characteristics. This study was designed to provide accurate ultrastructural depictions of progenitor cells isolated from inflamed tissue and normal tissue before and after cryopreservation and following selection of cells expressing both keratin (K) 14 (ectodermal) and cluster of differentiation (CD) 105 (mesodermal). Passage 3 cell ultrastructure was assessed following 2D culture and after 3D culture on decellularized hoof tissue scaffolds. Outcome measures included light, transmission electron, and scanning electron microscopy, immunocytochemistry, and CD105⁺K14⁺ cell trilineage plasticity. Cells from normal tissue had typical progenitor cell characteristics. Those from inflamed tissue had organelles and morphology consistent with catabolic activities including lysosomes, irregular rough endoplasmic reticulum, and fewer vacuoles and early endosomes than those from normal tissue. Cryopreserved tissue cells appeared apoptotic with an irregular cell membrane covered by cytoplasmic protrusions closely associated with endocytic and exocytic vesicles, chromatin aggregated on the nuclear envelop, abundant, poorly organized rough endoplasmic reticulum, and plentiful lysosomes. Cells that were CD105⁺K14⁺ were distinguishable from heterogenous cells by infrequent microvilli on the cell surface, sparse endosomes and vesicles, and desmosomes between cells. Cells expressed ectodermal (K15) and mesodermal (CD105) proteins in 2D and 3D cultures. Inflamed and cryopreserved tissue isolates attached poorly to tissue scaffold while normal tissue cells attached well, but only CD105⁺K14⁺ cells produced extracellular matrix after 4 d. The CD105⁺K14⁺ cells exhibited osteoblastic, adipocytic, and neurocytic differentiation. Ultrastructural information provided by this study contributes to understanding of equine hoof progenitor cells to predict their potential contributions to tissue maintenance, healing, and damage as well post-implantation behavior.

The effect of serum types on Chondrogenic differentiation of adipose-derived stem cells

Background

Fetal bovine serum (FBS) is the most essential supplement in culture media for cellular proliferation, metabolism, and differentiation. However, due to a limited supply and subsequently rising prices, a series of studies have investigated a biological feasibility of replaceable serums to substitute FBS. Along with the increasing interests to manufacture stem cell-based cellular products, optimizing the composition of culture media including serums and exogenous growth factors (GFs) is of importance. In this experiment, the effect of bovine serum (BS) and newborn calf serum (NCS) on proliferation and chondrogenic differentiation capacity of human adipose derived stem cells (ADSCs) was evaluated, especially in the chondrogenically supplemented culture condition.

Methods

ADSCs were chondrogenically cultured with FBS, BS, and NCS for 14 days. For the acceleration of in vitro chondrogenesis, exogenous insulin-like growth factor and transforming growth factor-β3 were added. Viability and proliferation of ADSCs were evaluated using Live/Dead fluorescence staining and DNA amount, respectively. To investigate a chondrogenic differentiation, a series of assays were performed including a quantification of glycosaminoglycan deposition, alcian blue staining, and RT-PCR analysis for type II collagen, aggrecan and Sox-9 genes.

Results

The results demonstrated that proliferation of ADSCs was facilitated in FBS condition as compared with other serum types. For chondrogenic marker gene expression, serum substitutes enhanced Sox-9 expression level on day 14. The deposition of glycosaminoglycan was more facilitated in BS condition regardless of additional chondrogenic GFs.

Conclusion

It could be presumably speculated that serum types and exogenous supplements of GFs could also be important parameters to optimize culture media composition, especially in order to maintain the enhanced levels of both proliferation and chondrogenic differentiation of ADSCs during expansion.

Cartilage regeneration and ageing: Targeting cellular plasticity in osteoarthritis

Ageing processes play a major contributing role for the development of Osteoarthritis (OA). This prototypic degenerative condition of ageing is the most common form of arthritis and is accompanied by a general decline, chronic pain and mobility deficits. The disease is primarily characterized by articular cartilage degradation, followed by subchondral bone thickening, osteophyte formation, synovial inflammation and joint degeneration. In the early stages, osteoarthritic chondrocytes undergo phenotypic changes that increase cell proliferation and cluster formation and enhance the production of matrix-remodelling enzymes. In fact, chondrocytes exhibit differentiation plasticity and undergo phenotypic changes during the healing process. Current studies are focusing on unravelling whether OA is a consequence of an abnormal wound healing response. Recent investigations suggest that alterations in different proteins, such as TGF-ß/BMPs, NF-Kß, Wnt, and Cx43, or SASP factors involved in signalling pathways in wound healing response, could be directly implicated in the initiation of OA. Several findings suggest that osteoarthritic chondrocytes remain in an immature state expressing stemness-associated cell surface markers. In fact, the efficacy of new disease-modifying OA drugs that promote chondrogenic differentiation in animal models indicates that this may be a drug-sensible state. In this review, we highlight the current knowledge regarding cellular plasticity in chondrocytes and OA. A better comprehension of the mechanisms involved in these processes may enable us to understand the molecular pathways that promote abnormal repair and cartilage degradation in OA. This understanding would be advantageous in identifying novel targets and designing therapies to promote effective cartilage repair and successful joint ageing by preventing functional limitations and disability.

Characterization of cellular and matrix alterations in the early pathogenesis of osteochondritis dissecans in pigs using second harmonic generation and two-photon excitation fluorescence microscopy

Osteochondritis dissecans is a joint disease that is observed in several species. The disease can develop as a cause of ischemic chondronecrosis in the epiphyseal growth cartilage. Some lesions of chondronecrosis undergo spontaneous resolution, but it is not possible to predict whether a lesion will resolve or progress and require intervention. Proliferation of cells into clusters occurs at the lesion margin, but it is unclear if the clusters have a repair function. The aims of the current study were to examine clusters and potential matrix changes in response to ischemic chondronecrosis in the distal femur of 10 pigs aged 70-180 days using advanced microscopy based on two-photon excitation fluorescence and second harmonic generation. These microscopy techniques can perform 3D imaging of cells and collagen without staining. The results indicated a lower collagen density in the chondronecrotic areas compared to the normal growth cartilage, and fissures and breaks in the matrix integrity were demonstrated that potentially can propagate and cause osteochondritis dissecans. A higher number of cells in clusters was correlated with reduction in collagen density in the lesions. Some of the cells in the clusters had a morphology similar to progenitor cells, suggesting a potential repair role of the clusters. The study has shed further light on the secondary responses after initial lesion formation, which information can be of potential use to create models that can predict lesion progression and that may hence avoid unnecessary interventions in the future. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Chondrosarcoma: A Rare Misfortune in Aging Human Cartilage? The Role of Stem and Progenitor Cells in Proliferation, Malignant Degeneration and Therapeutic Resistance

Unlike other malignant bone tumors including osteosarcomas and Ewing sarcomas with a peak incidence in adolescents and young adults, conventional and dedifferentiated chondrosarcomas mainly affect people in the 4th to 7th decade of life. To date, the cell type of chondrosarcoma origin is not clearly defined. However, it seems that mesenchymal stem and progenitor cells (MSPC) in the bone marrow facing a pro-proliferative as well as predominantly chondrogenic differentiation milieu, as is implicated in early stage osteoarthritis (OA) at that age, are the source of chondrosarcoma genesis. But how can MSPC become malignant? Indeed, only one person in 1,000,000 will develop a chondrosarcoma, whereas the incidence of OA is a thousandfold higher. This means a rare coincidence of factors allowing escape from senescence and apoptosis together with induction of angiogenesis and migration is needed to generate a chondrosarcoma. At early stages, chondrosarcomas are still assumed to be an intermediate type of tumor which rarely metastasizes. Unfortunately, advanced stages show a pronounced resistance both against chemo- and radiation-therapy and frequently metastasize. In this review, we elucidate signaling pathways involved in the genesis and therapeutic resistance of chondrosarcomas with a focus on MSPC compared to signaling in articular cartilage (AC).

Histopathological assessment of primary osteoarthritic knees in large patient cohort reveal the possibility of several potential patterns of osteoarthritis initiation

OBJECTIVE

The two main objectives of the study include (1) Test the hypothesis that the lateral femoral condyle (LFC) in patients with primary OA and varus knees undergoing total knee arthroplasty (TKA) can be used as a model to better characterize varying histological features of human OA, (2) Correlate characteristic OA features using the established histopathological scoring systems (HHGS and OARSI) to understand potential histopathological patterns of OA initiation.

DESIGN

Two osteochondral specimens (4×4×8mm) were collected from fifty patient's LFC at the time of TKA (total 100 specimens), who presented preserved lateral knee compartment with joint space width>2mm. Three independent readers graded the sections on three different occasions using HHGS and OARSI systems. The correlation between individual parameters of the two scoring systems and their inter- and intra-reader variability, reliability and reproducibility were estimated.

RESULTS

All samples in this cohort showed abnormal histopathological features. Total histopathological scores of the LFC ranged from HHGS median=4.6 (range=0 to 11), and OARSI median=5.2 (range=0 to 19.5). The four individual sub-items of HHGS scoring system (structure, cells, safraninO staining, tidemark) were weakly correlated, with the correlation between structure and cellularity being the strongest (r=0.40). Both the scoring systems had similar repeatability and reproducibility coefficients of<21%.

CONCLUSIONS

OA changes in the LFC are not confined to any one region, and maybe seen in different regions of cartilage, tidemark, subchondral bone, and/or the marrow space vascularity. These variations may point to the possibility of several potential patterns of initiation in OA.

Progenitor Cells from Cartilage: Grade Specific Differences in Stem Cell Marker Expression

Recent research has confirmed the presence of Mesenchymal stem cell (MSC)-like progenitors (MPC) in both normal and osteoarthritic cartilage. However, there is only limited information concerning how MPC markers are expressed with osteoarthritis (OA) progression. The purpose of this study was to compare the prevalence of various MPC markers in different OA grades. Human osteoarthritic tibial plateaus were obtained from ten patients undergoing total knee replacement. Each sample had been classified into a mild or severe group according to OARSI scoring. Tissue was taken from each specimen and mRNA expression levels of CD105, CD166, Notch 1, Sox9, Acan and Col II A1 were measured at day 0 and day 14 (2 weeks in vitro). Furthermore, MSC markers: Nucleostemin, CD90, CD73, CD166, CD105 and Notch 1 were studied by immunofluorescence. mRNA levels of MSC markers did not differ between mild and severe OA at day 0. At day 14, protein analysis showed that proliferated cells from both sources expressed all 6 MSC markers. Only cells from the mild OA subjects resulted in a significant increase of mRNA CD105 and CD166 after in vitro expansion. Moreover, cells from the mild OA subjects showed significantly higher levels of CD105, Sox9 and Acan compared with those from severe OA specimens. Results confirmed the presence of MSC markers in mild and severe OA tissue at both mRNA and protein levels. We found significant differences between cells obtained from mild compared to severe OA specimens suggests that mild OA derived cells may have a greater MSC potential.

Modulation of chondrocyte motility by tetrahedral DNA nanostructures

OBJECTIVES

Contemporarily, a highly increasing attention was paid to nanoconstructs, particularly DNA nanostructures possessing precise organization, functional manipulation, biocompatibility and biodegradability. Amongst these DNA nanomaterials, tetrahedral DNA nanostructures (TDNs) are a significantly ideal bionanomaterials with focusing on the property that can be internalized into cytoplasm in the absence of transfection. Therefore, the focus of this study was on investigating the influence of TDNs on the chondrocytes locomotion.

MATERIALS AND METHODS

Tetrahedral DNA nanostructures was confirmed by 6% polyacrylamide gel electrophoresis (PAGE) and dynamic light scattering (DLS). Subsequently, the effect of TDNs on chondrocyte locomotion was investigated by real-time cell analysis (RTCA) and wound healing assay. The variation of relevant genes and proteins was detected by quantitative polymerase chain reaction (qPCR), western blotting and immunofluorescence respectively.

RESULTS

We demonstrated that tetrahedral DNA nanostructures have positive influence on chondrocytes locomotion and promoted the expression of RhoA, ROCK2 and vinculin. Additionally, upon exposure to TDNs with the concentration of 250 nmol L^-1 , the chondrocytes were showed the highest motility via both RTCA and wound healing assay. Meanwhile, the mRNA and protein expression of RhoA, ROCK2 and vinculin were also significantly enhanced with the same concentration.

CONCLUSIONS

It can be concluded that the TDNs with the optimal concentration of 250 nmol L^-1 could extremely promoted the chondrocytes locomotion through facilitating the expression of RhoA, ROCK2 and vinculin. These results seemed to reveal that this special three-dimensional DNA tetrahedral nanostructures may be applied to cartilage repair and treatment in the future.

Cartilaginous Metabolomic Study Reveals Potential Mechanisms of Osteophyte Formation in Osteoarthritis

Osteophyte is one of the inevitable consequences of progressive osteoarthritis with the main characteristics of cartilage degeneration and endochondral ossification. The pathogenesis of osteophyte formation is not fully understood to date. In this work, metabolomic approaches were employed to explore potential mechanisms of osteophyte formation by detecting metabolic variations between extracts of osteophyte cartilage tissues (n = 32) and uninvolved control cartilage tissues (n = 34), based on the platform of ultraperformance liquid chromatography tandem quadrupole time-of-flight mass spectrometry, as well as the use of multivariate statistic analysis and univariate statistic analysis. The osteophyte group was significantly separated from the control group by the orthogonal partial least-squares discriminant analysis models, indicating that metabolic state of osteophyte cartilage had been changed. In total, 28 metabolic variations further validated by mass spectrum (MS) match, tandom mass spectrum (MS/MS) match, and standards match mainly included amino acids, sulfonic acids, glycerophospholipids, and fatty acyls. These metabolites were related to some specific physiological or pathological processes (collagen dissolution, boundary layers destroyed, self-restoration triggered, etc.) which might be associated with the procedure of osteophyte formation. Pathway analysis showed phenylalanine metabolism (PI = 0.168, p = 0.004) was highly correlative to this degenerative process. Our findings provided a direction for targeted metabolomic study and an insight into further reveal the molecular mechanisms of ostophyte formation.

The effects of different doses of IGF-1 on cartilage and subchondral bone during the repair of full-thickness articular cartilage defects in rabbits

OBJECTIVE

To investigate the effects of different doses of insulin-like growth factor 1 (IGF-1) on the cartilage layer and subchondral bone (SB) during repair of full-thickness articular cartilage (AC) defects.

DESIGN

IGF-1-loaded collagen membrane was implanted into full-thickness AC defects in rabbits. The effects of two different doses of IGF-1 on cartilage layer and SB adjacent to the defect, the cartilage structure, formation and integration, and the new SB formation were evaluated at the 1st, 4th and 8th week postoperation. Meanwhile, after 1 week treatment, the relative mRNA expressions in tissues adjacent to the defect, including cartilage and SB were determined by quantitative real-time RT-PCR (qRT-PCR), respectively.

RESULTS

Different doses of IGF-1 induced different gene expression profiles in tissues adjacent to the defect and resulted in different repair outcomes. Particularly, at high dose IGF-1 aided cell survival, regulated the gene expressions in cartilage layer adjacent defect and altered ECM composition more effectively, improved the formation and integrity of neo-cartilage. While, at low dose IGF-1 regulated the gene expressions in SB more efficaciously and subsequently promoted the SB remodeling and reconstruction.

CONCLUSION

Different doses of IGF-1 induced different responses of cartilage or SB during the repair of full-thickness AC defects. Particularly, high dose of IGF-1 was more beneficial to the neo-cartilage formation and integration, while low dose of it was more effective for the SB formation.

Vitamin D attenuates inflammation, fatty infiltration, and cartilage loss in the knee of hyperlipidemic microswine

Background

Osteoarthritis (OA) of the knee joint is a degenerative process resulting in cartilage loss. Recent evidence suggests that OA is not merely a disease of cartilage but a disease of the entire knee joint and that inflammation may play an important role. OA has been associated with vitamin D deficiency. Vitamin D as an immunomodulator and anti-inflammatory agent may attenuate inflammation in the knee. The aim of this study was to assess the anti-inflammatory effect of vitamin D on inflammation in the knee.

Methods

This study was conducted with 13 microswine on a high cholesterol diet categorized into three groups of vitamin D-deficient, vitamin D-sufficient, and vitamin D supplementation. After 1 year, microswine were killed, and their knee joint tissues were harvested. Histological and immunofluorescence studies were carried out on the tissue specimens to evaluate the effect of vitamin D status.

Results

Histological and immunofluorescence studies of the knee joint tissues showed (1) increased inflammation in the knee joint tissues, (2) fatty infiltration in quadriceps muscle, patellar tendon, and collateral ligaments, and (3) chondrocyte clustering in the vitamin D-deficient and vitamin D-sufficient groups compared with the vitamin D supplementation group. Architectural distortion of the quadriceps muscle, patellar tendon, and collateral ligaments was also seen in the areas of inflammatory foci and fatty infiltration in the vitamin D-deficient group.

Conclusions

Decreased inflammation and fatty infiltration in the vitamin D supplementation group suggest the potential role of vitamin D in attenuating inflammation and fatty infiltration as well as in protecting the architecture of the tissue in the knee joint.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1099-6) contains supplementary material, which is available to authorized users.

Spaceflight-Relevant Challenges of Radiation and/or Reduced Weight Bearing Cause Arthritic Responses in Knee Articular Cartilage

There is little known about the effect of both reduced weight bearing and exposure to radiation during spaceflight on the mechanically-sensitive cartilage lining the knee joint. In this study, we characterized cartilage damage in rat knees after periods of reduced weight bearing with/without exposure to solar-flare-relevant radiation, then cartilage recovery after return to weight bearing. Male Sprague Dawley rats (n = 120) were either hindlimb unloaded (HLU) via tail suspension or remained weight bearing in cages (GROUND). On day 5, half of the HLU and GROUND rats were 1 Gy total-body X-ray irradiated during HLU, and half were sham irradiated (SHAM), yielding 4 groups: GROUND-SHAM; GROUND-IR; HLU-SHAM; and HLU-IR. Hindlimbs were collected from half of each group of rats on day 13. The remaining rats were then removed from HLU or remained weight bearing, and hindlimbs from these rats were collected on day 62. On day 13, glycosaminoglycan (GAG) content in cartilage lining the tibial plateau and femoral condyles of HLU rats was lower than that of the GROUND animals. Likewise, on day 13, immunoreactivity of the collagen type II-degrading matrix metalloproteinase-13 (MMP-13) and of a resultant metalloproteinase-generated neoepitope VDIPEN was increased in all groups versus GROUND-SHAM. Clustering of chondrocytes indicating cartilage damage was present in all HLU and IR groups versus GROUND-SHAM on day 13. On day 62, after 49 days of reloading, the loss of GAG content was attenuated in the HLU-SHAM and HLU-IR groups, and the increased VDIPEN staining in all treatment groups was attenuated. However, the increased chondrocyte clustering remained in all treatment groups on day 62. MMP-13 activity also remained elevated in the GROUND-IR and HLU-IR groups. Increased T2 relaxation times, measured on day 62 using 7T MRI, were greater in GROUND-IR and HLU-IR knees, indicating persistent cartilage damage in the irradiated groups. Both HLU and total-body irradiation resulted in acute degenerative and pre-arthritic changes in the knee articular cartilage of rats. A return to normal weight bearing resulted in some recovery from cartilage degradation. However, radiation delivered as both a single challenge and when combined with HLU resulted in chronic cartilage damage. These findings suggest that radiation exposure during spaceflight leads to and/or impairs recovery of cartilage upon return to reloading, generating long-term joint problems for astronauts.

Ablation of Perlecan Domain 1 Heparan Sulfate Reduces Progressive Cartilage Degradation, Synovitis, and Osteophyte Size in a Preclinical Model of Posttraumatic Osteoarthritis

OBJECTIVE

To investigate the role of the heparan sulfate (HS) proteoglycan perlecan (HSPG-2) in regulating fibroblast growth factor (FGF) activity, bone and joint growth, and the onset and progression of posttraumatic osteoarthritis (OA) in a mouse gene-knockout model.

METHODS

Maturational changes were evaluated histologically in the knees of 3-, 6-, and 12-week-old wild-type (WT) mice and Hspg2(Δ3-/Δ3-) mice (Hspg2 lacking domain 1 HS, generated by ablation of exon 3 of perlecan). Cartilage damage, subchondral bone sclerosis, osteophytosis, and synovial inflammation were scored at 4 and 8 weeks after surgical induction of OA in WT and Hspg2(Δ3-/Δ3-) mice. Changes in cartilage expression of FGF-2, FGF-18, HSPG-2, FGF receptor 1 (FGFR-1), and FGFR-3 were examined immunohistochemically. Femoral head cartilage from both mouse genotypes was cultured in the presence or absence of interleukin-1α (IL-1α), FGF-2, and FGF-18, and the content and release of glycosaminoglycan (GAG) and expression of messenger RNA (mRNA) for key matrix molecules, enzymes, and inhibitors were quantified.

RESULTS

No effect of perlecan HS ablation on growth plate or joint development was detected. After induction of OA, Hspg2(Δ3-/Δ3-) mice had significantly reduced cartilage erosion, osteophytosis, and synovitis. OA-induced loss of chondrocyte expression of FGF-2, FGF-18, and HSPG-2 occurred in both genotypes. Expression of FGFR-1 after OA induction was maintained in WT mice, while FGFR-3 loss after OA induction was significantly reduced in Hspg2(Δ3-/Δ3-) mice. There were no genotypic differences in GAG content or release between unstimulated control cartilage and IL-1α-stimulated cartilage. However, IL-1α-induced cartilage expression of Mmp3 mRNA was significantly reduced in Hspg2(Δ3-/Δ3-) mice. Cartilage GAG release in either the presence or absence of IL-1α was unaltered by FGF-2 in both genotypes. In cartilage cultures with FGF-18, IL-1α-stimulated GAG loss was significantly reduced only in Hspg2(Δ3-/Δ3-) mice, and this was associated with maintained expression of Fgfr3 mRNA and reduced expression of Mmp2/Mmp3 mRNA.

CONCLUSION

Perlecan HS has significant roles in directing the development of posttraumatic OA, potentially via the alteration of FGF/HS/FGFR signaling. These data suggest that the chondroprotection conferred by perlecan HS ablation could be attributed, at least in part, to the preservation of FGFR-3 and increased FGF signaling.

Ageing and the pathogenesis of osteoarthritis

Ageing-associated changes that affect articular tissues promote the development of osteoarthritis (OA). Although ageing and OA are closely linked, they are independent processes. Several potential mechanisms by which ageing contributes to OA have been elucidated. This Review focuses on the contributions of the following factors: age-related inflammation (also referred to as 'inflammaging'); cellular senescence (including the senescence-associated secretory phenotype (SASP)); mitochondrial dysfunction and oxidative stress; dysfunction in energy metabolism due to reduced activity of 5'-AMP-activated protein kinase (AMPK), which is associated with reduced autophagy; and alterations in cell signalling due to age-related changes in the extracellular matrix. These various processes contribute to the development of OA by promoting a proinflammatory, catabolic state accompanied by increased susceptibility to cell death that together lead to increased joint tissue destruction and defective repair of damaged matrix. The majority of studies to date have focused on articular cartilage, and it will be important to determine whether similar mechanisms occur in other joint tissues. Improved understanding of ageing-related mechanisms that promote OA could lead to the discovery of new targets for therapies that aim to slow or stop the progression of this chronic and disabling condition.

Effect of Laminin-A4 inhibition on cluster formation of human osteoarthritic chondrocytes

Formation of chondrocyte clusters is not only a morphological sign of osteoarthritis but it is also observed in cell culture. Active locomotion of chondrocytes is controlled by integrins in vitro. Integrins bind to Laminin-A4 (LAMA4), a protein that is highly expressed in vivo in clusters of hypertrophic chondrocytes. We tested if LAMA4 is relevant for cluster formation. Human chondrocytes were cultured in a 2D matrigel model and treated with different concentrations of a monoclonal inhibitory anti-LAMA4-antibody. Migration and cluster formation was analysed using live cell imaging technique. Full genome gene expression analysis was performed to assess the effect of LAMA4 inhibition. The data set were screened for genes relevant to cell motility. F-actin staining was performed to document cytoskeletal changes. Anti-LAMA4 treatment significantly reduced the rate of cluster formation in human chondrocytes. Cells changed their surface morphology and exhibited fewer protrusions. Expression of genes associated with cellular motility and migration was affected by anti-LAMA4 treatment. LAMA4-integrin signalling affects chondrocyte morphology and gene expression in vitro, thereby contributing to cluster formation in human osteoarthritic chondrocytes.

Aberrant expression of Twist1 in diseased articular cartilage and a potential role in the modulation of osteoarthritis severity

The bHLH transcription factor Twist1 has emerged as a negative regulator of chondrogenesis in skeletal progenitor cells and as an inhibitor of maturation in growth plate chondrocytes. However, its role in articular cartilage remains obscure. Here we examine Twist1 expression during re-differentiation of expanded human articular chondrocytes, the distribution of Twist1 proteins in normal versus OA human articular cartilage, and its role in modulating OA development in mice. High levels of Twist1 transcripts were detected by qPCR analyses of expanded de-differentiated human articular chondrocytes that had acquired mesenchymal-like features. The induction of hallmark cartilage genes by Bmp-2 mediated chondrogenic differentiation was paralleled by the dramatic suppression of Twist1 in vitro. In normal human articular cartilage, Twist1-expressing chondrocytes were most abundant in the superficial zone with little to no expression in the middle and deep zones. However, our analyses revealed a higher proportion of deep zone articular chondrocytes expressing Twist1 in human OA cartilage as compared to normal articular cartilage. Moreover, Twist1 expression was prominent within proliferative cell clusters near fissure sites in more severely affected OA samples. To assess the role of Twist1 in OA pathophysiology, we subjected wild type mice and transgenic mice with gain of Twist1 function in cartilage to surgical destabilization of the medial meniscus. At 12 weeks post-surgery, micro-CT and histological analyses revealed attenuation of the OA phenotype in Twist1 transgenic mice compared to wild type mice. Collectively, the data reveal a role for Twist in articular cartilage maintenance and the attenuation of cartilage degeneration.

Age-independent effects of hyaluronan amide derivative and growth hormone on human osteoarthritic chondrocytes

AIM

Increased age is the most prominent risk factor for the initiation and progression of osteoarthritis (OA). The effects of human growth hormone (hGH) combined or not with hyaluronan amide derivative (HAD) were evaluated on human OA chondrocytes, to define their biological action and potentiality in OA treatment.

MATERIAL AND METHODS

Cell viability, metabolic activity, gene expression and factors released were tested at different time points on chondrocytes treated with different concentrations of hGH (0.01-10 μg/ml) alone or in combination with HAD (1 mg/ml).

RESULTS

We found that OA chondrocytes express GH receptor and that the different doses of hGH tested did not affect cell viability, metabolic activity or the expression of collagen type 2, 1, or 10 nor did it induce the release of IGF-1 or FGF-2. Conversely, hGH treatment increased the expression of hyaluronan receptor CD44. HAD combined with hGH reduced metabolic activity, IL6 release and gene expression, but not the suppressor of cytokine signaling 2 (SOCS2), which was significantly induced and translocated into the nucleus. The parameters analyzed, independently of the treatments used proportionally decreased with increasing age of the patients.

CONCLUSIONS

hGH only induced CD44 receptor on OA chondrocytes but did not affect other parameters, such as chondrocytic gene markers or IGF-1 or FGF-2 release. HAD reduced all the effects induced by hGH partially through a significant induction of SOCS2. These data show that GH or HAD treatment does not influence the response of the OA chondrocytes, thus the modulation of cellular response is age-independent.