Upregulation of matrix synthesis in chondrocyte-seeded agarose following sustained bi-axial cyclic loading

Mechanical overloading promotes chondrocyte senescence and osteoarthritis development through downregulating FBXW7

OBJECTIVES

To investigate the role of mechanical stress in cartilage ageing and identify the mechanistic association during osteoarthritis (OA) progression.

METHODS

F-box and WD repeat domain containing 7 (FBXW7) ubiquitin ligase expression and chondrocyte senescence were examined in vitro, in experimental OA mice and in human OA cartilage. Mice with Fbxw7 knockout in chondrocytes were generated and adenovirus-expressing Fbxw7 (AAV-Fbxw7) was injected intra-articularly in mice. Destabilised medial meniscus surgery was performed to induce OA. Cartilage damage was measured using the Osteoarthritis Research Society International score and the changes in chondrocyte senescence were determined. mRNA sequencing was performed in articular cartilage from Fbxw7 knockout and control mice.

RESULTS

Mechanical overloading accelerated senescence in cultured chondrocytes and in mice articular cartilage. FBXW7 was downregulated by mechanical overloading in primary chondrocytes and mice cartilage, and decreased in the cartilage of patients with OA, aged mice and OA mice. FBXW7 deletion in chondrocytes induced chondrocyte senescence and accelerated cartilage catabolism in mice, as manifested by an upregulation of p16INK4A, p21 and Colx and downregulation of Col2a1 and ACAN, which resulted in the exacerbation of OA. By contrast, intra-articular injection of adenovirus expressing Fbxw7 alleviated OA in mice. Mechanistically, mechanical overloading decreased Fbxw7 mRNA transcription and FBXW7-mediated MKK7 degradation, which consequently stimulated JNK signalling. In particular, inhibition of JNK activity by DTP3, a MKK7 inhibitor, ameliorated chondrocyte senescence and cartilage degeneration CONCLUSIONS: FBXW7 is a key factor in the association between mechanical overloading and chondrocyte senescence and cartilage ageing in the pathology of OA.

A Novel In Vitro and In Silico System for Analyzing Complex Mechanobiological Behavior of Chondrocytes in Three-Dimensional Hydrogel Constructs

Physiological loading is essential for the maintenance of articular cartilage through the regulation of tissue remodeling. To correctly understand the behavior of chondrocytes in their native environment, cell stimulating devices and bioreactors have been developed to examine the effect of mechanical stimuli on chondrocytes. This study describes the design and validation of a novel system for analyzing chondrocyte deformation patterns. This involves an in vitro mechanical device for a controlled application of multi-axial-loading regimes to chondrocyte-seeded agarose constructs and in silico models for analyzing chondrocyte deformation patterns. The computer-controlled device precisely applies compressive, tensile, and shear strains to hydrogel constructs using a customizable macro-based program. The synchronization of the displacements is shown to be accurate with a 1.2% error and is highly reproducible. The device design allows housing for up to eight novel designed free-swelling three-dimensional hydrogel constructs. Constructs include mesh ends and are optimized to withstand the application of up to 7% mechanical tensile and 15% shear strains. Constructs were characterized through mapping the strain within as mechanical load was applied and was validated using light microscopy methods, chondrocyte viability using live/dead imaging, and cell deformation strains. Images were then analyzed to determine the complex deformation strain patterns of chondrocytes under a range of dynamic mechanical stimulations. This is one of the first systems that have characterized construct strains to cellular strains. The features in this device make the system ideally suited for a systematic approach for the investigation of the response of chondrocytes to a complex physiologically relevant deformation profile.

Mechanical compression controls the biosynthesis of human osteoarthritic chondrocytes in vitro

BACKGROUND

Cartilage damage, which can potentially lead to osteoarthritis, is a leading cause of morbidity in the elderly population. Chondrocytes are sensitive to mechanical stimuli and their matrix-protein synthesis may be altered when chondrocytes experience a variety of in vivo loadings. Therefore, a study was conducted to evaluate the biosynthesis of isolated osteoarthritic chondrocytes which subjected to compression with varying dynamic compressive strains and loading durations.

METHODS

The proximal tibia was resected as a single osteochondral unit during total knee replacement from patients (N = 10). The osteoarthritic chondrocytes were isolated from the osteochondral units, and characterized using reverse transcriptase-polymerase chain reaction. The isolated osteoarthritic chondrocytes were cultured and embedded in agarose, and then subjected to 10% and 20% uniaxial dynamic compression up to 8-days using a bioreactor. The morphological features and changes in the osteoarthritic chondrocytes upon compression were evaluated using scanning electron microscopy. Safranin O was used to detect the presence of cartilage matrix proteoglycan expression while quantitative analysis was conducted by measuring type VI collagen using an immunohistochemistry and fluorescence intensity assay.

FINDINGS

Gene expression analysis indicated that the isolated osteoarthritic chondrocytes expressed chondrocyte-specific markers, including BGN, CD90 and HSPG-2. Moreover, the compressed osteoarthritic chondrocytes showed a more intense and broader deposition of proteoglycan and type VI collagen than control. The expression of type VI collagen was directly proportional to the duration of compression in which 8-days compression was significantly higher than 4-days compression. The 20% compression showed significantly higher intensity compared to 10% compression in 4- and 8-days.

INTERPRETATION

The biosynthetic activity of human chondrocytes from osteoarthritic joints can be enhanced using selected compression regimes.

Short-term Response of Serum Cartilage Oligomeric Matrix Protein to Different Types of Impact Loading Under Normal and Artificial Gravity

Microgravity during long-term space flights induces degeneration of articular cartilage. Artificial gravity through centrifugation combined with exercise has been suggested as a potential countermeasure for musculoskeletal degeneration. The purpose of this study was to investigate the effect of different types of impact loading under normal and artificial gravity conditions on serum concentrations of cartilage oligomeric matrix protein (COMP), a biomarker of cartilage metabolism. Fifteen healthy male adults (26 ± 4 years, 181 ± 4 cm, 77 ± 6 kg) performed four different 30-min impact loading protocols on four experimental days: jumping with artificial gravity elicited by centrifugation in a short-arm centrifuge (AGJ), jumping with artificial gravity generated by low-pressure cylinders in a sledge jump system (SJS), vertical jumping under Earth gravity (EGJ), and running under Earth gravity (RUN). Five blood samples per protocol were taken: 30 min before, immediately before, immediately after, 30 min after, and 60 min after impact loading. Serum COMP concentrations were analyzed in these samples. During the impact exercises, ground reaction forces were recorded. Peak ground reaction forces were significantly different between the three jumping protocols (p < 0.001), increasing from AGJ (14 N/kg) to SJS (22 N/kg) to EGJ (29 N/kg) but were similar in RUN (22 N/kg) compared to SJS. The serum COMP concentration was increased (p < 0.001) immediately after all loading protocols, and then decreased (p < 0.001) at 30 min post-exercise compared to immediately after the exercise. Jumping and running under Earth gravity (EGJ and RUN) resulted in a significantly higher (p < 0.05) increase of serum COMP levels 30 min after impact loading compared to the impact loading under artificial gravity (RUN +30%, EGJ +20%, AGJ +17%, and SJS +13% compared to baseline). In conclusion, both the amplitude and the number of the impacts contribute to inducing higher COMP responses and are therefore likely important factors affecting cartilage metabolism. RUN had the largest effect on serum COMP concentration, presumably due to the high number of impacts, which was 10 times higher than for the jump modalities. Future studies should aim at establishing a dose-response relationship for different types of exercise using comparable amounts of impacts.

Cell-derived matrices (CDM)-Methods, challenges and applications

Extracellular matrix (ECM) provides both physical support and bioactive signals such as growth factors and cytokines to cells at their microenvironment or niche. Engineering the matrix niche becomes an important approach to study or manipulate cellular fate. This work presents an overview on the reconstitution of the ECM niche through a wide range of approaches ranging from coating culture dish with ECM molecules to decellularization of native tissues. In particular, we focused on reconstituting the complex ECM niche through cell-derived matrix (CDM) by reviewing the methodological approaches used in our group to derive ECM from mature cells such as chondrocytes and nucleus pulposus cells (NPCs), undifferentiated stem cells such as mesenchymal stem cells (MSCs), as well as MSCs undergoing chondrogenic and osteogenic differentiation, in 2D or 3D models. Specific attention has also been given to key factors that should be considered in various applications and challenges in relation to the CDM. Last but not the least, a few future perspectives and their significance have been proposed.

Effects of hydrostatic pressure and deviatoric stress on human articular chondrocytes for designing neo-cartilage construct

Autologous chondrocyte implantation is a promising therapy for the treatment of the articular cartilage defects. Recently, we have developed a three-dimensional chondrocyte construct manufactured with a collagen gel/sponge scaffold and cyclic hydrostatic pressure. However, the roles of various mechanical stresses, specifically hydrostatic pressure and deviatoric stress, as well as poststress loading, were unclear on metabolic function in chondrocytes. We hypothesized that hydrostatic pressure and deviatoric stresses each alter individual metabolic characteristics of chondrocytes. We embedded human articular chondrocytes within an agarose hydrogel and applied hydrostatic pressure and/or deviatoric stress individually or simultaneously for 4 days. Subsequently, we kept the cell constructs without stress for an additional 3 days. With hydrostatic pressure and/or deviatoric stress, more cells proliferated significantly than no stress (p < .05) and more cells proliferated near the inner side of the construct than the outer (p < .05). Cartilage specific aggrecan core protein and collagen type II were upregulated significantly after off-loading hydrostatic pressure alone at Day 7 (p < .05). On the other hand, these molecules were upregulated significantly immediately after deviatoric stress alone and combined with hydrostatic pressure at Day 4 (p < .05). Tissue inhibitor of metalloproteinase-2 was upregulated significantly after off-loading hydrostatic pressure alone and combined deviatoric stress at Day 7 (p < .05). Metalloproteinnase-13 was upregulated significantly with deviatoric stress at Day 4 (p < .05) and combined with hydrostatic pressure at Day 4. These results suggest that metabolic functions are regulated by the combination of hydrostatic pressure and deviatoric stress and by the timing of stress loading.

In vitro models for the study of osteoarthritis

Osteoarthritis (OA) is a prevalent disease of most mammalian species and is a significant cause of welfare and economic morbidity in affected individuals and populations. In vitro models of osteoarthritis are vital to advance research into the causes of the disease, and the subsequent design and testing of potential therapeutics. However, a plethora of in vitro models have been used by researchers but with no consensus on the most appropriate model. Models attempt to mimic factors and conditions which initiate OA, or dissect the pathways active in the disease. Underlying uncertainty as to the cause of OA and the different attributes of isolated cells and tissues used mean that similar models may produce differing results and can differ from the naturally occurring disease. This review article assesses a selection of the in vitro models currently used in OA research, and considers the merits of each. Particular focus is placed on the more prevalent cytokine stimulation and load-based models. A brief review of the mechanism of these models is given, with their relevance to the naturally occurring disease. Most in vitro models have used supraphysiological loads or cytokine concentrations (compared with the natural disease) in order to impart a timely response from the cells or tissue assessed. Whilst models inducing OA-like pathology with a single stimulus can answer important biological questions about the behaviour of cells and tissues, the development of combinatorial models encompassing different physiological and molecular aspects of the disease should more accurately reflect the pathogenesis of the naturally occurring disease.