Effect of dermatan sulfate on the indentation and tensile properties of articular cartilage

Chondroitin and Dermatan Sulfate Bioinks for 3D Bioprinting and Cartilage Regeneration

Cartilage is a connective tissue which a limited capacity for healing and repairing. In this context, osteoarthritis disease may be developed with high prevalence in which the use of scaffolds may be a promising treatment. In addition, three-dimensional (3D) bioprinting has become an emerging additive manufacturing technology because of its rapid prototyping capacity and the possibility of creating complex structures. This study was focused on the development of nanocellulose-alginate (NC-Alg) based bioinks for 3D bioprinting for cartilage regeneration to which it was added chondroitin sulfate (CS) and dermatan sulfate (DS). First, rheological properties were evaluated. Then, sterilisation effect, biocompatibility and printability on developed NC-Alg-CS and NC-Alg-DS inks were evaluated. Subsequently, printed scaffolds were characterized. Finally, NC-Alg-CS and NC-Alg-DS inks were loaded with murine D1-MSCs-EPO and cell viability and functionality, as well as the chondrogenic differentiation ability were assessed. Results showed that the addition of both CS and DS to the NC-Alg ink improved its characteristics in terms of rheology and cell viability and functionality. Moreover, differentiation to cartilage was promoted on NC-Alg-CS and NC-Alg-DS scaffolds. Therefore, the utilization of MSCs containing NC-Alg-CS and NC-Alg-DS scaffolds may become a feasible tissue engineering approach for cartilage regeneration. This article is protected by copyright. All rights reserved.

Decorin Regulates the Aggrecan Network Integrity and Biomechanical Functions of Cartilage Extracellular Matrix

Joint biomechanical functions rely on the integrity of cartilage extracellular matrix. Understanding the molecular activities that govern cartilage matrix assembly is critical for developing effective cartilage regeneration strategies. This study elucidated the role of decorin, a small leucine-rich proteoglycan, in the structure and biomechanical functions of cartilage. In decorin-null cartilage, we discovered a substantial reduction of aggrecan content, the major proteoglycan of cartilage matrix, and mild changes in collagen fibril nanostructure. This loss of aggrecan resulted in significantly impaired biomechanical properties of cartilage, including decreased modulus, elevated hydraulic permeability, and reduced energy dissipation capabilities. At the cellular level, we found that decorin functions to increase the retention of aggrecan in the neo-matrix of chondrocytes, rather than to directly influence the biosynthesis of aggrecan. At the molecular level, we demonstrated that decorin significantly increases the adhesion between aggrecan and aggrecan molecules and between aggrecan molecules and collagen II fibrils. We hypothesize that decorin plays a crucial structural role in mediating the matrix integrity and biomechanical functions of cartilage by providing physical linkages to increase the adhesion and assembly of aggrecan molecules at the nanoscale.

High resistance of the mechanical properties of the chondrocyte pericellular matrix to proteoglycan digestion by chondroitinase, aggrecanase, or hyaluronidase

In articular cartilage, the extracellular matrix (ECM) and chondrocyte-associated pericellular matrix (PCM) are characterized by a high concentration of proteoglycans (PGs) and their associated glycosaminoglycans (GAGs). These molecules serve important biochemical, structural, and biomechanical roles in the tissue and differences in their regional distributions suggest that different GAG/PG species contribute to the specific biomechanical properties of the ECM and PCM. The objective of this study was to investigate region-specific contributions of aggrecan, chondroitin and dermatan sulfate, and hyaluronan to the micromechanical properties of articular cartilage PCM and ECM in situ. Cryosections of porcine cartilage underwent digestion with ADAMTS-4, chondroitinase ABC, bacterial hyaluronidase or human leukocyte elastase. Guided by immunofluorescence for type VI collagen, AFM stiffness mapping was used to evaluate the elastic properties of matched PCM and ECM regions in paired control and digested cartilage sections. These methods were used to test the hypotheses that specific enzymatic digestion of GAGs or PGs would reduce both PCM and ECM elastic moduli. Elastase, which digests a number of PGs, some types of collagen, and non-collagenous proteins, was used as a positive control. ECM elastic moduli were significantly reduced by all enzyme treatments. However, PCM micromechanical properties were unaffected by enzymatic digestion of aggrecan, chondroitin/dermatan sulfate, and hyaluronan but were significantly reduced by 24% following elastase digestion. Our results provide new evidence for high resistance of PCM micromechanical properties to PG digestion and suggest a potential role for elastase in the degradation of the ECM and PCM.

Time-dependent mechanical properties of aortic valve cusps: effect of glycosaminoglycan depletion

Aortic valve (AV) performance is closely linked to its structural components. Glycosaminoglycans (GAGs) are thought to influence the time-dependent properties of living tissues. This study investigates the effect of GAGs on the viscoelastic behaviour of the AV. Fresh porcine AV cusps were either treated enzymatically to remove GAGs or left untreated (control). The specimens were tested for stress relaxation and tensile properties under equibiaxial load conditions. The stress relaxation curves were fitted using a double exponential decay equation and the early relaxation constant (τ(1)) and late relaxation constant (τ(2)) calculated for each specimen. Immunohistochemistry confirmed the successful depletion of both sulphated and non-sulphated GAGs from the AV cusps. A statistical increase in τ(1) was found for both the radial and circumferential directions between the control and -GAGs group (radial, control 17.37s vs. -GAGs 25.65 s; circumferential, control 21.47s vs. -GAGs 27.37 s). It was also found that τ(1) differed between the two directions for the control group but not after GAG depletion (control, radial 17.37s vs. circumferential 21.47 s; -GAGs, radial 25.65 s vs. circumferential 27.37s). No effect on stiffness was found. The results showed that the presence of GAGs influences the mechanical viscoelastic properties of the AV but has no effect on the stiffness. The natural anisotropy, which reflects the relaxation kinematics, is lost after GAG depletion.

A method to cleave target molecules in a neocartilage

The mechanical function of many matrix molecules is unknown. A common method to determine whether a molecule is a load-carrying structural molecule is to measure the mechanical properties of a tissue, digest the tissue with an enzyme specific for cleaving that molecule, and then remeasure the mechanical properties. A limitation of this technique is that there are no specific lytic enzymes for most molecules of interest. This article introduces a method that may allow evaluation of a large number of candidate structural molecules. A translated thrombin proteolytic recognition and cleavage site is inserted in the cDNA of a target molecule, and the target molecule then expressed in a cell that produces a tissue. After growing the tissue with cells expressing the engineered target molecule, the traditional procedure of mechanical testing, digesting, and retesting is performed. This method was demonstrated using decorin and its dermatan sulfate (DS) glycosaminoglycan chain in a neocartilage. A tissue was generated with cells expressing a genetically engineered decorin with a thrombin cleavage site. The tissue was then tested in tension and compression, digested with thrombin, and mechanically retested. The decorin protein was found in the tissue, the DS glycosaminoglycan chain was removed with thrombin digestion, and there was no change in the mechanical properties of the tissue due to the thrombin digestion relative to controls. These findings were in agreement with previously reported tests on decorin, collectively supporting the proposed method. All methods involving animals were reviewed and approved by our Institutional Review Board.

Harnessing the purinergic receptor pathway to develop functional engineered cartilage constructs

OBJECTIVE

Mechanical stimulation is a widely used method to enhance the formation and properties of tissue-engineered cartilage. While this approach can be highly successful, it may be more efficient and effective to harness the known underlying mechanotransduction pathways responsible. With this aim, the purpose of this study was to assess the effect of directly stimulating the purinergic receptor pathway through exogenous adenosine 5'-triphosphate (ATP) in absence of externally applied forces.

METHODS

Isolated bovine articular chondrocytes were seeded in high density, 3D culture and supplemented with varying doses of ATP for up to 4 weeks. The effects on biosynthesis, extracellular matrix accumulation and mechanical properties were then evaluated. Experiments were also conducted to assess whether exogenous ATP elicited any undesirable effects, such as: inflammatory mediator release, matrix turn-over and mineralization.

RESULTS

Supplementation with ATP had a profound effect on the growth and maturation of the developed tissue. Exogenous ATP (62.5-250 microM) increased biosynthesis by 80-120%, and when stimulated for a period of 4 weeks resulted in increased matrix accumulation (80% increase in collagen and 60% increase in proteoglycans) and improved mechanical properties (6.5-fold increase in indentation modulus). While exogenous ATP did not stimulate the release of inflammatory mediators or induce mineralization, high doses of ATP (250 microM) elicited a 2-fold increase in matrix metalloproteinase-13 expression suggesting the emergence of a catabolic response.

CONCLUSIONS

Harnessing the ATP-purinergic receptor pathway is a highly effective approach to improve tissue formation and impart functional mechanical properties. However, the dose of ATP needs to be controlled as not to elicit a catabolic response.