Cartilage proteoglycans: structure and potential functions

Unveiling Charge-Pair Salt-Bridge Interaction Between GAGs and Collagen Protein in Cartilage: Atomic Evidence from DNP-Enhanced ssNMR at Natural Isotopic Abundance

The interactions between glycosaminoglycans (GAGs) and proteins are essential in numerous biochemical processes that involve ion-pair interactions. However, there is no evidence of direct and specific interactions between GAGs and collagen proteins in native cartilage. The resolution of solid-state NMR (ssNMR) can offer such information but the detection of GAG interactions in cartilage is limited by the sensitivity of the experiments when 13C and 15N isotopes are at natural abundance. In this communication, this limitation is overcome by taking advantage of dynamic nuclear polarization (DNP)-enhanced magic-angle spinning (MAS) experiments to obtain two-dimensional (2D) 15N-13C and 13C-13C correlations on native samples at natural abundance. These experiments unveiled inter-residue correlations in the aliphatic regions of the collagen protein previously unobserved. Additionally, our findings provide direct evidence of charge-pair salt-bridge interactions between negatively charged GAGs and positively charged arginine (Arg) residues of collagen protein. We also identified potential hydrogen bonding interactions between hydroxyproline (Hyp) and GAGs, offering atomic insights into the biochemical interactions within the extracellular matrix of native cartilage. Our approach may provide a new avenue for the structural characterization of other native systems.

Assessment of subchondral bone microdamage quantification using contrast-enhanced imaging techniques

Bone microdamage is common at subchondral bone (SCB) sites subjected to repeated high rate and magnitude of loading in the limbs of athletic animals and humans. Microdamage can affect the biomechanical behaviour of bone under physiological loading conditions. To understand the effects of microdamage on the mechanical properties of SCB, it is important to be able to quantify it. The extent of SCB microdamage had been previously estimated qualitatively using plain microcomputed tomography (μCT) and a radiocontrast quantification method has been used for trabecular bone but this method may not be directly applicable to SCB due to differences in bone structure. In the current study, SCB microdamage detection using lead uranyl acetate (LUA) and quantification by contrast-enhanced μCT and backscattered scanning electron microscopy (SEM) imaging techniques were assessed to determine the specificity of the labels to microdamage and the accuracy of damaged bone volume metrices. SCB specimens from the metacarpus of racehorses, with the hyaline articular cartilage (HAC) removed, were grouped into two with one group subjected to ex vivo uniaxial compression loading to create experimental bone damage. The other group was not loaded to preserve the pre-existing in vivo propagated bone microdamage. A subset of each group was stained with LUA using an established or a modified protocol to determine label penetration into SCB. The μCT and SEM images of stained specimens showed that penetration of LUA into the SCB was better using the modified protocol, and this protocol was repeated in SCB specimens with intact hyaline articular cartilage. The percentage of total label localised to bone microdamage was determined on SEM images, and the estimated labelled bone volume determined by μCT in SCB groups was compared. Label was present around diffuse and linear microdamage as well as oblique linear microcracks present at the articular surface, except in microcracks with high-density mineral infills. Bone surfaces lining pores with recent mineralisation were also labelled. Labelled bone volume fraction (LV/BV) estimated by μCT was higher in the absence of HAC. At least 50% of total labels were localised to bone microdamage when the bone area fraction (B.Ar/T.Ar) of the SCB was greater than 0.85 but less than 30% when B.Ar/T.Ar of the SCB was less than 0.85. To adjust for LUA labels on bone surfaces, a measure of the LV/BV corrected for bone surface area (LV/BV BS-1) was used to quantify damaged SCB. In conclusion, removal of HAC and using a modified labelling protocol effectively stained damaged SCB of the metacarpus of racehorses and represents a technique useful for quantifying microdamage in SCB. This method can facilitate future investigations of the effects of microdamage on joint physiology.

Perineuronal nets are phagocytosed by MMP-9 expressing microglia and astrocytes in the SOD1G93A ALS mouse model

AIMS

Perineuronal nets (PNNs) are an extracellular matrix structure that encases excitable neurons. PNNs play a role in neuroprotection against oxidative stress. Oxidative stress within motor neurons can trigger neuronal death, which has been implicated in amyotrophic lateral sclerosis (ALS). We investigated the spatio-temporal timeline of PNN breakdown and the contributing cellular factors in the SOD1G93A strain, a fast-onset ALS mouse model.

METHODS

This was conducted at the presymptomatic (P30), onset (P70), mid-stage (P130), and end-stage disease (P150) using immunofluorescent microscopy, as this characterisation has not been conducted in the SOD1G93A strain.

RESULTS

We observed a significant breakdown of PNNs around α-motor neurons in the ventral horn of onset and mid-stage disease SOD1G93A mice compared with wild-type controls. This was observed with increased numbers of microglia expressing matrix metallopeptidase-9 (MMP-9), an endopeptidase that degrades PNNs. Microglia also engulfed PNN components in the SOD1G93A mouse. Further increases in microglia and astrocyte number, MMP-9 expression, and engulfment of PNN components by glia were observed in mid-stage SOD1G93A mice. This was observed with increased expression of fractalkine, a signal for microglia engulfment, within α-motor neurons of SOD1G93A mice. Following PNN breakdown, α-motor neurons of onset and mid-stage SOD1G93A mice showed increased expression of 3-nitrotyrosine, a marker for protein oxidation, which could render them vulnerable to death.

CONCLUSIONS

Our observations suggest that increased numbers of MMP-9 expressing glia and their subsequent engulfment of PNNs around α-motor neurons render these neurons sensitive to oxidative damage and eventual death in the SOD1G93A ALS model mouse.

Physical Activity Associates with T1rho MRI of Femoral Cartilage After Anterior Cruciate Ligament Reconstruction

PURPOSE

Less physical activity has been associated with systemic biomarkers of cartilage breakdown after anterior cruciate ligament reconstruction (ACLR). However, previous research lacks analysis of deleterious cartilage compositional changes and objective physical activity after ACLR. The purpose of this study was to determine the association between physical activity quantified via accelerometer-based measures of daily steps and time in moderate-to-vigorous physical activity (MVPA), and T1rho magnetic resonance imaging (MRI) of the femoral articular cartilage, a marker of proteoglycan density in individuals with ACLR.

METHODS

Daily steps and MVPA were assessed over 7 d using an accelerometer worn on the hip in 26 individuals between 6 and 12 months after primary unilateral ACLR. Resting T1rho MRI was collected bilaterally, and T1rho MRI interlimb ratios (ILR: ACLR limb/contralateral limb) were calculated for lateral and medial femoral condyle regions of interest. We conducted univariate linear regression analyses to determine associations between T1rho MRI ILRs and daily steps and MVPA with and without controlling for sex.

RESULTS

Greater T1rho MRI ILR of the central lateral femoral condyle, indicative of less proteoglycan density in the ACLR limb, was associated with greater time in MVPA ( R2 = 0.178, P = 0.032). Sex-adjusted models showed significant interaction terms between daily steps and sex in the anterior ( P = 0.025), central ( P = 0.002), and posterior ( P = 0.002) medial femoral condyle.

CONCLUSIONS

Lesser physical activity may be a risk factor for maintaining cartilage health after ACLR; additionally, the relationship between physical activity and cartilage health may be different between males and females.

Assessment of articular cartilage degradation in response to an impact injury using µMRI

PURPOSE

Degradation of articular cartilage (AC) due to injury to the knee joint may initiate post-traumatic osteoarthritis (PTOA). Failure to diagnose the onset of the disease at an early stage makes the cure ineffective for PTOA. This study investigated the consequences of a mechanical injury to the knee in a rabbit model using microscopic magnetic resonance imaging (µMRI) at high resolution.

MATERIALS AND METHODS

A mechanical injury was induced to the knee joints of 12 rabbits. Cartilage blocks were extracted from the non-impacted and impacted knee joints after 2 and 14 weeks post-impact. The specimens were studied using µMRI T2 relaxation and inductively coupled plasma analysis to determine the early degradation of the articular cartilage.

RESULTS

The data established a connection between T2 relaxation time and the early progression of knee PTOA after an impact injury. T2 values were found to be higher in the impacted cartilage at both 2 and 14 weeks, in particular, T2-55° values in the impacted samples displayed a significant rise of 6.93% after 2 weeks and 20.02% after 14 weeks. Lower glycosaminoglycan measurement and higher water content in the impacted cartilage confirmed the µMRI results.

CONCLUSIONS

This µMRI T2 study was able to detect cartilage damage in the impacted knees. In addition, greater degradation in the affected knees at 14 weeks than at 2 weeks indicated the progressive nature of cartilage deterioration over time. The µMRI results were in accord with the biochemical analysis, indicating the detection of early structural damage in the cartilage.

Human Chondrocytes, Metabolism of Articular Cartilage, and Strategies for Application to Tissue Engineering

Hyaline cartilage, which is characterized by the absence of vascularization and innervation, has minimal self-repair potential in case of damage and defect formation in the chondral layer. Chondrocytes are specialized cells that ensure the synthesis of extracellular matrix components, namely type II collagen and aggregen. On their surface, they express integrins CD44, α1β1, α3β1, α5β1, α10β1, αVβ1, αVβ3, and αVβ5, which are also collagen-binding components of the extracellular matrix. This article aims to contribute to solving the problem of the possible repair of chondral defects through unique methods of tissue engineering, as well as the process of pathological events in articular cartilage. In vitro cell culture models used for hyaline cartilage repair could bring about advanced possibilities. Currently, there are several variants of the combination of natural and synthetic polymers and chondrocytes. In a three-dimensional environment, chondrocytes retain their production capacity. In the case of mesenchymal stromal cells, their favorable ability is to differentiate into a chondrogenic lineage in a three-dimensional culture.

Effects of glycosaminoglycan content in extracellular matrix of donor cartilage on the functional properties of osteochondral allografts evaluated by micro-CT non-destructive analysis

Osteochondral allograft (OCA) is an important surgical procedure used to repair extensive articular cartilage damage. It is known that chondrocyte viability is crucial for maintaining the biochemical and biomechanical properties of OCA, which is directly related to the clinical success of the operation and is the only standard for preoperative evaluation of OCA. However, there is a lack of systematic research on the effect of the content of cellular matrix in OCA cartilage tissue on the efficacy of transplantation. Therefore, we evaluated the effect of different GAG contents on the success of OCA transplantation in a rabbit animal model. Each rabbit OCA was treated with chondroitinase to regulate glycosaminoglycan (GAG) content in the tissue. Due to the different action times of chondroitinase, they were divided into 4 experimental groups (including control group, 2h, 4h, and 8h groups). The treated OCAs of each group were used for transplantation. In this study, transplant surgery effects were assessed using micro-computed tomography (μCT) and histological analysis. Our results showed that tissue integration at the graft site was poorer in the 4h and 8h groups compared to the control group at 4 and 12 weeks in vivo, as were the compressive modulus, GAG content, and cell density reduced. In conclusion, we evaluated the biochemical composition of OCAs before and after surgery using μCT analysis and demonstrated that the GAG content of the graft decreased, it also decreased during implantation; this resulted in decreased chondrocyte viability after transplantation and ultimately affected the functional success of OCAs.

Decellularized-disc based allograft and xenograft prosthesis for the long-term precise reconstruction of temporomandibular joint disc

Currently, no effective disc reconstruction treatment strategy is clinically available for temporomandibular joint (TMJ) disc-related diseases. To address this, we developed a prosthesis construct with laser-drilled decellularized natural disc reinforced by polycaprolactone, which mimics the natural morphology, and structural, biomechanical and biological property of the TMJ disc. The construct demonstrated good biocompatibility, safety and immunological tolerance both in vitro, and in a rat subcutaneous model. During 6 months implantation in an allogeneic rabbit TMJ disc reconstruction model, the disc prosthesis maintained its integrity, collagen fiber-orientation, mechanical property, joint structural stability and prevented articular cartilage and bone from damage. Furthermore, the "upgraded" disc prosthesis obtained from decellularized porcine disc was implanted into a goat TMJ disc reconstruction model. The xenograft prosthesis, with strength and viscoelasticity similar to a natural TMJ disc, was able to restore the structure and function of TMJ up to 20 weeks. These results demonstrate the translational feasibility of an allogeneic or xenogeneic decellularized disc prosthesis for treatment of advanced TMJ disc-related diseases. STATEMENT OF SIGNIFICANCE: This study makes a significant contribution to TMJ disc disease treatment both in theory and in clinics, because: (1) it provided an innovative approach to prepare an artificial TMJ disc with decent mechanical properties and long-term condyle-protecting effect; (2) it specified an advanced decellularized method for fibrocartilage decellularization and xenograft application; (3) it developed a facile and reproducible TMJ disc reconstruction model not only for middle size animal but also for large animal study; (4) the comprehensive and unreported biomechanical tests on the natural TMJ discs would act as a valuable reference for further research in the field of artificial TMJ disc materials or TMJ disc tissue engineering; (5) it suggested a potential treatment for patients with severe TMJ diseases that were commonly met but difficult to treat in clinics.

Histological Findings and T2 Relaxation Time in Canine Menisci of Elderly Dogs—An Ex Vivo Study in Stifle Joints

Osteoarthritis is a chronic disease that often affects the canine stifle joint. Due to their biomechanical function, the menisci in the canine stifle play an important role in osteoarthritis. They compensate for the incongruence in the joint and distribute and minimize compressive loads, protecting the hyaline articular cartilage from damage. Meniscal degeneration favors the development and progression of stifle joint osteoarthritis. Qualitative magnetic resonance imaging (MRI) is the current golden standard for detecting meniscal changes, but it has limitations in detecting early signs of meniscal degeneration. A quantitative MRI offers new options for detecting early structural changes. T2 mapping can especially visualize structural changes such as altered collagen structures and water content, as well as deviations in proteoglycan content. This study evaluated T2 mapping and performed a histological scoring of menisci in elderly dogs that had no or only low radiographic osteoarthritis grades. A total of 16 stifles from 8 older dogs of different sex and breed underwent ex vivo magnet resonance imaging, including a T2 mapping pulse sequence with multiple echoes. A histological analysis of corresponding menisci was performed using a modified scoring system. The mean T2 relaxation time was 18.2 ms and the mean histological score was 4.25. Descriptive statistics did not reveal a correlation between T2 relaxation time and histological score. Ex vivo T2 mapping of canine menisci did not demonstrate histological changes, suggesting that early meniscal degeneration can be present in the absence of radiological signs of osteoarthritis, including no significant changes in T2 relaxation time.

Contribution of collagen degradation and proteoglycan depletion to cartilage degeneration in primary and secondary osteoarthritis: an in silico study

OBJECTIVES

Current experimental approaches cannot elucidate the effect of maladaptive changes on the main cartilage constituents during the degeneration process in osteoarthritis (OA). In silico approaches, however, allow creating 'virtual knock-out' cases to elucidate these effects in a constituent-specific manner. We used such an approach to study the main mechanisms of cartilage degeneration in different mechanical loadings associated with the following OA etiologies: (1) physiological loading of degenerated cartilage, (2) injurious loading of healthy intact cartilage and (3) physiological loading of cartilage with a focal defect.

METHODS

We used the recently developed Cartilage Adaptive REorientation Degeneration (CARED) framework to simulate cartilage degeneration associated with primary and secondary OA (OA cases (1)-(3)). CARED incorporates numerical description of tissue-level cartilage degeneration mechanisms in OA, namely, collagen degradation, collagen reorientation, fixed charged density loss and tissue hydration increase following mechanical loading. We created 'virtual knock-out' scenarios by deactivating these degenerative processes one at a time in each of the three OA cases.

RESULTS

In the injurious loading of intact and physiological loading of degenerated cartilage, collagen degradation drives degenerative changes through fixed charge density loss and tissue hydration rise. In contrast, the two later mechanisms were more prominent in the focal defect cartilage model.

CONCLUSION

The virtual knock-out models reveal that injurious loading to intact cartilage and physiological loading to degenerated cartilage induce initial degenerative changes in the collagen network, whereas, in the presence of a focal cartilage defect, mechanical loading initially causes proteoglycans (PG) depletion, before changes in the collagen fibril network occur.

Hyperelastic characterization reveals proteoglycans drive the nanoscale strain-stiffening response in hyaline cartilage

Degenerative diseases such as osteoarthritis (OA) result in deterioration of cartilage extracellular matrix (ECM) components, significantly compromising tissue function. For measurement of mechanical properties at micron resolution, atomic force microscopy (AFM) is a leading technique in biomaterials research, including in the study of OA. It is common practice to determine material properties by applying classical Hertzian contact theory to AFM data. However, errors are consequential because the application of a linear elastic contact model to tissue ignores the fact that soft materials exhibit nonlinear properties even at small strains, influencing the biological conclusions of clinically-relevant studies. Additionally, nonlinear material properties are not well characterized, limiting physiological relevance of Young's modulus. Here, we probe the ECM of hyaline cartilage with AFM and explore the application of Hertzian theory in comparison to five hyperelastic models: NeoHookean, Mooney-Rivlin, Arruda-Boyce, Fung, and Ogden. The Fung and Ogden models achieved the best fits of the data, but the Fung model demonstrated robust sensitivity during model validation, demonstrating its ideal application to cartilage ECM and potentially other connective tissues. To develop a biological understanding of the Fung nonlinear parameter, we selectively degraded ECM components to target collagens (purified collagenase), hyaluronan (bacterial hyaluronidase), and glycosaminoglycans (chondroitinase ABC). We found significant differences in both Fung parameters in response to enzymatic treatment, indicating that proteoglycans drive the nonlinear response of cartilage ECM, and validating biological relevance of these phenomenological parameters. Our findings add value to the biomechanics community of using two-parameter material models for microindentation of soft biomaterials.

Tendon tissue engineering: An overview of biologics to promote tendon healing and repair

Tendons are dense connective tissues with a hierarchical polarized structure that respond to and adapt to the transmission of muscle contraction forces to the skeleton, enabling motion and maintaining posture. Tendon injuries, also known as tendinopathies, are becoming more common as populations age and participation in sports/leisure activities increases. The tendon has a poor ability to self-heal and regenerate given its intrinsic, constrained vascular supply and exposure to frequent, severe loading. There is a lack of understanding of the underlying pathophysiology, and it is not surprising that disorder-targeted medicines have only been partially effective at best. Recent tissue engineering approaches have emerged as a potential tool to drive tendon regeneration and healing. In this review, we investigated the physiochemical factors involved in tendon ontogeny and discussed their potential application in vitro to reproduce functional and self-renewing tendon tissue. We sought to understand whether stem cells are capable of forming tendons, how they can be directed towards the tenogenic lineage, and how their growth is regulated and monitored during the entire differentiation path. Finally, we showed recent developments in tendon tissue engineering, specifically the use of mesenchymal stem cells (MSCs), which can differentiate into tendon cells, as well as the potential role of extracellular vesicles (EVs) in tendon regeneration and their potential for use in accelerating the healing response after injury.

Obesity promotes lipid accumulation in mouse cartilage-A potential role of acetyl-CoA carboxylase (ACC) mediated chondrocyte de novo lipogenesis

Obesity promotes the development of osteoarthritis (OA). It is also well-established that obesity leads to excessive lipid deposition in nonadipose tissues, which often induces lipotoxicity. The objective of this study was to investigate changes in the levels of various lipids in mouse cartilage in the context of obesity and determine if chondrocyte de novo lipogenesis is altered. We used Oil Red O to determine the accumulation of lipid droplets in cartilage from mice fed high-fat diet (HFD) or low-fat diet (LFD). We further used mass spectrometry-based lipidomic analyses to quantify levels of different lipid species. Expression of genes involving in fatty acid (FA) uptake, synthesis, elongation, and desaturation were examined using quantitative polymerase chain reaction. To further study the potential mechanisms, we cultured primary mouse chondrocytes under high-glucose and high-insulin conditions to mimic the local microenvironment associated with obesity and subsequently examined the abundance of cellular lipid droplets. The acetyl-CoA carboxylase (ACC) inhibitor, ND-630, was added to the culture medium to examine the effect of inhibiting de novo lipogenesis on lipid accumulation in chondrocytes. When compared to the mice receiving LFD, the HFD group displayed more chondrocytes with visible intracellular lipid droplets. Significantly higher amounts of total FAs were also detected in the HFD group. Five out of six significantly upregulated FAs were ω-6 FAs, while the two significantly downregulated FAs were ω-3 FAs. Consequently, the HFD group displayed a significantly higher ω-6/ω-3 FA ratio. Ether linked phosphatidylcholine was also found to be higher in the HFD group. Fatty acid desaturase (Fad1-3), fatty acid-binding protein 4 (Fabp4), and fatty acid synthase (Fasn) transcripts were not found to be different between the treatment groups and fatty acid elongase (Elovl1-7) transcripts were undetectable in cartilage. Ceramide synthase 2 (Cers-2), the only transcript found to be changed in these studies, was significantly upregulated in the HFD group. In vitro, chondrocytes upregulated de novo lipogenesis when cultured under high-glucose, high-insulin conditions, and this observation was associated with the activation of ACC, which was attenuated by the addition of ND-630. This study provides the first evidence that lipid deposition is increased in cartilage with obesity and that this is associated with the upregulation of ACC-mediated de novo lipogenesis. This was supported by our observation that ACC inhibition ameliorated lipid accumulation in chondrocytes, thereby suggesting that ACC could potentially be targeted to treat obesity-associated OA.

Increased expression of bone/cartilage-associated genes and core transcription factors in keloids by RNA sequencing

Fibroblasts in keloids undergo cell identity transition with altered transcriptional characteristics. However, the core transcription factors driving this cellular reprogramming remain largely unknown. Here, we report the results of transcriptional profiling from 48 keloid and 24 control dermal tissues. We identified 1187 upregulated differentially expressed genes (foldchange > 2, false discovery rate < 0.05) in keloids, which were mainly enriched in extracellular matrix organization and bone/cartilage development, with significantly increased expression of bone/cartilage-associated collagens (COL5A1, COL10A1, and COL11A1) and glycoproteins (ACAN, COMP, and SPARC). Deconvolution analysis also revealed significantly increased composition of osteoblasts in keloid dermis. A total of 92 upregulated transcription factors were screened out from differentially expressed genes and mainly enriched in transcription process and skeleton development. Additional sequencing of six keloid individuals with multiple regions and intersection further narrow the list with 10 transcription factors. Finally, AEBP1, CREB3L1, RUNX2, and ZNF469 have been identified as candidate core regulators in promoting the gaining of bone/cartilage-like characteristics in keloids. RNA-sequencing of full-skin keloids consolidated the existence of these four transcription factors. Immunohistochemistry was employed to verify the expression of AEBP1, CREB3L1, RUNX2, and ZNF469 in keloid fibroblasts. In conclusion, we bioinformatically discovered the increased expression of bone/cartilage-associated genes and candidate core transcription factors in keloids. Our findings promise to provide molecular clues to develop novel therapeutic modalities against skin fibrosis.

CREB Ameliorates Osteoarthritis Progression Through Regulating Chondrocytes Autophagy via the miR-373/METTL3/TFEB Axis

Osteoarthritis (OA) is a degenerative joint disease characterized by articular cartilage degradation. Dysregulated autophagy is a major cause of OA. However, the underlying mechanism is unclear. Here, we found that the expression of element-binding protein (CREB) was downregulated in both cartilage tissues of OA patients and mouse OA model. In tert-butyl hydroperoxide solution-treated chondrocytes, increased apoptosis and autophagic blockage were attenuated by CREB overexpression. Mechanically, MiR-373 directly targeted the 3′UTR of methyltransferase-like 3 (METTL3) and led to its downregulation. METTL3 epigenetically suppressed TFEB. The upregulation of miR-373 by CREB overexpression induced the release of TFEB from METTL3 and restored the autophagy activity of chondrocytes. Taken together, our study showed that CREB alleviates OA injury through regulating the expression of miR-373, which directly targeted METTL3, and finally relieved TFEB from METTL3-mediated epigenetic suppression. The CREB/miR-373/METTL3/TFEB axis may be used as a potential target for the treatment of OA.

Collagen type II: From biosynthesis to advanced biomaterials for cartilage engineering

Collagen type II is the major constituent of cartilage tissue. Yet, cartilage engineering approaches are primarily based on collagen type I devices that are associated with suboptimal functional therapeutic outcomes. Herein, we briefly describe cartilage's development and cellular and extracellular composition and organisation. We also provide an overview of collagen type II biosynthesis and purification protocols from tissues of terrestrial and marine species and recombinant systems. We then advocate the use of collagen type II as a building block in cartilage engineering approaches, based on safety, efficiency and efficacy data that have been derived over the years from numerous in vitro and in vivo studies.

Enzymatic Degradation of Glycosaminoglycans and Proteoglycan-Mimetic Materials in Solution and on Polyelectrolyte Multilayer Surfaces

Proteoglycans (PGs) play many important roles in biology, contributing to the mechanical properties of tissues, helping to organize extracellular matrix components, and participating in signaling mechanisms related to mechanotransduction, cell differentiation, immune responses, and wound healing. Our lab has designed two different types of PG mimics: polyelectrolyte complex nanoparticles (PCNs) and PG-mimetic graft copolymers (GCs), both of which are prepared using naturally occurring glycosaminoglycans. This work evaluates the enzymatic stability of these PG mimics using hyaluronidases (I-S, IV-S, and II), chondroitinase ABC, and lysozyme, for PG mimics suspended in solution and adsorbed onto surfaces. Hyaluronan (HA)- and chondroitin sulfate (CS)-containing PG mimics are degraded by the hyaluronidases. PCNs prepared with CS and GCs prepared with heparin are the only CS- and HA-containing PG mimics protected from chondroitinase ABC. None of the materials are measurably degraded by lysozyme. Adsorption to polyelectrolyte multilayer surfaces protects PG mimics from degradation, compared to when PG mimics are combined with enzymes in solution; all surfaces are still intact after 21 days of enzyme exposure. This work reveals how the stability of PG mimics is controlled by both the composition and macromolecular assembly of the PG mimic and also by the size and specificity of the enzyme. Understanding and tuning these degradation susceptibilities are essential for advancing their applications in cardiovascular materials, orthopedic materials, and growth factor delivery applications.

Type I collagen scaffold with WNT5A plasmid for in situ cartilage tissue engineering

BACKGROUND

Cartilage tissue lacks the ability to heal. Cartilage tissue engineering using cell-free scaffolds has been increasingly used in recent years.

OBJECTIVE

This study describes the use of a type I collagen scaffold combined with WNT5A plasmid to promote chondrocyte proliferation and differentiation in a rabbit osteochondral defect model.

METHODS

Type I collagen was extracted and fabricated into a collagen scaffold. To improve gene transfection efficiency, a cationic chitosan derivative N,N,N-trimethyl chitosan chloride (TMC) vector was used. A solution of TMC/WNT5A complexes was adsorbed to the collagen scaffold to prepare a WNT5A scaffold. Osteochondral defects were created in the femoral condyles of rabbits. The rabbits were divided into defect, scaffold, and scaffold with WNT5A groups. At 6 and 12 weeks after creation of the osteochondral defects, samples were collected from all groups for macroscopic observation and gene expression analysis.

RESULTS

Samples from the defect group exhibited incomplete cartilage repair, while those from the scaffold and scaffold with WNT5A groups exhibited "preliminary cartilage" covering the defect. Cartilage regeneration was superior in the scaffold with WNT5A group compared to the scaffold group. Safranin O staining revealed more proteoglycans in the scaffold and scaffold with WNT5A groups compared to the defect group. The expression levels of aggrecan, collagen type II, and SOX9 genes were significantly higher in the scaffold with WNT5A group compared to the other two groups.

CONCLUSIONS

Type I collagen scaffold showed effective adsorption and guided the three-dimensional arrangement of stem cells. WNT5A plasmid promoted cartilage repair by stimulating the expression of aggrecan, type II collagen, and SOX9 genes and proteins, as well as inhibiting cartilage hypertrophy.

An in silico Framework of Cartilage Degeneration That Integrates Fibril Reorientation and Degradation Along With Altered Hydration and Fixed Charge Density Loss

Injurious mechanical loading of articular cartilage and associated lesions compromise the mechanical and structural integrity of joints and contribute to the onset and progression of cartilage degeneration leading to osteoarthritis (OA). Despite extensive in vitro and in vivo research, it remains unclear how the changes in cartilage composition and structure that occur during cartilage degeneration after injury, interact. Recently, in silico techniques provide a unique integrated platform to investigate the causal mechanisms by which the local mechanical environment of injured cartilage drives cartilage degeneration. Here, we introduce a novel integrated Cartilage Adaptive REorientation Degeneration (CARED) algorithm to predict the interaction between degenerative variations in main cartilage constituents, namely collagen fibril disorganization and degradation, proteoglycan (PG) loss, and change in water content. The algorithm iteratively interacts with a finite element (FE) model of a cartilage explant, with and without variable depth to full-thickness defects. In these FE models, intact and injured explants were subjected to normal (2 MPa unconfined compression in 0.1 s) and injurious mechanical loading (4 MPa unconfined compression in 0.1 s). Depending on the mechanical response of the FE model, the collagen fibril orientation and density, PG and water content were iteratively updated. In the CARED model, fixed charge density (FCD) loss and increased water content were related to decrease in PG content. Our model predictions were consistent with earlier experimental studies. In the intact explant model, minimal degenerative changes were observed under normal loading, while the injurious loading caused a reorientation of collagen fibrils toward the direction perpendicular to the surface, intense collagen degradation at the surface, and intense PG loss in the superficial and middle zones. In the injured explant models, normal loading induced intense collagen degradation, collagen reorientation, and PG depletion both on the surface and around the lesion. Our results confirm that the cartilage lesion depth is a crucial parameter affecting tissue degeneration, even under physiological loading conditions. The results suggest that potential fibril reorientation might prevent or slow down fibril degradation under conditions in which the tissue mechanical homeostasis is perturbed like the presence of defects or injurious loading.

Relaxation capacity of cartilage is a critical factor in rate- and integrity-dependent fracture

Articular cartilage heals poorly but experiences mechanically induced damage across a broad range of loading rates and matrix integrity. Because loading rates and matrix integrity affect cartilage mechanical responses due to poroviscoelastic relaxation mechanisms, their effects on cartilage failure are important for assessing and preventing failure. This paper investigated rate- and integrity-dependent crack nucleation in cartilage from pre- to post-relaxation timescales. Rate-dependent crack nucleation and relaxation responses were obtained as a function of matrix integrity through microindentation. Total work for crack nucleation increased with decreased matrix integrity, and with decreased loading rates. Critical energy release rate of intact cartilage was estimated as 2.39 ± 1.39 to 2.48 ± 1.26 kJ m-2 in a pre-relaxation timescale. These findings showed that crack nucleation is delayed when cartilage can accommodate localized loading through poroviscoelastic relaxation mechanisms before fracture at a given loading rate and integrity state.

Lipid metabolism in cartilage and its diseases: a concise review of the research progress

The homeostasis of the vertebrate body depends on anabolic and catabolic activities that are closely linked the inside and outside of the cell. Lipid metabolism plays an essential role in these metabolic activities. Although a large amount of evidence shows that normal lipid metabolism guarantees the conventional physiological activities of organs in the vertebrate body and that abnormal lipid metabolism plays an important role in the occurrence and deterioration of cardiovascular-related diseases, such as obesity, atherosclerosis, and type II diabetes, little is known about the role of lipid metabolism in cartilage and its diseases. This review aims to summarize the latest advances about the function of lipid metabolism in cartilage and its diseases including osteoarthritis, rheumatoid arthritis, and cartilage tumors. With the gradual in-depth understanding of lipid metabolism in cartilage, treatment methods could be explored to focus on this metabolic process in various cartilage diseases.

Gene Expression Profile Is Different between Intact and Enzymatically Digested Equine Articular Cartilage

OBJECTIVES

RNA isolation is necessary for the evaluation of gene expression. Due to the nature of its extracellular matrix, RNA isolation from articular hyaline cartilage is difficult and thus the tissue is commonly enzymatically digested in order to extract RNA from the obtained chondrocytes. We hypothesized that the digestion process affects the expression levels of common cartilage-associated genes.

DESIGN

Expression of cartilage-associated genes was compared between intact cartilage and digested chondrocytes from weight bearing and non-weight bearing regions of the equine fetlock joint.

RESULTS

The gene expression of SOX9, COL1A2, COL2A1, ACAN, and COLX were analyzed. Digested cartilage showed a significant decrease in the expression of COL1A2, COL2A1, and ACAN compared to intact cartilage in both joint regions, and an increase in COLX expression in non-weight bearing cartilage only.

CONCLUSIONS

Enzymatic digestion of cartilage significantly impacts gene expression profile. We conclude that while RNA isolation from intact cartilage is more technically difficult, determination of gene expression should be conducted on intact cartilage if true representation of the in vivo processes is sought.

3D-Printed Polycaprolactone Reinforced Hydrogel as an Artificial TMJ Disc

The replacement of a damaged temporomandibular joint (TMJ) disc remains a long-standing challenge in clinical settings. No study has reported a material with comprehensively excellent properties similar to a natural TMJ disc. In this work, we designed a novel artificial TMJ disc using polyvinyl alcohol (PVA) hydrogel crosslinked by cyclic freeze-thaw and reinforced by 3D-printed polycaprolactone (PCL) implants. The mechanical properties and surface morphologies of the artificial TMJ disc and the natural goat TMJ disc were tested and compared via compression, tensile, cyclic compression/tensile, creep, friction, scanning electron microscopy, and atomic force microscopy. The fibroblasts and chondrocytes were cultured on the artificial TMJ disc for 1, 3, and 5 d for cytotoxicity testing. Importantly, the artificial discs were placed into the TMJs of goats in an innovative way to induce disc defect repair for 12 wk. The PVA + PCL artificial disc demonstrated mechanical strength similar to that of natural disc, as well as 1) better fatigue resistance, viscoelasticity, and hydrophilicity; 2) less creep; and 3) low friction, cytotoxicity, and cell adhesion. By repairing the defects of the TMJ disc in goats, the artificial disc demonstrated the ability to maintain joint stability and protect condylar cartilage and bone from damage. These promising results indicate the feasibility of using a PVA + PCL artificial TMJ disc in a clinical context.

Evaluation of Knee Cartilage Diurnal, Activity, and BMI-Related Variations Using Quantitative T2 Mapping MRI and Fitbit Activity Tracking

The aim of this study is to evaluate diurnal variation in knee cartilage 3 Tesla magnetic resonance imaging (MRI) T2 mapping relaxation times, as well as activity- and body mass index (BMI)-dependent variability, using quantitative analysis of T2 values from segmented regions of the weight-bearing articular surfaces of the medial and lateral femoral condyles and tibial plateaus. Ten healthy volunteers' daily activity (steps) were tracked with Fitbit pedometers. Sagittal MRI T2 maps were obtained in the morning and afternoon on days 2 and 3. Mean T2 values were analyzed for variation related to the number of steps taken (activity), time of day (diurnal variation), and BMI using mixed effect model. Significant (albeit small) differences in the medial femoral and medial tibial cartilage regions were identified between morning and afternoon scans (diurnal variation). Daily activity did not result in significant changes and increasing BMI only demonstrated a slight increase in T2 values for the lateral tibial plateau. These findings suggest that it may be necessary to control diurnal variation when using quantitative MRI T2 mapping to assess articular cartilage longitudinally in healthy participants. Further investigation is needed to confirm these findings and determine if they also apply to symptomatic patients.

Isolation of Mouse Growth Plate and Articular Chondrocytes for Primary Cultures

Cartilage is a connective tissue presenting in several forms that are all essential components of the vertebrate skeleton. Complementing in vivo models, cultures of its resident cells-chondrocytes-are important experimental models in mechanistic and preclinical studies relevant to skeletal development and adult homeostasis and to such human pathologies as chondrodysplasias and osteoarthritis. Both growth plate and articular chondrocytes produce pancartilaginous extracellular matrix components, but the two cell subtypes also have distinct phenotypic properties that account for different structural features, functions, and fates of their tissues. Based on study goals, primary chondrocyte cultures should therefore be established from either growth plate or articular cartilage. Here, we describe the methods used in our laboratory to isolate and culture growth plate and articular chondrocytes from neonatal and adult mice, respectively. Both methods involve manual and enzymatic procedures to clean cartilage samples from contaminating tissues and to release chondrocytes as single-cell suspensions from their cartilage matrix.

Comprehensive phenotyping revealed transient startle response reduction and histopathological gadolinium localization to perineuronal nets after gadodiamide administration in rats

Gadolinium based contrast agents (GBCAs) are widely used in clinical MRI since the mid-1980s. Recently, concerns have been raised that trace amounts of Gadolinium (Gd), detected in brains even long time after GBCA application, may cause yet unrecognized clinical consequences. We therefore assessed the behavioral phenotype, neuro-histopathology, and Gd localization after repeated administration of linear (gadodiamide) or macrocyclic (gadobutrol) GBCA in rats. While most behavioral tests revealed no difference between treatment groups, we observed a transient and reversible decrease of the startle reflex after gadodiamide application. Residual Gd in the lateral cerebellar nucleus was neither associated with a general gene expression pathway deregulation nor with neuronal cell loss, but in gadodiamide-treated rats Gd was associated with the perineuronal net protein aggrecan and segregated to high molecular weight fractions. Our behavioral finding together with Gd distribution and speciation support a substance class difference for Gd presence in the brain after GBCA application.

Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

Pathophysiological landscape of osteoarthritis

A sharp rise in osteoarthritis (OA) incidence is expected as over 25% of world population ages in the coming decade. Although OA is considered a degenerative disease, mounting evidence suggests a strong connection with chronic metabolic conditions and low-grade inflammation. OA pathology is increasingly understood as a complex interplay of multiple pathological events including oxidative stress, synovitis and immune responses revealing its intricate nature. Cellular, biochemical and molecular aspects of these pathological events along with major outcomes of the relevant research studies in this area are discussed in the present review. With reference to their published and unpublished work, the authors strongly propose synovitis as a central OA pathology and the key OA pathological events are described in connection with it. Recent research outcomes also have succeeded to establish a linkage between metabolic syndrome and OA, which has been precisely included in the present review. Impact of aging process cannot be neglected in OA. Cell senescence is an important mechanism of aging through which it facilitates development of OA like other degenerative disorders, also discussed within a frame of OA. Conclusively, the reviewers urge low-grade inflammation linked to aging and derailed immune function as a pathological platform for OA development and progression. Thus, interventions targeted to prevent inflammaging hold a promising potential in effective OA management and efforts should be invested in this direction.

Effect of aggrecan degradation on the nanomechanics of hyaluronan in extra-fibrillar matrix of annulus fibrosus: A molecular dynamics investigation

Intervertebral Disc (IVD) Degeneration is one of the primary causes of low back pain among the adult population - the most significant cause being the degradation of aggrecan present in the extra-fibrillar matrix (EFM). Aggrecan degradation is closely associated with loss of water content leading to an alteration in the mechanical behaviour of the IVD. The loss in water content has a significant impact on the chemo-mechanical interplay of IVD biochemical constituents at the fundamental level. This work presents a mechanistic understanding of the effect of hydration, closely associated with aggrecan degradation, on the nanoscale mechanical behaviour of the hyaluronan present in the EFM of the Annulus Fibrosus. For this purpose, explicit three-dimensional molecular dynamics analyses of tensile and compressive tests are performed on a representative atomistic model of the hyaluronan present in the EFM. To account for the degradation of aggrecan, hydration levels are varied from 0 to 75% by weight of water. Analyses show that an increase in the hydration levels decreases the elastic modulus of hyaluronan in tension from ~4.6 GPa to ~2.1 GPa. On the other hand, the increase in hydration level increases the elastic moduli in axial compression from ~1.6 GPa in un-hydrated condition to ~6 GPa in 50% hydrated condition. But as the hydration levels increase to 75%, the elastic modulus reduces to ~3.5 GPa signifying a shift in load-bearing characteristic, from the solid hyaluronan component to the fluid component. Furthermore, analyses show a reduction in the intermolecular energy between hyaluronan and water, under axial tensile loading, indicating a nanoscale intermolecular debonding between hyaluronan and water molecules. This is attributed to the ability of hyaluronan to form stabilizing intra-molecular hydrogen bonds between adjacent residues. Compressive loading, on the other hand, causes intensive coiling of hyaluronan molecule, which traps more water through hydrogen bonding and aids in bearing compressive loads. Overall, study shows that hydration level has a strong influence on the atomistic level interactions between hyaluronan molecules and hyaluronan and water molecules in the EFM which influences the nanoscale mechanics of the Annulus Fibrosus.

Evidence of proteins, chromosomes and chemical markers of DNA in exceptionally preserved dinosaur cartilage

A histological ground-section from a duck-billed dinosaur nestling (Hypacrosaurus stebingeri) revealed microstructures morphologically consistent with nuclei and chromosomes in cells within calcified cartilage. We hypothesized that this exceptional cellular preservation extended to the molecular level and had molecular features in common with extant avian cartilage. Histochemical and immunological evidence supports in situ preservation of extracellular matrix components found in extant cartilage, including glycosaminoglycans and collagen type II. Furthermore, isolated Hypacrosaurus chondrocytes react positively with two DNA intercalating stains. Specific DNA staining is only observed inside the isolated cells, suggesting endogenous nuclear material survived fossilization. Our data support the hypothesis that calcified cartilage is preserved at the molecular level in this Mesozoic material, and suggest that remnants of once-living chondrocytes, including their DNA, may preserve for millions of years.

Hyaluronic Acid: Incorporating the Bio into the Material

In the last few decades, hyaluronic acid (HA) has become increasingly employed as a biomaterial in both clinical and research applications. The abundance of HA in many tissues, together with its amenability to chemical modification, has made HA an attractive material platform for a wide range of applications including regenerative medicine, drug delivery, and scaffolds for cell culture. HA has traditionally been appreciated to modulate tissue mechanics and remodeling through its distinctive biophysical properties and ability to organize other matrix proteins. However, HA can influence cell behavior in much more direct and specific ways by engaging cellular HA receptors, which can trigger signals that influence cell survival, proliferation, adhesion, and migration. In turn, cells modify HA by regulating synthesis and degradation through a dedicated arsenal of enzymes. Optimal design of HA-based biomaterials demands full consideration of these diverse modes of regulation. This review summarizes how HA-based signaling regulates cell behavior and discusses how these signals can be leveraged to create cell-instructive biomaterials.

Fate Distribution and Regulatory Role of Human Mesenchymal Stromal Cells in Engineered Hematopoietic Bone Organs

The generation of humanized ectopic ossicles (hOss) in mice has been proposed as an advanced translational and fundamental model to study the human hematopoietic system. The approach relies on the presence of human bone marrow-derived mesenchymal stromal cells (hMSCs) supporting the engraftment of transplanted human hematopoietic stem and progenitor cells (HSPCs). However, the functional distribution of hMSCs within the humanized microenvironment remains to be investigated. Here, we combined genetic tools and quantitative confocal microscopy to engineer and subsequently analyze hMSCs′ fate and distribution in hOss. Implanted hMSCs reconstituted a humanized environment including osteocytes, osteoblasts, adipocytes, and stromal cells associated with vessels. By imaging full hOss, we identified rare physical interactions between hMSCs and human CD45+/CD34+/CD90+ cells, supporting a functional contact-triggered regulatory role of hMSCs. Our study highlights the importance of compiling quantitative information from humanized organs, to decode the interactions between the hematopoietic and the stromal compartments.

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Mesenchymal cells can generate human bone organs with tailored molecular signature

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Mesenchymal cells reconstitute a human niche environment capable of regulating HSPCs

Articular fibrocartilage - Why does hyaline cartilage fail to repair?

Once damaged, articular cartilage has a limited potential to repair. Clinically, a repair tissue is formed, yet, it is often mechanically inferior fibrocartilage. The use of monolayer expanded versus naïve cells may explain one of the biggest discrepancies in mesenchymal stromal/stem cell (MSC) based cartilage regeneration. Namely, studies utilizing monolayer expanded MSCs, as indicated by numerous in vitro studies, report as a main limitation the induction of type X collagen and hypertrophy, a phenotype associated with endochondral bone formation. However, marrow stimulation and transfer studies report a mechanically inferior collagen I/II fibrocartilage as the main outcome. Therefore, this review will highlight the collagen species produced during the different therapeutic approaches. New developments in scaffold design and delivery of therapeutic molecules will be described. Potential future directions towards clinical translation will be discussed. New delivery mechanisms are being developed and they offer new hope in targeted therapeutic delivery.

IL-37 diminishes proteoglycan loss in human OA cartilage: donor-specific link between IL-37 and MMP-3

OBJECTIVE

A hallmark of osteoarthritis (OA) is degradation of articular cartilage proteoglycans. In isolated human OA chondrocytes, the anti-inflammatory cytokine Interleukin-37 (IL-37) lowers the expression of the proteolytic MMP and ADAMTS enzymes, which mediate this degradation. Therefore, we investigated if IL-37 protects against proteoglycan loss in freshly obtained human OA explants.

MATERIAL AND METHODS

Human OA cartilage explants were incubated with IL-37. Release of sulphated proteoglycans (sGAGs) was measured with the dimethylmethylene-blue assay. Production and degradation of newly synthesized proteoglycans was measured using ³⁵S-sulphate. Proteoglycan and proteolytic enzyme expression were analyzed by qPCR and Western Blot. Proteolytic activity was determined by measuring MMP- and ADAMTS-generated aggrecan neo-epitopes with ELISA and by using MMP-3-, MMP-13- or ADAMTS-5-inhibitors.

RESULTS

Over time, a linear release of sGAGs from OA cartilage was measured. IL-37 reduced this release by 87 μg/ml (24%) 95%CI [21.04-141.4]. IL-37 did not affect ³⁵S-sulphate incorporation or proteoglycan gene expression. In contrast, IL-37 reduced loss of ³⁵S-sulphate labeled GAGs and reduced MMP-3 protein expression, indicating that IL-37 inhibits proteoglycan degradation. Remarkably, we observed two groups of patients; one group in which MMP-3-inhibition lowered sGAG release, and one group in which ADAMTS5-inhibition had this effect. Remarkably, IL-37 was only functional in the group of patients that responded to MMP-3-inhibition.

CONCLUSION

We identified a relationship between IL-37 and reduced sGAG loss in OA cartilage. Most likely, this effect is mediated by inhibition of MMP-3 expression. These results suggest that IL-37 could be applied as therapy in a subgroup of OA patients, in which cartilage degradation is mediated by MMP-3.

Hyaluronan supplementation as a mechanical regulator of cartilage tissue development under joint-kinematic-mimicking loading

Articular cartilage plays an essential role in joint lubrication and impact absorption. Through this, the mechanical signals are coupled to the tissue's physiological response. Healthy synovial fluid has been shown to reduce and homogenize the shear stress acting on the cartilage surfaces due to its unique shear-thinning viscosity. As cartilage tissues are sensitive to mechanical changes in articulation, it was hypothesized that replacing the traditional culture medium with a healthy non-Newtonian lubricant could enhance tissue development in a cartilage engineering model, where joint-kinematic-mimicking mechanical loading is applied. Different amounts of hyaluronic acid were added to the culture medium to replicate the viscosities of synovial fluid at different health states. Hyaluronic acid supplementation, especially at a physiologically healthy concentration (2.0 mg ml^-1), promoted a better preservation of chondrocyte phenotype. The ratio of collagen II to collagen I mRNA was 4.5 times that of the control group, implying better tissue development (however, with no significant difference of measured collagen II content), with a good retention of collagen II and proteoglycan in the mechanically active region. Simulating synovial fluid properties by hyaluronic acid supplementation created a favourable mechanical environment for mechanically loaded constructs. These findings may help in understanding the influence of joint articulation on tissue homeostasis, and moreover, improve methods for functional cartilage tissue engineering.

Delivery of cellular factors to regulate bone healing

Bone tissue has a strong intrinsic regenerative capacity, thanks to a delicate and complex interplay of cellular and molecular processes, which tightly involve the immune system. Pathological settings of anatomical, biomechanical or inflammatory nature may lead to impaired bone healing. Innovative strategies to enhance bone repair, including the delivery of osteoprogenitor cells or of potent cytokines/morphogens, indicate the potential of 'orthobiologics', but are not fully satisfactory. Here, we review different approaches based on the delivery of regenerative cues produced by cells but in cell-free, possibly off-the-shelf configurations. Such strategies exploit the paracrine effect of the secretome of mesenchymal stem/stromal cells, presented in soluble form, shuttled through extracellular vesicles, or embedded within the network of extracellular matrix molecules. In addition to osteoinductive molecules, attention is given to factors targeting the resident immune cells, to reshape inflammatory and immunity processes from scarring to regenerative patterns.

Generating Mechanically Stable, Pediatric, and Scaffold-Free Nasal Cartilage Constructs In Vitro

Traditional methods of cartilage tissue engineering rely on the use of scaffolds. Although successful chondrogenesis has been reported in scaffold-based constructs, the use of exogenous materials has limited their application due to eliciting host immunogenic responses and potentially resulting in construct failure. As a result, tissue engineering approaches, which aim to generate scaffold-free cartilaginous constructs, have become of particular interest. Here, we generated stable three-dimensional scaffold-free cartilaginous constructs by cultivating expanded pediatric nasal chondrocyte multilayers in a slow turning lateral vessel bioreactor system under chemically defined media. Bioreactor cultivation resulted in increased construct cellularity, fourfold tissue thickness, and 200% sulfated glycosaminoglycan deposition with respect to static culture equivalent cultures. These improvements led to significantly enhanced mechanical and biochemical properties of bioreactor-cultivated constructs, allowing them to support their own weight, while static culture constructs remained fragile. Consequently, bioreactor-cultivated constructs closely resembled native nasal cartilage tissue histologically, mechanically, and biochemically. We propose that this method of cartilage construct formation could be used to obtain readily available human scaffold-free cartilaginous constructs.

Cresyl Violet Stains Mast Cells Selectively: Its Application to Counterstaining in Immunohistochemistry

The thiazine dye toluidine blue (TB) is well known to stain mast cells and hyaline cartilage metachromatically, and thus is mostly often used for their identification. However, TB is not suitable for counterstaining in immunohistochemistry, because of its high-background staining in the cytoplasm of other cell species and in extracellular structures. To expand the knowledge about dyestuffs staining mast cells in consideration with their usage in immunohistochemistry, we determined the stainability of several thiazines and oxazines, which are structurally related compounds to TB, using sections of mast cell-containing tissues. We found that all azine dyes used metachromatically stained mast cells and cartilage. Among these dyes, an oxazines cresyl violet (CV) stained mast cells with lower background, suggesting that those are useful for detecting mast cells and for counterstaining in immunohistochemistry. To ascertain its utility, CV was used in immunostaining of bHSDs in sections from adult rat ovary. Immunopositive signals reflected by DAB development in brown were clearly detected even after CV staining. We conclude that, similar to thiazines, oxazines stain mast cells metachromatically, and that of these, CV is more useful as a counterstain in immunohistochemistry than TB.

Impact of a daily exercise dose on knee joint cartilage - a systematic review and meta-analysis of randomized controlled trials in healthy animals

OBJECTIVE

To investigate the impact of a daily exercise dose on cartilage composition and thickness, by conducting a systematic review of randomized controlled trials (RCTs) involving healthy animals.

METHODS

A narrative synthesis of the effect of a daily exercise dose on knee cartilage aggrecan, collagen and thickness was performed. A subset of studies reporting sufficient data was combined in meta-analysis using a random-effects model. Meta-regression analyses were performed to investigate the impact of covariates.

RESULTS

Twenty-nine RCTs, involving 64 comparisons, were included. In the low dose exercise group, 21/25 comparisons reported decreased or no effect on cartilage aggrecan, collagen and thickness. In the moderate dose exercise group, all 12 comparisons reported either no or increased effect. In the high dose exercise group, 19/27 comparisons reported decreased effect. A meta-analysis of 14 studies investigating cartilage thickness showed no effect in the low dose exercise group (SMD -0.02; 95% CI -0.42 to 0.38; I² = 0.0%), large but non-significant cartilage thickening in the moderate dose exercise group (SMD 0.95; 95% CI -0.33 to 2.23; I² = 72.1%) and non-significant cartilage thinning in the high dose exercise group (SMD -0.19; 95% CI -0.49 to 0.12; I² = 0.0%). Results were independent of analyzed covariates. The overall quality of the studies was poor because of inadequate reporting of data and high risk of bias.

CONCLUSIONS

Our results suggest that the relationship between daily exercise dose and cartilage composition, but not necessarily cartilage thickness, may be non-linear. While we found inconclusive evidence for a low daily dose of exercise, a high daily dose of exercise may have negative effects and a moderate daily dose of exercise may have positive effects on cartilage matrix composition in healthy animals.

Structure and Properties of Cartilage Proteoglycans

The most abundant cartilage proteoglycan is aggrecan, a bottlebrush shaped molecule that possesses over 100 glycosaminoglycan (chondroitin sulfate and keratan sulfate) chains. The side-chains are linear sulfated polysaccharides that are negatively charged under physiological conditions. Aggrecan interacts with hyaluronic acid (HA) to form large aggregates. Osmotic pressure measurements and rheological measurements are used to study the static and dynamic behavior of aggrecan assemblies at the macroscopic length scales. The microscopic properties of aggrecan solutions are determined by small angle neutron scattering (SANS), and static and dynamic light scattering (SLS and DLS). In dilute solutions aggrecan forms microgels with a diffuse boundary, composed of loosely connected clusters. The osmotic pressure of the aggrecan-HA system decreases with increasing HA content. DLS yields a relaxation rate that varies as q3, arising from internal modes in the microgel. The relaxation rate in the solutions of the aggrecan-HA complex is slightly greater than in the pure aggrecan solution.

Hydrogel based cartilaginous tissue regeneration: recent insights and technologies

Hydrogel based technologies has been extensively employed in both exploratory research and clinical applications to address numerous existing challenges in the regeneration of articular cartilage and intervertebral disc.

The influences of different spatial resolutions on the characteristics of T2 relaxation times in articular cartilage: A coarse-graining study of the microscopic magnetic resonance imaging data

Microscopic magnetic resonance imaging (µMRI) T2 data from canine cartilage at different tibial locations were analyzed to investigate the influences of spatial resolution and pixel position on the T2 sensitivity to osteoarthritis (OA). Five experimental factors were investigated: inaccurate pixel position, different pixel resolutions, different specimen orientations in the magnetic field, topographical variations over the tibial surface, and different OA stages. A number of significant trends were identified in this analysis, which shows the subtle but substantial influences to our abilities of detecting OA due to T2 changes. In particular, any deviation in locating the cartilage pixels may result in erratic values near the cartilage surface. Significant differences were found in T2 values between nearly any two comparison-groups under all resolutions both in the meniscus-covered and -uncovered areas, which were also showed interaction between the OA degradation stages. This multiresolution project should help to improve the detection sensitivities of MRI toward cartilage degeneration. Microsc. Res. Tech. 79:754-765, 2016. © 2016 Wiley Periodicals, Inc.