Structure and function of aggrecan

Non-destructive detection of matrix stabilization correlates with enhanced mechanical properties of self-assembled articular cartilage

Tissue engineers rely on expensive, time-consuming, and destructive techniques to monitor the composition, microstructure, and function of engineered tissue equivalents. A non-destructive solution to monitor tissue quality and maturation would greatly reduce costs and accelerate the development of tissue-engineered products. The objectives of this study were to (a) determine whether matrix stabilization with exogenous lysyl oxidase-like protein-2 (LOXL2) with recombinant hyaluronan and proteoglycan link protein-1 (LINK) would result in increased compressive and tensile properties in self-assembled articular cartilage constructs, (b) evaluate whether label-free, non-destructive fluorescence lifetime imaging (FLIm) could be used to infer changes in both biochemical composition and biomechanical properties, (c) form quantitative relationships between destructive and non-destructive measurements to determine whether the strength of these correlations is sufficient to replace destructive testing methods, and (d) determine whether support vector machine (SVM) learning can predict LOXL2-induced collagen crosslinking. The combination of exogenous LOXL2 and LINK proteins created a synergistic 4.9-fold increase in collagen crosslinking density and an 8.3-fold increase in tensile strength as compared with control (CTL). Compressive relaxation modulus was increased 5.9-fold with addition of LOXL2 and 3.4-fold with combined treatments over CTL. FLIm parameters had strong and significant correlations with tensile properties (R²  = 0.82; p < 0.001) and compressive properties (R²  = 0.59; p < 0.001). SVM learning based on FLIm-derived parameters was capable of automating tissue maturation assessment with a discriminant ability of 98.4%. These results showed marked improvements in mechanical properties with matrix stabilization and suggest that FLIm-based tools have great potential for the non-destructive assessment of tissue-engineered cartilage.

MicroRNA-15a-5p Regulates the Development of Osteoarthritis by Targeting PTHrP in Chondrocytes

BACKGROUND AND AIMS

A growing body of research has demonstrated that the degeneration of chondrocytes is the primary cause of osteoarthritis (OA). Parathyroid hormone-related protein (PTHrP) can alleviate the degeneration of chondrocytes via promotion of chondrocyte proliferation and inhibition of terminal differentiation, but the underlying mechanism remains unknown. This study aimed to identify the microRNAs (miRNAs) that may target PTHrP and regulate the proliferation and terminal differentiation of chondrocytes.

METHODS

Bioinformatic analysis was used to predict which miRNAs target PTHrP. We collected human knee cartilage specimens to acquire the primary chondrocytes, which we then used to test the expression and function of the targeted miRNAs. To explore the effects of miR-15a-5p on the putative binding sites, specific mimics or inhibitors were transfected into the chondrocytes. Furthermore, a dual-luciferase reporter gene assay and chondrocyte degeneration-related factors were used to verify the possible mechanism.

RESULTS

The expression of PTHrP was upregulated in the OA chondrocytes, whilst miR-15a-5p was downregulated in the OA chondrocytes. A negative correlation was observed between PTHrP and miR-15a-5p. The knockdown of miR-15a-5p promoted the growth of chondrocytes and inhibited calcium deposition, whilst overexpression of miR-15a-5p reversed this trend. The effect of miR-15a-5p overexpression was neutralised by PTHrP. Dual-luciferase reporter assays revealed that PTHrP can be used as a novel targeting molecule for miR-15a-5p.

CONCLUSIONS

miR-15a-5p promotes the degeneration of chondrocytes by targeting PTHrP and, in addition to helping us understand the development of OA, may be a potential biomarker of OA.

Aggrecan Hypomorphism Compromises Articular Cartilage Biomechanical Properties and Is Associated with Increased Incidence of Spontaneous Osteoarthritis

The gene encoding the proteoglycan aggrecan (Agc1) is abundantly expressed in cartilage during development and adulthood, and the loss or diminished deposition of the protein results in a wide range of skeletal malformations. Furthermore, aggrecan degradation is a hallmark of cartilage degeneration occurring in osteoarthritis. In the present study, we investigated the consequences of a partial loss of aggrecan in the postnatal skeleton and in the articular cartilage of adult mice. We took advantage of the previously described Agc1^{tm(IRES-CreERT2)} mouse line, which allows for conditional and timely-regulated deletion of floxed, cartilage-expressed genes. As previously reported, the introduction of the CreER^T2 cassette in the 3’UTR causes a disruption of the normal expression of Agc1 resulting in a hypomorphic deposition of the protein. In homozygous mice, we observed a dwarf phenotype, which persisted throughout adulthood supporting the evidence that reduced aggrecan amount impairs skeletal growth. Homozygous mice exhibited reduced proteoglycan staining of the articular cartilage at 6 and 12 months of age, increased stiffening of the extracellular matrix at six months, and developed severe cartilage erosion by 12 months. The osteoarthritis in the hypomorph mice was not accompanied by increased expression of catabolic enzymes and matrix degradation neoepitopes. These findings suggest that the degeneration found in homozygous mice is likely due to the compromised mechanical properties of the cartilage tissue upon aggrecan reduction.

Microcarriers Based on Glycosaminoglycan-Like Marine Exopolysaccharide for TGF-β1 Long-Term Protection

Articular cartilage is an avascular, non-innervated connective tissue with limited ability to regenerate. Articular degenerative processes arising from trauma, inflammation or due to aging are thus irreversible and may induce the loss of the joint function. To repair cartilaginous defects, tissue engineering approaches are under intense development. Association of cells and signalling proteins, such as growth factors, with biocompatible hydrogel matrix may lead to the regeneration of the healthy tissue. One current strategy to enhance both growth factor bioactivity and bioavailability is based on the delivery of these signalling proteins in microcarriers. In this context, the aim of the present study was to develop microcarriers by encapsulating Transforming Growth Factor-β1 (TGF-β1) into microparticles based on marine exopolysaccharide (EPS), namely GY785 EPS, for further applications in cartilage engineering. Using a capillary microfluidic approach, two microcarriers were prepared. The growth factor was either encapsulated directly within the microparticles based on slightly sulphated derivative or complexed firstly with the highly sulphated derivative before being incorporated within the microparticles. TGF-β1 release, studied under in vitro model conditions, revealed that the majority of the growth factor was retained inside the microparticles. Bioactivity of released TGF-β1 was particularly enhanced in the presence of highly sulphated derivative. It comes out from this study that GY785 EPS based microcarriers may constitute TGF-β1 reservoirs spatially retaining the growth factor for a variety of tissue engineering applications and in particular cartilage regeneration, where the growth factor needs to remain in the target location long enough to induce robust regenerative responses.

The Late Osteoblast/Preosteocyte Cell Line MLO-A5 Displays Mesenchymal Lineage Plasticity In Vitro and In Vivo

The process of osteoblast switching to alternative mesenchymal phenotypes is incompletely understood. In this study, we tested the ability of the osteoblast/preosteocyte osteogenic cell line, MLO-A5, to also differentiate into either adipocytes or chondrocytes. MLO-A5 cells expressed a subset of skeletal stem cell markers, including Sca-1, CD44, CD73, CD146, and CD166. Confluent cultures of cells underwent differentiation within 3 days upon the addition of osteogenic medium. The same cultures were capable of undergoing adipogenic and chondrogenic differentiation under lineage-appropriate culture conditions, evidenced by lineage-specific gene expression analysis by real-time reverse-transcription-PCR, and by Oil Red O and alcian blue (pH 2.5) staining, respectively. Subcutaneous implantation of MLO-A5 cells in a gel foam into NOD SCID mice resulted in a woven bone-like structure containing embedded osteocytes and regions of cartilage-like tissue, which stained positive with both alcian blue (pH 2.5) and safranin O. Together, our findings show that MLO-A5 cells, despite being a strongly osteogenic cell line, exhibit characteristics of skeletal stem cells and display mesenchymal lineage plasticity in vitro and in vivo. These unique characteristics suggest that this cell line is a useful model with which to study aging and disease-related changes to the mesenchymal lineage composition of bone.

In Silico Analysis of Pacific Oyster (Crassostrea gigas) Transcriptome over Developmental Stages Reveals Candidate Genes for Larval Settlement

Following their planktonic phase, the larvae of benthic marine organisms must locate a suitable habitat to settle and metamorphose. For oysters, larval adhesion occurs at the pediveliger stage with the secretion of a proteinaceous bioadhesive produced by the foot, a specialized and ephemeral organ. Oyster bioadhesive is highly resistant to proteomic extraction and is only produced in very low quantities, which explains why it has been very little examined in larvae to date. In silico analysis of nucleic acid databases could help to identify genes of interest implicated in settlement. In this work, the publicly available transcriptome of Pacific oyster Crassostrea gigas over its developmental stages was mined to select genes highly expressed at the pediveliger stage. Our analysis revealed 59 sequences potentially implicated in adhesion of C. gigas larvae. Some related proteins contain conserved domains already described in other bioadhesives. We propose a hypothetic composition of C. gigas bioadhesive in which the protein constituent is probably composed of collagen and the von Willebrand Factor domain could play a role in adhesive cohesion. Genes coding for enzymes implicated in DOPA chemistry were also detected, indicating that this modification is also potentially present in the adhesive of pediveliger larvae.

Differential chondro- and osteo-stimulation in three-dimensional porous scaffolds with different topological surfaces provides a design strategy for biphasic osteochondral engineering

Bone/cartilage interfacial tissue engineering needs to satisfy the differential properties and architectures of the osteochondral region. Therefore, biphasic or multiphasic scaffolds that aim to mimic the gradient hierarchy are widely used. Here, we find that two differently structured (topographically) three-dimensional scaffolds, namely, "dense" and "nanofibrous" surfaces, show differential stimulation in osteo- and chondro-responses of cells. While the nanofibrous scaffolds accelerate the osteogenesis of mesenchymal stem cells, the dense scaffolds are better in preserving the phenotypes of chondrocytes. Two types of porous scaffolds, generated by a salt-leaching method combined with a phase-separation process using the poly(lactic acid) composition, had a similar level of porosity (~90%) and pore size (~150 μm). The major difference in the surface nanostructure led to substantial changes in the surface area and water hydrophilicity (nanofibrous ≫ dense); as a result, the nanofibrous scaffolds increased the cell-to-matrix adhesion of mesenchymal stem cells significantly while decreasing the cell-to-cell contracts. Importantly, the chondrocytes, when cultured on nanofibrous scaffolds, were prone to lose their phenotype, including reduced chondrogenic expressions (SOX-9, collagen type II, and Aggrecan) and glycosaminoglycan content, which was ascribed to the enhanced cell-matrix adhesion with reduced cell-cell contacts. On the contrary, the osteogenesis of mesenchymal stem cells was significantly accelerated by the improved cell-to-matrix adhesion, as evidenced in the enhanced osteogenic expressions (RUNX2, bone sialoprotein, and osteopontin) and cellular mineralization. Based on these findings, we consider that the dense scaffold is preferentially used for the chondral-part, whereas the nanofibrous structure is suitable for osteo-part, to provide an optimal biphasic matrix environment for osteochondral tissue engineering.

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.

Differential protein expression in human knee articular cartilage and medial meniscus using two different proteomic methods: a pilot analysis

Background

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

Methods

Healthy knee articular cartilage taken from the medial tibial condyle and medial meniscus samples taken from the body region were obtained from three adult forensic medicine cases. Proteins were extracted from tissue pieces and prepared for MS analysis. Each sample was subjected to liquid chromatography (LC)-MS/MS analysis using an Orbitrap mass spectrometer, and run in both DDA and DIA mode. Linear mixed effects models were used for statistical analysis.

Results

A total of 653 proteins were identified in the DDA analysis, of which the majority was present in both tissue types. Only proteins with quantitation information in both tissues (n = 90) were selected for more detailed analysis, of which the majority did not statistically significantly differ in abundance between the two tissue types, in either of the MS analyses. However, 21 proteins were statistically significantly different (p < 0.05) between meniscus and cartilage in the DIA analysis. Out of these, 11 proteins were also significantly different in the DDA analysis. Aggrecan core protein was the most abundant protein in articular cartilage and significantly differed between the two tissues in both methods. The corresponding protein in meniscus was serum albumin. Dermatopontin exhibited the highest meniscus vs articular cartilage ratio among the statistically significant proteins. The DIA method led to narrower confidence intervals for the abundance differences between the two tissue types than DDA.

Conclusions

Although articular cartilage and meniscus had similar proteomic composition, we detected several differences by MS. Between the two analyses, DIA yielded more precise estimates and more statistically significant different proteins than DDA, and had no missing values, which makes it preferable for future LC-MS/MS analyses.

Electronic supplementary material

The online version of this article (10.1186/s12891-018-2346-6) contains supplementary material, which is available to authorized users.

Inhibition of YAP with siRNA prevents cartilage degradation and ameliorates osteoarthritis development

The Hippo/YAP signaling pathway is important for mediating organ size and tissue homeostasis, but its role in osteoarthritis (OA) remains unclear. We aimed to investigate the role of Hippo/YAP signaling pathway in OA development. YAP expression in OA cartilage was assessed by immunohistochemistry, RT-qPCR, and Western blotting. The effects of YAP overexpression or knockdown on gene expression related to chondrocyte hypertrophy induced by IL-1β were examined. The in vivo effects of YAP inhibition were studied. Subchondral bone was analyzed by micro-CT. YAP was increased in mice and human OA articular cartilage and chondrocytes. YAP mRNA expression level was also increased in IL-1β-induced chondrocytes. YAP overexpression resulted in increased expression of catabolic genes in response to IL-1β. Suppression of YAP by siRNA inhibited IL-1β stimulated catabolic genes expression and chondrocytes apoptosis. Intra-articular injection of YAP siRNA ameliorated OA development in mice. Micro-CT results showed the aberrant subchondral bone formation was also reduced. We provided evidence that YAP was upregulated in OA cartilage. Inhibition of YAP using YAP siRNA is a promising way to prevent cartilage degradation in OA. KEY MESSAGES: YAP was upregulated in human and mice osteoarthritis cartilage and chondrocytes. YAP siRNA decreased IL-1β-induced catabolic gene expression. Intra-articular injection of YAP siRNA ameliorated OA development. Intra-articular injection of YAP siRNA reduced aberrant subchondral bone formation.

Conformations of polyelectrolyte molecular brushes: A mean-field theory

We present a mean-field theory for the solution properties of polyelectrolyte molecular brushes, comprising multiple ionically charged side chains tethered to the main chain (backbone). The power-law dependences for local and large-scale conformational properties, i.e., the brush thickness, extension of spacers between the grafts, and end-to-end distance for the main chain macromolecule, are derived as a function of architectural parameters (the lengths of the main chain and of the grafts, grafting density). We demonstrate that at high grafting density or/and a large fraction of charged monomer units in the grafts, the localization of counterions in the intra-molecular volume occurs and we specify the onset of this transition. We prove that such localization of the counterions is accompanied by full extension of the main chain of the polyelectrolyte molecular brush in salt-free solution. This stretching of the main chain is relaxed upon an increase in the salt concentration. The dependence of the macromolecular dimensions of the polyelectrolyte molecular brush on the salt concentration is derived, and multiple power-law exponents valid in different salt concentration ranges are predicted.

Calcium activated nucleotidase 1 (CANT1) is critical for glycosaminoglycan biosynthesis in cartilage and endochondral ossification

Desbuquois dysplasia type 1 (DBQD1) is a chondrodysplasia caused by mutations in CANT1 gene encoding an ER/Golgi calcium activated nucleotidase 1 that hydrolyses UDP. Here, using Cant1 knock-in and knock-out mice recapitulating DBQD1 phenotype, we report that CANT1 plays a crucial role in cartilage proteoglycan synthesis and in endochondral ossification. Specifically, the glycosaminoglycan synthesis was decreased in chondrocytes from Cant1 knock-out mice and their hydrodynamic size was reduced, whilst the sulfation was increased and the overall proteoglycan secretion was delayed. Interestingly, knock-out chondrocytes had dilated ER cisternae suggesting delayed protein secretion and cellular stress; however, no canonical ER stress response was detected using microarray analysis, Xbp1 splicing and protein levels of BiP and ATF4. The observed proteoglycan defects caused deregulated chondrocyte proliferation and maturation in the growth plate resulting in the reduced skeletal growth. In conclusion, the pathogenic mechanism of DBQD1 comprises deregulated chondrocyte performance due to defective intracellular proteoglycan synthesis and altered proteoglycan properties in the extracellular matrix.

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Desbuquois dysplasia type 1 (DBQD1) is a recessive skeletal dysplasia caused by mutations in CANT1 gene, a Calcium activated nucleotidase of the ER/Golgi.

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The Cant1 knock-out mouse recapitulates human DBQD1.

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Cant1 is critical for different steps of proteoglycan biosynthesis including glycosaminoglycan chain synthesis, length and sulfation.

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The intracellular GAG synthesis defects cause delayed proteoglycan secretion with ER enlargement.

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In Cant1 knock-out chondrocytes ER enlargement is not linked to canonical ER stress.

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The proteoglycan defects cause deregulated chondrocyte proliferation and maturation in the growth plate resulting in reduced skeletal growth.

The Zonal Architecture of the Mandibular Condyle Requires ADAMTS5

Temporomandibular joint (TMJ) osteoarthritis (TMJOA) disrupts extracellular matrix (ECM) homeostasis, leading to cartilage degradation. Upregulated a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-5 leads to cleavage of its substrate aggrecan (Acan) and is considered a hallmark of TMJOA. However, most research on ADAMTS5-Acan turnover has focused on hyaline cartilage, not fibrocartilage, which comprises the TMJ. The mandibular condylar cartilage (MCC) of the TMJ is organized in zones, and chondrocytes are arranged in axial rows, yet the molecular mechanisms required to generate the MCC zonal architecture have not been elucidated. Here, we test the hypothesis that ADAMTS5 is required for development of the TMJ MCC. Adamts5+/+ and Adamts5-/- murine TMJs were harvested at postnatal day 7 (P7), P21, 2 mo, and 6 mo of age; histomorphometrics indicated increased ECM. Immunohistochemistry and Western blots demonstrated the expanded ECM correlated with increased Acan localization in Adamts5-/- compared to Adamts5+/+. Cell volume was also decreased in the MCC of Adamts5-/- due to both a reduction in cell size and less mature hypertrophic chondrocytes. Analysis of chondrogenic maturation markers by quantitative real-time polymerase chain reaction indicated Col2a1, Col10a1, and Sox9 were significantly reduced in Adamts5-/- MCC compared to that of Adamts5+/+. The older (6 mo) Adamts5-/- MCC exhibited changes in chondrogenic cell arrangements, including clustering and chondrogenic atrophy, that correlated with early stages of TMJOA using modified Mankin scoring. These data indicate a potentially novel and critical role of ADAMTS5 for maturation of hypertrophic chondrocytes and establishment of the zonal architecture that, when disrupted, may lead to early onset of TMJOA.

3D printed biofunctionalized scaffolds for microfracture repair of cartilage defects

While articular cartilage defects affect millions of people worldwide from adolescents to adults, the repair of articular cartilage defects still remains challenging due to the limited endogenous regeneration of the tissue and poor integration with implants. In this study, we developed a 3D-printed scaffold functionalized with aggrecan that supports the cellular fraction of bone marrow released from microfracture, a widely used clinical procedure, and demonstrated tremendous improvement of regenerated cartilage tissue quality and joint function in a lapine model. Optical coherence tomography (OCT) revealed doubled thickness of the regenerated cartilage tissue in the group treated with our aggrecan functionalized scaffold compared to standard microfracture treatment. H&E staining showed 366 ± 95 chondrocytes present in the unit area of cartilage layer with the support of bioactive scaffold, while conventional microfracture group showed only 112 ± 26 chondrocytes. The expression of type II collagen appeared almost 10 times higher with our approach compared to normal microfracture, indicating the potential to overcome the fibro-cartilage formation associated with the current microfracture approach. The therapeutic effect was also evaluated at joint function level. The mobility was evaluated using a modified Basso, Beattie and Bresnahan (BBB) scale. While the defect control group showed no movement improvement over the course of study, all experimental groups showed a trend of increasing scores over time. The present work developed an effective method to regenerate critical articular defects by combining a 3D-printed therapeutic scaffold with the microfracture surgical procedure. This biofunctionalized acellular scaffold has great potential to be applied as a supplement for traditional microfracture to improve the quality of cartilage regeneration in a cost and labor effective way.

Cellular and molecular changes to chondrocytes in an in vitro model of developmental dysplasia of the hip‑an experimental model of DDH with swaddling position

The aim of the present study was to assess the cellular and molecular changes to chondrocytes in a developmental dysplasia of the hip (DDH) model and to investigate the early metabolism of chondrocytes in DDH. Neonatal Wistar rats were used for the DDH model with swaddling position. Primary cultures of chondrocytes were prepared at serial interval stages (2, 4, 6 and 8 weeks) to investigate cellular proliferation. The expression of collagen II and aggrecan mRNA was detected to assess the anabolic ability of chondrocytes. The expression of matrix metallopeptidase (MMP)-13 and ADAM metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS-5) mRNA was measured to investigate the degradation of collagen II and aggrecan, respectively. Morphological changes were observed in coronal dissection samples after the removal of fixation. Primary chondrocytes at serial intervals were assessed using a Cell Counting Kit-8 assay and the results revealed that DDH chondrocytes had more proliferative activity. The expression of collagen II mRNA was upregulated at 2 weeks and was more sensitive to mechanical loading compared with aggrecan. Similar changes occurred at 6 weeks. Furthermore, MMP-13 and ADAMTS-5 mRNA expression levels were upregulated at 2 weeks. It was also demonstrated that DDH chondrocytes exhibited high proliferative activity at the early stages and degeneration later.

Structure and properties of polydisperse polyelectrolyte brushes studied by self-consistent field theory

Two complementary self-consistent field theoretical approaches are used to analyze the equilibrium structure of binary and ternary brushes of polyions with different degrees of polymerization. Stratification in binary brushes is predicted: the shorter chains are entirely embedded in the proximal sublayer depleted of end-points of longer chains while the peripheral sublayer contains exclusively terminal segments of longer chains. The boundary between sublayers is enriched with counterions that neutralize the residual charge of the proximal sublayer. These analytical predictions for binary brushes are confirmed and extended to ternary brushes using the numerical Scheutjens-Fleer approach.

Aggrecan-like biomimetic proteoglycans (BPGs) composed of natural chondroitin sulfate bristles grafted onto a poly(acrylic acid) core for molecular engineering of the extracellular matrix

Biomimetic proteoglycans (BPGs) were designed to mimic the three-dimensional (3D) bottlebrush architecture of natural extracellular matrix (ECM) proteoglycans, such as aggrecan. BPGs were synthesized by grafting native chondroitin sulfate bristles onto a synthetic poly(acrylic acid) core to form BPGs at a molecular weight of approximately ∼1.6 MDa. The aggrecan mimics were characterized chemically, physically, and structurally, confirming the 3D bottlebrush architecture as well as a level of water uptake, which is greater than that of the natural proteoglycan, aggrecan. Aggrecan mimics were cytocompatible at physiological concentrations. Fluorescently labeled BPGs were injected into the nucleus pulposus of the intervertebral disc ex vivo and were retained in tissue before and after static loading and equilibrium conditioning. BPGs infiltrated the tissue, distributed and integrated with the ECM on a molecular scale, in the absence of a bolus, thus demonstrating a new molecular approach to tissue repair: molecular matrix engineering. Molecular matrix engineering may compliment or offer an acellular alternative to current regenerative medicine strategies.

STATEMENT OF SIGNIFICANCE

Aggrecan is a natural biomolecule that is essential for connective tissue hydration and mechanics. Aggrecan is composed of negatively charged chondroitin sulfate bristles attached to a protein core in a bottlebrush configuration. With age and degeneration, enzymatic degradation of aggrecan outpaces cellular synthesis resulting in a loss of this important molecule. We demonstrate a novel biomimetic molecule composed of natural chondroitin sulfate bristles grafted onto an enzymatically-resistant synthetic core. Our molecule mimics a 3D architecture and charge density of the natural aggrecan, can be delivered via a simple injection and is retained in tissue after equilibrium conditioning and loading. This novel material can serve as a platform for molecular repair, drug delivery and tissue engineering in regenerative medicine approaches.

Genome-wide profiling of adult human papillary and reticular fibroblasts identifies ACAN, Col XI α1, and PSG1 as general biomarkers of dermis ageing, and KANK4 as an exemplary effector of papillary fibroblast ageing, related to contractility

Deciphering the characteristics of dermal fibroblasts is critical to further understand skin ageing. We have conducted a genome-wide transcriptomic characterization of papillary (Fp) and reticular (Fr) fibroblasts extracted from human skin samples corresponding to younger and older adult ages. From this screen, biomarkers suitable for the assessment of chronological ageing were identified, and extrapolated to the context of photo-damaged skin. In particular, KANK4, ACAN, Col XI α1, and PSG1, were expressed at an increased level in both chronologically-aged and photo-damaged skin. Notably, analysis focused on Fp identified significant transcriptional signatures associated with ageing, which included transcripts related to extracellular matrix, focal adhesion points, and cytoskeleton, thus suggesting functional consequences on tissue structure. At a cellular level, an increased contractility was identified as a property of aged Fp. Accordingly, further investigations were conducted on the KN motif and ankyrin repeat-containing protein 4 (KANK4) to explore its possible function as an original effector involved in the acquisition of aged properties in Fp, notably their increased contractility. We show that KANK4 down-modulation using siRNA led to increased Rho pathway activity, thereby reducing their contractility. As a proof-of-principle, the present study shows that targeting KANK4 was efficient to attenuate aged Fp characteristics.

Effects of spaceflight on cartilage: implications on spinal physiology

Spaceflight alters normal physiology of cells and tissues observed on Earth. The effects of spaceflight on the musculoskeletal system have been thoroughly studied, however, the effects on cartilage have not. This area is gaining more relevance as long duration missions, such as Mars, are planned. The impact on intervertebral discs and articular cartilage are of particular interest to astronauts and their physicians. This review surveys the literature and reports on the current body of knowledge regarding the effects of spaceflight on cartilage, and specifically changes to the spine and intervertebral disc integrity and physiology. A systematic literature review was conducted using PubMed, MEDLINE, and Google Scholar. Eighty-six unique papers were identified, 15 of which were included. The effect of spaceflight on cartilage is comprehensively presented due to limited research on the effect of microgravity on the spine/intervertebral discs. Cellular, animal, and human studies are discussed, focusing on human physiologic changes, cartilage histology, mineralization, biomechanics, chondrogenesis, and tissue engineering. Several common themes were found, such as decreased structural integrity of intervertebral disks and impaired osteogenesis/ossification. However, studies also presented conflicting results, rendering strong conclusions difficult. The paucity of human cartilage studies in spaceflight leaves extrapolation from other model systems the only current option for drawing conclusions despite known and unknown limitations in applicability to human physiology, especially spinal pathophysiology which is special interest. The aerospace and biomedical research communities would benefit from further human spaceflight articular cartilage and intervertebral disc studies. Further research may yield beneficial application for spaceflight, and crossover in understanding and treating terrestrial diseases like osteoarthritis and vertebral disc degeneration.

Salmon Calcitonin Attenuates Degenerative Changes in Cartilage and Subchondral Bone in Lumbar Facet Joint in an Experimental Rat Model

Background

Facet joint degeneration (FJD) is one of the common causes of low back pain (LBP), and estrogen deficiency is one of the triggers for FJD. Calcitonin may possess the potential for treating osteoarthritis, but to date the hormone has not been studied in the treatment of FJD. Therefore, the aim of this study was to investigate the effects of salmon calcitonin (sCT) on FJD induced by estrogen deficiency after ovariectomy (OVX).

Material/Methods

Thirty female Sprague-Dawley rats were randomly assigned to 3 groups: the OVX group received bilateral OVX, the OVX + sCT group received subcutaneous administration of sCT (16 IU/kg/2 days) following bilateral OVX, and the Sham group received sham surgery. All rats were euthanized at 12 weeks post-OVX. Serum COMP level, cartilage degradation, and subchondral bone micro-architecture were evaluated.

Results

sCT relieved cartilage surface lesions, reduced histological score, and significantly increased cartilage thickness. The OVX + sCT group exhibited significantly increased expression of aggrecan, as well as significantly decreased levels of ADAMTS-4, MMP-13, and caspase-3. The results of micro-computed tomography analysis revealed that the OVX + sCT group exhibited higher BMD, BV/TV, and Tb.Th values but a lower Tb.Sp value than that of the OVX group. Serum COMP concentrations were significantly correlated with histological score and cartilage thickness.

Conclusions

sCT can inhibit the progression of FJD in OVX rats, which is attributed to its inhibitory effects on cartilage metabolism imbalance, chondrocyte apoptosis, and subchondral bone remodeling. Serum COMP has diagnostic potential for FJD.

Microscale mapping of extracellular matrix elasticity of mouse joint cartilage: an approach to extracting bulk elasticity of soft matter with surface roughness

Cartilage is composed of cells and an extracellular matrix, the latter being a composite of a collagen mesh interpenetrated by proteoglycans responsible for tissue osmotic swelling. The matrix composition and structure vary through the tissue depth. Mapping such variability requires tissue sectioning to gain access. The resulting surface roughness, and concomitant proteoglycan loss contribute to large uncertainties in elastic modulus estimates. To extract elasticity values for the bulk matrix which are not obfuscated by the indeterminate surface layer, we developed a novel experimental and data analysis methodology. We analyzed the surface roughness to optimize the probe size, and performed high-resolution (1 μm) elasticity mapping on thin (∼12 μm), epiphyseal newborn mouse cartilage sections cut parallel to the bone longitudinal axis or normal to the articular surface. Mild fixation prevented the major proteoglycan loss observed in unfixed specimens but not the stress release that resulted in thickness changes in the sectioned matrix. Our novel data analysis method introduces a virtual contact point as a fitting parameter for the Hertz model, to minimize the effects of surface roughness and corrects for the finite section thickness. Our estimates of cartilage elasticity converge with increasing indentation depth and, unlike previous data interpretations, are consistent with linearly elastic material. A high cell density that leaves narrow matrix septa between cells may cause the underestimation of elastic moduli, whereas fixation probably causes an overestimation. The proposed methodology has broader relevance to nano- and micro-indentation of soft materials with multiple length scales of organization and whenever surface effects (including roughness, electrostatics, van der Waals forces, etc.) become significant.

Keratan sulfate, a complex glycosaminoglycan with unique functional capability

From an evolutionary perspective keratan sulfate (KS) is the newest glycosaminoglycan (GAG) but the least understood. KS is a sophisticated molecule with a diverse structure, and unique functional roles continue to be uncovered for this GAG. The cornea is the richest tissue source of KS in the human body but the central and peripheral nervous systems also contain significant levels of KS and a diverse range of KS-proteoglycans with essential functional roles. KS also displays important cell regulatory properties in epithelial and mesenchymal tissues and in bone and in tumor development of diagnostic and prognostic utility. Corneal KS-I displays variable degrees of sulfation along the KS chain ranging from non-sulfated polylactosamine, mono-sulfated and disulfated disaccharide regions. Skeletal KS-II is almost completely sulfated consisting of disulfated disaccharides interrupted by occasional mono-sulfated N-acetyllactosamine residues. KS-III also contains highly sulfated KS disaccharides but differs from KS-I and KS-II through 2-O-mannose linkage to serine or threonine core protein residues on proteoglycans such as phosphacan and abakan in brain tissue. Historically, the major emphasis on the biology of KS has focused on its sulfated regions for good reason. The sulfation motifs on KS convey important molecular recognition information and direct cell behavior through a number of interactive proteins. Emerging evidence also suggest functional roles for the poly-N-acetyllactosamine regions of KS requiring further investigation. Thus further research is warranted to better understand the complexities of KS.

Giantin is required for coordinated production of aggrecan, link protein and type XI collagen during chondrogenesis

Extracellular matrix (ECM) constitutes a proper micro-environment for cell proliferation, migration and differentiation, as well as playing pivotal roles in developmental processes including endochondral ossification. Cartilage ECM is mainly composed of fibrous proteins, including collagen, proteoglycan, and hyaluronan. Because almost all ECM components are transported by intracellular vesicular transport systems, molecules that mediate vesicle transport are also important for endochondral ossification. Giantin, encoded by the Golgb1 gene, is a tethering factor for coatomer 1 (COPI) vesicles and functions in the cis-medial Golgi compartments. An insertion mutation in the Golgb1 gene, resulting in a lack of giantin protein expression, has been detected in ocd/ocd rats that exhibit a pleiotropic phenotype including osteochondrodysplasia. To reveal the function of giantin in chondrogenesis, the present study assessed the effects of loss of giantin expression on cartilage ECM and Golgi morphology. Giantin was expressed in normal, but not in ocd/ocd, chondrocytes in the epiphyseal areas of embryonic femurs, whereas GM130 was expressed in both normal and ocd/ocd chondrocytes. The staining intensities of safranin O and azan (aniline blue) were reduced and enhanced, respectively, in epiphyseal cartilage of ocd/ocd femurs. Immunostaining showed that levels of type II collagen and fibronectin were comparable in normal and ocd/ocd cartilage. Levels of type XI collagen were higher, while levels of aggrecan, link protein and hyaluronan were lower, in ocd/ocd than in normal cartilage, although semi-quantitative RT-PCR showed similar levels of type XI collagen, aggrecan and link protein mRNAs in normal and ocd/ocd cartilage. Isolated chondrocytes of ocd/ocd and normal rats showed similar immunostaining patterns for cis-, medial-, and trans-Golgi marker proteins, whereas monolayers of ocd/ocd chondrocytes showed reduced levels of aggrecan and link protein and increased level of type XI collagen in spite of similar transcripts levels. These findings suggest that giantin plays a pivotal role in coordinated production of aggrecan, link protein and type XI collagen in chondrocytes, and that loss of giantin causes osteochondrodysplasia with disturbance of these ECM components.

Glucose enhances aggrecan expression in chondrocytes via the PKCα/p38-miR141-3p signaling pathway

Aggrecan is a high molecular weight proteoglycan that plays a critical role in cartilage structure and the function of joints, providing intervertebral disc and cartilage with the ability to resist compressive loads. Aggrecan degradation in articular cartilage is a significant event in early-stage osteoarthritis (OA). Currently, no effective treatment exists for OA other than pain relief. Dextrose (D-glucose) prolotherapy has shown promising activity in the treatment of different musculoskeletal disorders, including OA. However, little is known about the molecular mechanism of the glucose effect in OA and on the regulation of chondrogenesis. We show for the first time that glucose upregulates aggrecan expression and subsequent chondrogenesis in ATDC5 cells. Moreover, we found that glucose-induced aggrecan expression is mediated through the protein kinase Cα (PKCα)- and p38-dependent pathway. As demonstrated by microRNA (miR) and luciferase analyses, the glucose-induced PKCα/p38 signaling axis is responsible for downregulating miR141-3p which targets to the 3'untranslated region of aggrecan. In summary, we show that glucose enhances chondrogenesis by upregulating aggrecan expression via the PKCα-p38-miR141-3p signaling pathway. This result provides new insights into the mechanism of glucose on chondrogenesis.

Massive aggrecan and versican accumulation in thoracic aortic aneurysm and dissection

Proteoglycan accumulation is a hallmark of medial degeneration in thoracic aortic aneurysm and dissection (TAAD). Here, we defined the aortic proteoglycanome using mass spectrometry, and based on the findings, investigated the large aggregating proteoglycans aggrecan and versican in human ascending TAAD and a mouse model of severe Marfan syndrome. The aortic proteoglycanome comprises 20 proteoglycans including aggrecan and versican. Antibodies against these proteoglycans intensely stained medial degeneration lesions in TAAD, contrasting with modest intralamellar staining in controls. Aggrecan, but not versican, was increased in longitudinal analysis of Fbn1mgR/mgR aortas. TAAD and Fbn1mgR/mgR aortas had increased aggrecan and versican mRNAs, and reduced expression of a key proteoglycanase gene, ADAMTS5, was seen in TAAD. Fbn1mgR/mgR mice with ascending aortic dissection and/or rupture had dramatically increased aggrecan staining compared with mice without these complications. Thus, aggrecan and versican accumulation in ascending TAAD occurs via increased synthesis and/or reduced proteolytic turnover, and correlates with aortic dissection/rupture in Fbn1mgR/mgR mice. Tissue swelling imposed by aggrecan and versican is proposed to be profoundly deleterious to aortic wall mechanics and smooth muscle cell homeostasis, predisposing to type-A dissections. These proteoglycans provide potential biomarkers for refined risk stratification and timing of elective aortic aneurysm repair.

Effects of mechanical loading on human mesenchymal stem cells for cartilage tissue engineering

Today, articular cartilage damage is a major health problem, affecting people of all ages. The existing conventional articular cartilage repair techniques, such as autologous chondrocyte implantation (ACI), microfracture, and mosaicplasty, have many shortcomings which negatively affect their clinical outcomes. Therefore, it is essential to develop an alternative and efficient articular repair technique that can address those shortcomings. Cartilage tissue engineering, which aims to create a tissue-engineered cartilage derived from human mesenchymal stem cells (MSCs), shows great promise for improving articular cartilage defect therapy. However, the use of tissue-engineered cartilage for the clinical therapy of articular cartilage defect still remains challenging. Despite the importance of mechanical loading to create a functional cartilage has been well demonstrated, the specific type of mechanical loading and its optimal loading regime is still under investigation. This review summarizes the most recent advances in the effects of mechanical loading on human MSCs. First, the existing conventional articular repair techniques and their shortcomings are highlighted. The important parameters for the evaluation of the tissue-engineered cartilage, including chondrogenic and hypertrophic differentiation of human MSCs are briefly discussed. The influence of mechanical loading on human MSCs is subsequently reviewed and the possible mechanotransduction signaling is highlighted. The development of non-hypertrophic chondrogenesis in response to the changing mechanical microenvironment will aid in the establishment of a tissue-engineered cartilage for efficient articular cartilage repair.

A method for characterising human intervertebral disc glycosaminoglycan disaccharides using liquid chromatography-mass spectrometry with multiple reaction monitoring

Intervertebral disc (IVD) degeneration results in the depletion of proteoglycans and glycosaminoglycans (GAGs), which can lead to structural and mechanical loss of IVD function, ingrowth of nociceptive nerve fibres and eventually discogenic pain. Specific GAG types as well as their disaccharide patterns can be predictive of disease and degeneration in several tissues but have not been comprehensively studied within the IVD. A highly sensitive mass spectrometry based technique with multiple reaction monitoring (MRM) was used to provide characterisation of chondroitin sulphate (CS), hyaluronic acid (HA), heparan sulphate (HS) and their disaccharide sulphation patterns across different anatomical regions of human IVDs. Principal component analysis further distinguished important regional variations and proposed potential ageing variations in GAG profiles. CS was the GAG in greatest abundance in the IVD followed by HA and HS. Principal component analysis identified clear separation of GAG profiles between nucleus pulposus and annulus fibrosus in young and old specimens. Distinct patterns of predominantly expressed disaccharides of CS and HS between young and old IVD samples, provided preliminary evidence that important alterations in disaccharides occur within IVDs during ageing. This technique offered a novel approach to identify and quantify specific GAG disaccharides in human IVDs and the data presented were the first to offer insight into the spatial distribution as well as association with ageing of GAGs and GAG disaccharide sulphation patterns across the human IVD.

The altered expression of perineuronal net elements during neural differentiation

Background

Perineuronal nets (PNNs), which are localized around neurons during development, are specialized forms of neural extracellular matrix with neuroprotective and plasticity-regulating roles. Hyaluronan and proteoglycan link protein 1 (HAPLN1), tenascin-R (TNR) and aggrecan (ACAN) are key elements of PNNs. In diseases characterized by neuritogenesis defects, the expression of these proteins is known to be downregulated, suggesting that PNNs may have a role in neural differentiation.

Methods

In this study, the mRNA and protein levels of HAPLN1, TNR and ACAN were determined and compared at specific time points of neural differentiation. We used PC12 cells as the in vitro model because they reflect this developmental process.

Results

On day 7, the HAPLN1 mRNA level showed a 2.9-fold increase compared to the non-differentiated state. However, the cellular HAPLN1 protein level showed a decrease, indicating that the protein may have roles in neural differentiation, and may be secreted during the early period of differentiation. By contrast, TNR mRNA and protein levels remained unchanged, and the amount of cellular ACAN protein showed a 3.7-fold increase at day 7. These results suggest that ACAN may be secreted after day 7, possibly due to its large amount of post-translational modifications.

Conclusions

Our results provide preliminary data on the expression of PNN elements during neural differentiation. Further investigations will be performed on the role of these elements in neurological disease models.

Biodiversity of CS–proteoglycan sulphation motifs: chemical messenger recognition modules with roles in information transfer, control of cellular behaviour and tissue morphogenesis

Chondroitin sulphate (CS) glycosaminoglycan chains on cell and extracellular matrix proteoglycans (PGs) can no longer be regarded as merely hydrodynamic space fillers. Overwhelming evidence over recent years indicates that sulphation motif sequences within the CS chain structure are a source of significant biological information to cells and their surrounding environment. CS sulphation motifs have been shown to interact with a wide variety of bioactive molecules, e.g. cytokines, growth factors, chemokines, morphogenetic proteins, enzymes and enzyme inhibitors, as well as structural components within the extracellular milieu. They are therefore capable of modulating a panoply of signalling pathways, thus controlling diverse cellular behaviours including proliferation, differentiation, migration and matrix synthesis. Consequently, through these motifs, CS PGs play significant roles in the maintenance of tissue homeostasis, morphogenesis, development, growth and disease. Here, we review (i) the biodiversity of CS PGs and their sulphation motif sequences and (ii) the current understanding of the signalling roles they play in regulating cellular behaviour during tissue development, growth, disease and repair.

Genomic Analysis Revealed New Oncogenic Signatures in TP53-Mutant Hepatocellular Carcinoma

The TP53 gene is the most commonly mutated gene in human cancers and mutations in TP53 have been shown to have either gain-of-function or loss-of-function effects. Using the data generated by The Cancer Genome Atlas, we sought to define the spectrum of TP53 mutations in hepatocellular carcinomas (HCCs) and their association with clinicopathologic features, and to determine the oncogenic and mutational signatures in TP53-mutant HCCs. Compared to other cancer types, HCCs harbored distinctive mutation hotspots at V157 and R249, whereas common mutation hotspots in other cancer types, R175 and R273, were extremely rare in HCCs. In terms of clinicopathologic features, in addition to the associations with chronic viral infection and high Edmondson grade, we found that TP53 somatic mutations were less frequent in HCCs with cholestasis or tumor infiltrating lymphocytes, but were more frequent in HCCs displaying necrotic areas. An analysis of the oncogenic signatures based on the genetic alterations found in genes recurrently altered in HCCs identified four distinct TP53-mutant subsets, three of which were defined by CTNNB1 mutations, 1q amplifications or 8q24 amplifications, respectively, that co-occurred with TP53 mutations. We also found that mutational signature 12, a liver cancer-specific signature characterized by T>C substitutions, was prevalent in HCCs with wild-type TP53 or with missense TP53 mutations, but not in HCCs with deleterious TP53 mutations. Finally, whereas patients with HCCs harboring deleterious TP53 mutations had worse overall and disease-free survival than patients with TP53-wild-type HCCs, patients with HCCs harboring missense TP53 mutations did not have worse prognosis. In conclusion, our results highlight the importance to consider the genetic heterogeneity among TP53-mutant HCCs in studies of biomarkers and molecular characterization of HCCs.

Differential tissue specific, temporal and spatial expression patterns of the Aggrecan gene is modulated by independent enhancer elements

The transcriptional mechanism through which chondrocytes control the spatial and temporal composition of the cartilage tissue has remained largely elusive. The central aim of this study was to identify whether transcriptional enhancers played a role in the organisation of the chondrocytes in cartilaginous tissue. We focused on the Aggrecan gene (Acan) as it is essential for the normal structure and function of cartilage and it is expressed developmentally in different stages of chondrocyte maturation. Using transgenic reporter studies in mice we identified four elements, two of which showed individual chondrocyte developmental stage specificity. In particular, one enhancer (-80) distinguishes itself from the others by being predominantly active in adult cartilage. Furthermore, the -62 element uniquely drove reporter activity in early chondrocytes. The remaining chondrocyte specific enhancers, +28 and -30, showed no preference to chondrocyte type. The transcription factor SOX9 interacted with all the enhancers in vitro and mutation of SOX9 binding sites in one of the enhancers (-30) resulted in a loss of its chondrocyte specificity and ectopic enhancer reporter activity. Thus, the Acan enhancers orchestrate the precise spatiotemporal expression of this gene in cartilage types at different stages of development and adulthood.

Construction of Multivalent Homo- and Heterofunctional ABO Blood Group Glycoconjugates Using a Trifunctional Linker Strategy

The design and synthesis of multivalent ligands displaying complex oligosaccharides is necessary for the development of therapeutics, diagnostics, and research tools. Here, we report an efficient conjugation strategy to prepare complex glycoconjugates with 4 copies of 1 or 2 separate glycan epitopes, providing 4-8 carbohydrate residues on a tetravalent poly(ethylene glycol) scaffold. This strategy provides complex glycoconjugates that approach the size of glycoproteins (15-18 kDa) while remaining well-defined. The synthetic strategy makes use of three orthogonal functional groups, including a reactive N-hydroxysuccinimide (NHS)-ester moiety on the linker to install the first carbohydrate epitope via reaction with an amine. A masked amine functionality on the linker is revealed after the removal of a fluorenylmethyloxycarbonyl (Fmoc)-protecting group, allowing the attachment to the NHS-activated poly(ethylene glycol) (PEG) scaffold. An azide group in the linker was then used to incorporate the second carbohydrate epitope via catalyzed alkyne-azide cycloaddition. Using a known tetravalent PEG scaffold (PDI, 1.025), we prepared homofunctional glycoconjugates that display four copies of lactose and the A-type II or the B-type II human blood group antigens. Using our trifunctional linker, we expanded this strategy to produce heterofunctional conjugates with four copies of two separate glycan epitopes. These heterofunctional conjugates included Neu5Ac, 3'-sialyllactose, or 6'-sialyllactose as a second antigen. Using an alternative strategy, we generated heterofunctional conjugates with three copies of the glycan epitope and one fluorescent group (on average) using a sequential dual-amine coupling strategy. These conjugation strategies should be easily generalized for conjugation of other complex glycans. We demonstrate that the glycan epitopes of heterofunctional conjugates engage and cluster target B-cell receptors and CD22 receptors on B cells, supporting the application of these reagents for investigating cellular response to carbohydrate antigens of the ABO blood group system.

Downregulation of Heat Shock Protein 70 Impairs Osteogenic and Chondrogenic Differentiation in Human Mesenchymal Stem Cells

Human mesenchymal stem cells (hMSCs) show promise for bone and cartilage regeneration. Our previous studies demonstrated that hMSCs with periodic mild heating had enhanced osteogenic and chondrogenic differentiation with significantly upregulated heat shock protein 70 (HSP70). However, the role of HSP70 in adult tissue regeneration is not well studied. Here, we revealed an essential regulatory mechanism of HSP70 in osteogenesis and chondrogenesis using adult hMSCs stably transfected with specific shRNAs to knockdown HSP70. Periodic heating at 39 °C was applied to hMSCs for up to 26 days. HSP70 knockdown resulted in significant reductions of alkaline phosphatase activity, calcium deposition, and gene expression of Runx2 and Osterix during osteogenesis. In addition, knockdown of HSP70 led to significant decreases of collagens II and X during chondrogenesis. Thus, downregulation of HSP70 impaired hMSC osteogenic and chondrogenic differentiation as well as the enhancement of these processes by thermal treatment. Taken together, these findings suggest a putative mechanism of thermal-enhanced bone and cartilage formation and underscore the importance of HSP70 in adult bone and cartilage differentiation.

Harnessing chondroitin sulphate in composite scaffolds to direct progenitor and stem cell function for tissue repair

This review details the inclusion of chondroitin sulphate in bioscaffolds for superior functional properties in tissue regenerative applications.

Genomic and transcriptomic heterogeneity in metaplastic carcinomas of the breast

Metaplastic breast cancer (MBC) is a rare special histologic type of triple-negative breast cancer, characterized by the presence of neoplastic cells showing differentiation towards squamous epithelium and/or mesenchymal elements. Here we sought to define whether histologically distinct subgroups of MBCs would be underpinned by distinct genomic and/or transcriptomic alterations. Microarray-based copy number profiling identified limited but significant differences between the distinct MBC subtypes studied here, despite the limited sample size (n = 17). In particular, we found that, compared to MBCs with chondroid or squamous cell metaplasia, MBCs with spindle cell differentiation less frequently harbored gain of 7q11.22-23 encompassing CLDN3 and CLDN4, consistent with their lower expression of claudins and their association with the claudin-low molecular classification. Microarray-based and RNA-sequencing-based gene expression profiling revealed that MBCs with spindle cell differentiation differ from MBCs with chondroid or squamous cell metaplasia on the expression of epithelial-to-mesenchymal transition-related genes, including down-regulation of CDH1 and EPCAM. In addition, RNA-sequencing revealed that the histologic patterns observed in MBCs are unlikely to be underpinned by a highly recurrent expressed fusion gene or a pathognomonic expressed mutation in cancer genes. Loss of PTEN expression or mutations affecting PIK3CA or TSC2 observed in 8/17 MBCs support the contention that PI3K pathway activation plays a role in the development of MBCs. Our data demonstrate that despite harboring largely similar patterns of gene copy number alterations, MBCs with spindle cell, chondroid and squamous differentiation are distinct at the transcriptomic level but are unlikely to be defined by specific pathognomonic genetic alterations.

Lysophosphatidylcholine acyltransferase 4 is involved in chondrogenic differentiation of ATDC5 cells

Glycerophospholipids have important structural and functional roles in cells and are the main components of cellular membranes. Glycerophospholipids are formed via the de novo pathway (Kennedy pathway) and are subsequently matured in the remodeling pathway (Lands’ cycle). Lands’ cycle consists of two steps: deacylation of phospholipids by phospholipases A₂ and reacylation of lysophospholipids by lysophospholipid acyltransferases (LPLATs). LPLATs play key roles in the maturation and maintenance of the fatty acid composition of biomembranes, and cell differentiation. We examined whether LPLATs are involved in chondrogenic differentiation of ATDC5 cells, which can differentiate into chondrocytes. Lysophosphatidylcholine acyltransferase 4 (LPCAT4) mRNA expression and LPCAT enzymatic activity towards 18:1-, 18:2-, 20:4-, and 22:6-CoA increased in the late stage of chondrogenic differentiation, when mineralization occurred. LPCAT4 knockdown decreased mRNA and protein levels of chondrogenic markers as well as Alcian blue staining intensity and alkaline phosphatase activity in ATDC5 cells. These results suggest that LPCAT4 plays important roles during the transition of chondrocytes into hypertrophic chondrocytes and/or a mineralized phenotype.

Sequencing the Dermatan Sulfate Chain of Decorin

Glycomics represents one of the last frontiers and most challenging in omic analysis. Glycosylation occurs in the endoplasmic reticulum and the Golgi organelle and its control is neither well-understood nor predictable based on proteomic or genomic analysis. One of the most structurally complex classes of glycoconjugates is the proteoglycans (PGs) and their glycosaminoglycan (GAG) side chains. Previously, our laboratory solved the structure of the chondroitin sulfate chain of the bikunin PG. The current study examines the much more complex structure of the dermatan sulfate GAG chain of decorin PG. By utilizing sophisticated separation methods followed by compositional analysis, domain mapping, and tandem mass spectrometry coupled with analysis by a modified genetic algorithm approach, the structural motif for the decorin dermatan sulfate chain was determined. This represents the second example of a GAG with a prominent structural motif, suggesting that the structural variability of this class of glycoconjugates is somewhat simpler than had been expected.