Differential proteome analysis of normal and osteoarthritic chondrocytes reveals distortion of vimentin network in osteoarthritis

Characterization of EpCAM in thyroid cancer biology by three-dimensional spheroids in vitro model

BACKGROUND

Thyroid cancer (TC) is the most common endocrine malignancy. Nowadays, undifferentiated thyroid cancers (UTCs) are still lethal, mostly due to the insurgence of therapy resistance and disease relapse. These events are believed to be caused by a subpopulation of cancer cells with stem-like phenotype and specific tumor-initiating abilities, known as tumor-initiating cells (TICs). A comprehensive understanding of how to isolate and target these cells is necessary. Here we provide insights into the role that the protein Epithelial Cell Adhesion Molecule (EpCAM), a known TICs marker for other solid tumors, may have in TC biology, thus considering EpCAM a potential marker of thyroid TICs in UTCs.

METHODS

The characterization of EpCAM was accomplished through Western Blot and Immunofluorescence on patient-derived tissue samples, adherent cell cultures, and 3D sphere cultures of poorly differentiated thyroid cancer (PDTC) and anaplastic thyroid cancer (ATC) cell lines. The frequency of tumor cells with putative tumor-initiating ability within the 3D cultures was assessed through extreme limiting dilution analysis (ELDA). EpCAM proteolytic cleavages were studied through treatments with different cleavages' inhibitors. To evaluate the involvement of EpCAM in inducing drug resistance, Vemurafenib (PLX-4032) treatments were assessed through MTT assay.

RESULTS

Variable EpCAM expression pattern was observed in TC tissue samples, with increased cleavage in the more UTC. We demonstrated that EpCAM is subjected to an intense cleavage process in ATC-derived 3D tumor spheres and that the 3D model faithfully mimics what was observed in patient's samples. We also proved that the integrity of the protein appears to be crucial for the generation of 3D spheres, and its expression and cleavage in a 3D system could contribute to drug resistance in thyroid TICs.

CONCLUSIONS

Our data provide novel information on the role of EpCAM expression and cleavage in the biology of thyroid TICs, and our 3D model reflects the variability of EpCAM cleavage observed in tissue samples. EpCAM evaluation could play a role in clinical decisions regarding patient therapy since its expression and cleavage may have a fundamental role in the switch to a drug-resistant phenotype of UTC cells.

Control of articular degeneration by extracellular vesicles from stem/stromal cells as a potential strategy for the treatment of osteoarthritis

Osteoarthritis (OA) is a degenerative joint condition that contributes to years lived with disability. Current therapeutic approaches are limited as there are no disease-modifying interventions able to delay or inhibit the progression of disease. In recent years there has been an increasing interest in the immunomodulatory and regenerative properties of mesenchymal stem/stromal cells (MSCs) to develop new OA therapies. Extracellular vesicles (EVs) mediate many of the biological effects of these cells and may represent an alternative avoiding the limitations of cell-based therapy. There is also a growing interest in EV modifications to enhance their efficacy and applications. Recent preclinical studies have provided strong evidence supporting the potential of MSC EVs for the development of OA treatments. Thus, MSC EVs may regulate chondrocyte functions to avoid cartilage destruction, inhibit abnormal subchondral bone metabolism and synovial tissue alterations, and control pain behavior. EV actions may be mediated by the transfer of their cargo to target cells, with an important role for proteins and non-coding RNAs modulating signaling pathways relevant for OA progression. Nevertheless, additional investigations are needed concerning EV optimization, and standardization of preparation procedures. More research is also required for a better knowledge of possible effects on different OA phenotypes, pharmacokinetics, mechanism of action, long-term effects and safety profile. Furthermore, MSC EVs have a high potential as vehicles for drug delivery or as adjuvant therapy to potentiate or complement the effects of other approaches.

Synovial Fluid Proteomics From Serial Aspirations of ACL-Injured Knees Identifies Candidate Biomarkers

BACKGROUND

Anterior cruciate ligament (ACL) tears often result in knee effusion and an increased risk for developing knee osteoarthritis (OA) in the long run. The molecular profile of these effusions could be informative regarding initial steps in the development of posttraumatic OA after an ACL tear.

HYPOTHESIS

The proteomics of knee synovial fluid changes over time after ACL injury.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Synovial fluid was collected from patients with an acute traumatic ACL tear presenting to the office for evaluation (18.31 ± 19.07 days from injury) (aspiration 1) and again at the time of surgery (35.41 ± 58.15 days after aspiration 1 (aspiration 2). High-resolution liquid chromatography mass spectrometry was used to assess the quantitative protein profile of synovial fluid, and differences in protein profile between the 2 aspirations were determined computationally.

RESULTS

A total of 58 synovial fluid samples collected from 29 patients (12 male, 17 female; 12 isolated ACL tear, 17 combined ACL and meniscal tear) with a mean age and body mass index of 27.01 ± 12.78 years and 26.30 ± 4.93, respectively, underwent unbiased proteomics analysis. The levels of 130 proteins in the synovial fluid changed over time (87 high, 43 low). Proteins of interest that were significantly higher in aspiration 2 included CRIP1, S100A11, PLS3, POSTN, and VIM, which represent catabolic/inflammatory activities in the joint. Proteins with a known role in chondroprotection and joint homeostasis such as CHI3L2 (YKL-39), TNFAIP6/TSG6, DEFA1, SPP1, and CILP were lower in aspiration 2.

CONCLUSION

Synovial fluid from knees with ACL tears exhibits an increased burden of inflammatory (catabolic) proteins relevant to OA with reduced levels of chondroprotective (anabolic) proteins.

CLINICAL RELEVANCE

This study identified a set of novel proteins that provide new biological insights into the aftermath of ACL tears. Elevated inflammation and decreased chondroprotection could represent initial disruption of homeostasis, potentially initiating the development of OA. Longitudinal follow-up and mechanistic studies are necessary to assess the functional role of these proteins in the joint. Ultimately, these investigations could lead to better approaches to predict and possibly improve patient outcomes.

In Vitro Models and Proteomics in Osteoarthritis Research

This review summarizes and exemplifies the current understanding of osteoarthritis in vitro models and describes their relevance for new insights in the future of osteoarthritis research. Our friend and highly appreciated colleague, Prof. Alan Grodzinsky has contributed greatly to the understanding of joint tissue biology and cartilage biomechanics. He frequently utilizes in vitro models and cartilage explant cultures, and recent work also includes proteomics studies. This review is dedicated to honor his 75-year birthday and will focus on recent proteomic in vitro studies related to osteoarthritis, and within this topic highlight some of his contributions to the field.

Tissue-Specific Methylation Biosignatures for Monitoring Diseases: An In Silico Approach

Tissue-specific gene methylation events are key to the pathogenesis of several diseases and can be utilized for diagnosis and monitoring. Here, we established an in silico pipeline to analyze high-throughput methylome datasets to identify specific methylation fingerprints in three pathological entities of major burden, i.e., breast cancer (BrCa), osteoarthritis (OA) and diabetes mellitus (DM). Differential methylation analysis was conducted to compare tissues/cells related to the pathology and different types of healthy tissues, revealing Differentially Methylated Genes (DMGs). Highly performing and low feature number biosignatures were built with automated machine learning, including: (1) a five-gene biosignature discriminating BrCa tissue from healthy tissues (AUC 0.987 and precision 0.987), (2) three equivalent OA cartilage-specific biosignatures containing four genes each (AUC 0.978 and precision 0.986) and (3) a four-gene pancreatic β-cell-specific biosignature (AUC 0.984 and precision 0.995). Next, the BrCa biosignature was validated using an independent ccfDNA dataset showing an AUC and precision of 1.000, verifying the biosignature’s applicability in liquid biopsy. Functional and protein interaction prediction analysis revealed that most DMGs identified are involved in pathways known to be related to the studied diseases or pointed to new ones. Overall, our data-driven approach contributes to the maximum exploitation of high-throughput methylome readings, helping to establish specific disease profiles to be applied in clinical practice and to understand human pathology.

Proteomic analysis of human articular cartilage unravels the dyscoagulation in osteoarthritis and the potential value of serpinA5 as a biomarker for osteoarthritis

PURPOSE

Nowadays, there is no clinically applicable biomarker for osteoarthritis (OA). Therefore, the aim of the study is to discover a potential biomarker for OA.

EXPERIMENTAL DESIGN

We performed a proteomics of eight cartilage samples (four damaged cartilage and four macroscopically intact cartilage) from four OA patients without any comorbidities to search for valuable OA biomarkers. Four rats underwent bilateral ovariectomy to induce the OA (OVX-OA) model, while another four underwent a sham procedure wherein the ovaries were exteriorized but not removed (SHAM). Selected candidate proteins were further verified in the patients and the OVX-OA animal model.

RESULTS

A comprehensive cartilage proteome profile of patients with OA was constructed. Additionally, the complement and coagulation cascades were found to be significantly altered, and serpinA5 was chosen as a protein of interest based on biological information analysis. The reduction of serpinA5 in locally damaged cartilage and serum of patients with OA compared to the control group was determined. Furthermore, we found that serpinA5 was decreased in OVX-OA rats compared to that in SHAM rats.

CONCLUSIONS AND CLINICAL RELEVANCE

Our results suggest that there is dyscoagulation in the OA process and that serpinA5 can serve as a potentially valuable OA biomarker.

Role of peroxiredoxin 6 in the chondroprotective effects of microvesicles from human adipose tissue-derived mesenchymal stem cells

Background

Osteoarthritis (OA) is a joint disease characterized by cartilage degradation, low-grade synovitis and subchondral bone alterations. In the damaged joint, there is a progressive increase of oxidative stress leading to disruption of chondrocyte homeostasis. The modulation of oxidative stress could control the expression of inflammatory and catabolic mediators involved in OA. We have previously demonstrated that extracellular vesicles (EVs) present in the secretome of human mesenchymal stem cells from adipose tissue (AD-MSCs) exert anti-inflammatory and anti-catabolic effects in OA chondrocytes. In the current work, we have investigated whether AD-MSC EVs could regulate oxidative stress in OA chondrocytes as well as the possible contribution of peroxiredoxin 6 (Prdx6).

Methods

Microvesicles (MV) and exosomes (EX) were isolated from AD-MSC conditioned medium by differential centrifugation with size filtration. The size and concentration of EVs were determined by resistive pulse sensing. OA chondrocytes were isolated from knee articular cartilage of advanced OA patients. 4-Hydroxynonenal adducts, IL-6 and MMP-13 were determined by enzyme-linked immunosorbent assay. Expression of Prdx6 and autophagic markers was assessed by immunofluorescence and Western blotting. Prdx6 was downregulated in AD-MSCs by transfection with a specific siRNA.

Results

MV and to a lesser extent EX significantly reduced the production of oxidative stress in OA chondrocytes stimulated with IL-1β. Treatment with MV resulted in a dramatic upregulation of Prdx6. MV also enhanced the expression of autophagy marker LC3B. We downregulated Prdx6 in AD-MSCs by using a specific siRNA and then MV were isolated. These Prdx6-silenced MV failed to modify oxidative stress and the expression of autophagy markers. We also assessed the possible contribution of Prdx6 to the effects of MV on IL-6 and MMP-13 production. The reduction in the levels of both mediators induced by MV was partly reverted after Prdx6 silencing.

Conclusion

Our results indicate that EVs from AD-MSCs regulate the production of oxidative stress in OA chondrocytes during inflammation. Prdx6 may mediate the antioxidant and protective effects of MV.

The translational potential of this article: This study gives insight into the protective properties of EVs from AD-MSCs in OA chondrocytes. Our findings support the development of novel therapies based on EVs to prevent or treat cartilage degradation.

G protein coupled estrogen receptor attenuates mechanical stress-mediated apoptosis of chondrocyte in osteoarthritis via suppression of Piezo1

BACKGROUND

Apoptosis of chondrocyte is involved in osteoarthritis (OA) pathogenesis, and mechanical stress plays a key role in this process by activation of Piezo1. However, the negative regulation of signal conduction mediated by mechanical stress is still unclear. Here, we elucidate that the critical role of G protein coupled estrogen receptor (GPER) in the regulation of mechanical stress-mediated signal transduction and chondrocyte apoptosis.

METHODS

The gene expression profile was detected by gene chip upon silencing Piezo1. The expression of GPER in cartilage tissue taken from the clinical patients was detected by RT-PCR and Western blot as well as immunohistochemistry, and the correlation between GPER expression and OA was also investigated. The chondrocytes exposed to mechanical stress were treated with estrogen, G-1, G15, GPER-siRNA and YAP (Yes-associated protein)-siRNA. The cell viability of chondrocytes was measured. The expression of polymerized actin and Piezo1 as well as the subcellular localization of YAP was observed under laser confocal microscope. Western blot confirmed the changes of YAP/ Rho GTPase activating protein 29 (ARHGAP29) /RhoA/LIMK /Cofilin pathway. The knee specimens of osteoarthritis model were stained with safranin and green. OARSI score was used to evaluate the joint lesions. The expressions of GPER and YAP were detected by immunochemistry.

RESULTS

Expression profiles of Piezo1- silenced chondrocytes showed that GPER expression was significantly upregulated. Moreover, GPER was negatively correlated with cartilage degeneration during OA pathogenesis. In addition, we uncovered that GPER directly targeted YAP and broadly restrained mechanical stress-triggered actin polymerization. Mechanism studies revealed that GPER inhibited mechanical stress-mediated RhoA/LIMK/cofilin pathway, as well as the actin polymerization, by promoting expression of YAP and ARHGAP29, and the YAP nuclear localization, eventually causing the inhibition of Piezo1. YAP was obviously decreased in degenerated cartilage. Silencing YAP caused significantly increased actin polymerization and activation of Piezo1, and an increase of chondrocyte apoptosis. In addition, intra-articular injection of G-1 to OA rat effectively attenuated cartilage degeneration.

CONCLUSION

We propose a novel regulatory mechanism underlying mechanical stress-mediated apoptosis of chondrocyte and elucidate the potential application value of GPER as therapy targets for OA.

Cell-associated type I collagen in nondegenerate and degenerate human articular cartilage

Chondrocytes with abnormal morphology are present in nondegenerate human cartilage suggesting dedifferentiation to a fibroblastic phenotype and production of a mechanically-weakened matrix of unknown composition. We determined the relationship between in situ chondrocyte morphology, chondrocyte clusters, and levels of cell-associated collagen type I. Chondrocyte morphology in fresh femoral head cartilage from 19 patients with femoral neck fracture and collagen type I labelling was identified with Cell Tracker^TM fluorescence and immunofluorescence, respectively, in axial/coronal orientations using confocal microscopy with images analysed by Imaris^TM . In axial images of grade 0 cartilage, 87 ± 8% were normal chondrocytes with a small (10 ± 6%) abnormal population possessing ≥1 cytoplasmic process. More normal chondrocytes (78 ± 11%) were collagen type I negative than those labelling positively (p < 0.001). For abnormal chondrocytes, 81 ± 14% labelled negatively for collagen type I compared to those labelling positively (19 ± 3%; p = 0.007; N(n)=11(3)). Overall, approximately 9% of the cells in normal cartilage labelled for collagen type I. With degeneration, the percentage of normal chondrocytes decreased (p < 0.001) but increased for abnormal cells (p = 0.036) and clusters (p = 0.003). A larger percentage of normal, abnormal and clustered chondrocytes now demonstrated collagen type I labelling (p = 0.004; p = 0.009; p = 0.001 respectively). Coronal images exhibited increased (p = 0.001) collagen type I labelling in the superficial zone of mildly degenerate cartilage with none in the mid or deep zones. These results show that collagen type I was identified around normal and abnormal chondrocytes in nondegenerate cartilage, which increased with degeneration. This suggested the presence of mechanically weak fibro-cartilaginous repair tissue in otherwise macroscopically nondegenerate human cartilage which progressed with degeneration as occurs in osteoarthritis.

Protein Levels and Microstructural Changes in Localized Regions of Early Cartilage Degeneration Compared with Adjacent Intact Cartilage

OBJECTIVE

It was hypothesized that the respective protein profiles of bovine cartilage from sites of localized mild to moderate (GI to GII) degeneration versus adjacent sites of intact tissue would vary in accordance with the tissue microstructural changes associated with a pre-osteoarthritic state.

METHODS

A total of 15 bovine patellae were obtained for this study. Paired samples of tissue were collected from the lateral region of each patella. If the patella contained a site of degeneration, a paired tissue set involved taking one sample each from the degenerated site and the intact tissue adjacent to it. Sufficient tissue was collected to facilitate 2 arms of investigation: microstructural imaging and proteome analysis. The microstructural analysis used a bespoke tissue preparation technique imaged with differential interference contrast optical microscopy to assess fibrillar scale destructuring and underlying bone spicule formation. An iTRAQ-based proteome analysis was performed using liquid chromatography-tandem mass spectrometry to identify the differential levels of proteins across the intact and degenerated cartilage and further, the results were validated with multiple reaction monitoring assay.

RESULTS

In the healthy cartilage pairs, there was no significant variation in protein profiles between 2 adjacent sample sites. In pairs of tissue that contained a sample of GI/GII tissue, there were both significant microstructural changes as well as the difference in abundance levels of 24 proteins.

CONCLUSIONS

From the known functions of the 24 proteins, found to be strongly aligned with the specific microstructural changes observed, a unique "proteins ensemble" involved in the initiation and progression of early cartilage degeneration is proposed.

Articular Chondrocyte Phenotype Regulation through the Cytoskeleton and the Signaling Processes That Originate from or Converge on the Cytoskeleton: Towards a Novel Understanding of the Intersection between Actin Dynamics and Chondrogenic Function

Numerous studies have assembled a complex picture, in which extracellular stimuli and intracellular signaling pathways modulate the chondrocyte phenotype. Because many diseases are mechanobiology-related, this review asked to what extent phenotype regulators control chondrocyte function through the cytoskeleton and cytoskeleton-regulating signaling processes. Such information would generate leverage for advanced articular cartilage repair. Serial passaging, pro-inflammatory cytokine signaling (TNF-α, IL-1α, IL-1β, IL-6, and IL-8), growth factors (TGF-α), and osteoarthritis not only induce dedifferentiation but also converge on RhoA/ROCK/Rac1/mDia1/mDia2/Cdc42 to promote actin polymerization/crosslinking for stress fiber (SF) formation. SF formation takes center stage in phenotype control, as both SF formation and SOX9 phosphorylation for COL2 expression are ROCK activity-dependent. Explaining how it is molecularly possible that dedifferentiation induces low COL2 expression but high SF formation, this review theorized that, in chondrocyte SOX9, phosphorylation by ROCK might effectively be sidelined in favor of other SF-promoting ROCK substrates, based on a differential ROCK affinity. In turn, actin depolymerization for redifferentiation would “free-up” ROCK to increase COL2 expression. Moreover, the actin cytoskeleton regulates COL1 expression, modulates COL2/aggrecan fragment generation, and mediates a fibrogenic/catabolic expression profile, highlighting that actin dynamics-regulating processes decisively control the chondrocyte phenotype. This suggests modulating the balance between actin polymerization/depolymerization for therapeutically controlling the chondrocyte phenotype.

Ex Vivo Equine Cartilage Explant Osteoarthritis Model: A Metabolomics and Proteomics Study

Osteoarthritis is an age-related degenerative musculoskeletal disease characterized by loss of articular cartilage, synovitis, and subchondral bone sclerosis. Osteoarthritis pathogenesis is yet to be fully elucidated with no osteoarthritis-specific biomarkers in clinical use. Ex vivo equine cartilage explants (n = 5) were incubated in tumor necrosis factor-α (TNF-α)/interleukin-1β (IL-1β)-supplemented culture media for 8 days, with the media removed and replaced at 2, 5, and 8 days. Acetonitrile metabolite extractions of 8 day cartilage explants and media samples at all time points underwent one-dimensional (1D) ¹H nuclear magnetic resonance metabolomic analysis, with media samples also undergoing mass spectrometry proteomic analysis. Within the cartilage, glucose and lysine were elevated following TNF-α/IL-1β treatment, while adenosine, alanine, betaine, creatine, myo-inositol, and uridine decreased. Within the culture media, 4, 4, and 6 differentially abundant metabolites and 154, 138, and 72 differentially abundant proteins were identified at 1–2, 3–5, and 6–8 days, respectively, including reduced alanine and increased isoleucine, enolase 1, vimentin, and lamin A/C following treatment. Nine potential novel osteoarthritis neopeptides were elevated in the treated media. Implicated pathways were dominated by those involved in cellular movement. Our innovative study has provided insightful information on early osteoarthritis pathogenesis, enabling potential translation for clinical markers and possible new therapeutic targets.

The Role of Chondrocyte Morphology and Volume in Controlling Phenotype-Implications for Osteoarthritis, Cartilage Repair, and Cartilage Engineering

PURPOSE OF REVIEW

Articular chondrocytes are exclusively responsible for the turnover of the extracellular matrix (ECM) of hyaline cartilage. However, chondrocytes are phenotypically unstable and, if they de-differentiate into hypertrophic or fibroblastic forms, will produce a defective and weak matrix. Chondrocyte volume and morphology exert a strong influence over phenotype and a full appreciation of the factors controlling chondrocyte phenotype stability is central to understanding (a) the mechanisms underlying the cartilage failure in osteoarthritis (OA), (b) the rationale for hyaline cartilage repair, and (c) the strategies for improving the engineering of resilient cartilage. The focus of this review is on the factors involved in, and the importance of regulating, chondrocyte morphology and volume as key controllers of chondrocyte phenotype.

RECENT FINDINGS

The visualisation of fluorescently-labelled in situ chondrocytes within non-degenerate and mildly degenerate cartilage, by confocal scanning laser microscopy (CLSM) and imaging software, has identified the marked heterogeneity of chondrocyte volume and morphology. The presence of chondrocytes with cytoplasmic processes, increased volume, and clustering suggests important early changes to their phenotype. Results from experiments more closely aligned to the normal physico-chemical environment of in situ chondrocytes are emphasising the importance of understanding the factors controlling chondrocyte morphology and volume that ultimately affect phenotype. An appreciation of the importance of chondrocyte volume and morphology for controlling the chondrocyte phenotype is advancing at a rapid pace and holds particular promise for developing strategies for protecting the chondrocytes against deleterious changes and thereby maintaining healthy and resilient cartilage.

SP600125 blocks the proteolysis of cytoskeletal proteins in apoptosis induced by gas signaling molecule (NO) via decreasing the activation of caspase-3 in rabbit chondrocytes

NO plays a key role in the pathological mechanisms of articular diseases. As cytoskeletal proteins are responsible for the polymerization, stabilization, and dynamics of the cytoskeleton network, we investigated whether cytoskeletal proteins are the intracellular pathological targets of NO. We aimed at clarifying whether the cytoskeleton perturbations involved in apoptosis are induced in rabbit articular chondrocytes by NO, which can be liberated by sodium nitroprusside (SNP) treatment. The first passage rabbit articular chondrocytes were cultured as monolayer for the experiments, and the effects of NO were tested in the presence of JNK-specific inhibitor, SP600125. SNP treatment of cultured chondrocytes caused significant apoptosis in a concentration-dependent manner (time and dose), as evaluated by TUNEL assay and Annexin V flow cytometry, while the apoptosis was reduced by the SP600125 addition 30 min before SNP treatment. Besides, SP600125 decreased significantly the protein expression of total caspase-3 and the intracellular gene expression of caspase-3, measured by Western blot analysis and PCR. SP600125 also increased the cytoskeletal protein expressions. These results suggested that JNK pathway plays a critical role in the NO-induced chondrocyte apoptosis, and SP600125 treatment blocks the dissolution of the cytoskeletal proteins via activation of caspase-3 pathways.

Effects of long-term low oxygen tension in human chondrosarcoma cells

The cell-based therapies could be potential methods to treat damaged cartilage tissues. Instead of native hyaline cartilage, the current therapies generate mainly weaker fibrocartilage-type of repair tissue. A correct microenvironment influences the cellular phenotype, and together with external factors it can be used, for example, to aid the differentiation of mesenchymal stem cells to defined types of differentiated adult cells. In this study, we investigated the effect of long-term exposure to 5% low oxygen atmosphere on human chondrosarcoma HCS-2/8 cells. This atmosphere is close to normal oxygen tension of cartilage tissue. The proteome was analyzed with label-free mass spectrometric method and further bioinformatic analysis. The qRT-PCR method was used to gene expression analysis, and ELISA and dimethylmethylene blue assays for type II collagen and sulfated glycosaminoglycan measurements. The 5% oxygen atmosphere did not influence cell proliferation, but enhanced slightly ACAN and COL2A1 gene expression. Proteomic screening revealed a number of low oxygen-induced protein level responses. Increased ones included NDUFA4L2, P4HA1, NDRG1, MIF, LDHA, PYGL, while TXNRD1, BAG2, TXN2, AQSTM1, TNFRSF1B, and EPHX1 decreased during the long-term low oxygen atmosphere. Also a number of proteins previously not related to low oxygen tension changed during the treatment. Of those S100P, RPSS26, NDUFB11, CDV3, and TUBB8 had elevated levels, while ALCAM, HLA-B, EIF1, and ACOT9 were lower in the samples cultured at low oxygen tension. In conclusion, low oxygen condition causes changes in the cellular amounts of several proteins.

Rho-kinase inhibitor Y-27632 and hypoxia synergistically enhance chondrocytic phenotype and modify S100 protein profiles in human chondrosarcoma cells

Articular chondrocytes are slowly dividing cells that tend to lose their cell type-specific phenotype and ability to produce structurally and functionally correct cartilage tissue when cultured. Thus, culture conditions, which enhance the maintenance of chondrocyte phenotype would be very useful for cartilage research. Here we show that Rho-kinase inhibition by Y-27632 under hypoxic conditions efficiently maintains and even enhances chondrocyte-specific extracellular matrix production by chondrocytic cells. The effects of long-term Y-27632 exposure to human chondrosarcoma 2/8 cell phenotype maintenance and extracellular matrix production were studied at normoxia and at a 5% low oxygen atmosphere. Y-27632 treatment at normoxia induced ACAN and COL2A1 gene up-regulation and a minor increase of sulfated glycosaminoglycans (sGAGs), while type II collagen expression was not significantly up-regulated. A further increase in expression of ACAN and COL2A1 was achieved with Y-27632 treatment and hypoxia. The production of sGAGs increased by 65.8%, and ELISA analysis revealed a 6-fold up-regulation of type II collagen. Y-27632 also induced the up-regulation of S100-A1 and S100-B proteins and modified the expression of several other S100 protein family members, such as S100-A4, S100-A6, S100-A13 and S100-A16. The up-regulation of S100-A1 and S100-B proteins is suggested to enhance the chondrocytic phenotype of these cells.

Deformability of Human Mesenchymal Stem Cells Is Dependent on Vimentin Intermediate Filaments

Mesenchymal stem cells (MSCs) are being studied extensively due to their potential as a therapeutic cell source for many load-bearing tissues. Compression of tissues and the subsequent deformation of cells are just one type physical strain MSCs will need to withstand in vivo. Mechanotransduction by MSCs and their mechanical properties are partially controlled by the cytoskeleton, including vimentin intermediate filaments (IFs). Vimentin IF deficiency has been tied to changes in mechanosensing and mechanical properties of cells in some cell types. However, how vimentin IFs contribute to MSC deformability has not been comprehensively studied. Investigating the role of vimentin IFs in MSC mechanosensing and mechanical properties will assist in functional understanding and development of MSC therapies. In this study, we examined vimentin IFs' contribution to MSCs' ability to deform under external deformation using RNA interference. Our results indicate that a deficient vimentin IF network decreases the deformability of MSCs, and that this may be caused by the remaining cytoskeletal network compensating for the vimentin IF network alteration. Our observations introduce another piece of information regarding how vimentin IFs are involved in the complex role the cytoskeleton plays in the mechanical properties of cells.

Differential proteomics of the synovial membrane between bilateral and unilateral knee osteoarthritis in surgery‑induced rabbit models

The present study investigated the differential proteomics of synovial membranes between bilateral and unilateral anterior cruciate ligament transection (ACLT) in rabbits with knee osteoarthritis (KOA), in order to elucidate the pathological biomarkers of different degrees of KOA. A total of 6 New Zealand rabbits were randomly divided into groups A and B (three rabbits per group). The two groups were subjected to bilateral and unilateral ACLT, respectively. A total of 6 weeks following surgery, proteins were extracted from the knee joint synovial membranes of KOA rabbits and were separated by two‑dimensional polyacrylamide gel electrophoresis. The differentially expressed proteins in the OA synovial membranes were selected for further analysis by linear ion trap‑Fourier transform ion cyclotron resonance mass spectrometry. Ten protein spots were identified to be different between the synovial membranes of the bilateral and unilateral KOA rabbits. Protein disulfide‑isomerase and creatine kinase M‑type were identified in the unilateral KOA rabbit synovial membranes. Serum albumin (three spots), lumican, α‑2‑HS‑glycoprotein and three uncharacterized proteins were identified in the synovial membranes of the bilateral KOA rabbits. The differential proteomic expression demonstrated the different biomarkers associated with bilateral and unilateral KOA, and indicated that spontaneous and secondary KOA require diverse methods of treatment; thus the underlying mechanism of KOA requires further investigation.

Functional genomics in osteoarthritis: Past, present, and future

Osteoarthritis (OA) is a common complex disease of high public health burden. OA is characterized by the degeneration of affected joints leading to pain and reduced mobility. Over the last few years, several studies have focused on the genomic changes underpinning OA. Here, we provide a comprehensive overview of genome-wide, non-hypothesis-driven functional genomics (methylation, gene, and protein expression) studies of knee and hip OA in humans. Individual studies have generally been limited in sample size and hence power, and have differed in their approaches; nonetheless, some common themes have started to emerge, notably the role played by biological processes related to the extracellular matrix, immune response, the WNT pathway, angiogenesis, and skeletal development. Larger-scale studies and streamlined, robust methodologies will be needed to further elucidate the biological etiology of OA going forward. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1105-1110, 2016.

Label-free proteomic analysis of the hydrophobic membrane protein complement in articular chondrocytes: a technique for identification of membrane biomarkers

CONTEXT

There is insufficient knowledge about the chondrocyte membranome and its molecular composition.

OBJECTIVE

To develop a Triton X-114 based separation technique using nanoLC-MS/MS combined with shotgun proteomics to identify chondrocyte membrane proteins.

MATERIALS AND METHODS

Articular chondrocytes from equine metacarpophalangeal joints were separated into hydrophobic and hydrophilic fractions; trypsin-digested proteins were analysed by nanoLC-MS/MS.

RESULTS

A total of 315 proteins were identified. The phase extraction method yielded a high proportion of membrane proteins (56%) including CD276, S100-A6 and three VDAC isoforms.

DISCUSSION

Defining the chondrocyte membranome is likely to reveal new biomarker targets for conventional and biological drug discovery.

Effects of vimentin disruption on the mechanoresponses of articular chondrocyte

Human articular cartilage is subjected to repetitive mechanical loading during life time. As the only cellular component of articular cartilage, chondrocytes play a key role in the mechanotransduction within this tissue. The mechanoresponses of chondrocytes are largely determined by the cytoskeleton. Vimentin intermediate filaments, one of the major cytoskeletal components, have been shown to regulate chondrocyte phenotype. However, the contribution of vimentin in chondrocyte mechanoresponses remains less studied. In this study, we seeded goat articular chondrocytes on a soft polyacrylamide gel, and disrupted the vimentin cytoskeleton using acrylamide. Then we applied a transient stretch or compression to the cells, and measured the changes of cellular stiffness and traction forces using Optical Magnetic Twisting Cytometry and Traction Force Microscopy, respectively. In addition, to study the effects of vimentin disruption on the intracellular force generation, we treated the cells with a variety of reagents that are known to increase or decrease cytoskeletal tension. We found that, after a compression, the contractile moment and cellular stiffness were not affected in untreated chondrocytes, but were decreased in vimentin-disrupted chondrocytes; after a stretch, vimentin-disrupted chondrocytes showed a lower level of fluidization-resolidification response compared to untreated cells. Moreover, vimentin-disrupted chondrocytes didn't show much difference to control cells in responding to reagents that target actin and ROCK pathway, but showed a weaker response to histamine and isoproterenol. These findings confirmed chondrocyte vimentin as a major contributor in withstanding compressive loading, and its minor role in regulating cytoskeletal tension.

Changes in Ultrastructure and Cytoskeletal Aspects of Human Normal and Osteoarthritic Chondrocytes Exposed to Interleukin-1β and Cyclical Hydrostatic Pressure

The aim of this study was to examine the ultrastructure and cytoskeletal organization in human normal and Osteoarhritic (OA) chondrocytes, exposed to interleukin-1β (IL-1β) and cyclic hydrostatic pressure (HP). Morphological examination by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) revealed differences between normal and OA chondrocytes at the nuclear and cytoplasmic level. IL-1β (5 ng/mL) induced a decrease of the number of mitochondria and Golgi bodies and a significant increase on the percentage of cells rich in vacuolization and in marginated chromatin. Cyclical HP (1–5 MPa, 0.25 Hz, for 3 h) did not change the morphology of normal chondrocytes, but had a beneficial effect on OA chondrocytes increasing the number of organelles. Normal and OA cells subjected to IL-1β and HP recovered cytoplasmic ultrastructure. Immunofluorescence (IF) examination of normal chondrocytes showed an actin signal polarized on the apical sides of the cytoplasm, tubulin and vimentin uniformly distributed throughout cytoplasm and vinculin revealed a punctuated pattern under the plasma membrane. In OA chondrocytes, these proteins partially lost their organization. Stimulation with IL-1β caused, in both type of cells, modification in the cytoskeletal organization; HP counteracted the negative effects of IL-1β. Our results showed structural differences at nuclear, cytoplasmic and cytoskeletal level between normal and OA chondrocytes. IL-1β induced ultrastructural and cytoskeletal modifications, counteracted by a cyclical low HP.

Lessons from the proteomic study of osteoarthritis

Osteoarthritis is the most common rheumatic pathology and one of the leading causes of disability worldwide. It is a very complex disease whose etiopathogenesis is not fully understood. Furthermore, there are serious limitations for its management, since it lacks specific and sensitive biomarkers for early diagnosis, prognosis and therapeutic monitoring. Proteomic approaches performed in the last few decades have contributed to the knowledge on the molecular mechanisms that participate in this pathology and they have also led to interesting panels of putative biomarker candidates. In the next few years, further efforts should be made for translating these findings into the clinical routines. It is expected that targeted proteomics strategies will be highly valuable for the verification and qualification of biomarkers of osteoarthritis.

Chondropenia: current concept review

The term "chondropenia" indicates the early stage of degenerative cartilage disease, and it has been identified by carefully monitoring early-stage osteoarthritis (OA). Not only is it the loss of articular cartilage volume, but it is also a rearrangement of biomechanical, ultrastructural, biochemical and molecular properties typical of healthy cartilage tissue. Diagnosing OA at an early stage or an advanced stage is valuable in terms of clinical and therapeutic outcome. In fact degenerative phenomena are supported by a complex biochemical cascade which unbalances the extracellular matrix homeostasis, closely regulated by chondrocytes. In the first stage an intense inflammatory reaction is triggered: pro-catabolic cytokines such as IL-1β and TNF-α triggering matrix metalloproteases and aggrecanase (ADAMT-4 and 5), responsible for the early loss of ultrastructural components, such as type II collagen and aggrecan. In addition nitric oxide and reactive oxygen species modulate the physiopathology of the condral matrix inducing apoptosis of chondrocytes through a mitochondria-dependent pathway. In addition, "Lonely Death": chondrocytes, are confined within a dense, avascular extracellular matrix capsule, and can trigger a genetically induced apoptosis and necrosis. The degenerative process starts from a central point and then spreads in a centrifugal manner in depth and in adjacent areas, eventually covering the whole joint; chondropenia represents a journey from the first clinically detectable time-point until it can be characterized as frank osteoarthritis. Currently, there are no instruments sensitive enough which allow a timely diagnosis of chondropenia. Innovative magnetic resonance imaging techniques, such as T2 mapping, can be effective and a sensitive diagnostic instrument for quantifying cartilage volume and proteoglycan content. However, avant-garde biophysical techniques, such as mechanical indenters, ultrasound and biochemical markers (uCTX-II), are rational and scientific tools applicable to the clinical and therapeutic management of early degenerative cartilage disease. The objective of this review on chondropenia is to present a state of the art and innovative concepts.

Proteomic Analysis of Connexin 43 Reveals Novel Interactors Related to Osteoarthritis

We have previously reported that articular chondrocytes in tissue contain long cytoplasmic arms that physically connect two distant cells. Cell-to-cell communication occurs through connexin channels termed Gap Junction (GJ) channels, which achieve direct cellular communication by allowing the intercellular exchange of ions, small RNAs, nutrients, and second messengers. The Cx43 protein is overexpressed in several human diseases and inflammation processes and in articular cartilage from patients with osteoarthritis (OA). An increase in the level of Cx43 is known to alter gene expression, cell signaling, growth, and cell proliferation. The interaction of proteins with the C-terminal tail of connexin 43 (Cx43) directly modulates GJ-dependent and -independent functions. Here, we describe the isolation of Cx43 complexes using mild extraction conditions and immunoaffinity purification. Cx43 complexes were extracted from human primary articular chondrocytes isolated from healthy donors and patients with OA. The proteomic content of the native complexes was determined using LC-MS/MS, and protein associations with Cx43 were validated using Western blot and immunolocalization experiments. We identified >100 Cx43-associated proteins including previously uncharacterized proteins related to nucleolar functions, RNA transport, and translation. We also identified several proteins involved in human diseases, cartilage structure, and OA as novel functional Cx43 interactors, which emphasized the importance of Cx43 in the normal physiology and structural and functional integrity of chondrocytes and articular cartilage. Gene Ontology (GO) terms of the proteins identified in the OA samples showed an enrichment of Cx43-interactors related to cell adhesion, calmodulin binding, the nucleolus, and the cytoskeleton in OA samples compared with healthy samples. However, the mitochondrial proteins SOD2 and ATP5J2 were identified only in samples from healthy donors. The identification of Cx43 interactors will provide clues to the functions of Cx43 in human cells and its roles in the development of several diseases, including OA.

A pharmacoproteomic study confirms the synergistic effect of chondroitin sulfate and glucosamine

Osteoarthritis (OA) is the most common age-related rheumatic disease. Chondrocytes play a primary role in mediating cartilage destruction and extracellular matrix (ECM) breakdown, which are main features of the OA joint. Quantitative proteomics technologies are demonstrating a very interesting power for studying the molecular effects of some drugs currently used to treat OA patients, such as chondroitin sulfate (CS) and glucosamine (GlcN). In this work, we employed the iTRAQ (isobaric tags for relative and absolute quantitation) technique to assess the effect of CS and GlcN, both alone and in combination, in modifying cartilage ECM metabolism by the analysis of OA chondrocytes secretome. 186 different proteins secreted by the treated OA chondrocytes were identified. 36 of them presented statistically significant differences (p ≤ 0.05) between untreated and treated samples: 32 were increased and 4 decreased. The synergistic chondroprotective effect of CS and GlcN, firstly reported by our group at the intracellular level, is now demonstrated also at the extracellular level.

Effects of laser treatment on the expression of cytosolic proteins in the synovium of patients with osteoarthritis

BACKGROUND AND OBJECTIVE

Low level laser therapy (LLLT) has been developed for non-invasive treatment of joint diseases. We have previously shown that LLLT influenced synovial protein expression in rheumatoid arthritis (RA). The aim of this study was to assess the effects of laser irradiation on osteoarthritic (OA) synovial protein expression.

STUDY DESIGN/MATERIALS AND METHODS

The synovial membrane samples removed from the knees of 6 OA patients were irradiated ex vivo using near infrared diode laser (807-811 nm; 25 J/cm(2) ). An untreated sample taken from the same patient served as control. Synovial protein separation and identification were performed by two-dimensional differential gel electrophoresis and mass spectrometry, respectively.

RESULTS

Eleven proteins showing altered expression due to laser irradiation were identified. There were three patients whose tissue samples demonstrated a significant increase (P < 0.05) in mitochondrial heat shock 60 kD protein 1 variant 1. The expression of the other proteins (calpain small subunit 1, tubulin alpha-1C and beta 2, vimentin variant 3, annexin A1, annexin A5, cofilin 1, transgelin, and collagen type VI alpha 2 chain precursor) significantly decreased (P < 0.05) compared to the control samples.

CONCLUSIONS

A single diode laser irradiation of the synovial samples of patients with osteoarthritis can statistically significantly alter the expression of some proteins in vitro. These findings provide some more evidence for biological efficacy of LLLT treatment, used for osteoarthritis.

Modeling of signaling pathways in chondrocytes based on phosphoproteomic and cytokine release data

OBJECTIVE

Chondrocyte signaling is widely identified as a key component in cartilage homeostasis. Dysregulations of the signaling processes in chondrocytes often result in degenerative diseases of the tissue. Traditionally, the literature has focused on the study of major players in chondrocyte signaling, but without considering the cross-talks between them. In this paper, we systematically interrogate the signal transduction pathways in chondrocytes, on both the phosphoproteomic and cytokine release levels.

METHODS

The signaling pathways downstream 78 receptors of interest are interrogated. On the phosphoproteomic level, 17 key phosphoproteins are measured upon stimulation with single treatments of 78 ligands. On the cytokine release level, 55 cytokines are measured in the supernatant upon stimulation with the same treatments. Using an Integer Linear Programming (ILP) formulation, the proteomic data is combined with a priori knowledge of proteins' connectivity to construct a mechanistic model, predictive of signal transduction in chondrocytes.

RESULTS

We were able to validate previous findings regarding major players of cartilage homeostasis and inflammation (e.g., IL1B, TNF, EGF, TGFA, INS, IGF1 and IL6). Moreover, we studied pro-inflammatory mediators (IL1B and TNF) together with pro-growth signals for investigating their role in chondrocytes hypertrophy and highlighted the role of underreported players such as Inhibin beta A (INHBA), Defensin beta 1 (DEFB1), CXCL1 and Flagellin, and uncovered the way they cross-react in the phosphoproteomic level.

CONCLUSIONS

The analysis presented herein, leveraged high throughput proteomic data via an ILP formulation to gain new insight into chondrocytes signaling and the pathophysiology of degenerative diseases in articular cartilage.

Proteomic analysis of osteoarthritic chondrocyte reveals the hyaluronic acid-regulated proteins involved in chondroprotective effect under oxidative stress

Osteoarthritis (OA), the most common type of arthritis, is a degenerative joint disease. Oxidative stress is well known to play important roles in cartilage degradation and pathogenesis of OA. The intra-articular injection of hyaluronic acid (IAHA) is accepted as an effective clinical therapy for OA, but we do not yet fully understand the mechanisms underlying the effects of HA on OA chondrocytes under oxidative stress. Here, we show for the first time that IAHA significantly reduces the synovial fluid levels of hydrogen peroxide (H2O2) and superoxide (O2(-)) in patients with knee OA. We also demonstrate that HA suppresses H2O2-induced cell death in human OA chondrocytes. Proteomic approaches (2-DE combined with mass spectrometry) allowed us to identify 13 protein spots corresponding to 12 non-redundant proteins as HA-regulated proteins in OA chondrocytes under oxidative stress. The expression levels of three putative HA-regulated proteins (TALDO, ANXA1 and EF2) in control, H2O2-, HA- and HA/H2O2-treated OA chondrocytes were verified by Western blotting and the results indeed support the notion that HA acts in anti-oxidation, anti-apoptosis, and the promotion of cell survival. Our results collectively demonstrate the utility of proteomic approaches and provide new insights into the chondroprotective effects of HA on OA.

BIOLOGICAL SIGNIFICANCE

In the present study, we show for the first time that IAHA reduces the levels of H2O2 and O2(-) in synovial fluids from OA patients. We used primary cultured human OA chondrocytes as a model, treated cells with H2O2 to partly mimic their physiological conditions under oxidative stress, and examined the protection effects of HA. The proteomic approach allowed us to identify candidate proteins regulated by H2O2 and/or HA in OA chondrocytes. We found that proteins functioning in stress responses, apoptosis and protein synthesis were consistently regulated by HA in chondrocytes under oxidative stress. These novel results contribute to our understanding of the molecular mechanisms underlying HA-mediated chondroprotection.

Network medicine analysis of chondrocyte proteins towards new treatments of osteoarthritis

Osteoarthritis (OA) is a progressive disorder with high incidence in the ageing human population that still has no treatment currently. This disorder induces the breakdown of articular cartilage, leading to the exposure and damage of bone surfaces. For a global understanding of OA development, the systematic integration of known OA-related proteins with protein-protein interaction (PPI) networks is required. In this work, the OA-related interactome was reconstructed using multiple data sources to have the most up-to-date information on OA-related proteins and their interactions. We then combined emergent concepts in network medicine to detect new unclassified OA-related proteins. The mapping of known OA-related proteins with PPI networks showed that these proteins are locally connected to each other and agglomerated in a large component. To expand this module, we applied a diffusion-based algorithm that probabilistically induces more searches in the vicinity of the seed OA-related proteins. As a result, the 10 topmost ranked proteins were connected to the OA disease module, supporting the local hypothesis. We computed structural modules and selected those that had the highest enrichment of OA-related proteins. The identified molecules show a link between structural topology and disease dysfunctionality. Interestingly, the protein Q6EEV6 was highlighted for OA association by both methods, reinforcing the potential involvement of this protein. These results suggest that similar disease-connected modules may exist in different human disorders, which could lead to systematic identification of genes or proteins that have a joint role in specific disease phenotypes.

Matrix-embedded cytokines to simulate osteoarthritis-like cartilage microenvironments

In vivo, cytokines noncovalently bind to the extracellular matrix (ECM), to facilitate intimate interactions with cellular receptors and potentiate biological activity. Development of a biomaterial that simulates this type of physiological binding and function is an exciting proposition for designing controlled advanced delivery systems for simulating in vivo conditions in vitro. We have decorated silk protein with sulfonated moieties through diazonium coupling reactions to noncovalently immobilize pro-inflammatory cytokines interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) in such a biomimetic manner. After adsorption of the cytokines to the diazonium-modified silk matrix, constant release of cytokines up to at least 3 days was demonstrated, as an initial step to simulate an osteoarthritic (OA) microenvironment in vitro. Matrix-embedded cytokines induced the formation of multiple elongated processes in chondrocytes in vitro, akin to what is seen in OA cartilage in vivo. Gene expression profiles with this in vitro tissue model of OA showed significant similarities to profiles from explanted OA cartilage tissues collected from patients who underwent total knee replacement surgery. The common markers of OA, including COL, MMP, TIMP, ADAMTS, and metallothioneins, were upregulated at least 35-fold in the in vitro model when compared to the control-non-OA in vitro generated tissue-engineered cartilage. The microarray data were validated by reverse transcriptase-polymerase chain reaction. Mechanistically, protein interaction studies indicated that TNF-α and IL-1β synergistically controlled the equilibrium between MMPs and their inhibitors, TIMPs, resulting in ECM degradation through the MAPK pathway. This study offers a promising initial step toward establishing a relevant in vitro OA disease model, which can be further modified to assess signaling mechanisms, responses to cell or drug treatments and patient-specific features.

Proteomic analysis of synovial fluid: insight into the pathogenesis of knee osteoarthritis

PURPOSE

We conducted a proteomic analysis of synovial fluid (SF) to identify differentially expressed proteins and analyse their correlation with osteoarthritis (OA) severity. Our primary purpose was to gain insight into the pathogenesis of OA.

METHODS

SF samples were acquired from 12 knee OA patients and 12 non-OA controls (ten had a meniscus injury, two had a discoid meniscus and all exhibited intact articular cartilage) and sequentially subjected to two-dimensional electrophoresis (2-DE). The radiographic grading of knee OA was performed using the Kellgren-Lawrence criteria. Differentially expressed proteins were identified by matrix-assisted laser desorption/ionisation time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF MS). Proteins of interest identified from SF were detected using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

A total of 31 protein spots showed significant differences (p < 0.05) between the sample groups; 25 of the 31 spots (80.6 %) were identified as proteins of interest. Among them 20 corresponded to up-regulation and five to down-regulation in OA samples. HLA-DR was one of the proteins up-regulated, which was confirmed by ELISA.

CONCLUSIONS

These observations have implications in delineating the protein expression underlying the pathogenesis of OA and facilitate further elucidation of molecular mechanisms involved in disease progression. Substantial alterations of the protein profile in SF may be associated with OA severity.

Pharmacoproteomic study of three different chondroitin sulfate compounds on intracellular and extracellular human chondrocyte proteomes

Chondroitin sulfate (CS) is a symptomatic slow acting drug for osteoarthritis (OA) widely used for the treatment of this highly prevalent disease, characterized by articular cartilage degradation. However, little is known about its mechanism of action, and recent large scale clinical trials have reported variable results on OA symptoms. Herein, we aimed to study the modulations in the intracellular proteome and the secretome of human articular cartilage cells (chondrocytes) treated with three different CS compounds, with different origin or purity, by two complementary proteomic approaches. Osteoarthritic cells were treated with 200 μg/ml of each brand of CS. Quantitative proteomics experiments were carried out by the DIGE and stable isotope labeling with amino acids in cell culture (SILAC) techniques, followed by LC-MALDI-MS/MS analysis. The DIGE study, carried out on chondrocyte whole cell extracts, led to the detection of 46 spots that were differential between conditions in our study: 27 were modulated by CS1, 4 were modulated by CS2, and 15 were modulated by CS3. The SILAC experiment, carried out on the subset of chondrocyte-secreted proteins, allowed us to identify 104 different proteins. Most of them were extracellular matrix components, and 21 were modulated by CS1, 13 were modulated by CS2, and 9 were modulated by CS3. Each of the studied compounds induces a characteristic protein profile in OA chondrocytes. CS1 displayed the widest effect but increased the mitochondrial superoxide dismutase, the cartilage oligomeric matrix protein, and some catabolic or inflammatory factors like interstitial collagenase, stromelysin-1, and pentraxin-related protein. CS2 and CS3, on the other hand, increased a number of structural proteins, growth factors, and extracellular matrix proteins. Our study shows how, from the three CS compounds tested, CS1 induces the activation of inflammatory and catabolic pathways, whereas CS2 and CS3 induce an anti-inflammatory and anabolic response. The data presented emphasize the importance of employing high quality CS compounds, supported by controlled clinical trials, in the therapy of OA. Finally, the present work exemplifies the usefulness of proteomic approaches in pharmacological studies.

The impact of focused Gene Ontology curation of specific mammalian systems

The Gene Ontology (GO) resource provides dynamic controlled vocabularies to provide an information-rich resource to aid in the consistent description of the functional attributes and subcellular locations of gene products from all taxonomic groups (www.geneontology.org). System-focused projects, such as the Renal and Cardiovascular GO Annotation Initiatives, aim to provide detailed GO data for proteins implicated in specific organ development and function. Such projects support the rapid evaluation of new experimental data and aid in the generation of novel biological insights to help alleviate human disease. This paper describes the improvement of GO data for renal and cardiovascular research communities and demonstrates that the cardiovascular-focused GO annotations, created over the past three years, have led to an evident improvement of microarray interpretation. The reanalysis of cardiovascular microarray datasets confirms the need to continue to improve the annotation of the human proteome.

AVAILABILITY

GO ANNOTATION DATA IS FREELY AVAILABLE FROM: ftp://ftp.geneontology.org/pub/go/gene-associations/

Application for proteomic techniques in studying osteoarthritis: a review

After the genomic era, proteomic corresponds to a wide variety of techniques that study the protein content of cells, tissue, or organism and that allow the isolation of protein of interest. It offers the choice between gel-based and gel-free methods or shotgun proteomics. Applications of proteomic technology may concern three principal objectives in several biomedical or clinical domains of research as in osteoarthritis: (i) to understand the physiopathology or underlying mechanisms leading to a disease or associated with a particular model, (ii), to find disease-specific biomarker, and (iii) to identify new therapeutic targets. This review aimed at gathering most of the data regarding the proteomic techniques and their applications to osteoarthritis research. It also reported technical limitations and solutions, as for example for sample preparation. Proteomics open wide perspectives in biochemical research but many technical matters still remain to be solved.

Label-free protein profiling of adipose-derived human stem cells under hyperosmotic treatment

Our previous work suggested that treatment of cells with hyperosmotic media during 2D passaging primes cells for cartilage tissue engineering applications. Here, we used label-free proteomic profiling to evaluate the effects of control and hyperosmotic treatment environments on the phenotype of multipotent adipose-derived stem cells (ASCs) cultivated with a chondrogenic growth factor cocktail. Spectra were recorded in a data-independent fashion at alternate low (precursor) and high (product) fragmentation voltages (MS(E)). This method was supplemented with data mining of accurate mass and retention time matches in precursor ion spectra across the experiment. The results indicated a complex cellular response to osmotic treatment, with a number of proteins differentially expressed between control and treated cell groups. The roles of some of these proteins have been documented in the literature as characteristic of the physiological states studied, especially aldose reductase (osmotic stress). This protein acted as a positive control in this work, providing independent corroborative validation. Other proteins, including 5'-nucleotidase and transgelin, have been previously linked to cell differentiation state. This study demonstrates that label-free profiling can serve as a useful tool in characterizing cellular responses to chondrogenic treatment regimes, recommending its use in optimization of cell priming protocols for cartilage tissue engineering.

Vimentin contributes to changes in chondrocyte stiffness in osteoarthritis

Actin and tubulin cytoskeletal components are studied extensively in chondrocytes, but less is known about vimentin intermediate filaments. In other cell types, vimentin is a determinant of cell stiffness and disruption of vimentin networks weakens the mechanical integrity of cells. Changes in vimentin organization correlate with osteoarthritis progression, but the functional consequences of these changes remain undetermined in chondrocytes. The objective of this study was to compare the contribution of vimentin to the mechanical stiffness of primary human chondrocytes isolated from normal versus osteoarthritic cartilage. Chondrocytes were embedded in alginate and vimentin networks disrupted with acrylamide. Constructs were imaged while subjected to 20% nominal strain on a confocal microscope stage, and the aspect ratios of approximately 1,900 cells were measured. Cytosolic stiffness was estimated with a finite element model, and live-cell imaging of GFP-vimentin was used to further analyze the nature of vimentin disruption. Vimentin in normal chondrocytes formed an inner cage-like network that was substantially stiffer than the rest of the cytosol and contributed significantly to overall cellular stiffness. Disruption of vimentin reduced stiffness approximately 2.8-fold in normal chondrocytes. In contrast, osteoarthritic chondrocytes were less stiff and less affected by vimentin disruption. This 3D experimental system revealed contributions of vimentin to chondrocyte stiffness previously not apparent, and correlated changes in vimentin-based chondrocyte stiffness with osteoarthritis.

Proteomics in rheumatology: the dawn of a new era

Most rheumatic autoimmune diseases are complex in terms of their genetic origins and underlying pathogenic processes. Non-hypothesis-driven scanning platforms are adding novel insights to our understanding of these multifactorial diseases. This review summarizes the handful of recent proteomic studies that have been executed using samples from patients with rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis, osteoarthritis, or Sjogren's syndrome. The candidate biomarkers that have been uncovered in the reviewed studies have potential applications in diagnosis, prognosis, and theranostics. Though we are at the infancy of the proteomics era in rheumatology, the limited number of molecules uncovered thus far already hold promise. Ongoing research in proteomics holds tremendous potential for shaping how rheumatic diseases are diagnosed, prognosticated, and managed clinically over the coming years.

REST corepressor (CoREST) repression induces phenotypic gene regulation in advanced osteoarthritic chondrocytes

Alternations in cartilage chondrocyte phenotype characteristic by the decreased type II collagen and aggrecan together with increased type X collagen synthesis serve as a beacon for osteoarthritis progression. However, little is known about the underlying molecular mechanisms. The current study seeks to discover molecules that involved in osteoarthritic chondrocytes phenotype regulation. Differential proteomics was generated with two-dimensional gel electrophoresis between normal articular cartilage (NAC) and advanced osteoarthritic cartilage (AOC). Those differentially expressed proteins were identified by mass spectrometry. The down-regulation of a neuronal silencer, the REST corepressor (CoREST) in AOC, was verified by Western blot. CoREST silencing was performed in primarily cultured NAC chondrocytes with specific siRNA to reveal the possible involvement of CoREST repression in chondrocyte phenotypic genes modulation. Ninteen differentially expressed proteins were screened and identified. Among these proteins, CoREST, HHL, and zinc finger protein 155 were estimated to be possible gene modulators. CoREST protein level was verified to be down-regulated by 69.5% (p < 0.001) in AOC. In response to CoREST knock-down by 64.8% (p < 0.001) in NAC chondrocytes, the gene expression level of the chondrocyte terminal differentiation marker gene, collagen X was found to be up-regulated by 40.0% (p = 0.017), whereas the chondrocyte differentiation phenotypic genes, collagen II and aggrecan were down-regulated by 71.4% (p < 0.001) and 57.6% (p < 0.001), respectively. The results indicate that the silencing of CoREST by siRNA transfection in NAC may reflect CoREST repression in AOC, which results in phenotypic genes modulation and suggests a homeostatic role of this transcription factor in articular chondrocyte.

Proximal interphalangeal joint arthritis

Proximal interphalangeal joint function is critical for proper finger and hand function and arthritis of this joint can lead to considerable hand impairment. Proximal interphalangeal joint arthritides are broadly categorized into nonerosive and erosive osteoarthritis (OA), posttraumatic arthritis, and inflammatory arthritis. The nonerosive type is considered idiopathic or primary OA, whereas the erosive form exhibits an inflammatory component. Idiopathic or primary OA occurs as a consequence of abnormal mechanical stress that leads to damage of cartilage and subchondral bone, with subsequent cytokine and growth factor activation. Individual genetics then mediate the cellular responses. Although erosive OA is described as a separate entity, this remains controversial, with many suggesting that it is merely a more aggressive form of nonerosive, primary OA. Inflammatory OA occurs when connective tissues are diseased, allowing for normal use to incite arthritic damage. Treatment modalities for proximal interphalangeal joint arthritis are currently limited.

The intermediate filament vimentin regulates chondrogenesis of adult human bone marrow-derived multipotent progenitor cells

Cytoskeletal proteins play important regulatory roles in a variety of cellular processes, including proliferation, migration, and differentiation. However, whereas actin and tubulin have established roles regulating developmental chondrogenesis, there is no evidence supporting a function for the intermediate filament vimentin in embryonic cartilage formation. We hypothesized that vimentin may regulate the chondrogenic differentiation of adult multipotent progenitor cells (MPCs), such as those involved in cartilage formation during bone fracture repair. As our model of adult progenitor cell chondrogenesis, we employed high-density pellet cultures of human bone marrow-derived MPCs. siRNA-mediated knockdown of vimentin mRNA and protein triggered a reduction in the extent of MPC cartilage formation, as evidenced by depressed accumulation of mRNAs for the cartilage-specific marker genes aggrecan and collagen type II, as well as reduced levels of Alcian blue-stainable proteoglycan and collagen II protein in the extracellular matrix. Moreover, mRNA and protein levels for the chondro-regulatory transcription factors SOX5, SOX6, and SOX9 were diminished by vimentin knockdown. Depleted cellular vimentin also induced a drastic reduction in PKA phosphorylation levels but did not affect the phosphorylation of multiple other chondro-regulatory kinases and transcription factors, including ERK1/2, p38, Smad2, and Smad1/5/8. Importantly, siRNA-mediated knockdown of PKA C-alpha mRNA and protein mimicked the reduction in chondrogenesis caused by diminished cellular vimentin. Finally, overexpression of vimentin in MPCs significantly enhanced the activity of a transfected collagen II promoter-luciferase reporter gene. In conclusion, we describe a novel role for the intermediate filament vimentin as a positive regulator of adult human bone marrow-derived MPC chondrogenesis.

Proteome characterization of human articular chondrocytes leads to novel insights in the function of small heat-shock proteins in chondrocyte homeostasis

OBJECTIVE

In recent years, studies have been initiated to disclose the proteome of human chondrocytes and cartilage. Despite these studies, comprehensive information of the chondrocyte proteome remains limited. This study aimed to further explore the proteome expressed by human knee chondrocytes, and to study the functional aspects of heat-shock protein 27 (HSP27), a protein related to the previously described alphaBcrystallin, in chondrocyte biology.

METHODS

Chondrocytes isolated from human knee articular cartilage were cultured in a three-dimensional alginate culture system. To simplify the protein mixtures, proteins extracted from chondrocyte cell lysates were fractionated based on hydrophobicity and molecular weight. Proteins were digested and the resulting peptides were separated and identified by an on-line two-dimensional (2-D) nanoliquid chromatography (nanoLC)-system coupled to a quadrupole time-of-flight (Qq-TOF) mass spectrometer. Differential expression analysis of HSP27 was performed by Western Blotting and quantitative polymerase chain reaction (QPCR). The effects of HSP27 on chondrocyte biology were explored by suppression of HSP27 expression induced by RNA interference (RNAi).

RESULTS

In this study, we identified proteins with unknown functions together with membrane proteins, transcription factors and other low abundant proteins, which have not yet been described in chondrocytes. Based on previous knowledge on the related protein alphaBcrystallin, we selected HSP27 from the chondrocyte proteome database. Differential expression analysis revealed a decreased expression of HSP27 in Osteoarthritic (OA) chondrocytes. RNAi experiments revealed that HSP27 is involved in interleukin-1beta (IL-1beta) induced IL-6 secretion.

CONCLUSION

These findings highlight that small HSPs, especially HSP27, play a prominent role in the maintenance of human articular chondrocyte homeostasis.

Comprehensive profiling of cartilage extracellular matrix formation and maturation using sequential extraction and label-free quantitative proteomics

Articular cartilage is indispensable for joint function but has limited capacity for self-repair. Engineering of neocartilage in vitro is therefore a major target for autologous cartilage repair in arthritis. Previous analysis of neocartilage has targeted cellular organization and specific molecular components. However, the complexity of extracellular matrix (ECM) development in neocartilage has not been investigated by proteomics. To redress this, we developed a mouse neocartilage culture system that produces a cartilaginous ECM. Differential analysis of the tissue proteome of 3-week neocartilage and 3-day postnatal mouse cartilage using solubility-based protein fractionation targeted components involved in neocartilage development, including ECM maturation. Initially, SDS-PAGE analysis of sequential extracts revealed the transition in protein solubility from a high proportion of readily soluble (NaCl-extracted) proteins in juvenile cartilage to a high proportion of poorly soluble (guanidine hydrochloride-extracted) proteins in neocartilage. Label-free quantitative mass spectrometry (LTQ-Orbitrap) and statistical analysis were then used to filter three significant protein groups: proteins enriched according to extraction condition, proteins differentially abundant between juvenile cartilage and neocartilage, and proteins with differential solubility properties between the two tissue types. Classification of proteins differentially abundant between NaCl and guanidine hydrochloride extracts (n = 403) using bioinformatics revealed effective partitioning of readily soluble components from subunits of larger protein complexes. Proteins significantly enriched in neocartilage (n = 78) included proteins previously not reported or with unknown function in cartilage (integrin-binding protein DEL1; coiled-coil domain-containing protein 80; emilin-1 and pigment epithelium derived factor). Proteins with differential extractability between juvenile cartilage and neocartilage included ECM components (nidogen-2, perlecan, collagen VI, matrilin-3, tenascin and thrombospondin-1), and the relationship between protein extractability and ECM ultrastructural organization was supported by electron microscopy. Additionally, one guanidine extract-specific neocartilage protein, protease nexin-1, was confirmed by immunohistochemistry as a novel component of developing articular cartilage in vivo. The extraction profile and matrix-associated immunostaining implicates protease nexin-1 in cartilage development in vitro and in vivo.