Applications of proteomics to osteoarthritis, a musculoskeletal disease characterized by aging

Proteomics profiling of human synovial fluid suggests increased protein interplay in early-osteoarthritis (OA) that is lost in late-stage OA

The underlying molecular mechanisms in osteoarthritis (OA) development are largely unknown. This study explores the proteome and the pairwise interplay of proteins in synovial fluid from patients with late-stage knee OA (arthroplasty), early knee OA (arthroscopy due to degenerative meniscal tear), and from deceased controls without knee OA. Synovial fluid samples were analyzed using state-of-the-art mass spectrometry with data-independent acquisition. The differential expression of the proteins detected was clustered and evaluated with data mining strategies and a multilevel model. Group-specific slopes of associations were estimated between expressions of each pair of identified proteins to assess the co-expression (i.e., interplay) between the proteins in each group. More proteins were increased in early-OA versus controls than late-stage OA versus controls. For most of these proteins, the fold changes between late-stage OA versus controls and early-stage OA versus controls were remarkably similar suggesting potential involvement in the OA process. Further, for the first time, this study illustrated distinct patterns in protein co-expression suggesting that the interplay between the protein machinery is increased in early-OA and lost in late-stage OA. Further efforts should focus on earlier stages of the disease than previously considered.

•

Synovial fluid proteomics study of different stages of osteoarthritis (OA).

•

Higher catabolic activity is found in both early- and late-stage OA.

•

Imbalance of the metabolic homeostasis in late-stage OA.

•

Understanding early-stage OA may lead to finding better effective therapies.

Ribosome dysfunction in osteoarthritis

PURPOSE OF REVIEW

Translation of genetic information encoded within mRNA molecules by ribosomes into proteins is a key part of the central dogma of molecular biology. Despite the central position of the ribosome in the translation of proteins, and considering the major proteomic changes that occur in the joint during osteoarthritis development and progression, the ribosome has received very limited attention as driver of osteoarthritis pathogenesis.

RECENT FINDINGS

We provide an overview of the limited literature regarding this developing topic for the osteoarthritis field. Recent key findings that connect ribosome biogenesis and activity with osteoarthritis include: ribosomal RNA transcription, processing and maturation, ribosomal protein expression, protein translation capacity and preferential translation.

SUMMARY

The ribosome as the central cellular protein synthesis hub is largely neglected in osteoarthritis research. Findings included in this review reveal that in osteoarthritis, ribosome aberrations have been found from early-stage ribosome biogenesis, through ribosome build-up and maturation, up to preferential translation. Classically, osteoarthritis has been explained as an imbalance between joint tissue anabolism and catabolism. We postulate that osteoarthritis can be interpreted as an acquired ribosomopathy. This hypothesis fine-tunes the dogmatic anabolism/katabolism point-of-view, and may provide novel molecular opportunities for the development of osteoarthritis disease-modifying treatments.

Comparative label-free proteomic analysis of equine osteochondrotic chondrocytes

Osteochondrosis is a developmental orthopedic disease affecting growing cartilage in young horses. In this study we compared the proteomes of equine chondrocytes obtained from healthy and osteochondrotic cartilage using a label-free mass spectrometry approach. Quantitative changes of some proteins selected for their involvement in different functional pathways highlighted by the bioinformatics analysis, were validated by western blotting, while biochemical alterations of extracellular matrix were confirmed via Raman spectroscopy analysis. In total 1637 proteins were identified, of which 59 were differentially abundant. Overall, the results highlighted differentially represented proteins involved in metabolic and functional pathways that may be related to the failure of the endochondral ossification process occurring in osteochondrosis. In particular, we identified proteins involved in extracellular matrix degradation and organization, vitamin metabolism, osteoblast differentiation, apoptosis, protein folding and localization, signalling and gene expression modulation and lysosomal activities. These results provide valuable new insights to elucidate the underlying molecular mechanisms associated with the development and progression of osteochondrosis. SIGNIFICANCE: Osteochondrosis is a common articular disorder in young horses mainly due to defects in endochondral ossification. The pathogenesis of osteochondrosis is still poorly understood and only a limited number of proteomic studies have been conducted. This study provides a comprehensive characterization of proteomic alterations occurring in equine osteochondrotic chondrocytes, the only resident cell type that modulates differentiation and maturation of articular cartilage. The results evidenced alterations in abundance of proteins involved in functional and metabolic pathways and in extracellular matrix remodelling. These findings could help clarify some molecular aspects of osteochondrosis and open new fields of research for elucidating the pathogenesis of this disease.

Functional analysis of synovial fluid from osteoarthritic knee and carpometacarpal joints unravels different molecular profiles

OBJECTIVE

In this work, we aimed to elucidate the molecular mechanisms driving primary OA. By studying the dynamics of protein expression in two different types of OA joints we searched for similarities and disparities to identify key molecular mechanisms driving OA.

METHODS

For this purpose, human SF samples were obtained from CMC-I OA and knee joint of OA patients. SF samples were analysed by label-free quantitative liquid chromatography mass spectrometry. Disease-relevant proteins identified in proteomics studies, such as clusterin, paraoxonase/arylesterase 1 (PON1) and transthyretin were validated by enzyme-linked immunosorbent assays, and on the mRNA level by droplet digital PCR. Functional studies were performed in vitro using primary chondrocytes.

RESULTS

Differential proteomic changes were observed in the concentration of 40 proteins including clusterin, PON1 and transthyretin. Immunoassay analyses of clusterin, PON1, transthyretin and other inflammatory cytokines confirmed significant differences in protein concentration in SF of CMC-I and knee OA patients, with primarily lower protein expression levels in CMC-I. Functional studies on chondrocytes unequivocally demonstrated that stimulation with SF obtained from knee OA, in contrast to CMC-I OA joint, caused a significant upregulation in pro-inflammatory response, cell death and hypertrophy.

CONCLUSION

This study demonstrates that differential expression of molecular players in SF from different OA joints evokes diverse effects on primary chondrocytes. The pathomolecular mechanisms of OA may significantly differ in various joints, a finding that brings a new dimension into the pathogenesis of primary OA.

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.

The use of native fluorescence analysis of synovial fluid in the diagnosis of medial compartment disease in medium- and large-breed dogs

We assumed that proteins are most likely responsible for synovial fluid fluorescence and that changes detected in fluorescence intensity are most likely the result of changes in the concentration of fluorescent proteins. Synchronous fluorescent matrices from synovial fluid samples were measured in the excitation wavelength range of 200-350 nm using a luminescence spectrophotometer. The synchronous matrix of synovial fluid consists of 2 dominant fluorescent centers (F1 and F2) in the ultraviolet region. The fluorescence intensities of both centers were significantly higher in pathological samples, with p = 0.001 (a 59% increase of the median value) for the F1 center and p = 0.002 (a 52% increase of the median value) for the F2 center. Receiver operating characteristic analysis confirmed that synovial fluid autofluorescence is a significant predictor of medial compartment disease in dogs, with the area under the curve at 0.776 (F1) and 0.778 (F2). We did not detect any differences in the autofluorescence of synovial fluid between male and female, or any breed-based changes. No position changes of fluorescent centers were recorded in the synovial fluid in diseased dogs compared with healthy dogs. The synovial fluid metabolic fingerprint of canine patients with medial compartment disease differed from that of healthy dogs. Our study demonstrated the feasibility of synovial fluid fingerprinting to identify disease-specific profiles of synovial fluid metabolites.

Osteoarthritis in the XXIst century: risk factors and behaviours that influence disease onset and progression

Osteoarthritis (OA) is a growing public health problem across the globe, affecting more than half of the over 65 population. In the past, OA was considered a wear and tear disease, leading to the loss of articular cartilage and joint disability. Nowadays, thanks to advancements in molecular biology, OA is believed to be a very complex multifactorial disease. OA is a degenerative disease characterized by “low-grade inflammation” in cartilage and synovium, resulting in the loss of joint structure and progressive deterioration of cartilage. Although the disease can be dependent on genetic and epigenetic factors, sex, ethnicity, and age (cellular senescence, apoptosis and lubricin), it is also associated with obesity and overweight, dietary factors, sedentary lifestyle and sport injuries. The aim of this review is to highlight how certain behaviors, habits and lifestyles may be involved in the onset and progression of OA and to summarize the principal risk factors involved in the development of this complicated joint disorder.

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.

Effects of a multimodal exercise program in pedal dexterity and balance: study with Portuguese older adults of different contexts

This study investigated the effects of a multimodal exercise program (MEP) on pedal dexterity and balance in two groups of older adult participants (65–92 years of age) from a psychiatric hospital center (HC), a residential care home (RCH), and a daily living center (DLC). The experimental group (EG) trained three times per week for 12 months, and the control group (CG) maintained their normal activities. The Mini-Mental State Examination and the Modified Baecke Questionnaire, as well as the Pedal Dexterity and the Tinetti tests, were applied to all subjects before and after the experimental protocol. Furthermore, the foot preference was controlled using the Lateral Preference Questionnaire proposed by Coren [10]. In the EG, the results from the Pedal Dexterity test showed that both males and females from the RCH and DLC improved their performances after the MEP. In the HC, the males slightly decreased their performance with both feet, contrarily to females. Both males and females from the CG decreased their pedal dexterity performance, namely, with the non-preferred foot. Concerning the Tinetti test, the EG of both males and females from the HC, the RCH (males were better than females regarding the gender factor), and the DLC improved their balance after the MEP. In the CG, no significant effects or interactions were found for any of the context groups.

The genetics and functional analysis of primary osteoarthritis susceptibility

Recent genome-wide association scans (GWASs) along with several adequately powered candidate gene studies have yielded a number of risk alleles for osteoarthritis (OA). This number is now sufficiently large to allow conclusions to be drawn regarding the nature of genetic susceptibility, including the fact that the risk alleles have variable effects depending on sex, ethnicity and on the skeletal site of the disease. Several of the alleles that have emerged from the GWASs are within or close to highly plausible candidate genes, including RUNX2 and CHST11. However, the majority of risk alleles do not map to genes previously reported to play a role in musculoskeletal biology, indicating that the GWAS datasets are telling us something new about the OA disease process. Functional studies have so far revealed that effects on gene expression are likely to be one of the main mechanisms through which OA susceptibility is acting. Epigenetic mechanisms such as DNA methylation also influence OA risk, and integration of genetic, transcriptomic and epigenetic data will allow us to use the genetic discoveries for informed development of new OA biological treatments.

Biochemical markers of aging for longitudinal studies in humans

Much progress has been made in the past decades in unraveling the mechanisms that are responsible for aging. The discovery that particular gene mutations in experimental species such as yeast, flies, and nematodes are associated with longevity has led to many important insights into pathways that regulate aging processes. However, extrapolating laboratory findings in experimental species to knowledge that is valid for the complexity of human physiology remains a major challenge. Apart from the restricted experimental possibilities, studying aging in humans is further complicated by the development of various age-related diseases. The availability of a set of biomarkers that really reflect underlying aging processes would be of much value in disentangling age-associated pathology from specific aging mechanisms. In this review, we survey the literature to identify promising biochemical markers of aging, with a particular focus on using them in longitudinal studies of aging in humans that entail repeated measurements on easily obtainable material, such as blood samples. Our search strategy was a 2-pronged approach, one focused on general mechanisms of aging and one including studies on clinical biomarkers of age-related diseases.

Osteoarthritis year 2012 in review: biomarkers

PURPOSE

Biomarkers provide useful diagnostic information by detecting cartilage degradation in osteoarthritis (OA), reflecting disease-relevant biological activity and predicting the course of disease progression. They also serve as surrogate endpoints in the drug discovery process. The aim of this narrative review was to focus on OA biomarker-related papers published between the osteoarthritis research society international (OARSI) 2011 meeting in San Diego and the OARSI 2012 meeting in Barcelona.

METHODS

The PubMed/MEDLINE and SciVerse Scopus bibliographic databases were searched using the keywords: 'biomarker' and 'osteoarthritis' and/or 'biomarker' and 'proteomics'.

RESULTS

Ninety-eight papers were found with the keywords 'biomarker' and 'osteoarthritis'. Fifteen papers were found with the keywords 'biomarker' and 'proteomics'. Review articles were also included. The most relevant published studies focused on extracellular matrix (ECM) molecules in body fluids. Enrichment of the deamidated epitope of cartilage oligomeric matrix protein (D-COMP) suggests that OA disease progression is associated with post-translational modifications that may show specificity for particular joint sites. Fibulin-3 peptides (Fib3-1 and Fib3-2) have been proposed as potential biomarkers of OA along with follistatin-like protein 1 (FSTL1), a new serum biomarker with the capacity to reflect the severity of joint damage. The 'membrane attack complex' (MAC) component of complement has also been implicated in OA.

CONCLUSION

Novel OA biomarkers are needed for sub-clinical disease diagnosis. Proteomic techniques are beginning to yield useful data and deliver new OA biomarkers in serum and urine. Combining biochemical markers with tissue and cell imaging techniques and bioinformatics (i.e., machine learning, clustering, data visualization) may facilitate the development of biomarker combinations enabling earlier detection of OA.