Understanding the role of chondrocytes in osteoarthritis: utilizing proteomics

Introduction: Proteomic analyses have been acknowledged to carry a significant prospective in elucidating the pathogenesis of several diseases, including osteoarthritis (OA). But it has not been an easy road: major technical issues, mainly derived from the complex and rigid nature of the cartilage tissue, had to be faced; an obstacle that led to the development of different approaches.

Areas covered: In this review, we categorized the proteomic studies undertaken (proteomic analyses of the cartilage, cartilage explants, cultured chondrocytes, and chondrocytes’ secretome) as part of the different strategies developed in order to overcome tissue and disease-specific challenges. Essentially these approaches aimed at identifying differences in the proteome of healthy vs diseased tissue. Our aim was to point out the novel players that have emerged from these analyses and highlight the associated mechanism(s) suggested to play a role in the pathogenesis of OA.

Expert commentary: The identified factors indicate the implication of age-associated mechanisms, such as metabolic deregulation, inflammation, and redox imbalance, in OA onset and/or progression. Taken together these results outline the causal network of the disease and place chondrocytes’ senescence at the center of the emerging aetiopathological atlas.     

New developments in osteoarthritis: Posttraumatic osteoarthritis: pathogenesis and pharmacological treatment options

Joint trauma can lead to a spectrum of acute lesions, including osteochondral fractures, ligament or meniscus tears and damage to the articular cartilage. This is often associated with intraarticular bleeding and causes posttraumatic joint inflammation. Although the acute symptoms resolve and some of the lesions can be surgically repaired, joint injury triggers a chronic remodeling process in cartilage and other joint tissues that ultimately manifests as osteoarthritis in a majority of cases. The objective of the present review is to summarize information on pathogenetic mechanisms involved in the acute and chronic consequences of joint trauma and discuss potential pharmacological interventions. The focus of the review is on the early events that follow joint trauma since therapies for posttraumatic joint inflammation are not available and this represents a unique window of opportunity to limit chronic consequences.     

Streptococcal toxins: role in pathogenesis and disease

Group A Streptococcus (Streptococcus pyogenes), group B Streptococcus (Streptococcus agalactiae) and Streptococcus pneumoniae (pneumococcus) are host‐adapted bacterial pathogens among the leading infectious causes of human morbidity and mortality. These microbes and related members of the genus Streptococcus produce an array of toxins that act against human cells or tissues, resulting in impaired immune responses and subversion of host physiological processes to benefit the invading microorganism. This toxin repertoire includes haemolysins, proteases, superantigens and other agents that ultimately enhance colonization and survival within the host and promote dissemination of the pathogen.     

New insights on the role of T cells in the pathogenesis of celiac disease

Despite intense investigation, the pathogenetic mechanisms leading to villous atrophy in Celiac disease (CD) remain not completely understood. The traditional interpretation is that CD4 cells recognize gliadin and develop an inflammatory reaction by production of Th1 cytokines at the mucosa level inducing CD8 cells to kill mucosal cells by a direct cytotoxic mechanism or by Fas-mediated apoptosis. Recent data, however, have shown that novel CD4 T-cells subpopulations, CD4+ CD25+ Regulatory T cells (Tregs) and Th17 cells also play a role in the ongoing inflammatory process. Both Tregs and Th17 cells are increased in active CD. However, because Tregs have a suppressive activity on inflammation, their role is controversial. In this editorial we discuss these recent findings and the hypothesis formulated to explain the increase of Tregs. To understand the pathogenesis of tissue damage of CD, we have focused on the duodenal micro-environment, introducing the new concept of immunological niche that in CD summarizes cellular and cytokine interactions in duodenal mucosa, where a high plasticity of T-cell subsets is present. CD is often complicated by T-cell lymphomas, especially in cases of refractory CD.     

The critical role of UDP-galactose-4-epimerase in osteoarthritis: Modulating proteoglycans synthesis of the articular chondrocytes

UDP-galactose-4-epimerase (GALE) is a key enzyme catalyzing the interconversion of UDP-glucose and UDP-galactose, as well as UDP-N-acetylglucosamine and UDP-N-acetylgalactosamine, which are all precursors for the proteoglycans (PGs) synthesis. However, whether GALE is essential in cartilage homeostasis remains unknown. Therefore, we investigated the role of GALE in PGs synthesis of human articular chondrocytes, the GALE expression in OA, and the regulation of GALE expression by interleukin-1beta (IL-1β). Silencing GALE gene with specific siRNAs resulted in a markedly inhibition of PGs synthesis in human articular chondrocytes. GALE protein levels were also decreased in both human and rat OA cartilage, thus leading to losses of PGs contents. Moreover, GALE mRNA expression was stimulated by IL-1β in early phase, but suppressed in late phase, while the suppression of GALE expression induced by IL-1β was mainly mediated by stress-activated protein kinase/c-Jun N-terminal kinase pathway. These data indicated a critical role of GALE in maintaining cartilage homeostasis, and suggested that GALE inhibition might contribute to OA progress.     

Human articular chondrocytes express 15-lipoxygenase-1 and -2: potential role in osteoarthritis

Introduction

Although cardiovascular morbidity and mortality are increased in rheumatoid arthritis, little is known about the burden of subclinical coronary atherosclerosis in these patients.

Methods

Using computed tomography, coronary artery calcification was measured in 195 men and women with rheumatoid arthritis aged 45 to 84 years without clinical cardiovascular disease and compared with 1,073 controls without rheumatoid arthritis enrolled in the Baltimore cohort of the Multi-Ethnic Study of Atherosclerosis.

Results

The prevalence of coronary calcification (Agatston score > 0) was significantly higher in men, but not women, with rheumatoid arthritis after adjusting for sociodemographic and cardiovascular risk factors (prevalence ratio = 1.19; P = 0.012). Among participants with prevalent calcification, those with rheumatoid arthritis had adjusted mean Agatston scores 53 units higher than controls (P = 0.002); a difference greater for men than women (P for interaction = 0.017). In all analyses, serum IL-6 attenuated the association between rheumatoid arthritis and coronary calcification, suggesting its role as a potential mediator of enhanced atherosclerosis. Notably, increasing severity of rheumatoid arthritis was associated with a higher prevalence and extent of coronary calcification among both men and women with rheumatoid arthritis, and for all age categories. The largest percentage difference in coronary arterial calcification between rheumatoid arthritis patients and their nonrheumatoid arthritis counterparts was observed in the youngest age category.

Conclusions

Increasing rheumatoid arthritis disease severity was associated with a higher prevalence and greater extent of coronary artery calcification, potentially mediated through an atherogenic effect of chronic systemic inflammation. Gender and age differences in association with coronary calcification suggest that preventive measures should be emphasized in men with rheumatoid arthritis, and considered even in younger rheumatoid arthritis patients with low levels of traditional cardiovascular risk factors.     

Molecular aspects of disease pathogenesis in the transmissible spongiform encephalopathies

The transmissible spongiform encephalopathies (TSE), or prion diseases, are a group of rare, fatal, and transmissible neurodegenerative diseases of mammals for which there are no known viral or bacterial etiological agents. The bovine form of these diseases, bovine spongiform encephalopathy (BSE), has crossed over into humans to cause variant Creutzfeldt-Jakob disease. As a result, BSE and the TSE diseases are now considered a significant threat to human health. Understanding the basic mechanisms of TSE pathogenesis is essential for the development of effective TSE diagnostic tests and anti-TSE therapeutic regimens. This review provides an overview of the molecular mechanisms that underlie this enigmatic group of diseases.     

Human articular chondrocytes express 15-lipoxygenase-1 and -2: potential role in osteoarthritis

Introduction  

15-Lipoxygenases and their metabolites have been shown to exhibit anti-inflammatory and immunomodulatory properties, but little is known regarding their expression and function in chondrocytes. The objective of this study was to evaluate the expression of 15-lipoxygenase-1 and -2 in human articular chondrocytes, and to investigate the effects of their metabolites 13(S)-hydroxy octadecadienoic and 15(S)-hydroxyeicosatetraenoic acids on IL-1β-induced matrix metalloproteinase (MMP)-1 and MMP-13 expression.     

CD14: Biology and role in the pathogenesis of disease

Human monocyte differentiation antigen CD14 is a pattern recognition receptor (PRR) that enhances innate immune responses. CD14 was first identified as a marker of monocytes to signal intracellular responses upon bacterial encounters. Given the absence of an intracellular tail, CD14 was doubted to have the signaling capacities. Later CD14 was confirmed as the TLR co-receptor for the detection of pathogen-associated molecular patterns. However, CD14 has been revealed as a multi-talented receptor. In last decade, CD14 was identified to activate NFAT to regulate the life cycle of myeloid cells in a TLR4-independent manner and to transport inflammatory lipids to induce phagocyte hyperactivation. And its influences on multiple related diseases have been further considered. In this review, we summarize advancements in the basic biology of the CD14 including its structure, binding ligands, signaling pathways, and its roles in the pathogenesis of inflammation, atherosclerosis, tumor and metabolic diseases. We also discuss the therapeutic potential of targeting the CD14 in related diseases.     

New aspects in the pathogenesis of infectious and tumor anaemia

From new evidence of increased adhesion of immune complexes in the plasma protein film of erythrocytes, the pathogenesis of tumor anaemia and anaemia in chronic infections is suggested to be a mechanism of the early sequestration of the erythrocytes by erythrophagocytosis following their coating with immune complexes and denaturated immunoglobulins.     

Streptococcal beta-hemolysins: genetics and role in disease pathogenesis

A zone of β-hemolysis surrounding colonies on blood-agar media is a hallmark phenotypic feature of the pathogens group A Streptococcus (GAS) and group B Streptococcus (GBS). In each case, lysis of red blood cells reflects the action of a potent protein exotoxin. Although these toxins have been the subjects of numerous investigations over the years, their purification and molecular identification have proven elusive. These difficulties reflect the instability of hemolytic activity, as both toxins function only in the context of the bacterial surface or certain high molecular weight ‘stabilizer’ molecules. This review highlights the recent discoveries of two markedly distinct genetic loci, necessary and sufficient for the β-hemolytic phenotypes of GAS and GBS, respectively. The generation of isogenic GAS and GBS β-hemolysin-deficient mutants and their analysis using in vitro and in vivo model systems has shown that both toxins function as virulence factors in the pathogenesis of invasive infections.     

Chagas disease: role of parasite genetic variation in pathogenesis

Chagas disease, caused by the parasite protozoan Trypanosoma cruzi, is characterised by a variable clinical course, from symptomless cases to severe chronic disease with cardiac and/or gastrointestinal involvement. This variability has been attributed both to differences in the host response and to genomic heterogeneity of the parasite. This article reviews the evidence in favour of an important role of the genetic constitution of T. cruzi in determining the clinical characteristics of Chagas disease and discusses the basis of the 'Clonal-Histotropic Model' for the pathogenesis of this disease.     

Shaping the role of mitochondria in the pathogenesis of Huntington's disease

Intense research on the pathogenesis of Huntington's disease (HD), a genetic neurodegenerative disease caused by a polyglutamine expansion in the Huntingtin (Htt) protein, revealed multiple potential mechanisms, among which mitochondrial alterations had emerged as key determinants of the natural history of the disease. Pharmacological and genetic animal models of mitochondrial dysfunction in the striatum, which is mostly affected in HD corroborated a key role for these organelles in the pathogenesis of the disease. Here, we will give an account of the recent evidence indicating that the mitochondria-shaping machinery is altered in HD models and patients. Since its correction can counteract HD mitochondrial dysfunction and cellular damage, drugs impacting on mitochondrial shape are emerging as a new possibility of treatment for this devastating condition.     

Comparative proteomic analysis of hypertrophic chondrocytes in osteoarthritis

Background

Osteoarthritis (OA) is a multi-factorial disease leading progressively to loss of articular cartilage and subsequently to loss of joint function. While hypertrophy of chondrocytes is a physiological process implicated in the longitudinal growth of long bones, hypertrophy-like alterations in chondrocytes play a major role in OA. We performed a quantitative proteomic analysis in osteoarthritic and normal chondrocytes followed by functional analyses to investigate proteome changes and molecular pathways involved in OA pathogenesis.

Methods

Chondrocytes were isolated from articular cartilage of ten patients with primary OA undergoing knee replacement surgery and six normal donors undergoing fracture repair surgery without history of joint disease and no OA clinical manifestations. We analyzed the proteome of chondrocytes using high resolution mass spectrometry and quantified it by label-free quantification and western blot analysis. We also used WebGestalt, a web-based enrichment tool for the functional annotation and pathway analysis of the differentially synthesized proteins, using the Wikipathways database. ClueGO, a Cytoscape plug-in, is also used to compare groups of proteins and to visualize the functionally organized Gene Ontology (GO) terms and pathways in the form of dynamical network structures.

Results

The proteomic analysis led to the identification of a total of ~2400 proteins. 269 of them showed differential synthesis levels between the two groups. Using functional annotation, we found that proteins belonging to pathways associated with regulation of the actin cytoskeleton, EGF/EGFR, TGF-β, MAPK signaling, integrin-mediated cell adhesion, and lipid metabolism were significantly enriched in the OA samples (p ≤10⁻⁵). We also observed that the proteins GSTP1, PLS3, MYOF, HSD17B12, PRDX2, APCS, PLA2G2A SERPINH1/HSP47 and MVP, show distinct synthesis levels, characteristic for OA or control chondrocytes.

Conclusion

In this study we compared the quantitative changes in proteins synthesized in osteoarthritic compared to normal chondrocytes. We identified several pathways and proteins to be associated with OA chondrocytes. This study provides evidence for further testing on the molecular mechanism of the disease and also propose proteins as candidate markers of OA chondrocyte phenotype.

Electronic supplementary material

The online version of this article (doi:10.1186/s12014-015-9085-6) contains supplementary material, which is available to authorized users.