Comparative proteomic analysis of hypertrophic chondrocytes in osteoarthritis.

Konstantinos C Tsolis,Michalis Zervakis,Konstantinos Malizos,Kalliopi Kalantzaki,Ekaterini S Bei,Ioanna Papathanasiou,Anastassios Economou,Aspasia Tsezou,Vassiliki Gkretsi,Fotini Kostopoulou

doi:10.1186/s12014-015-9085-6

Abstract

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

Highlights

Osteoarthritis (OA) is a multi-factorial disease leading progressively to loss of articular cartilage and subsequently to loss of joint function
Lack of identification for a given protein indicates that it is either not synthesized at all or that it exists in amounts that are below detection [22]
127 of the proteins shared between the chondrocytes from the OA and control groups, showed differential abundance (42 of them shown in Figure 2; for the complete set see Additional file 1 – “Over-synthesized in OA” and “Under-synthesized in OA”)

Summary

Introduction

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. OA affects the whole joint, leading to cartilage degradation, synovial inflammation and subchondral bone remodelling [1,2]. Structural alterations start before middle age but can be diagnosed when they become symptomatic where at that time there is a severe damage in the joint. Several patho-physiological processes are involved in the disease phenotype, the triggering event for disease onset is unknown, as a result OA is considered a multi-factorial disease [1,3,6,7,8]. Several risk factors have been associated with OA, including age, obesity, mechanical load, genetic predisposition, sex, and prior joint injury [7,9]

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