Genome-wide expression profiles of subchondral bone in osteoarthritis

Ching-Heng Chou,Liang-Suei Lu,Ming Ta Michael Lee,Virginia Kraus,Jer-Yuarn Wu,Chia-Chun Wu,Yuan-Tsong Chen,San-Yuan Kuo,Chian-Her Lee,Jen-Huei Chang,I-Wen Song,Hui-Ping Chuang

doi:10.1186/ar4380

Abstract

IntroductionThe aim of this study was to evaluate, for the first time, the differences in gene expression profiles of normal and osteoarthritic (OA) subchondral bone in human subjects.MethodsFollowing histological assessment of the integrity of overlying cartilage and the severity of bone abnormality by micro-computed tomography, we isolated total RNA from regions of interest from human OA (n = 20) and non-OA (n = 5) knee lateral tibial (LT) and medial tibial (MT) plateaus. A whole-genome profiling study was performed on an Agilent microarray platform and analyzed using Agilent GeneSpring GX11.5. Confirmatory quantitative reverse-transcription polymerase chain reaction (qRT-PCR) analysis was performed on samples from 9 OA individuals to confirm differential expression of 85 genes identified by microarray. Ingenuity Pathway Analysis (IPA) was used to investigate canonical pathways and immunohistochemical staining was performed to validate protein expression levels in samples.ResultsA total of 972 differentially expressed genes were identified (fold change ≥ ± 2, P ≤0.05) between LT (minimal degeneration) and MT (significant degeneration) regions from OA samples; these data implicated 279 canonical pathways in IPA. The qRT-PCR data strongly confirmed the accuracy of microarray results (R2 = 0.58, P <0.0001). Novel pathways were identified in this study including Periostin (POSTN) and Leptin (LEP), which are implicated in bone remodeling by osteoblasts.ConclusionsTo the best of our knowledge, this study represents the most comprehensive direct assessment to date of gene expression profiling in OA subchondral bone. This study provides insights that could contribute to the development of new biomarkers and therapeutic strategies for OA.

Highlights

The aim of this study was to evaluate, for the first time, the differences in gene expression profiles of normal and osteoarthritic (OA) subchondral bone in human subjects
Regions of interest were harvested for histological analysis of the articular cartilage, and subchondral bone structural parameters were determined by micro-computed tomography; regions immediately adjacent were harvested for RNA isolation and microarray analysis
Analysis of differential gene expression For the microarray analysis, 972 differentially expressed genes with ≥2 fold-changes between OA medial tibial (MT) and OA lateral tibial (LT) regions were identified; 420 of these genes were upregulated and 552 were downregulated in OA MT compared with OA LT (Additional file 4)

Summary

Introduction

The aim of this study was to evaluate, for the first time, the differences in gene expression profiles of normal and osteoarthritic (OA) subchondral bone in human subjects. A study comparing two guinea pig strains indicates that an increasing rate of knee subchondral bone remodeling is associated with the process of cartilage deterioration [9]. Human bone cell culture studies have shown that factors released from bone cells might affect cartilage metabolism [10,11]. These studies provide insights into a temporal relationship between subchondral structural changes and alterations in articular cartilage during the development of OA; they underscore the importance of elucidating the molecular changes in human subchondral bone to improve our understanding of the pathogenesis of OA

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