Differential upregulation of the three transforming growth factor beta isoforms in human osteoarthritic cartilage
ABSTRACT Decreased levels of transforming growth factor beta (TGFbeta) have been related to the failure of cartilage repair in experimental models of osteoarthritis. This study aimed to examine this aspect of osteoarthritis in human cartilage.
Cartilage samples were obtained from 11 patients with hip osteoarthritis and 11 patients with femoral neck fracture who were undergoing total hip replacement. Gene expression of the three TGFbeta isoforms, collagen type II (COL2A1) and aggrecan (AGC1) was analysed by reverse transcription quantitative PCR and immunohistochemistry.
Expression of the three TGFbeta isoforms was increased in osteoarthritis cartilage. The upregulation was more marked for the TGFbeta3 isoform (2.3-fold) than for TGFbeta1 (1.6-fold) or TGFbeta2 (1.7-fold). The messenger RNA levels of TGFbeta1 and TGFbeta2 were strongly correlated in osteoarthritis cartilage (r(s) = 0.83, p = 0.002), but levels of TGFbeta3 were uncorrelated with any of the two other TGFbeta isoforms. Immunohistochemistry showed an extension of immunoreactivity for the three TGFbeta isoforms to more chondrocytes and to deeper cartilage layers in the more severe osteoarthritis lesions. No correlation of TGFbeta isoforms with COL2A1 or AGC1 expression levels was found.
The three isoforms of TGFbeta were differentially upregulated in late osteoarthritis in relation to an increased percentage of TGFbeta-positive chondrocytes. These results indicate that cartilage damage progresses in spite of the TGFbeta stimulus for cartilage anabolism and that other causes of the failure to cope with the increased cartilage catabolism of osteoarthritis should be investigated.
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ABSTRACT: Osteoarthritis (OA) is the most common degenerative joint disease and no disease-modifying therapy for OA is currently available. Targeting articular cartilage alone may not be sufficient to halt this disease progression. Articular cartilage and subchondral bone act as a functional unit. Increasing evidence indicates that transforming growth factor β (TGFβ) plays a crucial role in maintaining homeostasis of both articular cartilage and subchondral bone. Activation of extracellular matrix (ECM) latent TGFβ at the appropriate time and location is a prerequisite for its function. Aberrant activation of TGFβ in the subchondral bone in response to an abnormal mechanical loading environment induces formation of osteroid islets at the onset of OA. As a result, alteration of subchondral bone structure changes the stress distribution on the articular cartilage and leads to its degeneration. Thus, inhibition of TGFβ activity in the subchondral bone may provide a new avenue of treatment for OA. In this review we will discuss the role of TGFβ in the homeostasis of articular cartilage and subchondral bone as a novel target for OA therapy.Trends in Pharmacological Sciences 04/2014; DOI:10.1016/j.tips.2014.03.005 · 9.99 Impact Factor
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ABSTRACT: Pain is the main problem for patients with OA. Pain is linked to inflammation, but in OA a subset of patients suffers from pain without inflammation, indicating an alternative source of pain. NGF inhibition is very efficient in blocking pain during OA, but the source of NGF is unclear. We hypothesize that damaged cartilage in OA releases TGF-beta, which in turn stimulates chondrocytes to produce NGF. Murine and human chondrocyte cell lines, primary bovine and human chondrocytes, and cartilage explants from bovine metacarpal joints and human OA joints were stimulated with TGF-β1 and/or IL-1β. We analyzed NGF expression on mRNA level with QPCR and stained human OA cartilage for NGF immunohistochemically. Cultures were additionally pre-incubated with inhibitors for TAK1, Smad2/3 or Smad1/5/8 signaling to identify the TGF-β pathway inducing NGF. NGF expression was consistently induced in higher levels by TGF-β than IL-1 in all of our experiments: murine, bovine and human origin, in cell lines, primary chondrocytes and explants cultures. TAK1 inhibition consistently reduced TGF-β-induced NGF whereas it fully blocked IL-1β-induced NGF expression. In contrast, ALK5-Smad2/3 inhibition fully blocked TGF-β-induced NGF expression. Despite the large variation in basal NGF in human OA samples (mRNA and histology), TGF-β exposure led to a consistent high level of NGF induction. We show for the first time that TGF-β induces NGF expression in chondrocytes, in a ALK5-Smad2/3 dependent manner. This reveals a potential alternative non-inflammatory source of pain in OA. Copyright © 2014 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.Osteoarthritis and Cartilage 12/2014; 23(3). DOI:10.1016/j.joca.2014.12.005 · 4.66 Impact Factor
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ABSTRACT: The development of osteoarthritis (OA) depends on genetic and environmental factors, which influence the biology of the chondrocyte via epigenetic regulation. Changes within the epigenome might lead the way to discovery of new pathogenetic pathways. We performed a genome-wide methylation screening to identify potential differences between paired mild and severe osteoarthritic human cartilage. Sixteen female patients suffering from OA underwent total knee joint replacement. Cartilage specimens collected from corresponding macroscopically undamaged and from damaged areas were processed for DNA extraction and histology to evaluate the histological grading of the disease. Paired specimens were analysed for the methylation status of the whole genome using human promoter microarrays (Agilent, Santa Clara, CA). Selected target genes were then validated via methylation-specific qPCR. One thousand two hundred and fourteen genetic targets were identified differentially methylated between mild and severe OA. One thousand and seventy of these targets were found hypermethylated and 144 hypomethylated. The descriptive analysis of these genes by Gene Ontology (GO), KEGG pathway and protein domain analyses points to pathways of development and differentiation. We identified a list of genes which are differently methylated in mild and severe OA cartilage. Within the pathways of growth and development new therapeutic targets might arise by improving our understanding of pathogenetic mechanisms in OA. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop ResJournal of Orthopaedic Research 12/2014; 32(12). DOI:10.1002/jor.22722 · 2.97 Impact Factor