Abstract
BackgroundCartilage damage is a crucial step in rheumatoid arthritis (RA) disease progress while its molecular mechanisms are not fully understood. Here we investigated the expression of hedgehog (Hh) signal pathway in articular cartilage of adjuvant-induced arthritis (AIA) rats and its possible pathological role in cartilage damage.Methods30 rats were divided into sham and AIA group (n = 15). Complete Freund’s adjuvant was used to induce AIA. Secondary paw swelling was measured on day 10, 14, 18, 22 and 26 after induction. Rats were sacrificed on day 26 and knee joints and cartilage tissues were collected. Paw swelling, cartilage histopathologic changes and OARSI scores were used to evaluate AIA in rats. The protein expression of Hh signal related genes (Shh, Ptch1, Smo and Gli1) in cartilage were assayed by immunohistochemistry. The mRNA levels of Shh, Ptch1, Smo, Gli1, type-II collagen (COII) and aggrecan in cartilage were assayed by real-time PCR. In vitro study, cultured AIA chondrocytes were treated with cyclopamine (a specific inhibitor of Hh signal) and the mRNA levels of Hh signal and ECM components (COII and aggrecan) were measured by real-time PCR.ResultsImmunohistochemical results revealed that Shh, Ptch1, Smo and Gli1 proteins showed higher expression in the articular cartilage of AIA rats than those of sham rats. Real-time PCR results confirmed that Shh, Ptch1, Smo and Gli1 mRNA levels in cartilage tissues of AIA rats were significantly increased compared with those of sham rats (1.6, 1.4, 1.6, 2.0 fold, respectively). The mRNA levels of Shh, Ptch1, Smo, and Gli1 were associated with the severity of cartilage damage (indicated by OARSI scores, COII and aggrecan mRNA levels in cartilage). In vitro, cyclopamine effectively decreased the mRNA levels of Shh, Ptch1, Smo and Gli1, and increased the mRNA levels of COII and aggrecan in AIA chondrocytes, suggesting Hh signal inhibition might directly promote ECM production.ConclusionsOur findings present certain experimental evidence that Hh signal pathway is involved in the pathogenesis of cartilage damage in RA.
Highlights
Cartilage damage is a crucial step in rheumatoid arthritis (RA) disease progress while its molecular mechanisms are not fully understood
We investigated the expression of Hh signal related genes (Shh, patched homologue 1 (Ptch1), Smo and Glioma-associated oncogene homolog 1 (Gli1)) at protein and mRNA levels in the articular cartilage of rats with adjuvant-induced arthritis (AIA)
Typical pathological characteristics of cartilage damage including cartilage loss, articular cartilage zone thinness and articular surface roughness were apparently found in AIA rats (Figure 1d)
Summary
Cartilage damage is a crucial step in rheumatoid arthritis (RA) disease progress while its molecular mechanisms are not fully understood. We investigated the expression of hedgehog (Hh) signal pathway in articular cartilage of adjuvant-induced arthritis (AIA) rats and its possible pathological role in cartilage damage. Rheumatoid arthritis (RA) is a chronic inflammatory disease that often leads to serious disability resulting from cartilage and joint destruction [1,2]. The detailed molecular mechanisms underlying cartilage damage in RA are not fully understood. Signaling by Smo results in the activation of transcription factors encoded by glioma-associated oncogene homolog (Gli) and consequent induction of Hh target genes (Gli, Ptch1), and the levels of these transcripts are regarded as surrogate markers of Hh pathway activity [9,10]
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