Abstract
IntroductionSclerostin (SOST), a soluble antagonist of Wnt signaling, is expressed in chondrocytes and contributes to chondrocytes’ hypertrophic differentiation; however its role in osteoarthritis (OA) pathogenesis is not well known. Based on our previous findings on the interaction between Wnt/β-catenin pathway and BMP-2 in OA, we aimed to investigate the role of DNA methylation and BMP-2 on SOST’s expression in OA chondrocytes.MethodsSOST mRNA and protein expression levels were investigated using real-time polymerase chain reaction (PCR) and Western blot, respectively. The methylation status of SOST promoter was analysed using methylation-specific PCR (MSP), quantitative methylation-specific PCR (qMSP) and bisulfite sequencing analysis. The effect of BMP-2 and 5’-Aza-2-deoxycytidine (5-AzadC) on SOST’s expression levels were investigated and Smad1/5/8 binding to SOST promoter was assessed by Chromatin Immunoprecipitation (ChΙP).ResultsWe observed that SOST’s expression was upregulated in OA chondrocytes compared to normal. Moreover, we found that the CpG region of SOST promoter was hypomethylated in OA chondrocytes and 5-AzadC treatment in normal chondrocytes resulted in decreased SOST methylation, whereas its expression was upregulated. BMP-2 treatment in 5-AzadC-treated normal chondrocytes resulted in SOST upregulation, which was mediated through Smad 1/5/8 binding on the CpG region of SOST promoter.ConclusionsWe report novel findings that DNA methylation regulates SOST’s expression in OA, by changing Smad 1/5/8 binding affinity to SOST promoter, providing evidence that changes in DNA methylation pattern could underlie changes in genes’ expression observed in OA.
Highlights
Sclerostin (SOST), a soluble antagonist of Wnt signaling, is expressed in chondrocytes and contributes to chondrocytes’ hypertrophic differentiation; its role in osteoarthritis (OA) pathogenesis is not well known
SOST mRNA and protein expression levels are increased in OA chondrocytes Using real-time polymerase chain reaction (PCR), we found higher SOST mRNA expression levels in OA compared to normal chondrocytes (p = 0.005) (Fig. 1a)
DNA methylation status of SOST promoter is different between normal and OA chondrocytes Taking into consideration recent reports that demonstrated involvement of epigenetics in the regulation of SOSTs expression, we tested whether the DNA methylation status of the SOST promoter is different between normal and OA chondrocytes
Summary
Sclerostin (SOST), a soluble antagonist of Wnt signaling, is expressed in chondrocytes and contributes to chondrocytes’ hypertrophic differentiation; its role in osteoarthritis (OA) pathogenesis is not well known. The central pathological features of OA are the progressive degradation of articular cartilage, new bone formation at joint margins (osteophytes) and changes in subchondral bone. SOST is a soluble antagonist of Wnt signaling [12] and it has been demonstrated that SOST loss-of-function mutations cause abnormal skeletal phenotypes in humans, characterized by high bone mineral density [13, 14], whereas transgenic mice that overexpress SOST are osteopenic due to reduced bone formation [15]. In OA, which is characterized by new bone formation, it has been reported that SOST is implicated in OA disease processes in both bone and cartilage with opposing effects, by promoting subchondral bone sclerosis while inhibiting cartilage degradation [9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
