Developmental switch in SOX9 expression in articular cartilage is regulated by epigenetic histone methylation

Abstract

intermediate (inner lateral tibial plateaus, iLT) and late stage (inner medial plateaus, iMT) of OA in Japanese. Methods: Genome-wide DNA methylation analysis was performed using Illumina Infinium HumanMethylation450 BeadChip array on DNA extracted from the cartilage of oLT, iLT and iMT region of 8 patients. Raw IDAT files were analyzed using package "minfi" in R. Data was normalized through SWAN (subquantile normalization) method. Multidimensional scaling (MDS) was used to identify the outliers. Probes that locate on X/Y chromosomes were removed before applying F test to find out the differential methylated sites of iLT vs oLT and iMT vs oLT. Multidimensional scaling of the methylation beta values revealed significantclusters related to cartilage. F test with p value less than 0.05 and jDbj greater than 0.15 were used to identify the differential methylated sites. Genes with differentially methylated CpG sites were analyzed to identify gene ontologies, pathways, and upstream regulators. Results: We identified 310 differentially methylated sites (DMS) covering 147 genes in comparison of iMT vs. oLT region. Of these, 122(39%) DMS were hypermethylated and 188 (61%) were hypomethylated. However, in the comparison of iLT vs. oLT region, we only found 22 differential methylated sites (12 hypermethylated and 10 hypomethylated). The dramatic difference in DMS numbers of iLT and iMT suggests that methylation is highly involved only at the very late stage of OA. The DMS we found in iMT cartilage include genes reported related to OA, for instance, BMP6, COL14A1, NFATC1, and SPOCK1. Enrichment analysis of the genes with DMS revealed significant enrichment of HOX family genes and development pathways.Conclusions: In the current study, we have identified the methylation changes in both the iLT region and iMT region, which represent the intermediat and late stage of OA disease. Our data suggested that the significant changes in methylation occurred at during the late stages of OA. The development pathways and HOX family genes enriched at the late stage of OA implicated new aspect of cartilage maintenance in adulthood. The further study of the underlying mechanism may supply a direction for future cartilage regeneration approaches.

Epigenetic mechanisms underlying the aberrant catabolic and anabolic activities of osteoarthritic chondrocytes

“…No histopathological features of osteoarthritis were observed in examined joints by 18 months. Epigenetic study revealed that the reduction of SOX9 expression in ACs of adult mice is primarily regulated by H3K4me2 (a histone modification for transcriptional activation) (Zhang et al, 2015a). miRNA-145 has been identified as an inhibitor of SOX9 expression in human cartilage and chondrosarcoma (Mak et al, 2015); increased miRNA-145 directly represses SOX9 expression, causing reduced expression of COL2A1 and aggrecan with an increased level of MMP13 (Martinez-Sanchez et al, 2012).…”