Expression of type II collagen and aggrecan genes is regulated through distinct epigenetic modifications of their multiple enhancer elements.

To maintain normal function of cartilage tissue normally, the presence of a sufficient amount of type II collagen and aggrecan is essential, and their synthesis is tightly regulated. Therefore, understanding the mechanisms that control the expression of type II collagen and aggrecan would be useful for understanding gene expression changes in diseases such as osteoarthritis. Recently, we have identified two pairs of enhancer elements, termed E1 and E2 in the type II collagen gene and Ea and Eb in the aggrecan gene. However, their different mechanisms of action remained unclear. Thus, the central aim of this study was to clarify the different transcriptional regulation mediated through each enhancer element. To this end, we established different stable reporter cell lines that express a reporter gene under the control of different enhancer elements using a silent reporter system we previously constructed. Using these cell lines, we found that dexamethasone, forskolin, and trichostatin A affect the gene expression of type II collagen and aggrecan via different enhancer elements. Moreover, we clarified that E1 and E2 enhancer activities are regulated through distinct epigenetic modifications by histone deacetylase 10 and sirtuin 6.

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