Abstract
Chondrocytes, comparable to many cells from the connective tissue, dedifferentiate and end up in a similar fibroblastoid cell type, marked by the loss of the specific expression pattern. Here, chondrocytes isolated from osteoarthritic (OA) patients were investigated. The OA chondrocytes used in this work were not affected by the loss of specific gene expression upon cell culture. The mRNA levels of known cartilage markers, such as SOX5, SOX6, SOX9, aggrecan and proteoglycan 4, remained unchanged. Since chondrocytes from OA and healthy tissue show different DNA methylation patterns, the underlying mechanisms of cartilage marker maintenance were investigated with a focus on the epigenetic modification by DNA methylation. The treatment of dedifferentiated chondrocytes with the DNA methyltransferase inhibitor 5-aza-2´-deoxycytidine (5-aza-dC) displayed no considerable impact on the maintenance of marker gene expression observed in the dedifferentiated state, while the chondrogenic differentiation capacity was compromised. On the other hand, the pre-cultivation with 5-aza-dC improved the osteogenesis and adipogenesis of OA chondrocytes. Contradictory to these effects, the DNA methylation levels were not reduced after treatment for four weeks with 1 μM 5-aza-dC. In conclusion, 5-aza-dC affects the differentiation capacity of OA chondrocytes, while the global DNA methylation level remains stable. Furthermore, dedifferentiated chondrocytes isolated from late-stage OA patients represent a reliable cell source for in vitro studies and disease models without the need for additional alterations.
Highlights
The loss of environmental signals occurring during injuries in multicellular organisms leads to a stepwise reprogramming or dedifferentiation of cells
Cell fate is stabilized by epigenetic modifications, such as those found in histone tail marks or DNA methylations
The enzymes responsible for the DNA methylation are encoded by the genes DNMT1, DNMT3a and DNMT3b (DNA methyltransferases: DNMTs)
Summary
The loss of environmental signals occurring during injuries in multicellular organisms leads to a stepwise reprogramming or dedifferentiation of cells. Cell fate is stabilized by epigenetic modifications, such as those found in histone tail marks or DNA methylations. In this context, tissue-dependent differentially methylated regions can be identified in differentiated cells. No in vivo mechanism of direct DNA demethylation has been described so far, modified intermediates, such as 5-hydroxymethylcytosine, 5-formylcytosine and 5-carboxylcytosine, have been found [4]. These further modifications of 5-methylcytosine are catalyzed by the TET (teneleven translocation) family
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