gms | German Medical Science

The study of epigenetic changes that affect gene expression patterns seems of increasing importance during stem cell differentiation, ageing and tumorigenesis. Only 3 years ago a new modification has been found: 5-Hydroxymethylcytosine (5hmC). For a long time 5-methylcytosine (5mC) seemed to be the only base modification in mammalian DNA. It is known that this modification can lead to a functional inactivation of gene transcription and thus plays a crucial role e.g. in tumorigenesis. In this context the discovery of the modification 5hmC offers numerous new questions to the emerging field of epigenetic research. What is the biological meaning of 5hmC? What is the role in tumorigenesis?

As an approach to understand the function of 5hmC we investigated both normal brain tissue as well as tissue derived from glioblastoma (WHO-grade IV tumor). We used immunohistochemistry (IHC) as well as mass spectrometry (LC-MS) to quantify the amount of 5hmC in both normal and tumor tissue. Furthermore we investigated the expression patterns of distinct proteins that are responsible for the hydroxylation reaction of 5mC to 5hmC, the ten-eleven-translocation (TET) proteins.

We observed that there is a significantly lower amount of 5hmC in glioblastoma compared to normal brain tissue both in IHC and LC-MS. Detailed investigations showed that there is a connection between the proliferation activity and the amount of 5hmC. Using immunofluorescence stainings we could demonstrate that proliferating cells (labelled with the Ki67 antibody) show significantly less 5hmC than non-proliferating cells. Additionally we noticed that there are distinct differences in the expression profile of the TET proteins in normal brain and glioblastoma tissue indicating a possible explanation for the imbalance of 5hmC in glioblastoma.

Summarizing, we show distinct differences between normal brain and glioblastoma with regard to 5hmC and indicate possible causes leading to this imbalance.