gms | German Medical Science

Objective: Ionizing radiation is a known risk factor for the development of meningiomas. However, the underlying mechanism is largely unknown. One of the most widely discussed hypotheses is potentially pluripotent meningioma stem cells (MSCs). These are characterized by a high relative expression of embryonic NANOG (NANOG1) as compared to tumor-specific NANOGP8. The aim of this study was to detect whether ionizing radiation induces the expression of embryonic NANOG and the associated formation of MSCs in human primary meningioma cells (PMCs).

Methods: Three PMC cultures were incubated under standard conditions in DMEM/10%FBS. The confluent monolayers were exposed to single doses of photon irradiation (1, 2, 4, 8, 12, 16, 20 Gy). One day after treatment and each time a confluent cell layer was reached, the cells were routinely passed and cultivated for a total of 10 passages (primary endpoint) or 84 days (secondary endpoint) respectively. At this point, cells were stained by immunocytochemistry for NANOG, vimentin and EMA. The cells were monitored for phenotypic changes and a sample was taken from each passage. To evaluate which form of NANOG has dominantly induced, the relative mRNA expression of NANOG1 and tumor-specific NANOGP8 were analyzed using qPCR.

Results: As expected, the analyzed cells showed clear signs of necrosis or senescence in the high-dose range (12–20 Gy) as well as longer doubling times. The cells irradiated with doses of 1–8 Gy constantly produce the meningioma-specific proteins (EMA and vimentin) and grow in vital spheroids. The NANOG protein was detected in up to 5% of the cells in the low-dose range. Transcriptional analysis of the gene variants of NANOG revealed a significantly (p=0.008) increased expression of NANOG1 in cells irradiated with 4 Gy (compared to non-irradiated cells) over the entire study period. Analysis of the tumor-specific NANOGP8 showed no significant (p>0.05) differences in relative expression between irradiated and non-irradiated cells.

Conclusion: Tumor-specific NANOGP8 was detected in all study groups as expected. However, the detection of the embryonic form of NANOG exclusively in irradiated cells proves a non-physiological state of these cells. This hints at a radiation induced mechanism that potentially facilitates formation of cells with embryonic stem cell characteristics. Low-dose irradiation (4Gy) might thus favour induction of tumor-inducing cells.