For many things in life, convenience comes at a cost. Like living in a great city with everything at your doorstep, but the rents are sky-high. A new report says that the use of BrdU, a popular tool for detecting replicating cells (such as neural stem cells in the brain), also comes with a cost, finding that neural stem cells exposed to BrdU lose global DNA methylation and start to differentiate.
Italian scientists applied BrdU to embryonic stem cell-derived neural stem cells (NSCs) at the same concentration typically used for DNA labeling and cell proliferation experiments. Surprisingly, BrdU-treated cells stopped dividing, while control cells kept on proliferating. Even concentrations as low as 100nM put the brakes on NSC cell division.
Looking more closely, the team saw signs that the NSCs were differentiating into astrocytes. For one thing, the cells looked more like astrocytes. And known markers of NSC-ness (like Nestin) decreased, while markers of astrocyte-ness (like GFAP) increased. The cells also lost DNA methylation, which the researchers tested with a new method they developed. The team got the same results when they studied BrdU’s effects on an ex vivo system of cells derived from NSCs from the mouse forebrain.
5-aza (Decitabine), a cytidine analog that is used in cancer therapy to stop tumors from growing, had a similar effect on cells. Although BrdU is a thymidine analog, it can sometimes sneak into places where Cs are supposed to be, which could explain its effect on methylation. BrdU is less toxic, however, so the researchers say that it should be re-evaluated as an anti-cancer agent.
The results also show that epigenetics researchers should be very careful when interpreting data from experiments using BrdU on stem cells, especially in living animals.