Reprogrammed neurons may fool you!

Associate Professor Agnete Kirkeby, from reNEW Copenhagen, has published the paper Forced LMX1A expression induces dorsal neural fates and disrupts patterning of human embryonic stem cells into ventral midbrain dopaminergic neurons, in Stem Cell Reports.

Dr Kirkeby and her team reveals in this work that although reprogrammed stem cell derived dopamine neurons may appear to look correct in the lab, their appearance may fool you, as they are not always what you think they are.

In this paper, the effect of a transcription factor called LMX1A on neural differentiation has been investigated. This transcription factor is of interest in the field of Parkinson’s disease, and it has been applied in numerous studies of direct reprogramming towards dopamine neurons. In these studies, LMX1A has been used to try to force cells to become dopamine neurons without going through the natural differentiation path. I.e. This is a type of fast-forward approach to get access to dopamine neurons in the lab for transplantation and disease modeling of Parkinson’s disease.

“What we’re doing in this study is, rather than just looking at the final cell you get from the LMX1A fast-forward reprogramming approach, we’re looking at the developmental path that the cell is taking to get there. And what we find is that, in fact, you get something different from what is expected, based on previous reports in the literature,” said Dr Kirkeby.

When looking closely at the path the forced LMX1A-derived dopamine neuron takes, it becomes evident that it is actually not going through the correct developmental path, and it is not generating the dopamine neurons which are required for Parkinson’s Disease.

The LMX1A reprogramming approach did generate some cells which expressed markers of dopamine neurons, but these cells lacked the key machinery for dopamine production and were therefore unlikely to be functional like correctly specified dopamine neurons. What was actually being created was a kind of in vitro artefact, caused by overexpression of a transcription factor, which has multiple different functions during development, and which is not only involved in dopamine neuron development. In fact, the LMX1A cells in some cases generated ectopic ventricles upon transplantation to rats rather than the dopamine neurons that would be expected. It turned out that this is due to the fact that LMX1A is also involved in the development of ventricles in the embryo.

“For me, the findings from this study support the notion that we should be extremely careful when using direct reprogramming approaches, because there is a risk that we are generating something artefactual – a type of cell that doesn’t exist in vivo, and you have no idea how it’s going to work,” said Dr Kirkeby.