MedicalResearch: What are the main findings of the study?
Dr. Philpott: A group of proteins known as transcription factors that control gene expression regulate production and maturation of nerve cells during embryonic development. Recently, it was found that by adding these proteins to skin cells, they can be reprogrammed to produce nerves, which can then be used to model human conditions such as Parkinsons Disease and Alzheimers. These cells are known as induced neurons, or iN cells. However, this method generates a low number of cells, and those that are produced are not fully functional, which is a requirement in order to be useful models of disease: for example, cortical neurons for stroke, or motor neurons for motor neuron disease. When cells are dividing, we found that transcription factors are modified by the addition of phosphate molecules, a process known as phosphorylation, and this can limit how well cells convert to mature nerves. By engineering proteins that cannot be modified by phosphate and adding them to human cells, we found we could produce nerve cells that were significantly more mature, and therefore more useful as models for disease such as Alzeheimers and Parkinsons.
MedicalResearch: Were any of the findings unexpected?
Dr. Philpott: It was previously not clear why nerve cells produced by reprogramming of fibroblasts are generally immature. By manipulating regulation of these transcription factors that we had characterized in developing embryos, we found we were able to promote cell differentiation and maturation, even in the presence of conflicting signals that were directing the cell to continue dividing. In fact, we’ve found that not only do you have to think about how you start the process of cell differentiation in stem cells, but you also have to think about what you must do to make differentiation complete. It is clear we can learn a lot from how cells in developing embryos manage this.
MedicalResearch: What should clinicians and patients take away from your report?
Dr. Philpott: When you reprogramme cells, you’re essentially converting them from one form to another but often the cells you end up with look like they come from embryos rather looking and acting like than more mature adult cells. In order to increase our understanding of diseases like Alzheimer’s, we need to be able to work with cells that look and behave like those you would see in older individuals who have developed the disease, so producing more “adult” cells after reprogramming is really important. To achieve this, a better understanding of nerve cell maturation in development will uncover ways that this process can be enhanced in cultured cells. We used this developmental understanding to increase nerve maturation in this study.
MedicalResearch: What recommendations do you have for future research as a result of this study?
Dr. Philpott: We have now shows that the same method of phosphorylation control works to limit the activity of several members of this transcription factor family. Other members play important roles in generation of other tissues in development, for instance pancreatic islets, the cell type that fails in Type II diabetes. As well as manipulating other similar proteins to further enhance the production of more mature nerves, we are now now using parallel methods to improve the function of insulin-producing pancreas cells for future therapeutic applications.
This work was funded by the Medical Research Council and the Rosetrees Trust.
The phosphorylation status of Ascl1 is a key determinant of neuronal differentiation and maturation in vivo and in vitro Development 2014 141:2216-2224; posted ahead of print May 12, 2014, doi:10.1242/dev.106377