Direct conversion of fibroblasts into neurons

Functional neurons are derived from human skin cells,
bypassing the stage of induced pluripotent stem cells
LifeSciencesToday based on Stanford University materials:
Scientists turn human skin cells directly into neurons, skipping iPS stage

Human skin cells can be directly transformed into functional neurons in a period of four to five weeks by adding just four proteins. This method, developed by scientists at the Stanford University School of Medicine, is of great importance, since it eliminates the need for the initial production of induced pluripotent stem cells. In addition, it can greatly facilitate the acquisition of neurons specific to a particular disease or a particular patient.

Based on the same proteins that are used to produce pluripotent cells, scientists may be able to solve another potential problem associated with induced pluripotent stem cells (iPS), which was recently reported in the journal Nature – the rejection of genetically identical iPS cells by laboratory mice.

In 2010, the group of Doctor of Medicine Marius Wernig, Associate Professor of Pathology and Researcher at the Institute of Stem Cell Biology and Regenerative Medicine (Institute for Stem Cell Biology and Regenerative Medicine) Stanford University has already proved the possibility of transforming skin cells (fibroblasts) of mice directly into neurons using a similar combination of proteins.

After successful experiments on laboratory mice, the results of which were published last year in the journal Nature (Vierbuchen et al., Direct conversion of fibroblasts to functional neurons by defined factors), scientists applied the same technique to human cells. First, they showed that it is possible to obtain neurons from human embryonic stem cells by infecting them with a virus expressing the same combination of proteins – transcription factors Brn2, Ascl1 and Myt1l. For brevity, they named their method to YOU. The VAM method easily transforms human embryonic stem cells into functional neurons within six days. It also works well on induced pluripotent stem cells.

Red objects – former mouse embryonic fibroblasts
with three added genes that prompted them to transform from skin cells into neurons. 
Photo: med.stanford.edu

However, when working with human cells, it turned out that the conversion of skin cells into neurons occurs more slowly and less efficiently. Turning to experiments with human fibroblasts of fetuses and newborns, the scientists found that the VAS method allowed mature cells to look like neurons, but the resulting cells are ultimately unable to generate electrical signals used by neurons for intercellular communication.

Scientists have come to the conclusion about the probable existence of some missing component. The addition of the fourth transcription factor, NeuroD, was a turning point: skin cells transformed into functional neurons in four to five weeks, demonstrating electrical activity and even integration and interaction with cultured mouse neurons.

Currently existing cell culture media allow only 2-4 percent of human fibroblasts to be transformed into functional neurons, although this percentage reaches 20 in mouse cells. While mouse cells undergo the entire transformation in just a few days, human cells take several weeks to complete. At the same time, they generate less strong electrical signals than ordinary neurons.

"Obviously, a mouse and a human are significantly different from each other," Dr. Wernig comments on these features.

Now he and his colleagues are working on optimizing their technology and cell culture conditions in order to increase the efficiency and speed of direct transformation.

The direct transformation of skin cells into neurons differs from similar studies in which scientists first transfer fibroblasts to a pluripotent, or flexible from the point of view of development, state, and then achieve their transformation into neurons or other specialized cells. Another group of Stanford scientists recently used this method to obtain neurons from the skin cells of a woman with Parkinson's disease, that is, neurons specific to a particular patient. However, this process is extremely time-consuming and is based on cell lines that may not fully reflect the cellular diversity observed in the natural population.

Dr. Wernig stresses the importance of continuing further development of both methods.

"An approach using induced pluripotent stem cells is feasible and works, as has already been shown," he says. "We need to work within both strategies."

It is possible that the choice of the optimal approach is determined by the disease or the characteristics of the study being conducted.

"Now we are much closer to being able to simulate neurological diseases in the laboratory," the scientist believes. "Maybe one day we will even be able to use these cells to treat people."

An article by American scientists (Pang et al., Induction of human neuronal cells by defined transcription factors) is published in Nature.

Portal "Eternal youth" http://vechnayamolodost.ru30.05.2011