13 April 2011

Induced pluripotent stem cells: microRNAs are 100 times better than genes

A new method for producing induced pluripotent stem cellsNanonews Network based on the materials of the University of Pennsylvania School of Medicine:

A New Way to Make Reprogrammed Stem Cells

Scientists at the University of Pennsylvania School of Medicine have developed a completely new and much more effective method for producing induced pluripotent stem cells (iPSCs) – immature cells capable of transforming into various types of body cells. A promising direction for the use of such cells is drug screening, as well as tissue regeneration.

Induced pluripotent stem cells (iPSCs) are usually obtained from adult somatic cells by the expression of four different genes called transcription factors. The first report on obtaining IPSC by this method was made in 2006 by Dr. Shinya Yamanaka. Since then, many scientific groups have achieved similar results using one or more of these four transcription factors.

The prospects of this line of research is to obtain patient-specific stem cells for the study of human diseases, as well as to create a cell "bank" for the regeneration of the patient's own cells, for example, heart or liver cells. Despite such broad prospects and the importance of this field of research, the production of IPSC is hampered by low efficiency, especially when using human cells.

"We have changed the rules of the game," says Edward Morrissey, PhD, professor of the Department of Medicine, Developmental Biology and Cell Biology, scientific director of the Institute of Regenerative Medicine at the University of Pennsylvania. "For the first time, it was possible to obtain induced pluripotent stem cells without using four transcription factors, while increasing the efficiency of the process by 100 times."

 "The effective production of induced pluripotent stem cells is of paramount importance for their potential therapeutic use," James Kiley, director of the Department of Pulmonary Diseases at the National Heart, Lung, and Blood Institute of the USA, comments on the results of the study. "This work is an important step in this direction. In addition, it will contribute to scientific research in the field of stem cell biology in general."

Prior to the development of a new method in which microRNAs (microRNA, miRNA) were used instead of four transcription factors, out of every 100,000 adult reprogrammed cells, scientists could obtain a small "handful" of iPSCs, usually less than 20. The use of the microRNA-based method allowed to increase this figure to approximately 10,000. microRNAs are short RNA molecules that bind to complementary sequences of matrix RNA (mRNA) and thus suppress the expression of the corresponding genes. The results of the work (Highly Efficient miRNA-Mediated Reprogramming of Mouse and Human Somatic Cells to Pluripotency) are published in the journal Cell Stem Cell.

Induced pluripotent mouse stem cells obtained by microRNA –
a method developed in the laboratory of Professor Morrisey.
Green fluorescence indicates Oct4 gene expression,
being a marker of pluripotent stem cells.
(Photo: Edward Morrisey, University of Pennsylvania School of Medicine)

Morrisey's lab developed its approach based on the study of the role of microRNAs in lung development. The scientists worked with a microRNA cluster called miR302/367, which plays an important role in the development of pulmonary endodermal progenitor cells. Embryonic stem cells are also known to demonstrate a high level of expression of the same microRNA cluster.

The researchers conducted a simple experiment. They expressed these microRNAs in mouse fibroblasts and were surprised to find colonies that looked like induced pluripotent stem cells.

"We were very surprised that this worked in the first experiment, and the method turned out to be much more effective than Dr. Yamanaka's approach based on transcription factors," Dr. Morrisey comments on the results.

Since microRNAs act as repressors of protein expression, it is likely that they can suppress repressors of the same four transcription factors, as well as other factors important for the preservation of the cell in a pluripotent stem state. However, what exactly is the difference between the work of microRNAs and transcription factors during the transformation of adult cells into iPSCs requires further study.

The iPSCs obtained using the microRNA–based method are able to transform into most, if not all, tissues of developing mice, including germ cells - eggs and spermatozoa. Now Morrisey's laboratory is collaborating with several scientists to differentiate its iPSCs into cardiomyocytes, hematopoietic (hematopoietic) cells and liver cells – hepatocytes.

Synthetic versions of microRNA molecules, called imitators or precursors, can be used to reprogram adult cells in iPSCs. Such simulators can be easily injected into cells in large quantities, which will allow obtaining iPSCs without using genetic methods.

"We hope to obtain synthetic microRNAs to transform adult cells into induced pluripotent stem cells, which can eventually be differentiated into other cell types, for example, liver cells, heart muscle cells or neurons," Professor Morrisey plans further research.

Portal "Eternal youth" http://vechnayamolodost.ru13.04.2011

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