Scientists from Canada and the UK have found a new way to create stem cells without using viruses to introduce genetic material into the nuclei to make the cells pluripotent, instead they insert four genes that reprogram the cells then remove them later. The researchers said their work could lead to possible cures for a range of degenerative diseases that destroy tissue, such as spinal cord injury, macular degeneration, diabetes and Parkinson’s disease.
The researchers in Canada were from the Samuel Lunenfeld Research Institute at Mount Sinai Hospital in Toronto, Ontario and the Department of Molecular Genetics at the University of Toronto, and the researchers in the UK were from the The Wellcome Trust Sanger Institute in Hinxton, Cambridgeshire, and the MRC Centre for Regenerative Medicine at the Institute for Stem Cell Research in the University of Edinburgh. The study is published in an advanced online 1 March issue of Nature.
The researchers found that introducing just four genes that act as transcription factors, called c-Myc, Klf4, Oct4 and Sox2 was enough to reprogram cells from adult tissue into pluripotent cells.
The pluripotent cells resembled embryonic stem cells in that they acquired the potential to differentiate into a wide range of adult cell types.
The current method for achieving this relies on using viruses (such as retroviruses, lentiviruses and adenoviruses) and plasmids (small pieces of DNA that self-replicate like viruses inside host cells) that introduce genetic material to induce pluripotency.
Retroviruses and lentiviruses bring with them the risk that they will damage host cell DNA and unleash uncontrolled cell growth, rather like cancer, and while the other two, lentiviruses and plasmids don’t, they have limited reprogramming potential.
So given these disadvantages, finding a new way to induce pluripotency without disrupting healthy genes is a real breakthrough in adult stem cell science, diminishing reliance on embryonic stem cells, which is controversial because it involves the destruction of embryos.
Senior author Dr Andras Nagy, who is a Senior Investigator at the Samuel Lunenfeld Research Institute of Mount Sinai Hospital, an Investigator at the McEwen Centre for Regenerative Medicine, and Canada Research Chair in Stem Cells and Regeneration, said:
“We hope that these stem cells will form the basis for treatment for many diseases and conditions that are currently considered incurable.”
“This new method of generating stem cells does not require embryos as starting points and could be used to generate cells from many adult tissues such as a patient’s own skin cells,” he added.
Nagy and colleagues used a new “wrapping” method to deliver the four transcription factor genes into the adult cells to reprogram then into stem cells. They wrote that this method, which is called “piggyBac (PB) transposition” is “host-factor independent, and has recently been demonstrated to be functional in various human and mouse cell lines”.
In this study the researchers were able to show successful and efficient reprogramming of mouse and human fibroblasts taken from embryonic stem cell lines, but there is no reason in principle why this could not happen to fibroblasts taken from adult tissue.
The stable pluripotent cells they created displayed all the characteristic markers of pluripotency and succeeded in a “series of rigorous differentiation assays”.
Nagy and colleagues also showed it was possible to remove the PB wrapping seamlessly from established pluripotent cell lines, which gives scientists an important tool for research.
They concluded that:
“We anticipate that the unique properties of this virus-independent simplification of iPS [induced pluripotent stem] cell production will accelerate this field further towards full exploration of the reprogramming process and future cell-based therapies.”
An important step in the study took place in the lab of co-author Dr Keisuke Kaji from the Medical Research Council (MRC) Centre for Regenerative Medicine at the University of Edinburgh. That work is the subject of a separate study in the same issue of the journal.
Kaji told the press that:
“I was very excited when I found stem cell-like cells in my culture dishes. Nobody, including me, thought it was really possible.”
“It is a step towards the practical use of reprogrammed cells in medicine,” Kaji added.
In 2005 Nagy created Canada’s first embryonic stem cell lines from embryos no longer needed by couples undergoing fertility treatment.
The Canadian Stem Cell Network and the Juvenile Diabetes Research Foundation (United States) paid for the research.
“piggyBac transposition reprograms fibroblasts to induced pluripotent stem cells.”
Knut Woltjen, Iacovos P. Michael, Paria Mohseni, Ridham Desai, Maria Mileikovsky, Riikka Hämäläinen, Rebecca Cowling, Wei Wang, Pentao Liu, Marina Gertsenstein, Keisuke Kaji, Hoon-Ki Sung & Andras Nagy.
Nature Advance Online Publication, 1 March 2009.
doi:10.1038/nature07863
“Virus-free induction of pluripotency and subsequent excision of reprogramming factors.”
Keisuke Kaji, Katherine Norrby, Agnieszka Paca, Maria Mileikovsky, Paria Mohseni & Knut Woltjen.
NatureAdvance Online Publication, 1 March 2009.
doi:10.1038/nature07864
Sources: Journal abstract, Samuel Lunenfeld Research Institute press statement.
Written by: Catharine Paddock, PhD