Main Category: Stem Cell Research
Article Date: 05 Aug 2013 – 0:00 PDT
Despite the fact that reprogramming adult cells without AID is inefficient, the researchers say that the method may offer another advantage besides increased safety.
The enormous promise of regenerative medicine is matched by equally enormous challenges. But a new finding by a team of researchers led by Weill Cornell Medical College has the potential to improve both the safety and performance of reprogrammed cells.
In order to push a cell, such as a fibroblast, to revert to an iPS cell, the epigenetic “markers” that define an adult cell must be removed. “All cells of the body have the same genes, but they are used differently in different tissues,” Dr. Evans explains. “If an undifferentiated cell becomes a heart cell, somehow it has to lock in and stabilize that particular adult phenotype and not forget what it is.”
The researchers’ study, published in the journal Nature, found that an enzyme, activation-induced cytidine deaminase (AID), helps in the process that changes an adult human cell into an induced pluripotent stem cell (iPS cell). These iPS cells can then be developed into any kind of cell needed to therapeutically restore tissues and organs.
They then created a mouse that did not produce AID to see if the animal’s adult fibroblast cells could be pushed back to iPS cells. “If you need AID to reprogram the cells, you shouldn’t be able to do it, or do it well.”
Surprisingly, they found that the cells at first seemed to want to reprogram even faster than normal cells, but most never fully reverted to a stem-cell-like state. “They eventually crashed and differentiated back into a fibroblast,” Dr. Evans says. “What that meant is that they never cleared their memory of being a fibroblast cell. AID efficiently removes that epigenetic memory, smoothing the way for a cell to morph into an undifferentiated state.”
iPS Cells Without AID Remember What They Once Were
One reason is that AID can cause genetic mutations that can lead to cancer. AID is best known as a master regulator of antibody diversity in B cells, and in order to create varied types of beneficial antibodies, it routinely mutates antibody genes. But sometimes the process goes awry, resulting in development of B cell lymphoma, Dr. Evans says. “That leads us to believe that if you can reprogram cells without AID, it could reduce risk of potential mutations, and thus be safer.”
Dr. Evans and his colleagues found that the AID enzyme removed those epigenetic markers.
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Weill Cornell Medical College. “Advance in regenerative medicine could make reprogrammed cells safer while improving their function.” Medical News Today. MediLexicon, Intl., 5 Aug. 2013. Web.
5 Aug. 2013. <http://www.medicalnewstoday.com/releases/264284.php>
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But some of the mouse adult fibroblasts lacking AID – those that Dr. Evans says they “babysat” – did become iPS cells.
Other study co-authors include Ritu Kumar, Ting-Chun Liu, Philipp Franck and Olivier Elemento from Weill Cornell Medical College; Lauren DiMenna, Nadine Schrode, Silvia Muñoz-Descalzo, Anna-Katerina Hadjantonakis and Jayanta Chaudhuri from Memorial Sloan-Kettering Cancer Institute; and Ali A. Zarrin from Genentech.
“The dispute was whether AID is required to make iPS cells, and we found that the enzyme does make reprogramming very efficient, although it is not absolutely necessary,” says Dr. Evans, an internationally-recognized authority on regenerative medicine. “In fact, we plan to test if reprogramming iPS cells without AID may even be helpful.”
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