As covered in a SciTechStory post February 15, 2010, Induced stem cells not such good news efforts to create the equivalent of human embryonic stem cells starting with adult cells have not turned out so well. A study done at the University of Wisconsin (Madison, USA) compared five embryonic stem cell lines with twelve induced stem cell lines. They found that the induced pluripotent stem cells (iPSC) converted to neuron cells do not match all the differentiations made by embryonic stem cells. The study also showed that iPS cells created without using genes, which in theory should have resulted in ‘cleaner’ differentiation, did no better than gene induced cells.

Now a new study from the Massachusetts General Hospital Center for Regenerative Medicine and Harvard Stem Cell Institute has identified a gene whose silencing may be responsible for at least some of the induced pluripotent stem cells’ limitations. By using the latest genetic assay tests on the DNA of stems cells from mice, they compared the developmental potential of two natural embryonic stem cell lines with induced pluripotent stem cell lines. By comparing the RNA transcriptions (copies made from the DNA) of each line, they found that the natural stem cells produced viable mice, and the induced cells did not. The difference was an obvious reduction in the transcription of two genes in the induced cells. These genes are found in a cluster on chromosome 12 and are normally imprinted maternally (only the mother’s genes are expressed).

In an examination of more than 60 other iPSC lines, the same pattern of silenced (non-expressing) genes was found in the vast majority. Tissues produced from these cell lines were genetically correct reproductions, but the gene silenced cells could not fully develop into live mice. Another experiment, this time reactivating the silenced genes in a few of the iPSC lines, and the cells were able to produce live animals. This may have been the first time that live animals were produced from induced pluripotent stem cells.

“The activation status of this imprinted cluster allowed us to prospectively identify iPSCs that have the full developmental potential of embryonic stem cells,” says Matthias Stadtfeld, PhD, a co-lead author of the report. “Identifying pluripotent cells of the highest quality is crucial to the development of therapeutic applications, so we can ensure that any transplanted cells function as well as normal cells. It’s going to be important to see whether iPSCs derived from human patients have similar differences in gene expression and if they can be as good as embryonic stem cells – which continue to be the gold standard – in giving rise to the 220 functional cell types in the human body.”

[Source: EurekAlert]

Pluripotent stem cells can also be created by nuclear transfer – removing the nucleus of an adult cell and replacing it with the nucleus of an embryonic cell…essentially the same technique used to clone animals. This approach also produces viable embryonic stem cells, but is difficult to perform in quantity. Consequently, the ability to make viable stem cells using induced methods may open the door to producing a greater quantity of high quality cells. Moving on from mouse stem cells, the next step is to perform similar experiments with human stem cells.

Telomeres are ‘tag ends’ of our DNA chromosomes. In the process of reproducing cells, the telomere signals where to stop transcribing genes. However, during the process of mitosis, when the DNA duplicates and a new cell is created, sometimes the telomere is cut (snipped) before the end. It becomes shorter. Eventually there may be no telomere remaining, and the cell will fail to replicate. This has been shown to relate to the aging process (SciTechStory, November 9, 2009: Study confirms telomere’s role in living longer).

Normally DNA attempts to keep the chromosomal telomeres at the proper length. In fact, it has at least one gene associated with the task: telomerase RNA component or TERC. The research shows that some people have variations, either in TERC or genes associated with it that prevent TERC from working properly. These people age early, or fall prey to diseases of old age earlier.

Professor Tim Spector from King’s College London and director of the TwinsUK study, who co-led this project, added:

“The variants identified lies near a gene called TERC which is already known to play an important role in maintaining telomere length. What our study suggests is that some people are genetically programmed to age at a faster rate. The effect was quite considerable in those with the variant, equivalent to between 3-4 years of ‘biological aging” as measured by telomere length loss. Alternatively genetically susceptible people may age even faster when exposed to proven ‘bad’ environments for telomeres like smoking, obesity or lack of exercise – and end up several years biologically older or succumbing to more age-related diseases. ”

[Source: EurekAlert]

Identification of the variant genes is, of course, just a start. Analyzing the relationship between ‘normal’ and ‘variant’ genes and how they affect the reproduction of telomeres is a next step. As with much of the work on gerontology – this avenue of approach is many years away from producing something to counteract the effects of aging.

The particular form of brain cancer was chosen because it is one of the most studied. More than a thousand labs worldwide have been working on glioblastoma (often abbreviated as GBM), as it is relatively common, and usually fatal. Having the complete DNA sequence at hand puts doctors in a position to compare against patient gene sequences, which could be the beginning of personalized treatment for this type of cancer. Doctors and researchers can use a website specifically created to share the genome information, and it is hoped that research groups will be able to re-examine some of their findings in light of more complete information on the genes affected by GBM.

“This is very exciting because we, as scientists, can now move forward with revealing complete cancer genomes,” said Nelson, who directs the cancer center’s Gene Expression Shared Resource. “Cancer is at its heart a genetic disease. Cancer cells have acquired mutations that allow them to invade tissues and to not live by the normal rules. The changes from normal (mutations) that have given the cancer these special properties are encoded in DNA, and the entire DNA sequence has just been to complex and costly to decode until now.”

“Sometimes it’s difficult to tell if a cancer is coming back or if what you’re seeing is scar tissue,” Nelson said. “Scientists could develop a sensitive molecular assay that looks for a unique mutation found only in the cancer cells and not in the healthy cells. If that mutation is found by the assay, the cancer has returned and patients could be promptly treated when the recurrence is at its earliest stage and easiest to treat. Conversely, such an assay could be used to determine when the cancer has been effectively eliminated and it’s safe to discontinue what are harmful treatments.”

[Source: EurekAlert]