Overexpression of Telomerase Confers Growth Advantage,
Stress Resistance, and Enhanced Differentiation of ESCs
Toward the Hematopoietic Lineage
L. Armstrong, G. Saretzki, H. Peters, I. Wappler, J. Evans, N. Hole, T. von Zglinicki, M. Lako
Stem Cells 2005; 23: 516—529
Article:
http://stemcells.alphamedpress.org/cgi/reprint/23/4/516.pdf
Telomeres are repeating DNA segments found at the ends of chromosomes. Most somatic cells in humans have very little telomerase activity and thus, their telomeres shorten with each replication. When the telomeres shorten, the cells begin to age and die. On the other hand, immortalized cells have noticeable amounts of telomerase activity and stable telomere lengths throughout each propagation. For example, embryonic stem cells (ESC) are pluripotent and can reproduce indefinitely in culture. Human ESC initially expresses a high level of telomerase activity due to the expression of the TERT gene (a reverse transcriptase responsible for adding on segments to the telomeres); but when ESC differentiate, TERT and telomerase activity decrease and telomeres shorten in the differentiated cells. Thus, enhancing or lengthening telomeres may lead to a revolutionary breakthrough in cell renewal technology.
In this study, the scientists over-expressed the TERT gene in mouse ESC and compared their performance and survival to a wild-type ESC (a control group). This is because in mice, ESCs also require telomerase RNA and its reverse transcriptase (TERT) to function. Also, mouse ESC decreases telomerase and TERT activity upon differentiation. However, scientists do not know if this down-regulation of telomerase is necessary for normal cell growth. Thus, the scientists wanted to look into the effects of continuous telomerase activity on cell proliferation, differentiation, death, and resistance to stresses for mouse ESC. They accomplished this through a various number of assays such as Flow Cytometry Analysis, Microarray Analysis, RT-PCR, Apoptosis Assay, and many others.
The results of the various assays showed that over-expressing TERT in mouse ESC increased the cell’s proliferation, resistance to apoptosis, enhanced the efficiency of differentiation (due to higher proliferation and better survival of progenitor cells in culture), and improved the cell’s resistance to oxidative stress. The paper also notes that results from other studies showed that telomerase had beneficial effects other than just extending telomere length—for example, it helped increase wound healing in mice. Overall, it was determined that telomerase is a “survival enzyme” for ESC and the cells it differentiates into. However, an important note the authors point out is that over-expression of TERT in differentiated cells have led to increased tumor growth—thus more work needs to be done to control TERT over-expression in differentiated cells.
I chose this paper because I was always interested in the fables of the fountain of youth. It seems that lengthening telomeres is the closest scientists have come to drinking from that fountain. This study is very important in that the results of increased ESC proliferation and enhancement of ESC differentiation due to TERT over-expression can have a great impact on tissue engineering treatments or cell-replacement therapies. For example, ESCs from bone, liver, or skin cells can be cultured to over-express TERT so that they can grow a workable number of cells for use in tissue engineered scaffolds. Or, one day, scientists may even be able to just grow the cells needed to directly replace the wounded or damaged organ. Much more work will need to be done, but this study was a promising step forward.
6 comments:
I believe that one could use this method to grow cells that are otherwise hard to grow and place them onto tissue engineered scaffolds. Or they could keep a bank of cells in perpetual growth and use them when needed--for example, grow numerous skin cells from the stem cells so that they could be stored and used when needed--much like a blood bank. If this technology is developed enough, maybe scientists can just grow enough cells to replace organs entirely. Of course, this is a long stretch, but it was really exciting for me to imagine that one day we can just replace old organs and maybe live forever. haha.
would over-expressing TERT in a device cause any side effects? Would we want to implant someone with cells that grow that quickly? Also does the over expression of TERT have any lasting effect on the ESC once they do differentiate?
One negative side effect is that TERT overexpression has been shown to increase tumor growth in the given organs--thus further study needs to be done to try and prevent this. The overexpression of TERT, in this study, showed a lasting effect on ESC's in helping them proliferate and differentiate better. Although ESC's can reproduce indefinitely, they can die when their telomeres shorten and degrade. Thus, an overexpression of TERT helps maintain a high level of telomerase, which in turn helps maintain a cell's telomere length and increases the stability and life of the cell.
Even though there are negative side effects, in my opinion, this treatment can still be used to prolong life. In another study, overexpression of TERT was used to treat liver cirrhosis in mice. Thus, in theory, a patient waiting for a liver transplant can implant a device or scaffold to overexpress TERT in his liver--even though tumors may grow, it will still give him a considerable amount of time to live. And, if he were lucky, the tumor could be local and be removed once he does come up on the transplant list.
When they experimented with stress condition, were ESC's viability high because the effect of stress was somehow reduced in the cells with over-expressed TERT? or were the cells with over-expressed TERT able to simply proliferate more?
Did the authors investigate what happens to TERT expression in cells that over-express TERT once the cells have differentiated?
It seems that this research might be useful in tissue engineered devices in the long term if they can solve tumor growth issues, but it is very practical in the short term for research purposes. Extending the life of cultures would be very useful for scientists growing cells in vitro that have to be passaged and replaced. This paper has good short term and long term applications
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