The researchers introduced modified RNA encoding a telomere-lengthening protein into cultured human cells. The cells’ ability to proliferate was greatly improved, resulting in a large number of cells available for study.
A new technology can quickly and effectively extend the length of human telomeres, according to scientists at Stanford University School of Medicine. Telomeres are protective caps at the ends of chromosomes that are associated with aging and disease.
The treated cells behaved much younger than the untreated cells and were able to multiply freely in the laboratory Petri dish rather than stagnate or die.
The scientists say the technology, which uses a modified form of RNA, will improve researchers’ ability to generate large numbers of cells for research or drug development. Skin cells whose telomeres were lengthened using the technique divided 40 times more than untreated cells. The study could point to new directions for treating diseases caused by shortened telomeres.
Telomeres are protective caps at the ends of DNA strands called chromosomes, which store our genome. In young people, telomeres are about 8,000 to 10,000 nucleotides long. However, they shorten with each cell division, and when they reach a critical length, the cell stops dividing or dies. This internal “clock” makes it difficult for most cells to grow beyond a few doublings in the lab.
“We’ve now found a way to extend human telomeres to 1,000 nucleotides, setting back the internal clock in these cells by many years, equivalent to a human lifespan,” said Helen Blau, PhD, professor of microbiology and immunology at Stanford and director of Stanford’s Baxter Laboratory of Stem Cell Biology. “This greatly increases the number of cells that can be used for studies such as drug testing or disease modeling.”
A paper describing the study was published today in The FASEB Journal. Blau, the paper’s senior author, is the Donald E. and Delia B. Baxter Professor. Stanford University postdoctoral fellow John Ramunas, Ph.D., co-authored the paper with Dr. Edward Yakubov of the Houston Methodist Research Institute.
To lengthen telomeres, the researchers used modified messenger RNA. RNA carries the instructions from genes in DNA to the protein factories in the cell. The RNA used in this experiment contains the coding sequence for TERT, the active component of the natural enzyme telomerase. Telomerase is expressed by stem cells, including those that give rise to sperm and eggs, to ensure that the telomeres of these cells remain in optimal condition for the next generation. However, most other cell types express very low levels of telomerase.
The newly developed technique has a key advantage over other potential approaches: It’s temporary. The modified RNA is designed to reduce the cells’ immune response to the treatment and allows the message encoding TERT to persist longer than the unmodified message. But it dissipates and disappears after about 48 hours. After that, the newly lengthened telomeres gradually shorten again with each cell division.
The short-term effect is a bit like stepping on the gas pedal in a line of cars that are slowly coming to a stop. The car with the extra energy will go further than the other cars, but will eventually stop when its momentum runs out. Biologically, this means that the treated cells will not divide indefinitely, making them too dangerous to use in human treatments due to the risk of cancer.
The researchers found that just three applications of the modified RNA over several days could significantly extend telomere length in cultured human muscle and skin cells. Telomere length increased by more than 10% for every 1,000 nucleotides added. These cells divided far more times in the petri dish than untreated cells: about 28 times more for skin cells and about three times more for muscle cells.
“We were surprised and excited that the modified TERT mRNA worked, since TERT is tightly regulated and must bind to another component of the telomerase enzyme,” Ramunas said. “Previous attempts to deliver mRNA encoding TERT have resulted in an immune response against telomerase, which can be harmful. In contrast, our technology is non-immunogenic. Existing temporary telomere-lengthening methods act slowly, whereas our method takes only a few days to reverse telomere shortening, which can last more than a decade during normal aging. This suggests that treatments using our approach may be short and need to be done less frequently.”
“This new approach opens the door to preventing and treating diseases of aging,” Blau said. “Serious genetic diseases associated with telomere shortening may also benefit from this potential therapeutic approach.”
Blau and her colleagues became interested in telomeres because previous research in her lab had shown that muscle stem cells from boys with Duchenne muscular dystrophy had much shorter telomeres than those from boys without the disease. The discovery not only sheds light on how these cells function (or don’t function) to create new muscle, but also helps explain the limited ability to grow the affected cells for study in the lab.
“This study is the first step in developing telomere-lengthening technology to improve cell therapy and potentially treat diseases associated with accelerated aging in humans,” said John Cook, MD, PhD. Cook, a co-author of the study and a former professor of cardiovascular medicine at Stanford University. He is currently chairman of the department of cardiovascular sciences at Houston Methodist Research Institute.
“We’re working to learn more about the differences between different cell types and how to overcome those differences to make this approach more applicable,” said Blau, who is also a member of the Stanford Institute for Stem Cell Biology and Regenerative Medicine.
“In the future, we may be able to target muscle stem cells from people with Duchenne muscular dystrophy and lengthen their telomeres. This could also have implications for treating diseases of aging, such as diabetes and heart disease. This really opens the door to looking at all the potential applications of this therapy.”
Other Stanford co-authors of the paper include postdoctoral scholars Jennifer Brady, PhD, and Moritz Brandt, MD; senior research scientist Stefan Korbel, PhD; research associate Colin Holbrook; and mechanical engineering professor Juan Santiago, PhD.
This work was supported by the National Institutes of Health (grants R01AR063963, U01HL100397, U01HL099997, and AG044815), the German Federal Ministry of Education and Research, Stanford Bio-X, and the Baxter Foundation.
Ramunas, Yakubov, Cook and Blau are the inventors of a patent for telomere lengthening using modified RNA.
The Stanford University Department of Microbiology and Immunology also supported this research, which can be found at http://microimmuno.stanford.edu.
Stanford Medicine is an integrated academic health system comprised of the Stanford School of Medicine and the Adult and Children’s Health Systems. Together, they realize the full potential of biomedicine through collaborative research, education, and clinical care. For more information, visit med.stanford.edu.
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