The laboratory of Helen Blau at Stanford University has devised a technique to lengthen the sequences that cap the ends of chromosomes in skin cells. This treatment enlivens the cells and makes them behave as though they were younger.
In order to properly protect linear chromosomes from loosing DNA at their ends, chromosomes have a special set of sequences called “telomeres” at their ends. Telomeres consists of short sequences that are repeated many times. A special enzyme called the telomerase replicates the telomeres and maintains them. As we age, telomerase activity wanes and the telomeres shorten. This threatens the genetic integrity of the chromosomes, since a loss of genes from the ends of chromosomes can be deleterious for cells. In young humans, the telomeres may be 8,000 to 10,000 bases long. When the telomeres shorten to a particular length, growth stops and the cells become quiescent.
Embryonic stem cells have long telomeres at the ends of their chromosomes and they also have robust telomerase activity. Adult stem cells have varied telomerase activity and telomere length, but it seems that the length of the telomeres and the activity of the telomerase correlates with the vitality of the stem cell population and its capacity to heal (see H. Saeed and M. Iqtedar (2013). J. Biosci. 38, 641–649). As we age our stem cell quality decreases as their telomeres shorten.
Blau and her colleagues used a modified type of RNA to lengthen the telomeres of large numbers of cells. According to Blau: “Now we have found a way to lengthen human telomeres by as much as 1,000 nucleotides, turning back the internal clock in these cells by the equivalent of many years of human life. This greatly increases the number of cells available for studies such as drug testing or disease modeling.”
In these experiments, Blau and her coworkers used chemically modified messenger RNA molecules that code for TERT, which is the protein component of the telomerase. The expression of these messenger RNAs in human cells greatly increased the levels of telomerase activity.
This technique devised by Blau and her team have distinct advantages of previously described protocols. First, this technique boosts telomerase activity temporarily. The modified messenger RNA sticks around for several hours and is translated into TERT protein, but this protein only lasts for about 48 hours, after which its activity dissipates. After the telomerase have lengthened the telomeres, they will shorten again after each cell division as before.
“This new approach paves the way toward preventing or treating diseases of aging,” said Blau. “There are also highly debilitating genetic diseases associated with telomere shortening that could benefit from such a potential treatment.”
Blau and her team are testing their technique in other cell types besides skin cells.