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Makeover: old mice can see again

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Researchers have restored the eyesight of old mice as well as rodents with damaged retinal nerves. To do this, they changed some of the thousands of chemical markers that are associated with cell aging. The study published in the magazine “Nature” suggests that age-related decay can be reversed in this way: The cells are returned to a “younger” state in which they can repair themselves or replace damaged tissue.

"A big breakthrough," says developmental biologist Juan Carlos Izpisua Belmonte from the Salk Institute for Biological Studies in La Jolla, California, who was not involved in the study. “The results clearly show that tissue regeneration can be promoted in mammals.” However, the procedure has so far only been successful in mice. It remains to be seen whether the method can also be transferred to humans or other tissues and organs, says the team of authors.

This article is featured in Spectrum Health, 3/2021

Age changes the body in many ways, including adding, removing, or altering methyl groups in DNA. These "epigenetic" changes accumulate with age. So some researchers have suggested using the changes as an epigenetic clock to measure biological age, which can vary from chronological age.

"We started with the question: If epigenetic changes drive aging, can the epigenome be reset?" Says geneticist David Sinclair of Harvard Medical School in Boston and co-author of the study. "Can we turn back the clock?"

There was some evidence that the idea might work. In 2016, Belmonte and his colleagues reported the effects of gene expression in mice. The animals were genetically modified in such a way that they aged faster than usual. Genes can be triggered in such a way that cells lose their "identity" - for example those characteristics that make a cell a skin cell - and develop back into a stem cell. That was known. But instead of leaving the genes in this state, Belmonte's team only switched them on for a few days and then switched them off again in the hope that they had merely put the cells in a "younger" state.

The result: the mice had a pattern of epigenetic markers that corresponded to that of younger animals. However, the technology also had disadvantages: Earlier work had shown that some mice develop tumors if genes were available in additional copies or if they were expressed for too long.