Worn-out cells eventually stop dividing

CELLS divide many times throughout their lives. But they cannot do it indefinitely. Once they have reached the limits of their reproductive powers, they enter a state called “senescence”, in which they carry on performing their duties but stop making new copies of themselves. For years it was assumed that, apart from their refusal to divide, senescent cells were otherwise identical to their replicating compatriots.There is mounting evidence, though, that this is untrue. One study in 2016 reported that senescent cells in the kidneys and heart produce a protein that causes nearby healthy tissues to deteriorate. Another study found that senescent cells contribute to diseases like atherosclerosis and arthritis. New work led by Darren Baker, a biologist at the Mayo Clinic in Minnesota, published in this week, suggests the accumulation of senescent cells within the brains of mice causes the animals to develop neurodegenerative diseases—and that clearing out these cells can help prevent them.