Zombie cells

The zombies are here, except turns out it’s on a cellular scale, so stop boarding up your windows and pick up that microscope! In new research from Dr Baker at the Mayo Clinic, scientists found that removing senescent cells, also known as ‘zombie’ cells, reduced symptoms associated with age related degenerative diseases.

Senescent cells are unable to perform the functions of a normal cell but are unable to die, meaning that they build up over time and are associated with a number of age-related diseases including atherosclerosis, osteoarthritis and Alzheimer’s. It had been thought that these were simply innocent bystanders that do not cause damage, however recent work has suggested that they release inflammatory signals, which disturb the surrounding cells.

Scientists found that when they cleared senescent cells in the mice brains, using a genetically modified enzyme, the mice retained the ability to form new memories and showed reduced outward signs of cognitive decline. They were also able to identify that two types of brain cells, ‘microglia’ and ‘astrocytes’, were the types that became senescent. These are immune cells linked to neuronal health and signalling.

This is one of the first pieces of evidence that senescent cells play a role in neurodegenerative diseases and opens potential new avenues for treatment. The scientist, in this study, also used drugs that have been shown to damage senescent cells to see if the drugs had a similar effect to the enzyme. When the drug was administered for the first six months of the mouse’s life, their brains had fewer tangles of a protein called tau, a marker of cognitive decline.

Whilst these findings are promising, a cure for neurodegenerative diseases isn’t quite on the horizon yet. The approach taken in these experiments represents the best-case scenario and would be difficult to apply clinically as it was a preventative measure. Also, targeted treatments can be difficult, as older people tend to have lots of cells that look like these harmful senescent cells, and so it remains to be seen if a treatment can distinguish between the two.

In the future, Dr Baker and his team will focus on treating animals after the disease has started, looking at specific alterations that happen on a molecular scale in the cells they identify.