How old are your organs? To scientists’ surprise, organs are a mix of young and old cells

Scientists once thought that neurons, or possibly heart cells, were the oldest cells in the body. Now, Salk Institute researchers have discovered that the mouse brain, liver and pancreas contain populations of cells and proteins with extremely long lifespans — some as old as neurons. The findings, demonstrating "age mosaicism," were published in Cell Metabolismon June 6, 2019.

 

The team’s methods could be applied to nearly any tissue in the body to provide valuable information about lifelong function of non-dividing cells and how cells lose control over the quality and integrity of proteins and important cell structures during aging.

"We were quite surprised to find cellular structures that are essentially as old as the organism they reside in," says Salk Vice President, Chief Science Officer Martin Hetzer, senior author and professor. "This suggests even greater cellular complexity than we previously imagined and has intriguing implications for how we think about the aging of organs, such as the brain, heart and pancreas."

 

Most neurons in the brain do not divide during adulthood and thus experience a long lifespan and age-related decline. Yet, largely due to technical limitations, the lifespan of cells outside of the brain was difficult to determine.

 

"Biologists have asked — how old are cells in an organism? There is this general idea that neurons are old, while other cells in the body are relatively young and regenerate throughout the organism’s lifetime," says Rafael Arrojo e Drigo, first author and Salk staff scientist. "We set out to see if it was possible that certain organs also have cells that were as long-lived as neurons in the brain."

 

Since the researchers knew that most neurons are not replaced during the lifespan, they used them as an "age baseline" to compare other non-dividing cells. The team combined electron isotope labeling with a hybrid imaging method (MIMS-EM) to visualize and quantify cell and protein age and turnover in the brain, pancreas and liver in young and old rodent models.

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