Science of Aging: What Can We Learn from Experiments in Mice

An experiment revealed that transfusing an older mouse’s blood into younger mice caused an aging effect. The previous studies with mice identified factors that could potentially help to treat some aging-related human conditions.

A study, published in Nature Metabolism, describes an experiment in which young mice aged three months were infused with blood from a mouse aged 22-24 months.

The mice were then tested for their physical endurance on a treadmill. It was found that they fatigued faster and ran a shorter distance compared to the control group, which included young mice who received a blood transfusion from another young mouse.

Mice infused with blood from an old mouse also showed signs of kidney damage and liver aging. At the same time, older mice infused with younger mice's blood saw their muscle endurance increase.

It is not the first study showing the effects of mixing the blood of young and older mice. In the previous experiments, researchers identified factors that might play a role in treating human age-related conditions.

Regenerating muscle capacity

In a 2021 study, the University of Pittsburgh Medical Center and the University of Pittsburgh researchers answered a decades-long question on why when old mice are given blood from young mice, youthful features are restored to many cells and tissues.

The researchers identified that circulating shuttles called extracellular vesicles (EVs) deliver genetic instructions for the longevity protein known as Klotho to muscle cells. Aged EVs carry fewer copies of these instructions and, therefore, may drive loss of muscle function and impaired muscle repair.

Researchers then suggested that EVs could be beneficial for boosting the regenerative muscle capacity in older individuals and improving functional recovery after an injury.

Producing new nerve cells

A 2011 Stanford University School of Medicine study found substances in the blood of old mice that make young brains act older. In the experiment, researchers connected the circulatory systems of pairs of old and young mice via a surgical procedure so that blood from the two mice commingled.

The mixing produced changes in both the young and the old mice’s brains. For example, the number of new nerve cells generated in old mice increased when they were exposed to the younger environment. In contrast, the young members of old/young mouse pairs exhibited fewer new nerve cells in the dentate gyrus — part of a key brain region, the hippocampus — than young mice untethered to elders.

To identify specific factors associated with aging and tissue degeneration or tissue regeneration, researchers assessed 66 different immune-signaling proteins found in mice’s blood.

Among them was eotaxin, a small protein that attracts a certain type of immune cells to areas where it has been secreted by other types of cells. After being given eotaxin injections, normal young-adult mice exhibited deficient generation of new nerve cells in their dentate gyrus.

The researchers then said they were testing eotaxin’s potential role in memory loss associated with Alzheimer’s disease. They were also developing expanded blood-protein assays in a hunt for “rejuvenating” factors in the blood that may prove useful in treating dementia and, perhaps, slowing the aging process in older brains.

Making hearts younger

In 2013, researchers from Harvard Stem Cell Institute (HSCI) identified a protein in the blood of mice and humans that may be used to treat the form of age-related heart failure.

In the experiment, researchers injected the protein called GDF-11 into old mice, which develop thickened heart walls in a manner similar to aging humans. After the injection, the hearts of old mice were reduced in size and thickness, resembling the healthy hearts of younger mice.

“In this study, we were able to show that a protein that circulates in the blood is related to this aging process, and if we gave older mice this protein, we could reverse the heart aging in a very short period of time,” said Richard T. Lee, a Harvard Medical School professor at the hospital in a press release.


1. Nature Metabolism. Systemic induction of senescence in young mice after single heterochronic blood exchange.

2. University of Pittsburgh Medical Center. Study Identifies Factor in ‘Young Blood’ That Helps Rejuvenate Aged Mouse Muscle.

3. Stanford University School of Medicine. Scientists discover blood factors that appear to cause aging in brains of mice.

4. Harvard Stem Cell Institute. Making old hearts younger - HSCI researchers find protein that reverses some effects of aging in mice.

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