29 July 2022

What is the harm of old blood

Young mice age if they are transfused with the blood of elderly individuals

Georgy Chistov, PCR.news

Cellular aging is a response to stress and damage that increases with age. Aging cells stop growing and secrete a special set of molecules. Their effect on body tissues is still poorly understood. There is evidence that after surgical connection of young and old mice, young individuals age, but the role of cellular aging in this process is still unclear.

Scientists from the USA and South Korea investigated this issue by transfusing blood from old mice to young ones. Unlike other methods, this technique allows the use of naturally aged cells and excludes other factors — the interaction of organs or joint physical exercises, as in the case of surgical stitching. Based on data from the literature, the authors hypothesized that cellular aging can be transmitted from old cells to young recipient cells.

First, scientists conducted experiments in vitro. They cultured mouse and human cells in serum from young and old animals. The "old" serum reduced the proliferating activity and led to the loss of lamin B1. Moreover, the expression of Cdkn2a, Cdkn1a and β-galactosidase increased in such cells — these proteins regulate aging or are associated with it. Serum cultivation from old individuals also led to the synthesis of aging signals — IL-6 and Mmp3. Scientists have noticed that after mixing serums from old and young individuals, the effect remains the same. This highlights the dominant role of aging factors.

The experiment was repeated in vivo. After transfusion of blood from old individuals to young ones, the researchers obtained the same results as on cell cultures. Interestingly, in this case, the effect was tissue-specific. For example, no changes were observed in the tissues of the lungs, heart and hippocampus.

The researchers turned their attention to the kidneys and liver. At first glance, the kidneys showed no obvious signs of necrosis, inflammation or other abnormalities. Nevertheless, the level of the biomarker of kidney damage KIM-1 was increased. For the liver, scientists found an increase in fibrous areas.

In addition, blood transfusion led to the accumulation of lipids in muscle tissue and an increase in their age-related atrophy. This affected the functional ability of the muscles — young mice after blood transfusion run a shorter distance and get tired faster.

To make sure that the induced aging comes from the old cells of the body, the scientists conducted another series of experiments. In them, they injected senolytics into old mice, which selectively destroyed old cells. After the treatment, the scientists again performed transfusion, but in this case the effect of induced aging was less.

Using histochemical methods, the scientists showed signs of induced aging in the satellite cells of skeletal muscles of young mice after transfusion. Scientists also found aging white blood cells in the muscles, but could not determine for sure whether they belong to an old donor or a young recipient.

The researchers also drew attention to data on the use of young blood to reduce the age of old individuals. They decided to check whether this effect is due to aging cells. To do this, they injected an old individual with senolytics and transfused her blood to another old individual. Such transfusion did not lead to a positive effect. The authors suggest that the rejuvenating effect of blood may be due to some other factors.

Article by Jeon et al. Systematic induction of senescence in young mice after single heterochronic blood exchange is published in the journal Nature Metabolism.

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