Heterochronic parabiosis is the conjoining of two animals of different ages, and is used to investigate the effects of sharing body parts of different ages with one another. In a new study, researchers conducted a similar procedure, but only exchanged blood between the two animals, not organs, and found the procedure to be minimally invasive with greater clinical application for humans.

As medical technology has improved, many causes of death in early life have been resolved. This has resulted in longer lifespans which come with increased age-related deterioration and disease. Scientists have looked at ways to rejuvenate aging bodies, with one proposed solution being to supply the old tissues with young circulatory systems to aid in regenerative processes.









One way scientists research this prospect is heterochronic parabiosis. In heterochronic parabiosis, an old animal and a young animal are surgically joined. This allows the two animals to share circulatory systems and organs, and leads to a rejuvenation of older tissue while also furthering the aging process of the younger tissue. However, this process does not help researchers specify what aspects of the parabiotic system result in improvements for the older animal. For human applications, blood sharing is the least invasive and most applicable means of introducing youthful factors into an older body, but complete parabiosis does not allow scientists to determine whether organ sharing or circulatory system sharing is the source of the benefits. Hence, a new study developed a blood exchange system that can be connected and disconnected at will, independent of shared organs.

In this study published in Nature, Rebo et al. performed blood exchange between 3-month-old mice and 23-month-old mice. Catheters were inserted into the right jugular vein, and blood was exchanged in 150 μL intervals. Some mice were also peripherally injured with intramuscular injections to determine the effect of blood exchange on injury. The effects of blood mixing, or heterochronic blood exchange, were examined in myogenesis (muscle cell regeneration), hepatogenesis (liver cell regeneration) and neurogenesis (brain cell regeneration), both with and without muscle injury.

Researchers found that heterochronic blood exchange had effects on myogenesis and hepatogenesis and neurogenesis within days after initiation. Myogenesis in the older animal was improved without detriment to the younger animal. The older animal’s blood had greater effect in hepatogenesis, as though older liver cell regeneration improved, the younger animal’s decreased, and it had an even greater effect in neurogenesis, where the rejuvenation from the young blood was far less than the inhibition from the older blood. Peripheral tissue injury had an effect on neurogenesis, exacerbating the negative effects of the old blood.

The research done in this study establishes that heterochronic blood exchange has almost immediate effects on the animals involved. It also shows different effects on myogenesis, hepatogenesis, and neurogenesis. The method developed in this study allows for further investigation into blood exchange and its clinical applications in treating diseases such as sickle cell anemia, hemolytic disease in newborns and severe malaria. Further studies can be conducted to study the long-term effects of blood exchange and the factors within the blood that cause different effects on myogenesis, hepatogenesis, and neurogenesis, with the hope of isolating factors to instill youthful benefits on the aging population.

Written By: Wesley Tin, BMSc







