Rejuvenation of young blood on aging organs: Effects, circulating factors, and mechanisms

Aging causes degenerative changes in organs, leading to a decline in physical function. Over the past two decades, researchers have made significant progress in understanding the rejuvenating effects of young blood on aging organs, benefiting from heterochronic parabiosis models that connect the blood circulation of aged and young rodents. It has been discovered that young blood can partially rejuvenate organs in old animals by regulating important aging-related signaling pathways. Clinical trials have also shown the effectiveness of young blood in treating aging-related diseases. However, the limited availability of young blood poses a challenge to implementing anti-aging therapies on a large scale for older individuals. As a promising alternative, scientists have identified some specific anti-aging circulating factors in young blood that have been shown to promote organ regeneration, reduce inflammation, and alleviate fibrosis associated with aging in animal experiments. While previous reviews have focused primarily on the effects and mechanisms of circulating factors on aging, it is important to acknowledge that studying the rejuvenating effects and mechanisms of young blood has been a significant source of inspiration in this field, and it will continue to be in the future. In recent years, new findings have emerged, further expanding our knowledge in this area. This review aims to summarize the rejuvenating effects and mechanisms of young blood and circulating factors, discussing their similarities and connections, addressing discrepancies in previous studies, outlining future research directions, and highlighting the potential for clinical translation in anti-aging interventions.