How great would it be if we knew how to reverse ageing and turn old organs into young ones? Actually, this might not be as crazy as it sounds. As a matter of fact, a team of scientists managed to regenerate the thymus in old mice and observe what closely resembles the juvenile thymus!
The thymus is a key organ of the immune system as it is where T cells, major actors of one’s immunity, develop and mature. In normal healthy people, the thymus degenerates with age (a process called thymic involution) and this results in a decline of the immune system function. Since our immune system is what protects us against diseases, it is evident that being able to restore the function of the thymus in elder people would be very beneficial.
Interestingly, in this study recently published in Development, Bredenkamp and colleagues achieved thymus regeneration in old mice. They observed a juvenile-like thymus after using genetic engineering to force the expression of the protein foxn1 in the aged thymus.
In this picture, you can observe the cortical thymic epithelial cell marker CDR1 in green and the medullary thymic epithelial cell marker keratin 14 (K14) in red. The cortex and the medulla are distinct regions of the thymus and they deteriorate during thymic involution. This results in reduced distinction between cortex and medulla as observed in the bottom picture taken in 24 months old mice. However, when foxn1 is over-expressed in the same 24 months old mice, you can observe that the clear distinction between cortex (green) and medulla (red) is restored, indicative of thymus regeneration.
In addition to the restoration of thymic architecture, the authors show that the regenerated organ has an increased T cell output and a gene expression profile similar to the juvenile thymus.
Most amazingly, apart from being able to “reverse ageing” in the thymus, they show that this regenerative process relies on the over-expression of a single factor (foxn1), making it a lot simpler than one might have anticipated! Thus, this study brings a new provocative concept that will most likely have a broad impact for regenerative biology.
Bredenkamp, N., Nowell, C., & Blackburn, C. (2014). Regeneration of the aged thymus by a single transcription factor Development, 141 (8), 1627-1637 DOI: 10.1242/dev.103614