Blood precursor cells become neural stem cells as molecular age gradually turns back

To understand how cells become younger, researchers need more than two snapshots taken before and after conversion; they also need a clear view of what happens in between. A team at the University of Bonn and University Hospital Bonn in Germany found that when human red blood cell precursors are directly converted into neural stem cells, their molecular aging clocks gradually turn back. This process, which can be tracked for more than a hundred days, provides an experimental model that makes cellular rejuvenation easier to examine closely.

The study was published in *Aging Cell*. The team used two transcription factors, SOX2 and cMYC, to change how cells read genetic instructions, converting red blood cell precursors into induced neural stem cells. This route produces cells that can subsequently generate neurons without first passing through a pluripotent stem cell stage capable of differentiating into multiple tissue types.

Changes in age were estimated using epigenetic markers on DNA. These markers do not alter the DNA sequence, but are associated with how genes are used and with cellular aging. Both the University of Bonn announcement and a university-provided report published in Medical Xpress cited the example of blood cells from an 80-year-old donor whose estimated molecular age fell to below 20 after conversion. However, this is a reading of molecular indicators and cannot be interpreted as the donor's body returning to a youthful state.

The speed of the change, rather than the number of years lost, was a particular focus of this study. Study leader Oliver Brüstle noted that rejuvenation is usually faster through a reprogramming route involving pluripotent stem cells; with direct conversion into neural stem cells, however, the process can be tracked for more than 100 days. The research paper also showed that differences in gene expression between cells from younger and older donors gradually faded as the conversion period lengthened.

This slow change offers an opportunity for intervention: researchers can introduce candidate substances at different time points to test which factors accelerate or slow the reorganization of aging markers. For neurodegenerative diseases closely associated with age, such as Alzheimer's disease, this can help researchers investigate which mechanisms connect changes in cell identity with the disappearance of aging characteristics.

But molecular clocks remain surrogate indicators of biological age and cannot, on their own, prove that all age-related functional changes have been reversed. The university report's description of transplanted neurons forming connections with existing neurons in mouse brains came from earlier research; the current work focuses on the dynamics of cellular rejuvenation and has not demonstrated treatment effects in patients. What it currently offers is a research window that allows tracking, comparison, and intervention.