Blood Cells Rewound: Direct Neural Conversion Slowly Erases Epigenetic Age

In a finding that could reshape how scientists think about cellular rejuvenation, researchers have shown that human blood cells can be directly converted into neural stem cells that shed nearly all traces of their epigenetic age — but only through a surprisingly slow process that unfolds over roughly fifty days. The study, published in Aging Cell, tracked the transformation of peripheral blood cells from donors ranging from newborns to a 101-year-old individual, and discovered that both the acquisition of a neural stem cell identity and the reversal of aging signatures proceed far more gradually than anyone anticipated.

The work builds on a technique known as direct conversion, in which specialized cells are pushed into a new identity without passing through the pluripotent state that defines induced pluripotent stem cells, or iPSCs. When somatic cells are reprogrammed into iPSCs, their DNA methylation age — a molecular readout of biological aging — is rewound to an embryonic state. In contrast, when cells are converted directly into post-mitotic neurons, they largely retain the age of the cells they came from. The new study sits intriguingly between these two poles: induced neural stem cells, or iNSCs, are self-renewing like stem cells, yet they are generated without a pluripotent intermediate.

The research team, led by investigators at the University of Bonn, used a Sendai virus system to deliver just two transcription factors, SOX2 and cMYC, into erythroid progenitor cells derived from easily accessible blood samples. Within days of infection, the blood cells downregulated the erythroid marker CD71, and by day twelve, the emerging cells expressed the neural stem cell markers DACH1 and PAX6. Morphologically, the cultures already resembled neuroepithelial tissue within the first two weeks. On the surface, the fate switch appeared to happen quickly.

But the molecular data told a different story. Using the epigenetic clock algorithm developed by Steve Horvath and colleagues, the researchers measured DNA methylation age across the conversion time course. While the starting blood cells correlated precisely with the chronological age of their donors, the converted iNSCs at low passage carried a DNA methylation age averaging only about thirteen percent of the donor’s chronological age — and in established lines, less than five percent. Remarkably, this de-aging did not happen in a burst. Instead, it stretched across approximately fifty days, with some individual lines requiring around seven weeks to reach roughly twenty percent of their original epigenetic age.

This slow kinetics stands in sharp contrast to classic iPSC reprogramming, where the epigenetic age reset is largely complete within about twenty days. The protracted timeline suggests that the molecular machinery responsible for erasing age-related methylation signatures operates on a different schedule when pluripotency is not engaged. The researchers also compared their iNSCs with isogenic iPSC-derived neural stem cells generated from the same blood samples, providing a matched reference for cells that have undergone a complete age reset through the pluripotent route.

Perhaps the most unexpected result came from experiments designed to test whether cell division drives the de-aging process. Because both iPSC reprogramming and iNSC conversion involve proliferating cells, while direct conversion into non-dividing neurons preserves epigenetic age, the team hypothesized that mitotic activity might be the engine of rejuvenation. To test this, they slowed proliferation during conversion using either glycerol or thymidine, both of which significantly reduced accumulated population doublings. Yet the epigenetic de-aging continued essentially unabated. Even when the researchers forced the converting cells to differentiate into neurons by overexpressing NGN2 — producing cultures dominated by TUBB3-positive neurons — the DNA methylation age continued to decline at a rate indistinguishable from proliferating controls.

This finding implies that epigenetic de-aging during neural conversion is not simply a byproduct of stem cell self-renewal. It may instead be driven by the sustained presence of the conversion factors themselves, or by molecular processes that operate independently of both cell division and fate consolidation. The researchers note that SOX2 is the one factor common to their system and to a separate study in which human fibroblasts were converted into neural plate border stem cells using BRN2, KLF4, ZIC3, and SOX2 — a conversion that also produced dramatically de-aged cells. That convergence makes SOX2 a compelling candidate for future investigations into the mechanisms of somatic cell rejuvenation.

The consolidation of neural identity itself proved equally drawn out. Genome-wide analysis of DNA methylation and RNA sequencing revealed that while early neural markers appeared within days, the full transcriptional and epigenetic remodeling continued for weeks. Genes associated with neurogenesis, axon development, and neuron projection morphogenesis were still being upregulated at the late, transgene-free stage, long after the cells had adopted a stable neural stem cell morphology. Pathways related to cell migration, adhesion, and the mesenchymal-to-epithelial transition — reflecting the dramatic shift from freely circulating blood progenitors to adherent neuroepithelial cells — were regulated across nearly all stages of conversion.

Intriguingly, the transcriptomic signatures that distinguish young from old donors faded faster than the epigenetic age markers. At the starting blood cell stage, more than 1,800 genes differed in expression between cells from newborns and those from elderly donors. By day fourteen of conversion, only twenty such genes remained differentially expressed, and at low passage, just twelve. This suggests that transcriptional de-aging may be achieved more rapidly than the deeper methylation-level reset, and that the overexpressed transcription factors may directly drive the early transcriptomic changes rather than acting through epigenetic intermediaries.

The implications extend beyond basic biology. Because iNSCs generated even from centenarian donors lack classic cellular aging hallmarks — including nuclear lamina abnormalities, impaired autophagy, mitochondrial dysfunction, and senescence markers — they closely resemble their iPSC-derived counterparts while offering a faster and more direct route to patient-specific neural cells. The extended fifty-day window of active de-aging also provides researchers with an unprecedented opportunity to dissect the mechanisms of epigenetic rejuvenation in real time, potentially offering an alternative to partial or interrupted reprogramming strategies currently being explored for anti-aging therapies. As the authors conclude, their conversion system may serve as a blueprint for future studies seeking to identify the true drivers of age reversal in somatic cells — a question that has become one of the most urgent in the biology of aging.

Subject of Research: Epigenetic de-aging and fate acquisition during direct conversion of human blood cells into induced neural stem cells

Article Title: Protracted Fate Acquisition and Epigenetic De‐Aging During Induced Neural Stem Cell Conversion of Human Blood Cells

Article References: Berg, L. J., Franzen, J., Buness, A., Konang, R., Sheng, C., Peitz, M., Till, A., Wagner, W., & Brüstle, O. (2026). Protracted Fate Acquisition and Epigenetic De‐Aging During Induced Neural Stem Cell Conversion of Human Blood Cells. Aging Cell, 25(10), Article e70751. https://doi.org/10.1111/acel.70751

Image Credits: AI Generated

DOI: 10.1111/acel.70751

Keywords: induced neural stem cells, epigenetic clock, DNA methylation age, cellular reprogramming, SOX2, cMYC, direct conversion, aging, neural stem cells, iPSC, rejuvenation, transcription factors