Reprogramming involves exposing cells to expression of one or more of the Yamanaka factors, c-Myc, Oct4, Sox2, and KLF4. This slowly alters cell state in a small fraction of exposed somatic cells, and these cells transform to become induced pluripotent stem cells, essentially the same as embryonic stem cells. This recapitulates some of the processes involved in embryogenesis. More rapidly and reliably than this change of state, a cell exposed to Yamanaka factor expression also exhibits rejuvenation of nuclear DNA structure and patterns of gene expression, leading to a restoration of youthful function. This cannot fix everything in an aged cell, such as mutational DNA damage, but it has a sizable enough effect on cells, and in mice, that partial reprogramming as a basis for rejuvenation therapies has become a popular area of development.
Can reprogramming of cell state be efficiently separated from reprogramming of nuclear structure? If we want reliable rejuvenation therapies, it seems likely that progress must be made on this front. Researchers are investigating the regulation of reprogramming downstream of the Yamanaka factors, but this is a painfully slow process. Still, every incremental advance in tracing the interactions of proteins might be the one that disentangles rejuvenation from state change, unleashing a much more efficient approach than offered by the present options capable of triggering reprogramming.
Most of the longevity industry now consists of reprogramming initiatives if measuring by investment size. Related to that, we might argue that most of the work carried out on reprogramming as a basis for rejuvenation therapies is in fact conducted outside academia at this point. In the long run this work will become just as visible as academic efforts, but for now it is dark matter. Thus to find ongoing indications of progress on picking apart the systems of regulation that produce rejuvenation in response to Yamanaka factor expression, one must keep up with the publication of academic papers – such as today’s example.
Conserved Master Regulators Orchestrate Cellular Reprogramming-Induced Rejuvenation
Partial somatic cell reprogramming has been proposed as a rejuvenation strategy, yet the regulatory architecture orchestrating age reversal remains unclear. What molecular systems allow partial relaxation of identity to restore youthful regulatory function while avoiding dedifferentiation? Previous work has identified chromatin regulators as central to this process. DNA methyltransferases Tet1 and Tet2 may be required for reprogramming-induced rejuvenation, and reprogramming-induced rejuvenated cells exhibit restored nucleosome regularity and recalibrated histone modification balance. However, identifying genes that change during rejuvenation does not reveal which factors actively drive the process versus those that respond as downstream consequences. Distinguishing upstream regulators from effector genes requires network-level analysis that can infer causal regulatory relationships.
Here, we performed gene regulatory network reconstruction across several independent systems to identify master regulators that coordinate reprogramming-induced rejuvenation (RIR). In mouse mesenchymal stem cells, mouse adipocytes, and human fibroblasts undergoing partial reprogramming, we identified genes showing opposite expression dynamics during aging and reprogramming. This approach revealed regulators governing rejuvenation rather than developmental programs. Despite divergent overall network architectures, nine transcription factors converged as master regulators across all three systems, including Ezh2, Parp1, and Brca1. These regulators undergo coordinated reorganization during reprogramming, characterized by broader target engagement and enhanced regulatory coherence.
We further demonstrated that direct perturbation of Ezh2 bidirectionally modulates transcriptomic age. Notably, overexpression of a catalytically inactive Ezh2 mutant achieved rejuvenation, suggesting mechanisms distinct from canonical H3K27me3-mediated regulation are involved in RIR. Our findings reveal that cellular rejuvenation is orchestrated by conserved master regulators whose network coordination can be targeted independently of the reprogramming process.
