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Zeb2-NAT lncRNA: Breaking Down Age-associated Reprogramming Barriers

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Review of “Silencing of the lncRNA Zeb2-NAT facilitates reprogramming of aged fibroblasts and safeguards stem cell pluripotency” from Nature Communications by Stuart P. Atkinson

Studies have suggested that the presence of an elevated number of senescent cells in older individuals leads to the observed reduction in reprogramming efficiency when generating induced pluripotent stem cells (iPSCs) [1]. Reducing the levels of senescence-associated proteins in aged cells can improve efficiency, although removing natural defenses to the development of tumorigenesis may add unnecessary risk to regenerative therapies.

This problem led researchers from the laboratory of Maria Carmo-Fonseca (Universidade de Lisboa, Portugal) to investigate novel age-associated barriers to the reprogramming process in a new Nature Communications study. Interestingly, Bernardes de Jesus et al. now suggest that targeting a long non-coding RNA (lncRNA) may represent a safe and efficient means of breaking down an age-associated reprogramming barrier and increasing reprogramming efficiency in aged cell samples [2].

To discover novel molecular pathways that represent age-associated reprogramming barriers, the authors searched for differences in the reprogramming process taking place in embryonic mouse fibroblasts and adult mouse fibroblasts. Unlike embryonic fibroblasts, adult fibroblasts exhibited higher mRNA levels of the Zeb2 epithelial-to-mesenchymal transition (EMT)-associated transcription factor and sustained higher expression levels throughout the reprogramming process. Expression of the Zeb2-NAT lncRNA promotes Zeb2 protein synthesis by enhancing translation [3], and the authors also discovered the overexpression of this lncRNA in adult fibroblasts. 

The reprogramming process requires the suppression of pro-EMT signals, and so, high levels of Zeb2/Zeb2-NAT may impede reprogramming of adult cells. To test this hypothesis, the authors downregulated Zeb2-NAT lncRNA levels via the transfection of adult fibroblasts with locked nucleic acid (LNA)-modified “Gapmers” [4] that hybridize and promote the degradation of Zeb2-NAT transcripts, finding that this reduced Zeb2 levels and enhanced reprogramming efficiency.

Further analysis employing mouse embryonic stem cells (mESCs) revealed additional fascinating properties of the Zeb2-NAT lncRNA. The knockdown of the already low level of Zeb2-NAT lncRNA expression in mESCs promoted maintenance of ground state or naïve pluripotency even in the face of differentiation signals, while high levels of Zeb2-NAT lncRNA expression correlated to the onset of differentiation, overall, suggesting a role for Zeb2-NAT lncRNA in stem cell commitment.

Older/elderly patients represent the demographic most likely to require regenerative/reparative strategies employing cells derived from iPSCs, and so, the need for efficient protocols to generate iPSCs is of great importance. This new study establishes that sustained pro-EMT signaling sustained by high levels of Zeb2-NAT lncRNA expression represents a significant barrier to the reprogramming process.

Will breaking down the Zeb2-NAT lncRNA age-associated reprogramming barrier lead to the enhanced generation of human aged iPSCs and boost regenerative/reparative strategies in the near future? Stay tuned to the Stem Cells Portal to find out! 

References

  1. Marion RM, Strati K, Li H, et al., A p53-mediated DNA damage response limits reprogramming to ensure iPS cell genomic integrity. Nature 2009;460:1149-53.
  2. Bernardes de Jesus B, Marinho SP, Barros S, et al., Silencing of the lncRNA Zeb2-NAT facilitates reprogramming of aged fibroblasts and safeguards stem cell pluripotency. Nat Commun 2018;9:94.
  3. Beltran M, Puig I, Peña C, et al., A natural antisense transcript regulates Zeb2/Sip1 gene expression during Snail1-induced epithelial–mesenchymal transition. Genes & Development 2008;22:756-769.
  4. Bennett CF and Swayze EE, RNA Targeting Therapeutics: Molecular Mechanisms of Antisense Oligonucleotides as a Therapeutic Platform. Annual Review of Pharmacology and Toxicology 2010;50:259-293.