Pluripotent stem cells escape from senescence-associated DNA methylation changes

Area of Science:

• Epigenetics
• Cellular senescence
• Stem cell biology

Background:

• Primary cells undergo replicative senescence, losing function due to DNA methylation changes.
• Pluripotent stem cells evade senescence, suggesting distinct epigenetic regulation.
• Senescence-associated DNA methylation (SA-DNAm) is a hallmark of cellular aging.

Purpose of the Study:

• Investigate SA-DNAm changes in mesenchymal stromal cells (MSCs) under various conditions.
• Determine if irradiation-induced senescence or immortalization affects SA-DNAm.
• Clarify the role of SA-DNAm in the escape from senescence by induced pluripotent stem cells (iPSCs).

Main Methods:

• Utilized high-density HumanMethylation450 BeadChips for DNA methylation analysis.
• Examined SA-DNAm in MSCs after long-term culture, irradiation, immortalization, and reprogramming.
• Correlated SA-DNAm with histone modifications (H3K9me3, H3K27me3) and gene targets.

Main Results:

• SA-DNAm changes are reproducible and enriched in developmental gene regions.
• Ionizing irradiation did not alter SA-DNAm, despite inducing senescence.
• TERT overexpression or immortalization did not prevent SA-DNAm, but iPSC reprogramming did.
• SA-hypomethylation associated with H3K9me3, H3K27me3, and Polycomb targets.

Conclusions:

• Long-term culture induces epigenetic changes that stall cell function.
• Irradiation-induced senescence and immortalization are not linked to SA-DNAm.
• The absence of SA-DNAm in iPSCs is critical for evading cellular senescence.