# Nitroxide Hormesis in Yeast: 4-Hydroxy-TEMPO Modulates Aging, and Cell Cycle

## TL;DR

This study explores how 4-hydroxy-TEMPO, a nitroxide radical, affects yeast aging and cell cycle, showing a hormetic effect depending on genetic background.

## Contribution

The study reveals a novel hormetic effect of 4-hydroxy-TEMPO on yeast aging and identifies a non-canonical redox-dependent transcriptional response.

## Key findings

- 4-hydroxy-TEMPO induces a strain-dependent hormetic response in chronological aging.
- It triggers a non-canonical transcriptional program involving stress-response and ribosomal genes.
- The compound preserves polysome structure and shows genoprotective effects at low concentrations.

## Abstract

4-hydroxy-TEMPO is a water-soluble nitroxide radical with potent antioxidant and redox-modulating properties. Its small molecular weight and membrane permeability enable it to act as a superoxide dismutase mimetic, efficiently scavenging reactive oxygen species and mitigating oxidative damage. In this study, we investigated the physiological and transcriptomic effects of 4-hydroxy-TEMPO in Saccharomyces cerevisiae, using wild-type and mutant strains deficient in key redox and DNA repair pathways (sod1Δ, sod2Δ, yap1Δ, rad52Δ). RNA-Seq analysis revealed widespread transcriptional reprogramming. Treatment with 4-hydroxy-TEMPO impaired cell growth, induced accumulation of cells with 1C (G1 phase) DNA content, and modulated chronological aging in a strain-dependent manner. Notably, low concentrations delayed aging in wild-type, yap1Δ, and rad52Δ strains, while accelerating it in sod1Δ mutants, consistent with a hormetic response. Unlike TEMPO, 4-hydroxy-TEMPO exhibited markedly reduced translational toxicity, preserved polysome structure at high doses, and triggered a non-canonical, redox-dependent transcriptional program characterized by induction of stress-response genes together with unexpected up-regulation of multiple ribosomal protein genes. This was accompanied by a biphasic, genotype-specific hormetic response and a measurable genoprotective effect. RT-qPCR confirmed key transcriptional changes, linking transcriptome remodeling to functional outcomes.