The mitochondrial and cytoplasmic superoxide anion imbalance trigger the expression of certain cellular aging markers in HaCaT keratinocytes.

In cells, the term "cellular aging" represents a collection of biological changes that can precede the proliferative senescence states. Cells more resistant to proliferative senescence, such as the ones found in the basal layer of the epidermis, may also exhibit these aging patterns. Therefore, cellular aging events could be induced by endogenous signals named here as cellular aging triggers (CATs) components. The superoxide anion (O₂⁻) could be a prime candidate for a CATs, as it is continuously produced by eukaryotic cells. To test this hypothesis, mitochondrial and cytoplasmic O₂⁻ imbalances were induced in HaCaT keratinocytes using rotenone (ROT, 30 µM), which inhibits mitochondrial complex I and paraquat (PQT, 30 µM), which increases O₂⁻ levels via redox cycling. ROT and PQT reduced cellular proliferation rate and elevated β-Galactosidase and transforming growth factor beta (TGF-β) levels. Furthermore, they increased the frequency of larger cells with nuclear alterations, the levels of oxidative markers, and interleukin 1β, a marker of the Senescence-Associated Secretory Phenotype (SASP). However, the mitochondrial O₂⁻ imbalance caused by ROT led to more pronounced alterations compared to PQT. These findings support the hypothesis that the existence of CAT components, such as the O2⁻ anion, plays a significant role in cellular aging.