Ultraviolet B radiation (UVB) causes direct DNA damage by inducing the formation of cyclobutane pyrimidine dimers (CPDs). These photolesions lead to diverse cellular effects, but their involvement in the regulation of mitochondrial function is unexplored. Here, we characterized the impact of UVB-induced DNA damage on the mitochondria using our established model system, in which human keratinocytes are transfected with methylpseudouridine-modified mRNA encoding CPD-photolyase.
Our results demonstrate that CPD removal by photoactivated CPD-photolyase in HaCaT cells reduces PARP activation and bulk autophagy after UVB exposure. Moreover, the CPD-photolyase prevents G2/M cell cycle arrest and restores cell viability. Removal of CPD also prevented the UVB-mediated increase in mitochondrial mass, mitochondrial biogenesis and morphological changes of mitochondria. Alterations in mitochondrial number, area, shape descriptors and expressional changes of fusion proteins indicated that photoactivation of CPD-photolyase can prevent UVB-induced mitochondrial fusion. As a result of photolyase activity mitochondrial membrane potential, superoxide production, glycolysis and oxidative phosphorylation were all reduced to baseline levels. We also demonstrated that following removal of CPDs the expression of the upstream regulators of oxidative phosphorylation was decreased, thus suggesting that UVB-initiated DNA damage likely induces nucleus-to-mitochondria signaling.
In conclusion, delivery of CPD-photolyase mRNA into cultured human keratinocytes provides a protective effect not only against DNA damage but also prevents morphological and functional changes of mitochondria after UVB exposure.

In vitro delivery of CPD-specific photolyase-encoding mRNA prevents UVB-induced mitochondrial changes