Temporal Regulation of UVA-Induced Ferroptosis-Associated Injury in Keratinocytes

Ferroptosis contributes to ultraviolet (UV)-induced epidermal injury, but whether circadian state modifies keratinocyte susceptibility remains unclear. We integrated human epidermal transcriptomic analyses with functional experiments in HaCaT keratinocytes to compare UVA- and UVB-induced ferroptosis-associated responses and assess their temporal regulation. Both wavelengths reduced cell viability and increased reactive oxygen species, lipid peroxidation, and intracellular Fe²⁺ accumulation; ferrostatin-1 provided partial protection. UVB reduced xCT and GPX4 and showed a proteasome-sensitive component of GPX4 loss, whereas UVA predominantly reduced GPX4 without detectably altering xCT. Human epidermal transcriptomes showed heterogeneous cross-sectional associations among circadian, oxidative-stress, and ferroptosis-related genes, while longitudinal profiles revealed positive temporal coupling between NR1D1-associated signals and GPX4. In synchronized HaCaT cells, ARNTL and NR1D1 displayed 24 h rhythmicity, whereas GPX4 and SLC7A11 did not meet the prespecified rhythmicity criterion. Nevertheless, UVA-induced cytotoxicity, oxidative stress, lipid peroxidation, and GPX4 loss varied across post-synchronization time points and were greatest at 24 h. SR8278 partially preserved GPX4 abundance and attenuated UVA-induced loss of viability, reactive oxygen species accumulation, and lipid peroxidation, without significantly affecting Fe²⁺ accumulation. These findings associate circadian state with temporal variation in UVA-induced ferroptosis susceptibility and implicate the broader clock-redox system rather than rhythmic expression of individual ferroptosis effectors.