Targeting non-classical autophagy-dependent ferroptosis and the subsequent HMGB1/TfR1 feedback loop accounts for alleviating solar dermatitis by senkyunolide I.

Given the substantial risks associated with ultraviolet B (UVB) radiation-induced solar dermatitis, enhancing current strategies to combat UVB regarding skin diseases is imperative. The cross-talk between ferroptosis and inflammation has been proven to be an essential factor in UVB-induced solar dermatitis, whereas detailed process of how their interaction contributes to this remains unclear. Therefore, further investigation of ferroptosis-mediated processes and identification of corresponding inhibitory approaches hold promise for repairing skin damage. Senkyunolide I (Sen I), a bioactive component mainly extracted from the traditional Chinese medicinal plants, Ligusticum chuanxiong Hort. and Angelica sinensis (Oliv.) Diels, has demonstrated efficacy in combating oxidative stress and inflammation. In this study, we utilized UVB-irradiated HaCaT cells as an in vitro model and C57BL/6J mice as an in vivo model of solar dermatitis. Our findings revealed the pivotal roles of autophagy and ferroptosis in inducing skin inflammation, particularly emphasizing the activation of ferroptosis through macroautophagy. Surprisingly, this mechanism operated independently of ferritinophagy, a classical autophagy-driven ferroptosis pathway. Instead, our results highlighted Transferrin Receptor 1 (TfR1), tightly controlled by autophagy, as a crucial mediator of ferroptosis execution and amplifier of subsequent lethal signals. Furthermore, extracellular High Mobility Group Box 1 protein (HMGB1), released following UVB-induced ferroptotic cells from activated autophagic flux, initiated a feedback loop with TfR1, propagating ferroptosis to neighboring cells and exacerbating damage. Remarkably, Sen I administration showed a significant protective effect against UVB damage in both in vitro and in vivo models by interrupting this cascade. Consequently, we have illuminated a novel therapeutic pathway post-UVB exposure and identified Sen I as a potent natural molecule that safeguarded against UVB-induced solar dermatitis by suppressing the autophagy-ferroptosis-HMGB1-TfR1 axis, highlighting a new frontier in photoprotection.