Rapamycin protects mouse skin from ultraviolet B-induced photodamage by modulating Hspb2-mediated autophagy and apoptosis

Background Continuous exposure to UVB is the main extrinsic cause of skin photodamage, which is associated with oxidative stress, DNA damage, apoptosis and degradation of collagen. Rapamycin, a mechanistic target inhibitor of rapamycin complex 1 (mTORC1), has been shown to play a crucial role anti-tumor and aging retardation, but its mechanism of action in UVB-induced photodamage still remains unknown. In this study, we investigated the role of rapamycin and Hspb2 (also known as Hsp27) in UVB-induced photodamage in mice. Methods and results We constructed skin acute photodamage models on the ears of WT and Hspb2 KO mice, respectively, and administered rapamycin treatment. Histological results showed that knockout of the hspb2 exacerbated the skin damage, as evidenced by thickening of the epidermis, breakage and disruption of collagen fibers and reduction in their number, which is reversed by rapamycin treatment. In addition, hspb2 knockout promoted UVB-induced apoptosis and reduced autophagy levels, with a significant increase in p53 levels and Bax/Bcl-2 ratio, a reduction in LC3II/I ratio and an increase in p62 levels in the KO mice compared to those in WT mice after the same dose of UVB irradiation. Rapamycin was also found to inhibit collagen degradation induced by hspb2 knockdown through activation of the TGF-β/Smad signaling pathway. Conclusions Rapamycin can alleviate skin photodamage from Hspb2 knockout to some extent. It may be a potential therapeutic drug for skin photodamage. Graphical abstract In this study, we investigated the role of rapamycin and Hspb2 in UVB-induced photodamage in mice. Histological results showed that knockout of the hspb2 exacerbated the skin damage, as evidenced by thickening of the epidermis, breakage and disruption of collagen fibers and reduction in their number, which is reversed by rapamycin treatment. In addition, hspb2 knockout promoted UVB-induced apoptosis and reduced autophagy levels. Rapamycin was also found to inhibit collagen degradation induced by hspb2 knockdown through activation of the TGF-β/Smad signaling pathway. We conclude that rapamycin and Hspb2 exert a synergistic protective effect in skin photodamage.