5‐aminolevulinic acid photodynamic therapy protects against UVB‐induced skin photoaging: A DNA‐repairing mechanism involving the BER signalling pathway

Abstract Low‐dose 5‐aminolevulinic acid photodynamic therapy (ALA‐PDT) has been used to cope with skin photoaging, and is thought to involve DNA damage repair responses. However, it is still unknown how low‐dose ALA‐PDT regulates DNA damage repair to curb skin photoaging. We established a photoaging model using human dermal fibroblasts (HDFs) and rat skin. RNA‐sequencing (RNA‐seq) analysis was conducted to identify differentially expressed genes (DEGs) in HDFs before and after low‐dose ALA‐PDT treatment, followed by bioinformatics analysis. Senescence‐associated β‐galactosidase (SA‐β‐gal) staining was employed to assess skin aging‐related manifestations and Western blotting to evaluate the expression of associated proteins. A comet assay was used to detect cellular DNA damage, while immunofluorescence to examine the expression of 8‐hydroxy‐2′‐deoxyguanosine (8‐oxo‐dG) in cells and skin tissues. In both in vivo and in vitro models, low‐dose ALA‐PDT alleviated the manifestations of ultraviolet B (UVB)‐induced skin photoaging. Low‐dose ALA‐PDT significantly reduced DNA damage in photoaged HDFs. Furthermore, low‐dose ALA‐PDT accelerated the clearance of the photoproduct 8‐oxo‐dG in photoaged HDFs and superficial dermis of photoaged rat skin. RNA‐seq analysis suggested that low‐dose ALA‐PDT upregulated the expression of key genes in the base excision repair (BER) pathway. Further functional validation showed that inhibition on BER expression by using UPF1069 significantly suppressed SA‐β‐gal activity, G2/M phase ratio, expression of aging‐associated proteins P16, P21, P53, and MUTYH proteins, as well as clearance of the photoproduct 8‐oxo‐dG in photoaged HDFs. Low‐dose ALA‐PDT exerts anti‐photoaging effects by activating the BER signalling pathway.