Protective autophagy enhances antistress ability through AMPK/ULK1 signaling pathway in human immortalized keratinocytes

Abstract

AbstractKeratinocytes, located in the outermost layer of human skin, are pivotal cells to resist environmental damage. Cellular autophagy plays a critical role in eliminating damaged organelles and maintaining skin cell homeostasis. Low‐dose 5‐Aminolevulinic acid photodynamic therapy (ALA‐PDT) has been demonstrated to enhance skin's antistress ability; however, the regulatory mechanisms of autophagy in keratinocytes remain unclear. In this study, we treated immortalized human keratinocytes (HaCaT cells) with low‐dose ALA‐PDT (0.5 mmol/L, 3 J/cm2). Through RNA‐sequencing analysis, we identified that low‐dose ALA‐PDT modulated autophagy‐related pathways in keratinocytes and pinpointed Unc‐51‐like kinase 1 (ULK1) as a key gene involved. Western blot results revealed that low‐dose ALA‐PDT treatment upregulated the expression of autophagy‐related proteins Beclin‐1 and LC3‐II/LC3‐I ratio. Notably, low‐dose ALA‐PDT regulated autophagy by inducing an appropriate level of reactive oxygen species (ROS), transiently reducing mitochondrial membrane potential, and decreasing adenosine triphosphate production; all these processes functioned on the AMP‐activated protein kinase (AMPK)/ULK1 pathway to activate autophagy. Finally, we simulated external environmental damage using ultraviolet B (UVB) at a dose of 60 mJ/cm2 and observed that low‐dose ALA‐PDT mitigated UVB‐induced cell apoptosis; however, this protective effect was reversed when using the autophagy inhibitor 3‐methyladenine. Overall, these findings highlight how low‐dose ALA‐PDT enhances antistress ability in HaCaT cells through controlling ROS generation and activating the AMPK/ULK1 pathway to arouse cellular autophagy.