The Reindeer's Secret: Salazinic Acid from Lichens as a Candidate Modulator of Autophagy.

Autophagy is a conserved lysosome-dependent process essential for cellular homeostasis, and pharmacological activation of autophagy has emerged as a promising therapeutic strategy for age-related, neurodegenerative, metabolic, and malignant diseases. Despite the growing interest in natural autophagy modulators, lichens remain largely unexplored as a source of autophagy-inducing compounds. Here, we tested ethanolic extracts from four commercially available lichens using LC3-II accumulation as a primary readout. Usnea sp. was identified as the most active species. Activity-guided fractionation followed by HRMS and NMR analyses identified salazinic acid as the active metabolite. Salazinic acid increased LC3-II accumulation, enhanced autophagic flux in the presence of bafilomycin A1, and promoted autophagosome formation as confirmed by transmission electron microscopy. The compound exhibited low cytotoxicity in human cell lines at concentrations exceeding those required for autophagy induction. Mechanistically, salazinic acid activated the phosphorylation of AMPK, ULK1, and AKT; however, it retained its ability to stimulate autophagic flux in AMPK- and ULK1-deficient cells, indicating that its activity is not strictly dependent on the canonical AMPK-ULK1 signaling pathway. Collectively, our findings identify salazinic acid as a previously unrecognized inducer of productive autophagic flux and demonstrate that lichen secondary metabolites represent a promising and largely untapped source of novel autophagy-modulating compounds.