ALA-PDT induces apoptosis in HPV-transformed cells through mtDNA release-mediated activation of the cGAS-STING pathway

Background: Aminolevulinic acid photodynamic therapy (ALA-PDT) is an effective and non-invasive treatment for HPV-related diseases, but its underlying mechanisms still need further investigation. cGAS-STING signaling pathway takes part in Antiviral innate immune defense, but its changes and regulatory mechanisms in ALA-PDT treatment remain unknown.

Methods: Under ALA-PDT treatment in HPV-transformed cells, the relative expression of mitochondrial DNA (mtDNA) was measured by qPCR. Cellular morphology and the spatial relationship between mitochondria and DNA were observed using confocal microscopy. Protein expression related to the cGAS-STING pathway was assessed by western blot, and Apoptosis was detected via flow cytometry. Corresponding statistical analyses were performed.

Results: ALA-PDT treatment induced mitochondrial DNA (mtDNA) release into the HeLa cells cytosol and activated the cGAS-STING pathway, evidenced by upregulated cGAS and STING expression, and promoted cell Apoptosis (P < 0.05). In addition, pharmacological inhibition of STING attenuated this effect. Notably, in mtDNA-depleted (ρ⁰) cells, the cGAS-STING response to ALA-PDT was markedly diminished, suggesting that the immunostimulatory effect of ALA-PDT may be mediated through mtDNA release.

Conclusion: We identified that ALA-PDT could induce mtDNA release from mitochondria into cytoplasm and then activate cGAS-STING signaling pathway in HPV infected HeLa cells. These results might help expand our knowledge of ALA-PDT intervention mechanisms and is possibly instrumental to further exploration of novel photodynamic, photo-immuno and photo-immune-gene therapies.