All-trans retinoic acid enhances the anti-angiogenic effects of hemoporfin-mediated photodynamic therapy via the ATM–SerRS–VEGFA axis in endothelial cells

BACKGROUND: Hemoporfin-mediated photodynamic therapy (HMME-PDT) is an established treatment for port-wine stains (PWS), but hypertrophic or nodular lesions often respond poorly, and the molecular mechanisms that govern treatment sensitivity remain unclear. The Ataxia Telangiectasia Mutated (ATM)-Seryl-tRNA synthetase (SerRS)-Vascular endothelial growth factor A (VEGFA) pathway has recently been implicated in hypoxia- and DNA damage-driven angiogenesis. METHODS: Human umbilical vein endothelial cells (HUVECs) were treated with HMME-PDT and/or all-trans retinoic acid (tRA). Cell viability was assessed by CCK-8 assay, angiogenic activity by tube formation assay, and mRNA expression of ATM, SerRS and VEGFA by quantitative real-time PCR. Protein levels of ATM, phosphorylated ATM (p-ATM), SerRS and VEGFA were evaluated by Western blotting. RESULTS: HMME-PDT significantly inhibited HUVEC viability and tube formation in a concentration- and light dose-dependent manner. HMME-PDT decreased total ATM and, more prominently, p-ATM, while upregulating SerRS and downregulating VEGFA at both mRNA and protein levels. tRA alone dose- and time-dependently reduced HUVEC proliferation, increased SerRS expression and suppressed VEGFA expression. Combined treatment with tRA and HMME-PDT produced the greatest inhibition of tube formation and the strongest induction of SerRS together with the most pronounced reduction in VEGFA, whereas changes in ATM and p-ATM were mainly driven by HMME-PDT. CONCLUSIONS: HMME-PDT exerts anti-angiogenic effects at least in part by modulating the ATM-SerRS-VEGFA axis in endothelial cells. Pharmacologic upregulation of SerRS by tRA further enhances VEGFA suppression and inhibition of angiogenesis, indicating a synergistic interaction between tRA and HMME-PDT. These findings provide a mechanistic rationale for tRA-augmented HMME-PDT as a potential strategy to improve outcomes in refractory PWS.