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Macrophage-derived foam cells are a major component of atherosclerotic plaques and have an important role in the progression of atherosclerotic plaques, thus posing a great threat to human health. Photodynamic therapy (PDT) has emerged as a therapeutic strategy for atherosclerosis. Here, we investigated the effect of PDT mediated by upconversion fluorescent nanoparticles encapsulating chlorin e6 (UCNPs-Ce6) on the cholesterol efflux of THP-1 macrophage-derived foam cells and explored the possible mechanism of this effect. First, we found that PDT notably enhanced the cholesterol efflux and the induction of autophagy in both THP-1 and peritoneal macrophage-derived foam cells. The autophagy inhibitor 3-methyladenine and an ATG5 siRNA significantly attenuated PDT-induced autophagy, which subsequently suppressed the ABCA1-mediated cholesterol efflux. Furthermore, the reactive oxygen species (ROS) produced by PDT were responsible for the induction of autophagy, which could be blocked by the ROS inhibitor N-acetyl cysteine (NAC). NAC also reversed the PDT-induced suppression of p-mTOR and p-Akt. Therefore, our findings demonstrate that PDT promotes cholesterol efflux by inducing autophagy, and the autophagy was mediated in part through the ROS/PI3K/Akt/mTOR signaling pathway in THP-1 and peritoneal macrophage-derived foam cells.

Impaired autophagy in macrophages accompanies the progression of atherosclerosis and contributes to lipid loading in plaques and ineffective lipid degradation. Therefore, evoking autophagy and its associated cholesterol efflux may provide a therapeutic treatment for atherosclerosis. In the present study, berberine-mediated sonodynamic therapy (BBR-SDT) was used to induce autophagy and cholesterol efflux in THP-1 macrophages and derived foam cells. Following BBR-SDT, autophagy was increased in the macrophages, autophagy resistance in the foam cells was prevented, and cholesterol efflux was induced. The first two effects were blocked by the reactive oxygen species scavenger, N-acetyl cysteine. BBR-SDT also reduced the phosphorylation of Akt and mTOR, two key molecules in the PI3K/AKT/mTOR signaling pathway, which is responsible for inducing autophagy. Correspondingly, treatment with the autophagy inhibitor, 3-methyladenine, or the PI3K inhibitor, LY294002, abolished the autophagy-induced effects of BBR-SDT. Furthermore, induction of cholesterol efflux by BBR-SDT was reversed by an inhibition of autophagy by 3-methyladenine or by a small interfering RNA targeting Atg5. Taken together, these results demonstrate that BBR-SDT effectively promotes cholesterol efflux by increasing reactive oxygen species generation, and this subsequently induces autophagy via the PI3K/AKT/mTOR signaling pathway in both 'normal' macrophages and lipid-loaded macrophages (foam cells). Thus, BBR-SDT may be a promising atheroprotective therapy to inhibit the progression of atherosclerosis and should be further studied.

Background/Aims: Atherosclerosis is a chronic inflammatory cardiovascular disease. Macrophages are major components of atherosclerotic plaques and play a key role in the development of atherosclerosis by secreting a variety of pro-inflammatory factors. Our previous studies have confirmed that upconversion nanoparticles encapsulating chlorin e6 (UCNPs-Ce6) mediated photodynamic therapy (PDT) can promote cholesterol efflux and induce apoptosis in THP-1 macrophages. In this study, we investigated whether reactive oxygen species (ROS) generated by UCNPs-Ce6-mediated PDT can induce autophagy to inhibit the expression of pro-inflammatory factor in M1 peritoneal macrophages. Methods: Peritoneal macrophages were collected from C57/BL6 mice injected with 3% thioglycollate broth medium and induced by lipopolysaccharides and interferon-γ. Intracellular ROS production was assessed by 2’-7’-dichloroforescein diacetate and flow cytometry. Autophagy was assayed by western blot, transmission electron microscopy and immunofluorescence. Pro-inflammatory cytokines were detected by enzyme-linked immunosorbent assay and western blot. Results: Model M1 peritoneal macrophages were established after 24 h induction. Protein expression levels of LC3 II and Beclin1, and degradation of p62 increased and peaked at 2 h in the PDT group. Meanwhile, levels of inflammatory cytokines iNOS, IL-12, and TNF-α markedly decreased after PDT. The increase in autophagy levels and decrease in pro-inflammatory cytokines were significantly inhibited by 3-methyladenine. Furthermore, ROS generated by UCNPs-Ce6 mediated PDT activated autophagy. The expression of autophagy related-protein and inflammatory cytokines iNOS, IL-12, and TNF-α were inhibited by the ROS inhibitor N-acetyl cysteine. Conclusions: ROS generated by UCNPs-Ce6-mediated PDT activated autophagy and inhibited the expression of pro-inflammatory factors of M1 peritoneal macrophage via the PI3K/AKT/mTOR signaling pathway. [ABSTRACT FROM AUTHOR]