Effects of aminolevulinic acid-based photodynamic therapy on the Toll-like receptor 2 signaling pathway in the murine macrophage line RAW264.7

Abstract

Objective To evaluate the effect of aminolevulinic acid-based photodynamic therapy (ALA-PDT) on the expression of Toll-like receptor 2 (TLR2) and downstream signaling pathway molecules, and secretion of cytokines in murine RAW264.7 cells. Methods The RAW264.7 murine macrophages were induced by inactivated Propionibacterium acnes suspension for the establishment of a cell model of inflammation. The cultured RAW264.7 cells were divided into 5 groups: blank control group receiving normal culture followed by the treatment with phosphate buffer saline (PBS) , model group treated with inactivated Propionibacterium acnes suspension followed by the treatment with PBS, and three ALA groups treated with inactivated Propionibacterium acnes suspension followed by the treatment with 0.03, 0.06 and 0.12 mmol/L ALA, respectively, and infrared radiation at a dose of 16 J/cm2. Enzyme-linked immunosorbent assay (ELISA) was performed to detect levels of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the culture supernatant of RAW264.7 cells, and Western blot analysis to determine the protein expression of TLR2 and myeloid differentiation factor 88 (MyD88) , as well as p38, c-Jun N-terminal kinase (JNK) , extracellular signal-regulated kinase (ERK) , inhibitor of κB kinase α (IκBα) and their phosphorylated forms (p-p38, p-JNK, p-ERK and p-IκBα) . Results Compared with the blank control group, the model group showed significantly higher levels of TNF-α ([0.34 ± 0.02]ng/L, P 0.05) , but a significantly lower level of IL-6 ([0.07 ± 0.01]ng/L, F= 114.813, P < 0.01) . The protein expression of TLR2, MyD88, p-p38, p-IκBα, p-JNK and p-ERK was all significantly higher in the model group (0.90 ± 0.14, 1.11 ± 0.13, 0.84 ± 0.04, 1.45 ± 0.20, 2.56 ± 0.06, 3.70 ± 0.40) than in the blank control group (all P < 0.01) , and gradually decreased along with the increase of ALA concentration in a dose-dependent manner. Conclusion Photodynamic therapy can suppress the expression of TLR2 in RAW264.7 murine macrophages, and decrease the secretion of cytokines likely by the TLR2 signaling pathway. Key words: Propionibacterium acnes; Acne vulgaris; Aminolevulinic acid; Photochemotherapy; Toll-like receptor 2; Signal transduction