Acrolein Promotes Retinal Inflammation Through Macrophage Chemotaxis by Inducing CCL2 Production From Müller Cells

This study aimed to investigate the inflammatory mechanisms induced by the toxic aldehyde acrolein in proliferative diabetic retinopathy (PDR). N^ε-(3-formyl-3, 4-dehydropiperidino) lysine adduct (FDP-lys), an acrolein-binding protein, and chemokine (C-C motif) ligand-2 (CCL2) levels in human vitreous fluid obtained from patients with PDR were measured using Luminex assay and ELISA. A rat Müller glial cell line (TR-MUL5) was exposed to acrolein (10-50 μM), and CCL2 expression was evaluated using real-time PCR and ELISA. Macrophage (RAW264.7) migration under the presence of acrolein-stimulated TR-MUL5 was assessed using a Transwell assay. High mobility group box-1 (HMGB1) translocation in TR-MUL5 was examined by immunofluorescence and cell fractionation. These analyses demonstrated that FDP-lys and CCL2 concentrations in the vitreous of patients with PDR were markedly higher than those in controls (n = 12, p < 0.01), and a significant correlation was observed between the two (R = 0.60, p < 0.05). Acrolein stimulation upregulated Ccl2 expression in TR-MUL5 cells (3.5 ± 0.4-fold at 25 μM; 10 ± 1.4-fold at 50 μM, n = 3, p < 0.01) and increased CCL2 protein levels dose-dependently (n = 3, p < 0.01). Macrophage migration increased 2.2 ± 0.3-fold with acrolein-stimulated TR-MUL5 but was attenuated by the CCR2 inhibitor RS504393 (n = 3, p < 0.01). Acrolein-induced HMGB1 translocation was confirmed in TR-MUL5, and glycyrrhizin, an HMGB1 inhibitor, reduced CCL2 levels. In conclusion, acrolein promotes PDR progression by enhancing macrophage migration through CCL2 secretion and HMGB1 translocation in Müller cells.