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Yiqin Zuo, Zhen-Yang Zhao, Pei Xu, Bo Yu, Yan Chen, Jiyang Cai; Macrophage Activation by RPE-Derived Exosomes. Invest. Ophthalmol. Vis. Sci. 2013;54(15):342.
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Altered innate immune responses, such as macrophage recruitment and complement deposition, play key roles in the pathogenesis of age-related macular degeneration (AMD). Exosomes are small membrane vesicles released by various cell types and participate in cell-cell communication. We investigated whether exosomes secreted by the retinal pigment epithelium (RPE) affect macrophage activation and polarization.
Exosomes were isolated from conditioned media of cultured APRE-19 cells by ultracentrifugation. Both bone marrow-derived mouse macrophages (BMDM) and THP1 human monocytic leukemia cells line were treated with different amounts of exosomes for 24 hours. Markers of activated macrophages were assessed by real time RT-PCR and flow cytometry. CCR7, IL-6, and monocyte chemotactic protein-1 (MCP-1) were used as M1 marker. IL-10 and mannose receptor C type 1 (MRC-1) were used as M2 marker. Immunohistochemistry was performed to stain for an exosome marker protein, CD9, on sections of human AMD eyes.
Cultured THP1 monocytes had undetectable level of M1 and M2 macrophage markers. Exosomes isolated from RPE-conditioned media induced a pro-inflammatory response with remarkably up-regulated mRNA levels of M1 markers, CCR7, IL-6 and MCP-1. Similar responses were achieved in THP-1 cells differentiated with phorbol-12-myristate-13-acetate (PMA) and mouse BMDM. Expression of the M2 marker, MRC-1, was decreased after exposure to exosomes. Increased exosome marker proteins were found in the regions near Bruch’s membrane and drusen of human AMD eyes.
Our study suggests that RPE-derived exosomes activate monocytes/macrophages and polarize them towards the pro-inflammatory subsets. Implications of those mechanisms in the etiology of AMD warrants further investigation.
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