Abstract
Purpose :
We have reported a protective role of pro-inflammatory cytokine, interleukin 33, in choroidal neovascularization (CNV) formation, by attenuating wound-healing responses. Mast cells are associated with fibrosis and are also known target cells of IL-33, but their role in CNV is not known. Based on our finding that RPE-derived IL-33 could activate bone-marrow-derived mast cells (BMMC), we hypothesized that IL-33 attenuated CNV by activating mast cells.
Methods :
Upon treatment, RPE cells (ARPE-19 and B6-RPE07) and bone-marrow-derived mast cells (BMMC) were assayed by RT-PCR and Western Blot and ELISA. Choroidal sprouting assay and laser-induced choroidal neovascularization (CNV) were used as models of ocular angiogenesis. RPE-choroid explants were treated with various doses of IL-33 and mast cell inhibitor ACK2 (anti-c-kit antibody), and assayed by ELISA. CNV was induced in WT and ST2-/- mice (C57BL/6) by laser photocoagulation (4 lesions per fundus). IL-33 alone or in combination with ACK2 was administered by intravitreal injection. The development of neovascular lesions was assessed by optical coherence tomography and immunofluorescence 7 days post injection. Mast cells (MC) infiltration was evaluated by immunohistochemistry.
Results :
Mast cells expressed high levels of ST2, and responded directly to IL-33 to produce many inflammatory cytokines and chemokines in vitro, when cultured with IL-33 rich RPE supernatant. Ex vivo, IL-33 treatment reduced vascular sprouting in RPE-choroidal explants, but this effect was perturbed when administered with mast cells inhibitor ACK2.
In vivo, choroidal MCs that had infiltrated the sites of laser injury and surrounding retina were observed 7 days following laser. Intravitreal IL-33 attenuated CNV formation, and this was accompanied by increased MC infiltration in the neovascular lesions. Conversely, in ST2-/- mice, similar treatment with IL-33 did not affect CNV size or extent of MC infiltration. Intravitreal administration of ACK2 with IL-33 reversed the anti-angiogenic properties of IL-33.
Conclusions :
IL-33/ST2 signaling regulates ocular angiogenesis, influencing tissue remodeling via an IL-33-driven, mast-cell-dependent pathway. Collectively, these data distinguishes pathways for subverting AMD pathology.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.