Selvam, Senthil; (2018) The role of inflammation in retinal ischaemia. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Purpose: The immune cascade is known to contribute to the pathology seen in oxygen induced retinopathy (OIR), however its exact role is poorly defined. We hypothesised that immune cell activation worsens hypoxia and exacerbates the neovascular sequelae seen in ischaemic retinopathy. Methods: We assess the effect of intraperitoneal lipopolysaccharide (IP LPS) injection in OIR mice. Neovascularisation was assessed by measuring the avascular area and neovascular tuft area at P17. Hypoxia was assessed using vessel tortuosity and EF5 hypoxia staining at P14. The activated retinal inflammatory cell population was characterised using immunohistochemistry and flow cytometry. Transgenic mice were bred to delete different subpopulations of inflammatory cells to define their role in hypoxia modulation. RNA sequencing performed on retinal tissue analysed the effect of systemic LPS on retinal cytokines and angiogenesis markers. Results: IP LPS injection at P12 in OIR mice significantly reduced neovascularisation at P17 and hypoxia at P14. Immunohistochemistry revealed an influx of round, CD11b+, lectin stained cells into the retina of LPS treated mice, which on flow cytometry were identified as myeloid cells, being predominantly Cd11b+Ly6Ghi neutrophils. Experimental depletion of the myeloid lineage was achieved using ROSA26eGFP-DTALysMcre, CCL2 and CCR2 knockout mouse lines and anti-CCR2 antibody MC21. However, when these mice were LPS treated, the effects on hypoxia readouts caused by LPS were still seen. Transcriptional profiling of the retina (using RNAseq) revealed a large upregulation in IL1β in the central, hypoxic retina of LPS treated mice. Injection of IL1β at P12 also mimicked the effects of LPS, suggesting that IL1β is a key mediator of the hypoxia reducing effect LPS has in the OIR model. Conclusions: These findings are counterintuitive to the current literature and provide new insight into the role the immune system has on regulating oxygen demand in the retina. This novel approach to reducing hypoxia has the potential to lead to novel therapies targeting hypoxia and preventing neovascularisation in ischaemic eye disease.

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