Innate immunomodulation of retinal neovascularization - Project Summary Proliferative retinopathies, characterized by the growth of pathological blood vessels (neovessels), are the leading causes of blindness in all age groups. Retinopathy of prematurity (ROP) is of particular significance in the pediatric population. In this condition, widespread ischemia drives retinal neovascularization that can lead to retinal detachment and permanent vision loss. The underlying signaling mechanisms that orchestrate the growth of neovessels remain incompletely understood. Defining the molecular basis that governs neovascularization (NV) is necessary for the development of new or improved therapeutic strategies. Our goal is to delineate the regulatory mechanisms that facilitate neovascular growth and regression. Normal retinal vascular development is tightly regulated by multicellular-derived cues. At early phases of physiological vascular growth, sprouting endothelial tip cells closely interact and migrate over the astrocytes template to form the primary retinal vascular layer. During this process, microglia facilitate the spatial establishment of the astrocyte and vascular networks. On the other hand, the cellular guidance mechanism(s) involved in pathological vascular growth are not clearly known. Our preliminary data shows that the ischemia- induced pathological vascular growth in the retina is guided by peripheral immune cells, and not by astrocytes or microglia. Further preliminary studies demonstrate that localized chemokine signaling aids the recruitment of peripheral immune cells that subsequently promotes neovascular growth. Although the microglial-neovessel interactions are absent at early phases of NV, microglial recruitment and wrapping of neovascular tufts are increased at peak phases of NV. Microglia are known to phagocytose and eliminate dying or immature cells through complement activation. Our preliminary data shows that the loss of complement receptors reduced neovascular regression. Based on these findings, we hypothesize that neovascular progression is related to distinct endothelial/myeloid cell-derived chemokine signaling, while neovascular regression is related to microglial activation of the complement pathway. We will substantiate or refute our hypothesis in the following two specific aims. Aim 1: To determine the role of chemokine signaling in facilitating non-resident immune cell recruitment and neovascular growth. Aim 2: To define the role of microglial complement receptors in regulating neovascular regression. We will utilize innovative multiplex in-situ hybridization, cell type-specific mRNA sequencing, multimodal single cell sequencing, unique reporter mice, and Cre-lox animals for cell-specific deletion. We anticipate that the successful completion of the proposed studies will significantly advance our understanding of spatiotemporal innate immune regulation of neovascularization and help identify novel or enhanced treatment strategies for related vaso-proliferative retinopathies.
