Past history of obesity triggers persistent epigenetic changes in innate immunity and exacerbates neuroinflammation.

Age-related macular degeneration is a prevalent neuroinflammatory condition and a major cause of blindness driven by genetic and environmental factors such as obesity. In diseases of aging, modifiable factors can be compounded over the life span. We report that diet-induced obesity earlier in life triggers persistent reprogramming of the innate immune system, lasting long after normalization of metabolic abnormalities. Stearic acid, acting through Toll-like receptor 4 (TLR4), is sufficient to remodel chromatin landscapes and selectively enhance accessibility at binding sites for activator protein-1 (AP-1). Myeloid cells show less oxidative phosphorylation and shift to glycolysis, ultimately leading to proinflammatory cytokine transcription, aggravation of pathological retinal angiogenesis, and neuronal degeneration associated with loss of visual function. Thus, a past history of obesity reprograms mononuclear phagocytes and predisposes to neuroinflammation.

Myeloid-resident neuropilin-1 promotes choroidal neovascularization while mitigating inflammation.

Age-related macular degeneration (AMD) in its various forms is a leading cause of blindness in industrialized countries. Here, we provide evidence that ligands for neuropilin-1 (NRP1), such as Semaphorin 3A and VEGF-A, are elevated in the vitreous of patients with AMD at times of active choroidal neovascularization (CNV). We further demonstrate that NRP1-expressing myeloid cells promote and maintain CNV. Expression of NRP1 on cells of myeloid lineage is critical for mitigating production of inflammatory factors such as IL6 and IL1ß. Therapeutically trapping ligands of NRP1 with an NRP1-derived trap reduces CNV. Collectively, our findings identify a role for NRP1-expressing myeloid cells in promoting pathological angiogenesis during CNV and introduce a therapeutic approach to counter neovascular AMD.

Neuropilin-1-Expressing Microglia Are Associated With Nascent Retinal Vasculature Yet Dispensable for Developmental Angiogenesis.

PURPOSE: Neuropilin-1 (NRP-1) is a transmembrane receptor that is critical for vascular development within the central nervous system (CNS). It binds and influences signaling of several key angiogenic factors, such as VEGF-165, semaphorin 3A, platelet derived growth factor, and more. Neuropilin-1 is expressed by neurons and endothelial cells as well as a subpopulation of proangiogenic macrophages/microglia that are thought to interact with endothelial tip cells to promote vascular anastomosis during brain vascularization. We previously demonstrated a significant role for NRP-1 in macrophage chemotaxis and showed that NRP-1-expressing microglia are major contributors to pathologic retinal angiogenesis. Given this influence on CNS angiogenesis, we now investigated the involvement of microglia-resident NRP-1 in developmental retinal vascularization. METHODS: We followed NRP-1 expressing microglia during retinal development. We used LysM-cre myeloid lineage-driver cre mice to reduce expression of NRP-1 in retinal myeloid-derived cells and performed a comprehensive morphometric analysis of retinal vasculature during development. RESULTS: We provide evidence that NRP-1+ microglia are present throughout the retina during vascular development with a preference for the non-vascularized retina. Using LysM-Cre/Nrp1(fl/fl) mice, we reduced NRP-1 expression by ~65% in retinal microglia and demonstrate that deficiency in NRP-1 in these microglia does not impair retinal angiogenesis. CONCLUSIONS: Our data draw a dichotomous role for NRP-1 in cells of myeloid lineage where it is dispensable for adequate retinal developmental vascularization yet obligate for pathologic retinal angiogenesis.