The role of plasmacytoid dendritic cells in ocular angiogenesis

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Project Summary Angiogenesis is precisely regulated by a balance of growth factors, chemokines, proteases, and inflammatory cells. Macrophages, monocytes, and conventional dendritic cells (cDCs) are involved in all stages of angiogenesis from degradation of local extracellular matrix to proliferation of endothelial cells and capillary formation. Despite the well-studied functions of these cells in angiogenesis, the role and source of endogenous anti-angiogenic molecules which preserve corneal angiogenic privilege or prevent retinal neovascularization is elusive. Moreover, the impact of recently identified plasmacytoid dendritic cells (pDCs), a vital subset of immune cells that reside in the cornea and retina, remains to be determined. These cells orchestrate and link innate and adaptive immune responses and are implicated in the induction of tolerance to transplanted tissues or tumors. Our preliminary experiments showed that depletion of pDCs is accompanied by abrupt and severe breakdown of angiogenic privilege of cornea and corneal pDCs co-stain with Endostatin, a well-known anti- angiogenic molecule. We hypothesize that pDCs exhibit anti-angiogenic functions by actively secreting anti- angiogenic molecules and are necessary for preserving corneal angiogenic privilege as well as limiting retinal neovascularization in pathologic conditions. Our aims include identification of pro- and anti-angiogenic molecules expressed by pDCs and their functional relevance on corneal angiogenic privilege, characterizing the impact of pDCs on the avascular state of the cornea in steady-state and during inflammation, describing the molecular and cellular participants involved in pDC-mediated inhibition of corneal angiogenesis during neovascularization, and assessing how activation of pDCs through activation of toll like receptors (TLR)-7 and TLR-9 via their synthetic agonists as well as Herpes Simplex Virus, their natural activator, affects angiogenesis. Further, we aim to assess the impact of pDCs in preventing oxygen- as well as laser-induced choroidal neovascularization and study the effectiveness of adoptive transfer of pDCs for treatment of retinal neovascularization in these conditions. The application proposes a paradigm shift in our understanding of the regulation of angiogenesis and corneal vascular privilege. Our fresh perspective on how pDCs contribute to avascular state of cornea and restrict retinal neovascularization has applications beyond ocular tissues. It would potentially introduce new therapeutic avenues in various pathologic conditions in which attenuation of angiogenesis would be potentially beneficial such as cancers and inflammatory diseases, as well as in conditions which induction of angiogenesis is advantageous, particularly in ischemic conditions.