In the central nervous system, endothelial cells (ECs) and pericytes (PCs) of blood vessel walls cooperatively form a physical and chemical barrier to maintain neural homeostasis. However, in diabetic retinopathy (DR), the loss of PCs from vessel walls is assumed to cause breakdown of the blood-retina barrier (BRB) and subsequent vision-threatening vascular dysfunctions. Nonetheless, the lack of adequate DR animal models has precluded disease understanding and drug discovery. Here, by using an anti-PDGFRβ antibody, we show that transient inhibition of the PC recruitment to developing retinal vessels sustained EC-PC dissociations and BRB breakdown in adult mouse retinas, reproducing characteristic features of DR such as hyperpermeability, hypoperfusion, and neoangiogenesis. Notably, PC depletion directly induced inflammatory responses in ECs and perivascular infiltration of macrophages, whereby macrophage-derived VEGF and placental growth factor (PlGF) activated VEGFR1 in macrophages and VEGFR2 in ECs. Moreover, angiopoietin-2 (Angpt2) upregulation and Tie1 downregulation activated FOXO1 in PC-free ECs locally at the leaky aneurysms. This cycle of vessel damage was shut down by simultaneously blocking VEGF, PlGF, and Angpt2, thus restoring the BRB integrity. Together, our model provides new opportunities for identifying the sequential events triggered by PC deficiency, not only in DR, but also in various neurological disorders.

Multifaceted microglial functions in the developing brain, such as promoting the differentiation of neural progenitors and contributing to the positioning and survival of neurons, have been progressively revealed. Although previous studies have noted the relationship between vascular endothelial cells and microglia in the developing brain, little attention has been given to the importance of pericytes, the mural cells surrounding endothelial cells. In this study, we attempted to dissect the role of pericytes in microglial distribution and function in developing mouse brains. Our immunohistochemical analysis showed that approximately half of the microglia attached to capillaries in the cerebral walls. Notably, a magnified observation of the position of microglia, vascular endothelial cells and pericytes demonstrated that microglia were preferentially associated with pericytes that covered 79.8% of the total capillary surface area. Through in vivo pericyte depletion induced by the intraventricular administration of a neutralizing antibody against platelet-derived growth factor receptor (PDGFR)b (clone APB5), we found that microglial density was markedly decreased compared with that in control antibody-treated brains because of their low proliferative capacity. Moreover, in vitro coculture of isolated CD11b 1 microglia and NG2 1 PDGFRacells, which are mostly composed of pericytes, from parenchymal cells indicated that pericytes promote microglial proliferation via the production of soluble factors. Furthermore, pericyte depletion by APB5 treatment resulted in a failure of microglia to promote the differentiation of neural stem cells into intermediate progenitors. Taken together, our findings suggest that pericytes facilitate microglial homeostasis in the developing brains, thereby indirectly supporting microglial effects on neural progenitors.

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Although prostaglandin D 2 (PGD 2 ) represents anti-angiogenic role in tumor model, its role in physiological and pathological angiogenesis still remain unknown. We here evaluated the role of PGD 2 on retinal angiogenesis using genetically modified mice. In postnatal 8th day retina of WT, lipocalin-type PGD synthase (L-PGDS) was expressed in endothelial cells. Gene deficiency of L-PGDS impaired the physiological angiogenesis of retina, accompanied with increased mRNA expression of pro-angiogenic factor VEGF. In vitro study showed that L-PGDS inhibition elevated the hypoxia-induced VEGF expression, which was inhibited by treatment of a PGD 2 metabolite 15d-PGJ 2 . We next generated a pericyte deficiency-induced retinal angiogenesis model by injection of anti-PDGFRβ antibody. In P8 retina of WT, the injection of antibody induces inflammation in retina, and infiltrating macrophages expressed hematopoietic PGD synthase (H-PGDS). Gene deficiency of H-PGDS or PGD receptor DP accelerated the angiogenesis. This phenomenon was accompanied with increased mRNA expression of one of the chemokines, Stromal derived factor 1α. In isolated macrophage, hypoxia increased the expression of cytokines, wich was inhibited by adding receptor inhibitor. Taken together, L-PGDS promotes physiological angiogenesis and H-PGDS attenuate pathological angiogenesis in mouse retina.