Visualization of vascular mural cells in developing brain using genetically labeled transgenic reporter mice

The establishment of a fully functional blood vascular system requires elaborate angiogenic and vascular maturation events in order to fulfill organ-specific anatomical and physiological needs. Although vascular mural cells, i.e. pericytes and vascular smooth muscle cells, are known to play fundamental roles during these processes, their characteristics during vascular development remain incompletely understood. In this report, we utilized transgenic reporter mice in which mural cells are genetically labeled to examine developing vascular mural cells in the central nervous system (CNS). We found platelet-derived growth factor receptor beta gene (Pdgfrb)-driven EGFP reporter expression as a suitable marker for vascular mural cells at the earliest stages of mouse brain vascularization. Furthermore, the combination of Pdgfrb and NG2 gene (Cspg4) driven reporter expression increased the specificity of brain vascular mural cell labeling at later stages. The expression of other known pericyte markers revealed time-,region-and marker-specific patterns, suggesting heterogeneity in mural cell maturation. We conclude that transgenic reporter mice provide an important tool to explore the development of CNS pericytes in health and disease

Adgrf5 contributes to patterning of the endothelial deep layer in retina

Neovascularization of the inner retinal space is a major cause of vision loss. In retinal angiomatous proliferation (RAP) syndrome, newly formed vessels originate from the retinal plexus and invade the inner retinal space. However, the molecular pathways preventing subretinal vascularization remain largely unknown. In most murine models of RAP, pathological neo-vascularization occurs concomitantly with the development of the retinal vasculature. Here, we demonstrate that disturbing the sequence of morphogenetic events that shape the three-layered retinal vascular network leads to subretinal vascularization. Sprouts emerging from the perivenous region after the first postnatal week extended toward the retinal space where they merged into the deep layer. The small GTPase Rac1 was required for the formation of these vascular extensions and the vascular inner plexus is formed coaxially to the overarching veins. The adhesion receptor Adgrf5 was highly expressed in the endothelium of the central nervous system, where it regulates blood-brain barrier formation. The vascular superficial plexus of Adgrf5 mutant mouse retinae exhibited an increased vascular density in the perivenous areas with increased projections toward the inner plexus where they subsequently created hyper-dense endothelial cells (EC) clusters. Disturbing the perivenous pool of EC thus significantly altered the inner plexus formation. These abnormalities culminated in transient vascular protrusions in the inner retinal space. Taken together, these results reveal a previously unobserved vascular morphogenetic defect in Adgrf5 knockout mice, implicating a role for ADGRF5 in the initiation of subretinal vascularization. Our findings also illustrate how vein-derived EC shape the inner retinal layer formation and could control the appearance of angiomatous malformations

Analysis of the brain mural cell transcriptome

Pericytes, the mural cells of blood microvessels, regulate microvascular development and function and have been implicated in many brain diseases. However, due to a paucity of defining markers, pericyte identification and functional characterization remain ambiguous and data interpretation problematic. In mice carrying two transgenic reporters, Pdgfrb-eGFP and NG2-DsRed, we found that double-positive cells were vascular mural cells, while the single reporters marked additional, but non-overlapping, neuroglial cells. Double-positive cells were isolated by fluorescence-activated cell sorting (FACS) and analyzed by RNA sequencing. To reveal defining patterns of mural cell transcripts, we compared the RNA sequencing data with data from four previously published studies. The meta-analysis provided a conservative catalogue of 260 brain mural cell-enriched gene transcripts. We validated pericyte-specific expression of two novel markers, vitronectin (Vtn) and interferon-induced transmembrane protein 1 (Ifitm1), using fluorescent in situ hybridization and immunohistochemistry. We further analyzed signaling pathways and interaction networks of the pericyte-enriched genes in silico. This work provides novel insight into the molecular composition of brain mural cells. The reported gene catalogue facilitates identification of brain pericytes by providing numerous new candidate marker genes and is a rich source for new hypotheses for future studies of brain mural cell physiology and pathophysiology

HDL activation of endothelial sphingosine-1-phosphate receptor-1 (S1P1) promotes regeneration and suppresses fibrosis in the liver

Regeneration of hepatic sinusoidal vasculature is essential for non-fibrotic liver regrowth and restoration of its metabolic capacity. However, little is known about how this specialized vascular niche is regenerated. Here we show that activation of endothelial sphingosine-1-phosphate receptor-1 (S1P(1)) by its natural ligand bound to HDL (HDL-S1P) induces liver regeneration and curtails fibrosis. In mice lacking HDL-S1P, liver regeneration after partial hepatectomy was impeded and associated with aberrant vascular remodeling, thrombosis and peri-sinusoidal fibrosis. Notably, this “maladaptive repair” phenotype was recapitulated in mice that lack S1P(1) in the endothelium. Reciprocally, enhanced plasma levels of HDL-S1P or administration of SEW2871, a pharmacological agonist specific for S1P(1) enhanced regeneration of metabolically functional vasculature and alleviated fibrosis in mouse chronic injury and cholestasis models. This study shows that natural and pharmacological ligands modulate endothelial S1P(1) to stimulate liver regeneration and inhibit fibrosis, suggesting that activation of this pathway may be a novel therapeutic strategy for liver fibrosis

Gpr116 Receptor Regulates Distinctive Functions in Pneumocytes and Vascular Endothelium.

Despite its known expression in both the vascular endothelium and the lung epithelium, until recently the physiological role of the adhesion receptor Gpr116/ADGRF5 has remained elusive. We generated a new mouse model of constitutive Gpr116 inactivation, with a large genetic deletion encompassing exon 4 to exon 21 of the Gpr116 gene. This model allowed us to confirm recent results defining Gpr116 as necessary regulator of surfactant homeostasis. The loss of Gpr116 provokes an early accumulation of surfactant in the lungs, followed by a massive infiltration of macrophages, and eventually progresses into an emphysema-like pathology. Further analysis of this knockout model revealed cerebral vascular leakage, beginning at around 1.5 months of age. Additionally, endothelial-specific deletion of Gpr116 resulted in a significant increase of the brain vascular leakage. Mice devoid of Gpr116 developed an anatomically normal and largely functional vascular network, surprisingly exhibited an attenuated pathological retinal vascular response in a model of oxygen-induced retinopathy. These data suggest that Gpr116 modulates endothelial properties, a previously unappreciated function despite the pan-vascular expression of this receptor. Our results support the key pulmonary function of Gpr116 and describe a new role in the central nervous system vasculature

PDGFRβ+ cells play a dual role as hematopoietic precursors and niche cells during mouse ontogeny

Hematopoietic stem cell (HSC) generation in the aorta-gonad-mesonephros region requires HSC specification signals from the surrounding microenvironment. In zebrafish, PDGF-B/PDGFR beta signaling controls hematopoietic stem/progenitor cell (HSPC) generation and is required in the HSC specification niche. Little is known about murine HSPC specification in vivo and whether PDGF-B/PDGFR beta is involved. Here, we show that PDGFR beta is expressed in distinct perivascular stromal cell layers surrounding the mid-gestation dorsal aorta, and its deletion impairs hematopoiesis. We demonstrate that PDGFR beta(+) cells play a dual role in murine hematopoiesis. They act in the aortic niche to support HSPCs, and in addition, PDGFR beta(+) embryonic precursors give rise to a subset of HSPCs that persist into adulthood. These findings provide crucial information for the controlled production of HSPCs in vitro

Massive accumulation phenotype in lungs of aged <i>Gpr116</i>^-/- mice.

<p>A. Bright field image of the inflated lung from <i>Gpr116</i> WT, heterozygous and knockout littermates. B. Weights of whole lungs over total body weight from <i>Gpr116</i> WT, heterozygous and knockout littermates (n≥5 mice per genotype). C. Bright field images of heart from <i>Gpr116</i> WT, heterozygous and knockout littermates. D. Weights of the heart (left) over total body weight from <i>Gpr116</i> WT, heterozygous and knockout littermates (n≥5 mice per genotype). E. Bright field images of the spleen from <i>Gpr116</i> WT, heterozygous and knockout littermates. F. Weights of the spleen (left) over total body weight from <i>Gpr116</i> WT, heterozygous and knockout littermates (n≥5 mice per genotype). G. BALF collected from <i>Gpr116</i> WT, heterozygous and knockout littermates (The picture shown is representative of 3 mice for each genotype). H. Quantification of saturated phosphatydilcholine in BALF by ELISA (n = 3 mice per genotype). I. Quantification of protein content in BALF by BCA assay (n = 3 mice per genotype). J. Surfactant proteins detection in BALF by western blot. Molecular weights are indicated on the right. (n = 2 mice per genotype). K. Bright field images of the lung, after hematoxylin and eosin staining. The black arrowheads indicate alveolar macrophages (the image is representative of 4 mice for each genotype). L. Electron microscopy view of <i>Gpr116</i> wildtype and knockout lungs (n = 2 mice for each genotype). M. Confocal images of lung sections stained with ADRP (white) and nuclear stain (Hoechst, blue). Note that a red autofluorescent signal appears in knockout lungs. (the image shown is representative of 2 mice for each genotype). N. Confocal images of lung sections stained with nuclear marker Hoechst (blue) to show autofluorescent cells accumulated in the alveolar space, either in the green or red channel (the image is representative of 3 mice for each genotype). O. Autofluorescence emission spectrum of macrophages in the old knockout lung, upon 405 nm excitation (the image is representative of 2 mice). P. Detection of autofluorescent cells from <i>Gpr116</i> knockout lung by FACS (n = 2 mice per genotype)</p