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Vascular dysfunction is a hallmark of chronic diseases in elderly. The contribution of the vasculature to lung repair and fibrosis is not fully understood. Here, we performed an epigenetic and transcriptional analysis of lung endothelial cells (ECs) from young and aged mice during the resolution or progression of bleomycin-induced lung fibrosis. We identified the transcription factor ETS-related gene (ERG) as putative orchestrator of lung capillary homeostasis and repair, and whose function is dysregulated in aging. ERG dysregulation is associated with reduced chromatin accessibility and maladaptive transcriptional responses to injury. Loss of endothelial ERG enhances paracrine fibroblast activation in vitro, and impairs lung fibrosis resolution in young mice in vivo. scRNA-seq of ERG deficient mouse lungs reveales transcriptional and fibrogenic abnormalities resembling those associated with aging and human lung fibrosis, including reduced number of general capillary (gCap) ECs. Our findings demonstrate that lung endothelial chromatin remodeling deteriorates with aging leading to abnormal transcription, vascular dysrepair, and persistent fibrosis following injury. Vascular dysfunction is associated with ageing and chronic diseases, but its role in lung repair and fibrosis is unclear. Here, the authors show that the endothelial transcription factor ERG is a mediator of vascular repair whose function declines in aged lungs resulting in sustained fibrosis

Progressive lung fibrosis is associated with poorly understood aging-related endothelial cell dysfunction. To gain insight into endothelial cell alterations in lung fibrosis we performed single cell RNA-sequencing of bleomycin-injured lungs from young and aged mice. Analysis reveals activated cell states enriched for hypoxia, glycolysis and YAP/TAZ activity in ACKR1+ venous and TrkB+ capillary endothelial cells. Endothelial cell activation is prevalent in lungs of aged mice and can also be detected in human fibrotic lungs. Longitudinal single cell RNA-sequencing combined with lineage tracing demonstrate that endothelial activation resolves in young mouse lungs but persists in aged ones, indicating a failure of the aged vasculature to return to quiescence. Genes associated with activated lung endothelial cells states in vivo can be induced in vitro by activating YAP/TAZ. YAP/TAZ also cooperate with BDNF, a TrkB ligand that is reduced in fibrotic lungs, to promote capillary morphogenesis. These findings offer insights into aging-related lung endothelial cell dysfunction that may contribute to defective lung injury repair and persistent fibrosis. The regenerative capacity of the lung in response to injury deteriorates with aging. Here, Raslan et al. discover that aging-associated progressive lung fibrosis is accompanied by persistent activation of blood vessels. The authors identified the vascular YAP/TrkB axis as a putative driver of this process and potential therapeutic target.

Progression of atherosclerotic plaques into life-threatening lesions is associated with angiogenesis which contributes to intraplaque hemorrhages and plaque instability. The lack of adequate models for the study of human plaque-induced angiogenesis has limited progress in this field. We describe here a novel ex vivo model which fills this gap. Plaques obtained from 15 patients who underwent endarterectomy procedures were co-cultured in collagen gels with rat aorta rings which served as read-out of human plaque angiogenic activity. The majority of plaque fragments markedly stimulated angiogenic sprouting from the aortic rings while concurrently promoting the outgrowth of resident macrophages from the aortic adventitia. This stimulatory activity correlated with the presence of intraplaque macrophages. Proteomic analysis of plaque secretomes revealed heterogeneity of macrophage-stimulatory cytokine and angiogenic factor production by different plaques. VEGF was identified in some of the plaque secretomes. Antibody-mediated blockade of VEGF had significant but transient inhibitory effect on angiogenesis, which suggested redundancy of plaque-derived angiogenic stimuli. Pharmacologic ablation of adventitial macrophages permanently impaired the angiogenic response of aortic rings to plaque stimuli. Our results show that human plaque-induced angiogenesis can be reproduced ex vivo using rat aortic rings as read-out of plaque angiogenic activity. This model can be used to identify key cellular and molecular mechanisms responsible for the neovascularization of human plaques.

Tissues respond to injury by releasing acute phase reaction (APR) proteins which regulate inflammation and angiogenesis. Among the genes upregulated in wounded tissues are tumor necrosis factor-alpha (TNFα) and the acute phase reactant orosomucoid-1 (ORM1). ORM1 has been shown to modulate the response of immune cells to TNFα, but its role on injury- and TNFα-induced angiogenesis has not been investigated. This study was designed to characterize the role of ORM1 in the angiogenic response to injury and TNFα. Angiogenesis was studied with in vitro, ex vivo, and in vivo angiogenesis assays. Injured rat aortic rings cultured in collagen gels produced an angiogenic response driven by macrophage-derived TNFα. Microarray analysis and qRT-PCR showed that TNFα and ORM1 were upregulated prior to angiogenic sprouting. Exogenous ORM1 delayed the angiogenic response to injury and inhibited the proangiogenic effect of TNFα in cultures of aortic rings or isolated endothelial cells, but stimulated aortic angiogenesis over time while promoting VEGF production and activity. ORM1 inhibited injury- and TNFα-induced phosphorylation of MEK1/2 and p38 MAPK in aortic rings, but not of NFκB. This effect was injury/TNFα-specific since ORM1 did not inhibit VEGF-induced signaling, and cell-specific since ORM1 inhibited TNFα-induced phosphorylation of MEK1/2 and p38 MAPK in macrophages and endothelial cells, but not mural cells. Experiments with specific inhibitors demonstrated that the MEK/ERK pathway was required for angiogenesis. ORM1 inhibited angiogenesis in a subcutaneous in vivo assay of aortic ring-induced angiogenesis, but stimulated developmental angiogenesis in the chorioallantoic membrane (CAM) assay. ORM1 regulates injury-induced angiogenesis in a time- and context-dependent manner by sequentially dampening the initial TNFα-induced angiogenic response and promoting the downstream stimulation of the angiogenic process by VEGF. The context-dependent nature of ORM1 angioregulatory function is further demonstrated in the CAM assay where ORM1 stimulates developmental angiogenesis without exerting any inhibitory activity.

Background The clinical manifestations of cerebrovascular disease are known to differ between the Chinese and United States (US) populations as do the plaque features on imaging. Objectives The aim of this study was to investigate and compare the histological features of excised carotid plaques from Chinese and US patients. Methods Carotid endarterectomy specimens collected from two prospective studies were included. The entire plaque was serially sectioned (10-µm thickness) at 0.5–1 mm intervals. Hematoxylin and eosin staining and Mallory’s trichrome staining were performed. The morphology and components of the plaques were measured and compared between the two groups. Results A total of 1152 histological sections from 75 Chinese patients and 1843 sections from 111 US patients were analyzed. The Chinese group had significantly smaller minimum lumen diameters (median: 1.1 vs. 1.3 mm, p  = 0.046) and a larger percent wall volume (median: 74% vs. 70%, p  = 0.018) than the US group. After adjusting for confounding factors, carotid plaques in the Chinese population had larger lipid pools ( β  = 10.0%, 95% CI : 4.9 to 15.9%), more recent intraplaque hemorrhage (IPH; β  = 8.4%, 95% CI : 4.5 to 12.7%), less late IPH ( β  = − 8.2%, 95% CI : − 11.3 to − 5.4), and fewer fibrous cap disruptions (45% vs. 67%, p  = 0.061). Chinese plaques were more homogeneous and had a higher percentage of plaques with features of xanthomas than did US plaques (20% vs 2.7%, p  < 0.001). Conclusions The histology of Chinese plaques differs significantly from that of U.S. plaques, suggesting substantial differences in the pathophysiology of atherosclerotic cerebrovascular disease between Chinese and North American populations, which indicates a need for a different management approach. Graphical Abstract

The angiogenic response to injury can be studied by culturing rat or mouse aortic explants in collagen gels. Gene expression studies show that aortic angiogenesis is preceded by an immune reaction with overexpression of Toll-like receptors (TLRs) and TLR-inducible genes. TLR1, 3, and 6 are transiently upregulated at 24 h whereas TLR2, 4, and 8 expression peaks at 24 h but remains elevated during angiogenesis and vascular regression. Expression of TLR5, 7 and 9 steadily increases over time and is highest during vascular regression. Studies with isolated cells show that TLRs are expressed at higher levels in aortic macrophages compared to endothelial or mural cells with the exception of TLR2 and TLR9 which are more abundant in the aortic endothelium. LPS and other TLR ligands dose dependently stimulate angiogenesis and vascular endothelial growth factor production. TLR9 ligands also influence the behavior of nonendothelial cell types by blocking mural cell recruitment and inducing formation of multinucleated giant cells by macrophages. TLR9-induced mural cell depletion is associated with reduced expression of the mural cell recruiting factor PDGFB. The spontaneous angiogenic response of the aortic rings to injury is reduced in cultures from mice deficient in myeloid differentiation primary response 88 (MyD88), a key adapter molecule of TLRs, and following treatment with an inhibitor of the NFκB pathway. These results suggest that the TLR system participates in the angiogenic response of the vessel wall to injury and may play an important role in the regulation of inflammatory angiogenesis in reactive and pathologic processes.

Progression of atherosclerosis is associated with a maladaptive form of angiogenesis which contributes to intraplaque hemorrhage and plaque disruption. Hypoxia has been implicated in mechanisms of angiogenic neovessel fragility and atherosclerotic plaque destabilization. We used ex vivo and in vivo models to characterize the effect of oxygen (O 2 ) on the formation, stability and tendency to bleed of human plaque-induced neovessels. Plaque explants potently stimulated the ex vivo angiogenic response of rat aortic rings at atmospheric O 2 levels. Severe hypoxia (1% O 2 ) inhibited plaque-induced angiogenesis and pericyte recruitment causing neovessel breakdown, whereas increasing O 2 levels dose dependently enhanced pericyte numbers and neovessel stability. Plaque fragments implanted subcutaneously with or without aortic rings in SCID mice stimulated the host angiogenic response with plaques causing minimal or no hemorrhages and plaques co-implanted with aortic rings causing marked hemorrhages. Plaque/aortic ring-induced hemorrhages were reduced in mice exposed to moderate hyperoxia (50% O 2 ). Hyperoxia downregulated expression of the hypoxia-sensitive genes Ca9 , Ca12 and VegfA and increased influx into implants of mesenchymal cells reactive for the pericyte marker NG2. In both ex vivo and in vivo models, O 2 promoted expression of vasostabilizing genes required for pericyte recruitment ( Angpt1 , Pdgfb ), basement membrane assembly ( Col4A1 ), and tight junction formation ( Cldn5 and/or Ocln ). Our results suggest that formation of neovessels that are stable, pericyte-coated, and resistant to bleeding requires adequate tissue oxygenation. Understanding the mechanisms by which O 2 stabilizes neovessels and mitigates neovessel bleeding may lead to new therapies for the prevention of atherosclerosis complications.

This study was designed to investigate how changes in O 2 levels affected angiogenesis in vascular organ culture. Although hypoxia is a potent inducer of angiogenesis, aortic rings cultured in collagen paradoxically failed to produce an angiogenic response in 1–4 % O 2 . Additionally, aortic neovessels preformed in atmospheric O 2 lost pericytes and regressed at a faster rate than control when exposed to hypoxia. Aortic explants remained viable in hypoxia and produced an angiogenic response when returned to atmospheric O 2 . Hypoxic aortic rings were unresponsive to VEGF, while increased oxygenation of the system dose-dependently enhanced VEGF-induced angiogenesis. Hypoxia-induced refractoriness to angiogenic stimulation was not restricted to the aorta because similar results were obtained with vena cava explants or isolated endothelial cells. Unlike endothelial cells, aorta-derived mural cells were unaffected by hypoxia. Hypoxia downregulated expression in aortic explants of key signaling molecules including VEGFR2, NRP1 and Prkc-beta while upregulating expression of VEGFR1. Medium conditioned by hypoxic cultures exhibited angiostatic and anti-VEGF activities likely mediated by sVEGFr1. Hypoxia reduced expression of VEGFR1 and VEGFR2 in endothelial cells while upregulating VEGFR1 in macrophages and VEGF in both macrophages and mural cells. Thus, changes in O 2 levels profoundly affect the endothelial response to angiogenic stimuli. These results suggest that hypoxia-induced angiogenesis is fine-tuned by complex regulatory mechanisms involving not only production of angiogenic factors including VEGF but also differential regulation of VEGFR expression in different cell types and production of inhibitors of VEGF function such as sVEGFR1.