Diabetic macular edema is a major complication of diabetes resulting in loss of central vision. Although heightened vessel leakiness has been linked to glial and neuronal-derived factors, relatively ...little is known on the mechanisms by which mature endothelial cells exit from a quiescent state and compromise barrier function. Here we report that endothelial NOTCH1 signaling in mature diabetic retinas contributes to increased vascular permeability. By providing both human and mouse data, we show that NOTCH1 ligands JAGGED1 and DELTA LIKE-4 are up-regulated secondary to hyperglycemia and activate both canonical and rapid noncanonical NOTCH1 pathways that ultimately disrupt endothelial adherens junctions in diabetic retinas by causing dissociation of vascular endothelial-cadherin from β-catenin. We further demonstrate that neutralization of NOTCH1 ligands prevents diabetes-induced retinal edema. Collectively, these results identify a fundamental process in diabetes-mediated vascular permeability and provide translational rational for targeting the NOTCH pathway (primarily JAGGED1) in conditions characterized by compromised vascular barrier function.
Pathological angiogenesis is the hallmark of diseases such as cancer and retinopathies. Although tissue hypoxia and inflammation are recognized as central drivers of vessel growth, relatively little ...is known about the process that bridges the two. In a mouse model of ischemic retinopathy, we found that hypoxic regions of the retina showed only modest rates of apoptosis despite severely compromised metabolic supply. Using transcriptomic analysis and inducible loss-of-function genetics, we demonstrated that ischemic retinal cells instead engage the endoplasmic reticulum stress inositol-requiring enzyme 1α (IRE1α) pathway that, through its endoribonuclease activity, induces a state of senescence in which cells adopt a senescence-associated secretory phenotype (SASP). We also detected SASP-associated cytokines (plasminogen activator inhibitor 1, interleukin-6, interleukin-8, and vascular endothelial growth factor) in the vitreous humor of patients suffering from proliferative diabetic retinopathy. Therapeutic inhibition of the SASP through intravitreal delivery of metformin or interference with effectors of senescence (semaphorin 3A or IRE1α) in mice reduced destructive retinal neovascularization in vivo. We conclude that the SASP contributes to pathological vessel growth, with ischemic retinal cells becoming prematurely senescent and secreting inflammatory cytokines that drive paracrine senescence, exacerbate destructive angiogenesis, and hinder reparative vascular regeneration. Reversal of this process may be therapeutically beneficial.
Cellular adaptation to low oxygen tension triggers primitive pathways that ensure proper cell function. Conditions of hypoxia and low glucose are characteristic of injured tissues and hence ...successive waves of inflammatory cells must be suited to function under low oxygen tension and metabolic stress. While Hypoxia-Inducible Factor (HIF)-1α has been shown to be essential for the inflammatory response of myeloid cells by regulating the metabolic switch to glycolysis, less is known about how HIF1α is triggered in inflammation. Here, we demonstrate that cells of the innate immune system require activity of the inositol-requiring enzyme 1α (IRE1α/XBP1) axis in order to initiate HIF1α-dependent production of cytokines such as IL1β, IL6 and VEGF-A. Knockout of either HIF1α or IRE1α in myeloid cells ameliorates vascular phenotypes in a model of retinal pathological angiogenesis driven by sterile inflammation. Thus, pathways associated with ER stress, in partnership with HIF1α, may co-regulate immune adaptation to low oxygen.
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 IL1β. 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.
Synopsis
A population of innate immune myeloid cells expressing NRP1 receptor invades the retina where it drives and maintains pathological neovascularization during age‐related macular degeneration (AMD). A recombinant NRP1‐derived trap prevents choroidal neovascularization‐associated pathological angiogenesis.
NRP1 ligands were elevated in patients with neovascular AMD and in a mouse model of choroidal neovascularization (CNV).
NRP1‐expressing mononuclear phagocytes rose in the retina upon injury and promoted CNV.
CNV was reduced in mice by therapeutic intravitreal administration of soluble NRP1.
A population of innate immune myeloid cells expressing NRP1 receptor invades the retina where it drives and maintains pathological neovascularization during age‐related macular degeneration (AMD). A recombinant NRP1‐derived trap prevents choroidal neovascularization‐associated pathological angiogenesis.
MicroRNAs are small non-coding RNAs that post-transcriptionally regulate gene expression. We recently demonstrated that levels of miR-106b were significantly decreased in the vitreous and plasma of ...patients with neovascular age-related macular degeneration (AMD). Here we show that expression of the miR-106b-25 cluster is negatively regulated by the unfolded protein response pathway of protein kinase RNA-like ER kinase (PERK) in a mouse model of neovascular AMD. A reduction in levels of miR-106b triggers vascular growth both
and
by inducing production of pro-angiogenic factors. We demonstrate that therapeutic delivery of miR-106b to the retina with lentiviral vectors protects against aberrant retinal angiogenesis in two distinct mouse models of pathological retinal neovascularization. Results from this study suggest that miRNAs such as miR-106b have the potential to be used as multitarget therapeutics for conditions characterized by pathological retinal angiogenesis.
Obesity gives rise to metabolic complications by mechanisms that are poorly understood. Although chronic inflammatory signaling in adipose tissue is typically associated with metabolic deficiencies ...linked to excessive weight gain, we identified a subset of neuropilin-1 (NRP1)-expressing myeloid cells that accumulate in adipose tissue and protect against obesity and metabolic syndrome. Ablation of NRP1 in macrophages compromised lipid uptake in these cells, which reduced substrates for fatty acid β-oxidation and shifted energy metabolism of these macrophages toward a more inflammatory glycolytic metabolism. Conditional deletion of NRP1 in LysM Cre-expressing cells leads to inadequate adipose vascularization, accelerated weight gain, and reduced insulin sensitivity even independent of weight gain. Transfer of NRP1
hematopoietic cells improved glucose homeostasis, resulting in the reversal of a prediabetic phenotype. Our findings suggest a pivotal role for adipose tissue-resident NRP1
-expressing macrophages in driving healthy weight gain and maintaining glucose tolerance.
Age‐related macular degeneration in its neovascular form (NV AMD) is the leading cause of vision loss among adults above the age of 60. Epidemiological data suggest that in men, overall abdominal ...obesity is the second most important environmental risk factor after smoking for progression to late‐stage NV AMD. To date, the mechanisms that underscore this observation remain ill‐defined. Given the impact of high‐fat diets on gut microbiota, we investigated whether commensal microbes influence the evolution of AMD. Using mouse models of NV AMD, microbiotal transplants, and other paradigms that modify the gut microbiome, we uncoupled weight gain from confounding factors and demonstrate that high‐fat diets exacerbate choroidal neovascularization (CNV) by altering gut microbiota. Gut dysbiosis leads to heightened intestinal permeability and chronic low‐grade inflammation characteristic of inflammaging with elevated production of IL‐6, IL‐1β, TNF‐α, and VEGF‐A that ultimately aggravate pathological angiogenesis.
Synopsis
Obesity is an important risk factor for neovascular AMD. We show that high‐fat diets induce gut microbial dysbiosis, resulting in heightened intestinal permeability, which leads to chronic low‐grade inflammation and ultimately increased choroidal neovascularization (CNV).
A high‐fat diet (HFD) induces a shift in commensal gut microbiota and increases permeability of the gut barrier.
Intestinal dysbiosis increases circulating pathogen‐associated molecular patterns (PAMPs), leading to low‐grade endotoxemia that triggers an inflammatory response through pattern recognition receptors (PRRs).
Increased concentrations of circulating and local inflammatory cytokines such as IL‐6, IL‐1β, TNF‐α, and VEGF‐A exacerbate CNV.
Microbiotal transplants confirm that HFD aggravates CNV through gut microbiota.
Obesity is an important risk factor for neovascular AMD. We show that high‐fat diets induce gut microbial dysbiosis, resulting in heightened intestinal permeability, which leads to chronic low‐grade inflammation and ultimately increased choroidal neovascularization (CNV).
Remodeling senescent blood vessels
The retina is a thin layer of nervous tissue at the back of the eye that transforms light into neuronal signals. The retina is essential for vision and is supported ...by networks of blood vessels. In diabetic retinopathy, a common cause of vision loss, these microvessels degenerate and regrow in an aberrant manner. Such degeneration and regrowth can compromise the functioning of retinal nerve cells. Binet
et al.
observed that, after rapid proliferation, vascular endothelial cells in diseased blood vessels engaged molecular pathways linked to cellular senescence (see the Perspective by Podrez and Byzova). Senescent vascular units summoned an inflammatory response in which neutrophils extruded neutrophil extracellular traps onto diseased vessels to remodel them. This endogenous repair mechanism promoted the elimination of senescent blood vessels and could lead to beneficial vascular remodeling.
Science
, this issue p.
eaay5356
; see also p.
919
Remodeling of senescent vascular endothelial cells in the retina is mediated through neutrophil extracellular traps.
INTRODUCTION
Vision provides a critical survival advantage but requires a tight coupling between neuronal energy demands and their vascular supply. The degeneration and consequent aberrant regrowth of retinal vasculature is the hallmark of diseases such as diabetic retinopathy, retinopathy of prematurity, and age-related macular degeneration, which collectively are the most common causes of loss of sight in industrialized countries. Although considerable effort has been devoted to understanding how diseased blood vessels form, relatively little is known of the processes at play during late stages of pathological angiogenesis when blood vessels remodel and subsets of diseased vasculature regress.
RATIONALE
The retina is part of the central nervous system and thus has limited regenerative capacity. A relative exception to this rule are retinal blood vessels, which have a greater propensity to remodel depending on metabolic demand. We investigated the cellular mechanisms activated during the remodeling and regression of pathological blood vessels in retinopathy. We focused on a mouse model of oxygen-induced retinopathy, which has distinct and timed phases of vascular degeneration, neovascularization, and vascular regression. Our findings were verified in human patients with proliferative diabetic retinopathy. Understanding how diseased blood vessels remodel and yield functional networks has the potential to lead to strategies that enhance vascular normalization and helps to explain why retinas in certain patients have the propensity to repair themselves more readily than others.
RESULTS
We found that vascular remodeling in retinopathy is associated with bouts of sterile inflammation and tardy recruitment of neutrophils, an immune population typically associated with a first wave of invading leukocytes. We observed that, after rapid proliferation, vascular endothelial cells in diseased blood vessels engaged molecular pathways shared with aging and cellular damage that lead to cellular senescence. Senescent vascular units then released a secretome of cytokines and factors that attracted neutrophils and triggered the production of neutrophil extracellular traps (NETs). Through extrusion of NETs, neutrophils eliminated diseased senescent vasculature by promoting its apoptosis. By crippling the ability of neutrophils to produce NETs by genetically removing the peptidyl arginine deiminase type IV (PAD4) enzyme, clearance of senescent cells was impaired and regression of pathological angiogenesis compromised. Similar effects were observed with the neutrophil-depleting antibody anti-Ly6G or by pharmacological inhibition of the neutrophil receptor CXCR2.
CONCLUSION
We conclude that neutrophils, through the release of NETs, targeted pathological senescent vasculature for clearance and thus prepare the ischemic retina for reparative vascular regeneration. These findings imply that elimination of senescent blood vessels leads to beneficial vascular remodeling. Although cellular senescence is not necessarily synonymous with aging, our study may provide insight into a general mechanism in which senescent endothelial cells trigger NETosis and predispose to thrombotic events such as myocardial infarction, atherosclerosis, and stroke, which are typically seen in older populations.
Senescent blood vessels trigger neutrophil extracellular traps in retinopathy.
(
A
) Human samples and a mouse model were used to elucidate mechanisms of vascular remodeling in retinopathy. (
B
) Upon rapid proliferation, vascular cells in pathological tufts triggered pathways of cellular senescence, leading to cytokine secretion and the recruitment of neutrophils. (
C
) Factors secreted by senescent cells triggered NETosis. (
D
) NETs promoted the removal of senescent endothelial cells, ultimately leading to regression of pathological angiogenesis and promoting the regeneration of functional vessels.
In developed countries, the leading causes of blindness such as diabetic retinopathy are characterized by disorganized vasculature that can become fibrotic. Although many such pathological vessels often naturally regress and spare sight-threatening complications, the underlying mechanisms remain unknown. Here, we used orthogonal approaches in human patients with proliferative diabetic retinopathy and a mouse model of ischemic retinopathies to identify an unconventional role for neutrophils in vascular remodeling during late-stage sterile inflammation. Senescent vasculature released a secretome that attracted neutrophils and triggered the production of neutrophil extracellular traps (NETs). NETs ultimately cleared diseased endothelial cells and remodeled unhealthy vessels. Genetic or pharmacological inhibition of NETosis prevented the regression of senescent vessels and prolonged disease. Thus, clearance of senescent retinal blood vessels leads to reparative vascular remodeling.
Diabetic retinopathy (DR) is a major complication of diabetes and a leading cause of blindness in the working-age population. Impaired blood-retinal barrier function leads to macular edema that is ...closely associated with the deterioration of central vision. We previously demonstrated that the neuronal guidance cue netrin-1 activates a program of reparative angiogenesis in microglia within the ischemic retina. Here, we provide evidence in both vitreous humor of diabetic patients and in retina of a murine model of diabetes that netrin-1 is metabolized into a bioactive fragment corresponding to domains VI and V of the full-length molecule. In contrast to the protective effects of full-length netrin-1 on retinal microvasculature, the VI-V fragment promoted vascular permeability through the uncoordinated 5B (UNC5B) receptor. The collagenase matrix metalloprotease 9 (MMP-9), which is increased in patients with diabetic macular edema, was capable of cleaving netrin-1 into the VI-V fragment. Thus, MMP-9 may release netrin-1 fragments from the extracellular matrix and facilitate diffusion. Nonspecific inhibition of collagenases or selective inhibition of MMP-9 decreased pathological vascular permeability in a murine model of diabetic retinal edema. This study reveals that netrin-1 degradation products are capable of modulating vascular permeability, suggesting that these fragments are of potential therapeutic interest for the treatment of DR.
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