FOXO1 represses Sprouty2 and Sprouty4 expression in endothelial cells to promote arterial specification and vascular remodeling in the mouse yolk sac

The establishment of a functional circulatory system is required for post-implantation development during mouse embryogenesis. Previous studies in null mouse models have reported that FOXO1, a Forkhead family transcription factor, is essential for yolk sac vascular remodeling and survival beyond embryonic day (E) 11. Here, we show that loss of FoxO1 in E8.25 endothelial cells results in increased Sprouty2 and Sprouty4 gene expression, reduced expression of arterial genes, and reduced Flk1/Vegfr2 expression without affecting overall endothelial cell identity, survival or proliferation. Using Dll4-BAC-nlacZ reporter, we found that one of the earliest expressed arterial genes, Dll4, is significantly reduced in the yolk sac of FoxO1 mutants without being substantially affected in the embryo. We show that in the yolk sac, FOXO1 not only binds directly to a subset of previously identified activating Sprouty2 regulatory regions and newly identified conserved Sprouty4 regulatory regions, but can also repress their expression. Additionally, over expression of Sprouty4 in E8.25 transient transgenic embryos largely recapitulates reduced expression of arterial genes seen in endothelial FoxO1 mutants. These data reveal a novel role for FOXO1 as a key transcriptional repressor in early, pre-flow arterial specification and subsequent vessel remodeling within the murine yolk sac.

WTAP-mediated GPX4 m6A methylation triggers PASMCs ferroptosis and pulmonary vascular fibrosis in pulmonary artery hypertension

Background and Purpose Ferroptosis is a new form of cell death discovered in recent years. PH is a pulmonary circulatory disease partially characterized by small pulmonary vessel remodeling and fibrosis. However, researchers have not clearly determined whether ferroptosis is involved in PH. Here, this study examined the role and regulatory mechanism of ferroptosis in PH and pulmonary fibrosis. Experimental Approach To evaluate the occurrence of ferroptosis in rat PH models and in hypoxic PASMCs, MDA, GSH and iron assay were performed. The therapeutic potential of ferroptosis inhibitor fer-1 was evaluated using echocardiography, hemodynamic analysis and ventricular weight measurement in rat PH models. Ferroptosis-related molecule was determined by western blotting and RT-PCR. Changes in autophagy and fibrosis were analyzed by western blotting analysis, RT-PCR and immunofluorescence. Key Results Ferroptosis was existence in vivo and vitro PH models. The fer-1 significantly improved the pathological symptoms of PH and inhibited the occurrence of pulmonary vascular fibrosis. GPX4 was significantly lower expression in PH models, and serves as a key driver of PH-related ferroptosis. A KEGG pathway analysis and RT-PCR detection revealed that GPX4 drives ferroptosis in an autophagy-dependent manner. The RIP experiment verified that WTAP bound to the GPX4 pre-mRNA, induced m6A methylation and promoted its pre-mRNA degradation, thereby reducing the expression of GPX4 in hypoxic PASMCs. Conclusion and Implications This study proposed ferroptosis as a novel form of cell death in PH, and revealed the regulatory mechanism of the ferroptosis in PH, which is based on GPX4 m6A methylation regulated by WTAP.

Shedding the Light on the Natural History of Intracranial Aneurysms: An Updated Overview

The exact molecular pathways underlying the multifactorial natural history of intracranial aneurysms (IAs) are still largely unknown, to the point that their understanding represents an imperative challenge in neurovascular research. Wall shear stress (WSS) promotes the genesis of IAs through an endothelial dysfunction causing an inflammatory cascade, vessel remodeling, phenotypic switching of the smooth muscle cells, and myointimal hyperplasia. Aneurysm growth is supported by endothelial oxidative stress and inflammatory mediators, whereas low and high WSS determine the rupture in sidewall and endwall IAs, respectively. Angioarchitecture, age older than 60 years, female gender, hypertension, cigarette smoking, alcohol abuse, and hypercholesterolemia also contribute to growth and rupture. The improvements of aneurysm wall imaging techniques and the implementation of target therapies targeted against inflammatory cascade may contribute to significantly modify the natural history of IAs. This narrative review strives to summarize the recent advances in the comprehension of the mechanisms underlying the genesis, growth, and rupture of IAs.

Cyclo-oxygenase 2, a putative mediator of vessel remodeling, is expressed in the brain AVM vessels and associates with inflammation

Background Brain arteriovenous malformations (bAVM) may rupture causing disability or death. BAVM vessels are characterized by abnormally high flow that in general triggers expansive vessel remodeling mediated by cyclo-oxygenase-2 (COX2), the target of non-steroidal anti-inflammatory drugs. We investigated whether COX2 is expressed in bAVMs and whether it associates with inflammation and haemorrhage in these lesions. Methods Tissue was obtained from surgery of 139 bAVMs and 21 normal Circle of Willis samples. The samples were studied with immunohistochemistry and real-time quantitative polymerase chain reaction (RT-PCR). Clinical data was collected from patient records. Results COX2 expression was found in 78% (109/139) of the bAVMs and localized to the vessels’ lumen or medial layer in 70% (95/135) of the bAVMs. Receptors for prostaglandin E2, a COX2-derived mediator of vascular remodeling, were found in the endothelial and smooth muscle cells and perivascular inflammatory cells of bAVMs. COX2 was expressed by infiltrating inflammatory cells and correlated with the extent of inflammation (r = .231, p = .007, Spearman rank correlation). COX2 expression did not associate with haemorrhage. Conclusion COX2 is induced in bAVMs, and possibly participates in the regulation of vessel wall remodelling and ongoing inflammation. Role of COX2 signalling in the pathobiology and clinical course of bAVMs merits further studies.

Remodeling of the Posterior Cerebral Artery P1-Segment after Pipeline Flow Diverter Treatment of Posterior Communicating Artery Aneurysms

Introduction: Flow diverters such as the pipeline embolization device (PED) cause hemodynamic changes of the treated vessel segment. In posterior communicating artery (PcomA), aneurysms’ unique anatomic consideration have to be taken in account due to the connection between the anterior and posterior circulation. We hypothesize that in conjunction with PcomA remodeling, there will also be remodeling of the ipsilateral P1 segment of the posterior cerebral artery (PCA) after PED treatment for PcomA aneurysms. Methods: We retrospectively collected radiological as well as clinical data of PcomA aneurysm patients treated with PED including PcomA and P1 vessel diameters before and after treatment as well as patient and aneurysm characteristics. Results: Overall, 14 PcomA aneurysm patients were included for analysis and PED treatment was performed without complications in all patients. In 10 out of 14 patients (71%), a decrease in PcomA diameter was observed and there was a significant mean decrease of 0.78 mm in PcomA diameter on angiographic last follow-up (LFU) (p = 0.003). In the same patient population (10 out of 14 patients), there was meanwhile a significant mean increase of 0.43 mm in the ipsilateral P1 segment diameter observed (p = 0.015). These vessel remodeling effects were in direct correlation with aneurysm occlusion since all of these patients showed aneurysm occlusion at LFU while 29% showed only partial occlusion without vessel remodeling effects. A decrease in PcomA diameter was directly associated with aneurysm occlusion (p = 0.042). There were no neurologic complications on LFU. Conclusion: In the treatment of PcomA aneurysms with PED, the P1 segment of the PCA increases in diameter while the PcomA diameter decreases. Our results suggest that this remodeling effect is associated with aneurysm occlusion and decrease of PcomA is hemodynamically compensated for by an increase in the ipsilateral P1 diameter.

Contribution of cell death signaling to blood vessel formation

The formation of new blood vessels is driven by proliferation of endothelial cells (ECs), elongation of maturing vessel sprouts and ultimately vessel remodeling to create a hierarchically structured vascular system. Vessel regression is an essential process to remove redundant vessel branches in order to adapt the final vessel density to the demands of the surrounding tissue. How exactly vessel regression occurs and whether and to which extent cell death contributes to this process has been in the focus of several studies within the last decade. On top, recent findings challenge our simplistic view of the cell death signaling machinery as a sole executer of cellular demise, as emerging evidences suggest that some of the classic cell death regulators even promote blood vessel formation. This review summarizes our current knowledge on the role of the cell death signaling machinery with a focus on the apoptosis and necroptosis signaling pathways during blood vessel formation in development and pathology.

Atorvastatin pleiotropically decreases intraplaque angiogenesis and intraplaque haemorrhage by inhibiting ANGPT2 release and VE-Cadherin internalization

Objective Statins pleiotropically provide additional benefits in reducing atherosclerosis, but their effects on intraplaque angiogenesis (IPA) and hemorrhage (IPH) remain unclear. Therefore, we discriminated statin’s lipid-lowering dependent and independent effects on IPA and IPH. Approach and results ApoE3*Leiden mice are statin-responsive due to ApoE and LDLR presence, but also allow to titrate plasma cholesterol levels by diet. Therefore, ApoE3*Leiden mice were fed a high-cholesterol-inducing-diet (HCD) with or without atorvastatin (A) or a moderate-cholesterol-inducing-diet (MCD). Mice underwent vein graft surgery to induce lesions with IPA and IPH. Cholesterol levels were significantly reduced in MCD (56%) and HCD + A (39%) compared to HCD with no significant differences between MCD and HCD + A. Both MCD and HCD + A have a similar reduction in vessel remodeling and inflammation comparing to HCD. IPA was significantly decreased by 30% in HCD + A compared to HCD or MCD. Atorvastatin treatment reduced the presence of immature vessels by 34% vs. HCD and by 25% vs. MCD, resulting in a significant reduction of IPH. Atorvastatin’s anti-angiogenic capacity was further illustrated by a dose-dependent reduction of ECs proliferation and migration. Cultured mouse aortic-segments lost sprouting capacity upon atorvastatin treatment and became 30% richer in VE-Cadherin expression and pericyte coverage. Moreover, Atorvastatin inhibited ANGPT2 release and decreased VE-Cadherin(Y685)-phosphorylation in ECs. Conclusions Atorvastatin has beneficial effects on vessel remodeling due to its lipid-lowering capacity. Atorvastatin has strong pleiotropic effects on IPA by decreasing the number of neovessels and on IPH by increasing vessel maturation. Atorvastatin improves vessel maturation by inhibiting ANGPT2 release and phospho(Y658)-mediated VE-Cadherin internalization.

Fibronectin-mediated inflammatory signaling through integrin α5 in vascular remodeling

Adhesion of vascular endothelial cells (ECs) to the underlying basement membrane potently modulates EC inflammatory activation. The normal basement membrane proteins laminin and collagen IV attenuate inflammatory signaling in part through integrin α2β1. In contrast, fibronectin, the provisional matrix protein found in injured, remodeling or inflamed vessels, sensitizes ECs to inflammatory stimuli through integrins α5β1and and αvβ3. A chimeric integrin in which the cytoplasmic domain of α5 is replaced with that of α2 pairs with β1 and binds fibronectin but signals like α2β1. Here, we examined mice in which integrin α5 is replaced with the α5/2 chimera, using the transverse aortic constriction (TAC) and partial carotid ligation (PCL) models of vessel remodeling. Following TAC and PCL surgery, WT mice showed increased fibronectin deposition and expression of inflammatory markers, which were strongly attenuated in a5/2 mice. α5/2 mice also showed reduced artery wall hypertrophy in the TAC model and diminished inward remodeling in the PCL model. Acute atherosclerosis after PCL in hyperlipidemic ApoE-/- mice on a high fat diet was dramatically decreased in α5/2 mice. These results underscore the key role for integrin α5 signaling in pathological vascular remodeling and support its potential as a therapeutic target.

Sox17 Controls Emergence and Remodeling of Nestin-Expressing Coronary Vessels

Rationale: The molecular mechanisms underlying the formation of coronary arteries during development and during cardiac neovascularization after injury are poorly understood. However, a detailed description of the relevant signaling pathways and functional TFs (transcription factors) regulating these processes is still incomplete. Objective: The goal of this study is to identify novel cardiac transcriptional mechanisms of coronary angiogenesis and vessel remodeling by defining the molecular signatures of coronary vascular endothelial cells during these complex processes. Methods and Results: We demonstrate that Nes-gfp and Nes-CreER T2 transgenic mouse lines are novel tools for studying the emergence of coronary endothelium and targeting sprouting coronary vessels (but not ventricular endocardium) during development. Furthermore, we identify Sox17 as a critical TF upregulated during the sprouting and remodeling of coronary vessels, visualized by a specific neural enhancer from the Nestin gene that is strongly induced in developing arterioles. Functionally, genetic-inducible endothelial deletion of Sox17 causes deficient cardiac remodeling of coronary vessels, resulting in improper coronary artery formation. Conclusions: We demonstrated that Sox17 TF regulates the transcriptional activation of Nestin ’s enhancer in developing coronary vessels while its genetic deletion leads to inadequate coronary artery formation. These findings identify Sox17 as a critical regulator for the remodeling of coronary vessels in the developing heart.