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Claudin-5 (CLDN5) is an endothelial tight junction protein essential for blood-brain barrier (BBB) formation. Abnormal CLDN5 expression is common in brain disease, and knockdown of Cldn5 at the BBB has been proposed to facilitate drug delivery to the brain. To study the consequences of CLDN5 loss in the mature brain, we induced mosaic endothelial-specific Cldn5 gene ablation in adult mice (Cldn5 iECKO). These mice displayed increased BBB permeability to tracers up to 10 kDa in size from 6 days post induction (dpi) and ensuing lethality from 10 dpi. Single-cell RNA sequencing at 11 dpi revealed profound transcriptomic differences in brain endothelial cells regardless of their Cldn5 status in mosaic mice, suggesting major non-cell-autonomous responses. Reactive microglia and astrocytes suggested rapid cellular responses to BBB leakage. Our study demonstrates a critical role for CLDN5 in the adult BBB and provides molecular insight into the consequences and risks associated with CLDN5 inhibition. [Display omitted] • Cldn5 mosaic loss causes size-selective BBB permeability to tracers up to 10 kDa in size • Adult-induced Cldn5 loss causes seizures and is lethal • scRNA-seq excludes cell-autonomous transcriptional changes in endothelial cells • Leakage causes endothelial and glial inflammation Induced mosaic deletion of Cldn5 in adult mice results in size-selective blood-brain barrier permeability and rapid death. Vázquez-Liébanas et al. show that, following CLDN5 loss, non-cell-autonomous changes appear in both the mutated and surrounding normal endothelial cells due to vascular leakage and ensuing brain inflammation. [ABSTRACT FROM AUTHOR]

The molecular mechanisms by which lymphatic vessels induce cell contact inhibition are not understood. Here, we identify the cGMP-dependent phosphodiesterase 2A (PDE2A) as a selective regulator of lymphatic but not of blood endothelial contact inhibition. Conditional deletion of Pde2a in mouse embryos reveals severe lymphatic dysplasia, whereas blood vessel architecture remains unaltered. In the absence of PDE2A, human lymphatic endothelial cells fail to induce mature junctions and cell cycle arrest, whereas cGMP levels, but not cAMP levels, are increased. Loss of PDE2A-mediated cGMP hydrolysis leads to the activation of p38 signaling and downregulation of NOTCH signaling. However, DLL4-induced NOTCH activation restores junctional maturation and contact inhibition in PDE2A-deficient human lymphatic endothelial cells. In postnatal mouse mesenteries, PDE2A is specifically enriched in collecting lymphatic valves, and loss of Pde2a results in the formation of abnormal valves. Our data demonstrate that PDE2A selectively finetunes a crosstalk of cGMP, p38, and NOTCH signaling during lymphatic vessel maturation. [Display omitted] • The phosphodiesterase 2A is enriched in lymphatic endothelial cells • Loss of lymphatic PDE2A prevents contact inhibition and junctional maturation • PDE2A controls p38 and Notch signaling in a cGMP-dependent manner • Postnatal mesenteric lymphatic valves are defective in the absence of PDE2A Carlantoni et al. demonstrate that loss of lymphatic PDE2A prevents the formation of mature lymphatic junctions, and this results in continuous proliferation and lymphatic dysfunction in human primary cells and mouse models. Lymphatic PDE2A exerts its function by controlling p38 and NOTCH signaling via cGMP modulation. [ABSTRACT FROM AUTHOR]

Objective The blood-brain barrier (BBB) of patients with moyamoya angiopathy (MMA) is unstable, which may contribute to transient neurologic symptoms (TNS) after direct bypass surgery. However, BBB-related proteins have never been investigated. The purpose of this study was to evaluate the perioperative serum levels of biomarkers representing BBB function in MMA patients based on the hypothesis that postoperative hemodynamic change may disrupt the BBB. Methods A total of 12 hemispheres in 11 patients with MMA were prospectively examined. Direct revascularization surgery was performed for all cases. The serum levels of tight junction (occludin and claudin 5), adherens junction (vascular endothelial−cadherin) proteins, and matrix metalloproteinase (MMP)-2 and MMP-9 were measured quantitatively 1 day before surgery and on postoperative days 1, 4, and 7. Results Successful patency of the direct bypass was achieved in all. The serum level of occludin was significantly increased on postoperative day 1, and the levels in 2 cases with TNS were markedly elevated over 10-fold higher than baseline. Furthermore, the postoperative MMP-9 levels were significantly elevated on each day. On the other hand, there was no significant fluctuation in claudin 5, vascular endothelial-cadherin, and MMP-2 level. Conclusions Marked changes in biomarkers representing the tight junction of the BBB were observed. These preliminary results suggest that marked hemodynamic change and TNS in some patients are associated with disruption of the BBB after direct bypass surgery for MMA. Highlights • Blood-brain barrier (BBB) of patients with moyamoya angiopathy (MMA) is unstable. • Direct bypass surgery was performed for MMA. • The serum levels of BBB-related proteins were measured before and after surgery. • The serum levels of OCLN and MMP-9 were significantly increased postoperatively. • Postoperative marked hemodynamic change may induce the disruption of the BBB. [ABSTRACT FROM AUTHOR]

Protease-activated receptor 1 (PAR1) is expressed in pneumocytes and endothelial cells of the alveolar barrier. Its activation by thrombin disrupts the barrier integrity dynamics and induces lung injury in in vitro and in vivo paradigms. Nonetheless, the role of PAR1, as a therapeutic target, in hind limb ischemia/reperfusion (I/R)-mediated remote lung injury has been unclear. Therefore, this study aimed to determine the potential benefit of PAR1 blockade using the selective antagonist SCH79797 in distant lung dysfunction following hind limb I/R injury with special emphasis on the extracellular signal-regulated kinase 5 (ERK5)/Krüppel-like factor 2 (KLF2) axis. Rats were subdivided into control, bilateral hind limb I/R, SCH79797, and SCH79797+BIX02189 (ERK5 inhibitor) groups. PAR1 blockade, ERK5-dependently, alleviated alveolar barrier disruption as evidenced by reductions in both pulmonary systemic leakage of surfactant protein-D and lung fluid accumulation with increase in pulmonary claudin 5, vascular endothelial cadherin, and connexin 37 levels. Such improvements are downstream targets of the ERK5/KLF2-mediated sphingosine-1-phosphate receptor 1 (S1PR1) upregulated expression and p S536-nuclear factor-κB (NF-κB) p65 inhibition. SCH79797 effectively impedes the evoked inflammatory response and oxidative burst by suppressing vascular endothelial growth factor, tumor necrosis factor-α, lipid peroxidation, and neutrophil infiltration while boosting the glutathione antioxidant defense. Accordingly, PAR1 could be a therapeutic target, where its blockade mitigated pulmonary-endothelial barrier disruption via mutual S1PR1 enhancement and NF-κB p65 inhibition following ERK5/KLF2 activation. [Display omitted] • PAR1 blockade alleviates alveolar barrier disruption after limb I/R. • ERK5/KLF2-dependently, PAR1 antagonism results in: • The upregulation of S1PR1 and inhibition of NF-κB. • This leads to claudin 5, VE-cadherin & connexin 37 augmentation. • With additional anti-inflammatory/antioxidant effects. [ABSTRACT FROM AUTHOR]