Angiopoietin-2-induced blood–brain barrier compromise and increased stroke size are rescued by VE-PTP-dependent restoration of Tie2 signaling

Abstract

The homeostasis of the central nervous system is maintained by the blood–brain barrier (BBB). Angiopoietins (Ang-1/Ang-2) act as antagonizing molecules to regulate angiogenesis, vascular stability, vascular permeability and lymphatic integrity. However, the precise role of angiopoietin/Tie2 signaling at the BBB remains unclear. We investigated the influence of Ang-2 on BBB permeability in wild-type and gain-of-function (GOF) mice and demonstrated an increase in permeability by Ang-2, both in vitro and in vivo. Expression analysis of brain endothelial cells from Ang-2 GOF mice showed a downregulation of tight/adherens junction molecules and increased caveolin-1, a vesicular permeability-related molecule. Immunohistochemistry revealed reduced pericyte coverage in Ang-2 GOF mice that was supported by electron microscopy analyses, which demonstrated defective intra-endothelial junctions with increased vesicles and decreased/disrupted glycocalyx. These results demonstrate that Ang-2 mediates permeability via paracellular and transcellular routes. In patients suffering from stroke, a cerebrovascular disorder associated with BBB disruption, Ang-2 levels were upregulated. In mice, Ang-2 GOF resulted in increased infarct sizes and vessel permeability upon experimental stroke, implicating a role of Ang-2 in stroke pathophysiology. Increased permeability and stroke size were rescued by activation of Tie2 signaling using a vascular endothelial protein tyrosine phosphatase inhibitor and were independent of VE-cadherin phosphorylation. We thus identified Ang-2 as an endothelial cell-derived regulator of BBB permeability. We postulate that novel therapeutics targeting Tie2 signaling could be of potential use for opening the BBB for increased CNS drug delivery or tighten it in neurological disorders associated with cerebrovascular leakage and brain edema.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-016-1551-3) contains supplementary material, which is available to authorized users.

Endothelial Activation and Blood–Brain Barrier Disruption in Neurotoxicity after Adoptive Immunotherapy with CD19 CAR-T Cells

“…In addition to regulating CAR-T cell activation and reducing production of cytokines that might activate ECs, strategies to stabilize ECs and minimize BBB disruption might be suitable to treat or prevent neurotoxicity. For example, recombinant Bow-Ang-1 was used to effectively prevent cerebral edema associated with malaria in mice (23), and modification of Tie2 signaling minimized injury associated with BBB disruption in stroke models (24). Other strategies such as hypertransfusion of platelets to augment Ang-1 levels, or plasma exchange to deplete cytokines and HMW VWF multimers could be studied in animal models or suitably designed clinical trials.…”

Alteration of sphingolipid metabolism as a putative mechanism underlying LPS‐induced BBB disruption

“…Isolation of mouse brain microvessels (MBMVs) was performed as previously described (Gurnik et al . ). Briefly, brains were separated and dissected free of cerebellum and olfactory lobes and rolled on a Whatman filter membrane (Schleicher & Schuell/Sigma Aldrich) to remove meninges, subsequently pooled and homogenized in MVB buffer using a dounce homogenizer (Wheaton, VWR, Darmstadt, Germany, 0.025 mm clearance).…”

“…Microvascular brain endothelial cells, the principal site of the BBB, are tightly sealed and together with astrocytes, pericytes, extracellular matrix, and neuronal processes form the neurovascular unit, which regulates microvascular permeability and cerebral microcirculation (Gurnik et al . ). At the BBB, LPS has been shown to induce inflammatory activation of astrocytes (Sambasivarao and McCluer ) and microglia (Nayak et al .…”

Proper autophagy is indispensable for angiogenesis during chick embryo development

“…For instance, Gurnik S. et al found that Ang2 could increase the permeability of the vasculature through depressing the tight junction and increasing the expression of caveolin-1, another vesicular permeability-related molecule. 31 However, Ang1 and Ang2 antagonized each other to modulate the permeability of the blood vessel, 32 and the imbalance of the both genes may result in the lost of the permeability of the vessels no matter autophagy is activated or inhibited. Likewise, we speculate that coordinated gene expressions for the formation of cell junction are also vital during embryonic angiogenesis.…”