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

Gurnik S, Devraj K, Macas J, Yamaji M, Starke J, Scholz A, Sommer K, Di Tacchio M, Vutukuri R, Beck H, Mittelbronn M, Foerch C, Pfeilschifter W, Liebner S, Peters KG, Plate KH, Reiss Y - Acta Neuropathol. (2016)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Neurology (Edinger Institute), Goethe University Medical School, Frankfurt, Germany.

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.

No MeSH data available.


Related in: MedlinePlus

Ang-2 expression analysis in normal brain and human stroke samples (grade I–III). a, b H&E/IHC staining of human stroke samples showed higher Ang-2 expression in the stroke area (n = 13). NAWM normal appearing white matter, NAGM normal appearing gray matter, i infarct, pn penumbra. c Serum ELISA from stroke (n = 4-lacunar, n = 15-territorial) and healthy subjects (n = 16) showed highest Ang-2 levels in territorial strokes
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Fig6: Ang-2 expression analysis in normal brain and human stroke samples (grade I–III). a, b H&E/IHC staining of human stroke samples showed higher Ang-2 expression in the stroke area (n = 13). NAWM normal appearing white matter, NAGM normal appearing gray matter, i infarct, pn penumbra. c Serum ELISA from stroke (n = 4-lacunar, n = 15-territorial) and healthy subjects (n = 16) showed highest Ang-2 levels in territorial strokes

Mentions: The above-mentioned findings prompted us to investigate the potential role of Ang-2 in human cerebrovascular disease. Expression levels of Ang-2 were assessed by IHC in human brain autopsy specimens and by ELISA in stroke patients compared to healthy volunteers. While Ang-2 expression was almost absent in normal brain tissue, the levels were higher in stroke grades I and II that are characterized by BBB leakage (Fig. 6a, b) and returned to low expression levels in grade III lesions (Fig. 6a, b). Serum analysis from stroke patients indicated a significantly higher level of hAng-2 in patients with territorial stroke compared to healthy humans (Fig. 6c). We subsequently employed a mouse permanent middle cerebral artery occlusion (pMCAO) model, where significantly larger infarcts were detected in Ang-2 GOF mice after 24 and 72 h compared to WT mice (Fig. 7a), whereas at 7 days post-stroke differences in infarct size between WT and GOF resolved. Additionally, the IgG permeability in the stroke area was increased in GOF mice compared to WT 24 h after occlusion (Fig. 7b) corroborating the permeability effects of Ang-2 in a stroke model.Fig. 6


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

Gurnik S, Devraj K, Macas J, Yamaji M, Starke J, Scholz A, Sommer K, Di Tacchio M, Vutukuri R, Beck H, Mittelbronn M, Foerch C, Pfeilschifter W, Liebner S, Peters KG, Plate KH, Reiss Y - Acta Neuropathol. (2016)

Ang-2 expression analysis in normal brain and human stroke samples (grade I–III). a, b H&E/IHC staining of human stroke samples showed higher Ang-2 expression in the stroke area (n = 13). NAWM normal appearing white matter, NAGM normal appearing gray matter, i infarct, pn penumbra. c Serum ELISA from stroke (n = 4-lacunar, n = 15-territorial) and healthy subjects (n = 16) showed highest Ang-2 levels in territorial strokes
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4835530&req=5

Fig6: Ang-2 expression analysis in normal brain and human stroke samples (grade I–III). a, b H&E/IHC staining of human stroke samples showed higher Ang-2 expression in the stroke area (n = 13). NAWM normal appearing white matter, NAGM normal appearing gray matter, i infarct, pn penumbra. c Serum ELISA from stroke (n = 4-lacunar, n = 15-territorial) and healthy subjects (n = 16) showed highest Ang-2 levels in territorial strokes
Mentions: The above-mentioned findings prompted us to investigate the potential role of Ang-2 in human cerebrovascular disease. Expression levels of Ang-2 were assessed by IHC in human brain autopsy specimens and by ELISA in stroke patients compared to healthy volunteers. While Ang-2 expression was almost absent in normal brain tissue, the levels were higher in stroke grades I and II that are characterized by BBB leakage (Fig. 6a, b) and returned to low expression levels in grade III lesions (Fig. 6a, b). Serum analysis from stroke patients indicated a significantly higher level of hAng-2 in patients with territorial stroke compared to healthy humans (Fig. 6c). We subsequently employed a mouse permanent middle cerebral artery occlusion (pMCAO) model, where significantly larger infarcts were detected in Ang-2 GOF mice after 24 and 72 h compared to WT mice (Fig. 7a), whereas at 7 days post-stroke differences in infarct size between WT and GOF resolved. Additionally, the IgG permeability in the stroke area was increased in GOF mice compared to WT 24 h after occlusion (Fig. 7b) corroborating the permeability effects of Ang-2 in a stroke model.Fig. 6

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Neurology (Edinger Institute), Goethe University Medical School, Frankfurt, Germany.

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.

No MeSH data available.


Related in: MedlinePlus