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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

Permeability analysis of Ang-2 GOF mice in vivo. a Permeability to LY and Texas Red-3 kD/TMR-dextran was higher in GOF brains (LY: n = 7, TXR: WT n = 12; GOF n = 16). b Evans blue dye permeability was not altered (n = 6). c Increased permeability of 3 kD TMR-dextran in Ang-2 GOF mice in cortex and subcortical white matter (SWM) (n = 3, scale bars 10 µm)
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Fig2: Permeability analysis of Ang-2 GOF mice in vivo. a Permeability to LY and Texas Red-3 kD/TMR-dextran was higher in GOF brains (LY: n = 7, TXR: WT n = 12; GOF n = 16). b Evans blue dye permeability was not altered (n = 6). c Increased permeability of 3 kD TMR-dextran in Ang-2 GOF mice in cortex and subcortical white matter (SWM) (n = 3, scale bars 10 µm)

Mentions: The effect of Ang-2 on BBB permeability was first assessed by transendothelial electrical resistance (TEER) and capacitance (Ccl) measurements on the primary mouse brain endothelial cells (MBMECs) (Fig. 1a). The TEER of MBMECs derived from Ang-2 GOF mice was lower compared to WT (Fig. 1b), and Ccl was higher (Suppl. Fig. 1a) indicating a barrier-opening effect of Ang-2. Similar results were obtained when WT-MBMECs were treated with recombinant Ang-2 (hAng-2, Fig. 1c). The permeability to fluorescent dextrans (3, 20, and 70 kD) and Lucifer Yellow (LY 0.45 kD) [15] was also increased in TEER measurement by hAng-2 (Fig. 1d), suggesting a direct effect of Ang-2 on brain EC permeability. In vivo, the permeability to LY and 3 kD dextrans (Texas Red and TMR) was significantly increased in Ang-2 GOF (Fig. 2a, c), with no difference for Evans blue dye (~70 kD) potentially owing to a tight barrier in vivo (Fig. 2b). The 0.45 kD LY and 3 kD dextran tracers were circulated for 4 min due to their rapid clearance from blood vessels at longer time points (Suppl. Fig. 1b). Kidneys served as a control for tracer permeability that was not altered between GOF and WT (Suppl. Fig. 1c). These results therefore demonstrate Ang-2-mediated brain endothelial permeability for low molecular weight solutes in vivo.Fig. 1


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)

Permeability analysis of Ang-2 GOF mice in vivo. a Permeability to LY and Texas Red-3 kD/TMR-dextran was higher in GOF brains (LY: n = 7, TXR: WT n = 12; GOF n = 16). b Evans blue dye permeability was not altered (n = 6). c Increased permeability of 3 kD TMR-dextran in Ang-2 GOF mice in cortex and subcortical white matter (SWM) (n = 3, scale bars 10 µm)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig2: Permeability analysis of Ang-2 GOF mice in vivo. a Permeability to LY and Texas Red-3 kD/TMR-dextran was higher in GOF brains (LY: n = 7, TXR: WT n = 12; GOF n = 16). b Evans blue dye permeability was not altered (n = 6). c Increased permeability of 3 kD TMR-dextran in Ang-2 GOF mice in cortex and subcortical white matter (SWM) (n = 3, scale bars 10 µm)
Mentions: The effect of Ang-2 on BBB permeability was first assessed by transendothelial electrical resistance (TEER) and capacitance (Ccl) measurements on the primary mouse brain endothelial cells (MBMECs) (Fig. 1a). The TEER of MBMECs derived from Ang-2 GOF mice was lower compared to WT (Fig. 1b), and Ccl was higher (Suppl. Fig. 1a) indicating a barrier-opening effect of Ang-2. Similar results were obtained when WT-MBMECs were treated with recombinant Ang-2 (hAng-2, Fig. 1c). The permeability to fluorescent dextrans (3, 20, and 70 kD) and Lucifer Yellow (LY 0.45 kD) [15] was also increased in TEER measurement by hAng-2 (Fig. 1d), suggesting a direct effect of Ang-2 on brain EC permeability. In vivo, the permeability to LY and 3 kD dextrans (Texas Red and TMR) was significantly increased in Ang-2 GOF (Fig. 2a, c), with no difference for Evans blue dye (~70 kD) potentially owing to a tight barrier in vivo (Fig. 2b). The 0.45 kD LY and 3 kD dextran tracers were circulated for 4 min due to their rapid clearance from blood vessels at longer time points (Suppl. Fig. 1b). Kidneys served as a control for tracer permeability that was not altered between GOF and WT (Suppl. Fig. 1c). These results therefore demonstrate Ang-2-mediated brain endothelial permeability for low molecular weight solutes in vivo.Fig. 1

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