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Disruption of astrocyte-vascular coupling and the blood-brain barrier by invading glioma cells.

Watkins S, Robel S, Kimbrough IF, Robert SM, Ellis-Davies G, Sontheimer H - Nat Commun (2014)

Bottom Line: Malignant gliomas are highly invasive tumours that use the perivascular space for invasion and co-opt existing vessels as satellite tumour form.This causes a focal breach in the BBB.These findings have important clinical implications regarding blood flow in the tumour-associated brain and the ability to locally deliver chemotherapeutic drugs in disease.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Neurobiology, Center for Glial Biology in Medicine, University of Alabama at Birmingham, 1719 6th Avenue South, CIRC 425, Birmingham, Alabama 35294, USA [2].

ABSTRACT
Astrocytic endfeet cover the entire cerebral vasculature and serve as exchange sites for ions, metabolites and energy substrates from the blood to the brain. They maintain endothelial tight junctions that form the blood-brain barrier (BBB) and release vasoactive molecules that regulate vascular tone. Malignant gliomas are highly invasive tumours that use the perivascular space for invasion and co-opt existing vessels as satellite tumour form. Here we use a clinically relevant mouse model of glioma and find that glioma cells, as they populate the perivascular space of preexisting vessels, displace astrocytic endfeet from endothelial or vascular smooth muscle cells. This causes a focal breach in the BBB. Furthermore, astrocyte-mediated gliovascular coupling is lost, and glioma cells seize control over the regulation of vascular tone through Ca(2+)-dependent release of K(+). These findings have important clinical implications regarding blood flow in the tumour-associated brain and the ability to locally deliver chemotherapeutic drugs in disease.

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Vascular responses to Ca2+ uncaging in astrocytes is impaired in vessels co-opted by glioma cells[Ca2+]i uncaging in an astrocyte endfoot or cell body close to an arteriole free of glioma cells leads to either constriction (a) or dilation (c) of the vessel. The vessel response is preceded by a rise in [Ca2+]i(b,d). The pink spot indicates the location of Ca2+ uncaging. Measurement of the Ca2+ response was performed in this region or in an immediate adjacent region. Vessels encased by glioma cells do not respond to Ca2+ uncaging in nearby astrocytes (e,f). Stimulation of astrocytes in tumor-free areas of the same vessel (downstream vessel area) causes constriction showing that the lack of response is specific for areas covered by glioma cells (f,g). The cumulative relative frequency distribution shows a wide range of dilatory or constricting vessel responses in controls, whereas most vessels associated with glioma do not respond or do so to a lesser extent (h). Statistical data in d: control dilating vessels, 60.05 ± 8.899 %, n=10 vessels, tumor dilating, 5.18 ± 1.493, n=8, two-tailed unpaired t-test, p ≤ 0.0001; control constricting vessels, -43.51 ± 6.283 % n=18 vessels, glioma constricting, -9.389 ± 2.611 %, n=9. two-tailed unpaired t-test, p≤ 0.001, error bars refer to SEM.Scale, 20 μm.
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Figure 5: Vascular responses to Ca2+ uncaging in astrocytes is impaired in vessels co-opted by glioma cells[Ca2+]i uncaging in an astrocyte endfoot or cell body close to an arteriole free of glioma cells leads to either constriction (a) or dilation (c) of the vessel. The vessel response is preceded by a rise in [Ca2+]i(b,d). The pink spot indicates the location of Ca2+ uncaging. Measurement of the Ca2+ response was performed in this region or in an immediate adjacent region. Vessels encased by glioma cells do not respond to Ca2+ uncaging in nearby astrocytes (e,f). Stimulation of astrocytes in tumor-free areas of the same vessel (downstream vessel area) causes constriction showing that the lack of response is specific for areas covered by glioma cells (f,g). The cumulative relative frequency distribution shows a wide range of dilatory or constricting vessel responses in controls, whereas most vessels associated with glioma do not respond or do so to a lesser extent (h). Statistical data in d: control dilating vessels, 60.05 ± 8.899 %, n=10 vessels, tumor dilating, 5.18 ± 1.493, n=8, two-tailed unpaired t-test, p ≤ 0.0001; control constricting vessels, -43.51 ± 6.283 % n=18 vessels, glioma constricting, -9.389 ± 2.611 %, n=9. two-tailed unpaired t-test, p≤ 0.001, error bars refer to SEM.Scale, 20 μm.

Mentions: To further ensure that the observed lack in vessel response is indeed due to diminished astrocyte-vascular coupling and not caused by unspecific effects of the drugs on other cell types, we stimulated single astrocytes surrounding vessels with or without glioma cells by uncaging [Ca2+]i after loading acute brain slices of tumor-bearing animals with DMNPE-4 caged Ca2+36. In control slices derived either from naïve animals or from brain regions devoid of tumor, uncaging Ca2+ corresponds to an increase in Ca2+ detected by the Ca2+-indicator dye Fluo-4, which was followed by either constriction or dilation of the nearby arteriole (Fig. 5a-c,g,h; Supplementary Movies 1,2).


Disruption of astrocyte-vascular coupling and the blood-brain barrier by invading glioma cells.

Watkins S, Robel S, Kimbrough IF, Robert SM, Ellis-Davies G, Sontheimer H - Nat Commun (2014)

Vascular responses to Ca2+ uncaging in astrocytes is impaired in vessels co-opted by glioma cells[Ca2+]i uncaging in an astrocyte endfoot or cell body close to an arteriole free of glioma cells leads to either constriction (a) or dilation (c) of the vessel. The vessel response is preceded by a rise in [Ca2+]i(b,d). The pink spot indicates the location of Ca2+ uncaging. Measurement of the Ca2+ response was performed in this region or in an immediate adjacent region. Vessels encased by glioma cells do not respond to Ca2+ uncaging in nearby astrocytes (e,f). Stimulation of astrocytes in tumor-free areas of the same vessel (downstream vessel area) causes constriction showing that the lack of response is specific for areas covered by glioma cells (f,g). The cumulative relative frequency distribution shows a wide range of dilatory or constricting vessel responses in controls, whereas most vessels associated with glioma do not respond or do so to a lesser extent (h). Statistical data in d: control dilating vessels, 60.05 ± 8.899 %, n=10 vessels, tumor dilating, 5.18 ± 1.493, n=8, two-tailed unpaired t-test, p ≤ 0.0001; control constricting vessels, -43.51 ± 6.283 % n=18 vessels, glioma constricting, -9.389 ± 2.611 %, n=9. two-tailed unpaired t-test, p≤ 0.001, error bars refer to SEM.Scale, 20 μm.
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Figure 5: Vascular responses to Ca2+ uncaging in astrocytes is impaired in vessels co-opted by glioma cells[Ca2+]i uncaging in an astrocyte endfoot or cell body close to an arteriole free of glioma cells leads to either constriction (a) or dilation (c) of the vessel. The vessel response is preceded by a rise in [Ca2+]i(b,d). The pink spot indicates the location of Ca2+ uncaging. Measurement of the Ca2+ response was performed in this region or in an immediate adjacent region. Vessels encased by glioma cells do not respond to Ca2+ uncaging in nearby astrocytes (e,f). Stimulation of astrocytes in tumor-free areas of the same vessel (downstream vessel area) causes constriction showing that the lack of response is specific for areas covered by glioma cells (f,g). The cumulative relative frequency distribution shows a wide range of dilatory or constricting vessel responses in controls, whereas most vessels associated with glioma do not respond or do so to a lesser extent (h). Statistical data in d: control dilating vessels, 60.05 ± 8.899 %, n=10 vessels, tumor dilating, 5.18 ± 1.493, n=8, two-tailed unpaired t-test, p ≤ 0.0001; control constricting vessels, -43.51 ± 6.283 % n=18 vessels, glioma constricting, -9.389 ± 2.611 %, n=9. two-tailed unpaired t-test, p≤ 0.001, error bars refer to SEM.Scale, 20 μm.
Mentions: To further ensure that the observed lack in vessel response is indeed due to diminished astrocyte-vascular coupling and not caused by unspecific effects of the drugs on other cell types, we stimulated single astrocytes surrounding vessels with or without glioma cells by uncaging [Ca2+]i after loading acute brain slices of tumor-bearing animals with DMNPE-4 caged Ca2+36. In control slices derived either from naïve animals or from brain regions devoid of tumor, uncaging Ca2+ corresponds to an increase in Ca2+ detected by the Ca2+-indicator dye Fluo-4, which was followed by either constriction or dilation of the nearby arteriole (Fig. 5a-c,g,h; Supplementary Movies 1,2).

Bottom Line: Malignant gliomas are highly invasive tumours that use the perivascular space for invasion and co-opt existing vessels as satellite tumour form.This causes a focal breach in the BBB.These findings have important clinical implications regarding blood flow in the tumour-associated brain and the ability to locally deliver chemotherapeutic drugs in disease.

View Article: PubMed Central - PubMed

Affiliation: 1] Department of Neurobiology, Center for Glial Biology in Medicine, University of Alabama at Birmingham, 1719 6th Avenue South, CIRC 425, Birmingham, Alabama 35294, USA [2].

ABSTRACT
Astrocytic endfeet cover the entire cerebral vasculature and serve as exchange sites for ions, metabolites and energy substrates from the blood to the brain. They maintain endothelial tight junctions that form the blood-brain barrier (BBB) and release vasoactive molecules that regulate vascular tone. Malignant gliomas are highly invasive tumours that use the perivascular space for invasion and co-opt existing vessels as satellite tumour form. Here we use a clinically relevant mouse model of glioma and find that glioma cells, as they populate the perivascular space of preexisting vessels, displace astrocytic endfeet from endothelial or vascular smooth muscle cells. This causes a focal breach in the BBB. Furthermore, astrocyte-mediated gliovascular coupling is lost, and glioma cells seize control over the regulation of vascular tone through Ca(2+)-dependent release of K(+). These findings have important clinical implications regarding blood flow in the tumour-associated brain and the ability to locally deliver chemotherapeutic drugs in disease.

Show MeSH
Related in: MedlinePlus