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Perivascular microglia promote blood vessel disintegration in the ischemic penumbra

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Abstract

The contribution of microglia to ischemic cortical stroke is of particular therapeutic interest because of the impact on the survival of brain tissue in the ischemic penumbra, a region that is potentially salvable upon a brain infarct. Whether or not tissue in the penumbra survives critically depends on blood flow and vessel perfusion. To study the role of microglia in cortical stroke and blood vessel stability, CX3CR1+/GFP mice were subjected to transient middle cerebral artery occlusion and then microglia were investigated using time-lapse two-photon microscopy in vivo. Soon after reperfusion, microglia became activated in the stroke penumbra and started to expand cellular protrusions towards adjacent blood vessels. All microglia in the penumbra were found associated with blood vessels within 24 h post reperfusion and partially fully engulfed them. In the same time frame blood vessels became permissive for blood serum components. Migration assays in vitro showed that blood serum proteins leaking into the tissue provided molecular cues leading to the recruitment of microglia to blood vessels and to their activation. Subsequently, these perivascular microglia started to eat up endothelial cells by phagocytosis, which caused an activation of the local endothelium and contributed to the disintegration of blood vessels with an eventual break down of the blood brain barrier. Loss-of-microglia-function studies using CX3CR1GFP/GFP mice displayed a decrease in stroke size and a reduction in the extravasation of contrast agent into the brain penumbra as measured by MRI. Potentially, medication directed at inhibiting microglia activation within the first day after stroke could stabilize blood vessels in the penumbra, increase blood flow, and serve as a valuable treatment for patients suffering from ischemic stroke.

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Acknowledgments

We thank Heike Ehrengard, Christin Liefländer, Christine Oswald, and Andreas Zymny for their excellent technical assistance and Darragh O’Neill for proofreading the manuscript. This work was supported by the Foundation Rhineland-Palatinate to FZ, by the German Research Foundation (DFG) via the collaborative research center 1080, projects A3 (MHHS) and B6 (MKS+FZ), DFG FOR1336 (AW) as well as the DFG Grant SCHM 2159/2-1 to MHHS.

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The authors declare no competing financial interests.

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Authors and Affiliations

  1. Department of Neurology, Focus Program Translational Neuroscience (FTN), Rhine Main Neuroscience Network (rmn2), Johannes Gutenberg University, University Medical Center, Mainz, Germany

    Valérie Jolivel, Robert Ploen, René Gollan, Betty Jurek, Jérôme Birkenstock, Laura Poisa-Beiro & Frauke Zipp

  2. Molecular Signal Transduction Laboratories, Institute for Microscopic Anatomy and Neurobiology, Focus Program Translational Neuroscience (FTN), Rhine Main Neuroscience Network (rmn2), Johannes Gutenberg University, University Medical Center, Langenbeckstr. 1, 55131, Mainz, Germany

    Frank Bicker, Stefanie Keller, Verena Opitz & Mirko H. H. Schmidt

  3. Molecular Cell Biology, Department of Biology, Johannes Gutenberg University, Mainz, Germany

    Fabien Binamé

  4. Institute for Molecular Medicine, Focus Program Translational Neuroscience (FTN), Rhine Main Neuroscience Network (rmn2), Johannes Gutenberg University, University Medical Center, Mainz, Germany

    Julia Bruttger & Ari Waisman

  5. Department of Anesthesiology, Focus Program Translational Neuroscience (FTN), Rhine Main Neuroscience Network (rmn2), Johannes Gutenberg University, University Medical Center, Mainz, Germany

    Serge C. Thal & Michael K. Schäfer

  6. Institute of Radiology, University Medical Center, Erlangen, Germany

    Tobias Bäuerle

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  1. Valérie Jolivel
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Correspondence to Mirko H. H. Schmidt.

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V. Jolivel and F. Bicker contributed equally as first but M. K. Schäfer, F. Zipp and M. H. H. Schmidt contributed equally as last authors.

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401_2014_1372_MOESM1_ESM.tif

Suppl. Fig. 1 At 24 h post reperfusion brain sections of MCAO-treated mice were immunohistochemically stained for Iba-1 (microglia) and CD31 (ECs) in combination with either the smooth muscle cell marker SMA (a–d) or the pericyte marker NG2 (e–h) Iba-1-positive cells are neither smooth muscle cells nor pericytes. Furthermore, perivascular microglia did not phagocytize these cell types. Cell nuclei were visualized with DAPI. Bars represent 25 µm. i–l Double staining of Iba-1 (microglia) and a combination of the neuronal marker MAP2 and the neurofilament marker NF160 revealed phagocytosis of endothelial (yellow particles, arrowheads) but not neuronal structures (magenta, absent) by perivascular microglia. Cell nuclei were visualized with DAPI. Bars represent 10 µm (TIFF 7741 kb)

401_2014_1372_MOESM2_ESM.tif

Suppl. Fig. 2 At 24 h post-reperfusion brain sections of MCAO-treated mice were immunohistochemically stained for the vessel markers CD31 and a–c Glut-1, d–f caveolin-1, g–i claudin-5, and j–l podocalyxin. All markers overlap to a large extent with CD31 in the brain endothelium. Cell nuclei were visualized with DAPI. Bars represent 10 µm (TIFF 5047 kb)

401_2014_1372_MOESM3_ESM.tif

Suppl. Fig. 3 Immunohistochemical double staining of brain sections of MCAO-treated mice 24 h post reperfusion using the EC markers a–c Glut1, d–f caveolin1, g–i claudin-5, or j–l podocalyxin and Iba-1 (microglia) reveals phagocytosis of blood vessel components by perivascular microglia as indicated by arrowheads. Cell nuclei were visualized with DAPI. Bars represent 10 µm (TIFF 6970 kb)

401_2014_1372_MOESM4_ESM.tif

Suppl. Fig. 4 At 24 h post-reperfusion brain sections of MCAO-treated mice were immunohistochemically stained for EGFL7 and the EC activation markers a–c VEGF, d–f PDGF-B, g–i vWF, and j–l ICAM-1. Blood vessels in the ischemic penumbra stained positive for EGFL7 and either EC activation marker. Cell nuclei were visualized with DAPI. Bar represents 10 µm (TIFF 8902 kb)

401_2014_1372_MOESM5_ESM.avi

Suppl. Movie 1 At 4 h after reperfusion microglia extend cellular processes towards blood vessels in the ischemic penumbra. In this 38-min-long time-lapse movie, the dynamic extension and retraction of GFP-positive microglia processes (green) towards rhodamine–dextran-labeled blood vessels (red) is studied using intravital two-photon microscopy in the ischemic penumbra. At 4 h post reperfusion, activation of microglia was detectable by microglial processes that switched from random palpation to a targeted extension towards blood vessels (arrow). Each frame in this movie represents a z-projection of a 70-µm-thick stack acquired at 1-min intervals in vivo (AVI 1758 kb)

Suppl. Movie 2 At 8 h after reperfusion perivascular microglia assume a spherical shape in the ischemic penumbra. In this 4.5-h-long time-lapse movie starting 4 h post reperfusion, activation of microglia was measured by intravital two-photon microscopy. At 8 h post reperfusion, microglia cell bodies changed from an elongated to a spherical shape (arrows). GFP-positive microglia are indicated in green, rhodamine–dextran-labeled blood vessels in red. Each frame in this movie represents a z-projection of a 70-µm-thick stack acquired at 1-min intervals in vivo (AVI 13793 kb)

Suppl. Movie 3 At 8 h after reperfusion microglia migrate towards blood vessels. In this 55-min-long time-lapse movie starting 8 h post reperfusion, intravital two-photon microscopy revealed the migration of GFP-positive microglia (green) towards rhodamine–dextran-labeled blood vessels (red) 8 h post reperfusion (arrows). Each frame in this movie represents a z-projection of a 70-µm-thick stack acquired at 1-min intervals in vivo (AVI 2064 kb)

Suppl. Movie 4 At 8 h after reperfusion a microglia cell migrates towards a blood vessel. This movie shows a magnification of a cell derived from supplementary movie 3 migrating towards a blood vessel 8 h post reperfusion. Each frame in this movie represents a z-projection of a 70-µm-thick stack acquired at 1-min intervals in vivo (AVI 300 kb)

Suppl. Movie 5 At 24 h post reperfusion microglia phagocytize blood vessel components. This 70-min-long intravital two-photon microscopy time-lapse movie shows GFP-positive microglia (green) aligning with rhodamine–dextran-labeled blood vessels (red, small arrow). At 24 h post reperfusion these cells started to phagocytize rhodamine–dextran-positive blood vessel components (yellow, big arrow). Each frame in this movie represents a z-projection of a 70-µm-thick stack acquired at 1-min intervals in vivo (AVI 4281 kb)

Suppl. Movie 6 At 24 h post reperfusion microglia disintegrate blood vessels. This 88-min-long intravital two-photon microscopy time-lapse movie shows GFP-positive activated microglia (green) that are mainly associated with blood vessels 24 h post reperfusion. Two of the microglia cells actively migrate towards blood vessels (big arrows) and scan them with their processes. The disintegration of the blood vasculature has already started, as demonstrated by patchy extravasation of rhodamine–dextran in the lower part of the video (small arrows). Each frame in this movie represents a z-projection of a 70-µm-thick stack acquired at 1-min intervals in vivo (AVI 7722 kb)

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Jolivel, V., Bicker, F., Binamé, F. et al. Perivascular microglia promote blood vessel disintegration in the ischemic penumbra. Acta Neuropathol 129, 279–295 (2015). https://doi.org/10.1007/s00401-014-1372-1

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