Rakers, Cordula Marijke: The role of glial calcium changes in animal models of stroke. - Bonn, 2015. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5n-42068
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5n-42068,
author = {{Cordula Marijke Rakers}},
title = {The role of glial calcium changes in animal models of stroke},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2015,
month = dec,

note = {Ischemic stroke represents one of the leading causes of death and disability. A main characteristic of the early phase of stroke is the spontaneous appearance of peri-infarct depolarizations (PIDs), which are known to negatively affect infarct size and clinical outcome. The aim of this work was to better define the dynamics of PIDs in the peri-infarct region (penumbra), and to investigate the underlying cellular pathways, with a particular emphasis on calcium signaling in astrocytes.
I combined the permanent middle cerebral artery occlusion (pMCAO) stroke model with in vivo two-photon (2-P) microscopy in transgenic mice expressing cyan fluorescent protein (CFP) selectively in astrocytes under the Cx43 promoter. Calcium dynamics and local changes in cerebral blood flow (CBF) were measured using the pharmacological calcium indicator Oregon Green 488 BAPTA-1 AM (OGB-1), and blood vessels were visualized by intravenous injection of Texas Red 70 kDa dextran. In addition, astroglial edema – i. e. volume changes in astrocytes during PIDs – was estimated by measuring somatic CFP fluorescence over time. Following pMCAO induction, anesthetized mice were imaged through a cranial window. I found that PIDs could be detected by this technique based on the appearance of a typical propagating wave of calcium changes in neurons and astrocytes that was accompanied by characteristic CBF changes and the development of astrocytic edema. I confirmed the propagation pattern as well as the typical electrophysiological characteristics of PIDs in separate groups by combining pMCAO with extracellular measurements of the direct current (DC) potential and with regional CBF measurements using laser speckle contrast imaging. In addition, the calcium changes in astrocytes during PID were confirmed using a mouse line that expresses the genetically encoded calcium indicator GCaMP3 in astrocytes using a Cre/loxP approach (GLAST-CreERT2:Ai38 line).
Subsequently, I aimed to identify the astroglial signaling pathways underlying calcium transients during PIDs, and their contribution to PID threshold and propagation. To this end, I induced pMCAO in transgenic mouse lines with deletions of inositol triphosphate receptor 2 (IP3R2), transient receptor vanilloid 4 (TRPV4) channel, or aquaporin-4 (AQP4). Each line was crossbred to Cx43 CFP mice for astrocyte identification. In addition, I tested the effect of pharmacological antagonists of these channels in wildtype mice as well as blockade of the astrocytic sodium calcium exchanger (NCX). I found that the amplitude of astroglial calcium changes during PID was significantly reduced in IP3R2-deficient mice. Calcium transients were also reduced in TRPV4-deficient mice and wildtype mice treated with TRPV4 or NCX blockers. These results indicate that TRPV4 and NCX channels mediate an influx of calcium from the extracellular space, and a substantial calcium release from the endoplasmic reticulum through IP3R2. Surprisingly, no changes were seen in AQP4-deficient mice. Moreover, I found that the delay between pMCAO onset and the first PID, as well as the frequency of subsequent PIDs, was significantly reduced in IP3R2-deficient mice. This was confirmed in separate groups using DC-potential recordings and laser speckle contrast imaging.
In conclusion, I have found that astrocyte-specific IP3R2 is an important contributor to PID threshold, and that IP3R2, TRPV4, and NCX contribute to calcium influx during PID. Since PIDs and cellular calcium overload are important determinants of stroke severity and outcome, pharmacological modulation of these channels in translational or clinical studies may prove therapeutically beneficial.},

url = {http://hdl.handle.net/20.500.11811/6573}

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