Lesion-Induced Alterations in Astrocyte Glutamate Transporter Expression and Function in the Hippocampus

Abstract

Astrocytes express the sodium-dependent glutamate transporters GLAST and GLT-1, which are critical to maintain low extracellular glutamate concentrations. Here, we analyzed changes in their expression and function following a mechanical lesion in the CA1 area of organotypic hippocampal slices. 6-7 days after lesion, a glial scar had formed along the injury site, containing strongly activated astrocytes with increased GFAP and S100β immunoreactivity, enlarged somata, and reduced capability for uptake of SR101. Astrocytes in the scar's periphery were swollen as well, but showed only moderate upregulation of GFAP and S100β and efficiently took up SR101. In the scar, clusters of GLT-1 and GLAST immunoreactivity colocalized with GFAP-positive fibers. Apart from these, GLT-1 immunoreactivity declined with increasing distance from the scar, whereas GLAST expression appeared largely uniform. Sodium imaging in reactive astrocytes indicated that glutamate uptake was strongly reduced in the scar but maintained in the periphery. Our results thus show that moderately reactive astrocytes in the lesion periphery maintain overall glutamate transporter expression and function. Strongly reactive astrocytes in the scar, however, display clusters of GLAST and GLT-1 immunoreactivity together with reduced glutamate transport activity. This reduction might contribute to increased extracellular glutamate concentrations and promote excitotoxic cell damage at the lesion site.

FRET‐based imaging of intracellular ATP in organotypic brain slices

“…They exhibit the major advantages of cell cultures such as accessibility and direct control of experimental conditions and, importantly, allow cell‐specific transduction and expression of genetically encoded sensors. While cultured tissue slices are covered by a layer of reactive astrocytes (e.g., Schreiner, Berlinger, Langer, Kafitz, and Rose []), recent studies have established that non‐reactive astrocytes are located in the tissue underneath this outer glial scar, enabling analysis of astrocytic morphology and neuron‐glia interactions (Benediktsson, Schachtele, Green, & Dailey, ; Haber, Zhou, & Murai, ). Moreover, astrocytes in organotypic slices retain their capacity to selectively take up the vital maker SR101 (sulforhodamine 101) (Kafitz, Meier, Stephan, & Rose, ; Nimmerjahn & Helmchen, ; Schreiner et al, ).…”

“…Moreover, astrocytes in organotypic slices retain their capacity to selectively take up the vital maker SR101 (sulforhodamine 101) (Kafitz, Meier, Stephan, & Rose, ; Nimmerjahn & Helmchen, ; Schreiner et al, ). This is in contrast to hypertrophic astrocytes located in the outer glial scar of these cultures, which loose SR101 labeling (Schreiner et al, ).…”

Neuroprotection by Combined Administration with Maslinic Acid, a Natural Product from Olea europaea, and MK-801 in the Cerebral Ischemia Model

“…In our study, maslinic acid slightly elevated GFAP levels after ischemia compared with vehicle treatment, indicating the involvement of maslinic acid in the functional role of reactive astrocytes. Moreover, it has been demonstrated that moderately reactive astrocytes maintain overall glutamate transporter expression and function, which contribute to decreased extracellular glutamate concentrations and prevent excitotoxic cell damage [25]. However, maslinic acid did not affect GFAP activation when it was given to rats not subjected to MCAO, suggesting that maslinic acid had few effects on glial function under normal physiological conditions.…”

Prostaglandin E2Produced by Alginate-Encapsulated Mesenchymal Stromal Cells Modulates the Astrocyte Inflammatory Response

“…However, it is important to consider all cell types present that contribute to the ongoing cell death, degeneration, and inhibition of regeneration. Astrocytes exhibit distinct responses to brain injury, and are a key player in several components of secondary injury including inflammation, 23,34 excitotoxicity, 35 and free radical-mediated injury. 36,37 Here, we focus on the role of these cells in mediating the neuroinflammatory component of secondary injury.…”