Rapid sodium signaling couples glutamate uptake to breakdown of ATP in perivascular astrocyte endfeet. Issue 2 (27th October 2016)

• Record Type: Journal Article
• Authors: Langer, Julia; Gerkau, Niklas J.; Derouiche, Amin; Kleinhans, Christian; Moshrefi‐Ravasdjani, Behrouz; Fredrich, Michaela; Kafitz, Karl W.; Seifert, Gerald; Steinhäuser, Christian; Rose, Christine R.
• Is Part Of: Glia. Volume 65:Issue 2(2017)
• Page Start: 293
• Page End: 308
• Publication Date: 2016-10-27
• Subjects: SBFI -- neuro‐metabolic coupling -- hippocampus -- GLAST -- GLT‐1; Neuroglia -- Periodicals; Neurology -- Periodicals; 611.0188
• DOI: 10.1002/glia.23092
• Languages: English
• ISSNs: 0894-1491

Abstract

Abstract : Perivascular endfeet of astrocytes are highly polarized compartments that ensheath blood vessels and contribute to the blood–brain barrier. They experience calcium transients with neuronal activity, a phenomenon involved in neurovascular coupling. Endfeet also mediate the uptake of glucose from the blood, a process stimulated in active brain regions. Here, we demonstrate in mouse hippocampal tissue slices that endfeet undergo sodium signaling upon stimulation of glutamatergic synaptic activity. Glutamate‐induced endfeet sodium transients were diminished by TFB‐TBOA, suggesting that they were generated by sodium‐dependent glutamate uptake. With local agonist application, they could be restricted to endfeet and immunohistochemical analysis revealed prominent expression of glutamate transporters GLAST and GLT‐1 localized towards the neuropil vs. the vascular side of endfeet. Endfeet sodium signals spread at an apparent maximum velocity of ∼120 µm/s and directly propagated from stimulated into neighboring endfeet; this spread was omitted in Cx30/Cx43 double‐deficient mice. Sodium transients resulted in elevation of intracellular magnesium, indicating a decrease in intracellular ATP. In summary, our results establish that excitatory synaptic activity and stimulation of glutamate uptake in astrocytes trigger transient sodium increases in perivascular endfeet which rapidly spread through gap junctions into neighboring endfeet and cause a reduction of intracellular ATP. The newly discovered endfeet sodium signaling thereby represents a fast, long‐lived and inter‐cellularly acting indicator of synaptic activity at the blood–brain barrier, which likely constitutes an important component of neuro‐metabolic coupling in the brain. GLIA 2017;65:293–308 Main Points: Neuronal activity stimulates glutamate uptake and sodium signaling in astrocyte endfeet. Sodium signals rapidly spread between endfeet and result in a breakdown of ATP. Endfeet sodium signals are likely to contribute to neuro‐metabolic coupling.