Astrocytes Control Breathing Through pH-Dependent Release of ATP

Abstract

Astrocytes provide structural and metabolic support for neuronal networks, but direct evidence demonstrating their active role in complex behaviors is limited. Central respiratory chemosensitivity is an essential mechanism which, via regulation of breathing, maintains constant levels of blood and brain PCO 2 /pH. We found that astrocytes of the brainstem chemoreceptor areas are highly chemosensitive. They responded to physiological decreases in pH with vigorous elevations in intracellular Ca 2+ and release of ATP. ATP propagated astrocytic Ca 2+ excitation, activated chemoreceptor neurons, and induced adaptive increases in breathing. Mimicking pHevoked Ca 2+ responses by optogenetic stimulation of astrocytes expressing channelrhodopsin-2 activated chemoreceptor neurons via ATP-dependent mechanism and triggered robust respiratory responses in vivo. This demonstrates a potentially crucial role for brain glial cells in mediating a fundamental physiological reflex.The role of astrocytes in the brain is by no means limited to just providing structural and metabolic support to neurons. Astrocytes are closely associated with cerebral blood vessels and are thought to regulate cerebrovascular tone adjusting blood supply to match local metabolic demands(1-6). A single astrocyte may enwrap several neuronal somata(7) and make contact with thousands of synapses(8), potentially regulating synaptic strength and information processing (4,(9)(10)(11)(12)(13)(14). However, direct evidence demonstrating the functional role of astrocytes in complex behaviors is only starting to emerge(15).Astrocytes provide a vascular-neuronal interface and are in a position to quickly relay bloodborne stimuli to the activities of neuronal networks. Does this have a functional significance for the detection of the relevant stimuli by brain chemosensors which monitor key homeostatic parameters including glucose concentration, pH and PCO 2 ? Here we tested the * This manuscript has been accepted for publication in Science. This version has not undergone final editing. Please refer to the complete version of record at http://www.sciencemag.org/. The manuscript may not be reproduced or used in any manner that does not fall within the fair use provisions of the Copyright Act without the prior, written permission of AAAS. Fig 1a). Subsequent histological examination of the chemoresponsive areas confirmed contacts of transduced astrocytes with pia mater and penetrating arterioles ( fig. S3). Supporting Online MaterialPropagating Ca 2+ excitation of ventral medullary astrocytes in response to acidification was also observed in different in vitro preparations such as acute horizontal brainstem slices of adult rats (n = 56 slices; Fig In brainstem slices of adult rats, in which blood vessels were visualized with lectin, many pH-sensitive astrocytes were found to be located adjacent to the VS vasculature (Fig. 1f).Acidification-induced Ca 2+ excitation of VS astrocytes is unlikely to be secondary to increased activity of local neurons. To minimize ne...

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“…2002, 2015; Gourine et al . 2010), because metabolic changes in response to local heating and cooling are relatively small (Barcroft & Edholm, 1943; Pearson et al . 2011).…”

Measurement of purine release with microelectrode biosensors

“…In parallel with this work, Gourine and colleagues have examined the sensitivity of astrocytes of the VMS to pH [52]. They have demonstrated that changes in pH can evoke Ca 2+ waves in these astrocytes that depend on the prior release of ATP (probably in this case via exocytosis).…”

“…However, this negative evidence has more recently been overturnedwhen challenged with a CO 2 stimulus in the neonate (as opposed to a pH stimulus), a significant component of the retrotrapezoid neuron responses is indeed ATP receptordependent [51]. At adult stages, the response of these neurons is almost entirely dependent on the prior release of ATP [52]. However, ATP biosensing has had two even more profound consequences for understanding of CO 2 chemosensory mechanisms.…”

Signal transduction in astrocytes: Localization and release of inorganic polyphosphate

“…sGFAP is a transcriptionally enhanced, bidirectional, shortened glial fibrillary acidic protein promoter which drives transgene expression in astrocytes (Figueiredo et al, 2011; Gourine et al, 2010; Liu, Paton, & Kasparov, 2008). Fusions with EGFP or mKate2.7 allow detection of transgene expression via green or red fluorescence, respectively.…”

“…Purinoceptors are expressed by astrocytes, and readily respond to the increases in extracellular ATP concentration (Angelova et al, 2015; Coco et al, 2003; Gourine et al, 2010). Regulated exocytosis of signaling molecules by astrocytes may involve different types of secretory organelles (synaptic‐like microvesicles, dense‐core vesicles, lysosomes, exosomes, and ectosomes (Oya et al, 2013; Verkhratsky, Matteoli, Parpura, Mothet, & Zorec, 2016).…”