Neuronal activity and glutamate uptake decrease mitochondrial mobility in astrocytes and position mitochondria near glutamate transporters.
Within neurons, mitochondria are nonuniformly distributed and are retained at sites of high activity and metabolic demand. Glutamate transport and the concomitant activation of the Na(+)/K(+)-ATPase represent a substantial energetic demand on astrocytes. We hypothesized that mitochondrial mobility within astrocytic processes might be regulated by neuronal activity and glutamate transport. We imaged organotypic hippocampal slice cultures of rat, in which astrocytes maintain their highly branched morphologies and express glutamate transporters. Using time-lapse confocal microscopy, the mobility of mitochondria within individual astrocytic processes and neuronal dendrites was tracked. Within neurons, a greater percentage of mitochondria were mobile than in astrocytes. Furthermore, they moved faster and farther than in astrocytes. Inhibiting neuronal activity with tetrodotoxin (TTX) increased the percentage of mobile mitochondria in astrocytes. Mitochondrial movement in astrocytes was inhibited by vinblastine and cytochalasin D, demonstrating that this mobility depends on both the microtubule and actin cytoskeletons. Inhibition of glutamate transport tripled the percentage of mobile mitochondria in astrocytes. Conversely, application of the transporter substrate d-aspartate reversed the TTX-induced increase in the percentage of mobile mitochondria. Inhibition of reversed Na(+)/Ca(2+) exchange also increased the percentage of mitochondria that were mobile. Last, we demonstrated that neuronal activity increases the probability that mitochondria appose GLT-1 particles within astrocyte processes, without changing the proximity of GLT-1 particles to VGLUT1. These results imply that neuronal activity and the resulting clearance of glutamate by astrocytes regulate the movement of astrocytic mitochondria and suggest a mechanism by which glutamate transporters might retain mitochondria at sites of glutamate uptake.
Children's Hospital of Philadelphia Research Institute, Department of Pediatrics, Department of Pharmacology, and Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
Joshua G
JG
Jackson
John C
JC
O'Donnell
Hajime
H
Takano
Douglas A
DA
Coulter
Michael B
MB
Robinson
D000704:Analysis of Variance; D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000648:ultrastructure*; D001640:Bicuculline / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D027342:Excitatory Amino Acid Transporter 2 / Q000378:metabolism*; D005260:Female; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000166:cytology* / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009536:Niacinamide / Q000031:analogs & derivatives / Q000494:pharmacology; D009924:Organ Culture Techniques; D051381:Rats; D019831:Sodium-Calcium Exchanger / Q000037:antagonists & inhibitors / Q000378:metabolism; D013779:Tetrodotoxin / Q000494:pharmacology; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology; D014162:Transfection; D050598:Vesicular Glutamate Transport Protein 1 / Q000378:metabolism
C101670:2-(2-(4-(4-nitrobenzyloxy)phenyl)ethyl)isothiourea methanesulfonate; D000779:Anesthetics, Local; D018691:Excitatory Amino Acid Antagonists; D027342:Excitatory Amino Acid Transporter 2; D058787:GABA-A Receptor Antagonists; D008164:Luminescent Proteins; C516554:N-(3-aminobenzyl)-6-(4-((3-fluorobenzyl)oxy)phenoxy)nicotinamide; C493395:Slc1a2 protein, rat; D019831:Sodium-Calcium Exchanger; D050598:Vesicular Glutamate Transport Protein 1; D009536:Niacinamide; D018698:Glutamic Acid; D013779:Tetrodotoxin; D013890:Thiourea; D001640:Bicuculline
GLT-1; astrocyte; glutamate; mitochondria; mobility; transporter