# Mitochondrial Ca2+ Signaling at the Tripartite Synapse: A Unifying Framework for Glutamate Homeostasis, Metabolic Coupling, and Network Vulnerability

## TL;DR

This paper explores how mitochondria regulate calcium signaling at synapses, linking it to glutamate balance, metabolism, and risks in neurodegenerative diseases like Alzheimer's.

## Contribution

The paper provides a unifying framework connecting mitochondrial Ca2+ signaling to synaptic function and disease vulnerability.

## Key findings

- Mitochondrial Ca2+ signaling regulates glutamate homeostasis and metabolic coupling at the tripartite synapse.
- Impairments in mitochondrial Ca2+ dynamics may lead to synaptic failure before energy collapse.
- Disruption of the mitochondria–glutamatergic axis contributes to synaptic dysfunction in Alzheimer's disease.

## Abstract

Mitochondrial Ca2+ signaling is increasingly recognized as a key integrator of synaptic activity, metabolism, and redox balance within the tripartite synapse. At excitatory synapses, Ca2+ influx through ionotropic glutamate receptors and voltage-gated channels is sensed and transduced by strategically positioned mitochondria, whose Ca2+ uptake and release tune tricarboxylic acid cycle activity, adenosine triphosphate synthesis, and reactive oxygen species (ROS) generation. Through these Ca2+-dependent processes, mitochondria are proposed to help set the threshold at which glutamatergic activity supports synaptic plasticity and homeostasis or, instead, drives hyperexcitability and excitotoxic stress. Here, we synthesize how mitochondrial Ca2+ dynamics in presynaptic terminals, postsynaptic spines, and perisynaptic astrocytic processes regulate glutamate uptake, recycling, and release, and how subtle impairments in these pathways may prime synapses for failure well before overt energetic collapse. We further examine the reciprocal interplay between Ca2+-dependent metabolic adaptations and glutamate homeostasis, the crosstalk between mitochondrial Ca2+ and ROS signals, and the distinct vulnerabilities of neuronal and astrocytic mitochondria. Finally, we discuss how disruption of this Ca2+-centered mitochondria–glutamatergic axis contributes to synaptic dysfunction and circuit vulnerability in neurodegenerative diseases, with a particular focus on Alzheimer’s disease.