Side-by-side comparison of the effects of Gq- and Gi-DREADD-mediated astrocyte modulation on intracellular calcium dynamics and synaptic plasticity in the hippocampal CA1

Abstract

Astrocytes express a plethora of G protein-coupled receptors (GPCRs) that are crucial for shaping synaptic activity. Upon GPCR activation, astrocytes can respond with transient variations in intracellular Ca2+. In addition, Ca2+-dependent and/or Ca2+-independent release of gliotransmitters can occur, allowing them to engage in bidirectional neuron-astrocyte communication. The development of designer receptors exclusively activated by designer drugs (DREADDs) has facilitated many new discoveries on the roles of astrocytes in both physiological and pathological conditions. They are an excellent tool, as they can target endogenous GPCR-mediated intracellular signal transduction pathways specifically in astrocytes. With increasing interest and accumulating research on this topic, several discrepancies on astrocytic Ca2+ signalling and astrocyte-mediated effects on synaptic plasticity have emerged, preventing a clear-cut consensus about the downstream effects of DREADDs in astrocytes. In the present study, we performed a side-by-side evaluation of the effects of bath application of the DREADD agonist, clozapine-N-oxide (10 µM), on Gq- and Gi-DREADD activation in mouse CA1 hippocampal astrocytes. In doing so, we aimed to avoid confounding factors, such as differences in experimental procedures, and to directly compare the actions of both DREADDs on astrocytic intracellular Ca2+ dynamics and synaptic plasticity in acute hippocampal slices. We used an adeno-associated viral vector approach to transduce dorsal hippocampi of male, 8-week-old C57BL6/J mice, to drive expression of either the Gq-DREADD or Gi-DREADD in CA1 astrocytes. A viral vector lacking the DREADD construct was used to generate controls. Here, we show that agonism of Gq-DREADDs, but not Gi-DREADDs, induced consistent increases in spontaneous astrocytic Ca2+ events. Moreover, we demonstrate that both Gq-DREADD as well as Gi-DREADD-mediated activation of CA1 astrocytes induces long-lasting synaptic potentiation in the hippocampal CA1 Schaffer collateral pathway in the absence of a high frequency stimulus. Moreover, we report for the first time that astrocytic Gi-DREADD activation is sufficient to elicit de novo potentiation. Our data demonstrate that activation of either Gq or Gi pathways drives synaptic potentiation through Ca2+-dependent and Ca2+-independent mechanisms, respectively.

Astrocyte calcium dysfunction causes early network hyperactivity in Alzheimer’s disease

“…DREADDs-mediated activation of astrocytes increases the amplitude and frequency of astrocyte calcium signals, as reported in other studies using astrocyte-specific DREADDs ( Adamsky et al., 2018 ; Durkee et al., 2019 ; Herrewegen et al., 2021 ), or pharmacological/sensory-evoked activation of astrocytes ( Ding et al., 2013 ; Lines et al., 2020 ; Wang et al., 2006 ). Recovery of deficient calcium signaling in cingulate cortex astrocytes of App NL-F mice normalizes neuronal hyperactivity and increased BOLD FC.…”

Early stress-induced impaired microglial pruning of excitatory synapses on immature CRH-expressing neurons provokes aberrant adult stress responses

“…Whereas this mechanism remains to be confirmed in microglial synaptic pruning, brain microglial engulfment requires process motility and actin cytoskeletal dynamics. Activation of Gq-DREADDs increases intracellular calcium concentrations via inositol triphosphate/diacylglycerol (IP3/DAG) in multiple cell types, including neurons and astrocytes ( van den Herrewegen et al, 2021 ). Increased intracellular calcium, in turn, augments microglial process extension and dynamics, facilitating synapse engulfment (see Figure S6 ).…”

Basolateral amygdala astrocytes are engaged by the acquisition and expression of a contextual fear memory

“…As astrocytes do not have typical “inhibition/excitation” properties which are more typically associated with neurons (Durkee et. al., 2019; Van Den Herrewegan et. al., 2021), future research may take its amore complex signaling pathways into account and yield crucial information in how astrocytes participate at the tripartite synapse to facilitate the learning of conditioned fear.…”