Chemogenetic stimulation of the G_i pathway in astrocytes suppresses neuroinflammation

Abstract

Engineered G protein‐coupled receptors (GPCRs) are commonly used in chemogenetics as designer receptors exclusively activated by designer drugs (DREADDs). Although several GPCRs have been studied in astrocytes using a chemogenetic approach, the functional role of the astrocytic Gi pathway is not clear, as the literature is conflicting depending on the brain regions or behaviors investigated. In this study, we evaluated the role of the astrocytic Gi pathway in neuroinflammation using a Gi‐coupled DREADD (hM4Di). Gi‐DREADD was expressed in hippocampal astrocytes of a lipopolysaccharide (LPS)‐induced neuroinflammation mouse model using adeno‐associated viruses. We found that astrocyte Gi‐DREADD stimulation using clozapine N‐oxide (CNO) inhibits neuroinflammation, as characterized by decreased levels of proinflammatory cytokines, glial activation, and cognitive impairment in mice. Subsequent experiments using primary astrocyte cultures revealed that Gi‐DREADD stimulation significantly downregulated LPS‐induced expression of Nos2 mRNA and nitric oxide production. Similarly, in vitro calcium imaging showed that activation of the astrocytic Gi pathway attenuated intracellular calcium transients triggered by LPS treatment, suggesting a positive correlation between enhanced calcium transients and the inflammatory phenotype of astrocytes observed in the inflamed brain. Taken together, our results indicate that the astrocytic Gi pathway plays an inhibitory role in neuroinflammation, providing an opportunity to identify potential cellular and molecular targets to control neuroinflammation.

Chronic ethanol consumption exacerbates future stress‐enhanced fear learning, an effect mediated by dorsal hippocampal astrocytes

“…In other words, when EtOH Diet/ Shock subjects experienced CNO administration during EtOH withdrawal, they no longer exhibited enhanced freezing behavior in Context B. Given that stimulation of astrocyte, G i signaling is known to decrease LPS-induced increases in GFAP positive cell counts and immunoreactivity and decrease proinflammatory cytokines (Kim et al, 2021), our causal DREADD manipulation likely decreased DH astroglial GFAP expression and/or proinflammatory cytokine signaling. As we have previously demonstrated the involvement of astrocyte-dependent cytokine signaling in the development of SEFL , as well as in opioid withdrawal-induced enhanced fear learning (Parekh et al, 2020), we hypothesize that astrocyte-dependent neuroimmune signaling is responsible for the development of an exacerbated PTSD-like phenotype in EtOH-dependent animals.…”

Anemoside B4 alleviates neuropathic pain through inhibiting inflammation

“…µ-opioid G protein-coupled receptor (µOR) acted on the adenylyl cyclase-inhibitory family of G proteins (Gi/o) to mediate signaling and play an analgesic role [39]. During the elimination of neuroin ammation, astrocytes inhibited neuroin ammation by down-regulating the expression of in ammatory factors through the Gi pathway in GPCR [40]. TPH1 (Tryptophan hydroxylase 1) worked as a rate-limiting enzyme in the biosynthesis of 5-Hydroxytryptamine (5-HT), and the reduction of which in cerebrospinal uid would led to mechanical hyperalgesia with central sensitization [41,42].…”

Neuroinflammation Induced by Transgenic Expression of Lipocalin-2 in Astrocytes

“…The concentration of protein extracted from transfected cells was measured using a bicinchoninic acid assay (Pierce, Waltham, MA; Kim et al, 2021b ). Protein samples were separated on SDS-PAGE gels.…”

“…To inject the virus, mice were maintained under isoflurane anesthesia and located in a stereotaxic device. The injection needles were placed bilaterally on the hippocampal CA1 using the following coordinates: AP −2 mm, L ± 1.8 mm from the bregma, and V −1.2 mm from the dura (Kim et al, 2021b ). Then, the virus was delivered (total; 0.5 μl, rate; 0.1 μl/min) into the hippocampus.…”