Adenosine A2A receptor modulates microglia-mediated synaptic pruning of the retinogeniculate pathway during postnatal development.

Synapse pruning is essential not only for the developmental establishment of synaptic connections in the brain but also for the pathogenesis of neurodevelopmental and neurodegenerative disorders. However, there are no effective pharmacological means to regulate synaptic pruning during early development. Using the eye-specific segregation of the dorsal lateral geniculate nucleus (dLGN) as a model of synaptic pruning coupled with adenosine A2A receptor (A2AR) antagonism and knockout, we demonstrated while genetic deletion of the A2AR throughout the development attenuated eye-specific segregation with the attenuated microglial phagocytosis at postnatal day 5 (P5), selective treatment with the A2AR antagonist KW6002 at P2-P4 facilitated synaptic pruning of visual pathway with microglial activation, increased lysosomal activity in microglia and increased microglial engulfment of retinal ganglion cell (RGC) inputs in the dLGN at P5 (but not P10). Furthermore, KW6002-mediated facilitation of synaptic pruning was activity-dependent since tetrodotoxin (TTX) treatment abolished the KW6002 facilitation. Moreover, the A2AR antagonist also modulated postsynaptic proteins and synaptic density at early postnatal stages as revealed by the reduced immunoreactivity of postsynaptic proteins (Homer1 and metabotropic glutamate receptor 5) and colocalization of presynaptic VGlut2 and postsynaptic Homer1 puncta in the dLGN. These findings suggest that A2AR can control pruning by multiple actions involving the retinal wave, microglia engulfment, and postsynaptic stability. Thus, A2AR antagonists may represent a novel pharmacological strategy to modulate microglia-mediated synaptic pruning and treatment of neurodevelopmental disorders associated with dysfunctional pruning.

Cocaine alters Homer1 natural antisense transcript in the nucleus accumbens.

Natural antisense transcripts (NATs) are an abundant class of long noncoding RNAs that have recently been shown to be key regulators of chromatin dynamics and gene expression in nervous system development and neurological disorders. However, it is currently unclear if NAT-based mechanisms also play a role in drug-induced neuroadaptations. Aberrant regulation of gene expression is one critical factor underlying the long-lasting behavioral abnormalities that characterize substance use disorder, and it is possible that some drug-induced transcriptional responses are mediated, in part, by perturbations in NAT activity. To test this hypothesis, we used an automated algorithm that mines the NCBI AceView transcriptomics database to identify NAT overlapping genes linked to addiction. We found that 22% of the genes examined contain NATs and that expression of Homer1 natural antisense transcript (Homer1-AS) was altered in the nucleus accumbens (NAc) of mice 2h and 10days following repeated cocaine administration. In in vitro studies, depletion of Homer1-AS lead to an increase in the corresponding sense gene expression, indicating a potential regulatory mechanisms of Homer1 expression by its corresponding antisense transcript. Future in vivo studies are needed to definitely determine a role for Homer1-AS in cocaine-induced behavioral and molecular adaptations.

Chronic intermittent alcohol disrupts the GluN2B-associated proteome and specifically regulates group I mGlu receptor-dependent long-term depression.

N-Methyl-d-aspartate receptors (NMDARs) are major targets of both acute and chronic alcohol, as well as regulators of plasticity in a number of brain regions. Aberrant plasticity may contribute to the treatment resistance and high relapse rates observed in alcoholics. Recent work suggests that chronic alcohol treatment preferentially modulates both the expression and subcellular localization of NMDARs containing the GluN2B subunit. Signaling through synaptic and extrasynaptic GluN2B-NMDARs has already been implicated in the pathophysiology of various other neurological disorders. NMDARs interact with a large number of proteins at the glutamate synapse, and a better understanding of how alcohol modulates this proteome is needed. We employed a discovery-based proteomic approach in subcellular fractions of hippocampal tissue from chronic intermittent alcohol (CIE)-exposed C57Bl/6J mice to gain insight into alcohol-induced changes in GluN2B signaling complexes. Protein enrichment analyses revealed changes in the association of post-synaptic proteins, including scaffolding, glutamate receptor and PDZ-domain binding proteins with GluN2B. In particular, GluN2B interaction with metabotropic glutamate (mGlu)1/5 receptor-dependent long-term depression (LTD)-associated proteins such as Arc and Homer 1 was increased, while GluA2 was decreased. Accordingly, we found a lack of mGlu1/5 -induced LTD while α1 -adrenergic receptor-induced LTD remained intact in hippocampal CA1 following CIE. These data suggest that CIE specifically disrupts mGlu1/5 -LTD, representing a possible connection between NMDAR and mGlu receptor signaling. These studies not only demonstrate a new way in which alcohol can modulate plasticity in the hippocampus but also emphasize the utility of this discovery-based proteomic approach to generate new hypotheses regarding alcohol-related mechanisms.