Type VI adenylyl cyclase negatively regulates GluN2B-mediated LTD and spatial reversal learning

Gm527 deficiency in dentate gyrus improves memory through upregulating dopamine D1 receptor pathway

AIMS

Dopamine D1 receptor (D1R) hypofunction is associated with negative and cognitive symptoms in schizophrenia; therefore, the mechanism of D1R function modulation needs further investigation. Gm527 is the rodent homologous of the schizophrenia-related gene C14orf28, encoding a predicated D1R-interacting protein. However, the role of Gm527-D1R interaction in schizophrenia needs to be clarified.

METHODS

Gm527-floxed mice were generated and crossed with D1-Cre mice (D1:Gm527-/-) to knockout Gm527 in D1R-positive neurons. Then behavioral tests were performed to explore the schizophrenia-related phenotypes. Immunofluorescence, fluorescence in situ hybridization, electrophysiological recording, quantitative real-time PCR, and western blotting were conducted to investigate the mechanisms.

RESULTS

Working memory, long-term memories, and adult neurogenesis in the DG were enhanced in D1:Gm527-/- mice. LTP was also increased in the DG in D1:Gm527-/- mice, resulting from the Gm527 knockout-induced D1R expression enhancement on the plasma membrane and subsequently cAMP signaling and NMDA receptor pathways activation. The requirement of Gm527 knockout in the DG was confirmed by reversing Gm527 expression or knockdown Gm527 in the DG D1R-positive neurons through AAV-CAG-FLEX-Gm527-GFP or AAV-CMV-FLEX-EGFP-Gm527-RNAi injection.

CONCLUSIONS

The DG Gm527 knockout induces D1R hyperfunction in improving schizophrenia cognitive symptoms.

Physiological roles of mammalian transmembrane adenylyl cyclase isoforms

Adenylyl cyclases (ACs) catalyze the conversion of ATP to the ubiquitous second messenger cAMP. Mammals possess nine isoforms of transmembrane ACs, dubbed AC1-9, that serve as major effector enzymes of G protein-coupled receptors (GPCRs). The transmembrane ACs display varying expression patterns across tissues, giving the potential for them to have a wide array of physiological roles. Cells express multiple AC isoforms, implying that ACs have redundant functions. Furthermore, all transmembrane ACs are activated by Gαs, so it was long assumed that all ACs are activated by Gαs-coupled GPCRs. AC isoforms partition to different microdomains of the plasma membrane and form prearranged signaling complexes with specific GPCRs that contribute to cAMP signaling compartments. This compartmentation allows for a diversity of cellular and physiological responses by enabling unique signaling events to be triggered by different pools of cAMP. Isoform-specific pharmacological activators or inhibitors are lacking for most ACs, making knockdown and overexpression the primary tools for examining the physiological roles of a given isoform. Much progress has been made in understanding the physiological effects mediated through individual transmembrane ACs. GPCR-AC-cAMP signaling pathways play significant roles in regulating functions of every cell and tissue, so understanding each AC isoform's role holds potential for uncovering new approaches for treating a vast array of pathophysiological conditions.

Equilibrative nucleoside transporter 1 inhibition rescues energy dysfunction and pathology in a model of tauopathy

Tau pathology is instrumental in the gradual loss of neuronal functions and cognitive decline in tauopathies, including Alzheimer's disease (AD). Earlier reports showed that adenosine metabolism is abnormal in the brain of AD patients while consequences remained ill-defined. Herein, we aimed at investigating whether manipulation of adenosine tone would impact Tau pathology, associated molecular alterations and subsequent neurodegeneration. We demonstrated that treatment with an inhibitor (J4) of equilibrative nucleoside transporter 1 (ENT1) exerted beneficial effects in a mouse model of Tauopathy. Treatment with J4 not only reduced Tau hyperphosphorylation but also rescued memory deficits, mitochondrial dysfunction, synaptic loss, and abnormal expression of immune-related gene signatures. These beneficial effects were particularly ascribed to the ability of J4 to suppress the overactivation of AMPK (an energy reduction sensor), suggesting that normalization of energy dysfunction mitigates neuronal dysfunctions in Tauopathy. Collectively, these data highlight that targeting adenosine metabolism is a novel strategy for tauopathies.

Genetic manipulation of cyclic nucleotide signaling during hippocampal neuroplasticity and memory formation

Decades of research have underscored the importance of cyclic nucleotide signaling in memory formation and synaptic plasticity. In recent years, several new genetic techniques have expanded the neuroscience toolbox, allowing researchers to measure and modulate cyclic nucleotide gradients with high spatiotemporal resolution. Here, we will provide an overview of studies using genetic approaches to interrogate the role cyclic nucleotide signaling plays in hippocampus-dependent memory processes and synaptic plasticity. Particular attention is given to genetic techniques that measure real-time changes in cyclic nucleotide levels as well as newly-developed genetic strategies to transiently manipulate cyclic nucleotide signaling in a subcellular compartment-specific manner with high temporal resolution.

Adenosine Augmentation Evoked by an ENT1 Inhibitor Improves Memory Impairment and Neuronal Plasticity in the APP/PS1 Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive impairment and synaptic dysfunction. Adenosine is an important homeostatic modulator that controls the bioenergetic network in the brain through regulating receptor-evoked signaling pathways, bioenergetic machineries, and epigenetic-mediated gene regulation. Equilibrative nucleoside transporter 1 (ENT1) is a major adenosine transporter that recycles adenosine from the extracellular space. In the present study, we report that a small adenosine analogue (designated J4) that inhibited ENT1 prevented the decline in spatial memory in an AD mouse model (APP/PS1). Electrophysiological and biochemical analyses further demonstrated that chronic treatment with J4 normalized the impaired basal synaptic transmission and long-term potentiation (LTP) at Schaffer collateral synapses as well as the aberrant expression of synaptic proteins (e.g., NR2A and NR2B), abnormal neuronal plasticity-related signaling pathways (e.g., PKA and GSK3β), and detrimental elevation in astrocytic A_2AR expression in the hippocampus and cortex of APP/PS1 mice. In conclusion, our findings suggest that modulation of adenosine homeostasis by J4 is beneficial in a mouse model of AD. Our study provides a potential therapeutic strategy to delay the progression of AD.

GSK3β negatively regulates TRAX, a scaffold protein implicated in mental disorders, for NHEJ-mediated DNA repair in neurons

Translin-associated protein X (TRAX) is a scaffold protein with various functions and has been associated with mental illnesses, including schizophrenia. We have previously demonstrated that TRAX interacts with a Gsα protein-coupled receptor, the A_2A adenosine receptor (A_2AR), and mediates the function of this receptor in neuritogenesis. In addition, stimulation of the A_2AR markedly ameliorates DNA damage evoked by elevated oxidative stress in neurons derived from induced pluripotent stem cells (iPSCs). Here, we report that glycogen synthase kinase 3 beta (GSK3β) and disrupted-in-schizophrenia 1 (DISC1) are two novel interacting proteins of TRAX. We present evidence to suggest that the stimulation of A_2AR markedly facilitated DNA repair through the TRAX/DISC1/GSK3β complex in a rat neuronal cell line (PC12), primary mouse neurons, and human medium spiny neurons derived from iPSCs. A_2AR stimulation led to the inhibition of GSK3β, thus dissociating the TRAX/DISC1/GSK3β complex and facilitating the non-homologous end-joining pathway (NHEJ) by enhancing the activation of a DNA-dependent protein kinase via phosphorylation at Thr²⁶⁰⁹. Similarly, pharmacological inhibition of GSK3β by SB216763 also facilitated the TRAX-mediated repair of oxidative DNA damage. Collectively, GSK3β binds with TRAX and negatively affects its ability to facilitate NHEJ repair. The suppression of GSK3β by A_2AR activation or a GSK3β inhibitor releases TRAX for the repair of oxidative DNA damage. Our findings shed new light on the molecular mechanisms underlying diseases associated with DNA damage and provides a novel target (i.e., the TRAX/DISC1/GSK3β complex) for future therapeutic development for mental disorders.