Alterations of GABAergic Neuron-Associated Extracellular Matrix and Synaptic Responses in Gad1-Heterozygous Mice Subjected to Prenatal Stress.

Tianying Wang,Atsuo Fukuda,Yuchio Yanagawa,Tenpei Akita,Adya Saran Sinha

doi:10.3389/fncel.2018.00284

Tianying Wang, Atsuo Fukuda + Show 3 more

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https://doi.org/10.3389/fncel.2018.00284

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Abstract

Exposure to prenatal stress (PS) and mutations in Gad1, which encodes GABA synthesizing enzyme glutamate decarboxylase (GAD) 67, are the primary risk factors for psychiatric disorders associated with abnormalities in parvalbumin (PV)-positive GABAergic interneurons in the medial prefrontal cortex (mPFC). Decreased expression of extracellular matrix (ECM) glycoproteins has also been reported in patients with these disorders, raising the possibility that ECM abnormalities may play a role in their pathogenesis. To elucidate pathophysiological changes in ECM induced by the gene–environment interaction, we examined heterozygous GAD67-GFP (Knock-In KI; GAD67+/GFP) mice subjected to PS from embryonic day 15.0 to 17.5. Consistent with our previous study, we confirmed a decrease in the density of PV neurons in the mPFC of postnatal GAD67+/GFP mice with PS, which was concurrent with a decrease in density of PV neurons surrounded by perineuronal nets (PNNs), a specialized ECM important for the maturation, synaptic stabilization and plasticity of PV neurons. Glycosylation of α-dystroglycan (α-DG) and its putative mediator fukutin (Fktn) in the ECM around inhibitory synapses has also been suggested to contribute to disease development. We found that both glycosylated α-DG and the mRNA level of Fktn were reduced in GAD67+/GFP mice with PS. None of these changes were detected in GAD67+/GFP naive mice or wild type (GAD67+/+) mice with PS, suggesting that both PS and reduced Gad1 gene expression are prerequisites for these changes. When assessing the function of interneurons in the mPFC of GAD67+/GFP mice with PS through evoked inhibitory post-synaptic currents (eIPSCs) in layer V pyramidal neurons, we found that the threshold stimulus intensity for eIPSC events was reduced and that the eIPSC amplitude was increased without changes in the paired-pulse ratio (PPR). Moreover, the decay rate of eIPSCs was also slowed. In line with eIPSC, spontaneous IPSC (sIPSC) amplitude, frequency and decay tau were altered. Thus, our study suggests that alterations in the ECM mediated by gene-environment interactions might be linked to the enhanced and prolonged GABA action that compensates for the decreased density of PV neurons. This might be one of the causes of the excitatory/inhibitory imbalance in the mPFC of psychiatric patients.

Highlights

Prenatal stress (PS) is a risk factor that can change the trajectory of fetal brain development and have long-term effects on adult brain function, which may result in psychiatric disorders like autism spectrum disorder (ASD), depression and schizophrenia (Bock et al, 2015)
To ascertain the alterations in GABAergic signaling as a consequence of changes in specialized extracellular matrix (ECM) components associated with GABAergic synapses in our model, we examined the evoked inhibitory post-synaptic currents (eIPSCs) characteristics in GAD67+/GFP mice with or without PS
Our findings show alterations of GABA neuronassociated ECM in the medial prefrontal cortex (mPFC), i.e., decreased Perineuronal nets (PNNs) densities along with the loss of PV neurons and decrease in the glycosylation of α-DG in GAD67+/GFP offsprings subjected to PS

Summary

Introduction

Prenatal stress (PS) is a risk factor that can change the trajectory of fetal brain development and have long-term effects on adult brain function, which may result in psychiatric disorders like autism spectrum disorder (ASD), depression and schizophrenia (Bock et al, 2015). To determine whether PS and GABA reduction may interact and worsen neural development, we previously examined (GAD67-green fluorescent protein (GFP) Knock-In (KI) GAD67+/GFP) mice, in which one Gad gene is replaced with the GFP gene to reduce GABA production by half (Tamamaki et al, 2003; Wang et al, 2009). Using these mice, we reported that the application of restraint PS through mother mice suppressed the neurogenesis of GABAergic neurons in the medial ganglionic eminence (MGE) of GAD67+/GFP embryos. The mechanism of interaction between PS and GABA reduction during development that causes PV interneuron dysfunction has not been elucidated

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