Long-Lasting Changes in Glial Cells Isolated From Rats Subjected to the Valproic Acid Model of Autism Spectrum Disorder.

Marianela Evelyn Traetta,Alberto Javier Ramos,Sandra Cristina Zárate,Dante Gómez Cuautle,Nonthué Alejandra Uccelli,Analía Reinés

doi:10.3389/fphar.2021.707859

Abstract

Synaptic alterations concomitant with neuroinflammation have been described in patients and experimental models of autism spectrum disorder (ASD). However, the role of microglia and astroglia in relation to synaptic changes is poorly understood. Male Wistar rats prenatally exposed to valproic acid (VPA, 450 mg/kg, i.p.) or saline (control) at embryonic day 10.5 were used to study synapses, microglia, and astroglia in the prefrontal cortex (PFC) at postnatal days 3 and 35 (PND3 and PND35). Primary cultures of cortical neurons, microglia, and astroglia isolated from control and VPA animals were used to study each cell type individually, neuron-microglia and microglia-astroglia crosstalk. In the PFC of VPA rats, synaptic changes characterized by an increase in the number of excitatory synapses were evidenced at PND3 and persisted until PND35. At PND3, microglia and astroglia from VPA animals were morphologically similar to those of age-matched controls, whereas at PND35, reactive microgliosis and astrogliosis were observed in the PFC of VPA animals. Cortical neurons isolated from VPA rats mimicked in vitro the synaptic pattern seen in vivo. Cortical microglia and astroglia isolated from VPA animals exhibited reactive morphology, increased pro-inflammatory cytokines, and a compromised miRNA processing machinery. Microglia from VPA animals also showed resistance to a phagocytic challenge. In the presence of neurons from VPA animals, microglia isolated from VPA rats revealed a non-reactive morphology and promoted neurite outgrowth, while microglia from control animals displayed a reactive profile and promoted dendritic retraction. In microglia-astroglia co-cultures, microglia from VPA animals displayed a reactive profile and exacerbated astrocyte reactivity. Our study indicates that cortical microglia from VPA animals are insensitive or adapted to neuronal cues expressed by neurons from VPA animals. Further, long-term in vivo microgliosis could be the result of altered microglia-astroglia crosstalk in VPA animals. Thus, our study highlights cortical microglia-astroglia communication as a new mechanism implicated in neuroinflammation in ASD; consequently, we propose that this crosstalk is a potential target for interventions in this disorder.

Highlights

Autism spectrum disorder (ASD) is a developmental condition characterized by social and communication deficits and restricted, repetitive patterns of behavior, interests, or activities (American Psychiatric Association, 2013)
Microglia isolated from valproic acid (VPA) animals did not show a statistically significant morphological response after exposure to synaptic terminals (Figures 4J,K), even when these cells increased their circularity in response to LPS (Figure 3H). These results indicate that cortical microglia isolated from VPA animals cannot alter synapse number when co-cultured with neurons and show resistance to the phagocytic stimulus by synaptosomes
This study provides evidence of long-lasting microglia and astroglia changes induced by prenatal exposure to VPA and suggests microglia-astroglia crosstalk as a key process implicated in neuroinflammation described for ASD

Summary

Introduction

Autism spectrum disorder (ASD) is a developmental condition characterized by social and communication deficits and restricted, repetitive patterns of behavior, interests, or activities (American Psychiatric Association, 2013). ASD neurobiology includes genetic and environmental factors (De Rubeis et al, 2014; Modabbernia et al, 2017). Several largescale genetic studies have highlighted many genes as risk factors for ASD pathogenesis (Sebat et al, 2007; Anney et al, 2010; De Rubeis et al, 2014; Iossifov et al, 2014). Given that affected genes are linked to synaptic function and plasticity (Bourgeron, 2015; Lin et al, 2016) and structural dendritic and synaptic alterations were described in ASD, this disorder has been proposed to be a synaptopathy (Guang et al, 2018)

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