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

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.

Head-to-Head Study of Developmental Neurotoxicity and Resultant Phenotype in Rats: α-Hexabromocyclododecane versus Valproic Acid, a Recognized Model of Reference for Autism Spectrum Disorders

“…No differences were observed following exposure to VPA or α-HBCDD in comparison to controls. These results are consistent with those of Traetta et al [45] and Bronzuoli et al [44], who also concluded that Iba1 was not affected at PND35 in the VPA model. Subsequently, we examined the glial fibrillary acidic protein (GFAP) and S100-β as markers of astrocytes, known to play a crucial role in brain homeostasis and neuronal and synapse function [53,54].…”

“…This increase was greater for α-HBCDD and was 31% higher than the VPA group (p < 0.05). An increase in this pre-synaptic protein following exposure to VPA was already demonstrated at PND35 in the prefrontal cortex (PFC) of rats [43,45] and more generally in the whole cortex [46]. Here, the α-HBCDD induced increase was even greater than that of VPA, showing a higher number of synapses and/or synaptic vesicles.…”

“…This change was again greater with α-HBCDD, with a 21% difference between VPA and α-HBCDD. Previous studies showed an increase in PSD95 in PFC [45] and cortex [46] following exposure to VPA. Since this marker is involved in glutamatergic transmission, these results suggest an increase in the number of excitatory synapses in the cortex following exposure.…”

“…Neuronal connectivity changes, as well as in glial cells, have been described in different brain regions of the VPA model [43][44][45]. Thus, the expression of synaptic plasticity marker and glial cell proteins was studied by western blot in the cortex of PND21 animals.…”

The Endocannabinoids-Microbiota Partnership in Gut-Brain Axis Homeostasis: Implications for Autism Spectrum Disorders

“…The focus on the immune dysregulation in ASD and the use of models such as MIA and prenatal exposure to VPA, allow us to emphasize the importance of both heritable and environmental factors during critical developmental periods. Interestingly, microglia isolated from animals that underwent the VPA model of ASD showed high reactive morphology and increased resistance to stimulation-induced phagocytosis (Traetta et al, 2021). The postnatal administration of the non-psychoactive phytocannabinoid cannabidivarin (CBDV) in rats underwent prenatal VPA exposure induced a recovery in the hippocampus of both glial fibrillary acidic protein (GFAP) and CD11b expression, as markers of astrocytes and microglia activation, respectively (Zamberletti et al, 2019).…”