Distinctive differentiation and synaptic profiles of hippocampal neurons in the VPA rat model of autism

CODAGNONE MARTIN; REINÉS ANALÍA; UCCELLI NONTHUE; TRAETTA MARIANELA; ZÁRATE SANDRA

Buenos Aires

Congreso; 3rd International Congress of Translational Medicine; 2016

Universidad de Buenos Aires

Autism spectrum disorders (ASD) are characterized by impairments in social interaction and stereotyped behaviors. Although the molecular basis remains unclear, alterations in adhesion molecules and other synaptic proteins were reported in ASD patients. Prenatal exposure to valproic acid (VPA), a well validated ASD animal model, mimics the main behavioral and neuroanatomical alterations found in these disorders. Regarding the cellular and molecular changes seen in the hippocampus of VPA rats, we previously reported a decrease in synaptic protein synaptophysin (SYN) and the polysialylated form of the neural cell adhesion molecule (PSA-NCAM). We hypothesized that prenatal VPA exposure may modify neuronal differentiation and/or synaptic formation and maturation either directly by epigenetic changes or indirectly through mechanisms involving other cells. Therefore, we tested whether in vitro postnatal hippocampal neurons from VPA rats show similar synaptic and PSA-NCAM expression patterns as those observed in vivo. An in vitro approach was performed by culturing hippocampal neurons from P1-P2 rat pups after in utero (E 10.5) VPA (500 mg/kg) or saline exposure. In order to study neuronal differentiation and synaptic formation, a time course was performed by fixing neurons at different days in vitro (DIV). During early neuronal differentiation in vitro (DIV 3-5), SYN immunostaining was increased in the VPA group. Notably, neurons from this group showed increased actin immunostaining accompanied with abundant dendritic and axonal filopodia. Not all synaptic proteins were increased since PSD-95 levels were lower than in control neurons. Later in culture (DIV 14), in the VPA group, a reduction was found both in SYN puncta area and number as well as a decrease in PSA-NCAM immunoreactivity. Furthermore, labeling of presynaptic boutons with FM4-64 dye revealed a diminution of functional synapses in the VPA group at this same stage. To sum up, we observed deep changes in hippocampal postnatal neurons from VPA animals which correlate with in vivo findings. Our results suggest that the early increase in SYN expression and actin sprouting might well represent a mechanism to promote synapse formation and those changes in neuronal programming may underlie the distinctive synaptic and differentiation profiles in the hippocampus of VPA animals.