Vascular endothelial growth factor (VEGF) expression and neuroinflammation is increased in the frontopolar cortex of individuals with autism spectrum disorder

Abstract

Autism spectrum disorder (ASD) etiology is a complex mixture of genetic and environmental factors, the relative contributions of which varies across patients. Despite complex etiology, researchers observe consistent neurodevelopmental features in ASD patients, notably atypical forebrain cortical development. Growth factors, cytokines, and chemokines are important mediators of forebrain cortical development, but have not been thoroughly examined in brain tissues from individuals with autism. Here, we performed an integrative analysis of RNA and protein expression using frontopolar cortex tissues dissected from individuals with ASD and controls, hypothesizing that ASD patients will exhibit aberrant expression of growth factors, cytokines, and chemokines critical for neurodevelopment. We performed group-wise comparisons of RNA expression via RNA-Seq and growth factor, cytokine, and chemokine expression via multiplex enzyme-linked immunosorbent assay (ELISA). We also analyzed single cell sequencing data from the frontopolar cortex of typically developed individuals to identify cell types that express the growth factors we found differentially expressed in ASD. Our RNA-Seq analysis revealed 11 differentially expressed genes in ASD versus control brains, the most significant of which encodes for vascular endothelial growth factor (VEGF-A). Both RNA and protein levels of VEGF-A were upregulated in ASD brains. Our single cell analysis revealed that VEGF is expressed primarily by non-neuronal cells. We also found that the differentially expressed genes from our RNA-Seq analysis are enriched in microglia. The increased VEGF-A expression we observed in ASD, coupled with the enrichment of differentially expressed genes in microglia, begs the question of the role VEGF-A is playing in ASD. Microglia activation, as indicated by our RNA-Seq results, and the VEGF-A isoform expression we see in the ASD cortex, leads us to conclude that VEGF-A is playing a pro-inflammatory role, perhaps with unwanted long-term consequences for neurodevelopment.