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

Abstract

14Autism spectrum disorder (ASD) etiology is a complex mixture of genetic and 15 environmental factors, the relative contributions of which varies across patients. Despite 16 complex etiology, researchers observe consistent neurodevelopmental features in ASD 17 patients, notably atypical forebrain cortical development. Growth factors, cytokines, and 18 chemokines are important mediators of forebrain cortical development, but have not been 19 thoroughly examined in brain tissues from individuals with autism. Here, we performed an 20 integrative analysis of RNA and protein expression using frontopolar cortex tissues dissected 21 from individuals with ASD and controls, hypothesizing that ASD patients will exhibit aberrant 22 expression of growth factors, cytokines, and chemokines critical for neurodevelopment. We 23 performed group-wise comparisons of RNA expression via RNA-Seq and growth factor, 24cytokine, and chemokine expression via multiplex enzyme-linked immunosorbent assay 25 (ELISA). We also analyzed single cell sequencing data from the frontopolar cortex of typically 26 developed individuals to identify cell types that express the growth factors we found differentially 27 expressed in ASD. Our RNA-Seq analysis revealed 11 differentially expressed genes in ASD 28 versus control brains, the most significant of which encodes for vascular endothelial growth 29 factor (VEGF-A). Both RNA and protein levels of VEGF-A were upregulated in ASD brains. Our 30 single cell analysis revealed that VEGF is expressed primarily by non-neuronal cells. We also 31 found that the differentially expressed genes from our RNA-Seq analysis are enriched in 32 microglia. The increased VEGF-A expression we observed in ASD, coupled with the enrichment 33 of differentially expressed genes in microglia, begs the question of the role VEGF-A is playing in 34 ASD. Microglia activation, as indicated by our RNA-Seq results, and the VEGF-A isoform 35 expression we see in the ASD cortex, leads us to conclude that VEGF-A is playing a pro-36 inflammatory role, perhaps with unwanted long-term consequences for neurodevelopment.