Impact of Reduced ASIC2a on Cortical Thickness, Microglia Density, and Brain Water Content in E18.5 Fetuses

Abstract

Acid‐sensing Ion Channels (ASICs) are ligand‐gated cation channels that respond to acidic stimuli. ASIC2 is widely expressed in neurons of the central and peripheral nervous system as well as on microglia. Although ASIC2 plays a role in cell migration, their role in brain development is not fully known. We tested the hypothesis that reduction or absence of ASIC2a contributes to changes in microglia density, cortical thickness, and brain water content during development. Brains were collected from ASIC2a wild type (WT, n=6), heterozygous (HET, n=4), and homozygous (HOMO, n=3) fetuses at E18.5. We used hematoxylin & eosin (H&E) staining for cortical thickness measurements, immunofluorescence staining using ionized calcium‐binding adapter molecule (Iba‐1) to measure microglia density, and wet weight to dry weight ratio for brain water content. Reduction of ASIC2a had no impact on cortical thickness (WT=499±21, HET=509±7, and HOMO=478±21 μm; p=0.60) or microglia density in the subventricular zone near the lateral ventricle (WT=22±2, HET=18±2, and HOMO=24±3; p=0.34) at E18.5. Interestingly, microglia morphology in HET fetuses were different compared to WT and HOMO mice with thinner and longer processes. Brain water content increased in HOMO mice (88.2±0.7%) compared to WT (86.5±0.3%, p<0.01) and HET (86.8±0.2%, p=0.02) fetuses. Our results indicate that while reduced ASIC2a does not contribute to changes in microglia density or cortical thickness in E18.5 mouse fetuses, reduced ASIC2a induces morphological changes in microglia and ASIC2 knockout increases brain water content at E18.5. Increased brain water content could be an indicator of hydrocephalus. In ongoing studies, we are determining whether reduced ASIC2a mediates structural and functional impairments in the neurovasculature of the maternal and developing brain.Support or Funding InformationNIH Grants: R00HL129192, R00HL129192‐S1