Dual-Hit: Glyphosate exposure at NOAEL level negatively impacts birth and glia-behavioural measures in heterozygous shank3 mutants

The omnipresence of environmental contaminants represents a health danger with ramifications for adverse neurological trajectories. Here, we tested the dual-hit hypothesis that continuous exposure to non-observable adverse effect level (NOAEL) glyphosate from pre-natal to adulthood represents a risk factor for neurological-associated adaptations when in the presence of the heterozygote or homozygote mutation of the Shank3 synaptic gene.Ultrasound analysis of pregnant dams revealed patterns of pre-natal mortality with effects dependent on wild-type, Shank3(Delta C/+), or Shank3(Delta C/Delta C) genotypes exposed to NOAEL glyphosate (GLY) compared to unexposed conditions. The postnatal survival rate was negatively impacted, specifically in Shank3(Delta C/+) exposed to GLY. Next, the resulting six groups of pups were tracked into adulthood and analyzed for signs of neuroinflammation and neurological adaptions. Sholl's analysis revealed cortical microgliosis across groups exposed to GLY, with Shank3(Delta C/+) mice presenting the most significant modifications. Brain tissues were devoid of astrocytosis, except for the perivascular compartment in the cortex in response to GLY. Distinct behavioral adaptations accompanied these cellular modifications, as locomotion and social preference were decreased in Shank3(Delta C/+) mice exposed to GLY. Notably, GLY exposure from weaning did not elicit glial or neurological adaptations across groups, indicating the importance of pre-natal contaminant exposure.These results unveil the intersection between continuous pre-natal to adulthood environmental input and a pre-existing synaptic mutation. In an animal model, NOAEL GLY predominantly impacted Shank3(Delta C/+) mice, compounding an otherwise mild phenotype compared to Shank3(Delta C/Delta C). The possible relevance of these findings to neurodevelopmental risk is critically discussed, along with avenues for future research.