Gene–environment interaction in neurodevelopmental disorders: Setd5 haploinsufficiency and prenatal carbon nanoparticle exposure synergistically induce ASD-like phenotypes in male mice

Background Perinatal exposure to fine particles increases the risk of autism spectrum disorder (ASD). Thus, to prevent exposure-related neurodevelopmental disorders, it is crucial to clarify how such particles influence ASD susceptibility. However, replicating ASD-like behaviors in animal models using realistic low-dose particle exposure remains challenging, impeding progress in elucidating the underlying mechanisms. This may be due to insufficient consideration of genetic factors because, unlike genetically uniform laboratory animals, human populations harbor risk variants that complicate ASD pathogenesis. This study focused on the ASD-associated gene Setd5 to evaluate how low-dose prenatal exposure to carbon black nanoparticle (CBNPs; a model of airborne particle) impacts brain development in Setd5 heterozygous knockout ( Setd5 ^+/− ) mice. Specifically, we investigated core social behaviors and parvalbumin-expressing interneurons (PV ⁺ -IN), which have been reported as substantially reduced in the brains of patients with ASD and linked to both particle exposure and Setd5 deficiency. Results To investigate the combined effects of genetic risk and particle exposure on ASD-like phenotypes, pregnant C57BL/6N mice on gestational days 5 and 9 received intranasal CBNP (95 µg/kg), or equivalent ultrapure water. Offspring were genotyped (Wild or Setd5 ^+/− ) and divided into Wild-Control, Wild-CBNP, Setd5 ^+/− -Control, and Setd5 ^+/− -CBNP groups, analyzed separately by sex. Only male offspring with both Setd5 ^+/− and CBNP exposure displayed a significant increase in individuals exhibiting conspicuous ASD-like behavior (i.e., reduced social novelty exploration and excessive fixation on a familiar mouse) accompanied by selective PV ⁺ -IN reduction. Setd5 ^+/− alone or CBNP exposure alone produced minimal behavioral changes, suggesting that subthreshold exposures may elicit ASD-like symptoms if combined with genetic factors. These behavioral and histological abnormalities appeared specifically in males, whereas no significant effects were noted in females. Conclusion This is the first study to assess ASD risk under combined conditions of low-dose particle exposure and a genetic risk. We found that combining Setd5 ^+/− with CBNP exposure robustly induced ASD-like symptoms in male mice, with sex-dependent effects. Additionally, PV ⁺ -IN loss in the prefrontal cortex was identified as a key underlying mechanism. Our findings highlight the importance of considering genetic polymorphisms when evaluating how particulate matter impacts neurodevelopment and suggest potential prevention strategies for particle-induced neurodevelopmental disorders.