Maternal High Fat Diet and Acute Viral Mimic Exposure Impact Placental Inflammation, Lipid Peroxidation, and Cellular Dynamics Across Mouse Pregnancy

Maternal obesity and viral infection induce placental inflammation, but how their co-exposure influence fetoplacental development remains unclear. We hypothesized that maternal high fat (HF) diet and viral infection would independently induce placental inflammation and lipid peroxidation, while reducing antioxidant defence, and cellular turnover. Further, HF diet would compromise the placenta’s capacity to adapt to a secondary stressor, which would exacerbate these effects. Female C57BL/6J mice were fed a control (CON) or 62% HF diet six weeks before and throughout pregnancy and injected with the viral mimic, poly(I:C) or vehicle (VEH) 24h before sacrifice at gestational days (GD) 12.5, 15.5, and 18.5 (n=5–8/group/GD). Placental inflammasome (NLRP3), oxidative stress (4-HNE), antioxidant defence (GPx-4), and cellular turnover (Ki-67, Caspase-3) were assessed by immunohistochemistry quantifying immunoreactive (ir) expression levels. mRNA expression of inflammatory mediators ( Tlr3, Irf3, Tlr4, Tirap , and Il-1β ) were measured by qPCR. Data were analysed by generalized linear mixed models (p<0.05). At GD12.5, infection, but not HF diet, was associated with increased Tlr3 mRNA and ir-4-HNE, and reduced ir-GPx-4 expression in the placental labyrinth zone (LZ). By GD15.5, HF diet was associated with increased ir-NLRP3 in both LZ and junctional zones (JZ), with co-exposure to HF diet and infection further increasing LZ ir-NLRP3. At GD18.5, HF diet, but not viral infection, was associated with increased Tirap and Il-1β mRNA expression, ir-4-HNE in the JZ and ir-Caspase-3 in the LZ. Together, these findings show that maternal HF diet and infection exert distinct yet interacting effects on the placenta across gestation. Their combined exposure can amplify inflammatory and oxidative pathways, suggesting that maternal overnutrition reduces the placenta’s capacity to handle adverse exposures, which may increase susceptibility to poor fetal outcomes.