Gestational Exposure to Ultrafine Particles Reveals Sex- and Dose-Specific Changes in Offspring Birth Outcomes, Placental Morphology, and Gene Networks

Abstract

Particulate matter (PM) causes adverse developmental outcomes following prenatal exposure, but the underlying biological mechanisms remain uncertain. Here we elucidate the effects of diesel exhaust ultrafine particle (UFP) exposure during pregnancy on placental and fetal development. Time-mated C57Bl/6n mice were gestationally exposed to UFPs at a low dose (LD, 100 µg/m3) or high dose (HD, 500 µg/m3) for 6 h daily. Phenotypic effects on fetuses and placental morphology at gestational day (GD) of 18.5 were evaluated, and RNA sequencing was characterized for transcriptomic changes in placental tissue from male and female offspring. A significant decrease in average placental weights and crown to rump lengths was observed in female offspring in the LD exposure group. Gestational UFP exposure altered placental morphology in a dose- and sex-specific manner. Average female decidua areas were significantly greater in the LD and HD groups. Maternal lacunae mean areas were increased in the female LD group, whereas fetal blood vessel mean areas were significantly greater in the male LD and HD groups. RNA sequencing indicated several disturbed cellular functions related to lipid metabolism, which were most pronounced in the LD group and especially in female placental tissue. Our findings demonstrate the vulnerability of offspring exposed to UFPs during pregnancy, highlighting sex-specific effects and emphasizing the importance of mitigating PM exposure to prevent adverse health outcomes.

Keywords: air pollution; developmental and reproductive toxicology; gestational exposure; placenta development; ultrafine particulate matter.

Figure 1.

Ultrafine particle characterization showing the size and concentration distributions. A, TEM of the preatomized PM solution. B, TEM of postatomized PM solution. Scale 0.2 µm = 200 nm. C, Low dose (LD) PM particle size (black) and concentration (gray) distribution, with the peak particle diameter of 0.049 µm (49 nm). D, High dose (HD) PM particle size (black) and concentration (gray) distribution, with the peak particle diameter of 0.066 µm (66 nm).

Figure 2.

Gestational exposure to UFPs impacts female offspring placental weight and crown to rump length. A, Average maternal weight gain ± SD across exposure groups. Groups include filtered air (FA) control (n = 6; black line), low dose (n = 6; LD) 100 µg/m³ (blue line), and high dose (n = 5; HD) 500 µg/m³ (red line). No significant differences were observed across groups. B, Fetal weights at GD 18.5 averaged by sex did not differ significantly across exposure groups. C, Average placental weights at GD 18.5 show a significant decrease in the LD female group compared with FA control. D, Average crown to rump lengths at GD 18.5 also show a decrease in the LD female group versus FA control. E, Placenta to fetal weight ratios at GD 18.5 did not vary significantly across exposure groups. Offspring sample sizes include FA male (n = 13), LD male (n = 22), HD male (n = 20), FA female (n = 18), LD female (n = 25), and HD female (n = 24). Error bars represent SD. Data analyzed separately by sex using 1-way ANOVA with Dunnett’s multiple comparison test. *p < .05.

Figure 3.

Gestational exposure to UFPs alters placenta morphology. A, Individual (DC, decidua, SP, spongiotrophoblast, and LB, labyrinth) and total area of placenta layers within each exposure group by offspring sex at GD 18.5. Average female decidua area was significantly greater in the LD and HD groups versus FA control. B, Representative hematoxylin and eosin (H&E)-stained GD 18.5 placenta showing separation by layers. C, Representative H&E-stained GD 18.5 placenta highlighting the labyrinth zone (40×). Arrows indicate fetal vessels whereas dotted outlines indicate maternal lacunae. D, Mean area of maternal lacunae show increase in the female LD group compared with FA control. E, Mean area of fetal blood vessels was significantly greater in the male LD and HD groups versus FA control. Error bars represent SD. Data analyzed separately by sex using 1-way ANOVA with Dunnett’s multiple comparison test. *p < .05; **p < .01; ****p < .0001.

Figure 4.

Volcano plots identifying differentially expressed genes in placenta in response to UFP exposure. Each dot represents an individual gene that each display variance in respect to p value and fold change. The 4 plots indicate the exposure groups by sex, including (A) male LD versus FA, (B) female LD versus FA, (C) male HD versus FA, and (D) female HD versus FA.

Figure 5.

Top canonical pathways as identified by ingenuity pathway analysis (IPA). The 4 plots indicate the exposure groups by sex, including (A) male LD versus FA, (B) female LD versus FA, (C) male HD versus FA, and (D) female HD versus FA.