# Secondhand Smoke Exposure Timing Triggers Distinct Placental Responses in Mouse Pregnancy

## TL;DR

Exposure to secondhand smoke during different stages of mouse pregnancy causes unique placental gene expression changes linked to complications like preeclampsia and growth restriction.

## Contribution

The study reveals that the timing of secondhand smoke exposure during pregnancy leads to distinct placental gene regulation patterns in mice.

## Key findings

- SHS exposure after spiral artery invasion increases inflammation-related genes and reduces complement activation pathway genes.
- SHS exposure before spiral artery invasion lowers collagen-related genes and increases cell lysis-related genes.
- Most differentially expressed genes from SHS exposure have been previously reported, but few are linked to preeclampsia or IUGR.

## Abstract

Secondhand smoke (SHS), found in about 57.6% of global public areas as a widespread environmental hazard, has been associated with negative effects during pregnancy, such as preeclampsia (PE) and intrauterine growth restriction (IUGR). Our research investigated the impact of SHS on placental issues in a C57BL/6 model that simulates PE and IUGR in mice. We administered SHS to pregnant mice through a nose-only delivery method, beginning either on embryonic day 12.5 (prior to spiral artery (SA) invasion; labeled SHS-6D) or day 14.5 (following SA invasion; labeled SHS-4D), continuing up to E18.5. Control animals received only ambient air. We employed bulk RNA sequencing to assess and describe changes in placental gene expression patterns. For the SHS-4D group, which mimicked IUGR, compared to untreated controls, results showed elevated levels of inflammation-related genes (IL11RA, CHI3L1) alongside likely interference in pathways for antibody-triggered complement activation, marked by reduced expression of C1QA, C1QB, and C1QC. Immune profiling also indicated decreased macrophage activity in the placentas of the SHS-4D group relative to those from normal pregnancies at term. In contrast, the SHS-6D versus control analysis revealed lowered expression of collagen-related genes (COL1A1, COL4A5, COL4A6, COL17A1). Additionally, SHS-6D exhibited higher levels of genes associated with cell-based lysis processes compared to SHS-4D. An evaluation of the existing literature revealed that nearly every differentially expressed gene (DEG) identified in our work has been reported in studies associated with SHS exposure. Yet, few of these DEGs are discussed alongside PE or IUGR in prior reports, highlighting gaps in knowledge about how SHS triggers these conditions. Overall, we determined that the timing of SHS exposure in pregnant mice results in unique patterns of gene regulation and involvement in biological pathways.