RNA-seq analysis of the rat placentation site reveals maternal obesity-associated changes in placental and offspring thyroid hormone signaling.

INTRODUCTION: In animal models, maternal obesity (OB) leads to augmented risk of offspring OB. While placental function is influenced by maternal habitus, the effect of maternal obesity on the interacting zones of the placenta [the labyrinth (LZ), junctional (JZ) and metrial gland (MG)] remains unknown. METHODS: Using a rat maternal obesity model, we conducted transcriptomic profiling of the utero-placental compartments and fetal liver (FL) at dpc 18.5, in conjunction with analyses of mRNA expression of key thyroid hormone (TH) signaling genes in the placenta, fetus and weanling offspring. RESULTS AND DISCUSSION: Gene expression analysis of placenta and offspring revealed that each utero-placental compartment responds distinctly to maternal OB with changes in inflammatory signaling, lipid metabolism and hormone stimulus being the predominant effects. OB-induced alterations in 17 genes were confirmed by qPCR, including reductions in thyrotropin-releasing hormone (Trh) in JZ. We further characterized mRNA and protein expression of TH signaling regulators including deiodinases (Dio), TH receptors (Tr), and downstream targets (uncoupling proteins (Ucp)). A concerted down-regulation of multiple facets of thyroid hormone signaling in the JZ and FL was observed. JZ expression of thyroid hormone signaling components Trh, Dio2, Trα, and Ucp2 were negatively associated with maternal leptin. mRNA expression of TRH, TRß and UCP1 were also decreased in term placenta from OB women. Finally, our studies identified persistent impairments in expression of TH related genes in tissues from offspring of obese dams. CONCLUSIONS: The role of lower placental thyroid expression is worthy of further study as a possible pathway that leads to low energy metabolism and obesity in animals born to obese mothers.

Maternal obesity is associated with a lipotoxic placental environment.

Maternal obesity is associated with placental lipotoxicity, oxidative stress, and inflammation, where MAPK activity may play a central role. Accordingly, we have previously shown that placenta from obese women have increased activation of MAPK-JNK. Here, we performed RNA-sequencing on term placenta from twenty-two subjects who were dichotomized based on pre-pregnancy BMI into lean (BMI 19-24 kg/m(2); n = 12) and obese groups (BMI, 32-43 kg/m(2); n = 12). RNA-seq revealed 288 genes to be significantly different in placenta from obese women by ≥ 1.4-fold. GO analysis identified genes related to lipid metabolism, angiogenesis, hormone activity, and cytokine activity to be altered in placenta from obese women. Indicative of a lipotoxic environment, increased placental lipid and CIDEA protein were associated with decreased AMPK and increased activation of NF-κB (p65) in placenta from obese women. Furthermore, we observed a 25% decrease in total antioxidant capacity and increased nuclear FOXO4 localization in placenta from obese women that was significantly associated with JNK activation, suggesting that maternal obesity may also be associated with increased oxidative stress in placenta. Maternal obesity was also associated with decreased HIF-1α protein expression, suggesting a potential link between increased inflammation/oxidative stress and decreased angiogenic factors. Together, these findings indicate that maternal obesity leads to a lipotoxic placental environment that is associated with decreased regulators of angiogenesis and increased markers of inflammation and oxidative stress.

A comprehensive analysis of the human placenta transcriptome.

As the conduit for nutrients and growth signals, the placenta is critical to establishing an environment sufficient for fetal growth and development. To better understand the mechanisms regulating placental development and gene expression, we characterized the transcriptome of term placenta from 20 healthy women with uncomplicated pregnancies using RNA-seq. To identify genes that were highly expressed and unique to the placenta we compared placental RNA-seq data to data from 7 other tissues (adipose, breast, hear, kidney, liver, lung, and smooth muscle) and identified several genes novel to placental biology (QSOX1, DLG5, and SEMA7A). Semi-quantitative RT-PCR confirmed the RNA-seq results and immunohistochemistry indicated these proteins were highly expressed in the placental syncytium. Additionally, we mined our RNA-seq data to map the relative expression of key developmental gene families (Fox, Sox, Gata, Tead, and Wnt) within the placenta. We identified FOXO4, GATA3, and WNT7A to be amongst the highest expressed members of these families. Overall, these findings provide a new reference for understanding of placental transcriptome and can aid in the identification of novel pathways regulating placenta physiology that may be dysregulated in placental disease.