OS055. Sex-dependent differences in expression of FLT-1 variants andJMJD6 in mouse placenta.

INTRODUCTION: There is evidence for fetal sex-dependent differences in the way in which preeclamptic pregnancies proceed, and in maternal and neonatal outcomes. Mouse models are common in the study of preeclampsia and pooled tissue from multiple placentae is often used to obtain samples for expression studies. Potential concerns regarding this practice are the sex-dependent differences in placental expression of candidate factors. One biomolecule of interest is soluble fms-like tyrosine kinase 1 (sFLT-1) which is a known marker of preeclampsia and commonly used to determine the severity of the induced preeclampsia-like syndrome in rodent models.

OBJECTIVES: It was the aim of this preliminary study to determine whether variation exists in the expression of different genes in murine placenta based on pup sex in C57BL/6JArc mice. A novel gene, Jumonji domain-containing protein 6 (Jmjd6) that may prove to have a role in the pathogenesis of preeclampsia, mFLT-1 and sFLT-1 were selected as targets.

METHODS: Seventeen pups were retrieved from three normal pregnant female mice euthanized via cervical dislocation (CD) on day 17.5 or 18.5. Tails and corresponding placentas were collected from the pups, snap frozen in liquid nitrogen and stored at -80°C. Tails were used to accurately determine pup sex via PCR amplification of sex chromosome-specific sequences and revealed the presence of 3 females and 14 males. Quantitative PCR was used to determine the relative expression of the FLT-1 and Jmjd6 transcripts in each placenta. The placenta collected from the first pup of the first pregnant female served as the reference sample and transcript expression in the remaining samples was expressed relative to this sample. General linear modelling using linear regression with categorical variables was used to evaluate the difference in transcript expression between the sexes and Pearson's correlation coefficient used to examine relationships between variables.

RESULTS: Pup sex was found to have a significant effect on the relative expression of sFLT-1 after controlling for litter, pup weight and gestational age (p=0.013), with 1.5 times more expression in the placentas of female pups. The expression of sFLT-1 was highly correlated with mFLT-1 (r=0.690,p=0.002). The relative expression of Jmjd6 was not significantly different in male and female placentas and sFlt-1 was not correlated with Jmjd6.

CONCLUSION: This is the first study to demonstrate a link between fetal sex and placental sFLT-1 expression in mice, finding increased levels of this gene in the placentas of female pups. It is possible that in normal pregnancies, female placentas produce more sFLT-1 which acts to condition them and offer some protection during the sFLT-1 spike seen in preeclampsia. The findings of this study also highlight a possible need to consider sex as a variable in placental expression studies using mice to ensure the accuracy of results.