Expression Profile of VEGF and VEGFR2 in the Female Reproductive Tract at the Time of Placentation in a Porcine Model of Von Willebrand Disease Type 1

Objectives: Clinical studies showed that women affected by von Willebrand disease (VWD) trend towards higher rates of miscarriages, but the underlying pathomechanisms remain unclear. Several in vitro studies demonstrated an influence of von Willebrand factor (VWF) on angiogenesis, which seems to be partly mediated via VEGF. Since angiogenesis in the reproductive organs is essential to establish and maintain pregnancy, we aimed to investigate gene expression of VWF, VEGF, and its receptor VEGFR2 in non-pregnant and pregnant individuals, using a porcine model of VWD type 1.

Methods: Tissue samples of uterus, oviduct and ovary were harvested from eight female pigs of which four were pregnant on day 30 (time of placentation) and four were non-pregnant and in estrus. Of each group, two were affected by VWD type 1 and two were wildtype (WT) individuals. The gene expression of VWF, VEGF, and VEGFR2 was measured by qRT-PCR and relatively quantified against the endothelial specific housekeeping genes PROCR and CD31 using the ΔΔC_T method and calculating the respective x-fold changes. The gene expression differences were compared between both genotypes as well as between both reproductive states Mean differences were taken into account, if the divergences were consistent in both individuals of each group and not within the range of the group they were compared to.

Results: Regarding the non-pregnant sows, VWF expression was lower in uterus and ovary of the VWD type 1 animals. This difference was not seen comparing the pregnant animals of each genotype, but the VWD type 1 animals showed higher VEGF expression in oviduct and higher VEGF and VEGFR2 expression in the ovary. The expression of VEGFR2 was reduced in the uterus. Comparing the non-pregnant with the pregnant animals within each genotype, the following results were found: the pregnant WT pigs showed increased expression of VEGFR2 in uterus and ovary, but decreased expression of VEGF in the uterus. For the pregnant VWD type 1 animals increased expression was found for VWF and VEGFR2 in the ovary, and decreased expression for VEGF in uterus and oviduct and VEGFR2 in the uterus.

Discussion and Conclusion: Comparison of the different groups revealed differences of gene expression in the female reproductive tract during early pregnancy. The expectedly lower expression of VWF in the VWD type 1 animals was not found for the pregnant animals. Apparently, there is an increase of VWF levels during pregnancy as seen in women. While VEGFR2 expression in the uterus increases during placentation in the WT animals, it decreases in the VWD type 1 animals. This suggests altered regulation of early angiogenesis, which is essential during placentation. Expression of VEGF and VEGFR2 was increased in the ovaries of the VWD type 1 animals. This points to an enhanced involvement of this pathway during conversion of the ruptured follicles to sufficient corpora lutea graviditates, which may affect this process. Enhanced angiogenesis via the VEGF/VEGFR2-pathway due to lack of VWF was already shown in vitro. Our study shows that the expression of VEGF and VEGFR2 differs during early pregnancy in VWD type 1 compared to wildtype sows. Therefore, this pathway may influence angiogenesis in the reproductive tract.