Effect of PRRSV2 on tight junctions in the porcine maternal-fetal interface

Abstract

Existing strategies to control porcine reproductive and respiratory syndrome (PRRS) are not completely effective and require alternative approaches. Although intrauterine growth restricted (IUGR) fetuses are more resilient to transplacental PRRS virus-2 (PRRSV2) infection compared to normal fetuses, the underlying mechanisms are unknown. The overall aim of this research was to assess a subset of tight junction (TJ) proteins in the maternal-fetal interface (MFI) of PRRSV-infected versus control fetuses, across various fetal preservation statuses including uninfected (UNIF) and viable (VIA) and meconium stained (MEC), and in IUGR and non (N)- IUGR fetuses. The specific objectives of chapter 2 were to evaluate the abundance and localization of a small subset of TJ proteins in the MFI of non-infected control (CTRL), and in PRRSV2 infected IUGR, N-IUGR and MEC fetuses and identify any alterations that may affect the movement of nutrients or PRRSV2 across the epitheliochorial placenta. Expanding on these results, the objective of chapter 3 was to evaluate the expression of a larger number of TJ genes in the placenta and endometrium of PRRSV2-infected fetuses, firstly across IUGR/N-IUGR and CTRL/PRRSV2-infected high viral load (HVL) groups using a 2 x 2 factorial approach, and secondly across disease progression groups by comparing CTRL, UNIF, HVL-VIA fetuses, and HVL MEC in the body (HVL-MEC-B) fetuses. In non-infected CTRL, immunostaining for TJP1 was consistent and abundant across all MFI regions, except for maternal and fetal endothelial cells. Immunostaining for claudins (CLDN) 1, 4, and 7 was more variable across the MFI regions. Cellular localization of TJP1 was apical in every region assessed, whereas the claudins were more variable. Immunostaining in the maternal villus base/tip epithelium and areolae had mostly basolateral cellular localization. Fetal villus tip/base, amnion and areolae had mostly paracellular cellular localization, while glandular epithelium and endothelial cells had primarily intracellular cellular localization. In PRRSVinfected fetal groups, the intensity of CLDN1 was lower in placenta of IUGR, MEC, and N-IUGR fetuses compared to CTRL, mainly in fetal epithelium and maternal endothelial cells. CLDN4 intensity was lower in maternal endothelial cells of IUGR compared to CTRL and MEC fetuses. Finally, TJP1 intensity was lower in maternal and fetal epithelia of placenta in IUGR, MEC, and N-IUGR fetuses versus CTRL. In conclusion, these results provided a baseline of cellular localization and intensity of a subset of TJ proteins in the porcine MFI and confirmed changes in the course of infection. Interestingly, only CLDN4 abundance in maternal endothelial cells was significantly different in PRRSV2 infected IUGR fetuses compared to CTRL and MEC fetuses, but it did not differ from N-IUGR fetuses. In chapter three, the expression of CLDN 1, 3, 4, 5, 6, 7, 10, TJP1 and occludin (OCLN) genes were evaluated by PCR. There were no significant group differences among IUGR and NIUGR groups, regardless of infection status, that explained the resilience of IUGR fetuses. Across disease progression groups, elevated CLDN3 and suppressed TJP1 were observed in UNIF fetuses, CLDN6 expression was lower in PLC when the fetus became infected (HVL-VIA), and CLDN10 expression was upregulated in PLC in fetuses showing evidence of compromise (HVL-MEC-B). Lastly, OCLN gene expression was higher in the END and PLC following maternal infection. In conclusion, no relationship between TJ abundance or expression and IUGR resilience were found following PRRSV infection. However, differences in TJ integrity were observed following PRRSV2 infection with stepwise changes corresponding with disease progression. These results provide insights into the potential mechanisms of transplacental PRRSV2 pathogenesis.