Poor reproductive performance causes economic loss to the dairy industry. Early embryonic mortality is a major component and is at least in part caused by failure of pregnancy recognition (PR). In the cows, PR is initiated by interferon tau (IFNT) released from trophoectoderm of the conceptus acting on the uterine endometrium to 1) inhibit luteolysis via preventing the pulsatile release of prostaglandin (PG) F2α and switching the PG production to PGE2 and 2) stimulate expression of type I interferon stimulated genes (ISGs). This creates a receptive environment for implantation. There is strong evidence to suggest that bovine viral diarrhoea viral (BVDV) is one of the potential causes of PR failure. We hypothesized that BVDV infection disrupts PR via altering PG and ISG signalling pathways in the uterus. We established an in vitro PR model in which bovine uterine endometrial cells from healthy cyclic cows were cultured and treated with 0 or 100 ng/ml IFNT for 24 hours in the presence or absence of non-cytopathic (ncp) BVDV infection. We investigated activation of the pathways involved in maternal PR. The results showed that the effect of BVDV alone on the pathways tested were moderate while it significantly inhibited the pathways activated by IFNT. In the oxytocin-PG signalling pathway, IFNT challenge significantly stimulated PTGS1 and PTGER3 expression and PGE2 production whereas these stimulatory effects were neutralised in the presence of ncpBVDV infection. Both IFNT and BVDV did not significantly affect expression of PGR, OXTR and ESR1 mRNA. In the uterine ISG signalling pathway, IFNT treatment alone significantly increased expression of all 17 ISGs tested. In contrast to the limited effect of ncpBVDV alone, the virus significantly inhibited IFNT-stimulated expression of 15 ISGs (ISG15, HERC5, USP18, DDX58, IFIH1, IFIT1, IFIT3, BST2, MX1, MX2, RSAD2, OAS1Y, SAMD9, GBP4 and PLAC8). For the upstream ISG regulatory pathway – interferon regulatory factors and signal transducer and activator of transcription (STAT) 1 and 2, IFNT significantly stimulated the expression of STAT1, STAT2, IRF9, IRF7 and TYK2 mRNA, however, in the presence of ncpBVDV infection, the IFNT induced expression of STAT1, STAT2, IRF9 and TYK2 was significantly suppressed. We tested ISG15 and STAT2 proteins and their IFNT-stimulation and BVDV-inhibition patterns were consistent with their genes. This suggests that ncpBVDV infection inhibits activation of the pathways required by successful PR, which may lead to PR failure and embryonic mortality.
Dr Zhangrui Cheng received his BSc and MSc in veterinary medicine in Hunan Agricultural University and Beijing Agricultural Universities, respectively, and PhD in veterinary pharmacology and therapeutics in Glasgow University, UK. He joined Royal Veterinary College (RVC), University of London as a postdoctoral research assistant in 1997. He is now a research fellow employed on permanent basis in RVC. His research interests include reproductive physiology and infection, bioinformatics and antimicrobial pharmacology. He has published over 80 papers in the peer-reviewed journals, including 8 recent publications about effect of BVDV infection on reproductive function.