Role of focal adhesion molecules in maternal recognition of pregnancy in the mare

Abstract Text:

The mechanism responsible for maternal recognition of pregnancy (MRP) in the mare remains unknown.  During early pregnancy the equine conceptus and endometrium communicate to attenuate prostaglandin F2_α(PGF) secretion thus sparing the corpus luteum and maintaining progesterone production. Based on previous experiments we identified focal adhesion molecules (FAM) as potentially playing a key role in this process.  We hypothesize that contact of an embryo with equine endometrium causes (i) a change in FAM transcription and (ii) decrease PGF secretion. We designed an in vitro experiment to test this hypothesis.  Endometrial biopsies were obtained from mares in a crossover design, with each mare providing samples from a pregnant and non-pregnant (non-mated) control cycle (n = 3/sample day) on d 9 and 11 post-ovulation, a critical time immediately prior to and during MRP. Pregnancy was confirmed by ultrasonography and presence of an embryo following uterine lavage.  Mares were matched by day and embryos collected were used in co-culture experiment.  Endometrial samples were divided and placed in culture with or without contact by an equine embryo for 24 h.  Total RNA from endometrial biopsies was evaluated by qPCR using primers designed to detect 22 equine-specific FAM transcripts and ELISA was used to assay PGF content in medium. All comparisons were made within day between groups and pregnancy status. Differential expression of 4 and 6 FAM were noted in samples collected on d 9 (P≤0.02) and 11 (P≤0.05) respectively, when compared by pregnancy status alone.  No changes were detected in FAM expression in samples collected from pregnant mares due to the presence or absence of an embryo, while 1 and 4 FAM differed when embryos were co-cultured with endometrial samples from non-mated mares at d 9 (P=0.04) and 11 (P≤0.04) respectively.  Secretion of PGF was not attenuated with embryo contact on d 9 regardless of pregnancy status.  Embryo contact resulted in dramatic decreases (P<0.003) in PGF secretion in samples collected from both pregnant and non-pregnant mares 11 d post-ovulation. These data support our hypothesis that FAM expression is altered with the presence of an embryo and implicates FAM in the modulation of PGF secretion. Together these provide new insight into a potential mechanism for MRP in mares.

Keywords: embryo, endometrium, equine, focal adhesion molecule, maternal recognition of pregnancy