112 EFFECT OF ASYNCHRONOUS EMBRYO TRANSFER ON GLUCOSE TRANSPORTER EXPRESSION IN EQUINE TROPHECTODERM

Abstract

Equine pregnancy is characterised by an unusually long pre-implantation period (40 days) during which the conceptus is entirely dependent on uterine secretions for nutrient provision; although glucose is an important nutrient during development post-blastocyst formation, little is known about its transport into the early horse conceptus. Equine embryos are also known to tolerate an unusually large degree of uterine asynchrony following embryo transfer (ET). However, negative asynchrony (recipient behind the donor) of more than 5 days markedly retards conceptus growth and development, and thereby offers a unique tool for studying the effect of the uterine environment on early development. In a preliminary study, we detected abundant mRNA expression for the facilitative glucose transporters (SLC2As) 1–3, 5, 8 and 10 and sodium-glucose co-transporter (SLC5A)11 in Day 14 to 28 equine conceptus membranes. In the current study, we evaluated the effect of uterine asynchrony on trophectodermal glucose transporter expression. Day 8 horse embryos were transferred to recipient mares that ovulated on the same day (synchronous; n = 10) or 5 days after (asynchronous; n = 10) the donor mare. The conceptuses were collected 6 or 11 days after ET (Day 14 or 19 of embryo development: n = 5 per group). Trophectodermal mRNA expression for glucose transporters was evaluated by RT-qPCR, and the effects of asynchronous ET and stage of pregnancy were analysed by two-way ANOVA followed by independent-samples t-tests. Gene expression for SLC2A3 and 8 was stable over time and treatment. Expression of SLC2A1 and SLC5A11 decreased between Days 14 and 19 in synchronous pregnancies only (P < 0.05). SLC2A2 expression increased markedly on Day 19 in synchronous (P < 0.01) but not asynchronous pregnancies (P < 0.05). SLC2A5 expression was lower in the asynchronous group on Day 14, but increased beyond expression levels in synchronous pregnancies by Day 19 (P < 0.05). In summary, expression of SLC2A1 and 3, the major placental glucose transporters, was not affected by asynchronous ET. The marked up-regulation of SLC2A2 expression between Days 14 and 19 of synchronous but not asynchronous pregnancy suggests a stage-specific function, whereas the increase in SLC2A5 at Day 19 after asynchronous ET could be a compensatory response to growth retardation.

This study was funded by EpiHealthNet (Project number 317146).