Conceptus-mediated endometrial vascular changes during early pregnancy in mares: an anatomic, histomorphometric, and vascular endothelial growth factor receptor system immunolocalization and gene expression study

Abstract

This work examined how the conceptus modulates endometrial tissue remodeling and vascular development prior to implantation in mares. A macroscopic uterine examination was completed at day 21 of pregnancy. In situ morphology revealed that the endometrium involved in encroachment is restricted to the dorsal endometrium immediately overlying the yolk sac. The amount of stromal area occupied by blood vessels and the number of endometrial glands were increased during early pregnancy. Endometrial histomorphometry as well as the endometrial mRNA abundance and immunolocalization of VEGF, VEGFR1, VEGFR2, and Ki-67 was completed at days 14 and 21 of pregnancy, at day 10 of the estrous cycle, and during estrus. No obvious differences in VEGF and VEGFR1 protein localization were detected between pregnant and cycling mares but differential staining pattern for VEGFR2 and Ki-67 was observed. VEGFR2 localized to luminal and glandular epithelium of pregnant mares, while luminal epithelium was negative in cycling mares. Ki-67 staining was weak during the luteal phase but exhibited prominent luminal epithelium staining during estrus. In pregnant mares, all endometrial layers were Ki-67 positive. Quantitative RT-PCR revealed a greater abundance of VEGF mRNA during pregnancy. VEGFR2 transcript abundance was greatest in pregnant mares on day 21. This study supports the concept that the conceptus plays an active role in directing vasculogenesis within the uterus and thereby establishing hemotrophic nutrition that supports pregnancy after implantation.

Exploration of Global Gene Expression Changes During the Estrous Cycle in Equine Endometrium1

“…In correlation with the observation that the genes assigned to the functional categories blood circulation and angiogenesis were predominantly found in the expression clusters with highest mRNA concentrations during estrus and in expression clusters with highest mRNA concentrations on Days 8 or 12, studies of uterine blood flow in cyclic mares found highest blood flow on Days 0 and 10/11 [55,56]. The comparison to studies of gene expression during the time around MRP [14,16] shows that expression of similar genes is induced during estrus and on Days 12 and 14 of pregnancy, indicating a specific induction of those genes by the presence of the conceptus, probably by conceptus estrogens.…”

“…In addition to genes involved in PG metabolism and signaling, a number of other genes involved in regulation of cyclic changes in the endometrium have been investigated, such as estrogen and P4 receptor genes [15], genes related to endometrial vascular changes [16], and wingless-type (WNT) genes and their antagonists [17]. To get a holistic overview of dynamic gene expression changes during the estrous cycle in equine endometrium, a DNA microarray analysis of endometrial biopsy samples was performed, which were collected at five defined time points of the estrous cycle: Day 16 (beginning of follicular phase), Day 0 (day of ovulation), Day 3 (early luteal phase), Day 8 (midluteal phase), and Day 12 (late luteal phase).…”

Equine Endometrial Explants Undergo Significant Degenerative Changes in Culture

“…Steady expression levels of ESR1 are important when studying estrogen‐responsive genes and indeed explants can be used to study the regulation of estrogen‐responsive genes such as Milk fat globule‐EGF factor 8 (unpublished observation). VEGF plays a role in plays an important role in endometrial angiogenesis (Silva et al, ). Increased expression as a sequel to hypoxia has been reported for human endometrial cells in culture; given the three‐dimensional structure of explants, an increase in expression following in vitro culture can be expected.…”

Effects of Intrauterine Devices in Mares: A Histomorphological and Immunohistochemical Evaluation of the Endometrium

“…Immunohistochemical detection of the proliferation marker Ki‐67 antigen monitors mitotic activity in the mare endometrium (Silva et al. ).…”

“…These proteins are suitable for comparative analysis as they have different functions during reproductive cycle and inflammatory reaction and are well established in the immunohistochemical evaluation of pregnant and cyclic equine endometrium. Immunohistochemical detection of the proliferation marker Ki-67 antigen monitors mitotic activity in the mare endometrium (Silva et al 2011).…”