Hedgehog signaling in the maintenance of endometrial thickness and pregnancy

PROPOSAL SUMMARY The inner lining of the uterus, the endometrium, is an important determinant of gestational outcomes even prior to the implantation of an embryo. In humans, a thin endometrium increases risk for miscarriage, preterm delivery, and low birth weight. Currently, it is unknown what causes a thin endometrium and how it leads to the later gestational outcomes. Much of what is currently known about the endometrium relates to how the epithelium and underlying stroma respond to steroid hormone signals. We know substantially less about what other downstream cell signaling occurs to thicken the endometrium. Members of the Hedgehog (Hh) signaling pathway, including Gli2, change expression dramatically across the 4-7 day mouse estrous (menstrual) cycle and are known to have important roles in implantation. Prior work in the field has shown that decreased Gli2 expression in mouse placentas results in decreased blood flow to the fetus and changes in the structure of the labyrinth layer of the placenta. There is also decreased Gli2 expression in human placentas affected by preeclampsia. However, the cell and molecular role of Gli2 in either the cycling endometrium or gestational success is largely unknown. Therefore, the overarching objective of this proposal is to close this knowledge gap by investigating the role of Gli2 in endometrial remodeling and placental development. In order to accomplish this, we developed a mouse model with conditionally deleted uterine Gli2. My preliminary data shows that the endometrium does not expand normally during the estrous cycle, resulting in a thin endometrium. These animals are still able to produce offspring, but each litter has fewer pups compared to controls. My preliminary work also shows that Gli2 deficiency does not affect the initial number of implantation sites, so the subfertility is likely occurring after implantation and before birth. Therefore, my central hypothesis is that Gli2 is necessary for supporting gestation by regulating cell proliferation at three important times: in the cycling uterus, at decidualization, and during syncytiotrophoblast expansion. To test this hypothesis, I will conditionally delete Gli2 in the uterus and in the placenta. In Aim 1, I will use high-resolution imaging to analyze stromal and decidual proliferation at two estrous cycle phases and gestational timepoints, respectively, in order to identify perturbations with loss of uterine Gli2. Aim 2 will utilize the placenta-specific knockout of Gli2 to assess changes to fertility when endometrial Gli2 remains intact. I will also use this placenta Gli2 ablation model to measure proliferation of syncytiotrophoblasts, a key placental labyrinth cell type, using imaging techniques congruent to Aim 1. Collectively, these data will significantly advance our understanding of the cell signaling underlying endometrial thickness and ability to maintain gestation. Additionally, it will describe Gli2 as a common factor that is necessary in both endometrial and placental functions to prevent gestational failure. This proposal will have broad implications in understanding how a thin endometrium occurs and subsequently contributes to unfavorable gestational outcomes. Project Number: 1F31HD121164-01 | Fiscal Year: 2026 | NIH Institute/Center: Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) | Principal Investigator: Ashlyn Stahly | Institution: UNIVERSITY OF COLORADO DENVER, Aurora, CO | Award Amount: $41,183 | Activity Code: F31 | Study Section: Special Emphasis Panel[ZRG1 F06A-D (20)] View on NIH RePORTER: https://reporter.nih.gov/project-details/1F31HD12116401