(75) Effects of Estradiol and Progesterone on Uterine Epithelial Glycogen in Mice

Pedram Zarei¹, Arpna Sharma¹, Garima Thapa¹, Sameeksha Bhaye¹, Kassandra Sandoval², Sijie Chen¹, Madison Fugiel¹, Matthew Dean^1,2

¹Department of Animal Science, University of Illinois Urbana-Champaign, Urbana, IL, 61801
²Division of Nutritional Science, University of Illinois Urbana-Champaign, Urbana, IL, 61801

Abstract Text: Early pregnancy loss remains a serious issue with significant economic and psychological challenges. Research has demonstrated that several factors need to be firmly regulated to establish a successful pregnancy. Glucose is of critical importance during this period as it is one of the most required energy supplies. Previous studies have shown that while glucose needs of the developing embryo increase substantially by the blastocyst stage, glucose levels must be tightly regulated as high glucose concentrations impair embryo development. Gluconeogenic enzymes are not expressed in the uterus. The maternal circulation must provide the uterus with glucose. One way for the uterus to precisely regulate the amount of glucose secreted into the uterine lumen is via glycogen metabolism. Glycogen is a highly branched polysaccharide composed of thousands of glucose units and serves as the primary storage form of glucose. It has been suggested that estradiol (E2) and progesterone (P4) play roles in regulating changes in the uterine epithelial glycogen pool during the preimplantation period. Thus, the objective of this study was to investigate the role of these hormones in uterine epithelial glycogen metabolism. Mice (24) were ovariectomized at 8 weeks of age and were given two weeks to heal. Mice were then randomly divided into 4 groups as follows: control (vehicle), E2 (100 ng/day), P4 (1 mg/day), and E2+P4 (100 ng/day E2 and 1 mg/day P4). Mice were subcutaneously injected with hormones or corn oil daily for 4 days. Within 6 hours following the last treatment, mice were sacrificed, and the uteri were collected. Diastase labile Periodic Acid-Schiff (PAS) staining shows that glycogen was increased by E2 treatment. P4 had no effect by itself and was able to block the effects of E2 when given in combination.  Immunohistochemistry (IHC) was performed to compare the levels of enzymes associated with glycogen metabolism. There was no difference in the immunostaining levels of hexokinase (HK1, the enzyme that phosphorylates glucose) among treatments.  E2-treated mice had higher levels of glycogen synthase 1 (GYS1) immunostaining in both luminal (LE) and glandular epithelium (GE) compared to control. Again, P4 had no effect and was able to block the effect of E2. We have previously suggested that the effect of E2 is mediated by insulin-like growth factor 1 (IGF1). Immunostaining levels in the stroma for IGF1 were higher in all hormone-treated groups compared to control. Glucose-6-phosphate is trapped inside the cells unless it is dephosphorylated by glucose-6-phosphatase (G6PC). Immunostaining levels of G6PC3 were higher in both P4 and E2+P4 treated groups compared to E2 or control groups. The levels of glycogen phosphorylase (PYGM, the enzyme that breaks down glycogen) did not differ among groups. Immunostaining levels of pyruvate kinase (PKM2, a rate-limiting enzyme in glycolysis) were higher in both P4 and E2+P4 treated groups compared to both E2 or control groups. These results indicate that estradiol has glycogenic effects on both LE and GE mediated by increased IGF1. P4 stimulates glycogenolysis in both LE and GE. G6P from glycogen could be dephosphorylated and secreted into the luminal epithelium or metabolized via glycolysis to produce ATP in the uterine epithelium.