Uterine lipid metabolism--a review of the literature

Analysis of the uterine lumen in fertility-classified heifers: I. Glucose, prostaglandins, and lipids†

Survival and growth of the bovine conceptus (embryo and associated extraembryonic membranes) are dependent on endometrial secretions or histotroph found in the uterine lumen. Previously, serial embryo transfer was used to classify heifers as high fertile (HF), subfertile (SF), or infertile (IF). Here, we investigated specific histotroph components [glucose, prostaglandins (PGs), and lipids] in the uterine lumen of day 17 pregnant and open fertility-classified heifers. Concentrations of glucose in the uterine lumen were increased by pregnancy but did not differ among fertility-classified heifers. Differences in expression of genes encoding glucose transporters and involved with glycolysis and gluconeogenesis were observed between conceptuses collected from HF and SF heifers. In the uterine lumen, PGE2 and PGF2α were increased by pregnancy, and HF heifers had higher concentrations of PGE2, PGF2α, and 6-keto-PFG1α than SF heifers. Differences were found in expression of genes regulating PG signaling, arachidonic acid metabolism, and peroxisome proliferator-activated receptor signaling among conceptuses and endometrium from fertility-classified heifers. Lipidomics was conducted exclusively in samples from HF heifers, and phosphatidylcholine was the main lipid class that increased in the uterine lumen by pregnancy. Expression of several lipid metabolism genes differed between HF and SF conceptuses, and a number of fatty acids were differentially abundant in the uterine lumen of pregnant HF and SF heifers. These results support the ideas that uterine luminal histotroph impacts conceptus survival and programs its development and is a facet of dysregulated conceptus-endometrial interactions that result in loss of the conceptus in SF cattle during the implantation period of pregnancy establishment.

Dietary exposure to mycotoxin zearalenone (ZEA) during post-implantation adversely affects placental development in mice

Zearalenone (ZEA) is a common food contaminant (ppb-ppm) derived from Fusarium fungi. With its estrogenicity and potential chronic exposure, ZEA poses a risk to pregnancy. Our previous studies implied post-implantational lethality by ZEA. Since a functional placenta is essential for fetal development and survival, it was hypothesized that ZEA may have adverse effects on placental development leading to post-implantational lethality. Exposure of young mice to 0, 0.8, 4, 10, and 40 ppm ZEA diets from gestation day 5.5 (D5.5) to D13.5 led to increased resorption of implantation sites, increased placental hemorrhage, decreased placental and fetal weights, proportionally reduced placental layers, and disorganized placental labyrinth vascular spaces in the 40 ppm ZEA group, as well as lipid accumulation in the labyrinth layer of all four ZEA treatment groups examined on D13.5. These data demonstrate adverse effects of ZEA on placental development.

Changes in uterine endometrial phospholipids and fatty acids throughout the oestrous cycle and early pregnancy in the ewe

This study examined changes in ovine endometrial phospholipids and fatty acid concentrations associated with luteolysis and the establishment of pregnancy in the ewe on days 3, 12 and 15, respectively. Results from this study indicate that endometrial lipids increased as the oestrous cycle progressed from days 3 to 12 and 15, whereas during early pregnancy, endometrial lipids decreased on day 15 of pregnancy when compared to days 3 and 12 of pregnancy. Phosphatidylcholine followed a similar pattern to that of total lipids, with an increase in phosphatidylcholine concentrations as the oestrous cycle progressed. During the early stages of pregnancy, phosphatidylcholine increased from day 3 to day 12, but then returned to previous levels by day 15 of pregnancy. Phosphatidylethanolamine increased late in the oestrous cycle, on day 15 as compared to days 3 and 12. This increase did not occur during early pregnancy, with phosphatidylethanolamine concentrations being constant from day 3 to day 15 of pregnancy. Both phosphatidylinositol and phosphatidylserine followed a similar pattern to phosphatidylethanolamine during the oestrous cycle and remained constant during early pregnancy. The fatty acid content of the major phospholipids involved in prostaglandin synthesis were examined over the range of fatty acids from C14:0 to C24:1omega9. Although changes in arachidonic acid were observed, there were no clear indications that these changes were directly related to the changes in PGF2alpha synthesis.

Purification and characterization of glutathione S-transferases of rat uterus

Glutathione S-transferases (GSTs) provide protection to cells against electrophilic xenobiotics as well as lipid hydroperoxides and 4-hydroxynonenal generated during lipid peroxidation. The catalytic properties of the alpha class GSTs are well suited for detoxification of electrophilic products of lipid peroxidation. An immunologically distinct subgroup of the alpha class GST isozymes having high activity towards 4-hydroxynonenal has been recently identified in several mammalian tissues [Zimniak et al. (1994) J. Biol. Chem. 269, 992-1000]. Since oxidative stress can exert deleterious effects during gestation, the present studies were performed to determine whether the rat homolog of this group of GSTs, rGST 8-8, is expressed in gravid rat uterus, where it may function as a defense mechanism against oxidative stress. GSTs were purified by GSH-affinity chromatography. Individual GST isozymes were separated by column isoelectric focusing and their immunologic identities were established using highly specific polyclonal antibodies in Western blot analysis. Their expression was quantified and kinetic properties were characterized. Rat uterus contained an alpha class GST (pI 9.8), a pi class GST (pI 8.1), two mu class GSTs (pI 6.7 and 6.2) and rGST 8-8. This result indicated that rGST subunits 1, 2, 3, 4, 7 and 8 are present in rat uterus. The relative abundance of rGST 8-8 in the gravid rat uterus was found to be about three-fold higher as compared with that previously seen in rat liver. Higher relative abundance of rGST8-8 in gravid rat uterus suggests that it may play a protective role against the deleterious effects of lipid peroxidation during gestation.

Lipid peroxidation in rat uterus

Lipid peroxidation in rat uterus has been studied using NADPH- and ascorbate-induced systems. Lipid peroxidation in rat uterus is low as compared to rat liver. Uterus is more sensitive to ascorbate-induced lipid peroxidation than that induced by NADPH. Uterus contains lower amounts of phospholipids and has a lesser degree of unsaturation in lipids. Co-factor studies show that Fe2+ is more important for ascorbate-induced lipid peroxidation. Endometrium is more sensitive to ascorbate-induced lipid peroxidation than myometrium. It also contains more total lipids and phospholipids besides having a higher degree of unsaturation in the lipids as compared to myometrium. Among the subcellular fractions, mitochondria are more prone to ascorbate-induced lipid peroxidation, whereas microsomes are more sensitive to NADPH-induced lipid peroxidation. Uteri from old rats (24 months) and pregnant rats are more resistant to lipid peroxidation than those from 3-month-old control rats. Uterus of pregnant rats contains more factors which inhibit lipid peroxidation and also has a lesser degree of unsaturation in lipids compared with uterus of control rats. The possible consequences of the resistance of uterus to lipid peroxidation, especially during pregnancy and senescence, are discussed.

Stimulation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase in mouse uterine epithelial cells by oestradiol-17 beta

The characteristics of 3-hydroxy-3-methylglutaryl-CoA reductase from mouse uterine epithelial cells were studied. Preliminary experiments showed that enzyme activity was stimulated approx. 10-fold 18h after administration of 100ng of oestradiol-17 beta. This activity was associated with all particulate fractions of the uterine luminal cell. The Km for D-3-hydroxy-3-methylglutaryl-CoA was 5.54 +/- 1.12 microM. The detailed time-course of oestrogen stimulation showed two peaks of activity, 9 and 15h after hormone treatment. The DNA content of the epithelial cells doubled between 6 and 12h after hormone treatment, whereas the protein content increased linearly over the 18h period. The peak of enzyme activity at 9h is associated with early S phase of the epithelial cells; the peak at 15h may be associated with a second S phase or with mitosis. Pretreatment with progesterone for 3 days before injection of oestradiol-17 beta (a treatment which inhibits uterine epithelial DNA synthesis) reduced the oestrogenic stimulation of enzyme activity by 63%; progesterone treatment alone did not stimulate enzyme activity. These data suggest that uterine epithelial 3-hydroxy-3-methylglutaryl-CoA reductase may play an important role in the cell cycle in this tissue.