Postnatal exposure to chromium through mother's milk accelerates follicular atresia in F1 offspring through increased oxidative stress and depletion of antioxidant enzymes

Hexavalent chromium, CrVI, is a heavy metal endocrine disruptor, known as a mutagen, teratogen, and a group A carcinogen. Environmental contamination with CrVI, including drinking water, has been increasing in more than 30 cities in the United States. CrVI is rapidly converted to CrIII intracellularly, and CrIII can cause DNA strand breaks and cancer or apoptosis through different mechanisms. Our previous study demonstrated that lactational exposure to chromium results in a delay or arrest in follicle development and a decrease in steroid hormone levels in F1 female rats, both of which are mitigated (partial inhibition) by vitamin C. The current study tested the hypothesis that lactational exposure to CrIII accelerates follicle atresia in F1 offspring by increasing reactive oxygen species (ROS) and decreasing cellular antioxidants. Results showed that lactational exposure to CrIII dose-dependently increased follicular atresia and decreased steroidogenesis in postnatal day 25, 45, and 65 rats. Vitamin C mitigated or inhibited the effects of CrIII at all doses. CrIII increased hydrogen peroxide and lipid hydroperoxide in plasma and ovary; decreased the antioxidant enzymes (AOXs) GPx1, GR, SOD, and catalase; and increased glutathione S-transferase in plasma and ovary. To understand the effects of CrVI on ROS and AOXs in granulosa (GC) and theca (TC) cell compartments in the ovary, ROS levels and mRNA expression of cytosolic and mitochondrial AOXs, such as SOD1, SOD2, catalase, GLRX1, GSTM1, GSTM2, GSTA4, GR, TXN1, TXN2, TXNRD2, and PRDX3, were studied in GCs and TCs and in a spontaneously immortalized granulosa cell line (SIGC). Overall, CrVI downregulated each of the AOXs; and vitamin C mitigated the effects of CrVI on these enzymes in GCs and SIGCs, but failed to mitigate CrVI effects on GSTM1, GSTM2, TXN1, and TXN2 in TCs. Thus, these data for the first time reveal that lactational exposure to CrIII accelerated follicular atresia and decreased steroidogenesis in F1 female offspring by altering the ratio of ROS and AOXs in the ovary. Vitamin C is able to protect the ovary from CrIII-induced oxidative stress and follicle atresia through protective effects on GCs rather than TCs.

Early pregnancy induced expression of prostaglandin E2 receptors EP2 and EP4 in the ovine endometrium and regulated by interferon tau through multiple cell signaling pathways

Prostaglandin E2 (PGE(2)) plays pleiotropic roles at fetal-maternal interface during establishment of pregnancy. The objectives of the study were to: (i) determine regulation of PGE2 receptors EP1, EP2, EP3, and EP4 in the endometrium during the estrous cycle and early pregnancy; and (ii) understand endometrial epithelial and stromal cell-specific hormonal regulation of EP2 and EP4 in sheep. Results indicate that: (i) early pregnancy induces expression of EP2 and EP4 but not EP1 and EP3 proteins in the endometrium on days 12-16 compared to that of estrous cycle; (ii) intrauterine infusion of interferon tau (IFNT) increases expression of EP2 and EP4 proteins in endometrium; and (iii) IFNT activates distinct epithelial and stromal cell-specific JAK, EGFR, ERK1/2, AKT, or JNK signaling module to regulate expression of EP2 and EP4 proteins in the ovine endometrium. Our results indicate a role for EP2 and EP4-mediated PGE(2) signaling in endometrial functions and establishment of pregnancy in ruminants.

Chromium-VI arrests cell cycle and decreases granulosa cell proliferation by down-regulating cyclin-dependent kinases (CDK) and cyclins and up-regulating CDK-inhibitors

Environmental contamination with hexavalent chromium (CrVI) has been increasing in the drinking water of the USA and developing countries. CrVI causes various health problems including menstrual disorders and infertility. Recently, we reported that CrVI causes granulosa cell apoptosis through the intrinsic apoptotic pathway. Our previous studies showed that postnatal exposure to CrVI arrests follicle development. In order to explore the underlying mechanism, primary and immortalized granulosa cells from rats were treated with 10 μM potassium dichromate and analyses of the cell cycle, and cell cycle regulatory proteins were performed. CrVI decreased cell proliferation as a result of cell cycle arrest and down-regulated cyclin-dependent kinases (CDK), cyclins, and PCNA while up-regulating CDK-inhibitors and down-regulating FSH receptor and ERβ. Vitamin C mitigated the effects of CrVI. This study shows that CrVI causes cell cycle arrest in granulosa cells by altering cell cycle regulatory proteins with potential intervention by vitamin C.

Interferon tau regulates PGF2alpha release from the ovine endometrial epithelial cells via activation of novel JAK/EGFR/ERK/EGR-1 pathways

In ruminants, pulsatile release of prostaglandin F2α (PGF(2α)) from the endometrium is transported to the ovary and induces luteolysis thereby allowing new estrous cycle. Interferon tau (IFNT), a type 1 IFN secreted by the trophoblast cells of the developing conceptus, acts on endometrial luminal epithelial (LE) cells and inhibits pulsatile release of PGF(2α) and establishes pregnancy. One of the unknown mechanisms is that endometrial pulsatile release of PGF(2α) is inhibited whereas basal release of PGF(2α) is increased in pregnant compared with nonpregnant sheep. We have recently found that pulsatile release of PGF(2α) from the endometrium is regulated by prostaglandin transporter (PGT)-mediated mechanisms. We hypothesize that modulation in the endometrial pulsatile vs. basal release of PGF(2α) likely requires PGT-mediated selective transport, and IFNT interacts with PGT protein and modulates pulsatile vs. basal release of PGF(2α). The new findings of the present study are: 1) IFNT activates novel JAK-SRC kinase-EGFR-RAS-RAF-ERK1/2-early growth response (EGR)-1 signaling module in LE cells; 2) IFNT increases interactions between PGT and ERK1/2 or EGR-1 proteins and alters phosphorylation of PGT protein; 3) IFNT precludes action of protein kinase C and Ca(2+) on PGT function; and 4) IFNT inhibits 80% PGT-mediated but not 20% simple diffusion-mediated release of PGF(2α) from the endometrial LE cells through this novel signaling module. The results of the present study provide important new insights on IFNT signaling and molecular control of PGT-mediated release of PGF(2α) and unravel the underlying mechanisms responsible for the increased basal release of PGF(2α) at the time of establishment of pregnancy in ruminants.

Transport of prostaglandin F(2alpha) pulses from the uterus to the ovary at the time of luteolysis in ruminants is regulated by prostaglandin transporter-mediated mechanisms

In ruminants, prostaglandin F2alpha (PGF(2alpha)) is the uterine luteolytic hormone. During luteolysis, PGF(2alpha) is synthesized and released from the endometrium in a pulsatile pattern. The unique structure of the vascular utero-ovarian plexus (UOP) allows transport of luteolytic PGF(2alpha) pulses directly from the uterus to the ovary, thus bypassing the systemic circulation. However, the underlying molecular mechanism is not known. The objective of the present study was to determine a role for PG transporter protein (PGT) in the compartmental transport of PGF(2alpha) from uterus to ovary through the UOP at the time of luteolysis using the sheep as a ruminant model. [(3)H]PGF(2alpha), with or without a PGT inhibitor, was infused into UOP, and PGF(2alpha) transport and PGT protein expression were determined. Results indicate that PGT protein is expressed in tunica intima, tunica media, and tunica adventitia of the utero-ovarian vein and the ovarian artery of the UOP, and the expression levels are higher on d 10-15 compared with d 3-6 of the estrous cycle. Pharmacological inhibition of PGT prevented transport of exogenous [(3)H]PGF(2alpha) as well as oxytocin-induced endogenous luteolytic PGF(2alpha) pulse up to 80% from uterine venous blood into ovarian arterial blood through the UOP at the time of luteolysis in sheep. Taken together, these results indicate that at the time of luteolysis, transport of PGF(2alpha) from uterus to ovary through the UOP is regulated by PGT-mediated mechanisms. These findings also suggest that impaired PGT-mediated transport of PGF(2alpha) from the utero-ovarian vein into the ovarian artery could adversely influence luteolysis and thus affect fertility in ruminants.