Sequence of interleukin 1beta actions on corpus luteum regression: relationship with inducible cyclooxygenase and nitric oxide synthase expression

Luteal fibroblasts produce prostaglandins in response to IL1β in a MAPK-mediated manner

The corpus luteum is a temporary endocrine gland that is crucial for pregnancy, as it produces the progesterone needed to maintain optimal uterine conditions for implantation. In the absence of a conceptus, the corpus luteum becomes non-functional and undergoes rapid tissue remodeling to regress into a fibrotic corpus albicans. Early luteal regression is characterized by increased cytokine release. Because the role of fibroblasts in the bovine corpus luteum remains to be elucidated, the aim of this study was to elucidate the response of bovine luteal fibroblasts to inflammatory cytokines, tumor necrosis factor α (TNFα), and interleukin 1β (IL1β). Both cytokines induced canonical mitogen activated protein kinase (MAPK) signaling in luteal fibroblasts by phosphorylation of ERK1/2, p38 MAPK, and JNK. IL1β elevated expression and phosphorylation of cytosolic phospholipase A2 (cPLA2), an enzyme that mobilizes arachidonic acid for prostanoid synthesis. IL1β also elevated expression of prostaglandin-endoperoxide synthase 2 (PTGS2), another enzyme needed to synthesize prostanoids. IL1β increased PGF2α and PGE2 levels in the culture medium over 20-fold. Inhibition of MAPKs with small-molecule inhibitors abrogated the stimulatory effects of IL1β. IL1β also induced prostaglandin production in steroidogenic cells; however, there was no elevation in cPLA2. Therefore, actions of IL1β differ based on ovarian cell type. All together, we have identified luteal fibroblasts as potential inflammatory mediators during luteal regression.

Mechanisms of angioregression of the corpus luteum

The corpus luteum is a transient ovarian endocrine gland that produces the progesterone necessary for the establishment and maintenance of pregnancy. The formation and function of this gland involves angiogenesis, establishing the tissue with a robust blood flow and vast microvasculature required to support production of progesterone. Every steroidogenic cell within the corpus luteum is in direct contact with a capillary, and disruption of angiogenesis impairs luteal development and function. At the end of a reproductive cycle, the corpus luteum ceases progesterone production and undergoes rapid structural regression into a nonfunctional corpus albicans in a process initiated and exacerbated by the luteolysin prostaglandin F2α (PGF2α). Structural regression is accompanied by complete regression of the luteal microvasculature in which endothelial cells die and are sloughed off into capillaries and lymphatic vessels. During luteal regression, changes in nitric oxide transiently increase blood flow, followed by a reduction in blood flow and progesterone secretion. Early luteal regression is marked by an increased production of cytokines and chemokines and influx of immune cells. Microvascular endothelial cells are sensitive to released factors during luteolysis, including thrombospondin, endothelin, and cytokines like tumor necrosis factor alpha (TNF) and transforming growth factor β 1 (TGFB1). Although PGF2α is known to be a vasoconstrictor, endothelial cells do not express receptors for PGF2α, therefore it is believed that the angioregression occurring during luteolysis is mediated by factors downstream of PGF2α signaling. Yet, the exact mechanisms responsible for angioregression in the corpus luteum remain unknown. This review describes the current knowledge on angioregression of the corpus luteum and the roles of vasoactive factors released during luteolysis on luteal vasculature and endothelial cells of the microvasculature.

Transcriptome profiling of different developmental stages of corpus luteum during the estrous cycle in pigs

To better understand the molecular basis of corpus luteum (CL) development and function RNA-Seq was utilized to identify differentially expressed genes (DEGs) in porcine CL during different physiological stages of the estrous cycle viz. early (EL), mid (ML), late (LL) and regressed (R) luteal. Stage wise comparisons obtained 717 (EL vs. ML), 568 (EL vs. LL), 527 (EL vs. R), 786 (ML vs. LL), 474 (ML vs. R) and 534 (LL vs. R) DEGs with log₂(FC) ≥1 and p < 0.05. The process of angiogenesis, steroidogenesis, signal transduction, translation, cell proliferation and tissue remodelling were significantly (p < 0.05) enriched in EL, ML and LL stages, where as apoptosis was most active in regressed stage. Pathway analysis revealed that most annotated genes were associated with lipid metabolism, translation, immune and endocrine system pathways depicting intra-luteal control of diverse CL function. The network analysis identified genes AR, FOS, CDKN1A, which were likely the novel hub genes regulating CL physiology.

Perturbations in Lineage Specification of Granulosa and Theca Cells May Alter Corpus Luteum Formation and Function

Anovulation is a major cause of infertility, and it is the major leading reproductive disorder in mammalian females. Without ovulation, an oocyte is not released from the ovarian follicle to be fertilized and a corpus luteum is not formed. The corpus luteum formed from the luteinized somatic follicular cells following ovulation, vasculature cells, and immune cells is critical for progesterone production and maintenance of pregnancy. Follicular theca cells differentiate into small luteal cells (SLCs) that produce progesterone in response to luteinizing hormone (LH), and granulosa cells luteinize to become large luteal cells (LLCs) that have a high rate of basal production of progesterone. The formation and function of the corpus luteum rely on the appropriate proliferation and differentiation of both granulosa and theca cells. If any aspect of granulosa or theca cell luteinization is perturbed, then the resulting luteal cell populations (SLC, LLC, vascular, and immune cells) may be reduced and compromise progesterone production. Thus, many factors that affect the differentiation/lineage of the somatic cells and their gene expression profiles can alter the ability of a corpus luteum to produce the progesterone critical for pregnancy. Our laboratory has identified genes that are enriched in somatic follicular cells and luteal cells through gene expression microarray. This work was the first to compare the gene expression profiles of the four somatic cell types involved in the follicle-to-luteal transition and to support previous immunofluorescence data indicating theca cells differentiate into SLCs while granulosa cells become LLCs. Using these data and incorporating knowledge about the ways in which luteinization can go awry, we can extrapolate the impact that alterations in the theca and granulosa cell gene expression profiles and lineages could have on the formation and function of the corpus luteum. While interactions with other cell types such as vascular and immune cells are critical for appropriate corpus luteum function, we are restricting this review to focus on granulosa, theca, and luteal cells and how perturbations such as androgen excess and inflammation may affect their function and fertility.

Cytokines and angiogenesis in the corpus luteum

In adults, physiological angiogenesis is a rare event, with few exceptions as the vasculogenesis needed for tissue growth and function in female reproductive organs. Particularly in the corpus luteum (CL), regulation of angiogenic process seems to be tightly controlled by opposite actions resultant from the balance between pro- and antiangiogenic factors. It is the extremely rapid sequence of events that determines the dramatic changes on vascular and nonvascular structures, qualifying the CL as a great model for angiogenesis studies. Using the mare CL as a model, reports on locally produced cytokines, such as tumor necrosis factor α (TNF), interferon gamma (IFNG), or Fas ligand (FASL), pointed out their role on angiogenic activity modulation throughout the luteal phase. Thus, the main purpose of this review is to highlight the interaction between immune, endothelial, and luteal steroidogenic cells, regarding vascular dynamics/changes during establishment and regression of the equine CL.

Regulation of functional and regressing stages of corpus luteum development in mice. Role of reactive oxygen species

The endocrine and immune systems modulate ovarian function. The aim of the present work was to compare the status of various modulating factors in two well-defined stages of corpus luteum (CL) development (the functional stage and the regressing stage) by means of a gonadotropin-synchronised mouse model. At the regressing stage of CL development, we found that ovarian tissue showed increased prostaglandin (PG) F(2alpha) and diminished PGE levels concomitantly with enhanced protein abundance of ovarian cyclooxygenase 2, the inducible isoform of the limiting enzyme of PG synthesis. We also found both enhanced lipid peroxidation and enhanced total superoxide dismutase activity, as well as inhibited catalase activity and inhibited total hydroxyl radical scavenger capacity, when compared with ovaries at the functional stage. In addition, at the regressing stage we observed an increased percentage of CD8+ (cytotoxic/suppressor) T-cells and a decreased percentage of CD4+ (helper) T-cells from ovarian-draining lymph nodes. Also, the serum interleukin (IL)-2, IL-4 and IL-10 were diminished as compared with the functional stage. We conclude that a pro-oxidant status together with a pro-inflammatory response is responsible for the loss of luteal function.

Mifepristone attenuates human chorionic gonadotropin–induced extracellular signal–regulated kinase 1/2 phosphorylation, cyclooxygenase-2, and prostaglandin E2 production in human granulosa luteal cells

OBJECTIVE

To elucidate the role of RU486 in regulating the function of granulosa luteal cells and its possible involvement in ovarian dysfunction.

DESIGN

An in vitro study.

SETTING

University hospital.

PATIENT(S)

Our subjects were women under the age of 40 who were unable to get pregnant as a result of male-factor infertility.

INTERVENTION(S)

HCG and RU486 were added to cultured granulosa luteal cells; after incubation for 12 hours, the harvested cells were subjected to total mRNA and protein measurements.

MAIN OUTCOME MEASURE(S)

Reverse transcriptase-polymerase chain reaction, immunoblot assay, immunocytochemistry, and enzyme immunoassay were performed.

RESULT(S)

RU486 attenuates hCG-induced cyclooxygenase-2 (COX-2) mRNA and protein expression and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation and decreases the hCG-induced prostaglandin E2 (PGE2) production in a dose-dependent manner. RU486 treatment had no significant effect on COX-1 mRNA expression.

CONCLUSION(S)

Treatments using gonadotropins are able to induce ERK1/2 phosphorylation resulting in increased COX-2 protein expression and prostaglandin synthesis. RU486 attenuates the activation of ERK1/2, decreases the expression of COX-2, and affects PGE2 production by inhibiting hCG-induced COX-2 expression.

Interleukin-1β up-regulates nitrite production: effects on ovarian function

We have previously reported that Interleukin-1beta (IL-1beta) affects ovarian function in the rat, modulating prostaglandin and progesterone (P) production. As IL-1beta effects were associated to nitric oxide (NO) synthesis, in the present work we have further examined the role of ovarian NOS-system, in IL-1beta antisteroidogenic action. Mid-luteal explants from rats were incubated for 4 h in the presence of IL-1beta (1-35 ng/ml)-alone or in combination with NOS-inhibitors-and then assayed for P and nitrite production. IL-1beta treatment reduced P levels in a dose-dependent manner, returning to basal levels at 35 ng/ml. This reduction in steroid synthesis was paralleled by a dose-dependent increase in nitrite levels, reaching a maximum at 25 ng/ml but without effect at 35 ng/ml. L-Arginine (1 and 2 mM) was able to mimic IL-1beta actions and the NOS blocker L-Nitro-Arginin-Methyl Ester reverted these effects. Moreover, the selective iNOS inhibitor, 1400 W, completely abolished IL-1beta antisteroidogenic effect, therefore confirming the dependence of IL-1beta action upon iNOS activation. Finally, IL-1beta did not affect eNOS expression but up-regulated iNOS mRNA and protein levels. Our results suggest an interaction between IL-1beta and the NOS-system. Thus, we may conclude that in the rat iNOS-derived NO production, induced by IL-1beta, affects ovarian P biosynthesis and hence NO may be a major effector molecule of ovarian IL-1 system.