Donna W. Payne

Cytokine-mediated regulation of ovarian function: Tumor necrosis factor a inhibits gonadotropin-supported progesterone accumulation by differentiating and luteinized murine granulosa cells

Current views favor the notion that resident ovarian macrophages play an in situ role in the regulation of ovarian function through the local secretion of regulatory molecule(s) (i.e., cytokines). Herein we report on the potential ovarian relevance of one such macrophage product, tumor necrosis factor (TNF) alpha, a polypeptide capable of oncolytic as well as pleiotropic noncytotoxic biologic activities. Our findings suggest that the ability of TNF alpha to diminish the gonadotropin-supported accumulation of progesterone by granulosa/luteal cells is largely due to attenuation of key biosynthetic steps leading to progesterone production. These findings are in keeping with the notion that TNF alpha, possibly of intraovarian (e.g., macrophage or granulosa cell) origin, may comprise the centerpiece of a regulatory loop designed to attenuate gonadotropin hormonal action. Acting at or adjacent to its site of synthesis, TNF alpha may thus partake in the modulation of ovarian progestin economy, possibly in connection with the death of the corpus luteum.

A Novel Nonhepatic Hydroxycholesterol 7α-Hydroxylase That Is Markedly Stimulated by Interleukin-1β CHARACTERIZATION IN THE IMMATURE RAT OVARY

During studies on the regulation of rat ovarian steroidogenic enzymes by interleukin-1β (IL-1β), we observed substantial metabolism of 25-hydroxycholesterol to two unusual polar products. This unexpected effect was observed both in isolated granulosa cells and in whole ovarian dispersates and was also induced by tumor necrosis factor α, but not by insulin-like growth factor I or follicle-stimulating hormone. The effect was dependent on time and the dose of IL-1β and was blocked by an IL-1 receptor antagonist. The formation of the polar metabolites was inhibited by ketoconazole and trilostane, but not by aminoglutethimide. Subsequent purification of these novel metabolites and analysis by gas chromatography/mass spectrometry, NMR, and high performance liquid chromatography revealed them to be related 7α-hydroxylated hydroxycholesterols (cholest-4-ene-7α,25-diol-3-one and cholest-5-ene-3β,7α,25-triol). IL-1β-stimulated ovarian 7α-hydroxylase activity (3-10 pmol/min/mg of cellular protein) was nearly 4-fold that of control levels using 25-hydroxycholesterol as substrate. Activities at or below control levels were observed when IL-1β-treated cell sonicates were boiled or assayed in the presence of NADH (rather than NADPH), indicating that involvement of a nonenzymatic process was unlikely. IL-1β-stimulated 7α-hydroxylase activity was inhibited to basal levels by a 10-fold excess of unlabeled 25- or 27-hydroxycholesterol, but not by cholesterol, pregnenolone, progesterone, testosterone, or dehydroepiandrosterone, suggesting that ovarian 7α-hydroxylase is specific for hydroxycholesterols. Furthermore, when IL-1β-treated ovarian cultures were incubated with radiolabeled cholesterol or testosterone, no 7α-hydroxylated products were observed. We were also unable to detect any mRNA transcripts for liver cholesterol 7α-hydroxylase in IL-1β-stimulated ovarian cultures. This study describes an ovarian hydroxycholesterol 7α-hydroxylase that differs from liver cholesterol 7α-hydroxylase and from other nonhepatic progestin/androgen 7α-hydroxylases. The novel finding of the regulation of a 7α-hydroxylase by IL-1β (and tumor necrosis factor α) suggests a unique role for cytokines in the regulation of cholesterol metabolism in the ovary and possibly other tissues.

The rat ovarian phospholipase A2 system: Gene expression, cellular localization, activity characterization, and interleukin-1 dependence

We have previously demonstrated that interleukin-1 beta (IL-1 beta), a putative intermediary in the ovulatory process, is a potent stimulator of ovarian PG biosynthesis. In this communication, we examine the possibility that this IL-1 effect reflects in part the induction of arachidonic acid mobilization by phospholipase A2 (PLA2). Molecular probing of whole ovarian material revealed the immature rat ovary to be a site of modest secretory PLA2 (sPLA2) gene expression. However, no change in ovarian sPLA2 gene expression was noted during the periovulatory period. Comparable probing for cytosolic PLA2 (cPLA2) failed to disclose a quantifiable signal. However, in situ hybridization localized both sPLA2 and cPLA2 (sPLA2 > cPLA2) transcripts to the granulosa cell layer of the ovarian follicle. Treatment of cultured whole ovarian dispersates with IL-1 beta produced significant (P < 0.01) increments in the steady state levels of transcripts corresponding to both sPLA2 (1.7-fold increase) and cPLA2 (5-fold increase), an effect reversed by an IL-1 receptor antagonist, suggesting mediation via a specific IL-1 receptor. Treatment with cycloheximide, a protein synthesis inhibitor, resulted in significant attenuation of the ability of IL-1 beta to up-regulate sPLA2 and cPLA2 gene expression as well as medium PLA2 activity. Treatment with aminoguanidine, an inhibitor of inducible nitric oxide synthase, led to augmentation of the ability of IL-1 beta to up-regulate sPLA2 and cPLA2 gene expression as well as medium PLA2 activity. Total cellular PLA2 activity proved time, cell density, and calcium dependent, with an optimal pH of 8.0-9.0 and K(m) values in the low micromolar range (2-5 microM). Our observations 1) establish the rat ovary as a site of sPLA2 and cPLA2 gene expression, 2) localize the corresponding transcripts to the granulosa cell layer, and 3) establish IL-1 beta as an up-regulatory agent for ovarian sPLA2 and cPLA2 gene expression as well as for ovarian PLA2 activity. These findings also indicate that the IL-1 effect is 1) receptor mediated, 2) contingent in part upon de novo protein biosynthesis, and 3) inhibited by nitric oxide. These observations support the proposition that PLA2 may be a key component in the IL-1-stimulated biosynthesis of ovarian PGs.

Glucocorticoids suppress basal (but not interleukin-1-supported) ovarian phospholipase A2 activity:: Evidence for glucocorticoid receptor-mediated regulation

Ovulation may constitute a cyclic, inflammatory-like process, wherein the increased expression of interleukin (IL)-1 and the biosynthesis of prostaglandins may be established corollaries. In this communication we hypothesize that glucocorticoids, potent anti-inflammatory principles, may exert an antiovulatory effect by interfering with ovarian IL-1-driven prostaglandin biosynthesis. To test this hypothesis, we examined the effect of treatment with dexamethasone on the activity of ovarian phospholipase A2 (PLA2), the event-limiting enzyme in prostaglandin biosynthesis, and on the gene expression pattern of secretory and cytosolic PLA2 (sPLA2 and cPLA2, respectively). Whole ovarian dispersates from immature rats were cultured under serum-free conditions for 48 h in the absence or presence of dexamethasone. At the conclusion of this culture period, PLA2 activity was determined in cell sonicates and conditioned media. Parallel probing for sPLA2 and cPLA2 transcripts was also undertaken using a solution hybridization/RNAse protection assay. Treatment of whole ovarian dispersates with dexamethasone produced a significant (P < 0.005) decrease in basal cellular and extracellular PLA2 activity to 27 and 40% of controls, respectively. A 5-fold decrease in the basal steady state levels of sPLA2 (but not cPLA2) transcripts was also noted. Co-treatment with dexamethasone produced complete inhibition of IL-1-stimulated cPLA2 transcripts but not of IL-1-supported cellular and extracellular PLA2 activity or sPLA2 transcripts. A glucocorticoid receptor antagonist (RU486), blocked the ability of dexamethasone to inhibit basal sPLA2 transcripts and extracellular PLA2 activity. The inhibitory effect of dexamethasone proved glucocorticoid-specific in that aldosterone and 17beta-estradiol were without effect. Taken together, these observations suggest that dexamethasone is capable of inhibiting basal (but not IL-1-supported) ovarian PLA2 activity, a glucocorticoid receptor-mediated effect due, in part, to a decrease in sPLA2 gene expression. Our findings further suggest that sPLA2 and cPLA2 are differentially regulated and that they may well differ in their relative contribution to ovarian prostaglandin biosynthesis in general and to PLA2 activity in particular. To the extent that IL-1 plays a central role in the ovulatory process, these findings argue against the view that the chronic anovulatory state induced by glucocorticoid excess is due, if only in part, to suppression of ovarian IL-1-dependent PLA2 activity.

Interleukin-1β Stimulates Ovarian Phospholipase A2 (PLA2) Expression and Activity: Up-Regulation of Both Secretory and Cytosolic PLA21

Interleukin (IL)-1β has been shown to stimulate ovarian prostaglandin biosynthesis. We hypothesized that this effect entails the induction of phospholipase A2 (PLA2). Treatment of cultured whole ovarian dispersates of immature rat origin with IL-1β produced significant increases in [3H]arachidonic acid (AA) release and [3H]prostanoid accumulation as well as increases in cellular PLA2 activity and in secretory PLA2 and cytosolic PLA2 transcripts. Cotreatment with IL-1 receptor antagonist reversed IL-mediated (and basal) release of [3H]labeled AA and prostaglandin products, as well as cellular PLA2 activity. Treatment with IL-1β also promoted a significant decrease in the cellular content of[ 3H]phospholipids (apparently phosphatidylethanolamine but not phosphatidylcholine). These observations establish the ovary as a site of IL-1-dependent sPLA2 and cPLA2 gene expression, document the presence of a possible phosphatidylethanolamine-dependent PLA2 activity in cultured whole ovarian dispersates, reveal the u...