Targeting Tryptophan Catabolism in Ovarian Cancer to Attenuate Macrophage Infiltration and PD-L1 Expression

High-grade serous carcinoma (HGSC) of the fallopian tube, ovary, and peritoneum is the most common type of ovarian cancer and is predicted to be immunogenic because the presence of tumor-infiltrating lymphocytes conveys a better prognosis. However, the efficacy of immunotherapies has been limited because of the immune-suppressed tumor microenvironment (TME). Tumor metabolism and immune-suppressive metabolites directly affect immune cell function through the depletion of nutrients and activation of immune-suppressive transcriptional programs. Tryptophan (TRP) catabolism is a contributor to HGSC disease progression. Two structurally distinct rate-limiting TRP catabolizing enzymes, indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2), evolved separately to catabolize TRP. IDO1/TDO2 are aberrantly expressed in carcinomas and metabolize TRP into the immune-suppressive metabolite kynurenine (KYN), which can engage the aryl hydrocarbon receptor to drive immunosuppressive transcriptional programs. To date, IDO inhibitors tested in clinical trials have had limited efficacy, but those inhibitors did not target TDO2, and we find that HGSC cell lines and clinical outcomes are more dependent on TDO2 than IDO1. To identify inflammatory HGSC cancers with poor prognosis, we stratified patient ascites samples by IL6 status, which correlates with poor prognosis. Metabolomics revealed that IL6-high patient samples had enriched KYN. TDO2 knockdown significantly inhibited HGSC growth and TRP catabolism. The orally available dual IDO1/TDO2 inhibitor, AT-0174, significantly inhibited tumor progression, reduced tumor-associated macrophages, and reduced expression of immune-suppressive proteins on immune and tumor cells. These studies demonstrate the importance of TDO2 and the therapeutic potential of AT-0174 to overcome an immune-suppressed TME.

SIGNIFICANCE

Developing strategies to improve response to chemotherapy is essential to extending disease-free intervals for patients with HGSC of the fallopian tube, ovary, and peritoneum. In this article, we demonstrate that targeting TRP catabolism, particularly with dual inhibition of TDO2 and IDO1, attenuates the immune-suppressive microenvironment and, when combined with chemotherapy, extends survival compared with chemotherapy alone.

Early Ovarian Cancer Detection in the Age of Fallopian Tube Precursors: A Systematic Review

OBJECTIVE

To determine biomarkers other than CA 125 that could be used in identifying early-stage ovarian cancer.

DATA SOURCES

Ovid MEDLINE ALL, EMBASE, Web of Science Core Collection, ScienceDirect, Clinicaltrials.gov , and CAB Direct were searched for English-language studies between January 2008 and April 2023 for the concepts of high-grade serous ovarian cancer, testing, and prevention or early diagnosis.

METHODS OF STUDY SELECTION

The 5,523 related articles were uploaded to Covidence. Screening by two independent reviewers of the article abstracts led to the identification of 245 peer-reviewed primary research articles for full-text review. Full-text review by those reviewers led to the identification of 131 peer-reviewed primary research articles used for this review.

TABULATION, INTEGRATION, AND RESULTS

Of 131 studies, only 55 reported sensitivity, specificity, or area under the curve (AUC), with 36 of the studies reporting at least one biomarker with a specificity of 80% or greater specificity or 0.9 or greater AUC.

CONCLUSION

These findings suggest that although many types of biomarkers are being tested in ovarian cancer, most have similar or worse detection rates compared with CA 125 and have the same limitations of poor detection rates in early-stage disease. However, 27.5% of articles (36/131) reported biomarkers with better sensitivity and an AUC greater than 0.9 compared with CA 125 alone and deserve further exploration.

CASC4/GOLM2 drives high grade serous carcinoma anoikis resistance through the recycling of EGFR

Ovarian cancer is the deadliest gynecological malignancy, and accounts for over 150,000 deaths per year worldwide. The high grade serous ovarian carcinoma (HGSC) subtype accounts for almost 70% of ovarian cancers and is the deadliest. HGSC originates in the fimbria of the fallopian tube and disseminates through the peritoneal cavity. HGSC survival in peritoneal fluid requires cells to resist anoikis (anchorage-independent apoptosis). Most anoikis resistant mechanisms are dependent on microenvironment interactions with cell surface-associated proteins, such as integrins and receptor tyrosine kinases (RTKs). We previously identified the gene CASC4 as a driver of anoikis resistance. CASC4 is predicted to be a Golgi-associated protein that may regulate protein trafficking to the plasma membrane, but CASC4 is largely uncharacterized in literature; thus, we sought to determine how CASC4 confers anoikis resistance to HGSC cells. Mining of publicly available ovarian cancer datasets (TCGA) showed that CASC4 is associated with worse overall survival and increased resistance to platinum-based chemotherapies. For experiments, we cultured three human HGSC cell lines (PEO1, CaOV3, OVCAR3), and a murine HGSC cell line, (ID8) with shRNA-mediated CASC4 knockdowns (CASC4 KD) in suspension, to recapitulate the peritoneal fluid environment in vitro. CASC4 KD significantly inhibited cell proliferation and colony formation ability, and increased apoptosis. A Reverse Phase Protein Assay (RPPA) showed that CASC4 KD resulted in a broad re-programming of membrane-associated proteins. Specifically, CASC4 KD led to decreased protein levels of the RTK Epidermal Growth Factor Receptor (EGFR), an initiator of several oncogenic signaling pathways, leading us to hypothesize that CASC4 drives HGSC survival through mediating recycling and trafficking of EGFR. Indeed, loss of CASC4 led to a decrease in both EGFR membrane localization, reduced turnover of EGFR, and increased EGFR ubiquitination. Moreover, a syngeneic ID8 murine model of ovarian cancer showed that knocking down CASC4 leads to decreased tumor burden and dissemination.

Claudin-4 modulates autophagy via SLC1A5/LAT1 as a tolerance mechanism for genomic instability in ovarian cancer

Genome instability is key for tumor heterogeneity and derives from defects in cell division and DNA damage repair. Tumors show tolerance for this characteristic, but its accumulation is regulated somehow to avoid catastrophic chromosomal alterations and cell death. Claudin-4 is upregulated and closely associated with genome instability and worse patient outcome in ovarian cancer. This protein is commonly described as a junctional protein participating in processes such as cell proliferation and DNA repair. However, its biological association with genomic instability is still poorly-understood. Here, we used CRISPRi and a claudin mimic peptide (CMP) to modulate the cladudin-4 expression and its function, respectively in in-vitro (high-grade serous carcinoma cells) and in-vivo (patient-derived xenograft in a humanized-mice model) systems. We found that claudin-4 promotes a protective cellular-mechanism that links cell-cell junctions to genome integrity. Disruption of this axis leads to irregular cellular connections and cell cycle that results in chromosomal alterations, a phenomenon associated with a novel functional link between claudin-4 and SLC1A5/LAT1 in regulating autophagy. Consequently, claudin-4's disruption increased autophagy and associated with engulfment of cytoplasm-localized DNA. Furthermore, the claudin-4/SLC1A5/LAT1 biological axis correlates with decrease ovarian cancer patient survival and targeting claudin-4 in-vivo with CMP resulted in increased niraparib (PARPi) efficacy, correlating with increased tumoral infiltration of T CD8+ lymphocytes. Our results show that the upregulation of claudin-4 enables a mechanism that promotes tolerance to genomic instability and immune evasion in ovarian cancer; thus, suggesting the potential of claudin-4 as a translational target for enhancing ovarian cancer treatment.

Novel chromobox 2 inhibitory peptide decreases tumor progression

BACKGROUND

The Polycomb Repressor Complex 1 (PRC1) is an epigenetic regulator of differentiation and development, consisting of multiple subunits including RING1, BMI1, and Chromobox. The composition of PRC1 dictates its function and aberrant expression of specific subunits contributes to several diseases including cancer. Specifically, the reader protein Chromobox2 (CBX2) recognizes the repressive modifications including histone H3 lysine 27 tri-methylation (H3K27me3) and H3 lysine 9 dimethylation (H3K9me2). CBX2 is overexpressed in several cancers compared to the non-transformed cell counterparts, it promotes both cancer progression and chemotherapy resistance. Thus, inhibiting the reader function of CBX2 is an attractive and unique anti-cancer approach.

RESEARCH DESIGN & METHODS

Compared with other CBX family members, CBX2 has a unique A/T-hook DNA binding domain that is juxtaposed to the chromodomain (CD). Using a computational approach, we constructed a homology model of CBX2 encompassing the CD and A/T hook domain. We used the model as a basis for peptide design and identified blocking peptides that are predicted to directly bind the CD and A/T-hook regions of CBX2. These peptides were tested in vitro and in vivo models.

CONCLUSION

The CBX2 blocking peptide significantly inhibited both 2D and 3D growth of ovarian cancer cells, downregulated a CBX2 target gene, and blunted tumor growth in vivo.

Combinatory EHMT and PARP inhibition induces an interferon response and a CD8 T cell-dependent tumor regression in PARP inhibitor-resistant models

Euchromatic histone lysine methyltransferases 1 and 2 (EHMT1/2), which catalyze demethylation of histone H3 lysine 9 (H3K9me2), contribute to tumorigenesis and therapy resistance through unknown mechanisms of action. In ovarian cancer, EHMT1/2 and H3K9me2 are directly linked to acquired resistance to poly-ADP-ribose polymerase (PARP) inhibitors and are correlated with poor clinical outcomes. Using a combination of experimental and bioinformatic analyses in several PARP inhibitor resistant ovarian cancer models, we demonstrate that combinatory inhibition of EHMT and PARP is effective in treating PARP inhibitor resistant ovarian cancers. Our in vitro studies show that combinatory therapy reactivates transposable elements, increases immunostimulatory dsRNA formation, and elicits several immune signaling pathways. Our in vivo studies show that both single inhibition of EHMT and combinatory inhibition of EHMT and PARP reduces tumor burden, and that this reduction is dependent on CD8 T cells. Together, our results uncover a direct mechanism by which EHMT inhibition helps to overcome PARP inhibitor resistance and shows how an epigenetic therapy can be used to enhance anti-tumor immunity and address therapy resistance.

Targeting DUSP Activity as a Treatment for High-Grade Serous Ovarian Carcinoma

Identifying novel, durable treatments for high-grade serous ovarian cancer (HGSOC) is paramount to extend both progression-free survival (PFS) and overall survival (OS) in patients afflicted with this disease. Dual-specificity phosphatase 1 (DUSP1) was identified as one of seven genes that may significantly affect prognosis in patients with HGSOC; however, the role of DUSP inhibition (DUSPi) in the treatment of HGSOC remains largely unknown. In this study, we show that DUSP1 is highly expressed in HGSOC and confers worse PFS and OS. Further, we corroborate data that show DUSP1 expression is directly associated with therapy resistance. Using a tissue microarray of 137 different serous ovarian carcinomas, we demonstrate the high expression of DUSP1 in primary and recurrent serous ovarian cancer. In both acquired and de novo therapy HGSOC-resistant models, DUSPi both inhibited cellular proliferation and promoted cell death. RPPA analysis of HGSOC cells revealed DUSPi led to the differential regulation of several pathways, including AMPK and mTORC. Further, in a patient-derived xenograft HGSOC model, DUSPi significantly inhibited tumor progression.

Loss of Claudin-4 Reduces DNA Damage Repair and Increases Sensitivity to PARP Inhibitors

High-grade serous ovarian cancer is the deadliest gynecologic malignancy due to progression to resistant disease. Claudin-4 is classically defined as a tight junction protein and is often associated with epithelial cancers. Claudin-4 is aberrantly expressed in nearly 70% of all ovarian cancer tumors and conveys a worse overall prognosis. Elevated claudin-4 expression correlates to increased DNA repair activity and resistance to DNA damaging agents. PARP inhibitors are emerging as an effective therapeutic option for patients with ovarian cancer and function by promoting DNA damage. The study examines the relationship between claudin-4 expression and the response to PARP inhibitors using both genetic and pharmacologic inhibition of claudin-4 in in vitro and ex vivo models of ovarian cancer to examine DNA repair markers and functional activity. Genetic inhibition of claudin-4 results in the downregulation of several DNA damage repair effectors, including 53BP1 and XRCC1. Claudin-4 knockdown did not change homology-directed repair but inhibited nonhomologous end-joining and reduced 53BP1 foci formation. In 15 primary ovarian cancer tumors, higher claudin-4 expression significantly correlated to a dampened PARP inhibitor-mediated antiproliferation response. Further, claudin-4 inhibition in high claudin-4 tumors sensitized tumor sections to PARP inhibition. These data highlight that claudin-4 expression in ovarian cancer tumors could serve as both a marker of PARP inhibitor response and a therapeutic target to improve PARP inhibitor response.

Abstract PO043: Targeting beta-catenin and Wnt signaling in CTNNB1-mutated endometrial cancer

Background: CTNNB1 mutations convey increased rates of disease recurrence in early stage, low grade endometrial cancer (EC). The role of beta-catenin transcriptional activity in CTNNB1-mutated EC recurrence is not well understood. We aim to assess the impact of Wnt/beta-catenin inhibition in EC models.

Methods: Data mining The Cancer Genome Atlas (TCGA) of endometrial carcinoma (PanCancer Atlas), we evaluated CTNNB1-mutated vs -wildtype tumors in a low-risk population. We then studied EC cell lines that are CTNNB1-wildtype (HEC1B, Ishikawa) or CTNNB1-mutated (HEC108, HEC265, HEC1B-S33Y, Ishikawa-S33Y). CTNNB1-S33Y cell lines were created via retroviral transduction. Treatment dose curves were determined for 5 Wnt/beta-catenin pathway inhibitors (Wnt-C59, XAV-939, PyrPam, PRI-724, SM04690). Cell viability was assessed with Licor Cell Staining. TCF transcriptional activity was determined via TOP/FOP reporter assay. Apoptosis following treatment with SM04690 was evaluated via Annexin V/propidium iodide (PI). HEC1B, HEC1B-S33Y and HEC265 tumor-bearing athymic nude mice were treated with vehicle or SM04690 25mg/kg. Tumor size was measured using calipers. Tumor cell proliferation and apoptosis were evaluated with immunohistochemistry for Ki67 and Cleaved Caspase 3.

Results: TCGA database analysis parallels previous findings that CTNNB1 mutations are enriched in recurrent low-risk EC. XAV939, Wnt-C59 and PyrPam all inhibit function upstream of beta-catenin transcriptional activity and were ineffective at inhibiting EC cell viability. In contrast, PRI724 and SM04690 indirectly inhibit beta-catenin transcriptional activity and significantly reduce cell viability in CTNNB1-mutated EC cell lines. Treatment with SM04690 reduced cell viability in all EC cell lines, but was significantly lower in HEC108, HEC265 and HEC1B-S33Y compared to HEC1B (24.2%, 32.3%, 44.4%, 71.4%, p<0.01). Compared to control, SM04690 significantly induced apoptosis in HEC265 cells (3.98% vs. 6.91% AnnexinV/PI+, p=0.0443) and reduced TCF transcriptional activity in HEC1B-S33Y (-84%, p=0.017) and HEC108 (-74%, p=0.002) cells. In the mouse model, HEC1B, HEC1B-S33Y and HEC265 tumors treated with SM04690 had smaller mean tumor volumes than those treated with vehicle (146.4 vs 335.4cm3, p<0.001; 136.4 vs. 243.1cm3, p=0.014; 105.7 vs. 321.8cm3, p=0.06). In HEC1B-S33Y tumors, SM04690 treatment significantly reduced Ki67 H-scores compared to vehicle (129.8 vs. 146.7, p=0.0351).

Conclusions: Targeting the Wnt/beta-catenin pathway in CTNNB1-mutated EC effectively inhibited proliferation and beta-catenin/TCF transcriptional activity. Further, the inhibitor SM04690 blunted tumor progression in multiple in vivo models. These studies demonstrate beta-catenin transcriptional inhibitors are effective in CTNNB1-mutated EC and have a more significant effect in CTNNB1-mutated EC than CTNNB1-wildtype EC. These findings highlight a potential therapeutic vulnerability for treatment of CTNNB1-mutated EC.

Citation Format: Marisa R. Moroney, Elizabeth R. Woodruff, Lubna Qamar, Benjamin G. Bitler, Bradley R. Corr. Targeting beta-catenin and Wnt signaling in CTNNB1-mutated endometrial cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference: Endometrial Cancer: New Biology Driving Research and Treatment; 2020 Nov 9-10. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(3_Suppl):Abstract nr PO043.

Glucocorticoid hormones are both a major circadian signal and major stress signal: How this shared signal contributes to a dynamic relationship between the circadian and stress systems

Glucocorticoid hormones are a powerful mammalian systemic hormonal signal that exerts regulatory effects on almost every cell and system of the body. Glucocorticoids act in a circadian and stress-directed manner to aid in adaptation to an ever-changing environment. Circadian glucocorticoid secretion provides for a daily waxing and waning influence on target cell function. In addition, the daily circadian peak of glucocorticoid secretion serves as a timing signal that helps entrain intrinsic molecular clock phase in tissue cells distributed throughout the body. Stress-induced glucocorticoid secretion also modulates the state of these same cells in response to both physiological and psychological stressors. We review the strong functional interrelationships between glucocorticoids and the circadian system, and discuss how these interactions optimize the appropriate cellular and systems response to stress throughout the day. We also discuss clinical implications of this dual aspect of glucocorticoid signaling, especially for conditions of circadian and HPA axis dysregulation.

Adrenal-dependent and -independent stress-induced Per1 mRNA in hypothalamic paraventricular nucleus and prefrontal cortex of male and female rats

Oscillating clock gene expression gives rise to a molecular clock that is present not only in the body's master circadian pacemaker, the hypothalamic suprachiasmatic nucleus (SCN), but also in extra-SCN brain regions. These extra-SCN molecular clocks depend on the SCN for entrainment to a light:dark cycle. The SCN has limited neural efferents, so it may entrain extra-SCN molecular clocks through its well-established circadian control of glucocorticoid hormone secretion. Glucocorticoids can regulate the normal rhythmic expression of clock genes in some extra-SCN tissues. Untimely stress-induced glucocorticoid secretion may compromise extra-SCN molecular clock function. We examined whether acute restraint stress during the rat's inactive phase can rapidly (within 30 min) alter clock gene (Per1, Per2, Bmal1) and cFos mRNA (in situ hybridization) in the SCN, hypothalamic paraventricular nucleus (PVN), and prefrontal cortex (PFC) of male and female rats (6 rats per treatment group). Restraint stress increased Per1 and cFos mRNA in the PVN and PFC of both sexes. Stress also increased cFos mRNA in the SCN of male rats, but not when subsequently tested during their active phase. We also examined in male rats whether endogenous glucocorticoids are necessary for stress-induced Per1 mRNA (6-7 rats per treatment group). Adrenalectomy attenuated stress-induced Per1 mRNA in the PVN and ventral orbital cortex, but not in the medial PFC. These data indicate that increased Per1 mRNA may be a means by which extra-SCN molecular clocks adapt to environmental stimuli (e.g. stress), and in the PFC this effect is largely independent of glucocorticoids.

Analysis of c-Fos induction in response to social interaction in male and female Fisher 344 rats

Sex differences in the expression of social behavior are typically apparent in adolescent and adult rats. While the neurobiology underlying juvenile social play behavior has been well characterized, less is known about discrete brain regions involved in adult responsiveness to a same sex peer. Furthermore, whether adult males and females differ in their responsiveness to a social interaction in terms of neuronal activation indexed via immediate early gene (IEG) expression remains to be determined. Thus, the present study was designed to identify key sites relevant to the processing of sensory stimuli (generally) or social stimuli (specifically) after brief exposure to a same-sex social partner by assessing IEG expression. Four-month-old male and female Fisher (F) 344 rats (N=38; n=5-8/group) were either left undisturbed in their home cage as controls (HCC), exposed to a testing context alone for 30min (CXT), or were placed in the context for 20min and then allowed to socially interact (SI) with a sex-matched conspecific for 10min. Females demonstrated greater levels of social behavior, relative to males. Analysis of c-Fos induction revealed that females exhibited greater c-Fos expression in the prefrontal cortex, regardless of condition. In many brain regions, induction was similar in the CXT and SI groups. However, in the bed nucleus of the stria terminalis (BNST), females exhibited greater c-Fos induction in response to the social interaction relative to their male counterparts, indicating a sex difference in responsivity to social stimuli. Taken together, these data suggest that the BNST is a sexually dimorphic region in terms of activation in response to social stimuli.

Dynamic glucocorticoid-dependent regulation of Sgk1 expression in oligodendrocytes of adult male rat brain by acute stress and time of day

Recent studies support plasticity in adult brain white matter structure and myelination in response to various experiential factors. One possible contributor to this plasticity may be activity-dependent modulation of serum- and glucocorticoid-inducible kinase 1 (Sgk1) expression in oligodendrocytes. We examined whether Sgk1 expression in adult rat brain white matter is increased by acute stress-induced elevations in endogenous corticosterone and whether it fluctuates with diurnal variations in corticosterone. We observed rapid increases (within 30 min) in Sgk1 mRNA in the corpus callosum in response to acute stress, as well as large increases at the beginning of the rat's active period (the time of peak corticosterone secretion). These increases were absent in adrenalectomized rats. Corticosterone treatment of adrenalectomized rats also rapidly increased corpus callosum Sgk1 mRNA. The majority of Sgk1 mRNA in corpus callosum was co-localized with myelin basic protein mRNA, suggesting that mature oligodendrocytes respond dynamically to acute stress and circadian rhythms. The regulation of Sgk1 expression by acute stress and time of day was selective for white matter, with limited alteration of Sgk1 expression by these factors in hippocampus and somatosensory cortex. These results indicate a unique sensitivity of oligodendrocyte Sgk1 expression to activity-dependent fluctuations in corticosterone hormone secretion, and raises the prospect that hypothalamic-pituitary-adrenal axis dysregulation or glucocorticoid pharmacotherapy may compromise the normal activity-dependent interactions between oligodendrocytes and neurons.

Glucocorticoid Fast Feedback Inhibition of Stress-Induced ACTH Secretion in the Male Rat: Rate Independence and Stress-State Resistance

Normal glucocorticoid secretion is critical for physiological and mental health. Glucocorticoid secretion is dynamically regulated by glucocorticoid-negative feedback; however, the mechanisms of that feedback process are poorly understood. We assessed the temporal characteristics of glucocorticoid-negative feedback in vivo using a procedure for drug infusions and serial blood collection in unanesthetized rats that produced a minimal disruption of basal ACTH plasma levels. We compared the negative feedback effectiveness present when stress onset coincides with corticosterone's (CORT) rapidly rising phase (30 sec pretreatment), high plateau phase (15 min pretreatment), or restored basal phase (60 min pretreatment) as well as effectiveness when CORT infusion occurs after the onset of stress (5 min poststress onset). CORT treatment prior to stress onset acted remarkably fast (within 30 sec) to suppress stress-induced ACTH secretion. Furthermore, fast feedback induction did not require rapid increases in CORT at the time of stress onset (hormone rate independent), and those feedback actions were relatively long lasting (≥15 min). In contrast, CORT elevation after stress onset produced limited and delayed ACTH suppression (stress state resistance). There was a parallel stress-state resistance for CORT inhibition of stress-induced Crh heteronuclear RNA in the paraventricular nucleus but not Pomc heteronuclear RNA in the anterior pituitary. CORT treatment did not suppress stress-induced prolactin secretion, suggesting that CORT feedback is restricted to the control of hypothalamic-pituitary-adrenal axis elements of a stress response. These temporal, stress-state, and system-level features of in vivo CORT feedback provide an important physiological context for ex vivo studies of molecular and cellular mechanisms of CORT-negative feedback.

Diurnal Corticosterone Presence and Phase Modulate Clock Gene Expression in the Male Rat Prefrontal Cortex

Mood disorders are associated with dysregulation of prefrontal cortex (PFC) function, circadian rhythms, and diurnal glucocorticoid (corticosterone [CORT]) circulation. Entrainment of clock gene expression in some peripheral tissues depends on CORT. In this study, we characterized over the course of the day the mRNA expression pattern of the core clock genes Per1, Per2, and Bmal1 in the male rat PFC and suprachiasmatic nucleus (SCN) under different diurnal CORT conditions. In experiment 1, rats were left adrenal-intact (sham) or were adrenalectomized (ADX) followed by 10 daily antiphasic (opposite time of day of the endogenous CORT peak) ip injections of either vehicle or 2.5 mg/kg CORT. In experiment 2, all rats received ADX surgery followed by 13 daily injections of vehicle or CORT either antiphasic or in-phase with the endogenous CORT peak. In sham rats clock gene mRNA levels displayed a diurnal pattern of expression in the PFC and the SCN, but the phase differed between the 2 structures. ADX substantially altered clock gene expression patterns in the PFC. This alteration was normalized by in-phase CORT treatment, whereas antiphasic CORT treatment appears to have eliminated a diurnal pattern (Per1 and Bmal1) or dampened/inverted its phase (Per2). There was very little effect of CORT condition on clock gene expression in the SCN. These experiments suggest that an important component of glucocorticoid circadian physiology entails CORT regulation of the molecular clock in the PFC. Consequently, they also point to a possible mechanism that contributes to PFC disrupted function in disorders associated with abnormal CORT circulation.

Variations in Phase and Amplitude of Rhythmic Clock Gene Expression across Prefrontal Cortex, Hippocampus, Amygdala, and Hypothalamic Paraventricular and Suprachiasmatic Nuclei of Male and Female Rats

The molecular circadian clock is a self-regulating transcription/translation cycle of positive (Bmal1, Clock/Npas2) and negative (Per1,2,3, Cry1,2) regulatory components. While the molecular clock has been well characterized in the body's master circadian pacemaker, the hypothalamic suprachiasmatic nucleus (SCN), only a few studies have examined both the positive and negative clock components in extra-SCN brain tissue. Furthermore, there has yet to be a direct comparison of male and female clock gene expression in the brain. This comparison is warranted, as there are sex differences in circadian functioning and disorders associated with disrupted clock gene expression. This study examined basal clock gene expression (Per1, Per2, Bmal1 mRNA) in the SCN, prefrontal cortex (PFC), rostral agranular insula, hypothalamic paraventricular nucleus (PVN), amygdala, and hippocampus of male and female rats at 4-h intervals throughout a 12:12 h light:dark cycle. There was a significant rhythm of Per1, Per2, and Bmal1 in the SCN, PFC, insula, PVN, subregions of the hippocampus, and amygdala with a 24-h period, suggesting the importance of an oscillating molecular clock in extra-SCN brain regions. There were 3 distinct clock gene expression profiles across the brain regions, indicative of diversity among brain clocks. Although, generally, the clock gene expression profiles were similar between male and female rats, there were some sex differences in the robustness of clock gene expression (e.g., females had fewer robust rhythms in the medial PFC, more robust rhythms in the hippocampus, and a greater mesor in the medial amygdala). Furthermore, females with a regular estrous cycle had attenuated aggregate rhythms in clock gene expression in the PFC compared with noncycling females. This suggests that gonadal hormones may modulate the expression of the molecular clock.

Adrenal-dependent diurnal modulation of conditioned fear extinction learning

Post traumatic stress disorder (PTSD) is associated with altered conditioned fear extinction expression and impaired circadian function including dysregulation of glucocorticoid hormone secretion. We examined in adult male rats the relationship between conditioned fear extinction learning, circadian phase, and endogenous glucocorticoids (CORT). Rats maintained on a 12h light:dark cycle were trained and tested across 3 separate daily sessions (conditioned fear acquisition and 2 extinction sessions) that were administered during either the rats' active or inactive circadian phase. In an initial experiment we found that rats at both circadian phases acquired and extinguished auditory cue conditioned fear to a similar degree in the first extinction session. However, rats trained and tested at zeitgeber time-16 (ZT16) (active phase) showed enhanced extinction memory expression during the second extinction session compared to rats trained and tested at ZT4 (inactive phase). In a follow-up experiment, adrenalectomized (ADX) or sham surgery rats were similarly trained and tested across 3 separate daily sessions at either ZT4 or ZT16. ADX had no effect on conditioned fear acquisition or conditioned fear memory. Sham ADX rats trained and tested at ZT16 exhibited better extinction learning across the two extinction sessions compared to all other groups of rats. These results indicate that conditioned fear extinction learning is modulated by time of day, and this diurnal modulation requires the presence of adrenal hormones. These results support an important role of CORT-dependent circadian processes in regulating conditioned fear extinction learning, which may be capitalized upon to optimize effective treatment of PTSD.