Cerebral hypoperfusion increases estrogen receptor abundance in the ovine fetal brain and pituitary

Thrombosis and bleeding after COVID-19 vaccination: do differences in sex matter?

Gender medicine deals with differences in approach to diagnostic work-up and management according to gender. Although the issue is relevant in every field of medicine, it is often neglected. However, the recent SARS-CoV-2 pandemic has made consideration of gender even more urgent. In fact, available literature has suggested a higher number of deaths among infected men than in women and more side effects in women than in male recipients of certain anti-COVID-19 vaccines. This review examines sex-disaggregated data on thrombotic and bleeding events associated with vaccination against COVID-19. Thrombotic complications are by far more frequently reported than bleeding events after vaccination and are mostly observed in young women receiving viral-vectored vaccines. However, detailed data that could help better stratify the risk according to sex/gender are generally lacking. Likewise, overall bleeding complications and those associated with a specific vaccine are mainly reported as aggregated data, including thrombocytopenia that is reported to occur in the presence or absence of thrombotic complications. Such information is important as it underlines the need to differentiate between thrombocytopenia with and without thrombosis because management and prognosis differ according to the association of thrombotic events. Here, we highlight how the lack of disaggregated data has led to the publication of conflicting information about adverse events by sex in recipients of viral-vectored vaccines. Lastly, we examine the possible mechanisms underlying vaccine-associated thrombotic and bleeding complications according to sex/gender.

A transcriptomics model of estrogen action in the ovine fetal hypothalamus: evidence for estrogenic effects of ICI 182,780

Estradiol plays a critical role in stimulating the fetal hypothalamus-pituitary-adrenal axis at the end of gestation. Estradiol action is mediated through nuclear and membrane receptors that can be modulated by ICI 182,780, a pure antiestrogen compound. The objective of this study was to evaluate the transcriptomic profile of estradiol and ICI 182,780, testing the hypothesis that ICI 182,780 antagonizes the action of estradiol in the fetal hypothalamus. Chronically catheterized ovine fetuses were infused for 48 h with: vehicle (Control, n = 6), 17β-estradiol 500 μg/kg/day (Estradiol, n = 4), ICI 182,780 5 μg/kg/day (ICI 5 μg, n = 4) and ICI 182,780 5 mg/kg/day (ICI 5 mg, n = 5). Fetal hypothalami were collected afterward, and gene expression was measured through microarray. Statistical analysis of transcriptomic data was performed with Bioconductor-R and Cytoscape software. Unexpectedly, 35% and 15.5% of the upregulated differentially expressed genes (DEG) by Estradiol significantly overlapped (P < 0.05) with upregulated DEG by ICI 5 mg and ICI 5 μg, respectively. For the downregulated DEG, these percentages were 29.9% and 15.5%, respectively. There was almost no overlap for DEG following opposite directions between Estradiol and ICI ICI 5 mg or ICI 5 μg. Furthermore, most of the genes in the estrogen signaling pathway - after activation of the epidermal growth factor receptor - followed the same direction in Estradiol, ICI 5 μg or ICI 5 mg compared to Control. In conclusion, estradiol and ICI 182,780 have estrogenic genomic effects in the developing brain, suggesting the possibility that the major action of estradiol on the fetal hypothalamus involves another receptor system rather than estrogen receptors.

Estradiol Protects White Matter of Male C57BL6J Mice against Experimental Chronic Cerebral Hypoperfusion

BACKGROUND AND PURPOSE

Estradiol is a sex steroid hormone known to protect the brain against damage related to transient and global cerebral ischemia. In the present study, we leverage an experimental murine model of bilateral carotid artery stenosis (BCAS) to examine the putative effects of estradiol therapy on chronic cerebral hypoperfusion. We hypothesize that long-term estradiol therapy protects against white matter injury and declarative memory deficits associated with chronic cerebral hypoperfusion.

METHODS

Adult male C57BL/6J mice underwent either surgical BCAS or sham procedures. Two days after surgery, the mice were given oral estradiol (Sham+E, BCAS+E) or placebo (Sham+P, BCAS+P) treatments daily for 31-34 days. All mice underwent Novel Object Recognition (NOR) testing 31-34 days after the start of oral treatments. Following sacrifice, blood was collected and brains fixed, sliced, and prepared for histological examination of white matter injury and extracellular signal-regulated kinase (ERK) expression.

RESULTS

Animals receiving long-term oral estradiol therapy (BCAS-E2 and Sham-E2) had higher plasma estradiol levels than those receiving placebo treatment (BCAS-P and Sham-P). BCAS-E2 mice demonstrated less white matter injury (Klüver-Barrera staining) and performed better on the NOR task compared to BCAS-P mice. ERK expression in the brain was increased in the BCAS compared to sham cohorts. Among the BCAS mice, the BCAS-E2 cohort had a greater number of ERK + cells.

CONCLUSION

This study demonstrates a potentially protective role for oral estradiol therapy in the setting of white matter injury and declarative memory deficits secondary to murine chronic cerebral hypoperfusion.

Transcriptomics of the fetal hypothalamic response to brachiocephalic occlusion and estradiol treatment

Estradiol (E2) is a well-known modulator of fetal neuroendocrine activity and has been proposed as a critical endocrine signal readying the fetus for birth and postnatal life. To investigate the modulatory role of E2 on fetal stress responsiveness and the response of the fetal brain to asphyxic stress, we subjected chronically catheterized fetal sheep to a transient (10 min) brachiocephalic artery occlusion (BCO) or sham occlusion. Half of the fetuses received subcutaneous pellets that increased plasma E2 concentrations within the physiological range. Hypothalamic mRNA was analyzed using the Agilent 8x15k ovine array (019921), processed and annotated as previously reported by our laboratory. Analysis of the data by ANOVA revealed that E2 differentially regulated (DR) 561 genes, and BCO DR 894 genes compared with control and E2+BCO DR 1,153 genes compared with BCO alone (all P < 0.05). E2 upregulated epigenetic pathways and downregulated local steroid biosynthesis but did not significantly involve genes known to directly respond to the estrogen receptor. Brachiocephalic occlusion upregulated kinase pathways as well as genes associated with lymphocyte infiltration into the brain and downregulated neuropeptide synthesis. E2 upregulated immune- and apoptosis-related pathways after BCO and reduced kinase and epigenetic pathway responses to the BCO. Responses to BCO are different from responses to hypoxic hypoxia suggesting that mechanisms of responses to these two forms of brain hypoxia are distinct. We conclude that cerebral ischemia caused by BCO might stimulate lymphocyte infiltration into the brain and that this response appears to be modified by estradiol.

Genomics of the fetal hypothalamic cellular response to transient hypoxia: endocrine, immune, and metabolic responses

Fetuses respond to transient hypoxia (a common stressor in utero) with cellular responses that are appropriate for promoting survival of the fetus. The present experiment was performed to identify the acute genomic responses of the fetal hypothalamus to transient hypoxia. Three fetal sheep were exposed to 30 min of hypoxia and hypothalamic mRNA extracted from samples collected 30 min after return to normoxia. These samples were compared with those from four normoxic control fetuses by the Agilent 019921 ovine array. Differentially regulated genes were analyzed by network analysis and by gene ontology analysis, identifying statistically significant overrepresentation of biological processes. Real-time PCR of selected genes supported the validity of the array data. Hypoxia induced increased expression of genes involved in response to oxygen stimulus, RNA splicing, antiapoptosis, vascular smooth muscle proliferation, and positive regulation of Notch receptor target. Downregulated genes were involved in metabolism, antigen receptor-mediated immunity, macromolecular complex assembly, S-phase, translation elongation, RNA splicing, protein transport, and posttranscriptional regulation. We conclude that these results emphasize that the cellular response to hypoxia involves reduced metabolism, the involvement of the fetal immune system, and the importance of glucocorticoid signaling.

Complex actions of estradiol-3-sulfate in late gestation fetal brain

The most abundant form of estrogen circulating in fetal plasma is sulfo-conjugated estrogen; for example, estradiol-3-sulfate (E(2)SO(4)) is more highly abundant than estradiol (E(2)). The present study investigated the ontogeny of the deconjugating (steroid sulfatase [STS]) and conjugating (estrogen sulfotransferase [STF]) enzymes in ovine fetal brain and tested the hypothesis that treatment with E(2)SO(4) would alter the expression of one or both enzymes. Steroid sulfatase was more highly expressed than STF, and both changed as a function of gestational age. Estradiol-3-sulfate infused intracerebroventricularly (icv) significantly increased plasma adrenocorticotropic hormone (ACTH) and cortisol concentrations. Plasma E(2) and E(2)SO(4) were increased, and brain expression of estrogen receptor α was decreased. The proteins STS and STF were up- and downregulated, respectively. Pituitary proopiomelanocortin (POMC) and follicle-stimulating hormone (FSH) and hypothalamic corticotrophin-releasing hormone (CRH) messenger RNA (mRNA) was decreased. We conclude that E(2)SO(4) has complex actions on the fetal brain, which might involve deconjugation by STS, but that the net result of direct E(2)SO(4) icv infusion is more complex than can be accounted for by infusion of E(2) alone.

Influence of estradiol and fetal stress on luteinizing hormone, follicle-stimulating hormone, and prolactin in late-gestation fetal sheep

BACKGROUND

Hypotension and reduced cerebral blood flow secondary to brachiocephalic occlusion (BCO) stimulate various homeostatic physiological and endocrine responses. Our previous studies have also suggested a role of estradiol in augmenting the fetal stress response to BCO.

OBJECTIVES

We tested the hypothesis that gonadotropins and/or prolactin (PRL) are upregulated in fetal pituitary in response to fetal stress and play a role in the response to BCO-induced stress.

METHODS

We performed 3 studies: one in which we measured ovine fetal pituitary PRL, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) mRNA throughout the latter half of gestation in order to better understand the ontogenetic changes upon which dynamic responses are superimposed; one in which we measured these mRNA abundances in response to BCO and/or estrogen treatment, and one in which we measured plasma LH responses to BCO in chronically catheterized late-gestation fetal sheep.

RESULTS

PRL gene expression is increased dramatically in the last 20% of gestation. LH and FSH mRNAs were unchanged except for a transient dip in the expression of LH in the last few days before the normal time of spontaneous parturition. Chronic treatment with estradiol decreased LH and FSH mRNA, but increased PRL mRNA abundance after BCO. In contrast, BCO alone increases the abundance of LH, but not FSH or PRL mRNA in fetal pituitary. Plasma LH concentrations were not increased in response to BCO.

CONCLUSIONS

We conclude that the late-gestation fetal sheep responds to hypotensive stress with increases in LH mRNA but not LH secretion. LH, FSH and PRL changes are therefore unlikely to contribute to the fetal response to cerebral hypoperfusion.

Blockade of estrogen action upregulates estrogen receptor-alpha mRNA in the fetal brain

BACKGROUND

Fetal neuroendocrine maturation in late gestation is critical for maintenance of fetal homeostasis, growth, and readiness for birth. Sheep express estrogen receptors (ERs) in various brain regions. However, little is known about the regulation of ER-alpha and ER-beta in the ovine brain prenatally.

OBJECTIVE

The present study was designed to test the hypothesis that the expression of ER is influenced by circulating estrogens in the late-gestation sheep fetus.

METHODS

Six chronically-catheterized twin fetal sheep were treated with vehicle or the ER blocker ICI 182,780 i.c.v. (0.25 microg/day). Fetuses were sacrificed 6-14 days after surgery and start of infusion. Brain regions were rapidly isolated and snap-frozen for later extraction of mRNA and protein. ER-alpha and ER-beta mRNA was measured using real-time PCR and protein was measured using Western blot.

RESULTS

Treatment with ICI 182,780 increased ER-alpha mRNA, especially in cerebellum and hippocampus. There were no changes in ER-alpha protein and no changes in ER-beta at either the mRNA or protein level.

CONCLUSION

Expression of ER-alpha is influenced by endogenous estrogens in the ovine fetal brain.