The G protein-coupled estrogen receptor (GPER) regulates recognition and aversively-motivated memory in male rats

The Lysine Acetyltransferase PCAF Functionally Interacts with Estrogen Receptor Alpha in the Hippocampus of Gonadally Intact Male-But Not Female-Rats to Enhance Short-Term Memory

Acetylation of histone proteins by histone acetyltransferases (HATs), and the resultant change in gene expression, is a well-established mechanism necessary for long-term memory (LTM) consolidation, which is not required for short-term memory (STM). However, we previously demonstrated that the HAT p300/CBP-associated factor (PCAF) also influences hippocampus (HPC)-dependent STM in male rats. In addition to their epigenetic activity, HATs acetylate nonhistone proteins involved in nongenomic cellular processes, such as estrogen receptors (ERs). Given that ERs have rapid, nongenomic effects on HPC-dependent STM, we investigated the potential interaction between ERs and PCAF for STM mediated by the dorsal hippocampus (dHPC). Using a series of pharmacological agents administered directly into the dHPC, we reveal a functional interaction between PCAF and ERα in the facilitation of short-term object-in-place memory in male but not female rats. This interaction was specific to ERα, while ERβ agonism did not enhance STM. It was further specific to dHPC STM, as the effect was not present in the dHPC for LTM or in the perirhinal cortex. Further, while STM required local (i.e., dHPC) estrogen synthesis, the facilitatory interaction effect appeared independent of estrogens. Finally, western blot analyses demonstrated that PCAF activation in the dHPC rapidly (5 min) activated downstream estrogen-related cell signaling kinases (c-Jun N-terminal kinase and extracellular signal-related kinase). Collectively, these findings indicate that PCAF, which is typically implicated in LTM through epigenetic processes, also influences STM in the dHPC, possibly via nongenomic ER activity. Critically, this novel PCAF-ER interaction might exist as a male-specific mechanism supporting STM.

Exploring the physiological role of the G protein-coupled estrogen receptor (GPER) and its associations with human diseases

Estrogen is a group of hormones that collaborate with the nervous system to impact the overall well-being of all genders. It influences many processes, including those occurring in the central nervous system, affecting learning and memory, and playing roles in neurodegenerative diseases and mental disorders. The hormone's action is mediated by specific receptors. Significant roles of classical estrogen receptors, ERα and ERβ, in various diseases were known since many years, but after identifying a structurally and locationally distinct receptor, the G protein-coupled estrogen receptor (GPER), its role in human physiology and pathophysiology was investigated. This review compiles GPER-related information, highlighting its impact on homeostasis and diseases, while putting special attention on functions and dysfunctions of this receptor in neurobiology and biobehavioral processes. Understanding the receptor modulation possibilities is essential for therapy, as disruptions in receptors can lead to diseases or disorders, irrespective of correct estrogen levels. We conclude that studies on the GPER receptor have the potential to develop therapies that regulate estrogen and positively impact human health.

Joint Inflammation Correlates with Joint GPR30 Expression in Males and Hippocampal GPR30 Expression in Females in a Rat Model of Rheumatoid Arthritis

It is not entirely clear how the interaction between joint inflammation and the central nervous system (CNS) response in rheumatoid arthritis (RA) works, and what pathophysiology underlies the sex differences in coexisting neuropsychiatric comorbidities. It is known that estrogen hormones reduce inflammation in RA and that this occurs mainly via the stimulation of G protein-coupled receptor-30 (GPR30), also known as G protein-coupled estrogen receptor (GPER) 1. However, changes in GPR30 expression and sex differences induced by local and systemic inflammation in RA are not yet known. Our aim was to reveal sex differences in the expression and association of joint GPR30 with local and systemic inflammation, clinical course and furthermore with hippocampal GPR30 expression during pristane-induced arthritis (PIA) in Dark Agouti (DA) rats, an animal model of RA. Furthermore, we demonstrated sex-specific differences in the association between joint and systemic inflammation and hippocampal microglia during PIA. Our results suggest sex-specific differences not only in the clinical course and serum levels of pro-inflammatory cytokines but also in the expression of GPR30. Female rats show greater synovial inflammation and greater damage to the articular cartilage compared to males during PIA attack. Male rats express higher levels of synovial and cartilaginous GPR30 than females during PIA, which correlates with a less severe clinical course. The correlation between synovial and cartilaginous GPR30 and joint inflammation scores (Krenn and Mankin) in male rats suggests that the more severe the joint inflammation, the higher the GPR30 expression. At the same time, there is no particular upregulation of hippocampal GPR30 in males. On the other hand, female rats express higher levels of neuroprotective GPR30 in the hippocampus than male rats at the basic level and during PIA attack. In addition, females have a higher number of Iba-1+ cells in the hippocampus during PIA attack that strongly correlates with the clinical score, serum levels of IL-17A, and Krenn and Mankin scores. These results suggest that male rats are better protected from inflammation in the joints and female rats are better protected from the inflammation in the hippocampus during a PIA attack, independently of microglia proliferation. However, in the remission phase, synovial GPR30 expression suddenly increases in female rats, as does hippocampal GPR30 expression in males. Further experiments with a longer remission period are needed to investigate the molecular background of these sex differences, as well as microglia phenotype profiling.

G protein-coupled estrogen receptor (GPER) in the dorsal hippocampus regulates memory consolidation in gonadectomized male mice, likely via different signaling mechanisms than in female mice

Studies in ovariectomized (OVX) female rodents suggest that G protein-coupled estrogen receptor (GPER) is a key regulator of memory, yet little is known about its importance to memory in males or the cellular mechanisms underlying its mnemonic effects in either sex. In OVX mice, bilateral infusion of the GPER agonist G-1 into the dorsal hippocampus (DH) enhances object recognition and spatial memory consolidation in a manner dependent on rapid activation of c-Jun N-terminal kinase (JNK) signaling, cofilin phosphorylation, and actin polymerization in the DH. However, the effects of GPER on memory consolidation and DH cell signaling in males are unknown. Thus, the present study first assessed effects of DH infusion of G-1 or the GPER antagonist G-15 on object recognition and spatial memory consolidation in gonadectomized (GDX) male mice. As in OVX mice, immediate post-training bilateral DH infusion of G-1 enhanced, whereas G-15 impaired, memory consolidation in the object recognition and object placement tasks. However, G-1 did not increase levels of phosphorylated JNK (p46, p54) or cofilin in the DH 5, 15, or 30 min after infusion, nor did it affect phosphorylation of ERK (p42, p44), PI3K, or Akt. Levels of phospho-cAMP-responsive element binding protein (CREB) were elevated in the DH 30 min following G-1 infusion, indicating that GPER in males activates a yet unknown signaling mechanism that triggers CREB-mediated gene transcription. Our findings show for the first time that GPER in the DH regulates memory consolidation in males and suggests sex differences in underlying signaling mechanisms.

Sex-dependent differences in animal cognition

The differences in cognitive processes driven by biological sex are the issues that have gotten growing attention recently. Considering the increasing population suffering from various cognitive impairments and the development of therapeutic strategies, it is essential that we recognize the mechanisms responsible for discrepancies observed in male and female learning and memory functions. In this review, we discuss recent reports from preclinical studies on rodents regarding selected cognitive domains to explore the state of knowledge on sex-dependent differences and point to challenges encountered during such research. We focus on spatial, recognition, and emotional memory, as well as on executive functions, such as attention, cognitive flexibility, and working memory. This review will help to acknowledge sex-related differences in cognition and indicate some fields that lack sufficient data.

The G protein-coupled oestrogen receptor GPER in health and disease: an update

Oestrogens and their receptors contribute broadly to physiology and diseases. In premenopausal women, endogenous oestrogens protect against cardiovascular, metabolic and neurological diseases and are involved in hormone-sensitive cancers such as breast cancer. Oestrogens and oestrogen mimetics mediate their effects via the cytosolic and nuclear receptors oestrogen receptor-α (ERα) and oestrogen receptor-β (ERβ) and membrane subpopulations as well as the 7-transmembrane G protein-coupled oestrogen receptor (GPER). GPER, which dates back more than 450 million years in evolution, mediates both rapid signalling and transcriptional regulation. Oestrogen mimetics (such as phytooestrogens and xenooestrogens including endocrine disruptors) and licensed drugs such as selective oestrogen receptor modulators (SERMs) and downregulators (SERDs) also modulate oestrogen receptor activity in both health and disease. Following up on our previous Review of 2011, we herein summarize the progress made in the field of GPER research over the past decade. We will review molecular, cellular and pharmacological aspects of GPER signalling and function, its contribution to physiology, health and disease, and the potential of GPER to serve as a therapeutic target and prognostic indicator of numerous diseases. We also discuss the first clinical trial evaluating a GPER-selective drug and the opportunity of repurposing licensed drugs for the targeting of GPER in clinical medicine.

G Protein-Coupled Estrogen Receptor GPER: Molecular Pharmacology and Therapeutic Applications

The actions of estrogens and related estrogenic molecules are complex and multifaceted in both sexes. A wide array of natural, synthetic, and therapeutic molecules target pathways that produce and respond to estrogens. Multiple receptors promulgate these responses, including the classical estrogen receptors of the nuclear hormone receptor family (estrogen receptors α and β), which function largely as ligand-activated transcription factors, and the 7-transmembrane G protein-coupled estrogen receptor, GPER, which activates a diverse array of signaling pathways. The pharmacology and functional roles of GPER in physiology and disease reveal important roles in responses to both natural and synthetic estrogenic compounds in numerous physiological systems. These functions have implications in the treatment of myriad disease states, including cancer, cardiovascular diseases, and metabolic disorders. This review focuses on the complex pharmacology of GPER and summarizes major physiological functions of GPER and the therapeutic implications and ongoing applications of GPER-targeted compounds.

The effects of GPER on age-associated memory impairment induced by decreased estrogen levels

Estrogen, as a pleiotropic endocrine hormone, not only regulates the physiological functions of peripheral tissues but also exerts vital neuroregulatory effects in the central nervous system (CNS), such as the development of neurons and the formation of neural network connections, wherein rapid estrogen-mediated reactions positively stimulate spinogenesis and regulate synaptic plasticity and synaptic transmission to facilitate cognitive and memory performance. These fast non-genomic effects can be initiated by membrane-bound estrogen receptors (ERs), three best known of which are ERα, ERβ, and G protein-coupled estrogen receptor (GPER). To date, the effects of ERα and ERβ have been well studied in age-associated memory impairment, whereas there is still a lack of attention to the role of GPER in age-associated memory impairment, and there are still disputes about whether GPER indeed functions as an ER to enhance learning and memory. In this review, we provide a systematic overview of the role of GPER in age-associated memory impairment based on its expression, distribution, and signaling pathways, which might bring some inspiration for translational drugs targeting GPER for age-related diseases and update knowledge on the role of estrogen and its receptor system in the brain.