Loss of estrogen-related receptor alpha disrupts ventral-striatal synaptic function in female mice

Comprehensive insights into emerging advances in the Neurobiology of anorexia

BACKGROUND

Anorexia is a complex eating disorder influenced by genetic, environmental, psychological, and socio-cultural factors. Research into its molecular mechanisms and neural circuits has deepened our understanding of its pathogenesis. Recent advances in neuroscience, molecular biology, and genetics have revealed key molecular and neural circuit mechanisms underlying anorexia.

AIM OF REVIEW

Clarify the peripheral and central molecular mechanisms regulating various types of anorexia, identify key cytokines and neural circuits, and propose new strategies for its treatment. Key scientific concepts of review: Anorexia animal models, including activity-induced, genetic mutation, and inflammation-induced types, are explored for their relevance to studying the disorder. Anorexic behavior is regulated by cytokines, hormones (like GDF15, GLP-1, and leptin), and neural circuits such as AgRP, serotonergic, dopaminergic, and glutamatergic pathways. Disruptions in these pathways, including GABAergic signaling in AgRP neurons and 5-HT2C and D2 receptors, contribute to anorexia. Potential therapies target neurotransmitter receptors, ghrelin receptors, and the GDF15-GFRAL pathway, offering insights for treating anorexia, immune responses, and obesity.

Estrogen-related receptor gamma is a regulator of mitochondrial, autophagy, and immediate-early gene programs in spiny projection neurons: Relevance for transcriptional changes in Huntington disease

Mitochondrial dysfunction, transcriptional dysregulation, and protein aggregation are hallmarks of multiple neurodegenerative disorders, including Huntington's disease (HD). Strategies are needed to counteract these processes to restore neuronal health and function in HD. Recent evidence indicates that the transcription factor estrogen-related receptor gamma (ERRγ/Esrrg) is required for normal expression of mitochondrial, synaptic, and autophagy genes in neurons. Further, overexpression of Esrrg in dopaminergic neurons reduces synuclein load in the pre-formed fibril model of synucleinopathy. For these reasons, we sought to understand ERRγ's role in transcriptional regulation in spiny projection neurons (SPNs), one of the neuronal populations vulnerable to transcriptional dysregulation, mitochondrial dysfunction, and protein aggregation in HD. Here, we demonstrate that developmental deletion of Esrrg selectively in SPNs causes a transcriptional pattern consistent with a reduction of Drd1 and Drd2-positive neurons in the mouse dorsolateral striatum. To avoid effects of developmental deletion and explore Esrrg's role within adult SPN populations, we deleted or overexpressed Esrrg in adult SPNs. While overexpression was sufficient to increase the expression of mitochondrial and lysosome-related transcripts, Esrrg deletion surprisingly caused increased expression of immediate-early genes and genes with enrichment of binding sites for transcriptional repressors. In contrast, these genes were downregulated by Esrrg overexpression. Concordantly, Esrrg-deficient mice exhibited lack of amphetamine-induced hyperactivity and further upregulation of immediate-early genes. To determine whether the alterations observed with ERRγ modulation have any relevance for understanding transcriptional changes in SPNs in neurodegeneration, we measured Esrrg and its responsive genes in two mouse models of HD. We found an increase in Esrrg expression in HD models, accompanied by a transcriptional profile with similarities to that observed with Esrrg overexpression, suggesting the existence of an ERRγ-dependent, stress-related response. Altogether, these studies suggest that ERRγ is a key activator of mitochondrial and lysosomal transcripts in SPNs with a potential bi-functional role as a mediator of immediate-early gene repression. Ongoing studies are investigating mechanisms underlying ERRγ's roles in transcriptional activation and repression in SPNs to inform strategies to promote neuroprotective actions of ERRγ in SPNs in HD.

Sex differences in mitochondrial gene expression during viral myocarditis

BACKGROUND

Myocarditis is an inflammation of the heart muscle most often caused by viral infections. Sex differences in the immune response during myocarditis have been well described but upstream mechanisms in the heart that might influence sex differences in disease are not completely understood.

METHODS

Male and female BALB/c wild type mice received an intraperitoneal injection of heart-passaged coxsackievirus B3 (CVB3) or vehicle control. Bulk-tissue RNA-sequencing was conducted to better understand sex differences in CVB3 myocarditis. We performed enrichment analysis and functional validation to understand sex differences in the transcriptional landscape of myocarditis and identify factors that might drive sex differences in myocarditis.

RESULTS

As expected, the hearts of male and female mice with myocarditis were significantly enriched for pathways related to an innate and adaptive immune response compared to uninfected controls. Unique to this study, we found that males were enriched for inflammatory pathways and gene changes that suggested worse mitochondrial electron transport function while females were enriched for pathways related to mitochondrial homeostasis. Mitochondria isolated from the heart of males were confirmed to have worse mitochondrial respiration than females during myocarditis. Unbiased TRANSFAC analysis identified estrogen-related receptor alpha (ERRα) as a transcription factor that may mediate sex differences in mitochondrial function during myocarditis. Transcript and protein levels of ERRα were confirmed as elevated in females with myocarditis compared to males. Differential binding analysis from chromatin immunoprecipitation (ChIP) sequencing confirmed that ERRα bound highly to select predicted respiratory chain genes in females more than males during myocarditis.

CONCLUSIONS

Females with viral myocarditis regulate mitochondrial homeostasis by upregulating master regulators of mitochondrial transcription including ERRα.

Mechanisms underlying sex differences in autoimmunity

Autoimmune diseases are a leading cause of disability worldwide. Most autoimmune diseases occur more often in women than men, with rheumatic autoimmune diseases being among those most highly expressed in women. Several key factors, identified mainly in animal models and cell culture experiments, are important in increasing autoimmune disease in females. These include sex hormones, immune genes including those found on the X chromosome, sex-specific epigenetic effects on genes by estrogen and the environment, and regulation of genes and messenger RNA by microRNAs found in extracellular vesicles. Evidence is also emerging that viruses as well as drugs or toxins that damage mitochondria may contribute to increased levels of autoantibodies against nuclear and mitochondrial antigens, which are common in many autoimmune diseases. The purpose of this Review is to summarize our current understanding of mechanisms that may determine sex differences in autoimmune disease.

APOE2 protects against Aβ pathology by improving neuronal mitochondrial function through ERRα signaling

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease and apolipoprotein E (APOE) genotypes (APOE2, APOE3, and APOE4) show different AD susceptibility. Previous studies indicated that individuals carrying the APOE2 allele reduce the risk of developing AD, which may be attributed to the potential neuroprotective role of APOE2. However, the mechanisms underlying the protective effects of APOE2 is still unclear.

METHODS

We analyzed single-nucleus RNA sequencing and bulk RNA sequencing data of APOE2 and APOE3 carriers from the Religious Orders Study and Memory and Aging Project (ROSMAP) cohort. We validated the findings in SH-SY5Y cells and AD model mice by evaluating mitochondrial functions and cognitive behaviors respectively.

RESULTS

The pathway analysis of six major cell types revealed a strong association between APOE2 and cellular stress and energy metabolism, particularly in excitatory and inhibitory neurons, which was found to be more pronounced in the presence of beta-amyloid (Aβ). Moreover, APOE2 overexpression alleviates Aβ1-42-induced mitochondrial dysfunction and reduces the generation of reactive oxygen species in SH-SY5Y cells. These protective effects may be due to ApoE2 interacting with estrogen-related receptor alpha (ERRα). ERRα overexpression by plasmids or activation by agonist was also found to show similar mitochondrial protective effects in Aβ1-42-stimulated SH-SY5Y cells. Additionally, ERRα agonist treatment improve the cognitive performance of Aβ injected mice in both Y maze and novel object recognition tests. ERRα agonist treatment increased PSD95 expression in the cortex of agonist-treated-AD mice.

CONCLUSIONS

APOE2 appears to enhance neural mitochondrial function via the activation of ERRα signaling, which may be the protective effect of APOE2 to treat AD.

ERRα: unraveling its role as a key player in cell migration

Cell migration is essential throughout the life of multicellular organisms, and largely depends on the spatial and temporal regulation of cytoskeletal dynamics, cell adhesion and signal transduction. Interestingly, Estrogen-related receptor alpha (ERRα) has been identified as a major regulator of cell migration in both physiological and pathological conditions. ERRα is an orphan member of the nuclear hormone receptor superfamily of transcription factors and displays many biological functions. ERRα is a global regulator of energy metabolism, and it is also highly involved in bone homeostasis, development, differentiation, immunity and cancer progression. Importantly, in some instances, the regulation of these biological processes relies on the ability to orchestrate cell movements. Therefore, this review describes how ERRα-mediated cell migration contributes not only to tissue homeostasis but also to tumorigenesis and metastasis, and highlights the molecular and cellular mechanisms by which ERRα finely controls the cell migratory potential.

ERRα regulates synaptic transmission through reactive oxygen species in hippocampal neurons

Reactive oxygen species (ROS) play multiple roles in synaptic transmission, and estrogen-related receptor α (ERRα) is involved in regulating ROS production. The purpose of our study was to explore the underlying effect of ERRα on ROS production, neurite formation and synaptic transmission. Our results revealed that knocking down ERRα expression affected the formation of neuronal neurites and dendritic spines, which are the basic structures of synaptic transmission and play important roles in learning, memory and neuronal plasticity; moreover, the amplitude and frequency of miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs) were decreased. These abnormalities were reversed by overexpression of human ERRα. Additionally, we also found that knocking down ERRα expression increased intracellular ROS levels in neurons. ROS inhibitor PBN rescued the changes in neurite formation and synaptic transmission induced by ERRα knockdown. These results indicate a new possible cellular mechanism by which ERRα affects intracellular ROS levels, which in turn regulate neurite and dendritic spine formation and synaptic transmission.

Sex differences in mitochondrial gene expression during viral myocarditis

Background

Myocarditis is an inflammation of the heart muscle most often caused by an immune response to viral infections. Sex differences in the immune response during myocarditis have been well described but upstream mechanisms in the heart that might influence sex differences in disease are not completely understood.

Methods

Male and female BALB/c wild type mice received an intraperitoneal injection of heart-passaged coxsackievirus B3 (CVB3) or vehicle control. Bulk-tissue RNA-sequencing was conducted to better understand sex differences in CVB3 myocarditis. We performed enrichment analysis to understand sex differences in the transcriptional landscape of myocarditis and identify candidate transcription factors that might drive sex differences in myocarditis.

Results

The hearts of male and female mice with myocarditis were significantly enriched for pathways related to an innate and adaptive immune response compared to uninfected controls. When comparing females to males with myocarditis, males were enriched for inflammatory pathways and gene changes that suggested worse mitochondrial transcriptional support (e.g., mitochondrial electron transport genes). In contrast, females were enriched for pathways related to mitochondrial respiration and bioenergetics, which were confirmed by higher transcript levels of master regulators of mitochondrial function including peroxisome proliferator-activated receptor gamma coactivator 1 (PGC1α), nuclear respiratory factor 1 (NRF1) and estrogen-related receptor alpha (ERRα). TRANSFAC analysis identified ERRa as a transcription factor that may mediate sex differences in mitochondrial function during myocarditis.

Conclusions

Master regulators of mitochondrial function were elevated in females with myocarditis compared to males and may promote sex differences in mitochondrial respiratory transcript expression during viral myocarditis resulting in less severe myocarditis in females following viral infection.

Estrogen-related Receptor Alpha (ERRα) is Required for PGC-1α-dependent Gene Expression in the Mouse Brain

Deficiency in peroxisome proliferator-activated receptor gamma coactivator 1-alpha. (PGC-1α) expression or function is implicated in numerous neurological and psychiatric disorders. PGC-1α is required for the expression of genes involved in synchronous neurotransmitter release, axonal integrity, and metabolism, especially in parvalbumin-positive interneurons. As a transcriptional coactivator, PGC-1α requires transcription factors to specify cell-type-specific gene programs; while much is known about these factors in peripheral tissues, it is unclear if PGC-1α utilizes these same factors in neurons. Here, we identified putative transcription factors controlling PGC-1α-dependent gene expression in the brain using bioinformatics and then validated the role of the top candidate in a knockout mouse model. We transcriptionally profiled cells overexpressing PGC-1α and searched for over-represented binding motifs in the promoters of upregulated genes. Binding sites of the estrogen-related receptor (ERR) family of transcription factors were enriched, and blockade of ERRα attenuated PGC-1α-mediated induction of mitochondrial and synaptic genes in cell culture. Localization in the mouse brain revealed enrichment of ERRα expression in parvalbumin-expressing neurons with tight correlation of expression with PGC-1α across brain regions. In ERRα null mice, PGC-1α-dependent genes were reduced in multiple regions, including neocortex, hippocampus, and cerebellum, though not to the extent observed in PGC-1α null mice. Behavioral assessment revealed ambulatory hyperactivity in response to amphetamine and impairments in sensorimotor gating without the overt motor impairment characteristic of PGC-1α null mice. These data suggest that ERRα is required for normal levels of expression of PGC-1α-dependent genes in neurons but that additional factors may be involved in their regulation.

Emerging Roles of Estrogen-Related Receptors in the Brain: Potential Interactions with Estrogen Signaling

In addition to their well-known role in the female reproductive system, estrogens can act in the brain to regulate a wide range of behaviors and physiological functions in both sexes. Over the past few decades, genetically modified animal models have greatly increased our knowledge about the roles of estrogen receptor (ER) signaling in the brain in behavioral and physiological regulations. However, less attention has been paid to the estrogen-related receptors (ERRs), the members of orphan nuclear receptors whose sequences are homologous to ERs but lack estrogen-binding ability. While endogenous ligands of ERRs remain to be determined, they seemingly share transcriptional targets with ERs and their expression can be directly regulated by ERs through the estrogen-response element embedded within the regulatory region of the genes encoding ERRs. Despite the broad expression of ERRs in the brain, we have just begun to understand the fundamental roles they play at molecular, cellular, and circuit levels. Here, we review recent research advancement in understanding the roles of ERs and ERRs in the brain, with particular emphasis on ERRs, and discuss possible cross-talk between ERs and ERRs in behavioral and physiological regulations.

Identification of Estrogen-Related Receptor α Agonists in the Tox21 Compound Library

The estrogen-related receptor α (ERRα) is an orphan nuclear receptor (NR) that plays a role in energy homeostasis and controls mitochondrial oxidative respiration. Increased expression of ERRα in certain ovarian, breast, and colon cancers has a negative prognosis, indicating an important role for ERRα in cancer progression. An interaction between ERRα and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) has also recently been shown to regulate an enzyme in the β-oxidation of free fatty acids, thereby suggesting that ERRα plays an important role in obesity and type 2 diabetes. Therefore, it would be prudent to identify compounds that can act as activators of ERRα. In this study, we screened ∼10,000 (8311 unique) compounds, known as the Tox21 10K collection, to identify agonists of ERRα. We performed this screen using two stably transfected HEK 293 cell lines, one with the ERRα-reporter alone and the other with both ERRα-reporter and PGC-1α expression vectors. After the primary screening, we identified more than five agonist clusters based on compound structural similarity analysis (e.g., statins). By examining the activities of the confirmed ERRα modulators in other Tox21 NR assays, eliminating those with promiscuous NR activity, and performing follow-up assays (e.g., small interfering RNA knockdown), we identified compounds that might act as endocrine disrupters through effects on ERRα signaling. To our knowledge, this study is the first comprehensive analysis in discovering potential endocrine disrupters that affect the ERRα signaling pathway.

The Eating-Disorder Associated HDAC4A778T Mutation Alters Feeding Behaviors in Female Mice

BACKGROUND

While eating disorders (EDs) are thought to result from a combination of environmental and psychological stressors superimposed on genetic vulnerability, the neurobiological basis of EDs remains incompletely understood. We recently reported that a rare missense mutation in the gene for the transcriptional repressor histone deacetylase 4 (HDAC4) is associated with the risk of developing an ED in humans.

METHODS

To understand the biological consequences of this missense mutation, we created transgenic mice carrying this mutation by introducing the alanine to threonine mutation at position 778 of mouse Hdac4 (corresponding to position 786 of the human protein). Bioinformatic analysis to identify Hdac4-regulated genes was performed using available databases.

RESULTS

Male mice heterozygous for HDAC4^A778T did not show any metabolic or behavioral differences. In contrast, female mice heterozygous for HDAC4^A778T display several ED-related feeding and behavioral deficits depending on housing condition. Individually housed HDAC4^A778T female mice exhibit reduced effortful responding for high-fat diet and compulsive grooming, whereas group-housed female mice display increased weight gain on high-fat diet, reduced behavioral despair, and increased anxiety-like behaviors. Bioinformatic analysis identifies mitochondrial biogenesis including synthesis of glutamate/gamma-aminobutyric acid as a potential transcriptional target of HDAC4^A778T activity relevant to the behavioral deficits identified in this new mouse model of disordered eating.

CONCLUSIONS

The HDAC4^A778T mouse line is a novel model of ED-related behaviors and identifies mitochondrial biogenesis as a potential molecular pathway contributing to behavioral deficits.