Modulation of mitochondrial Ca(2+) uptake by estrogen receptor agonists and antagonists

Regulation of mitochondrial dysfunction by estrogens and estrogen receptors in Alzheimer's disease: A focused review

Alzheimer's disease (AD) is a neurodegenerative disorder that primarily manifests itself by progressive memory loss and cognitive decline, thus significantly affecting memory functions and quality of life. In this review, we proceed from the understanding that the canonical amyloid-β hypothesis, while significant, has faced setbacks, highlighting the need to adopt a broader perspective considering the intricate interplay of diverse pathological pathways for effective AD treatments. Sex differences in AD offer valuable insights into a better understanding of its pathophysiology. Fluctuation of the levels of ovarian sex hormones during perimenopause is associated with changes in glucose metabolism, as a possible window of opportunity to further understand the roles of sex steroid hormones and their associated receptors in the pathophysiology of AD. We review these dimensions, emphasizing the potential of estrogen receptors (ERs) to reveal mitochondrial functions in the search for further research and therapeutic strategies for AD pharmacotherapy. Understanding and addressing the intricate interactions of mitochondrial dysfunction and ERs potentially pave the way for more effective approaches to AD therapy.

Calcium signaling in endothelial and vascular smooth muscle cells: sex differences and the influence of estrogens and androgens

Calcium signaling in vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) is essential for the regulation of vascular tone. However, the changes to intracellular Ca2+ concentrations are often influenced by sex differences. Furthermore, a large body of evidence shows that sex hormone imbalance leads to dysregulation of Ca2+ signaling and this is a key factor in the pathogenesis of cardiovascular diseases. In this review, the effects of estrogens and androgens on vascular calcium-handling proteins are discussed, with emphasis on the associated genomic or nongenomic molecular mechanisms. The experimental models from which data were collected were also considered. The review highlights 1) in female ECs, transient receptor potential vanilloid 4 (TRPV4) and mitochondrial Ca2+ uniporter (MCU) enhance Ca2+-dependent nitric oxide (NO) generation. In males, only transient receptor potential canonical 3 (TRPC3) plays a fundamental role in this effect. 2) Female VSMCs have lower cytosolic Ca2+ levels than males due to differences in the activity and expression of stromal interaction molecule 1 (STIM1), calcium release-activated calcium modulator 1 (Orai1), calcium voltage-gated channel subunit-α1C (CaV1.2), Na+-K+-2Cl- symporter (NKCC1), and the Na+/K+-ATPase. 3) When compared with androgens, the influence of estrogens on Ca2+ homeostasis, vascular tone, and incidence of vascular disease is better documented. 4) Many studies use supraphysiological concentrations of sex hormones, which may limit the physiological relevance of outcomes. 5) Sex-dependent differences in Ca2+ signaling mean both sexes ought to be included in experimental design.

Safety and efficacy of tamoxifen in boys with Duchenne muscular dystrophy (TAMDMD): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial

BACKGROUND

Drug repurposing could provide novel treatment options for Duchenne muscular dystrophy. Because tamoxifen-an oestrogen receptor regulator-reduced signs of muscular pathology in a Duchenne muscular dystrophy mouse model, we aimed to assess the safety and efficacy of tamoxifen in humans as an adjunct to corticosteroid therapy over a period of 48 weeks.

METHODS

We did a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial at 12 study centres in seven European countries. We enrolled ambulant boys aged 6·5-12·0 years with a genetically confirmed diagnosis of Duchenne muscular dystrophy and who were on stable corticosteroid treatment for more than 6 months. Exclusion criteria included ophthalmological disorders, including cataracts, and haematological disorders. We randomly assigned (1:1) participants using an online randomisation tool to either 20 mg tamoxifen orally per day or matched placebo, stratified by centre and corticosteroid intake. Participants, caregivers, and clinical investigators were masked to treatment assignments. Tamoxifen was taken in addition to standard care with corticosteroids, and participants attended study visits for examinations every 12 weeks. The primary efficacy outcome was the change from baseline to week 48 in scores on the D1 domain of the Motor Function Measure in the intention-to-treat population (defined as all patients who fulfilled the inclusion criteria and began treatment). This study is registered with ClinicalTrials.gov (NCT03354039) and is completed.

FINDINGS

Between May 24, 2018, and Oct 14, 2020, 95 boys were screened for inclusion, and 82 met inclusion criteria and were initially enrolled into the study. Three boys were excluded after initial screening due to cataract diagnosis or revoked consent directly after screening, but before randomisation. A further boy assigned to the placebo group did not begin treatment. Therefore, 40 individuals assigned tamoxifen and 38 allocated placebo were included in the intention-to-treat population. The primary efficacy outcome did not differ significantly between tamoxifen (-3·05%, 95% CI -7·02 to 0·91) and placebo (-6·15%, -9·19 to -3·11; 2·90% difference, -3·02 to 8·82, p=0·33). Severe adverse events occurred in two participants: one participant who received tamoxifen had a fall, and one who received placebo suffered a panic attack. No deaths or life-threatening serious adverse events occurred. Viral infections were the most common adverse events.

INTERPRETATION

Tamoxifen was safe and well tolerated, but no difference between groups was reported for the primary efficacy endpoint. Slower disease progression, defined by loss of motor function over time, was indicated in the tamoxifen group compared with the placebo group, but differences in outcome measures were neither clinically nor statistically significant. Currently, we cannot recommend the use of tamoxifen in daily clinical practice as a treatment option for boys with Duchenne muscular dystrophy due to insufficient clinical evidence.

FUNDING

Thomi Hopf Foundation, ERA-Net, Swiss National Science Foundation, Duchenne UK, Joining Jack, Duchenne Parent Project, Duchenne Parent Project Spain, Fondation Suisse de Recherche sur les Maladies Musculaires, Association Monegasque contre les Myopathies.

The mitochondrial calcium uniporter complex–A play in five acts

Mitochondrial Ca²⁺ (mitCa²⁺) uptake controls both intraorganellar and cytosolic functions. Within the organelle, [Ca²⁺] increases regulate the activity of tricarboxylic acid (TCA) cycle enzymes, thus sustaining oxidative metabolism and ATP production. Reactive oxygen species (ROS) are also generated as side products of oxygen consumption. At the same time, mitochondria act as buffers of cytosolic Ca²⁺ (cytCa²⁺) increases, thus regulating Ca²⁺-dependent cellular processes. In pathological conditions, mitCa²⁺ overload triggers the opening of the mitochondrial permeability transition pore (mPTP) and the release of apoptotic cofactors. MitCa²⁺ uptake occurs in response of local [Ca²⁺] increases in sites of proximity between the endoplasmic reticulum (ER) and the mitochondria and is mediated by the mitochondrial Ca²⁺ uniporter (MCU), a highly selective channel of the inner mitochondrial membrane (IMM). Both channel and regulatory subunits form the MCU complex (MCUC). Cryogenic electron microscopy (Cryo-EM) and crystal structures revealed the correct assembly of MCUC and the function of critical residues for the regulation of Ca²⁺ conductance.

Estrogen signaling as a bridge between the nucleus and mitochondria in cardiovascular diseases

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. Epidemiological studies indicate that pre-menopausal women are more protected against the development of CVDs compared to men of the same age. This effect is attributed to the action/effects of sex steroid hormones on the cardiovascular system. In this context, estrogen modulates cardiovascular function in physiological and pathological conditions, being one of the main physiological cardioprotective agents. Here we describe the common pathways and mechanisms by which estrogens modulate the retrograde and anterograde communication between the nucleus and mitochondria, highlighting the role of genomic and non-genomic pathways mediated by estrogen receptors. Additionally, we discuss the presumable role of bromodomain-containing protein 4 (BRD4) in enhancing mitochondrial biogenesis and function in different CVD models and how this protein could act as a master regulator of estrogen protective activity. Altogether, this review focuses on estrogenic control in gene expression and molecular pathways, how this activity governs nucleus-mitochondria communication, and its projection for a future generation of strategies in CVDs treatment.

Predominant cause of faster force recovery in females than males after intense eccentric contractions in mouse fast-twitch muscle

KEY POINTS

We investigated the mechanisms underlying faster force recovery from eccentric contractions (ECCs) in female than in male mice, focusing on mitochondrial responses. At 3 days after repeated ECCs (REC3), female mice showed faster recovery from ECC-induced force depression than male mice. At REC3, the mitochondria in females displayed superior responses to those in males: (i) mitochondrial Ca²⁺ uniporter content of muscles at REC3 was higher than that of rested muscles in females, and (ii) mitochondrial volume density in females was higher than that in males at REC3. Ovariectomized (OVX) female mice showed lower mitochondrial responses at REC3, similar to those observed in male mice, but oestrogen replacement nullified such lower responses in OVX. We concluded that: (i) superior mitochondrial responses after ECCs, at least in part, cause faster force recovery from ECCs in females than in males, and (ii) oestrogen contributes to such superior responses in the mitochondria in females.

ABSTRACT

The purpose of this study was to investigate the mechanisms underlying sex differences in force recovery after eccentric contractions (ECCs). The left limbs of female and male mice were exposed to repeated ECCs (five sets of 50 contractions) elicited in vivo in the plantar flexor muscles. Isometric torques were measured before, immediately and at 3 days after ECCs (REC3), and gastrocnemius muscles obtained at REC3 were used for biochemical and morphological analyses. At REC3, a greater torque depression at 40 Hz was observed in males than females. Additionally, the following differences were observed at REC3: (i) in males but not females, triad structure was distorted, (ii) mitochondrial Ca²⁺ uniporter (MCU) content was increased in females but not in males, and (iii) mitochondrial volume density at REC3 was lower in males than in females. To examine the contribution of oestrogen to torque recovery, female mice were assigned to sham-operated (Sham), ovariectomized (OVX) and OVX treated with 17β-oestradiol (OVX + E2) groups. At REC3, (i) greater torque depression at 40 Hz was observed in the OVX group than in the Sham and OVX + E2 groups, (ii) MCU content was increased in the Sham and OVX + E2 groups but not the OVX group, and (iii) mitochondrial volume density at REC3 was lower in the OVX group than the Sham and OVX + E2 groups. These results suggest that faster force recovery in females than in males is, at least partly, ascribable to superior mitochondrial responses, and oestrogen supplementation, in part, enhances such responses.

Identification and functional validation of FDA-approved positive and negative modulators of the mitochondrial calcium uniporter

The mitochondrial calcium uniporter (MCU), the highly selective channel responsible for mitochondrial Ca²⁺ entry, plays important roles in physiology and pathology. However, only few pharmacological compounds directly and selectively modulate its activity. Here, we perform high-throughput screening on a US Food and Drug Administration (FDA)-approved drug library comprising 1,600 compounds to identify molecules modulating mitochondrial Ca²⁺ uptake. We find amorolfine and benzethonium to be positive and negative MCU modulators, respectively. In agreement with the positive effect of MCU in muscle trophism, amorolfine increases muscle size, and MCU silencing is sufficient to blunt amorolfine-induced hypertrophy. Conversely, in the triple-negative breast cancer cell line MDA-MB-231, benzethonium delays cell growth and migration in an MCU-dependent manner and protects from ceramide-induced apoptosis, in line with the role of mitochondrial Ca²⁺ uptake in cancer progression. Overall, we identify amorolfine and benzethonium as effective MCU-targeting drugs applicable to a wide array of experimental and disease conditions.

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We screen an FDA-approved drug library for mitochondrial Ca²⁺ uptake modulators

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Amorolfine and benzethonium modulate MCU activity

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Amorolfine increases MCU-dependent mitochondrial metabolism and muscle size

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Benzethonium decreases MCU-dependent cancer cell growth and migration

Akkouh I, Hughes T, Frei E, A. Andreassen O, Djurovic S. Using iPSC Models to Understand the Role of Estrogen in Neuron-Glia Interactions in Schizophrenia and Bipolar Disorder

Schizophrenia (SCZ) and bipolar disorder (BIP) are severe mental disorders with a considerable disease burden worldwide due to early age of onset, chronicity, and lack of efficient treatments or prevention strategies. Whilst our current knowledge is that SCZ and BIP are highly heritable and share common pathophysiological mechanisms associated with cellular signaling, neurotransmission, energy metabolism, and neuroinflammation, the development of novel therapies has been hampered by the unavailability of appropriate models to identify novel targetable pathomechanisms. Recent data suggest that neuron-glia interactions are disturbed in SCZ and BIP, and are modulated by estrogen (E2). However, most of the knowledge we have so far on the neuromodulatory effects of E2 came from studies on animal models and human cell lines, and may not accurately reflect many processes occurring exclusively in the human brain. Thus, here we highlight the advantages of using induced pluripotent stem cell (iPSC) models to revisit studies of mechanisms underlying beneficial effects of E2 in human brain cells. A better understanding of these mechanisms opens the opportunity to identify putative targets of novel therapeutic agents for SCZ and BIP. In this review, we first summarize the literature on the molecular mechanisms involved in SCZ and BIP pathology and the beneficial effects of E2 on neuron-glia interactions. Then, we briefly present the most recent developments in the iPSC field, emphasizing the potential of using patient-derived iPSCs as more relevant models to study the effects of E2 on neuron-glia interactions.

Overexpressed p32 localized in the endoplasmic reticulum and mitochondria negatively regulates calcium‑dependent endothelial nitric oxide synthase activit

The p32 protein plays a crucial role in the regulation of cytosolic Ca²⁺ concentrations ([Ca2+]c) that contributes to the Ca²⁺-dependent signaling cascade. Using an adenovirus and plasmid p32-overexpression system, the aim of the study was to evaluate the role of p32 in the regulation of [Ca²⁺] and its potential associated with Ca²⁺-dependent endothelial nitric oxide synthase (eNOS) activation in endothelial cells. Using electron and confocal microscopic analysis, p32 overexpression was observed to be localized to mitochondria and the endoplasmic reticulum and played an important role in Ca²⁺ translocation, resulting in increased [Ca²⁺] in these organelles and reducing cytosolic [Ca²⁺] ([Ca²⁺]c). This decreased [Ca²⁺]c following p32 overexpression attenuated the Ca²⁺-dependent signaling cascade of calcium/calmodulin dependent protein kinase II (CaMKII)/AKT/eNOS phosphorylation. Moreover, in aortic endothelia of wild-type mice intravenously administered adenovirus encoding the p32 gene, increased p32 levels reduced NO production and accelerated reactive oxygen species (ROS) generation. In a vascular tension assay, p32 overexpression decreased acetylcholine (Ach)-induced vasorelaxation and augmented phenylephrine (PE)-dependent vasoconstriction. Notably, decreased levels of arginase II (ArgII) protein using siArgII were associated with downregulation of overexpressed p32 protein, which contributed to CaMKII-dependent eNOS phosphorylation at Ser1177. These results indicated that increased protein levels of p32 caused endothelial dysfunction through attenuation of the Ca²⁺-dependent signaling cascade and that ArgII protein participated in the stability of p32. Therefore, p32 may be a novel target for the treatment of vascular diseases associated with endothelial disorders.

Targeting mitochondrial calcium pathways as a potential treatment against Parkinson's disease

Parkinson's disease (PD) is a major health problem worldwide affecting millions of people and is a result of neurodegeneration in a small part of the brain known as substantia nigra pars compacta. Aberration in mitochondrial Ca²⁺ homeostasis plays, among several other factors, an important role for the neuronal loss in PD. Mitochondria are vital for cellular physiology, e.g. for ATP generation, and mitochondrial Ca²⁺ is a key player in cell functioning and survival. Mitochondrial Ca²⁺ homeostasis is maintained by a fine balance between the activities of proteins mediating the influx and efflux of Ca²⁺ across mitochondrial membranes. Malfunctioning of these proteins leading to Ca²⁺ overload promotes ROS generation, which induces cell death by triggering the opening of mitochondrial permeability transition pore. Till now PD remains incurable and the "gold standard" drug which can only delays the disease progression is l-Dopa from the 1960s and therefore, the situation warrants the search for novel targets for the treatment of the PD patients. In this review, we summarize the current views that suggest mitochondrial Ca²⁺ regulatory pathways are good candidates for the treatment of PD.

17β‑estradiol‑induced mitochondrial dysfunction and Warburg effect in cervical cancer cells allow cell survival under metabolic stress

Mitochondria from different types of cancer show bioenergetics and dysfunction that favor cell proliferation. The mechanistic understanding of estrogen in cervical cancer is poorly understood. Therefore, the objective of this study was to determine how 17β-estradiol (E2) affects mitochondrial function and the Warburg effect in SiHa, HeLa and C33A cervical cancer cells. Mitochondrial compromise was evaluated measuring changes in the membrane permeability by immunofluorescence, calcium concentration, redox status, iron and ferritin reserves. Glucose consumption and lactic acid assays were used to detect the metabolic activity. Results were confirmed at molecular level by analysis of the differential gene expression using RNA sequencing. E2 modified the mitochondrial permeability and produced an alteration in the calcium signaling pathway. In HeLa and SiHa, there was a significant decrease in nitric oxide levels and lipid peroxidation, and an increase in glucose consumption and lactic acid levels when stimulated with E2. Intracellular iron or ferritin reserves were not affected by the E2 treatment. Genes differentially modulated by E2 were involved in the mitochondrial electron transport chain, oxidative phosphorylation system, glycolysis, pentose phosphate pathway and the regulation of metabolic signaling pathways. Herein, we provide evidence for a primary effect of estrogen on mitochondrial function and the Warburg effect, favoring the metabolic adaptation of the cervical cancer cell lines and their survival.

Arginase II Contributes to the Ca2+/CaMKII/eNOS Axis by Regulating Ca2+ Concentration Between the Cytosol and Mitochondria in a p32-Dependent Manner

Background

Arginase II activity contributes to reciprocal regulation of endothelial nitric oxide synthase (eNOS). We tested the hypotheses that arginase II activity participates in the regulation of Ca²⁺/Ca²⁺/calmodulin‐dependent kinase II/eNOS activation, and this process is dependent on mitochondrial p32.

Methods and Results

Downregulation of arginase II increased the concentration of cytosolic Ca²⁺ ([Ca²⁺]c) and decreased mitochondrial Ca²⁺ ([Ca²⁺]m) in microscopic and fluorescence‐activated cell sorting analyses, resulting in augmented eNOS Ser1177 phosphorylation and decreased eNOS Thr495 phosphorylation through Ca²⁺/Ca²⁺/calmodulin‐dependent kinase II. These changes were observed in human umbilical vein endothelial cells treated with small interfering RNA against p32 (sip32). Using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry, fluorescence immunoassay, and ion chromatography, inhibition of arginase II reduced the amount of spermine, a binding molecule, and the release of Ca²⁺ from p32. In addition, arginase II gene knockdown using small interfering RNA and knockout arginase II‐null mice resulted in reduced p32 protein level. In the aortas of wild‐type mice, small interfering RNA against p32 induced eNOS Ser1177 phosphorylation and enhanced NO‐dependent vasorelaxation. Arginase activity, p32 protein expression, spermine amount, and [Ca²⁺]m were increased in the aortas from apolipoprotein E (ApoE^−/−) mice fed a high‐cholesterol diet, and intravenous administration of small interfering RNA against p32 restored Ca²⁺/Ca²⁺/calmodulin‐dependent kinase II‐dependent eNOS Ser1177 phosphorylation and improved endothelial dysfunction. The effects of arginase II downregulation were not associated with elevated NO production when tested in aortic endothelia from eNOS knockout mice.

Conclusions

These data demonstrate a novel function of arginase II in regulation of Ca²⁺‐dependent eNOS phosphorylation. This novel mechanism drives arginase activation, mitochondrial dysfunction, endothelial dysfunction, and atherogenesis.

[Inhibitory effect of diethylstilbestrol on clinical strains of Candida albicans susceptible and resistant to azoles]

BACKGROUND

Candida albicans is a microorganism frequently involved in several infections; the patient's oral cavity, caries niches or periodontal disease can sometimes be the reservoir.. The fungal resistance to the available treatments, among other reasons, has led to the search for new antifungal alternatives.

AIMS

To carry out a comparative study of the in vitro effects of diethylstilboestrol (DES) and fluconazole (FLZ) on the growth of clinical strains of C. albicans.

METHODS

Seven strains of C. albicans were used: a) one FLZ-sensitive culture collection strain, ATCC 90028 (ATCC); b) four oral isolates from four oncological patients with periodontal disease (period 8, 9, 10, and 11); and c) two oral isolates from an AIDS patient with oropharyngeal candidiasis: one FLZ- sensitive (2-76), and another FLZ- resistant (12-99). The MIC was evaluated by standard spectrophotometric techniques using the CLSI (M27-A3) guidelines. The inhibitory concentration 50% (IC₅₀) was calculated using functional analysis with the Graph Pad software.

RESULTS

DES inhibited the growth of all C. albicans strains, whether sensitive or resistant to FLZ. Experimental data fitted non-linear functions of inhibitor concentration versus response. Minimum inhibitory concentrations (MIC) for DES and FLZ were as follows: 28.18µg/ml and 4.90µg/ml (ATCC); 17.16µg/ml and 3.14µg/ml (period); 27.64µg/ml and 4.22µg/ml (2-76); 6.16µg/ml and 438.19µg/ml (12-99), respectively.

CONCLUSIONS

DES showed antifungal activity on all clinical C. albicans strains isolated from patients with dental and medical diseases. It showed the highest potency on the FLZ-resistant isolate.

Sex Differences in Ischemia/Reperfusion Injury: The Role of Mitochondrial Permeability Transition

Brain and heart ischemia are among the leading causes of death and disability in both men and women, but there are significant sex differences in the incidence and severity of these diseases. Ca²⁺ dysregulation in response to ischemia/reperfusion injury (I/RI) is a well-recognized pathogenic mechanism leading to the death of affected cells. Excess intracellular Ca²⁺ causes mitochondrial matrix Ca²⁺ overload that can result in mitochondrial permeability transition (MPT), which can have severe consequences for mitochondrial function and trigger cell death. Recent findings indicate that estrogens and their related receptors are involved in the regulation of MPT, suggesting that sex differences in I/RI could be linked to estrogen-dependent modulation of mitochondrial Ca²⁺. Here, we review the evidence supporting sex differences in I/RI and the role of estrogen and estrogen receptors in producing these differences, the involvement of mitochondrial Ca²⁺ overload in disease pathogenesis, and the estrogen-dependent modulation of MPT that may contribute to sex differences.

Estrogen regulates spatially distinct cardiac mitochondrial subpopulations

Increased susceptibility to permeability transition pore (mPTP) is a significant concern to decreased cardiac performance in postmenopausal females. The goal of this study was to assess the effects of estrogen deficiency on the two spatially distinct mitochondrial subpopulations from left ventricle: subsarcolemmal mitochondria (SSM) and intermyofibrillar mitochondria (IFM) based on: morphology, membrane potential, oxidative phosphorylation, mPTP and reactive oxygen species production. Female rats (8weeks old) that underwent bilateral ovariectomy were randomly assigned to receive daily treatment with placebo (OVX), estrogen replacement (OVX+E2) and Sham for 60days. The yield for IFM was found higher in the OVX group and lower in the SSM. SSM internal complexity and size were higher in the OVX group, although membrane potential was not different. The maximal rate of mitochondrial respiration, states 3 and 4, using glutamate+malate as substrate, were higher in IFM and SSM from the OVX group. The respiratory control ratio (RCR - state3/state 4), was not different in both SSM and IFM with glutamate+malate. The ADP:O ratio was found lower in IFM and SSM from OVX compared to Sham. When pyruvate was used, state 3 was found unchanged in both IFM and SSM, state 4 was greater in IFM from OVX rats compared to Sham and the ADP/O ratio was decreased. The RCR was unchanged in both subpopulations. The IFM from OVX rats presented a lower Ca²⁺retention capacity compared to Sham, however, the SSM remained unchanged. Hydrogen peroxide formation was found increased in the IFM from OVX animals with glutamate+malate and rotenone+succinate as substrates. The SSM showed increased ROS production only with rotenone+succinate. Western blot analyzes showed decreased levels of PGC-1α and NRF-1 in the OVX group. Estrogen replacement was able to restore most of the alterations induced by ovariectomy. In conclusion, our data shows that estrogen deficiency has distinct effects on the two spatially distinct mitochondrial subpopulations in oxidative phosphorylation, morphology, calcium retention capacity and ROS production.

The Mitochondrial Ca2+ Uniporter: Structure, Function, and Pharmacology

Mitochondrial Ca²⁺ uptake is crucial for an array of cellular functions while an imbalance can elicit cell death. In this chapter, we briefly reviewed the various modes of mitochondrial Ca²⁺ uptake and our current understanding of mitochondrial Ca²⁺ homeostasis in regards to cell physiology and pathophysiology. Further, this chapter focuses on the molecular identities, intracellular regulators as well as the pharmacology of mitochondrial Ca²⁺ uniporter complex.

Chemotherapeutic effect of tamoxifen on temozolomide-resistant gliomas

Tamoxifen, a selective estrogen receptor modulator, is widely used in the chemotherapy of estrogen receptor-positive breast cancer. Recent studies have indicated that tamoxifen might have a potential chemotherapeutic effect on glioma. In the present study, we determined the chemotherapeutic action of tamoxifen on human glioma cell lines. Methylation of 06-methylguanine-DNA methyltransferase was identified in A172, U251, and BT325 glioma cell lines, but not in the U87 cell line. Consistently, A172, U251, and BT325 cell lines are resistant to temozolomide. Tamoxifen induced significant cytotoxic action in A172, U251, BT325, and U87 cell lines. Further, Hoechst 33342 staining and apoptosis flow cytometric analysis demonstrated that tamoxifen induced apoptosis in the BT325 cell line. Mitochondrial complex analysis indicated that tamoxifen, but not other estrogen receptor modulators, dose-dependently inhibits complex I activity. In summary, our study suggests that tamoxifen might have a chemotherapeutic effect on temozolomide-resistant glioma through its direct action on mitochondrial complex I inhibition and could provide further evidence to support future clinical trials of tamoxifen for the treatment of glioblastoma.

Estrogen receptor-β in mitochondria: implications for mitochondrial bioenergetics and tumorigenesis

Estrogen enhances mitochondrial function by enhancing mitochondrial biogenesis and sustaining mitochondrial energy-transducing capacity. Shifts in mitochondrial bioenergetic pathways from oxidative phosphorylation to glycolysis have been hypothesized to be involved in estrogen-induced tumorigenesis. Studies have shown that mitochondria are an important target of estrogen. Estrogen receptor-β (ERβ) has been shown to localize to mitochondria in a ligand-dependent or -independent manner and can affect mitochondrial bioenergetics and anti-apoptotic signaling. However, the functional role of mitochondrial ERβ in tumorigenesis remains unclear. Clinical studies of ERβ-related tumorigenesis have shown that ERβ stimulates mitochondrial metabolism to meet the high energy demands of processes such as cell proliferation, cell survival, and transformation. Thus, in elucidating the precise role of mitochondrial ERβ in cell transformation and tumorigenesis, it will be particularly valuable to explore new approaches for the development of medical treatments targeting mitochondrial ERβ-mediated mitochondrial function and preventing apoptosis.

Sex differences in the adolescent developmental trajectory of parvalbumin interneurons in the hippocampus: a role for estradiol

OBJECTIVE

Gender differences in the neurodevelopmental disorder, schizophrenia, have been described for nearly all features of the illness. Reduced hippocampal expression of the GABAergic interneuron marker, parvalbumin (PV), and GABA synthesizing enzyme, GAD67, are consistently reported in schizophrenia. However, little is known of the expression patterns of hippocampal PV and GAD67 during adolescence and their interaction with sex steroid hormones during adolescent development. This study examined the effects of altered sex steroid hormone levels during adolescence on protein levels of PV, GAD67 and estrogen receptors (ERα/β) in the hippocampus of mice.

METHODS

Protein expression of PV and GAD67 was measured in the dorsal (DHP) and ventral (VHP) hippocampus of female and male C57Bl/6 mice by Western blot in a week by week analysis from pre-pubescence to adulthood (week 3-12). Fluorescent immunohistochemistry (IHC) was used to investigate the relationship between ERs and PV(+) cells in the hippocampus of female mice at young adulthood (week 10-11). To further examine the role of sex steroid hormones on PV and GAD67 expression, gonadectomy and hormone replacement was done at 5 weeks of age.

RESULTS

Female mice showed a significant gradual increase in PV expression from 3 to 12 weeks of age in the DHP and VHP which correlated with serum 17β-estradiol levels. Fluorescent IHC showed approximately 30-50% co-localization of ER-α in PV(+) cells in the female DHP and VHP (dentate gryus/hilus and CA1-CA3). Adolescent ovariectomy significantly reduced PV expression in the DHP but not VHP of female mice, while 17β-estradiol replacement prevented this deficit in DHP PV levels. ER-α expression, but not ER-β, was also reduced in the DHP following ovariectomy with no significant effect of 17β-estradiol replacement. In contrast to female mice, male mice did not show any significant changes in hippocampal PV/GAD67 expression throughout adolescent development. Furthermore, adolescent castration and treatment with testosterone or dihydrotestosterone produced no changes in PV/GAD67 expression.

CONCLUSIONS

Our data suggest a differential developmental trajectory of PV expression between the sexes and manipulating circulating levels of sex steroid hormones by ovariectomy alters this trajectory in a region-dependent manner. This may be mediated via ER-α signaling as this receptor was found to be co-localized with PV(+) cells in the female mouse hippocampus. Alternative mechanisms of 17β-estradiol-induced regulation of PV expression are also discussed herein. Together, results from the present study may offer more insight into neurodevelopmental disorders, including schizophrenia, where sex steroid hormones and GABAergic markers are implicated in the pathophysiology of the illness.

Estrogenic endocrine-disrupting chemicals: molecular mechanisms of actions on putative human diseases

Endocrine-disrupting chemicals (EDC), including phthalates, bisphenol A (BPA), phytoestrogens such as genistein and daidzein, dichlorodiphenyltrichloroethane (DDT), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), are associated with a variety of adverse health effects in organisms or progeny by altering the endocrine system. Environmental estrogens, including BPA, phthalates, and phytoestrogens, are the most extensively studied and are considered to mimic the actions of endogenous estrogen, 17β-estradiol (E2). Diverse modes of action of estrogen and estrogen receptors (ERα and ERβ) have been described, but the mode of action of estrogenic EDC is postulated to be more complex and needs to be more clearly elucidated. This review examines the adverse effects of estrogenic EDC on male or female reproductive systems and molecular mechanisms underlying EDC effects that modulate ER-mediated signaling. Mechanisms of action for estrogenic EDC may involve both ER-dependent and ER-independent pathways. Recent findings from systems toxicology of examining estrogenic EDC are also discussed.

The anticancer drug tamoxifen counteracts the pathology in a mouse model of duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a severe disorder characterized by progressive muscle wasting,respiratory and cardiac impairments, and premature death. No treatment exists so far, and the identification of active substances to fight DMD is urgently needed. We found that tamoxifen, a drug used to treat estrogen-dependent breast cancer, caused remarkable improvements of muscle force and of diaphragm and cardiac structure in the mdx(5Cv) mouse model of DMD. Oral tamoxifen treatment from 3 weeks of age for 15 months at a dose of 10 mg/kg/day stabilized myofiber membranes, normalized whole body force, and increased force production and resistance to repeated contractions of the triceps muscle above normal values. Tamoxifen improved the structure of leg muscles and diminished cardiac fibrosis by~ 50%. Tamoxifen also reduced fibrosis in the diaphragm, while increasing its thickness,myofiber count, and myofiber diameter, thereby augmenting by 72% the amount of contractile tissue available for respiratory function. Tamoxifen conferred a markedly slower phenotype to the muscles.Tamoxifen and its metabolites were present in nanomolar concentrations in plasma and muscles,suggesting signaling through high-affinity targets. Interestingly, the estrogen receptors ERa and ERb were several times more abundant in dystrophic than in normal muscles, and tamoxifen normalized the relative abundance of ERb isoforms. Our findings suggest that tamoxifen might be a useful therapy for DMD.

Connexin 43 impacts on mitochondrial potassium uptake

In cardiomyocytes, connexin 43 (Cx43) forms gap junctions and unopposed hemichannels at the plasma membrane, but the protein is also present at the inner membrane of subsarcolemmal mitochondria (SSM). Both inhibition and genetic ablation of Cx43 reduce ADP-stimulated complex 1 respiration. Since mitochondrial potassium influx impacts on oxygen consumption, we investigated whether or not inhibition or ablation of mitochondrial Cx43 alters mitochondrial potassium uptake. SSM were isolated from rat left ventricular myocardium and loaded with the potassium-sensitive dye PBFI (potassium-binding benzofuran isophthalate). Intramitochondrial potassium was replaced by tetraethylammonium. Mitochondria were incubated under control conditions or treated with 250 μM Gap19, a peptide that specifically inhibits Cx43-based hemichannels at plasma membranes. Subsequently, 140 mM KCl was added and the slope of the increase in PBFI fluorescence over time was calculated. The slope of the PBFI fluorescence of the control mitochondria was set to 100%. In the presence of Gap19, the mitochondrial potassium influx was reduced from 100 ± 11.6% in control mitochondria to 65.5 ± 10.7% (n = 6, p < 0.05). In addition to the pharmacological inhibition of Cx43, potassium influx was studied in mitochondria isolated from conditional Cx43 knockout mice. Here, the ablation of Cx43 was achieved by the injection of 4-hydroxytamoxifen (4-OHT; Cx43(Cre-ER(T)/fl) + 4-OHT). The mitochondria of the Cx43(Cre-ER(T)/fl) + 4-OHT mice contained 3 ± 1% Cx43 (n = 6) of that in control mitochondria (100 ± 11%, n = 8, p < 0.05). The ablation of Cx43 (n = 5) reduced the velocity of the potassium influx from 100 ± 11.2% in control mitochondria (n = 9) to 66.6 ± 5.5% (p < 0.05). Taken together, our data indicate that both pharmacological inhibition and genetic ablation of Cx43 reduce mitochondrial potassium influx.

Tualang honey promotes apoptotic cell death induced by tamoxifen in breast cancer cell lines

Tualang honey (TH) is rich in flavonoids and phenolic acids and has significant anticancer activity against breast cancer cells comparable to the effect of tamoxifen (TAM), in vitro. The current study evaluated the effects of TH when used in combination with TAM on MCF-7 and MDA-MB-231 cells. We observed that TH promoted the anticancer activity of TAM in both the estrogen receptor-(ER-)responsive and ER-nonresponsive human breast cancer cell lines. Flow cytometric analyses indicated accelerated apoptosis especially in MDA-MB-231 cells and with the involvement of caspase-3/7, -8 and -9 activation as shown by fluorescence microscopy. Depolarization of the mitochondrial membrane was also increased in both cell lines when TH was used in combination with TAM compared to TAM treatment alone. TH may therefore be a potential adjuvant to be used with TAM for reducing the dose of TAM, hence, reducing TAM-induced adverse effects.

The mitochondrial calcium regulator cyclophilin D is an essential component of oestrogen-mediated neuroprotection in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a devastating neurodegenerative disorder that is more prevalent in males than in females. A similar gender difference has been reported in some strains of transgenic mouse models of familial amyotrophic lateral sclerosis harbouring the G93A mutation in CuZn superoxide dismutase. Mitochondrial damage caused by pathological alterations in Ca(2+) accumulation is frequently involved in neurodegenerative diseases, including CuZn superoxide dismutase-related amyotrophic lateral sclerosis, but its association with gender is not firmly established. In this study, we examined the effects of genetic ablation of cyclophilin D on gender differences in mice expressing G93A mutant CuZn superoxide dismutase. Cyclophilin D is a mitochondrial protein that promotes mitochondrial damage from accumulated Ca(2+). As anticipated, we found that cyclophilin D ablation markedly increased Ca(2+) retention in brain mitochondria of both males and females. Surprisingly, cyclophilin D ablation completely abolished the phenotypic advantage of G93A females, with no effect on disease in males. We also found that the 17β-oestradiol decreased Ca(2+) retention in brain mitochondria, and that cyclophilin D ablation abolished this effect. Furthermore, 17β-oestradiol protected G93A cortical neurons and spinal cord motor neurons against glutamate toxicity, but the protection was lost in neurons lacking cyclophilin D. Taken together, these results identify a novel mechanism of oestrogen-mediated neuroprotection in CuZn superoxide dismutase-related amyotrophic lateral sclerosis, whereby Ca(2+) overload and mitochondrial damage are prevented in a cyclophilin D-dependent manner. Such a protective mechanism may contribute to the lower incidence and later onset of amyotrophic lateral sclerosis, and perhaps other chronic neurodegenerative diseases, in females.

Uncoupling protein 3 adjusts mitochondrial Ca(2+) uptake to high and low Ca(2+) signals

Uncoupling proteins 2 and 3 (UCP2/3) are essential for mitochondrial Ca²⁺ uptake but both proteins exhibit distinct activities in regard to the source and mode of Ca²⁺ mobilization. In the present work, structural determinants of their contribution to mitochondrial Ca²⁺ uptake were explored. Previous findings indicate the importance of the intermembrane loop 2 (IML2) for the contribution of UCP2/3. Thus, the IML2 of UCP2/3 was substituted by that of UCP1. These chimeras had no activity in mitochondrial uptake of intracellularly released Ca²⁺, while they mimicked the wild-type proteins by potentiating mitochondrial sequestration of entering Ca²⁺. Alignment of the IML2 sequences revealed that UCP1, UCP2 and UCP3 share a basic amino acid in positions 163, 164 and 167, while only UCP2 and UCP3 contain a second basic residue in positions 168 and 171, respectively. Accordingly, mutants of UCP3 in positions 167 and 171/172 were made. In permeabilized cells, these mutants exhibited distinct Ca²⁺ sensitivities in regard to mitochondrial Ca²⁺ sequestration. In intact cells, these mutants established different activities in mitochondrial uptake of either intracellularly released (UCP3^R171,E172) or entering (UCP3^R167) Ca²⁺. Our data demonstrate that distinct sites in the IML2 of UCP3 effect mitochondrial uptake of high and low Ca²⁺ signals.

Protective potential of 17β-estradiol against co-exposure of 4-hydroxynonenal and 6-hydroxydopamine in PC12 cells

4-hydroxynonenal (4-HNE) and 6-hydroxydopamine (6-OHDA)-mediated damage in dopaminergic neurons is well documented. Protective potential of steroidal hormone (17β-estradiol) has also been suggested. However, therapeutic potential of such promising hormone is hampered due to complex brain anatomy and physiology. Thus, the present investigations were studied to suggest the applicability of dopamine expressing PC12 cells as in vitro tool to screen the pharmacological potential of 17β-estradiol against 4-HNE and 6-OHDA. MTT assay was conducted for cytotoxicity assessment of both 4-HNE (1 μM to 50 μM) and 6-OHDA (10-4 to 10-7 M). Non-cytotoxic concentrations, that is, 4-HNE (1 μM) and 6-OHDA (10-6 M) were selected to study the synergetic/additive responses. PC12 cells were found to be more vulnerable towards co-exposure of individual exposure of 4-HNE and 6-OHDA, even at non-cytotoxic concentrations. Then, cells were subjected to pre-treatment (24 hours) of 17β-estradiol (1 μM), followed by a permutation of combinations of both 4-HNE and 6-OHDA. Pretreatment of 17β-estradiol was found to be significantly effective against the cytotoxic responses of 4-HNE and 6-OHDA, when the damage was at lower level. However, 17β-estradiol was found to be ineffective against higher concentrations. Physiological-specific responses of PC12 cells against 4-HNE/6-OHDA and 17β-estradiol suggest its applicability as first tier of screening tool.

Nuclear and cytoplasmic expressions of ERβ1 and ERβ2 are predictive of response to therapy and alters prognosis in familial breast cancers

Estrogen receptor (ER) α has been studied extensively in familial breast cancers but there are limited data on ERβ and its isoforms. This is an important issue since many BRCA1-associated tumours are "triple negative" and are resistant to conventional and targeted therapies. We performed an immunohistochemical study of pan-ERβ, ERβ1 and ERβ2 in a cohort of 123 familial breast carcinomas (35 BRCA1, 33 BRCA2 and 55 BRCAX) using a cut-off for positivity at 20% (Shaaban et al. in Clin Cancer Res 14:5228-5235, 2008). BRCA1 cancers were more likely to be nuclear ERα negative and nuclear pan-ERβ positive (21/32, 66%) when compared with BRCA2 (2/29, 7%) and BRCAX cancers (11/49, 22%) (both P < 0.001). For survival analysis, expression was also stratified using cut-offs defined by Bates et al. (Breast Cancer Res Treat 111:453-459, 2008) (score out of 7). Cytoplasmic ERβ2 expression correlated with shorter overall survival at 15 years regardless of cut-off used (both P < 0.046) At a cut-off score of 6 out of 7, cytoplasmic ERβ2 expression correlated with a poorer response to chemotherapy in both univariate (P = 0.011) and multivariate analyses including grade, lymph node status and chemotherapy as an interaction variable (P = 0.045, Hazard ratio 1.22, 95% CI 1.004-9.87). A similar trend was seen in a univariate analysis with a cut-off of 20% although this did not reach statistical significance (P = 0.057). Expression of nuclear ERβ1 was associated with a favourable response to endocrine therapy at 15 years regardless of cut-offs employed (both P < 0.025). However, this did not reach statistical significance in a multivariate analysis (P > 0.05). Since a significant proportion of ERα negative familial breast carcinomas are positive for nuclear ERβ1 and cytoplasmic ERβ2, the different ERβ isoforms and their intracellular location may need to be assessed, to identify patients that may benefit from hormonal and chemotherapy.

Calcium uptake mechanisms of mitochondria

The ability of mitochondria to capture Ca2+ ions has important functional implications for cells, because mitochondria shape cellular Ca2+ signals by acting as a Ca2+ buffer and respond to Ca2+ elevations either by increasing the cell energy supply or by triggering the cell death program of apoptosis. A mitochondrial Ca2+ channel known as the uniporter drives the rapid and massive entry of Ca2+ ions into mitochondria. The uniporter operates at high, micromolar cytosolic Ca2+ concentrations that are only reached transiently in cells, near Ca2+ release channels. Mitochondria can also take up Ca2+ at low, nanomolar concentrations, but this high affinity mode of Ca2+ uptake is not well characterized. Recently, leucine-zipper-EF hand-containing transmembrane region (Letm1) was proposed to be an electrogenic 1:1 mitochondrial Ca2+/H+ antiporter that drives the uptake of Ca2+ into mitochondria at nanomolar cytosolic Ca2+ concentrations. In this article, we will review the properties of the Ca2+ import systems of mitochondria and discuss how Ca2+ uptake via an electrogenic 1:1 Ca2+/H+ antiport challenges our current thinking of the mitochondrial Ca2+ uptake mechanism.

Regulation of mitochondrial respiratory chain biogenesis by estrogens/estrogen receptors and physiological, pathological and pharmacological implications

There has been increasing evidence pointing to the mitochondrial respiratory chain (MRC) as a novel and important target for the actions of 17beta-estradiol (E(2)) and estrogen receptors (ER) in a number of cell types and tissues that have high demands for mitochondrial energy metabolism. This novel E(2)-mediated mitochondrial pathway involves the cooperation of both nuclear and mitochondrial ERalpha and ERbeta and their co-activators on the coordinate regulation of both nuclear DNA- and mitochondrial DNA-encoded genes for MRC proteins. In this paper, we have: 1) comprehensively reviewed studies that reveal a novel role of estrogens and ERs in the regulation of MRC biogenesis; 2) discussed their physiological, pathological and pharmacological implications in the control of cell proliferation and apoptosis in relation to estrogen-mediated carcinogenesis, anti-cancer drug resistance in human breast cancer cells, neuroprotection for Alzheimer's disease and Parkinson's disease in brain, cardiovascular protection in human heart and their beneficial effects in lens physiology related to cataract in the eye; and 3) pointed out new research directions to address the key questions in this important and newly emerging area. We also suggest a novel conceptual approach that will contribute to innovative regimens for the prevention or treatment of a wide variety of medical complications based on E(2)/ER-mediated MRC biogenesis pathway.

Controlling metabolism and cell death: at the heart of mitochondrial calcium signalling

Transient increases in intracellular calcium concentration activate and coordinate a wide variety of cellular processes in virtually every cell type. This review describes the main homeostatic mechanisms that control Ca(2+) transients, focusing on the mitochondrial checkpoint. We subsequently extend this paradigm to the cardiomyocyte and to the interplay between cytosol, endoplasmic reticulum and mitochondria that occurs beat-to-beat in excitation-contraction coupling. The mechanisms whereby mitochondria decode fast cytosolic calcium spikes are discussed in the light of the results obtained with recombinant photoproteins targeted to the mitochondrial matrix of contracting cardiomyocytes. Mitochondrial calcium homeostasis is then highlighted as a crucial point of convergence of the environmental signals that mediate cardiac cell death, both by necrosis and by apoptosis. Altogether we point to a role of the mitochondrion as an integrator of calcium signalling and a fundamental decision maker in cardiomyocyte metabolism and survival.

Effects of beta-amyloid peptide and estrogen on platelet mitochondrial function of Sprague-Dawley rats

Beta-amyloid peptide (Abeta) peptides play a central role in the development of Alzheimer's disease. They are known to induce mitochondrial dysfunction and caspase activation, resulting in apoptosis of neuronal cells. In the present experiment, an Abeta-induced damage model of platelets was established to observe the effects of Abeta, estradiol benzoate (EB) and genistein on platelets and platelet mitochondria. It was found that after the addition of Abeta, platelet number, platelet mitochondrial membrane potential (DeltaPsim) and adenosine triphosphate (ATP) content were lowered while no protective effects of EB and genistein had been observed. The platelets could serve as a biomarker for detection of mitochondrial function and age related disease.

Rapid estrogen regulation of DHEA metabolism in the male and female songbird brain

In the songbird brain, dehydroepiandrosterone (DHEA) is metabolized to the active and aromatizable androgen androstenedione (AE) by 3beta-hydroxysteroid dehydrogenase/Delta5-Delta4 isomerase (3beta-HSD). Thus, brain 3beta-HSD plays a key role in regulating the steroidal milieu of the nervous system. Previous studies have shown that stress rapidly regulates brain 3beta-HSD activity in a sex-specific manner. To elucidate endocrine regulation of brain 3beta-HSD, we asked whether 17beta-estradiol (E(2)) regulates DHEA metabolism in adult zebra finch (Taeniopygia guttata) and whether there are sex-specific effects. Brain tissue was homogenized and centrifuged to obtain supernatant lacking whole cells and cell nuclei. Supernatant was incubated with [(3)H]DHEA and radioinert E(2)in vitro. Within only 10 min, E(2) significantly reduced 3beta-HSD activity in both male and female brain. Interestingly, the rapid effects of E(2) were more pronounced in females than males. These are the first data to show a rapid effect of estrogens on the songbird brain and suggest that rapid estrogen effects differ between male and female brains.

Mitochondria and Ca(2+) signaling: old guests, new functions

Mitochondria are ancient endosymbiotic guests that joined the cells in the evolution of complex life. While the unique ability of mitochondria to produce adenosine triphosphate (ATP) and their contribution to cellular nutrition metabolism received condign attention, our understanding of the organelle's contribution to Ca(2+) homeostasis was restricted to serve as passive Ca(2+) sinks that accumulate Ca(2+) along the organelle's negative membrane potential. This paradigm has changed radically. Nowadays, mitochondria are known to respond to environmental Ca(2+) and to contribute actively to the regulation of spatial and temporal patterns of intracellular Ca(2+) signaling. Accordingly, mitochondria contribute to many signal transduction pathways and are actively involved in the maintenance of capacitative Ca(2+) entry, the accomplishment of Ca(2+) refilling of the endoplasmic reticulum and Ca(2+)-dependent protein folding. Mitochondrial Ca(2+) homeostasis is complex and regulated by numerous, so far, genetically unidentified Ca(2+) channels, pumps and exchangers that concertedly accomplish the organelle's Ca(2+) demand. Notably, mitochondrial Ca(2+) homeostasis and functions are crucially influenced by the organelle's structural organization and motility that, in turn, is controlled by matrix/cytosolic Ca(2+). This review intends to provide a condensed overview on the molecular mechanisms of mitochondrial Ca(2+) homeostasis (uptake, buffering and storage, extrusion), its modulation by other ions, kinases and small molecules, and its contribution to cellular processes as fundamental basis for the organelle's contribution to signaling pathways. Hence, emphasis is given to the structure-to-function and mobility-to-function relationship of the mitochondria and, thereby, bridging our most recent knowledge on mitochondria with the best-established mitochondrial function: metabolism and ATP production.

The plasma membrane Na+/Ca2+ exchange inhibitor KB-R7943 is also a potent inhibitor of the mitochondrial Ca2+ uniporter

BACKGROUND AND PURPOSE

The thiourea derivative KB-R7943, originally developed as inhibitor of the plasma membrane Na(+)/Ca(2+) exchanger, has been shown to protect against myocardial ischemia-reperfusion injury. We have studied here its effects on mitochondrial Ca(2+) fluxes.

EXPERIMENTAL APPROACH

[Ca(2+)] in cytosol, mitochondria and endoplasmic reticulum (ER), and mitochondrial membrane potential were monitored using both luminescent (targeted aequorins) and fluorescent (fura-2, tetramethylrhodamine ethyl ester) probes in HeLa cells.

KEY RESULTS

KB-R7943 was also a potent inhibitor of the mitochondrial Ca(2+) uniporter (MCU). In permeabilized HeLa cells, KB-R7943 inhibited mitochondrial Ca(2+) uptake with a Ki of 5.5+/-1.3 microM (mean+/-S.D.). In intact cells, 10 microM KB-R7943 reduced by 80% the mitochondrial [Ca(2+)] peak induced by histamine. KB-R7943 did not modify the mitochondrial membrane potential and had no effect on the mitochondrial Na(+)/Ca(2+) exchanger. KB-R7943 inhibited histamine-induced ER-Ca(2+) release in intact cells, but not in cells loaded with a Ca(2+)-chelator to damp cytosolic [Ca(2+)] changes. Therefore, inhibition of ER-Ca(2+)-release by KB-R7943 was probably due to the increased feedback Ca(2+)-inhibition of inositol 1,4,5-trisphosphate receptors after MCU block. This mechanism also explains why KB-R7943 reversibly blocked histamine-induced cytosolic [Ca(2+)] oscillations in the same range of concentrations required to inhibit MCU.

CONCLUSIONS AND IMPLICATIONS

Inhibition of MCU by KB-R7943 may contribute to its cardioprotective activity by preventing mitochondrial Ca(2+)-overload during ischemia-reperfusion. In addition, the effects of KB-R7943 on Ca(2+) homeostasis provide new evidence for the role of mitochondria modulating Ca(2+)-release and regenerative Ca(2+)-oscillations. Search for permeable and selective MCU inhibitors may yield useful pharmacological tools in the future.

Modulation of Ca(2+) release and Ca(2+) oscillations in HeLa cells and fibroblasts by mitochondrial Ca(2+) uniporter stimulation

The recent availability of activators of the mitochondrial Ca(2+) uniporter allows direct testing of the influence of mitochondrial Ca(2+) uptake on the overall Ca(2+) homeostasis of the cell. We show here that activation of mitochondrial Ca(2+) uptake by 4,4',4''-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT) or kaempferol stimulates histamine-induced Ca(2+) release from the endoplasmic reticulum (ER) and that this effect is enhanced if the mitochondrial Na(+)-Ca(2+) exchanger is simultaneously inhibited with CGP37157. This suggests that both Ca(2+) uptake and release from mitochondria control the ability of local Ca(2+) microdomains to produce feedback inhibition of inositol 1,4,5-trisphosphate receptors (InsP(3)Rs). In addition, the ability of mitochondria to control Ca(2+) release from the ER allows them to modulate cytosolic Ca(2+) oscillations. In histamine stimulated HeLa cells and human fibroblasts, both PPT and kaempferol initially stimulated and later inhibited oscillations, although kaempferol usually induced a more prolonged period of stimulation. Both compounds were also able to induce the generation of Ca(2+) oscillations in previously silent fibroblasts. Our data suggest that cytosolic Ca(2+) oscillations are exquisitely sensitive to the rates of mitochondrial Ca(2+) uptake and release, which precisely control the size of the local Ca(2+) microdomains around InsP(3)Rs and thus the ability to produce feedback activation or inhibition of Ca(2+) release.

Actions of estrogen and estrogen receptors in nonclassical target tissues

Hormonal effects on classical endocrine target organs such as the female reproductive tract, mammary gland, ovary, and neuroendocrine system have been thoroughly studied, with significant advancements in our understanding of estrogen actions and disease conditions from both cell culture as well as new experimental animal models. Knowledge of the highly appreciated effects of estrogen in nonclassical endocrine organ systems, arising from epidemiological and clinical findings in the cardiovascular, immune, GI tract, and liver, is only now becoming clarified from the development and use of knock-out or transgenic animal models for the study of both estrogen and ER activities. There are considerable epidemiological data showing that premenopausal females (Barrett-Connor 1997; Crabbe et al. 2003) have reduced risk for cardiovascular disease. However, a recent large clinical trial failed to show cardioprotection for postmenopausal females on estrogen-progestin replacement (Rossouw et al. 2002). In fact, the Women's Health Initiative Study showed increased cardiovascular risk for females taking an estrogen-progestin combination. These studies suggest that we need a better understanding of the mechanisms responsible for cardioprotection in females.

Rapid endocrine disruption: environmental estrogen actions triggered outside the nucleus

An exogenous substance is defined as an endocrine disrupter chemical (EDC) if it alters the function of the endocrine system provoking adverse health effects. Environmental estrogens are the most studied EDCs. They follow the same mechanisms of action as the gonadal hormone 17beta-estradiol. Up to now, the estrogenicity of environmental estrogenic pollutants has been based on the property of these compounds to bind to estrogen receptors (ERs), either ERalpha or ERbeta, and to act subsequently as transcription factors when binding to the estrogen response element (ERE) in the DNA. All the estrogenic bioassays currently used are based on this mechanism of action. New evidence indicates that the definition of estrogenicity for a chemical should take into account other estrogen receptors as well as new signaling pathways. These include the activation of additional transcription factors as well as the action of xenoestrogens through estrogen receptors located outside the nucleus: in the plasma membrane, mitochondria and probably the cytosol. Therefore, new estrogenic bioassays should be developed to include the novel concept of rapid endocrine disruption.

Calcium microdomains in mitochondria and nucleus

Endomembranes modify the progression of the cytosolic Ca(2+) wave and contribute to generate Ca(2+) microdomains, both in the cytosol and inside the own organella. The concentration of Ca(2+) in the cytosol ([Ca(2+)](C)), the mitochondria ([Ca(2+)](M)) and the nucleus ([Ca(2+)](N)) are similar at rest, but may become very different during cell activation. Mitochondria avidly take up Ca(2+) from the high [Ca(2+)](C) microdomains generated during cell activation near Ca(2+) channels of the plasma membrane and/or the endomembranes and prevent propagation of the high Ca(2+) signal to the bulk cytosol. This shaping of [Ca(2+)](C) signaling is essential for independent regulation of compartmentalized cell functions. On the other hand, a high [Ca(2+)](M) signal is generated selectively in the mitochondria close to the active areas, which tunes up respiration to the increased local needs. The progression of the [Ca(2+)](C) signal to the nucleus may be dampened by mitochondria, the nuclear envelope or higher buffering power inside the nucleoplasm. On the other hand, selective [Ca(2+)](N) signals could be generated by direct release of stored Ca(2+) into the nucleoplasm. Ca(2+) release could even be restricted to subnuclear domains. Putative Ca(2+) stores include the nuclear envelope, their invaginations inside the nucleoplasm (nucleoplasmic reticulum) and nuclear microvesicles. Inositol trisphosphate, cyclic ADP-ribose and nicotinic acid adenine dinucleotide phosphate have all been reported to produce release of Ca(2+) into the nucleoplasm, but contribution of these mechanisms under physiological conditions is still uncertain.

Extranuclear estrogen receptor beta immunoreactivity is on doublecortin-containing cells in the adult and neonatal rat dentate gyrus

In adult female rats, estrogen receptor (ER) activation, particularly of ERbeta, promotes hippocampal neurogenesis. We previously reported that extranuclear ERbeta immunoreactivity (ir) in adult rats is on cellular profiles in or near the granule cell layer, which is the location of newly generated cells. During development, cells in or near the granule cell layer transiently express high levels of estrogen binding and nuclear ERs. Thus, we sought to determine if extranuclear ERbeta is in newly generated cells in adult and neonatal rat dentate gyrus. Sections from the dentate gyrus of adult proestrus or postnatal day 7 and 14 female rats were dual-labeled for ERbeta and the new-cell marker doublecortin (DCX) and examined by electron microscopy. DCX-containing neurons were found in the subgranular hilus in adult rats and were more widespread throughout the granule cell layer and hilus of neonatal rats. In both adults and neonatal rats, ERbeta immunoreactivity was found in a subset of DCX-labeled neurons. Electron microscopic examination of the adult dentate gyrus revealed that most perikarya with DCX-ir had the morphological characteristics of granule cells, although a few resembled interneurons. Dendrites with DCX-ir also were observed. In both adults and neonates, DCX-labeled neuronal perikarya and dendrites contained ERbeta-ir; ERbeta-ir usually was aggregated near the plasma membrane, mitochondria or endoplasmic reticula. ERbeta-ir was in glial profiles that apposed DCX-labeled perikarya and dendrites. These findings are consistent with data showing that estrogens can exert non-genomic effects directly and indirectly on newly generated cells in neonatal and adult rat dentate gyrus.

Effects of estrogen receptor subtype-selective agonists on immune functions in ovariectomized mice

Estrogens have multiple influences on immune functions. Estrogen receptors (ERs) have two distinct subtypes - alpha and beta. To explore the specific roles of each ER subtype in estrogen-mediated immunomodulation, we investigated the effects of ER subtype-selective agonists on immune functions in ovariectomized Balb/c mice. Treatment with ERalpha-selective agonist propyl pyrazole triol (PPT) caused thymic atrophy and significant changes in thymic CD4/CD8 phenotypic profile. In contrast, ERbeta-selective agonist diarylpropionitrile (DPN) alone had no effect on thymic weight, cellularity or CD4/CD8 phenotype expression. When coadministered with PPT, DPN partially antagonized PPT-evoked decrease in thymic cellularity and also partially attenuated PPT-induced shifts in thymic T-cell phenotype. These results indicate that ERalpha plays a predominant role in estrogen-induced thymic atrophy and ERbeta activation may partially down-regulate ERalpha-mediated effects on thymic cellularity and T-cell phenotype expression. In addition, PPT administration induced a reduction in the percentage of mature B cells in the spleen, and enhanced IFN-gamma production but suppressed IL-6 production from in vitro Con A-stimulated splenocytes as estradiol (E(2)) did, whereas DPN treatment had no effects either alone or with PPT, suggesting ERalpha mediates these estrogen actions. Treatment with PPT or DPN did not augment anti-DNP antibody production after DNP-KLH immunization as E(2) did, implying that not merely one ER signaling pathway is involved in mediating estrogen's effects on specific humoral immune responses. Our study further indicates ER subtype-selective agonists provide a novel approach to explore each ER subtype-mediated immunomodulation.

Estrogen exerts a spatial and temporal influence on reactive oxygen species generation that precedes calcium uptake in high-capacity mitochondria: implications for rapid nongenomic signaling of cell growth

Novel findings that emerged from this study underscore the fact that the dynamic nature of mitochondria leads to functional heterogeneity of [Ca(2+)](mito) with respect to estrogen actions in MCF7 cells. We show that estrogen exposure to cells increased [Ca(2+)](mito) in a high-calcium capacity mitochondrial population but not in low-calcium capacity mitochondria. Physiological concentrations of 17beta-estradiol (E2) modulated Ca(2+)(mito) uptake within 90 s. Interestingly, this calcium response lagged behind the induction of mitochondrial reactive oxygen species (mtROS). The rapid induction of Ca(2+)(mito) in response to E2 and its inhibition by mitochondrial blockers suggest that mitochondria are early nongenomic targets of E2. This suggests that a subpopulation of mitochondria is recruited to respond to new metabolic requirements required by estrogen triggers or, as in this case, E2-induced Ca(2+)(mito) and/or mtROS promotes oxidative signaling without involving nuclear estrogen receptor signaling. Although the early E2-induced Ca(2+) did not alter the expression of genes involved in calcium signaling pathways, an intracellular calcium chelator BAPTA-AM and the Ca(2+)(mito) uniporter blocker ruthenium red prevented E2-induced cell growth. We have shown recently that E2-mediated ROS production controls the promoter activity of cyclin D1 by post-translational modification of calcium sensitive transcription factor CREB. The findings of this study offer a new paradigm that rapid E2-induced changes in mtROS and Ca(2+)(mito) are involved in cell cycle progression presumably through the control of early cell cycle genes. Targeting mitochondria to disrupt communication between mitochondria and ROS/Ca(2+) signaling pathways may provide the basis for a novel anticancer strategy for the treatment of estrogen-dependent breast cancer.

Dilatory responses to estrogenic compounds in small femoral arteries of male and female estrogen receptor-β knockout mice

The objectives of this study were to determine whether acute dilatory responses to estrogen receptor agonists are altered in isolated arteries from estrogen receptor β-deficient mice (β-ERKO) and to gain insight into the role of nitric oxide (NO) in these responses. Femoral arteries (∼250 μm) from male and female β-ERKO mice and wild-type (WT) littermates (26 female, 13 in each group; and 24 male, 12 in each group) were mounted on a Multi-Myograph. Concentration-response curves to 17β-estradiol (17β-E2) and the selective estrogen receptor-α (ER-α) agonist propyl-[1H]-pyrazole-1,3,5-triy-trisphenol (PPT) were obtained before and after NO synthase (NOS) inhibition [ Nω-nitro-l-arginine methyl ester (l-NAME), 0.1 mM] in arteries preconstricted with U-46619 (a thromboxane analog). In WT mice, responses to the potent estrogen receptor-β (ER-β) agonist 2,3-bis(4-hydroxyphenyl)-propionitrile (DPN) and the contribution of NO were also assessed. Concentration-response curves to 17β-E2and PPT were similar in arteries from WT and β-ERKO mice of both genders, but NO-mediated relaxation was different, since l-NAME reduced 17β-E2mediated relaxation in arteries from male and female β-ERKO but not WT mice ( P < 0.05). NOS inhibition reduced dilation to PPT in arteries from male and female WT mice, as well as arteries from female β-ERKO mice ( P < 0.05). Responses to DPN in arteries from WT female and male mice did not differ after NOS inhibition. The acute dilatory responses to estrogenic compounds are similar in WT and β-ERKO mice but differ mechanistically. Because NO appeared to contribute to responses to 17β-E2in arteries from β-ERKO but not WT mice, the presence of ER-β apparently inhibits ER-α-mediated NO relaxation.