Estrogen receptors alpha and beta (ERalpha and ERbeta) and androgen receptor (AR) in human sperm: localization of ERbeta and AR in mitochondria of the midpiece

Oestrogens and spermatogenesis

The role of oestrogens in male reproductive tract physiology has for a long time been a subject of debate. The testis produces significant amounts of oestrogenic hormones, via aromatase, and oestrogen receptors (ERs)alpha (ESR1) and ERbeta (ESR2) are selectively expressed in cells of the testis as well as the epididymal epithelium, depending upon species. This review summarizes the current knowledge concerning the presence and activity of aromatase and ERs in testis and sperm and the potential roles that oestrogens may have in mammalian spermatogenesis. Data show that physiology of the male gonad is in part under the control of a balance of androgens and oestrogens, with aromatase serving as a modulator.

Manganese superoxide dismutase vs. p53: regulation of mitochondrial ROS

Coordination of mitochondrial and nuclear activities is vital for cellular homeostasis, and many signaling molecules and transcription factors are regulated by mitochondria-derived reactive oxygen species (ROS) to carry out this interorganellar communication. The tumor suppressor p53 regulates myriad cellular functions through transcription-dependent and -independent mechanisms at both the nucleus and mitochondria. p53 affect mitochondrial ROS production, in part, by regulating the expression of the mitochondrial antioxidant enzyme manganese superoxide dismutase (MnSOD). Recent evidence suggests mitochondrial regulation of p53 activity through mechanisms that affect ROS production, and a breakdown of communication amongst mitochondria, p53, and the nucleus can have broad implications in disease development.

Seasonal variations of melatonin in ram seminal plasma are correlated to those of testosterone and antioxidant enzymes

BACKGROUND

Some breeds of sheep are highly seasonal in terms of reproductive capability, and these changes are regulated by photoperiod and melatonin secretion. These changes affect the reproductive performance of rams, impairing semen quality and modifying hormonal profiles. Also, the antioxidant defence systems seem to be modulated by melatonin secretion, and shows seasonal variations. The aim of this study was to investigate the presence of melatonin and testosterone in ram seminal plasma and their variations between the breeding and non-breeding seasons. In addition, we analyzed the possible correlations between these hormones and the antioxidant enzyme defence system activity.

METHODS

Seminal plasma from nine Rasa Aragonesa rams were collected for one year, and their levels of melatonin, testosterone, superoxide dismutase (SOD), glutathione reductase (GRD), glutathione peroxidase (GPX) and catalase (CAT) were measured.

RESULTS

All samples presented measurable quantities of hormones and antioxidant enzymes. Both hormones showed monthly variations, with a decrease after the winter solstice and a rise after the summer solstice that reached the maximum levels in October-November, and a marked seasonal variation (P < 0.01) with higher levels in the breeding season. The yearly pattern of GRD and catalase was close to that of melatonin, and GRD showed a significant seasonal variation (P < 0.01) with a higher activity during the breeding season. Linear regression analysis between the studied hormones and antioxidant enzymes showed a significant correlation between melatonin and testosterone, GRD, SOD and catalase.

CONCLUSIONS

These results show the presence of melatonin and testosterone in ram seminal plasma, and that both hormones have seasonal variations, and support the idea that seasonal variations of fertility in the ram involve interplay between melatonin and the antioxidant defence system.

A compendium of human mitochondrial gene expression machinery with links to disease

Mammalian mitochondrial DNA encodes 37 essential genes required for ATP production via oxidative phosphorylation, instability or misregulation of which is associated with human diseases and aging. Other than the mtDNA-encoded RNA species (13 mRNAs, 12S and 16S rRNAs, and 22 tRNAs), the remaining factors needed for mitochondrial gene expression (i.e., transcription, RNA processing/modification, and translation), including a dedicated set of mitochondrial ribosomal proteins, are products of nuclear genes that are imported into the mitochondrial matrix. Herein, we inventory the human mitochondrial gene expression machinery, and, while doing so, we highlight specific associations of these regulatory factors with human disease. Major new breakthroughs have been made recently in this burgeoning area that set the stage for exciting future studies on the key outstanding issue of how mitochondrial gene expression is regulated differentially in vivo. This should promote a greater understanding of why mtDNA mutations and dysfunction cause the complex and tissue-specific pathology characteristic of mitochondrial disease states and how mitochondrial dysfunction contributes to more common human pathology and aging.

Aromatase, oestrogens and human male reproduction

In most mammalian species aromatase is encoded by a single gene (Cyp19), which contains 18 exons, nine of them being translated. In man, the presence of a biologically active aromatase and oestrogen receptors (ERalpha and ERbeta) has been reported in Leydig cells, and also in immature germ cells and ejaculated spermatozoa. Concerning aromatase, the amount of transcript and enzymatic activity are decreased in immotile compared with motile sperm. We have amplified aromatase mRNA by real-time polymerase chain reaction in spermatozoa from asthenospermic, teratospermic and asthenoteratospermic men and recorded, respectively, 44, 52 and 67 per cent decreases of the amount of transcripts compared with fertile donors. A high degree of correlation (r = -0.64) between the abnormal spermatozoa (especially microcephaly and acrosome malformations) and aromatase/GAPDH transcript ratio has been observed. Idiopathic infertility is a wide health problem and no treatment is currently available. In humans, even if the role of oestrogens in spermatogenesis is still a matter of debate, the observations of decreased sperm number and motility in men genetically deficient in aromatase, together with our data and those reported in the literature, may suggest a role for aromatase/oestrogens not only during the development and maintenance of spermatogenesis but also in the final maturation of spermatozoa.

Ontogeny of the oestrogen receptors ESR1 and ESR2 during gonadal development in the tammar wallaby, Macropus eugenii

Oestrogen has wide ranging effects in development mediated mainly via the two oestrogen receptors, α (ESR1, also known as ERα) and β (ESR2, also known as ERβ). Oestrogen is the key factor that directs the indifferent gonad to become an ovary in many non-mammalian vertebrates. Oestrogen is not required for early ovarian differentiation in mammals but can disrupt normal testicular development in eutherians. Surprisingly, exogenous oestrogen can cause sex reversal of an XY gonad in two marsupials, the North American opossum and the tammar wallaby. To understand the mechanism by which oestrogen induces sex reversal, we characterised the genes for ESR1 and ESR2 and examined their expression during gonadal differentiation in the tammar wallaby, Macropus eugenii. Both receptors were expressed in the somatic cells and germ cells of the indifferent gonad in both XX and XY foetuses throughout all stages of development, and persisted in these cells into adulthood. ERs were also present in many other tissues including kidney, pituitary and mammary gland. ER mRNA was not significantly altered by exogenous oestrogen in cultured XY gonads but the receptors translocated to the nucleus in its presence. These findings confirm that there is conserved expression of the ERs in the indifferent gonad despite the lack of available ligand during early gonadal development. The receptors can respond to exogenous estrogen at this early stage and are capable of transducing signals in the early mammalian gonad. However, the selective forces that maintained conserved ER expression in this tissue remain unknown.

Enhanced ERbeta immunoexpression and apoptosis in the germ cells of cimetidine-treated rats

BACKGROUND

Cimetidine, refereed as antiandrogenic drug, causes hormonal changes in male patients such as increased testosterone and FSH levels. In the rat testis, structural alterations in the seminiferous tubules have been related to germ cell loss and Sertoli cell death by apoptosis. Regarding the important role of Sertoli cells in the conversion of testosterone into estrogen, via aromatase, the immunoexpression of estrogen receptors-beta (ERbeta) was evaluated in the germ cells of untreated and treated rats with cimetidine. A relationship between ERbeta immunoreactivity and apoptosis was also investigated in the germ cells of damaged tubules.

METHODS

Immunohistochemistry for detection of ERbeta and TUNEL method were performed in testicular sections of adult male rats treated with 50 mg/Kg of cimetidine (CmG) or saline solution (CG) for 52 days.

RESULTS

In CG, a cytoplasmic immunoexpression for ERbeta was observed in spermatogonia, primary spermatocytes and spermatids. An evident ERbeta immunoreactivity was always observed in the flagellum and residual bodies of late spermatids. In CmG, the cytoplasm or cytoplasm and nuclei of germ cells of the damaged tubules by cimetidine showed enhanced ERbeta immunostaining. TUNEL-labeling was usually observed in the same germ cell types exhibiting enhanced ERbeta immunoreactivity.

CONCLUSION

The presence of ERbeta immunolabeling in the flagellum and residual bodies of spermatids reinforces the role of estrogen in spermiogenesis. The overexpression of ERbeta in the germ cells of CmG could be related to a possible interference of cimetidine on tubular androgenization and/or on the intratubular aromatase due to Sertoli cell damage. The parallelism between ERbeta overexpression and apoptosis indicates a participation of ERbeta on germ cell death.

Androgen receptor as a potential sign of prostate cancer metastasis

BACKGROUND

Androgen receptor (AR) expression and its modulation through the carcinogenesis process have been investigated in several studies with conflicting results.

MATERIALS AND METHODS

In situ hybridization and immunocytochemistry were used to examine AR expression in prostatic needle core biopsies of benign, high grade prostatic intraepithelial neoplasia (HGPIN) and prostatic adenocarcinoma.

RESULTS

A significant increase in AR mRNA levels was found in the cancerous prostatic cells when compared with the benign tissue biopsies. AR abundance in HGPIN was found to be almost half-way between that observed in benign and in cancerous tissue. In the benign prostatic epithelium, the immunocytochemistry data show that AR is exclusively expressed in the nuclei of epithelial cells. However, in 72% of examined cancer biopsies, AR was expressed in both the cytoplasm and nuclei. After examination of medical records of 100 patients diagnosed with prostate cancer, it was found that the AR was expressed in both cellular compartments of cancer cells in 81% of cases when cancer was found to have metastasized outside the prostate. In contrast, when the cancer was organ-confined, AR was localized in both the nuclei and cytoplasm in only 66% of cases. Moreover, when the AR was expressed in the cytoplasm of cancerous cells, consecutive serial sections immunostained with the mitochondrial marker suggest that AR is localized in the mitochondria.

CONCLUSIONS

AR mRNA expression is significantly higher in prostate cancer when compared to benign prostatic tissue.

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.

Activity and intracellular location of estrogen receptors alpha and beta in human bronchial epithelial cells

Gender differences in lung disease and cancer are well-established. We reported estrogenic transcriptional responses in lung adenocarcinoma cells from females but not males despite similar estrogen receptor (ER) expression. Here we tested the hypothesis that normal human bronchial epithelial cells (HBECs) show gender-independent estrogenic responses. We report that a small sample of HBECs express approximately twice as much ERbeta as ERalpha. ERalpha and ERbeta were located in the cytoplasm, nucleus, and mitochondria. In contrast to lung adenocarcinoma cells, estradiol (E2) induced estrogen response element (ERE)-mediated luciferase reporter activity in transiently transfected HBECs regardless of donor gender. Overexpression of ERalpha-VP16 increased ERE-mediated transcriptional activity in all HBECs. E2 increased and 4-hydroxytamoxifen and ICI 182,780 inhibited HBEC proliferation and cyclin D1 expression in a cell line-specific manner. In conclusion, the response of HBECs to ER ligands is gender-independent suggesting that estrogenic sensitivity may be acquired during lung carcinogenesis.

Watching the watcher: regulation of p53 by mitochondria

p53 has been referred to as the 'guardian of the genome' because of its role in protecting the cell from DNA damage. p53 performs its duties by regulating cell-cycle progression and DNA repair and, in cases of irreparable DNA damage, by executing programmed cell death. Mitochondria are an important target of transcription-dependent and -independent actions of p53 to carry out the apoptotic function. However, increasing evidence suggests that p53 activity is regulated by mitochondria. Cellular insults that alter mitochondrial function can have important consequences on p53 activity. In light of these new findings, the following review focuses on p53/mitochondria connections, in particular how reactive oxygen species generated at mitochondria regulate p53 activity. A better understanding of the mechanisms by which mitochondria regulate p53 may have an impact on our understanding of the development and progression of many diseases, especially cancer.

Regulation of energy metabolism pathways by estrogens and estrogenic chemicals and potential implications in obesity associated with increased exposure to endocrine disruptors

The prevalence of obesity among children, adolescents and adults has been dramatically increasing worldwide during the last several decades. The obesity epidemic has been recognized as one of the major global health problems, because its health hazard is linked to a number of common diseases including breast and prostate cancers. Obesity is caused by combination of genetic and environmental factors. While genetic contribution to obesity has been known to be significant, the genetic factors remain relatively unchanged. Recent studies have highlighted the involvement of environmental "obesogens", i.e. the xenobiotic chemicals that can disrupt the normal development and homeostatic control over adipogenesis and energy balance. Several lines of evidence suggest that increasing exposure to chemicals with endocrine-disrupting activities (endocrine-disrupting chemicals, EDCs) contributes to the increased obesity. The cellular and molecular mechanisms underlying obesogen-associated obesity are just now being appreciated. In this paper, we comprehensively reviewed current knowledge about the role of estrogen receptors alpha and beta (ERalpha and ERbeta) in regulation of energy metabolism pathways, including glucose transport, glycolysis, tricarboxylic acid (TCA) cycle, mitochondrial respiratory chain (MRC), adenosine nucleotide translocator (ANT) and fatty acid beta-oxidation and synthesis, by estrogens; and then examined the disturbance of E(2)/ER-mediated energy metabolism pathways by environmental obesogens; and finally, we discussed the potential implications of disturbance of energy metabolism pathways by obesogens in obesity and pointed out several key aspects of this area that need to be further explored. A better understanding of the cellular and molecular mechanisms underlying obesogen-associated obesity will lead to new approaches for slow down and/or prevention of the increased trend of obesity associated with exposure to obesogens.

Estrogen receptor beta as a mitochondrial vulnerability factor

We recently demonstrated mitochondrial localization of estrogen receptor beta (ERbeta). We herein confirm the mitochondrial localization of ERbeta by the loss of mitochondrial ERbeta immunoreactivity in ERbeta knockdown cells. A phenotype change characterized as an increase in resistance to oxidative stressors is associated with ERbeta knockdown. ERbeta knockdown results in a lower resting mitochondrial membrane potential (Deltapsim) and increase in resistance to hydrogen peroxide-induced Deltapsim depolarization in both immortal hippocampal cells and primary hippocampal neurons. ERbeta knockdown cells maintained ATP concentrations despite insults that compromise ATP production and produce less mitochondrial superoxide under oxidative stress. Furthermore, similar mitochondrial phenotype changes were identified in primary hippocampal neurons derived from ERbeta knock-out mice. These data demonstrate that ERbeta is expressed in mitochondria and function as a mitochondrial vulnerability factor involved in Deltapsim maintenance, potentially through a mitochondrial transcription dependent mechanism.

Androgen receptor roles in spermatogenesis and fertility: lessons from testicular cell-specific androgen receptor knockout mice

Androgens are critical steroid hormones that determine the expression of the male phenotype, including the outward development of secondary sex characteristics as well as the initiation and maintenance of spermatogenesis. Their actions are mediated by the androgen receptor (AR), a member of the nuclear receptor superfamily. AR functions as a ligand-dependent transcription factor, regulating expression of an array of androgen-responsive genes. Androgen and the AR play important roles in male spermatogenesis and fertility. The recent generation and characterization of male total and conditional AR knockout mice from different laboratories demonstrated the necessity of AR signaling for both external and internal male phenotype development. As expected, the male total AR knockout mice exhibited female-typical external appearance (including a vagina with a blind end and a clitoris-like phallus), the testis was located abdominally, and germ cell development was severely disrupted, which was similar to a human complete androgen insensitivity syndrome or testicular feminization mouse. However, the process of spermatogenesis is highly dependent on autocrine and paracrine communication among testicular cell types, and the disruption of AR throughout an experimental animal cannot answer the question about how AR in each type of testicular cell can play roles in the process of spermatogenesis. In this review, we provide new insights by comparing the results of cell-specific AR knockout in germ cells, peritubular myoid cells, Leydig cells, and Sertoli cells mouse models that were generated by different laboratories to see the consequent defects in spermatogenesis due to AR loss in different testicular cell types in spermatogenesis. Briefly, this review summarizes these results as follows: 1) the impact of lacking AR in Sertoli cells mainly affects Sertoli cell functions to support and nurture germ cells, leading to spermatogenesis arrest at the diplotene primary spermatocyte stage prior to the accomplishment of first meiotic division; 2) the impact of lacking AR in Leydig cells mainly affects steroidogenic functions leading to arrest of spermatogenesis at the round spermatid stage; 3) the impact of lacking AR in the smooth muscle cells and peritubular myoid cells in mice results in similar fertility despite decreased sperm output as compared to wild-type controls; and 4) the deletion of AR gene in mouse germ cells does not affect spermatogenesis and male fertility. This review tries to clarify the useful information regarding how androgen/AR functions in individual cells of the testis. The future studies of detailed molecular mechanisms in these in vivo animals with cell-specific AR knockout could possibly lead to useful insights for improvements in the treatment of male infertility, hypogonadism, and testicular dysgenesis syndrome, and in attempts to create safe as well as effective male contraceptive methods.

Aromatase and estrogens in man reproduction: a review and latest advances

The mammalian testis is a complex organ which produces spermatozoa and synthesizes steroids. The transformation of androgens into estrogens is catalyzed by aromatase, an enzymatic complex encoded by a single copy-gene (cyp19) which contains 18 exons, 9 of them being translated. In man besides Leydig cells, we have demonstrated the existence of a biologically active aromatase in immature germ cells and in ejaculated spermatozoa. In addition the presence of estrogen receptors (ERalpha and ERss) in immature germ cells and in spermatozoa has been reported. Concerning aromatase, a 30% decrease of the amount of mRNA is observed in immotile compared to motile sperm fraction from the same sample. In asthenoteratozoospermic, teratozoospermic and asthenozoospermic patients, the aromatase gene expression is decreased respectively by 67%, 52% and 44%, when compared to normospermic controls. Statistical analyses between the sperm morphology and the aromatase/GAPDH ratio have revealed a high degree of correlation (r=-0.64) between that ratio and the percentage of abnormal spermatozoa (especially microcephaly). In men genetically deficient in aromatase diminutions of sperm number and motility have been published. Therefore besides gonadotrophins and testosterone, estrogens are likely playing a relevant role in spermiogenesis and human male gamete maturation.

Mitochondria in mammalian sperm physiology and pathology: a review

While, for a long time, the role of mitochondria in sperm physiology and pathology has been largely ignored, recent research points out the mitochondria as a major organelle with key roles in sperm function both under physiological and biotechnological conditions. This paper briefly reviews these novel findings regarding the role of mitochondria in sperm, paying special attention to the most practical, readily applicable, aspects of the topic such as their role as a major source of the sublethal damage that sperm experiments after cryopreservation.

Mitochondrial abnormalities in spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is a motor neuron disease caused by polyglutamine expansion mutation in the androgen receptor (AR). We investigated whether the mutant protein alters mitochondrial function. We found that constitutive and doxycycline-induced expression of the mutant AR in MN-1 and PC12 cells, respectively, are associated with depolarization of the mitochondrial membrane. This was mitigated by cyclosporine A, which inhibits opening of the mitochondrial permeability transition pore. We also found that the expression of the mutant protein in the presence of ligand results in an elevated level of reactive oxygen species, which is blocked by the treatment with the antioxidants co-enzyme Q10 and idebenone. The mutant protein in MN-1 cells also resulted in increased Bax, caspase 9 and caspase 3. We assessed the effects of mutant AR on the transcription of mitochondrial proteins and found altered expression of the peroxisome proliferator-activated receptor γ coactivator 1 and the mitochondrial specific antioxidant superoxide dismutase-2 in affected tissues of SBMA knock-in mice. In addition, we found that the AR associates with mitochondria in cultured cells. This study thus provides evidence for mitochondrial dysfunction in SBMA cell and animal models, either through indirect effects on the transcription of nuclear-encoded mitochondrial genes or through direct effects of the mutant protein on mitochondria or both. These findings indicate possible benefit from mitochondrial therapy for SBMA.

Estrogen actions on mitochondria--physiological and pathological implications

Estrogens are potent neuroprotective hormones and mitochondria are the site of cellular life-death decisions. As such, it is not surprising that we and others have shown that estrogens have remarkable effects on mitochondrial function. Herein we provide evidence for a primary effect of estrogens on mitochondrial function, achieved in part by the import of estrogen receptor beta (ERbeta) into the mitochondria where it mediates a number of estrogen actions on this vital organelle. ERbeta is imported into the mitochondria, through tethering to cytosolic chaperone protein and/or through direct interaction with mitochondrial import proteins. In the mitochondria, ERbeta can affect transcription of critical mitochondrial genes through the interaction with estrogen response elements (ERE) or through protein-protein interactions with mitochondrially imported transcription factors. The potent effects of estrogens on mitochondrial function, particularly during mitochondrial stress, argues for a role of estrogens in the treatment of mitochondrial defects in chronic neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD) and more acute conditions of mitochondrial compromise, like cerebral ischemia and traumatic brain injury.

Steroid and thyroid hormone receptors in mitochondria

Receptors for glucocorticoids, estrogens, androgens, and thyroid hormones have been detected in mitochondria of various cell types by Western blotting, immunofluorescence labeling, confocal microscopy, and immunogold electron microscopy. A role of these receptors in mitochondrial transcription, OXPHOS biosynthesis, and apoptosis is now being revealed. Steroid and thyroid hormones regulate energy production, inducing nuclear and mitochondrial OXPHOS genes by way of cognate receptors. In addition to the action of the nuclearly localized receptors on nuclear OXPHOS gene transcription, a parallel direct action of the mitochondrially localized receptors on mitochondrial transcription has been demonstrated. The coordination of transcription activation in nuclei and mitochondria by the respective receptors is in part realized by their binding to common trans acting elements in the two genomes. Recent evidence points to a role of the mitochondrial receptors in cell survival and apoptosis, exerted by genomic and nongenomic mechanisms. The identification of additional receptors of the superfamily of nuclear receptors and of other nuclear transcription factors in mitochondria increases their arsenal of regulatory molecules and further underlines the central role of these organelles in the integration of growth, metabolic, and cell survival signals.

Evidence for association of sex hormone-binding globulin and androgen receptor genes with semen quality

The roles of androgen receptor AR(CAG)n gene polymorphisms and sex hormone-binding globulin SHBG(TAAAA)n gene polymorphisms on semen quality were studied. One hundred fourteen men were included in the study: 85 with normal sperm count and 29 oligospermic. The genotype analysis, on DNA extracted from spermatozoa, revealed five SHBG(TAAAA)n alleles with 6-10 repeats and 18 AR(CAG)n alleles with 12-32 repeats. The SHBG allelic distribution showed that in men with normal sperm count and motility, those with short SHBG alleles had higher sperm concentration than men with long SHBG alleles (P = 0.039). As concerns AR(CAG)n polymorphisms, men with short AR alleles had lower sperm motility compared to those with long AR alleles (P < 0.001) in both total study population and normal sperm count men. The synergistic effect analysis of the two polymorphisms revealed an association between sperm motility (P = 0.036), because of the effect of AR(CAG)n polymorphism on sperm motility. In conclusion, long AR alleles were found to be associated with higher sperm motility, while short SHBG alleles were associated with higher sperm concentration, supporting the significance of these genes in spermatogenesis and semen quality.

Classical androgen receptors in non-classical sites in the brain

Androgen receptors are expressed in many different neuronal populations in the central nervous system where they often act as transcription factors in the cell nucleus. However, recent studies have detected androgen receptor immunoreactivity in neuronal and glial processes of the adult rat neocortex, hippocampal formation, and amygdala as well as in the telencephalon of eastern fence and green anole lizards. This review discusses previously published findings on extranuclear androgen receptors, as well as new experimental results that begin to establish a possible functional role for androgen receptors in axons within cortical regions. Electron microscopic studies have revealed that androgen receptor immunoreactive processes in the rat brain correspond to axons, dendrites and glial processes. New results show that lesions of the dorsal CA1 region by local administration of ibotenic acid reduce the density of androgen receptor immunoreactive axons in the cerebral cortex and the amygdala, suggesting that these axons may originate in the hippocampus. Androgen receptor immunoreactivity in axons is also decreased by the intracerebroventricular administration of colchicine, suggesting that androgen receptor protein is transported from the perikaryon to the axons by fast axonal transport. Androgen receptors in axons located in the cerebral cortex and amygdala and originating in the hippocampus may play an important role in the rapid behavioral effects of androgens.

Androgen receptor is expressed in both X- and Y-carrier human spermatozoa

OBJECTIVE

To quantify the amount of AR messenger RNA (mRNA) and to analyze the presence and functionality of the AR protein in X- and Y-carrier human spermatozoa.

DESIGN

A molecular and cellular research study.

SETTING

Academic research clinic and laboratories.

PATIENT(S)

Ten normozoospermic volunteers.

INTERVENTION(S)

Sperm were analyzed for expression of AR mRNA and protein. The functionality of AR protein was assessed after incubation with 1 nM of synthetic androgen.

MAIN OUTCOME MEASURE(S)

Reverse-transcription polymerase chain reaction (PCR), real-time PCR, Western immunoblotting, confocal immunofluorescence, and fluorescence in situ hybridization analysis were performed.

RESULT(S)

A significant amount of AR mRNA (around 30% of that found in the testis) was found in sperm. Androgen receptor protein was found in both X- and Y-carrier spermatozoa and translocates into the nucleus in the presence of synthetic androgen.

CONCLUSION(S)

A functional AR is expressed in human sperm. In view of the fact that AR protein is found in both X- and Y-carrier spermatozoa, it most probably is translated in earlier steps of spermatogenesis and moves to Y-carrier spermatids through the cytoplasmic bridges.

Estrogens and male reproduction: a new concept

The mammalian testis serves two main functions: production of spermatozoa and synthesis of steroids; among them estrogens are the end products obtained from the irreversible transformation of androgens by a microsomal enzymatic complex named aromatase. The aromatase is encoded by a single gene (cyp19) in humans which contains 18 exons, 9 of them being translated. In rats, the aromatase activity is mainly located in Sertoli cells of immature rats and then in Leydig cells of adult rats. We have demonstrated that germ cells represent an important source of estrogens: the amount of P450arom transcript is 3-fold higher in pachytene spermatocytes compared to gonocytes or round spermatids; conversely, aromatase activity is more intense in haploid cells. Male germ cells of mice, bank voles, bears, and monkeys express aromatase. In humans, we have shown the presence of a biologically active aromatase and of estrogen receptors (alpha and ss) in ejaculated spermatozoa and in immature germ cells in addition to Leydig cells. Moreover, we have demonstrated that the amount of P450arom transcripts is 30% lower in immotile than in motile spermatozoa. Alterations of spermatogenesis in terms of number and motility of spermatozoa have been described in men genetically deficient in aromatase. These last observations, together with our data showing a significant decrease of aromatase in immotile spermatozoa, suggest that aromatase could be involved in the acquisition of sperm motility. Thus, taking into account the widespread localization of aromatase and estrogen receptors in testicular cells, it is obvious that, besides gonadotrophins and androgens, estrogens produced locally should be considered to be physiologically relevant hormones involved in the regulation of spermatogenesis and spermiogenesis.

Mechanisms of hormone carcinogenesis: evolution of views, role of mitochondria

CumuIative and excessive exposure to estrogens is associated with increased breast cancer risk. The traditional mechanism explaining this association is that estrogens affect the rate of cell division and apoptosis and thus manifest their effect on the risk of breast cancer by affecting the growth of breast epithelial tissues. Highly proliferative cells are susceptible to genetic errors during DNA replication. The action of estrogen metabolites offers a complementary genotoxic pathway mediated by the generation of reactive estrogen quinone metabolites that can form adducts with DNA and generate reactive oxygen species through redox cycling. In this chapter, we discussed a novel mitochondrial pathway mediated by estrogens and their cognate estrogen receptors (ERs) and its potential implications in estrogen-dependent carcinogenesis. Several lines of evidence are presented to show: (1) mitochondrial localization of ERs in human breast cancer cells and other cell types; (2) a functional role for the mitochondrial ERs in regulation of the mitochondrial respiratory chain (MRC) proteins and (3) potential implications of the mitochondrial ER-mediated pathway in stimulation of cell proliferation, inhibition of apoptosis and oxidative damage to mitochondrial DNA. The possible involvement of estrogens and ERs in deregulation of mitochondrial bioenergetics, an important hallmark of cancer cells, is also described. An evolutionary view is presented to suggest that persistent stimulation by estrogens through ER signaling pathways of MRC proteins and energy metabolic pathways leads to the alterations in mitochondrial bioenergetics and contributes to the development of estrogen-related cancers.

Nuclear receptors and other nuclear transcription factors in mitochondria: regulatory molecules in a new environment

The mitochondrion is the major energy generating organelle of the cell and the site of other basic processes, including apoptosis. The mitochondrial functions are performed in concert with other cell compartments and are regulated by various extracellular and intracellular signals. Several nuclear receptors and other nuclear transcription factors, such as NF-kappa B, AP-1, CREB and p53, involved in growth, metabolic and developmental processes, have been detected in mitochondria. This finding raises the question as to the role of these regulatory molecules in their "new" environment. Experimental evidence supports the action of the mitochondrially localized transcription factors on mitochondrial transcription, energy yield and apoptosis, extending the known nuclear role of these molecules outside the nucleus. A principle of coordination of nuclear and mitochondrial gene transcription has been ascertained as regards the regulatory action of steroid and thyroid hormones on energy yield. Accordingly, the same nuclear receptors, localized in the two compartments-nuclei and mitochondria-regulate transcription of genes serving a common function by way of interaction with common binding sites in the two genomes. This principle is now expanding to encompass other nuclearly and mitochondrially localized transcription factors.

RNA dynamics of fertile and infertile spermatozoa

The presence of a complex population of mRNAs in human mature spermatozoa is well documented; among them, transcripts of aromatase and ERs (oestrogen receptors) have been described but their significance is not clear. Therefore, to clarify the role of this complex population of mRNAs in human ejaculated sperm, we have isolated on discontinuous density gradients two main fractions from the same sample: high- and low-motile spermatozoa. The levels of different transcripts coding for molecules involved in nuclear condensation [Prm-1 (protamine 1) and Prm-2], capacitation [eNOS (endothelial nitric oxide synthase), nNOS (neuronal nitric oxide synthase), c-myc], motility and sperm survival (aromatase) have been assessed using semi-quantitative RT (reverse transcriptase)-PCR. The viability of sperm as well as the percentage of apoptosis were identical in high- and low-motile fractions. No significant change in the c-myc/Prm-2 ratio between the two populations of spermatozoa was observed. Conversely the amount of Prm-1 mRNA was significantly higher in low-motile than in high-motile fraction; in most of the high-motile sperm samples analysed, eNOS and nNOS transcripts were undetectable, whereas they were observed in low-motile sperm. Moreover, a partial or complete disappearance of c-myc transcripts was observed after capacitation. As to the aromatase expression, a significant decrease in the amount of transcripts in immotile sperm fraction was recorded in all samples studied. To conclude, analysing mRNA profiles in humans could be helpful either as a diagnostic tool to evaluate male fertility, since they reflect spermatogenesis gene expression, and/or a prognosis value for fertilization, since these RNAs are delivered to oocytes.

Expression of various CDC25B isoforms in human spermatozoa

OBJECTIVE

To explore the role of CDC25B protein in postmeiotic germ cells.

DESIGN

In vitro experiment.

SETTING

University-based reproductive genetics laboratory.

PATIENT(S)

Fertile and infertile volunteers.

INTERVENTION(S)

Reverse transcription-polymerase chain reaction (RT-PCR), real-time RT-PCR, and immunostaining for CDC25B.

MAIN OUTCOME MEASURE

Expression profiling of CDC25B in human spermatozoa.

RESULT(S)

Four splicing variants (CDC25B1, B2, B3, and B4) are expressed in human spermatozoa. Immunofluorescence staining showed strong homogeneous staining in the midpiece of spermatozoa, and weak staining in the principal piece and cytosol of the head. The messenger RNA (mRNA) transcript level of CDC25B was increased in sperm samples of men with asthenospermia.

CONCLUSION(S)

The expression of CDC25B in different cellular compartments of human spermatozoa suggests that there are diverse noncell-cycle-related functions of CDC25B in terminally differentiated human germ cells.

Effect of tamoxifen treatment on the semen quality and fertility of the male rat

OBJECTIVES

To determine the effects of tamoxifen treatment on the seminal quality and fertility of the male Wistar rat.

DESIGN

Experimental prospective study.

SETTING

Animal research and university laboratory facility.

SUBJECT(S)

Seventy-five-day-old male and female Wistar rats.

INTERVENTION(S)

Sperm quality parameters were assayed in seminal and epididymal sperm samples in control and treated rats at a dose of 0.4 mg tamoxifen/kg per day. In addition, mating studies were performed, and different fertility parameters were assayed.

RESULT(S)

Tamoxifen treatment significantly decreased sperm concentration and motility in seminal and epididymal sperm. Sperm viability and hypo-osmotic swelling test results were shown not to be altered. The copulatory plug was absent or severely impaired in tamoxifen-treated males. When mating experiments were performed, a significant decrease in the fertility index and increased percentages of preimplantation and postimplantation embryo loss were also observed.

CONCLUSION(S)

Tamoxifen treatment significantly altered sperm quality in seminal and epididymal sperm. These alterations were present in testis and epididymis, and additional negative effects on the sexual accessory glands were observed. Finally, these alterations were capable of seriously compromising fertility ability of these male rats.

Cytochrome P450arom, androgen and estrogen receptors in pig sperm

BACKGROUND

Androgens and estrogens are crucial for mammalian sperm differentiation but their role in biology of mature male gamete is not still defined. The expression of proteins involved in the biosynthesis and action of these steroid hormones has been demonstrated in human spermatozoa, but very few data have been reported in mature sperm from non human species. The purpose of the current study was to investigate the expression of aromatase (P450arom), estrogen (ERalpha/ERbeta) and androgen (AR) receptors in ejaculated spermatozoa of pig.

METHODS

The immunfluorescence experiments were carried out treating pig sperm with anti-P450arom, anti-ERalpha, anti-ERbeta and anti-AR as primary antibodies, while Texas-Red/FITC conjugated IgG were applied as secondary antibodies. Furthermore, Western blot analysis was performed on sperm lysates.

RESULTS

Aromatase was immunolocalized in the sperm tail, ERalpha and AR were localised in the sperm midpiece, while ERbeta was confined in the acrosomal region of the male gamete. Immunoblots detected a ~52 kDa aromatase band, a ~110 kDa AR band, a ~67 kDa ERalpha and two ERbeta bands, at ~50 kDa and ~59 kDa.

CONCLUSION

This is the first report demonstrating that pig ejaculated spermatozoa express aromatase, estrogen and androgen receptors with a differential intra-cellular localization revealing a species-specific expression pattern. Therefore, pig sperm could be considered as a potential estrogen source while the different hormone cellular sites suggest distinct roles of androgens and estrogens in pig sperm physiology.

Oculocutaneous Oncocytic Tumors: Clinicopathologic and Immunohistochemical Study of 2 Cases With Literature Review

Oculocutaneous oncocytic tumors (OCOTs) are uncommon neoplasms that have been reported only rarely in the dermatopathology literature and whose immunophenotypic profile has not been well characterized. The clinical, histologic, and immunophenotypic features of 2 cases seen by the authors were assessed, and relevant publications in the literature were reviewed. Both patients with OCOTs were adult women with gradually enlarging, asymptomatic lesions involving the caruncle; they were locally excised. Histologically, the tumors were well-circumscribed nodules comprised of large oxyphilic cells arranged in confluent sheets and forming glandular spaces with secretory material. Microcystic areas and sparse intermingled goblet-cells were also apparent. Nuclear atypia and infiltrative growth were absent. Mitotic activity was absent in one case; a single mitotic figure was identified in the other. Immunostains demonstrated uniform expression of pankeratin and mitochondrial antigens. Both neoplasms were also labeled for markers associated with cutaneous adnexal, lacrimal, and minor salivary glandular tissue, including alpha-1-antitrypsin, gross cystic disease fluid protein-15, carcinoembryonic antigen, lysozyme and MUC1; each case expressed 4 of the 5 substances. Some cells expressed cytokeratins 5/6 and p63 consistent with the presence of basal-type differentiation in a subset of cells. No definite evidence of myoepithelial differentiation was demonstrated, as stains for smooth muscle actin, muscle-specific actin, and S100 protein were negative. Estrogen and progesterone receptor proteins were absent; strong cytoplasmic immunoreactivity for androgen receptor protein was evident, but nuclear staining was absent. The authors conclude that OCOTs show glandular differentiation. A review of the literature disclosed that none of these lesions arising in the caruncle behaved aggressively, in contrast to occasional tumors in other oculocutaneous sites.

ERbeta shifts from mitochondria to nucleus during estrogen-induced neoplastic transformation of human breast epithelial cells and is involved in estrogen-induced synthesis of mitochondrial respiratory chain proteins

Both estrogen receptors (ER) alpha (ERalpha) and beta (ERbeta) are localized in the nucleus, plasma membrane, and mitochondria, where they mediate the different physiological effects of estrogens. It has been observed that the relative subcellular localization of ERs is altered in several cancer cells. We have demonstrated that MCF-10F cells, the immortal and non-tumorigenic human breast epithelial cells (HBEC) that are ERalpha-negative and ERbeta-positive, are transformed in vitro by 17beta-estradiol (E(2)), generating highly invasive cells that are tumorigenic in severe combined immunodeficient mice. E(2)-transformed MCF-10F (trMCF) cells exhibit progressive loss of ductulogenesis, invasive (bsMCF) and tumorigenic (caMCF) phenotypes. Immunolocalization of ERbeta by confocal fluorescent microscopy and electron microscopy revealed that ERbeta is predominantly localized in mitochondria of MCF-10F and trMCF cells. Silencing ERbeta expression with ERbeta-specific small interference RNA (siRNA-ERbeta) markedly diminishes both nuclear and mitochondrial ERbeta in MCF-10F cells. The ERbeta shifts from its predominant localization in the mitochondria of MCF-10F and trMCF cells to the nucleus of bsMCF cells, becoming predominantly nuclear in caMCF cells. Furthermore, we demonstrated that the mitochondrial ERbeta in MCF-10F cells is involved in E(2)-induced expression of mitochondrial DNA (mtDNA)-encoded respiratory chain (MRC) proteins. This is the first report of an association of changes in the subcellular localization of ERbeta with various stages of E(2)-induced transformation of HBEC and a functional role of mitochondrial ERbeta in mediating E(2)-induced MRC protein synthesis. Our findings provide a new insight into one of the potential roles of ERbeta in human breast cancer.

A role for tachykinins in the regulation of human sperm motility

BACKGROUND

Tachykinins and tachykinin receptors are widely distributed in the male reproductive tract and appear to be involved in reproduction. However, the function and expression of tachykinins and their receptors in human spermatozoa remain poorly studied. We analysed the effects of tachykinins on sperm motility and characterized the population of tachykinin receptors in human spermatozoa.

METHODS AND RESULTS

Motility analysis was performed following World Health Organization guidelines and we found that substance P (SP), human hemokinin-1 (hHK-1), neurokinin A (NKA) and neurokinin B (NKB) produced concentration-dependent increases in sperm progressive motility. The effects of tachykinins were antagonized by the NK(1) receptor-selective antagonist SR 140333, the NK(2) receptor-selective antagonist, SR 48968 and, to a lesser extent, also by the NK(3) receptor-selective antagonist SR 142801. Immunocytochemistry studies showed expression of the NK(1), NK(2) and NK(3) tachykinin receptor proteins in spermatozoa with different major sites of localization for each receptor. Western blot analysis confirmed the presence of tachykinin receptors in sperm cell homogenates. RT-PCR demonstrated expression of the genes that encode SP/NKA (TAC1), NKB (TAC3) and hHK-1 (TAC4) but not the genes TACR1, TACR2 and TACR3 encoding NK(1), NK(2) and NK(3) receptors, respectively.

CONCLUSIONS

These results show for the first time that the NK(1), NK(2) and NK(3) tachykinin receptor proteins are present in human spermatozoa. Our findings suggest that tachykinins, probably acting through these three tachykinin receptors, play a role in the regulation of human sperm motility.

ESCI Award 2006. Mitochondrial function and endocrine diseases

Mitochondria are fundamental for oxidative energy production and impairment of their functionality can lead to reduced ATP synthesis and contribute to initiation of apoptosis. Endocrine tissues critically rely on oxidative phosphorylation so that mitochondrial abnormalities may either be causes or consequences of diminished hormone production or action. Abnormalities typical for diseases caused by mitochondrial DNA mutations such as Kearns-Sayre syndrome or mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes syndrome are also seen in certain endocrine diseases. Lack or excess of thyroid hormones, major ubiquitous regulators of mitochondrial content and activity, cause muscular abnormalities and multisystem disorders. Mitochondria are a further prerequisite for steroidogenesis as well as insulin secretion and action. Recent studies showed that reduced mitochondrial ATP synthesis in skeletal muscle is a feature of certain hereditary and acquired forms of insulin resistance and diabetes mellitus. Finally, ageing is not only accompanied by various degrees of hormonal deficiency and insulin resistance but is also associated with a progressive decline of mitochondrial number and function. Future research is needed to examine whether mitochondrial abnormalities are the cause or consequence of ageing and frequent metabolic diseases such as obesity and type 2 diabetes mellitus, and to address mitochondria as a target for novel therapeutic regimes.

Mitochondrial localization of P2Y1, P2Y2 and P2Y12 receptors in rat astrocytes and glioma C6 cells

We have previously shown that P2Y1, P2Y2 and P2Y12 nucleotide receptors are functionally expressed and active on the cell surface of rat glioma C6 cells. In the present study, we have immunocytochemically shown their sub-cellular colocalization with mitochondria in these cells. The same colocalization of above receptors has been found in rat astrocytes. Additionally, differences in intracellular distribution of examined receptors between both cell lines have been observed. This data indicates that P2Y1, P2Y2 and P2Y12 receptor proteins exist within mitochondria of astrocytes and C6 cells, although their role in these sub-cellular structures remains unclear.

Expression and localization of delta-, kappa-, and mu-opioid receptors in human spermatozoa and implications for sperm motility

CONTEXT

Endogenous opioid peptides signal through delta-, kappa-, and mu-opioid receptors. Some of these peptides such as endorphins and enkephalins are present in the male reproductive tract, but the presence of the corresponding receptors in human sperm cells has not yet been reported.

OBJECTIVE

Our objective was to study the expression and localization of delta-, kappa-, and mu-opioid receptors on human spermatozoa and the implication in sperm motility.

METHODS

The expression of receptors was studied by RT-PCR, Western blot, and immunofluorescence techniques. We evaluated the effects of activation of each opioid receptor by specific agonist and antagonist.

RESULTS

Human spermatozoa express delta-, kappa-, and mu-opioid receptors. These receptors were located in different parts of the head, in the middle region, and in the tail of the sperm. Progressive motility of spermatozoa, an important parameter to evaluate male fertility, was found to be significantly reduced after incubation with the mu-receptor agonist morphine, whereas this effect was antagonized in the presence of the corresponding antagonist naloxone. The delta-receptor antagonist naltrindole significantly reduced progressive motility immediately after its addition. However, the delta-receptor agonist DPDPE had no significant effect. Finally, neither the kappa-receptor agonist U50488 nor its antagonist nor-binaltorphimine significantly affected the progressive motility of human spermatozoa.

CONCLUSION

We report for first time the presence of functional delta-, kappa-, and mu-opioid receptors in human sperm membranes. These findings are indicative of a role for the opioid system in the regulation of sperm physiology.

The Mitochondrion as a Primary Site of Action of Regulatory Agents Involved in Neuroimmunomodulation

A major system of neuroimmunomodulation is the hypothalamic-pituitary-adrenocortical (HPA) axis, acting through glucocorticoids and their intracellular signaling components, exerting both stimulatory and inhibitory effects on the immune reaction. Glucocorticoids inhibit the production of proinflammatory cytokines by interacting with nuclear transcription factors (nuclear factor [NF]-kappaB, activated protein [AP]-1) and induce the production of several anti-inflammatory cytokines by gene activation. In some cells and/or in extreme stress conditions, apoptosis is evoked. In most processes related to neuroimmunomodulation a prominent role is emerging for mitochondria. These organelles generate more than 90% of the cell's energy requirements through oxidative phosphorylation (OXPHOS), which is regulated by several agents, including steroid and thyroid hormones. These hormones are inducers of nuclear and mitochondrial OXPHOS gene transcription and they exert a primary action not only on nuclear but also on mitochondrial genes by way of cognate receptors. Recently, additional nuclear transcription factors involved in neuroimmunomodulation have been detected in mitochondria (NF-kappaB, AP-1, p53, calcium/cAMP response element binding protein [CREB]), and binding sites of these and putative binding sites of other nuclear transcription factors have been identified in the mitochondrial genome. The interaction of these factors with mitochondrial regulatory proteins, with receptors and with the genome has been shown and, in some cases, modulation of mitochondrial transcription was observed with possible effects on energy yield. The mitochondria store a host of critical apoptotic activators and inhibitors in their intermembrane space and the release of these factors could be another possible mode of action of the mitochondrially translocated regulatory agents and receptors.

Detection of estrogen receptors ER-alpha and ER-beta in human ejaculated immature spermatozoa with excess residual cytoplasm

BACKGROUND

A key role of estrogens in human sperm biology has been recently suggested by aromatase and estrogen receptor detection in human testicular germ cells and ejaculated spermatozoa. However, the involvement of these hormones in the sperm maturation process is still not defined. The aim of this work was to investigate the expression of estrogen receptors, ER-alpha and ER-beta, in human ejaculated immature spermatozoa with excess residual cytoplasm.

METHODS

Immunofluorescence labelling has been used to localize ER-alpha and ER-beta proteins in immature spermatozoa isolated by Percoll gradient, while Western blot analysis was carried out on sperm protein extracts.

RESULTS

Both estrogen receptors were localized in excess residual cytoplasm of immature sperm, while sperm tails showed only ER-beta. Furthermore, in the same cells, immunoblots detected the presence of the full-length (approximately 67 kDa) ER-alpha and (approximately 59 kDa) ER-beta proteins, together with a approximately 50 kDa ER-beta species, lacking in mature sperm.

CONCLUSION

The present investigation demonstrated ER-alpha and ER-beta presence in excess residual cytoplasm of human abnormal sperm cells, suggesting the hypothesis that both the 'classical' ERs could be able to mediate estrogen action in spermatogenetic cells. Furthermore, the presence of the short ER-beta form in abnormal germ cells and its disappearance in mature sperm, support estrogen modulation via different ER forms during sperm maturation.

Correspondence regarding Schwend and Gustafsson, “False positives in MALDI-TOF detection of ERβ in mitochondria”

Recently, Schwend and Gustafsson tried to use the MALDI-TOF methods to confirm one of the results reported by Yang et al., which provided definitive evidences to demonstrate the localization of estrogen receptor beta (ERbeta) in the mitochondria of multiple cell types, using immunocytochemistry, immunoblot, and proteomic approaches. Analysis of the data with the MASCOT database algorithm provided no evidence for the presence of ERbeta in the mouse live mitochondria, in which very low ERbeta expression has been detected in their own report. On the other hand, our MALDI-TOF analysis using human heart mitochondrial protein has identified 7 and 8 sequences that could be potentially from ERbeta and ERbeta3, respectively, but not from ATP synthases. Further, none of the sequences identified by us as those of ERbeta and ERbeta3 shares m/z targeted by Schwend and Gustafsson in their measurements. Therefore, the claim by Gustafsson's laboratory about false positives in MALDI-TOF detection of ERbeta in mitochondria has no relevance to our report.

The mitochondrion as a primary site of action of steroid and thyroid hormones: presence and action of steroid and thyroid hormone receptors in mitochondria of animal cells

Mitochondria are key cellular organelles that regulate events related to energy production and apoptosis. These processes are modulated, in turn, by steroid and thyroid hormones in the course of their actions on metabolism, growth and development. In this context, a direct effect of these hormones on the mitochondrial-linked processes, possibly by way of cognate mitochondrial receptors, has been proposed. In this paper we review data from the literature and present new findings supporting this concept. Receptors for steroid hormones, glucocorticoids and estrogens, and for T(3), have been detected in mitochondria by immunofluorescence labeling and confocal laser microscopy, by Western blotting of mitochondrial proteins and by immunogold electron microscopy. Furthermore, the mitochondrial genome contains nucleotide sequences with high similarity to known hormone-responsive elements, which interact with the appropriate receptors to confer hormone-dependent activation of reporter genes in transfection experiments. Thus, thyroid hormone stimulates mitochondrial transcription mediated by the cognate receptor when added to an in organello mitochondrial system, capable of faithful transcription.