Variants in the estrogen receptor alpha gene and its mRNA contribute to risk for schizophrenia

Estrogen modifies human emotion and cognition and impacts symptoms of schizophrenia. We hypothesized that the variation in the estrogen receptor alpha (ESR1) gene and cortical ESR1 mRNA is associated with schizophrenia. In a small case–control genetic association analysis of postmortem brain tissue, genotype CC (rs2234693) and haplotypes containing the C allele of a single-nucleotide polymorphism (SNP) in intron1 (PvuII) were more frequent in African American schizophrenics (P = 0.01–0.001). In a follow-up family-based association analysis, we found overtransmission of PvuII allele C and a PvuII C-containing haplotype (P = 0.01–0.03) to African American and Caucasian patients with schizophrenia. Schizophrenics with the ‘at risk’ PvuII genotype had lower ESR1 mRNA levels in the frontal cortex. Eighteen ESR1 splice variants and decreased frequencies of the wild-type ESR1 mRNA were detected in schizophrenia. In one patient, a unique ESR1 transcript with a genomic insert encoding a premature stop codon and a truncated ESR1 protein lacking most of the estrogen binding domain was the only transcript detected. Using a luciferase assay, we found that mRNA encoding a truncated ESR1 significantly attenuates gene expression at estrogen-response elements demonstrating a dominant negative function. An intron 6 SNP [rs2273207(G)] was associated with an ESR1 splice variant missing exon seven. The T allele of another intron 6 SNP was part of a 3′ haplotype less common in schizophrenia [rs2273206(T), rs2273207(G), rs2228480(G)]. Thus, the variation in the ESR1 gene is associated with schizophrenia and the mechanism of this association may involve alternative gene regulation and transcript processing.

Age-related differences in glucocorticoid receptor mRNA levels in the human brain

Glucocorticoids and their receptors (GRs) are implicated in dynamic cognitive and neuroendocrine processes mediated by the prefrontal cortex and hippocampus. Additionally, a primary defect in forebrain GR levels can mimic symptoms of depression. We hypothesized that changes in GR mRNA levels may occur in the human brain across the life span thus positioning GR to differentially influence behavior and disease susceptibility. Following in situ hybridization with a riboprobe for human GR mRNA, we employed quantitative film autoradiography to measure expression levels in the prefrontal cortex and hippocampus in five age groups (infants, adolescents, young adults, adults, and aged) and in primary visual and visual association cortices for comparison. We detected a main effect of age group on cortical, but not hippocampal GR mRNA, with greater cortical expression in adolescents and adults than in infants or the aged. Increased GR mRNA in prefrontal cortex during adolescence and adulthood suggests that human GR-mediated forebrain regulation of cognition and the neuroendocrine stress response may be more salient during late maturation and at maturity.

Alteration in estrogen receptor alpha mRNA levels in frontal cortex and hippocampus of patients with major mental illness

BACKGROUND

Gender differences have been described in major mental illnesses (MMI). The dorsolateral prefrontal cortex (DLPFC) and hippocampus are estrogen-sensitive brain regions structurally and functionally altered in patients with MMI. We hypothesized that gender-specific alterations in DLPFC and hippocampus estrogen receptor alpha (ERalpha) mRNA levels may exist in MMI patients.

METHODS

We used Northern blot analysis to survey the expression of ERalpha mRNA transcripts in brain and body, detected by our human ERalpha riboprobe and in situ hybridization, to examine the expression pattern and quantify ERalpha mRNA levels in DLPFC and anterior hippocampus of patients with major depressive disorder (MDD), schizophrenia, and bipolar disorder compared with normal control subjects.

RESULTS

Northern blotting revealed brain-region-specific differences in expression levels of a 5 kb ERalpha mRNA transcript. By in situ hybridization, ERalpha mRNA was detected in all layers of DLPFC and all hippocampal subfields in all subjects. We detected greater DLPFC ERalpha mRNA expression in male compared with female MDD subjects and reduced ERalpha mRNA levels in the dentate gyrus of schizophrenics compared with control subjects.

CONCLUSIONS

Our results suggest that alterations in ERalpha mRNA levels exist in distinct telencephalic regions in male and female MDD patients, and in both genders in schizophrenia.

Expression of estrogen receptor alpha exon-deleted mRNA variants in the human and non-human primate frontal cortex

Although estrogen receptor alpha (ERalpha) mRNA has been detected in the primate frontal cortex, the types of ERalpha transcripts expressed, including exon-deleted variants (Delta), have not been determined in the monkey or human frontal cortex. Because the types of ERalpha mRNA expressed in brain could define neuronal responses to estrogens, we examined the transcript pool of ERalpha mRNAs expressed in normal adult and developing human and macaque frontal cortex. We reverse transcribed total RNA from the postmortem frontal cortex of 29 normal adult humans, 12 rhesus macaques, and 19 people ranging from infants to adults and employed two rounds of nested polymerase chain reaction (PCR) to generate ERalpha products spanning the coding domain. In a third nested PCR, we used primers specific for novel sequences of exon-exon junctions created when whole exons are missing. By sequencing PCR products, we detected 60 instances of 12 distinct DeltaERalpha mRNAs in adult humans and 94 instances of 13 distinct DeltaERalpha mRNAs in monkeys in differing patterns from one individual to another. In adult humans, 83% of individuals expressed at least 1 DeltaERalpha mRNA variant, and 100% of the monkeys expressed at least 1 DeltaERalpha mRNA variant. The single Delta2, Delta5, and Delta7 variants were frequently expressed in both human and monkey frontal cortex, Delta3 variants were rare in both species, and Delta6 variants were more frequently expressed in monkeys. In both species, we detected double, triple and quadruple Deltas, but these were less common than single Deltas. The pattern of human variant expression did not appear to change dramatically as a function of age. These findings imply the potential to produce different ERalpha proteins in frontal cortex, possibly with altered structure and function which may have physiological relevance for gene transcription by virtue of altered functional interactions with each other, other steroid hormone receptors, and genomic DNA.

Reduced glucocorticoid and estrogen receptor alpha messenger ribonucleic acid levels in the amygdala of patients with major mental illness

BACKGROUND

The amygdala is a limbic structure involved in the stress response and the regulation of emotional behaviors, both of which are disrupted in patients with neuropsychiatric illnesses. Because glucocorticoids are mediators of the stress response, we hypothesized that glucocorticoid receptor (GR) messenger ribonucleic acid (mRNA) levels might be altered in the amygdala. We also hypothesized that estrogen receptor alpha (ERalpha) mRNA expression might be altered in the amygdala, on the basis of observed gender differences in mental illness.

METHODS

Using quantitative film autoradiography after in situ hybridization with human GR and ERalpha probes, we measured mRNA levels on adjacent amygdala sections in four groups (n = 15 each of subjects with schizophrenia, major depressive disorder, and bipolar disorder, and unaffected control subjects) provided by the Stanley Consortium.

RESULTS

We detected main effects of diagnosis and exposure to antidepressant medication on the levels of both mRNAs but no main effect of gender. Compared with control subjects, GR mRNA expression was reduced in the basolateral/lateral nuclei in schizophrenia and bipolar disorder. Estrogen receptor alpha mRNA levels were reduced in the basomedial nucleus in major depressive disorder and bipolar disorder.

CONCLUSIONS

Our results support and extend previous findings describing a pattern of steroid hormone mRNA alterations that differs depending on which brain region is being examined in a given mental illness.

Estradiol alters transcription factor gene expression in primate prefrontal cortex

Estrogen protects neurons from a variety of experimental insults in vitro, and is thought to protect from acute and chronic neurodegenerative processes in vivo. Estrogen also enhances higher-level cognitive functions that are centered in the dorsolateral prefrontal cortex (DLPFC) in human and non-human primates. To investigate genomic mechanisms involved in estrogenic effects on the primate brain in vivo, we compared transcription factor mRNA and protein expression in the DLPFC of ovariectomized rhesus monkeys treated with either vehicle or estradiol (E2). c-FOS, E2F1, and general transcription factor IIB (TFIIB) mRNA and protein expression were altered significantly by short-term E2 treatment, as shown by DNA array, in situ hybridization, and immunohistochemical and immunoblot evaluations. C-FOS expression was increased significantly whereas E2F1 and TFIIB levels were decreased in the DLPFC of E2-treated animals. These transcription factors were concentrated in cortical pyramids, as were estrogen receptors alpha and beta. These data indicate that estrogen may have direct as well as indirect effects on neuronal gene expression in the primate prefrontal cortex.

Postmortem investigations of the pathophysiology of schizophrenia: the role of susceptibility genes

Despite robust evidence for the heritability of schizophrenia, postmortem studies have not traditionally linked cellular and molecular neuropathology with underlying genetic mechanisms in this disorder. The completion of the first draft of the Human Genome Project and the use of novel strategies in studying complex genetic disorders including schizophrenia have led to the identification of a growing list of schizophrenia susceptibility genes. In this review, we describe the strategy used to incorporate 2 potential schizophrenia susceptibility genes in the postmortem investigation of the pathophysiology of schizophrenia driven by 2 well-established hypotheses, the dopamine hypothesis and the neurodevelopmental hypothesis. The first gene codes for catechol-O-methyltransferase, an enzyme involved in catecholamine degradation, and the second gene codes for brain-derived neurotrophic factor, a growth factor implicated in cell survival, synaptogenesis and the development of cortical pyramidal neurons.

Expression of androgen receptor mRNA in zebra finch song system: Developmental regulation by estrogen

By using improved methods for in situ hybridization to detect expression of androgen receptor (AR) mRNA, the distribution of expression was mapped in the adult male zebra finch brain. In the neural song circuit, robust expression was found in area X of the lobus parolfactorius (LPO) as well as in other song regions previously reported. Expression was also found in many areas of the hypothalamus and dorsal thalamic nuclei, nucleus intercollicularis and ventricular areas of the midbrain, cerebellar Purkinje and granule cells, the hyperstriatum, medial neostriatum, medial LPO, and archistriatum. In juvenile males, AR mRNA expression was first detected in nucleus high vocal center (HVC) at posthatch day 9 (P9), in area X at P9-P11, and in the region of the robust nucleus (RA) in the medial archistriatum by P7. Estrogen treatment of hatchling females caused an increase in the expression of AR mRNA in HVC and area X by P11, whereas treatment of hatchling males with the aromatase inhibitor fadrozole decreased the expression of AR mRNA at P11. The present results indicate that masculine development of AR expression begins in area X and HVC before they are thought to be synaptically connected, suggesting that different song nuclei initiate sexual differentiation independently of transsynaptic masculinizing influences. The present results suggest that estrogen is necessary for full masculine AR expression in the song system and that the estrogenic regulation of AR contributes to subsequent differential actions of androgen in male and female song nuclei.

Expression of estrogen receptor and aromatase mRNAs in embryonic and posthatch zebra finch brain

Male zebra finches sing and females normally do not. This sexually dimorphic behavior is mediated by a sexually dimorphic series of interconnected nuclei that are larger and more developed in males. Estradiol administered to females as early as the day of hatching (P1) causes profound masculinization of this song system. The exact timing of estrogen action is unknown, and there is little information concerning the times and sites of expression of estrogen receptors and aromatase before P5. We measured the expression of mRNAs encoding these proteins in brain during late embryogenesis and on P1 to determine if estrogen synthesis or receptor-mediated actions on the song system, as part of the program of sexual differentiation, might be possible during this period. Using highly sensitive and specific in situ hybridization procedures for mRNAs encoding ERalpha, ERbeta, and aromatase, we detected mRNA for ERs in archistriatal regions as early as embryonic stage 34, and in diencephalic regions as early as embryonic stage 30. ERalpha mRNA was also detected in the dorsal mesencephalon at P1. Aromatase mRNA expression was present as early as embryonic stage 30 in diencephalic and mesencephalic regions. No obvious sex differences in the spatio-temporal pattern of mRNA expression were detected. Our results suggest that estrogen can influence cell growth and differentiation in zebra finch brain well before hatching and into posthatching life. The results fail to provide support for the hypothesis that sexual differentiation of the song system is mediated by sex differences in the expression of these mRNAs at these ages.

Expression of androgen receptor mRNA in the late embryonic and early posthatch zebra finch brain

Zebra finch males sing and females do not, and the underlying neural circuitry in males is more developed than that in females. Sex steroid hormones influence the development of sex differences in this circuitry, including differences in androgen receptor (AR) expression, although the role of androgens has been controversial. We isolated a cDNA encoding a portion of the zebra finch AR and used in situ hybridization to examine the spatiotemporal pattern of AR mRNA expression in the brain during late embryonic development and at hatching. We detected AR mRNA in all the major subdivisions of the brain as early as embryonic day 10. No qualitative sex differences in AR mRNA expression patterns were observed. Cells lining the ventral arm of the lateral telencephalic ventricles expressed AR mRNA on embryonic day 11 and posthatching day 1, as did cells lining the third ventricle at all three developmental stages examined, suggesting that androgens may play a role in early stages of cellular proliferation, migration, or differentiation. AR mRNA was also detected in the hippocampus, neostriatum, septum, ventromedial archistriatum, hypothalamic regions, dorsal mesencephalon, and in and around the brainstem nucleus tracheosyringealis. Our results suggested that androgens act early in neural development and therefore may contribute to the process of sexual differentiation.

Cloning and expression of zebra finch (Taeniopygia guttata) steroidogenic factor 1: overlap with hypothalamic but not with telencephalic aromatase

The zebra finch (Taeniopygia guttata) brain is highly sexually dimorphic. The organization and production of sex-specific song is considerably influenced by estrogens and androgens. Because the brain itself expresses several steroidogenic enzymes, the local production of sex steroids may contribute to sex differences in neural development. Sex steroid production in gonads is directed by a master regulatory factor, steroidogenic factor 1 (SF1). We have identified a cDNA encoding the homologue of SF1 in the zebra finch and utilized reverse transcription-polymerase chain reaction and in situ hybridization to examine early and late developmental expression of SF1 in brain and in early gonadal development. We found that SF1 is expressed early in embryonic development in the Rathke pouch, beginning at stage 15 and extending to at least stage 27 in both males and females. The earliest expression of SF1 in gonads was found at stage 17 for both males and females and extended to at least stage 27. In brain, we assessed SF1 mRNA expression in posthatch and adult telencephalon, and we compared SF1 and aromatase mRNA expression in adult hypothalamus. In the telencephalon and hippocampus, aromatase was expressed independently of SF1, whereas in the hypothalamus, aromatase and SF1 expression were more closely associated. Expression of SF1 and of aromatase overlapped in restricted regions of the hypothalamus, suggesting that SF1 may regulate aromatase expression in these regions. These findings suggest that steroidogenesis in the zebra finch brain may be regulated by both SF1-dependent and SF1-independent mechanisms. No sex differences were detected in SF1 expression in brain.