Defects of androgen receptor function: from sex reversal to motor neurone disease

Extensive Variation in Gene Expression is Revealed in 13 Fertility-Related Genes Using RNA-Seq, ISO-Seq, and CAGE-Seq From Brahman Cattle

Fertility is a key driver of economic profitability in cattle production. A number of studies have identified genes associated with fertility using genome wide association studies and differential gene expression analysis; however, the genes themselves are poorly characterized in cattle. Here, we selected 13 genes from the literature which have previously been shown to have strong evidence for an association with fertility in Brahman cattle (Bos taurus indicus) or closely related breeds. We examine the expression variation of the 13 genes that are associated with cattle fertility using RNA-seq, CAGE-seq, and ISO-seq data from 11 different tissue samples from an adult Brahman cow and a Brahman fetus. Tissues examined include blood, liver, lung, kidney, muscle, spleen, ovary, and uterus from the cow and liver and lung from the fetus. The analysis revealed several novel isoforms, including seven from SERPINA7. The use of three expression characterization methodologies (5′ cap selected ISO-seq, CAGE-seq, and RNA-seq) allowed the identification of isoforms that varied in their length of 5′ and 3′ untranslated regions, variation otherwise undetectable (collapsed as degraded RNA) in generic isoform identification pipelines. The combinations of different sequencing technologies allowed us to overcome the limitations of relatively low sequence depth in the ISO-seq data. The lower sequence depth of the ISO-seq data was also reflected in the lack of observed expression of some genes that were observed in the CAGE-seq and RNA-seq data from the same tissue. We identified allele specific expression that was tissue-specific in AR, IGF1, SOX9, STAT3, and TAF9B. Finally, we characterized an exon of TAF9B as partially nested within the neighboring gene phosphoglycerate kinase 1. As this study only examined two animals, even more transcriptional variation may be present in a genetically diverse population. This analysis reveals the large amount of transcriptional variation within mammalian fertility genes and illuminates the fact that the transcriptional landscape cannot be fully characterized using a single technology alone.

Targeting matrix metalloproteinase activity and expression for the treatment of viral myocarditis

Infectious agents including viruses can infect the heart muscle, resulting in the development of heart inflammation called myocarditis. Chronic myocarditis can lead to dilated cardiomyopathy (DCM). DCM develops from the extensive extracellular matrix (ECM) remodeling caused by myocarditis and may result in heart failure. Epidemiological data for viral myocarditis has long suggested a worse pathology in males, with more recent data demonstrating sex-dependent pathogenesis in DCM as well. Matrix metalloproteinases (MMPs), long known modulators of the extracellular matrix, have important roles in mediating heart inflammation and remodeling during disease and in convalescence. This ability of MMPs to control both the inflammatory response and ECM remodeling during myocarditis makes them potential drug targets. In this review, we analyze the role of MMPs in mediating myocarditis/DCM disease progression, their sex-dependent expression, and their potential as drug targets during viral myocarditis and DCM.

Age-dependent differences in androgen binding affinity in a family with spinal and bulbar muscular atrophy

OBJECTIVES

To investigate androgen receptor (AR) function in spinal and bulbar muscular atrophy (SBMA).

METHODS

A kindred was identified with five individuals carrying the AR gene CAG repeat expansion that causes SBMA. Androgen binding was measured in cultured genital skin fibroblasts from three affected individuals. One newborn, pre-symptomatic, individual showed normal androgen binding, but two older, symptomatic individuals showed a decrease in androgen binding affinity. This difference was not related to AR CAG repeat size, as all affected individuals in this kindred had 49 repeats (normal range 6-35). Post-mortem analysis in one subject confirmed the signs of androgen insufficiency in the testis, with marked seminiferous tubule atrophy, and the absence of germinal cells. The characteristic neuronal depletion in the anterior horn gray matter was also observed.

CONCLUSION

This report raises the possibility that age- or puberty-related changes in androgen binding could occur, which could potentially contribute to the progressive development of androgen resistance in affected men.

Hormonal abnormalities leading to disorders of sexual development

Normal human sexual development occurs in a highly regulated process that comprises three distinct phases: establishment of chromosomal sex, development of the sex-specific gonads and phenotypic differentiation of the internal ductal anatomy and external genitalia. The latter two phases are mediated by specific hormonal effector molecules, including anti-Müllerian hormone and testosterone, and their dysregulation often leads to the development of a phenotypic disorder of sexual differentiation. This review describes the hormonal mediators that are involved in sexual development and the disorders of sexual differentiation that arise from their dysfunction.

Progesterone, glucocorticoid, but not estrogen receptor mRNA is altered in breast cancer stroma

Our laboratory has previously found that anti-mitogenic nuclear receptor mRNA is elevated in late stage tumours and this study was performed to scrutinize the possibility of cancer-stroma crosstalk using hormone signaling in these tissues. RNA levels in stromal tissue were examined for the estrogen alpha, estrogen beta, androgen, progesterone and glucocorticoid nuclear receptors by a semi-quantitative PCR. Significant differences in expression between the cancer stroma and control tissue were seen, analyzing for both cancer grade and estrogen receptor status. Stroma and control tissue were significantly different for the progesterone and glucocorticoid nuclear receptors (p=5.908 x 10(-7) and 2.761 x 10(-5), respectively). Glucocorticoid receptor also showed a significant increase to mRNA levels in the stroma of estrogen receptor negative tumours (p=5.85 x 10(-5)). By contrast, the estrogen receptors alpha and beta, those most closely associated with breast tissue growth, showed no significant change in mRNA (p=0.372 and 0.655, respectively). Androgen receptor mRNA also remained unaffected (p=0.174).

Osteoblast deletion of exon 3 of the androgen receptor gene results in trabecular bone loss in adult male mice

The mechanism of androgen action on bone was studied in male mice with the AR deleted in mature osteoblasts. These mice had decreased trabecular bone volume associated with a decrease in trabecular number, suggesting that androgens may act directly on osteoblasts to maintain trabecular bone.

INTRODUCTION

Androgens modulate bone cell activity and are important for the maintenance of bone mass. However, the mechanisms by which they exert these actions on bone remain poorly defined. The aim of this study was to investigate the role of androgens acting through the classical androgen receptor (AR) signaling pathways (i.e., DNA-binding dependent pathways) in osteoblasts using male mice in which exon 3 of the AR gene was deleted specifically in mature osteoblasts.

MATERIALS AND METHODS

Mice with a floxed exon 3 of the AR gene were bred with Col 2.3-cre transgenic mice, in which Cre recombinase is expressed in mineralizing osteoblasts. The skeletal phenotype of mutant mice was assessed by histomorphometry and quantitative microCT at 6, 12, and 32 weeks of age (n=8 per group). Wildtype, hemizygous exon 3 floxed and hemizygous Col 2.3-cre male littermates were used as controls. Data were analyzed by one-way ANOVA and Tukey's posthoc test.

RESULTS

microCT analysis of the fifth lumbar vertebral body showed that these mice had reduced trabecular bone volume (p<0.05) at 32 weeks of age compared with controls. This was associated with a decrease in trabecular number (p<0.01) at 12 and 32 weeks of age, suggesting increased bone resorption. These effects were accompanied by a reduction in connectivity density (p<0.01) and an increase in trabecular separation (p<0.01). A similar pattern of trabecular bone loss was observed in the distal femoral metaphysis at 32 weeks of age.

CONCLUSIONS

These findings show that inactivation of the DNA binding-dependent functions of the AR, specifically in mature osteoblasts in male mice, results in increased bone resorption and decreased structural integrity of the bone, leading to a reduction in trabecular bone volume at 32 weeks of age. These data provide evidence of a role for androgens in the maintenance of trabecular bone volume directly through DNA binding-dependent actions of the AR in mature osteoblasts.

Genetic and epigenetic risks of intracytoplasmic sperm injection method

Pregnancies achieved by assisted reproduction technologies, particularly by intracytoplasmic sperm injection (ICSI) procedures, are susceptible to genetic risks inherent to the male population treated with ICSI and additional risks inherent to this innovative procedure. The documented, as well as the theoretical, risks are discussed in the present review study. These risks mainly represent that consequences of the genetic abnormalities underlying male subfertility (or infertility) and might become stimulators for the development of novel approaches and applications in the treatment of infertility. In addition, risks with a polygenic background appearing at birth as congenital anomalies and other theoretical or stochastic risks are discussed. Recent data suggest that assisted reproductive technology might also affect epigenetic characteristics of the male gamete, the female gamete, or might have an impact on early embryogenesis. It might be also associated with an increased risk for genomic imprinting abnormalities.

The androgen receptor mRNA

Androgens (testosterone), acting via the androgen receptor (AR) a nuclear transcription factor, regulate male sexual development and body composition. In addition, AR expression plays an important role in the proliferation of human prostate cancer and confers a better prognosis in breast cancer. AR mRNA stability is central to the regulation of AR expression in prostate and breast cancer cells, and recent studies have demonstrated binding by members of the ELAV/Hu and poly(C) RNA-binding protein families to a highly conserved UC-rich element in the 3'-untranslated region of AR mRNA, with functional impact on AR protein expression. Remarkably, a CAG trinucleotide repeat in exon 1 of the AR, the length of which has been linked to prostate cancer survival, is also a target for multiple RNA-binding proteins from a variety of human and murine tissues. In this review, we will detail the current knowledge of the mechanisms involved in regulating AR mRNA stability, the nature, potential role and structural biology of several novel AR mRNA-protein interactions, and the implications for novel therapeutics in human prostate cancer.

Transgenic mouse models of spinal and bulbar muscular atrophy (SBMA)

Spinal and bulbar muscular atrophy (SBMA) is a late-onset motor neuron disease characterized by proximal muscle atrophy, weakness, contraction fasciculations, and bulbar involvement. Only males develop symptoms, while female carriers usually are asymptomatic. A specific treatment for SBMA has not been established. The molecular basis of SBMA is the expansion of a trinucleotide CAG repeat, which encodes the polyglutamine (polyQ) tract, in the first exon of the androgen receptor (AR) gene. The pathologic hallmark is nuclear inclusions (NIs) containing the mutant and truncated AR with expanded polyQ in the residual motor neurons in the brainstem and spinal cord as well as in some other visceral organs. Several transgenic (Tg) mouse models have been created for studying the pathogenesis of SBMA. The Tg mouse model carrying pure 239 CAGs under human AR promoter and another model carrying truncated AR with expanded CAGs show motor impairment and nuclear NIs in spinal motor neurons. Interestingly, Tg mice carrying full-length human AR with expanded polyQ demonstrate progressive motor impairment and neurogenic pathology as well as sexual difference of phenotypes. These models recapitulate the phenotypic expression observed in SBMA. The ligand-dependent nuclear localization of the mutant AR is found to be involved in the disease mechanism, and hormonal therapy is suggested to be a therapeutic approach applicable to SBMA.

Molecular epidemiology of hypospadias: Review of genetic and environmental risk factors

Hypospadias is one of the most common congenital anomalies in the United States, occurring in approximately 1 in 125 live male births. It is characterized by altered development of the urethra, foreskin, and ventral surface of the penis. In this review, the embryology, epidemiology, risk factors, genetic predisposition, and likely candidate genes for hypospadias are described. Recent reports have identified increases in the birth prevalence of mild and severe forms of hypospadias in the United States from the 1960s to the present. Studies in consanguineous families and small case series have identified allelic variants in genes controlling androgen action and metabolism that cause hypospadias, but the relevance of these findings to the general population is unknown. Concern has also focused on whether exposure to endocrine disrupting chemicals (EDC) with antiandrogenic activity is the cause of this increase. Hypospadias is believed to have a multifactorial etiology in which allelic variants in genes controlling androgen action and metabolism predispose individuals to develop this condition. When genetic susceptibility is combined with exposure to antiandrogenic agents, a threshold is surpassed, resulting in the manifestation of this birth defect. A clear role for exposure to antiandrogenic environmental chemicals has yet to be established in the etiology of hypospadias, although results from laboratory animal models indicate that a number of environmental chemicals could be implicated. Molecular epidemiology studies that simultaneously examine the roles of allelic variants in genes controlling androgen action and metabolism, and environmental exposures are needed to elucidate the risk factors for these anomalies and the causes of the increased rate of hypospadias.

Leuprorelin rescues polyglutamine-dependent phenotypes in a transgenic mouse model of spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is an adult-onset motor neuron disease that affects males. It is caused by the expansion of a polyglutamine (polyQ) tract in androgen receptors. Female carriers are usually asymptomatic. No specific treatment has been established. Our transgenic mouse model carrying a full-length human androgen receptor with expanded polyQ has considerable gender-related motor impairment. This phenotype was abrogated by castration, which prevented nuclear translocation of mutant androgen receptors. We examined the effect of androgen-blockade drugs on our mouse model. Leuprorelin, a lutenizing hormone-releasing hormone (LHRH) agonist that reduces testosterone release from the testis, rescued motor dysfunction and nuclear accumulation of mutant androgen receptors in male transgenic mice. Moreover, leuprorelin treatment reversed the behavioral and histopathological phenotypes that were once caused by transient increases in serum testosterone. Flutamide, an androgen antagonist promoting nuclear translocation of androgen receptors, yielded no therapeutic effect. Leuprorelin thus seems to be a promising candidate for the treatment of SBMA.

Testosterone reduction prevents phenotypic expression in a transgenic mouse model of spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is a polyglutamine disease caused by the expansion of a CAG repeat in the androgen receptor (AR) gene. We generated a transgenic mouse model carrying a full-length AR containing 97 CAGs. Three of the five lines showed progressive muscular atrophy and weakness as well as diffuse nuclear staining and nuclear inclusions consisting of the mutant AR. These phenotypes were markedly pronounced in male transgenic mice, and dramatically rescued by castration. Female transgenic mice showed only a few manifestations that markedly deteriorated with testosterone administration. Nuclear translocation of the mutant AR by testosterone contributed to the phenotypic difference with gender and the effects of hormonal interventions. These results suggest the therapeutic potential of hormonal intervention for SBMA.

Trinucleotide repeats: mechanisms and pathophysiology

Within the closing decade of the twentieth century, 14 neurological disorders were shown to result from the expansion of unstable trinucleotide repeats, establishing this once unique mutational mechanism as the basis of an expanding class of diseases. Trinucleotide repeat diseases can be categorized into two subclasses based on the location of the trinucleotide repeats: diseases involving noncoding repeats (untranslated sequences) and diseases involving repeats within coding sequences (exonic). The large body of knowledge accumulating in this fast moving field has provided exciting clues and inspired many unresolved questions about the pathogenesis of diseases caused by expanded trinucleotide repeats. This review summarizes the current understanding of the molecular pathology of each of these diseases, starting with a clinical picture followed by a focused description of the disease genes, the proteins involved, and the studies that have lent insight into their pathophysiology.

BDNF regulation of androgen receptor expression in axotomized SNB motoneurons of adult male rats

Brain-derived neurotrophic factor (BDNF) prevents the axotomy-induced loss of androgen receptor-like immunoreactivity (AR-LI) in the spinal nucleus of the bulbocavernosus (SNB) motoneurons of adult male rats. In this report, we investigated the dose-response effect of BDNF on androgen receptor expression in axotomized SNB motoneurons, and examined whether delayed application of BDNF to the cut SNB axons can completely reverse the axotomy-induced loss of androgen receptor expression. We also used autoradiography to test whether axotomy decreases the ability of SNB motoneurons to accumulate androgens. SNB motoneurons were axotomized bilaterally and BDNF or PBS was applied to the proximal ends of the axons. The percentage of SNB motoneurons expressing medium or high AR-LI was the major measure of androgen receptor expression. AR-LI was significantly higher on the BDNF-treated side than on the contralateral side treated with phosphate-buffered saline (PBS) for all three doses of BDNF (1.45, 2.9, and 5.8 mg/ml) and was higher than in rats treated bilaterally with PBS. Moreover, AR-LI at the highest dose of BDNF was not different from that in intact SNB motoneurons. Delayed application of BDNF to the axotomized SNB motoneurons restored the AR-LI to the intact level. The AR-LI decreased by axotomy started to increase significantly 4 days after BDNF application and returned to the intact level by 10 days. Furthermore, axotomy significantly decreased the percentage of SNB motoneurons to accumulate tritiated testosterone or its metabolites. In conclusion, our data demonstrate that BDNF completely prevents and reverses the axotomy-induced loss of AR-LI. Moreover, decrease of AR-LI by axotomy reflects the decrease in the ability of SNB motoneurons to accumulate androgens.

Immunolocalization of androgen receptors in testicular cells during postnatal development of the bank vole (Clethrionomys glareolus, S.)

Determination of the cellular distribution of the androgen receptors within the testis is of great importance for an understanding of their essential role in mediating of androgen action in the male gonad. In bank voles, which are seasonally breeding rodents, photoperiod is one of the most important factors inducing profound changes in the morphology and hormonal activity of the testes. Immunolocalization of androgen receptors was found in all somatic cells such as Sertoli cells, Leydig cells, and peritubular-myoid cells, however, distribution of the androgen receptors in various cell types depended on age of animals. Intensity of immunoreactivity was noticed as age and photoperiod-dependent. Males reared under different light regimes showed a significant correlation between the length of light and sexual maturation. Therefore, morphology of the testis from young and adult bank voles was also presented.

Linkage between male infertility and trinucleotide repeat expansion in the androgen-receptor gene

BACKGROUND

Androgens acting via the androgen receptor bring about stimulation and maintenance of spermatogenesis. If mutations in the androgen-receptor gene interfere with the receptor's function, this effect may partly account for impaired spermatogenesis. We aimed to find out whether expansion of a trinucleotide repeat in the androgen-receptor gene is associated with male infertility.

METHODS

We analysed 67 coded semen and blood samples from a predominantly white group of male infertility patients and controls. Clinical analyses included cause of infertility, sperm count, and reproductive hormone concentrations. Analysis of trinucleotide (CAG) repeat length and point mutations in the androgen-receptor gene was done by PCR, single-stranded conformational polymorphism, and DNA sequencing.

FINDINGS

Screening and characterisation of the androgen-receptor gene in 35 patients and 32 controls showed no point mutations in the gene. 30 of the infertile patients had idiopathic azoospermia or oligozoospermia, and these men had significantly longer CAG repeat tracts than controls (mean 23.2 [SE 0.7] vs 20.5 [0.3], p=0.0001). The odds of having CAG repeat lengths of 20 were six-fold higher for fertile men than for men with a spermatogenic disorder.

INTERPRETATION

Our results indicate a relation between CAG repeat length in the androgen-receptor gene and the risk of defective spermatogenesis. With the use of intracytoplasmic sperm injection, this mutation could be inherited, possibly leading to an increase in male infertility in future generations. Should further elongation of the CAG repeat occur in these future generations, there is an added risk of increased severity of male infertility, and potentially an increased incidence of neurodegenerative disease.

Genetic risks of intracytoplasmic sperm injection in the treatment of male infertility: recommendations for genetic counseling and screening

OBJECTIVE

To review the most clinically significant genetic disorders associated with severe oligospermia and azoospermia in males, and to present recommendations for the genetic counseling and screening of infertile males and their partners before undertaking intracytoplasmic sperm injection (ICSI)-assisted reproduction.

DESIGN

The literature on genetic disorders associated with severe oligospermia and azoospermia was reviewed, and the most recent outcome data from surveys of ICSI-derived offspring are presented. Studies related to this topic were identified through MEDLINE.

RESULT(S)

Genetic disorders are not infrequent causes of severe oligospermia and azoospermia in males undergoing ICSI-assisted reproduction. The application of ICSI in the treatment of oligospermic or azoospermic males may result in the transmission or de novo introduction of genetic mutations or chromosomal abnormalities in their offspring. Genetic counseling and appropriate screening of couples with male infertility should be performed before their undertaking ICSI-assisted reproduction.

CONCLUSIONS

An understanding of the genetic risks and possible consequences that are inherent when ICSI is used to assist fertilization in couples with male infertility is necessary for clinicians and their patients.

Mutations of androgen receptor gene in Brazilian patients with male pseudohermaphroditism

We describe the identification of point mutations in the androgen receptor gene in five Brazilian patients with female assignment and behavior. The eight exons of the gene were amplified by the polymerase chain reaction (PCR) and analyzed for single-strand conformation polymorphism (SSCP) to detect the mutations. Direct sequencing of the mutant PCR products demonstrated single transitions in three of these cases: G-->A in case 1, within exon C, changing codon 615 from Arg to His; G-->A in case 2, within exon E, changing codon 752 from Arg to Gln, and C-->T in case 3, within exon B, but without amino acid change.

One additional mutation at exon A amplifies thermolability of androgen receptor in a case with complete androgen insensitivity syndrome

We have previously demonstrated a substitutional mutation (glycine to alanine at position 820) of the androgen receptor (AR) gene in a patient with complete androgen insensitivity syndrome (CAIS). We first examined whether the mutation could lead to a disorder in AR binding activity in in vitro expression experiments. In a luciferase assay, the effect of the mutant AR on a target's gene was definitely impaired. However, the mutant AR had less thermal instability compared to that of the patient's fibroblast cell lines established in a whole-cell binding assay. In order to analyze the cause of the thermal instability, a further analysis of exon A in the AR gene was performed because the previous study had been performed only between exon B and H encoding the DNA-binding domain and the hormone-binding domain. The second mutation (leucine to proline at position 257) was newly identified. In in vitro expression experiments, the AR with both mutations showed marked thermal instability, whereas the AR with a mutation in exon A had no effect on thermal stability. The results show that the N-terminal domain might also play an important role in amplifying or modifying the AR binding activity.

Androgen insensitivity syndrome in the era of molecular genetics and the Internet: a point of view

The era of molecular genetics has seen the discovery of a great deal of scientific information about the androgen receptor (AR) and about the many AR mutations that have been identified in patients with Androgen Insensitivity Syndrome (AIS). In families with well-characterised mutations, carriers can now be identified and prenatal testing can be offered. An unexpected finding is that an AR mutation also causes X-linked spinobulbar muscular atrophy. The intersex community has established two influential support groups, the AIS Support Group (which has branches in the UK, North America and Australia) and the Intersex Society of North America (ISNA). It is ironic that at a time when advances in biomedical science regarding AIS are a source of pride, these support groups are accusing the medical profession of having ignored the real needs of patients with AIS. Since the support groups are willing to assist the medical profession to develop better approaches to the management of intersex disorders, a collaborative approach is likely to be mutually beneficial for patients and physicians. ISNA has alienated many doctors by advocating a radical approach, namely that surgery should not be performed to 'correct' ambiguous genitalia until the individual is old enough to express a gender preference. Many children born in developing countries have either no genital surgery to correct ambiguity, or surgery is carried out very late. Long term outcome studies, carried out in developing countries and sensitive to the cultural background, would provide information on how non-Western societies can accept genital abnormalities that would be considered unacceptable in the West.

Nuclear receptors: structure, function and involvement in disease

Nuclear hormone receptors are acting as transcription factors in the cell nucleus. They regulate gene expression of hormonal regulated target genes. The role of hormone in the transcriptional process is to modulate and change the nuclear receptor functionality. Receptors contain a DNA binding domain that enables them to bind to hormone response elements of target genes. Nuclear hormone receptors bind to lipophilic hormones produced by the organisms' endocrine system, which links the secretion of hormones directly to regulation of gene expression of responsive tissues. In recent years increasing numbers of naturally occurring mutations of a variety of nuclear hormone receptor genes were identified in patients showing abnormalities in hormonal response. Here, we present an overview of nuclear receptors and their mutant forms which cause human syndromes or are associated with cancer progression. The major scope of this article is to give an overview on the structural-functional relationship and based on that, to understand the effects of naturally occurring receptor mutants on the molecular level. Thereby, functional aberrations of naturally occurring receptors for androgen, glucocorticoids, mineralocorticoid, estrogen, vitamin D3, retinoic acid, and thyroid hormone as well as the orphan receptor DAX1 are discussed.