Androgen-induced up-regulation of tubulin isoforms in neuroblastoma cells

Sex Differences in Taxane Toxicities

Simple Summary

Clinically observed sex differences in acute and long-term taxane chemotherapy-induced normal tissue toxicity are routinely documented but remain poorly understood despite the significant impact such toxicities have on treatment tolerance and quality of life outcomes in cancer survivors. This review draws from pre-clinical and clinical literature to highlight sex-specific mechanisms of action in taxane drug toxicity and proposes hypotheses for sex-specific clinical discrepancies in taxane-induced acute and long-term toxicities. To our knowledge, this is the first review exploring how sex as a biological variable impacts taxane-mediated mechanisms of action and clinical outcomes. In doing so, we have provided a novel framework to investigate and understand common sex differences observed in clinical and pre-clinical research.

Abstract

The taxane family of microtubule poisons and chemotherapeutics have been studied for over 50 years and are among the most frequently used antineoplastic agents today. Still, limited research exists characterizing taxane-induced sex-specific mechanisms of action and toxicities in cancer and non-cancerous tissue. Such research is important to advance cancer treatment outcomes as well as to address clinically observed sex-differences in short- and long-term taxane-induced toxicities that have disproportionate effects on female and male cancer patients. To gain more insight into these underlying differences between the sexes, the following review draws from pre-clinical and clinical paclitaxel and taxane oncology literature, examines sex-discrepancies, and highlights uncharacterized sex-dependent mechanisms of action and clinical outcomes. To our knowledge, this is the first literature review to provide a current overview of the basic and clinical sex dimorphisms of taxane-induced effects. Most importantly, we hope to provide a starting point for improving and advancing sex-specific personalized chemotherapy and cancer treatment strategies as well as to present a novel approach to review sex as a biological variable in basic and clinical biology.

βIII-Tubulin Gene Regulation in Health and Disease

Microtubule proteins form a dynamic component of the cytoskeleton, and play key roles in cellular processes, such as vesicular transport, cell motility and mitosis. Expression of microtubule proteins are often dysregulated in cancer. In particular, the microtubule protein βIII-tubulin, encoded by the TUBB3 gene, is aberrantly expressed in a range of epithelial tumours and is associated with drug resistance and aggressive disease. In normal cells, TUBB3 expression is tightly restricted, and is found almost exclusively in neuronal and testicular tissues. Understanding the mechanisms that control TUBB3 expression, both in cancer, mature and developing tissues will help to unravel the basic biology of the protein, its role in cancer, and may ultimately lead to the development of new therapeutic approaches to target this protein. This review is devoted to the transcriptional and posttranscriptional regulation of TUBB3 in normal and cancerous tissue.

Structurally different anabolic androgenic steroids reduce neurite outgrowth and neuronal viability in primary rat cortical cell cultures

The illicit use of anabolic androgenic steroids (AAS) among adolescents and young adults is a major concern due to the unknown and unpredictable impact of AAS on the developing brain and the consequences of this on mental health, cognitive function and behaviour. The present study aimed to investigate the effects of supra-physiological doses of four structurally different AAS (testosterone, nandrolone, stanozolol and trenbolone) on neurite development and cell viability using an in vitro model of immature primary rat cortical cell cultures. A high-throughput screening image-based approach, measuring the neurite length and number of neurons, was used for the analysis of neurite outgrowth. In addition, cell viability and expression of the Tubb3 gene (encoding the protein beta-III tubulin) were investigated. Testosterone, nandrolone, and trenbolone elicited adverse effects on neurite outgrowth as deduced from an observed reduced neurite length per neuron. Trenbolone was the only AAS that reduced the cell viability as indicated by a decreased number of neurons and declined mitochondrial function. Moreover, trenbolone downregulated the Tubb3 mRNA expression. The adverse impact on neurite development was neither inhibited nor supressed by the selective androgen receptor (AR) antagonist, flutamide, suggesting that the observed effects result from another mechanism or mechanisms of action that are operating apart from AR activation. The results demonstrate a possible AAS-induced detrimental effect on neuronal development and regenerative functions. An impact on these events, that are essential mechanisms for maintaining normal brain function, could possibly contribute to behavioural alterations seen in AAS users.

Sex Differences in Biological Processes and Nitrergic Signaling in Mouse Brain

Nitric oxide (NO) represents an important signaling molecule which modulates the functions of different organs, including the brain. S-nitrosylation (SNO), a post-translational modification that involves the binding of the NO group to a cysteine residue, is a key mechanism of nitrergic signaling. Most of the experimental studies are carried out on male animals. However, significant differences exist between males and females in the signaling mechanisms. To investigate the sex differences in the SNO-based regulation of biological functions and signaling pathways in the cortices of 6–8-weeks-old mice, we used the mass spectrometry technique, to identify S-nitrosylated proteins, followed by large-scale computational biology. This work revealed significant sex differences in the NO and SNO-related biological functions in the cortices of mice for the first-time. The study showed significant SNO-induced enrichment of the synaptic processes in female mice, but enhanced SNO-related cytoskeletal processes in the male mice. Proteins, which were S-nitrosylated in the cortices of mice of both groups, were more abundant in the female brain. Finally, we investigated the shared molecular processes that were found in both sexes. This study presents a mechanistic insight into the role of S-nitrosylation in both sexes and provides strong evidence of sex difference in many biological processes and signalling pathways, which will open future research directions on sex differences in neurological disorders.

Androgen Receptor Regulates the Growth of Neuroblastoma Cells in vitro and in vivo

Background: Neuroblastoma is the most common extracranial tumors in children. At present about the true etiology of neuroblastoma is unclear and many studies have tried to find effective treatments for these primary malignant tumors. Although it has been illustrated that androgen receptor (AR) was expressed in neuroblastoma cells in some former reports, the biological role of androgen receptor in the development of neuroblastoma is not fully understood.

Methods: Androgen (R1881) and the antagonists of androgen receptor (MDV3100 and ARN509) were used to study the role of the androgen receptor signaling pathway in vitro and in vivo on SH-SY5Y and Neuro-2a (N2a) cell lines.

Results: We found that AR expression showed an R1881 dose-dependent manner in neuroblastoma cells in vitro and R1881was able to increase, while both antagonists of androgen receptor (MDV3100 and ARN509) significantly decrease, the proliferation, migration, invasion and sphere formation of SH-SY5Y and N2a cells. Moreover, androgen promoted the growth of N2a tumor in vivo. However, when androgen receptor (AR) was effectively knocked down in the two cell lines by siRNA, either promoting or inhibiting effect of the androgen or androgen receptor antagonists, respectively, was attenuated.

Conclusion: Our results suggested that androgen receptor may involve in the progression of neuroblastoma as well as provided insight into a new target for the diagnosis and treatment of neuroblastoma patients.

Improved Mitochondrial and Methylglyoxal-Related Metabolisms Support Hyperproliferation Induced by 50 Hz Magnetic Field in Neuroblastoma Cells

Extremely low frequency magnetic fields (ELF-MF) are common environmental agents that are suspected to promote later stages of tumorigenesis, especially in brain-derived malignancies. Even though ELF magnetic fields have been previously linked to increased proliferation in neuroblastoma cells, no previous work has studied whether ELF-MF exposure may change key biomolecular features, such as anti-glycative defence and energy re-programming, both of which are currently considered as crucial factors involved in the phenotype and progression of many malignancies. Our study investigated whether the hyperproliferation that is induced in SH-SY5Y human neuroblastoma cells by a 50 Hz, 1 mT ELF magnetic field is supported by an improved defense towards methylglyoxal (MG), which is an endogenous cancer-static and glycating α-oxoaldehyde, and by rewiring of energy metabolism. Our findings show that not only the ELF magnetic field interfered with the biology of neuron-derived malignant cells, by de-differentiating further the cellular phenotype and by increasing the proliferative activity, but also triggered cytoprotective mechanisms through the enhancement of the defense against MG, along with a more efficient management of metabolic energy, presumably to support the rapid cell outgrowth. Intriguingly, we also revealed that the MF-induced bioeffects took place after an initial imbalance of the cellular homeostasis, which most likely created a transient unstable milieu. The biochemical pathways and molecular targets revealed in this research could be exploited for future approaches aimed at limiting or suppressing the deleterious effects of ELF magnetic fields. J. Cell. Physiol. 231: 2014-2025, 2016. © 2016 Wiley Periodicals, Inc.

Puberty and testosterone shape the corticospinal tract during male adolescence

Some of the known sex differences in white matter emerge during adolescence. Here, we replicate and extend our previous findings of sex differences in the structure of the corticospinal tract (Perrin et al. 2009; Hervé et al. 2009). In a large normative sample of adolescents, we observed age × sex interactions in the signal intensity of T1-weighted (T1W) images (n = 941) and in magnetization transfer ratio (MTR; n = 761); both features were inversely associated with age in males but not in females. Moreover, we hypothesized that the age-related differences in CST structure exhibited by males would be mediated by differences in puberty stage and levels of bioavailable testosterone. We confirmed this prediction using mediation analysis with bootstrapping. These findings suggest that sex differences in the CST structure observed during male adolescence may be due to multiple processes associated with puberty, including (but not limited to) the rising levels of testosterone.

Interaction between docetaxel resistance and castration resistance in prostate cancer: implications of Twist1, YB-1, and androgen receptor

BACKGROUND

Taxanes, including docetaxel, are currently the only cytotoxic chemotherapeutic agents proven to confer survival benefit in patients with castration-resistant prostate cancer (CRPC). However, the merits of taxanes remain modest, and efforts are needed to improve their therapeutic efficacy.

METHODS

We evaluated the sensitivity of prostate cancer cells to various agents using cytotoxicity assays. Gene and protein expression levels were evaluated by quantitative real-time polymerase chain reaction and Western blotting analysis, respectively.

RESULTS

Hydrogen peroxide-resistant and castration-resistant cells that overexpressed Twist1 and Y-box binding protein-1 (YB-1) were cross-resistant to cytotoxic agents, including docetaxel. Twist1 regulated YB-1 expression in prostate cancer cells, supported by the induction of Twist1 and YB-1 by transforming-growth factor-β, which is critical for taxane resistance. Twist1 and/or YB-1 were activated in docetaxel-resistant prostate cancer cells, and YB-1 was activated by docetaxel treatment. Conversely, Twist1 and YB-1 knockdown sensitized prostate cancer cells to cytotoxic agents, including docetaxel. In addition, androgen receptor (AR) knockdown increased cellular sensitivity to docetaxel, though AR expression in docetaxel-resistant LNCaP cells was paradoxically lower than in parental cells. Intriguingly, androgen deprivation treatment was more effective in docetaxel-resistant LNCaP cells compared with parental cells.

CONCLUSIONS

Twist1/YB-1 and AR signaling promote docetaxel resistance in CRPC cells. However, docetaxel-resistant cells were collaterally sensitive to androgen deprivation because of down-regulation of AR expression, suggesting that the therapeutic effect of initial taxane treatment in hormone-naïve prostate cancer may be superior to that of salvage taxane treatment in CRPC.

Estradiol and testosterone regulate arginine-vasopressin expression in SH-SY5Y human female neuroblastoma cells through estrogen receptors-α and -β

The expression of arginine-vasopressin (AVP) is regulated by estradiol and testosterone (T) in different neuronal populations by mechanisms that are not yet fully understood. Estrogen receptors (ERs) have been shown to participate in the regulation of AVP neurons by estradiol. In addition, there is evidence of the participation of ERβ in the regulation of AVP expression exerted by T via its metabolite 5α-dihydrotestosterone (5α-DHT) and its further conversion in the androgen metabolite and ERβ ligand 3β-diol. In this study we have explored the role of ERs in the regulation exerted by estradiol and T on AVP expression, using the human neuroblastoma cell line SH-SY5Y. Estradiol treatment increased AVP mRNA levels in SH-SY5Y cells in comparison with cells treated with vehicle. The stimulatory effect of estradiol on AVP expression was imitated by the ERα agonist 4,4',4',-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol and blocked by the ER antagonist, ICI 182,780, and the ERα antagonist 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1hpyrazoledihydrochloride. In contrast, the ERβ agonist 2,3-bis(4-hydroxyphenyl)-propionitrile reduced AVP expression, whereas the ERβ antagonist 4-[2-phenyl-5,7-bis(trifluoromethyl) pyrazolo[1,5-a]pyrimidin-3-yl]phenol enhanced the action of estradiol on AVP expression. T increased AVP expression in SH-SY5Y cells by a mechanism that was dependent on aromatase but not on 5α-reductase activity. The T effect was not affected by blocking the androgen receptor, was not imitated by the T metabolite 5α-DHT, and was blocked by the ERα antagonist 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinylethoxy)phenol]-1hpyrazoledihydrochloride. In contrast, 5α-DHT had a similar effect as the ERβ agonists 2,3-bis(4-hydroxyphenyl)-propionitrile and 3β-diol, reducing AVP expression. These findings suggest that estradiol and T regulate AVP expression in SH-SY5Y cells through ERs, exerting a stimulatory action via ERα and an inhibitory action via ERβ.

Pro-survival and anti-apoptotic properties of androgen receptor signaling by oxidative stress promote treatment resistance in prostate cancer

Oxidative stress caused by an increase in reactive oxygen species levels or a decrease in cellular antioxidant capacity can evoke the modulation of various cellular events including androgen receptor (AR) signaling via direct or indirect interactions. In this review, we summarize the mechanisms of AR activation by oxidative stress including: i) AR overexpression; ii) AR activation by AR co-regulators or intracellular signal transduction pathways; iii) generation of AR mutations or splice variants; and iv) de novo androgen synthesis. AR signaling augmented by oxidative stress appears to contribute to pro-survival and anti-apoptotic effects in prostate cancer cells in response to androgen deprivation therapy. In addition, AR signaling suppresses anti-survival and pro-apoptotic effects in prostate cancer cells in response to various cytotoxic and tumor-suppressive interventions including taxanes and radiation through the modulation of βIII-tubulin and ataxia telangiectasia-mutated kinase expression respectively. Taken together, AR signaling appears to render prostate cancer cells refractory to various therapeutic interventions including castration, taxanes, and radiation, indicating that AR signaling is a comprehensive resistant factor and crucial target for prostate cancer treatment.

Disruption of nongenomic testosterone signaling in a model of spinal and bulbar muscular atrophy

As one of the nine hereditary neurodegenerative polyQ disorders, spinal and bulbar muscular atrophy (SBMA) results from a polyQ tract expansion in androgen receptor (AR). Although protein aggregates are the pathological hallmark of many neurodegenerative diseases, their direct role in the neurodegeneration is more and more questioned. To determine the early molecular mechanisms causing motor neuron degeneration in SBMA, we established an in vitro system based on the tetracycline-inducible expression of normal (AR20Q), the mutated, 51 glutamine-extended (AR51Q), or polyQ-deleted (AR0Q) AR in NSC34, a motor neuron-like cell line lacking endogenous AR. Although no intracellular aggregates were formed, the expression of the AR51Q leads to a loss of function characterized by reduced neurite outgrowth and to a toxic gain of function resulting in decreased cell viability. In this study, we show that both AR20Q and AR51Q are recruited to lipid rafts in response to testosterone stimulation. However, whereas testosterone induces the activation of the c-jun N-terminal kinase/c-jun pathway via membrane-associated AR20Q, it does not so in NSC34 expressing AR51Q. Phosphorylation of c-jun N-terminal kinase plays a crucial role in AR20Q-dependent survival and differentiation of NSC34. Moreover, c-jun protein levels decrease more slowly in AR20Q- than in AR51Q-expressing NSC34 cells. This is due to a rapid and transient inhibition of glycogen synthase kinase 3α occurring in a phosphatidylinositol 3-kinase-independent manner. Our results demonstrate that the deregulation of nongenomic AR signaling may be involved in SBMA establishment, opening new therapeutic perspectives.

Expression of Tubb3, a beta-tubulin isotype, is regulated by androgens in mouse and rat Sertoli cells

Our previous analysis of Sertoli cell androgen receptor (AR) knockout (SCARKO) mice revealed that several cytoskeletal components are a potential target of androgen action. Here, we found that one of these components, the beta-tubulin isotype Tubb3, is differentially regulated in testes from SCARKO mice (relative to littermate controls) from Postnatal Day 10 to adulthood. The Tubb3 gene is unique in this respect, as at Day 10, no other beta-tubulin genes are significantly regulated by AR. We further characterized androgen regulation of Tubb3 in vivo and in vitro and demonstrated that it is a conserved feature in both mice and rats. To investigate whether androgens directly regulate Tubb3 expression, we screened for androgen response elements (AREs) in the Tubb3 gene. In silico analysis revealed the presence of four ARE motifs in Tubb3 intron 1, two of which bind to AR in vitro. Mutation of one of these (ARE1) strongly reduced androgen-dependent reporter gene expression. These results, coupled with the finding that the AR binds to the Tubb3 ARE region in vivo, suggest that Tubb3 is a direct target of AR. Our data strengthen the contention that androgens exert their effects on spermatogenesis, in part, through modulation of the Sertoli cell cytoskeleton. Androgen regulation of beta-tubulin has also been described in neurons, fortifying the already known similarity in microtubule organization in Sertoli cell processes and neurons, the only other cell type in which Tubb3 is known to be expressed.

Handedness, motor skills and maturation of the corticospinal tract in the adolescent brain

With anatomical magnetic resonance imaging, the signal intensity of the corticospinal tract (CST) at the level of the internal capsule is often paradoxically similar to that of grey matter. As shown previously in histological studies, this is likely due to the presence of very large axons. We measured the apparent grey-matter density (aGMd) of the putative CST (pCST) in a large cohort of adolescents (n = 409, aged 12-18 years). We tested the following hypotheses: (1) The aGMd in the pCST shows a hemispheric asymmetry that is, in turn, related to hand preference; (2) the maturation of the CST during adolescence differs between both sexes, due to the influence of testosterone; (3) variations in aGMd in the pCST reflect inter-individual differences in manual skills. We confirmed the first two predictions. Thus, we found a strong left > right hemispheric asymmetry in aGMd that was, on average, less marked in the 40 left-handed subjects. Apparent GMd in the pCST increased with age in adolescent males but not females, and this was particularly related to rising plasma levels of testosterone in male adolescents. This finding is compatible with the idea that testosterone influences axonal calibre rather than myelination. The third prediction, namely that of a relationship between age-related changes in manual skills and maturation of the pCST, was not confirmed. We conclude that the leftward asymmetry of the pCST may reflect an early established asymmetry in the number of large corticomotoneuronal fibres in the pCST.

Growth of white matter in the adolescent brain: myelin or axon?

White matter occupies almost half of the human brain. It contains axons connecting spatially segregated modules and, as such, it is essential for the smooth flow of information in functional networks. Structural maturation of white matter continues during adolescence, as reflected in age-related changes in its volume, as well as in its microstructure. Here I review recent observations obtained with magnetic resonance imaging in typically developing adolescents and point out some of the known variations in structural properties of white matter vis-à-vis brain function in health and disease. I conclude by re-focusing the interpretations of MR-based studies of white matter from myelin to axon.

Could Sex Differences in White Matter be Explained by g ratio?

Recent studies with magnetic resonance imaging suggest that age-related changes in white matter during male adolescence may indicate an increase in g ratio wherein the radial growth of an axon outpaces a corresponding increase in myelin thickness. We review the original Rushton (1951) model where a g ratio of approximately 0.6 represents an optimal relationship between the axon and fibre diameters vis-à-vis conduction velocity, and point out evidence indicating slightly higher g ratio in large-diameter fibres. We estimate that fibres with a diameter larger than 9.6 mum will have a relatively thinner myelin sheath, and brains with increasingly larger proportions of such large-diameter fibres will have progressively lower concentration of myelin. We conclude by pointing out possible implications of "suboptimal" g ratio for the emergence of "disconnection" disorders, such as schizophrenia, in late adolescence.

Early effects of Sertoli cell-selective androgen receptor ablation on testicular gene expression

Evidence from several models of hormone depletion and/or replacement and from knockout animals points to a key role of androgens in the control of spermatogenesis. In testes of mice with a Sertoli cell-selective ablation of the androgen receptor (SCARKO), transcriptional profiling, using microarray technology, revealed that, already on postnatal day 10,692 genes are differentially expressed compared with testes of control mice. Further evaluation of a subset of these genes by quantitative RT-PCR suggested that differences in expression may already be evident on day 8 or earlier. As the androgen receptor in mouse Sertoli cells becomes immunologically detectable around day 5, we tried to identify the earliest responses to androgens by a new transcriptional profiling study on testes from 6-day-old SCARKO and control mice. No obvious and novel early androgen response genes, potentially acting as mediators of subsequent indirect androgen actions, could be identified. However, several genes differentially expressed on day 10 already displayed a response to androgen receptor ablation on day 6. Quantitative RT-PCR studies for 12 of these genes on 10 paired SCARKO and control testes from 4-, 6-, 8-, 10-, 20- and 50-day-old mice revealed significant differences in expression level from day 4 onwards for three genes (Eppin, PCI, Cldn11) and from day 6 onwards for one more gene (Rhox5). For at least two of these genes (Rhox5 and Eppin), there is evidence for direct regulation via the androgen receptor. For three additional genes (Gpd1, Tubb3 and Tpd52l1) significantly lower expression in the SCARKO was noted from day 8 onwards. For all the studied genes, an impressive increase in transcript levels was observed between day 4-50 and differential expression was maintained in adulthood. It is concluded that the SCARKO model indicates incipient androgen action in mouse Sertoli cells from day 4 onwards.

Differential effects of steroids on the synthesis of polyunsaturated fatty acids by human neuroblastoma cells

Polyunsaturated fatty acids (PUFA) are crucial for proper functioning of cell membranes, particularly in brain. Biologically important PUFA include docosahexaenoic acid (n-3 series) and arachidonic acid (n-6 series) which can be formed from their respective dietary essential precursors, alpha-linolenic acid (ALA) and linoleic acid (LA). Steroid hormones are thought to modulate PUFA synthesis in humans but whether they regulate PUFA status in brain and/or in neural membranes is unknown. In human neuroblastoma SH-SY5Y cells, we compared the effect of estradiol, testosterone, and progesterone on PUFA synthesis. Cells were incubated with ALA and/or LA 7 microM in combination with estradiol, testosterone, or progesterone at 10 nM without serum. The fatty acid composition was determined by gas chromatography and the mRNA expression of genes involved in PUFA metabolism by real-time RT-PCR. Estradiol affected both the n-3 and the n-6 PUFA conversion, the n-3 PUFA pathway being more sensitive to the estradiol treatment. In ALA-supplemented cells, estradiol increased while testosterone decreased the long-chain n-3 PUFA content (+17% and -15%, respectively) and the mRNA expression of the Delta5-desaturase (+11% and -9%), these two events being strongly correlated. Progesterone did not affect the PUFA composition. The positive effect of estradiol was blocked by the estrogen receptor antagonist ICI-182,780. We conclude that steroids have differential effects on PUFA synthesis and that their mode of action could involve the modulation of the Delta5-desaturase mRNA expression in neuroblastoma cells. These results help our understanding of the regulation of brain PUFA metabolism by steroid hormones.

Sex differences in the growth of white matter during adolescence

The purpose of this study was to examine sex differences in the maturation of white matter during adolescence (12 to 18 years of age). We measured lobular volumes of white matter and white-matter "density" throughout the brain using T1-weighted images, and estimated the myelination index using magnetisation-transfer ratio (MTR). In male adolescents, we observed age-related increases in white-matter lobular volumes accompanied by decreases in the lobular values of white-matter MTR. White-matter density in the putative cortico-spinal tract (pCST) decreased with age. In female adolescents, on the other hand, we found only small age-related increase in white-matter volumes and no age-related changes in white-matter MTR, with the exception of the frontal lobe where MTR increased. White-matter density in the pCST also increased with age. These results suggest that sex-specific mechanisms may underlie the growth of white matter during adolescence. We speculate that these mechanisms involve primarily age-related increases in axonal calibre in males and increased myelination in females.

Growth of white matter in the adolescent brain: role of testosterone and androgen receptor

The growth of white matter during human adolescence shows a striking sexual dimorphism; the volume of white matter increases with age slightly in girls and steeply in boys. Here, we provide evidence supporting the role of androgen receptor (AR) in mediating the effect of testosterone on white matter. In a large sample of typically developing adolescents (n = 408, 204 males), we used magnetic resonance imaging and acquired T1-weighted and magnetization transfer ratio (MTR) images. We also measured plasma levels of testosterone and genotyped a functional polymorphism in the AR gene, namely the number of CAG repeats in exon 1 believed to be inversely proportional to the AR transcriptional activity. We found that the testosterone-related increase of white-matter volume was stronger in male adolescents with the lower versus higher number of CAG repeats in the AR gene, with testosterone explaining, respectively, 26 and 8% of variance in the volume. The MTR results suggest that this growth is not related to myelination; the MTR decreased with age in male adolescents. We speculate that testosterone affects axonal caliber rather than the thickness of the myelin sheath.

Androgen regulation of axon growth and neurite extension in motoneurons

Androgens act on the CNS to affect motor function through interaction with a widespread distribution of intracellular androgen receptors (AR). This review highlights our work on androgens and process outgrowth in motoneurons, both in vitro and in vivo. The actions of androgens on motoneurons involve the generation of novel neuronal interactions that are mediated by the induction of androgen-dependent neurite or axonal outgrowth. Here, we summarize the experimental evidence for the androgenic regulation of the extension and regeneration of motoneuron neurites in vitro using cultured immortalized motoneurons, and axons in vivo using the hamster facial nerve crush paradigm. We place particular emphasis on the relevance of these effects to SBMA and peripheral nerve injuries.

All-trans-retinoic acid inhibits collapsin response mediator protein-2 transcriptional activity during SH-SY5Y neuroblastoma cell differentiation

Neurons are highly polarized cells composed of two structurally and functionally distinct parts, the axon and the dendrite. The establishment of this asymmetric structure is a tightly regulated process. In fact, alterations in the proteins involved in the configuration of the microtubule lattice are frequent in neuro-oncologic diseases. One of these cytoplasmic mediators is the protein known as collapsin response mediator protein-2, which interacts with and promotes tubulin polymerization. In this study, we investigated collapsin response mediator protein-2 transcriptional regulation during all-trans-retinoic acid-induced differentiation of SH-SY5Y neuroblastoma cells. All-trans-retinoic acid is considered to be a potential preventive and therapeutic agent, and has been extensively used to differentiate neuroblastoma cells in vitro. Therefore, we first demonstrated that collapsin response mediator protein-2 mRNA levels are downregulated during the differentiation process. After completion of deletion construct analysis and mutagenesis and mobility shift assays, we concluded that collapsin response mediator protein-2 basal promoter activity is regulated by the transcription factors AP-2 and Pax-3, whereas E2F, Sp1 and NeuroD1 seem not to participate in its regulation. Furthermore, we finally established that reduced expression of collapsin response mediator protein-2 after all-trans-retinoic acid exposure is associated with impaired Pax-3 and AP-2 binding to their consensus sequences in the collapsin response mediator protein-2 promoter. Decreased attachment of AP-2 is a consequence of its accumulation in the cytoplasm. On the other hand, Pax-3 shows lower binding due to all-trans-retinoic acid-mediated transcriptional repression. Unraveling the molecular mechanisms behind the action of all-trans-retinoic acid on neuroblastoma cells may well offer new perspectives for its clinical application.

2-D DIGE as a quantitative tool for investigating the HUPO Brain Proteome Project mouse series

Brain development and aging is a complex process involving proliferation, differentiation and apoptosis. Elucidating proteome changes in these processes can help to understand the mechanisms of brain development and maintenance as well as neurodegenerative diseases. The research reported here is a contribution to the HUPO Brain Proteome Project mouse pilot study. Whole, frozen C57BL/6J mouse brain comprising three different developmental stages (embryonic day 16, postnatal day 7, and postnatal days 54-58) were processed by using 2-D DIGE. A total of 1999 spots were matched between all gels. Of these, 206 spots were differentially expressed between the different stages: 122 spots were highest in intensity in embryonic stage E16, 26 highest in the juvenile group P7 and 58 spots highest in P56, the adult stage. The results show a pattern of temporal expression. Based on the expression patterns we tentatively suggest that proteins involved in the establishment of primary structures in the brain are expressed highest in the embryonic mouse. Proteins involved in the development of the brain are expressed highest in the juvenile phase and proteins that make utilization of the brain possible by delivering energy are expressed highest in the adult mice.

Application of differential display in the identification of androgen-regulated genes

Identification of androgen-regulated genes in neurons is an important step in understanding the mechanisms involved in androgen action. The aim of the current study was to identify androgen-responsive genes in the neural cells using the technique of differential display reverse transcription polymerase chain reaction (DDRT-PCR) on the human neuroblastoma cell line, SK-N-MC. Using this analysis, 18 putatively androgen-regulated cDNA species were identified, ranging in size from 280 to 800 bp. Of these, 14 were found to be negatively regulated and 4 positively regulated by androgens. Only 12 were successfully re-amplified, and of these, 8 were found to contain multiple species of cDNA fragments. When Northern analysis was conducted using the 21 different cDNA fragments as probes, only one was found to confirm the androgen regulation demonstrated via DDRT-PCR. While this putatively regulated gene remains to be fully characterized, future studies of may provide insights into the molecular mechanisms governing androgen action in neural cells.

Gene expression changes following androgen receptor elimination in LNCaP prostate cancer cells

We have shown recently that inhibition of androgen receptor (AR) expression with an antisense AR oligonucleotide (ODN) inhibits LNCaP prostate tumor cells in vitro as well as in vivo. In this study, we investigated gene expression changes that occur after AR signaling blockade, either through AR elimination by antisense treatment or through complete androgen receptor inhibition by androgen deprivation combined with the antiandrogen bicalutamide, in order to search for genes that are directly or indirectly regulated through the AR. Gene expression changes were investigated with cDNA NIH 10K gene microarrays in response to treatment over 48 h. Expression of selected genes was further analyzed by real-time reverse transcriptase (RT)-polymerase chain reaction (PCR), Western blotting, and radioimmunoassay. A comparison of antisense-treated and androgen-deprived cells revealed several concordances such as significant downregulation of prostate-specific genes, cell-cycle regulatory genes, genes of the cholesterol biosynthesis pathway, and several cytoskeletal genes. However, there were also several genes that were differentially regulated. Among the genes that were exclusively changed by treatment with the antisense AR ODN were the insulin-like growth factor binding protein 2 (IGFBP2) and the phosphatidylinositol-4-phosphate 5-kinase type I alpha (PIP5KIA). On the other hand, complete androgen receptor blockade induced changes in the expression of the prostate overexpressed gene 1 and the S100 calcium binding protein P. In summary, we identified a cohort of interesting genes whose expression was highly affected by elimination of the AR in LNCaP prostate cancer cells. Further investigations are warranted to clarify their role in the AR signaling pathway and their susceptibility as a target for the treatment of prostate cancer.

Trinucleotide repeat disease. The androgen receptor in spinal and bulbar muscular atrophy

It has been more than 10 years since the discovery that the expansion of a simple CAG trinucleotide repeat within the coding region of the androgen receptor gene leads to the motor neuronopathy spinal and bulbar muscular atrophy (SBMA). A flurry of investigation into this and the other, more recently discovered, polyglutamine diseases has led to an understanding of many aspects of the molecular pathogenesis of this family of diseases. A characteristics pathological feature of the polyglutamine diseases is the occurrence in affected neurons of ubiquitinated aggregates; such aggregates also contain, among others, proteins involved in the folding and degradation of the mutant proteins. Aggregates themselves are likely not directly cytotoxic, but rather mark the accumulation of all or part of the mutant protein. Furthermore, aggregation occurs because of the inefficient clearance of the mutant protein by the ubiquitin-proteasome pathway for protein degradation. These findings are common to the polyglutamine diseases and reflect the general problem of folding/degrading expanded polyglutamines. In SBMA, the altered metabolism of the androgen receptor is ligand dependent. How the accumulation of the mutant protein causes neuronal dysfunction and disease is not well understood, but several cellular processes have been implicated. Although these findings provide insight into the toxic function of the expanded polyglutamine protein, additional investigations have led to the finding that intrinsic AR transactivational function is somewhat diminished in the presence of the expanded polyglutamine; this likely leads to the partial androgen insensitivity that characterizes patients with SBMA. The recent development of useful animal and cell models of SBMA will lead to increased understanding of disease pathogenesis, as well as to the development of new and better therapeutic strategies.

Kennedy's disease: a triplet repeat disorder or a motor neuron disease?

Two definite genetic causes of adult motor neuron degeneration have been identified to date: CAG repeat expansion in the androgen receptor gene in Kennedy's disease and point mutations in the SOD1 gene, encoding the enzyme, Cu/Zn superoxide dismutase, in some familial forms of amyotrophic lateral sclerosis. Although both have unrelated genetic causes, Kennedy's disease and SOD1-linked amyotrophic lateral sclerosis share several pathogenic features. First, expanded androgen receptor and mutant Cu/Zn superoxide dismutase have a propensity to aggregate into insoluble complexes and form inclusion bodies in affected neurons. Deposits of mutant proteins could be detrimental to neuronal viability by interfering with the normal housekeeping functions of chaperones and of the ubiquitin/proteasome system. Secondly, cytoskeletal function may be impaired in both diseases as decreased transactivational activity of expanded androgen receptor may cause an abnormal pattern of tubulin expression in motor neurons in Kennedy's disease and disruption of neurofilament organisation is a hallmark of amyotrophic lateral sclerosis. The concept of activation of overlapping cell death cascades by two distinct genetic defects could help elucidating downstream pathogenic processes and may provide novel targets for pharmacological intervention or gene therapy for the treatment of motor neuron disorders.