Androgen Receptor Aggregation Research Articles

Mutant androgen receptor induces neurite loss and senescence independently of ARE binding in a neuronal model of SBMA

Spinal and bulbar muscular atrophy (SBMA) is a slowly progressing neuromuscular disease caused by a polyglutamine (polyQ)-encoding CAG trinucleotide repeat expansion in the androgen receptor (AR) gene, leading to AR aggregation, lower motor neuron death, and muscle atrophy. AR is a ligand-activated transcription factor that regulates neuronal architecture and promotes axon regeneration; however, whether AR transcriptional functions contribute to disease pathogenesis is not fully understood. Using a differentiated PC12 cell model of SBMA, we identified dysfunction of polyQ-expanded AR in its regulation of neurite growth and maintenance. Specifically, we found that in the presence of androgens, polyQ-expanded AR inhibited neurite outgrowth, induced neurite retraction, and inhibited neurite regrowth. This dysfunction was independent of polyQ-expanded AR transcriptional activity at androgen response elements (ARE). We further showed that the formation of polyQ-expanded AR intranuclear inclusions promoted neurite retraction, which coincided with reduced expression of the neuronal differentiation marker β-III-Tubulin. Finally, we revealed that cell death is not the primary outcome for cells undergoing neurite retraction; rather, these cells become senescent. Our findings reveal that mechanisms independent of AR canonical transcriptional activity underly neurite defects in a cell model of SBMA and identify senescence as a pathway implicated in this pathology. These findings suggest that in the absence of a role for AR canonical transcriptional activity in the SBMA pathologies described here, the development of SBMA therapeutics that preserve this activity may be desirable. This approach may be broadly applicable to other polyglutamine diseases such as Huntington's disease and spinocerebellar ataxias.

Reduced mesencephalic astrocyte-derived neurotrophic factor expression by mutant androgen receptor contributes to neurodegeneration in a model of spinal and bulbar muscular atrophy pathology.

Spinal and bulbar muscular atrophy (SBMA) is a neurodegenerative disease caused by extended CAG trinucleotide repeats in the androgen receptor (AR) gene, which encodes a ligand-dependent transcription factor. The mutant AR protein, characterized by polyglutamine expansion, is prone to misfolding and forms aggregates in both the nucleus and cytoplasm in the brain in SBMA patients. These aggregates alter protein-protein interactions and compromise transcriptional activity. In this study, we reported that in both cultured N2a cells and mouse brain, mutant AR with polyglutamine expansion causes reduced expression of mesencephalic astrocyte-derived neurotrophic factor (MANF). Overexpression of MANF ameliorated the neurotoxicity of mutant AR through the inhibition of mutant AR aggregation. Conversely, knocking down endogenous MANF in the mouse brain exacerbated neuronal damage and mutant AR aggregation. Our findings suggest that inhibition of MANF expression by mutant AR is a potential mechanism underlying neurodegeneration in SBMA.

Blocking the dimerization of polyglutamine-expanded androgen receptor protects cells from DHT-induced toxicity by increasing AR turnover

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular degenerative disease caused by a polyglutamine expansion in the androgen receptor (AR). This mutation causes AR to misfold and aggregate, contributing to toxicity in and degeneration of motor neurons and skeletal muscle. There is currently no effective treatment or cure for this disease. The role of an interdomain interaction between the amino- and carboxyl-termini of AR, termed the N/C interaction, has been previously identified as a component of androgen receptor-induced toxicity in cell and mouse models of SBMA. However, the mechanism by which this interaction contributes to disease pathology is unclear. This work seeks to investigate this mechanism by interrogating the role of AR homodimerization- a unique form of the N/C-interaction- in SBMA. We show that, although the AR N/C-interaction is reduced by polyglutamine-expansion, homodimers of 5α-dihydrotestosterone (DHT)-bound AR are increased. Additionally, blocking homodimerization results in decreased AR aggregation and toxicity in cell models. Blocking homodimerization results in the increased degradation of AR, which likely plays a role in the protective effects of this mutation. Overall, this work identifies a novel mechanism in SBMA pathology that may represent a novel target for the development of therapeutics for this disease.

Bicalutamide and Trehalose Ameliorate Spinal and Bulbar Muscular Atrophy Pathology in Mice

Spinal and bulbar muscular atrophy (SBMA) is characterized by motor neuron (MN) degeneration that leads to slowly progressive muscle weakness. It is considered a neuromuscular disease since muscle has a primary role in disease onset and progression. SBMA is caused by a CAG triplet repeat expansion in the androgen receptor (AR) gene. The translated poly-glutamine (polyQ) tract confers a toxic gain of function to the mutant AR altering its folding, causing its aggregation into intracellular inclusions, and impairing the autophagic flux. In an in vitro SBMA neuronal model, we previously showed that the antiandrogen bicalutamide and trehalose, a natural disaccharide stimulating autophagy, block ARpolyQ activation, reduce its nuclear translocation and toxicity and facilitate the autophagic degradation of cytoplasmic AR aggregates. Here, in a knock-in SBMA mouse model (KI AR113Q), we show that bicalutamide and trehalose ameliorated SBMA pathology. Bicalutamide reversed the formation of the AR insoluble forms in KI AR113Q muscle, preventing autophagic flux blockage. We demonstrated that apoptosis is activated in KI AR113Q muscle, and that both compounds prevented its activation. We detected a decrease of mtDNA and an increase of OXPHOS enzymes, already at early symptomatic stages; these alterations were reverted by trehalose. Overall, bicalutamide and/or trehalose led to a partial recovery of muscle morphology and function, and improved SBMA mouse motor behavior, inducing an extension of their survival. Thus, bicalutamide and trehalose, by counteracting ARpolyQ toxicity in skeletal muscle, are valuable candidates for future clinical trials in SBMA patients.

Inhibition of Polyglutamine Misfolding with D-Enantiomeric Peptides Identified by Mirror Image Phage Display Selection.

Nine heritable diseases are known that are caused by unphysiologically elongated polyglutamine tracts in human proteins leading to misfolding, aggregation and neurodegeneration. Current therapeutic strategies include efforts to inhibit the expression of the respective gene coding for the polyglutamine-containing proteins. There are, however, concerns that this may interfere with the physiological function of the respective protein. We aim to stabilize the protein’s native conformation by D-enantiomeric peptide ligands to prevent misfolding and aggregation, shift the equilibrium between aggregates and monomers towards monomers and dissolve already existing aggregates into non-toxic and functional monomers. Here, we performed a mirror image phage display selection on the polyglutamine containing a fragment of the androgen receptor. An elongated polyglutamine tract in the androgen receptor causes spinal and bulbar muscular atrophy (SBMA). The selected D-enantiomeric peptides were tested for their ability to inhibit polyglutamine-induced androgen receptor aggregation. We identified D-enantiomeric peptide QF2D-2 (sqsqwstpqGkwshwprrr) as the most promising candidate. It binds to an androgen receptor fragment with 46 consecutive glutamine residues and decelerates its aggregation, even in seeded experiments. Therefore, QF2D-2 may be a promising drug candidate for SBMA treatment or even for all nine heritable polyglutamine diseases, since its aggregation-inhibiting property was shown also for a more general polyglutamine target.

Deubiquitinase USP7 contributes to the pathogenicity of spinal and bulbar muscular atrophy.

Polyglutamine (polyQ) diseases are devastating, slowly progressing neurodegenerative conditions caused by expansion of polyQ-encoding CAG repeats within the coding regions of distinct, unrelated genes. In spinal and bulbar muscular atrophy (SBMA), polyQ expansion within the androgen receptor (AR) causes progressive neuromuscular toxicity, the molecular basis of which is unclear. Using quantitative proteomics, we identified changes in the AR interactome caused by polyQ expansion. We found that the deubiquitinase USP7 preferentially interacts with polyQ-expanded AR and that lowering USP7 levels reduced mutant AR aggregation and cytotoxicity in cell models of SBMA. Moreover, USP7 knockdown suppressed disease phenotypes in SBMA and spinocerebellar ataxia type 3 (SCA3) fly models, and monoallelic knockout of Usp7 ameliorated several motor deficiencies in transgenic SBMA mice. USP7 overexpression resulted in reduced AR ubiquitination, indicating the direct action of USP7 on AR. Using quantitative proteomics, we identified the ubiquitinated lysine residues on mutant AR that are regulated by USP7. Finally, we found that USP7 also differentially interacts with mutant Huntingtin (HTT) protein in striatum and frontal cortex of a knockin mouse model of Huntington's disease. Taken together, our findings reveal a critical role for USP7 in the pathophysiology of SBMA and suggest a similar role in SCA3 and Huntington's disease.

Unveiling synapse pathology in spinal bulbar muscular atrophy by genome-wide transcriptome analysis of purified motor neurons derived from disease specific iPSCs

Spinal bulbar muscular atrophy (SBMA) is an adult-onset, slowly progressive motor neuron disease caused by abnormal CAG repeat expansion in the androgen receptor (AR) gene. Although ligand (testosterone)-dependent mutant AR aggregation has been shown to play important roles in motor neuronal degeneration by the analyses of transgenic mice models and in vitro cell culture models, the underlying disease mechanisms remain to be fully elucidated because of the discrepancy between model mice and SBMA patients. Thus, novel human disease models that recapitulate SBMA patients’ pathology more accurately are required for more precise pathophysiological analysis and the development of novel therapeutics. Here, we established disease specific iPSCs from four SBMA patients, and differentiated them into spinal motor neurons. To investigate motor neuron specific pathology, we purified iPSC-derived motor neurons using flow cytometry and cell sorting based on the motor neuron specific reporter, HB9e438::Venus, and proceeded to the genome-wide transcriptome analysis by RNA sequences. The results revealed the involvement of the pathology associated with synapses, epigenetics, and endoplasmic reticulum (ER) in SBMA. Notably, we demonstrated the involvement of the neuromuscular synapse via significant upregulation of Synaptotagmin, R-Spondin2 (RSPO2), and WNT ligands in motor neurons derived from SBMA patients, which are known to be associated with neuromuscular junction (NMJ) formation and acetylcholine receptor (AChR) clustering. These aberrant gene expression in neuromuscular synapses might represent a novel therapeutic target for SBMA.

Hsp70 and Hsp40 inhibit an inter-domain interaction necessary for transcriptional activity in the androgen receptor

Molecular chaperones such as Hsp40 and Hsp70 hold the androgen receptor (AR) in an inactive conformation. They are released in the presence of androgens, enabling transactivation and causing the receptor to become aggregation-prone. Here we show that these molecular chaperones recognize a region of the AR N-terminal domain (NTD), including a FQNLF motif, that interacts with the AR ligand-binding domain (LBD) upon activation. This suggests that competition between molecular chaperones and the LBD for the FQNLF motif regulates AR activation. We also show that, while the free NTD oligomerizes, binding to Hsp70 increases its solubility. Stabilizing the NTD-Hsp70 interaction with small molecules reduces AR aggregation and promotes its degradation in cellular and mouse models of the neuromuscular disorder spinal bulbar muscular atrophy. These results help resolve the mechanisms by which molecular chaperones regulate the balance between AR aggregation, activation and quality control.

Abstract A010: ETS-related gene mediated androgen receptor aggregation and endoplasmic reticulum stress in prostate cancer development

Abstract Introduction: AR-mediated activation of ETS Related Gene (ERG) represents one of the most common and validated prostate cancer driver genes. Recently, we have shown novel morphologic phenotypes of endoplasmic reticulum (ER) stress in prostate glands of ARR2PB-ERG transgenic mouse. Since AR regulates ERG expression through TMPRSS2 promoter in human prostate cancer, we continue to investigate the post-translational interactions between ERG and AR leading to ER stress and subsequently to cell survival mechanisms. Understanding these mechanisms will potentially have major therapeutic implications. Methods: Light and electron microscopy were used to examine the morphologic and subcellular differences. AR aggregations, Co-IP and Proximal Ligation Assay for protein-protein interactions were studied in LNCaP, HEK293 cells. N-terminal and C-deletions of AR were utilized to identify specific AR domain interactions with ERG. Luminal cell surface markers on the isolated mouse prostate glands and spontaneously immortalized mouse prostate epithelial cells from ERG transgenic mouse (MoE1) were analyzed by FACS analysis. Results: Coexpression of ERG and AR showed significant aggregation of AR in filter assays. Co-IP experiments and PLA assays revealed that significant interactions occur through N-terminal domain of AR with ERG. Epithelial cells of ERG-Tg mouse prostates showed ~70% increase in CD49f (low) and Sca-1 (med) population with increased sphere formation capability and resistance to radiation-induced cell death. Both epithelial cells grown into spheres and established MoE1 cells displayed increased CD49f (low) and significant increase in the EpCAM negative population. Conclusions: Overall, our experiments demonstrate the mechanistic link that the physical interactions between ERG and AR lead to ER stress in prostate epithelium through AR misfolding/aggregation. Our observations of ERG-induced AR aggregation as one of the initial events that lead to ER stress and to cell survival indicate a critical function for ERG in the etiology of prostate cancer initiation and progression. Citation Format: Taduru L. Sreenath, Shiela S. Macalindong, Natallia Mikhalkevich, Shashwat Sharad, Ahmed Mohamed, Denise Young, Borbiev Talaibek, Charles Xavier, Rishita Gupta, Muhammad Jamal, Kevin Babcock, Shyh-Han Tan Tan, Marja T. Nevalainen, Albert Dobi, Gyorgy Petrovics, Isabell A. Sesterhenn, Inger L. Rosner, Charles J. Bieberich, Peter Nelson, Valeri Vasioukhin, Shiv Srivastava. ETS-related gene mediated androgen receptor aggregation and endoplasmic reticulum stress in prostate cancer development [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr A010.

Abstract 4504: Androgen receptor aggregation is a key regulator of endoplasmic reticulum stress and cell survival in ETS-related gene driven prostate carcinogenesis

Abstract Introduction and Objectives: Deregulated androgen receptor (AR) signaling due to either mutations or altered expression of the AR and its cofactors (activators or suppressors) has been identified as critical in prostate cancer development and progression. AR regulated oncogenic activation of Ets Related Gene (ERG) represents one of the most common and validated prostate cancer driver gene. In our recent studies using prostate specific ERG transgenic mouse prostate glands, we observed novel morphological phenotypes of endoplasmic reticulum (ER) stress. Since AR was the critical regulator of ERG expression through TMPRSS2 promoter in human prostate cancer, the present study was aimed towards understanding the post-translational interactions between ERG and AR in ER stress and subsequent cell survival mechanisms in mouse and cell culture models. Understanding such mechanistic insights will potentially have major therapeutic implications. Methods: Histological phenotype in the mouse prostate glands were examined by light and electron microscopy. Cell culture models of LNCaP, HEK293 and COS7 cells were utilized to examine the AR aggregations, Co-IP and Proximal Ligation Assay in the presence and absence of ERG. Various domain deletions of AR were utilized to identify specific AR domain interactions with ERG and its contribution in AR aggregation. Luminal cell surface markers on the isolated mouse prostate glands and spontaneously immortalized mouse prostate epithelial cells from ERG transgenic mouse (MoE1) were analyzed by FACS analysis. Results: Co-expression of ERG and AR in LNCaP and COS-7 cells showed significant aggregation of AR in filter assays. Co-IP experiments and PLA assays in VCaP, LNCaP and HEK 293 cell revealed that ERG physically interacts with AR. Epithelial cells of ERG-Tg mouse prostates showed ~70% increase in CD49f (low) and Sca-1 (med) population with increased sphere formation capability and resistance to radiation induced cell death. Both epithelial cells grown into spheres and established MoE1 cells displayed increased CD49f (low) and significant increase in the EpCAM negative population. Conclusions: Overall, our experiments demonstrate the mechanistic link that the physical interactions between ERG and AR initiate the ER stress in prostate epithelium through AR misfolding/aggregation. Our observation of ERG induced AR aggregation is one of the initial events that lead to ER stress to cell survival indicate a critical function for ERG in the etiology of prostate cancer initiation and progression. Funding: This research in part was supported by the National Cancer Institute R01CA162383 (S. S.) and HU0001-10-2-0002 funds. Citation Format: Taduru L. Sreenath, Natallia Mikhalkevich, Shashwat Sharad, Rishita Gupta, Oluwatosin Diaro, Kevin Babcock, Charles Xavier, Ahmed Mohamed, Muhammad Jamal, Shyh-Han Tan, Albert Dobi, Gyorgy Petrovics, Isabell A. Sesterhenn, David G. McLeod, Inger L. Rosner, Shiv Srivastava. Androgen receptor aggregation is a key regulator of endoplasmic reticulum stress and cell survival in ETS-related gene driven prostate carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4504. doi:10.1158/1538-7445.AM2017-4504

The 11S Proteasomal Activator REGγ Impacts Polyglutamine-Expanded Androgen Receptor Aggregation and Motor Neuron Viability through Distinct Mechanisms.

Spinal and bulbar muscular atrophy (SBMA) is caused by expression of a polyglutamine (polyQ)-expanded androgen receptor (AR). The inefficient nuclear proteasomal degradation of the mutant AR results in the formation of nuclear inclusions containing amino-terminal fragments of the mutant AR. PA28γ (also referred to as REGγ) is a nuclear 11S-proteasomal activator with limited proteasome activation capabilities compared to its cytoplasmic 11S (PA28α, PA28β) counterparts. To clarify the role of REGγ in polyQ-expanded AR metabolism, we carried out genetic and biochemical studies in cell models of SBMA. Overexpression of REGγ in a PC12 cell model of SBMA increased polyQ-expanded AR aggregation and contributed to polyQ-expanded AR toxicity in the presence of dihydrotestosterone (DHT). These effects of REGγ were independent of its association with the proteasome and may be due, in part, to the decreased binding of polyQ-expanded AR by the E3 ubiquitin-ligase MDM2. Unlike its effects in PC12 cells, REGγ overexpression rescued transgenic SBMA motor neurons from DHT-induced toxicity in a proteasome binding-dependent manner, suggesting that the degradation of a specific 11S proteasome substrate or substrates promotes motor neuron viability. One potential substrate that we found to play a role in mutant AR toxicity is the splicing factor SC35. These studies reveal that, depending on the cellular context, two biological roles for REGγ impact cell viability in the face of polyQ-expanded AR; a proteasome binding-independent mechanism directly promotes mutant AR aggregation while a proteasome binding-dependent mechanism promotes cell viability. The balance between these functions likely determines REGγ effects on polyQ-expanded AR-expressing cells.

ETS Related Gene mediated Androgen Receptor Aggregation and Endoplasmic Reticulum Stress in Prostate Cancer Development

Mechanistic studies of deregulated ERG in prostate cancer and other cancers continue to enhance its role in cancer biology and its utility as a biomarker and therapeutic target. Here, we show that ERG, through its physical interaction with androgen receptor, induces AR aggregation and endoplasmic reticulum stress in the prostate glands of ERG transgenic mice. Histomorphological alterations and the expression of ER stress sensors Atf6, Ire1α, Perk, their downstream effectors Grp78/BiP and eIF2α in ERG transgenic mouse prostate glands indicate the presence of chronic ER stress. Transient activation of apoptotic cell death during early age correlated well with the differential regulation of ER stress sensors, in particular Perk. Epithelial cells derived from ERG transgenic mouse prostates have increased prostasphere formation with resistance to radiation induced cell death. Continued activation of cell survival factors, Atf6 and Ire1α during chronic ER stress due to presence of ERG in prostate epithelium induces survival pathways and provides a selection pressure in the continuum of ERG dependent neoplastic process. These novel insights will enhance the understanding of the mechanistic functions of ERG in prostate tumor biology and towards development of early targeted therapeutic strategies for prostate cancer.

MP87-19 ETS RELATED GENE (ERG) DRIVEN ANDROGEN RECEPTOR AGGREGATION IS A KEY REGULATOR OF ENDOPLASMIC STRESS AND CELL SURVIVAL DURING PROSTATE CARCINOGENESIS

You have accessJournal of UrologyProstate Cancer: Basic Research & Pathophysiology III1 Apr 2017MP87-19 ETS RELATED GENE (ERG) DRIVEN ANDROGEN RECEPTOR AGGREGATION IS A KEY REGULATOR OF ENDOPLASMIC STRESS AND CELL SURVIVAL DURING PROSTATE CARCINOGENESIS Taduru Sreenath, Natallia Mikhalkevich, Shashwat Sharad, Rishita Gupta, Oluwatosin Diaro, Kevin Babcock, Charles Xavier, Ahmed Mohamed, Muhammad Jamal, Shyh-Han Tan, Albert Dobi, Gyorgy Petrovics, Isabell Sesterhenn, David McLeod, Inger Rosner, and Shiv Srivastava Taduru SreenathTaduru Sreenath More articles by this author , Natallia MikhalkevichNatallia Mikhalkevich More articles by this author , Shashwat SharadShashwat Sharad More articles by this author , Rishita GuptaRishita Gupta More articles by this author , Oluwatosin DiaroOluwatosin Diaro More articles by this author , Kevin BabcockKevin Babcock More articles by this author , Charles XavierCharles Xavier More articles by this author , Ahmed MohamedAhmed Mohamed More articles by this author , Muhammad JamalMuhammad Jamal More articles by this author , Shyh-Han TanShyh-Han Tan More articles by this author , Albert DobiAlbert Dobi More articles by this author , Gyorgy PetrovicsGyorgy Petrovics More articles by this author , Isabell SesterhennIsabell Sesterhenn More articles by this author , David McLeodDavid McLeod More articles by this author , Inger RosnerInger Rosner More articles by this author , and Shiv SrivastavaShiv Srivastava More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2017.02.2723AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Deregulated androgen receptor (AR) signaling due to either mutations or altered expression of the AR and its cofactors (activators or suppressors) has been identified as critical in prostate cancer development and progression. AR regulated oncogenic activation of Ets Related Gene (ERG) represents one of the most common and validated prostate cancer driver gene. In our recent studies using prostate specific ERG transgenic mouse prostate glands, we a observed novel morphological phenotypes of endoplasmic reticulum (ER) stress. Since AR was the critical regulator of ERG expression through TMPRSS2 promoter in human prostate cancer, the present study was aimed towards understanding the post-translational interactions between ERG and AR in ER stress and subsequent cell survival mechanisms in mouse and cell culture models. Understanding such mechanistic insights will potentially have major therapeutic implications. METHODS Histological phenotype in the mouse prostate glands were examined by light and electron microscopy. Cell culture models of LNCaP, HEK293 and COS7 cells were utilized to examine the AR aggregations, Co-IP and Proximal Ligation Assay in the presence and absence of ERG. Various domain deletions of AR were utilized to identify specific AR domain interactions with ERG and its contribution in AR aggregation. Luminal cell surface markers on the isolated mouse prostate glands and spontaneously immortalized mouse prostate epithelial cells from ERG transgenic mouse (MoE1) were analyzed by FACS analysis. RESULTS Co-expression of ERG and AR in LNCaP and COS-7 cells showed significant aggregation of AR in filter assays. Co-IP experiments and PLA assays in VCaP, LNCaP and HEK 293 cell revealed that ERG physically interacts with AR. Epithelial cells of ERG-Tg mouse prostates showed ~70% increase in CD49f (low) and Sca-1 (med) population with increased sphere formation capability and resistance to radiation induced cell death. Both epithelial cells grown into spheres and established MoE1 cells displayed increased CD49f (low) and significant increase in the EpCAM negative population. CONCLUSIONS Overall, our experiments demonstrate the mechanistic link that the physical interactions between ERG and AR initiate the ER stress in prostate epithelium through AR misfolding/aggregation. Our observation of ERG induced AR aggregation is one of the initial events that lead to ER stress to cell survival indicate a critical function for ERG in the etiology of prostate cancer initiation and progression. © 2017FiguresReferencesRelatedDetails Volume 197Issue 4SApril 2017Page: e1173 Advertisement Copyright & Permissions© 2017MetricsAuthor Information Taduru Sreenath More articles by this author Natallia Mikhalkevich More articles by this author Shashwat Sharad More articles by this author Rishita Gupta More articles by this author Oluwatosin Diaro More articles by this author Kevin Babcock More articles by this author Charles Xavier More articles by this author Ahmed Mohamed More articles by this author Muhammad Jamal More articles by this author Shyh-Han Tan More articles by this author Albert Dobi More articles by this author Gyorgy Petrovics More articles by this author Isabell Sesterhenn More articles by this author David McLeod More articles by this author Inger Rosner More articles by this author Shiv Srivastava More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Identification of novel polyglutamine-expanded aggregation species in spinal and bulbar muscular atrophy

Polyglutamine-repeat disorders are part of a larger family of neurodegenerative diseases characterized by protein misfolding and aggregation. In spinal and bulbar muscular atrophy (SBMA), polyglutamine expansion within the androgen receptor (AR) causes progressive debilitating muscular atrophy and lower motor neuron loss in males. Although soluble polyglutamine-expanded aggregation species are considered toxic intermediates in the aggregation process, relatively little is known about the spectrum of structures that are formed. Here we identify novel polyglutamine-expanded AR aggregates that are SDS-soluble and bind the toxicity-predicting antibody 3B5H10. Soluble, 3B5H10-reactive aggregation species exist in low-density conformations and are larger by atomic force microscopy, suggesting that they may be less compact than later-stage, insoluble aggregates. We demonstrate disease-relevance in vivo and draw correlations with toxicity in vitro.This article is part of a Special Issue entitled SI: Neuroprotection.

Proteasome-mediated Proteolysis of the Polyglutamine-expanded Androgen Receptor Is a Late Event in Spinal and Bulbar Muscular Atrophy (SBMA) Pathogenesis

Proteolysis of polyglutamine-expanded proteins is thought to be a required step in the pathogenesis of several neurodegenerative diseases. The accepted view for many polyglutamine proteins is that proteolysis of the mutant protein produces a "toxic fragment" that induces neuronal dysfunction and death in a soluble form; toxicity of the fragment is buffered by its incorporation into amyloid-like inclusions. In contrast to this view, we show that, in the polyglutamine disease spinal and bulbar muscular atrophy, proteolysis of the mutant androgen receptor (AR) is a late event. Immunocytochemical and biochemical analyses revealed that the mutant AR aggregates as a full-length protein, becoming proteolyzed to a smaller fragment through a process requiring the proteasome after it is incorporated into intranuclear inclusions. Moreover, the toxicity-predicting conformational antibody 3B5H10 bound to soluble full-length AR species but not to fragment-containing nuclear inclusions. These data suggest that the AR is toxic as a full-length protein, challenging the notion of polyglutamine protein fragment-associated toxicity by redefining the role of AR proteolysis in spinal and bulbar muscular atrophy pathogenesis.

Disrupting SUMOylation enhances transcriptional function and ameliorates polyglutamine androgen receptor-mediated disease.

Expansion of the polyglutamine (polyQ) tract within the androgen receptor (AR) causes neuromuscular degeneration in individuals with spinobulbar muscular atrophy (SBMA). PolyQ AR has diminished transcriptional function and exhibits ligand-dependent proteotoxicity, features that have both been implicated in SBMA; however, the extent to which altered AR transcriptional function contributes to pathogenesis remains controversial. Here, we sought to dissociate effects of diminished AR function from polyQ-mediated proteotoxicity by enhancing the transcriptional activity of polyQ AR. To accomplish this, we bypassed the inhibitory effect of AR SUMOylation (where SUMO indicates small ubiquitin-like modifier) by mutating conserved lysines in the polyQ AR that are sites of SUMOylation. We determined that replacement of these residues by arginine enhances polyQ AR activity as a hormone-dependent transcriptional regulator. In a murine model, disruption of polyQ AR SUMOylation rescued exercise endurance and type I muscle fiber atrophy; it also prolonged survival. These changes occurred without overt alterations in polyQ AR expression or aggregation, revealing the favorable trophic support exerted by the ligand-activated receptor. Our findings demonstrate beneficial effects of enhancing the transcriptional function of the ligand-activated polyQ AR and indicate that the SUMOylation pathway may be a potential target for therapeutic intervention in SBMA.

Androgen receptor inclusions acquire GRP78/BiP to ameliorate androgen-induced protein misfolding stress in embryonic stem cells

Commitment of differentiating embryonic stem cells (ESCs) toward the various lineages is influenced by many factors, including androgens. However, the mechanisms underlying proteotoxic stress conferred by androgen receptor (AR) actions on embryonic cell fate remains unclear. Here we show that mouse ESCs display stress-related cellular phenotypes in response to androgens during early phase of differentiation. Androgen induced a significant increase in the percentage of ESCs and embryoid bodies with the intranuclear and juxtanuclear AR inclusions, which were colocalized with the E3 ubiquitin ligase, C terminus of Hsc70-interacting protein. Caspase-3 activity corresponded with AR expression, was enhanced in cells engaged more differentiation phenotypes. Androgen-mediated accumulation of AR aggregates exacerbated endoplasmic reticulum (ER) stress and rendered ESCs susceptible to apoptosis. Increasing expression levels of the ER chaperones, GRP78/BiP and GRP94, as well as ER stress markers, such as ATF6, phosphorylated PERK, GADD153/CHOP and spliced XBP-1 mRNA, were dramatically elevated in ESCs overexpressing AR. We found that androgen induced GRP78/BiP to dissociate from ATF6, and act as an AR-interacting protein, which was recruited into AR inclusions in ESCs. GRP78/BiP was also colocalized with AR inclusions in the cells of spinal bulbar muscular atrophy transgenic mouse model. Overexpression of GRP78/BiP suppressed ubiquitination of AR aggregates and ameliorated the misfolded AR-mediated cytopathology in ESCs, whereas knockdown of GRP78/BiP increased the accumulation of AR aggregates and significantly higher levels of caspase-3 activity and cell apoptosis. These results generate novel insight into how ESCs respond to stress induced by misfolded AR proteins and identify GRP78/BiP as a novel regulator of the AR protein quality control.

Enhanced Aggregation of Androgen Receptor in Induced Pluripotent Stem Cell-derived Neurons from Spinal and Bulbar Muscular Atrophy

Spinal and bulbar muscular atrophy (SBMA) is an X-linked motor neuron disease caused by a CAG repeat expansion in the androgen receptor (AR) gene. Ligand-dependent nuclear accumulation of mutant AR protein is a critical characteristic of the pathogenesis of SBMA. SBMA has been modeled in AR-overexpressing animals, but precisely how the polyglutamine (polyQ) expansion leads to neurodegeneration is unclear. Induced pluripotent stem cells (iPSCs) are a new technology that can be used to model human diseases, study pathogenic mechanisms, and develop novel drugs. We established SBMA patient-derived iPSCs, investigated their cellular biochemical characteristics, and found that SBMA-iPSCs can differentiate into motor neurons. The CAG repeat numbers in the AR gene of SBMA-iPSCs and also in the atrophin-1 gene of iPSCs derived from another polyQ disease, dentato-rubro-pallido-luysian atrophy (DRPLA), remain unchanged during reprogramming, long term passage, and differentiation, indicating that polyQ disease-associated CAG repeats are stable during maintenance of iPSCs. The level of AR expression is up-regulated by neuronal differentiation and treatment with the AR ligand dihydrotestosterone. Filter retardation assays indicated that aggregation of ARs following dihydrotestosterone treatment in neurons derived from SBMA-iPSCs increases significantly compared with neurological control iPSCs, easily recapitulating the pathological feature of mutant ARs in SBMA-iPSCs. This phenomenon was not observed in iPSCs and fibroblasts, thereby showing the neuron-dominant phenotype of this disease. Furthermore, the HSP90 inhibitor 17-allylaminogeldanamycin sharply decreased the level of aggregated AR in neurons derived from SBMA-iPSCs, indicating a potential for discovery and validation of candidate drugs. We found that SBMA-iPSCs possess disease-specific biochemical features and could thus open new avenues of research into not only SBMA, but also other polyglutamine diseases.

Insulinlike Growth Factor (IGF)-1 Administration Ameliorates Disease Manifestations in a Mouse Model of Spinal and Bulbar Muscular Atrophy

Spinal and bulbar muscular atrophy is an X-linked motor neuron disease caused by polyglutamine expansion in the androgen receptor. Patients develop slowly progressive proximal muscle weakness, muscle atrophy and fasciculations. Affected individuals often show gynecomastia, testicular atrophy and reduced fertility as a result of mild androgen insensitivity. No effective disease-modifying therapy is currently available for this disease. Our recent studies have demonstrated that insulinlike growth factor (IGF)-1 reduces the mutant androgen receptor toxicity through activation of Akt in vitro, and spinal and bulbar muscular atrophy transgenic mice that also overexpress a noncirculating muscle isoform of IGF-1 have a less severe phenotype. Here we sought to establish the efficacy of daily intraperitoneal injections of mecasermin rinfabate, recombinant human IGF-1 and IGF-1 binding protein 3, in a transgenic mouse model expressing the mutant androgen receptor with an expanded 97 glutamine tract. The study was done in a controlled, randomized, blinded fashion, and, to reflect the clinical settings, the injections were started after the onset of disease manifestations. The treatment resulted in increased Akt phosphorylation and reduced mutant androgen receptor aggregation in muscle. In comparison to vehicle-treated controls, IGF-1-treated transgenic mice showed improved motor performance, attenuated weight loss and increased survival. Our results suggest that peripheral tissue can be targeted to improve the spinal and bulbar muscular atrophy phenotype and indicate that IGF-1 warrants further investigation in clinical trials as a potential treatment for this disease.

Toxic and non-toxic aggregates from the SBMA and normal forms of androgen receptor have distinct oligomeric structures

Hormone-dependent aggregation of the androgen receptor (AR) with a polyglutamine (polyQ) stretch amplification (>38) is considered to be the causative agent of the neurodegenerative disorder spinal and bulbar muscular atrophy (SBMA), consistent with related neurodegenerative diseases involving polyQ-extended proteins. In spite of the widespread acceptance of this common causal hypothesis, little attention has been paid to its apparent incompatibility with the observation of AR aggregation in healthy individuals with no polyQ stretch amplification. Here we used atomic force microscopy (AFM) to characterize sub-micrometer scale aggregates of the wild-type (22 glutamines) and the SBMA form (65 glutamines), as well as a polyQ deletion mutant (1 glutamine) and a variant with a normal length polyQ stretch but with a serine to alanine double mutation elsewhere in the protein. We used a baculovirus-insect cell expression system to produce full-length proteins for these structural analyses. We related the AFM findings to cytotoxicity as measured by expression of the receptors in Drosophila motoneurons or in neuronal cells in culture. We found that the pathogenic AR mutants formed oligomeric fibrils up to 300–600nm in length. These were clearly different from annular oligomers 120–180nm in diameter formed by the nonpathogenic receptors. We could also show that melatonin, which is known to ameliorate the pathological phenotype in the fly model, caused polyQ-extended AR to form annular oligomers. Further comparative investigation of these reproducibly distinct toxic and non-toxic oligomers could advance our understanding of the molecular basis of the polyQ pathologies.