What is the impact of androgens on age-related diseases, such as prostate cancer and neurodegeneration?
How does the amplification of androgen receptor function alter gene expression ultimately triggering cancer and neurodegeneration?
Cancer and neurodegenerative diseases represent a major health burden for the world. Aging is the major risk factor for these untreatable diseases. We are interested in understanding i) What is the relationship between protein context (structure and function) and neurotoxicity/cancer; ii) How specific extra- and intra-cellular signaling pathways directly target the disease-related protein through post-translational modifications that suppress and enhance toxicity; iii) How single-cell molecular identity shapes selective neuronal vulnerability; and iv) What is the role of peripheral tissues in the neurodegenerative process.
Androgen receptor (AR) belongs to the family of nuclear hormone receptors, which also includes oestrogen, glucocorticoid, progesterone, and mineralocorticoid receptors. In its inactive state, AR resides in the cytosol in association with heat shock proteins (HSPs). Upon binding to its natural ligands, testosterone (T) and the more potent derivative dihydrotestosterone (DHT), AR dissociates from HSPs, dimerizes and translocates to nucleus, where it binds to specific sequences on the DNA known as androgen-responsive elements (ARE). Upon interaction with transcription co-factors (co-activators and co-repressors) and the basal transcription complex machinery, AR regulates the expression of the androgen-responsive genes. In addition, AR undergoes several post-translational modifications (PTMs), such as phosphorylation, methylation, acetylation and ubiquitination. AR is a ubiquitous protein. Partial or complete AR loss-of-function (LOF) mutations lead to different degrees of androgen insensitivity syndrome, whereas gain-of-function (GOF) mutations result in two clinically distinct age-related diseases, prostate cancer (PC) and spinobulbar muscular atrophy (SBMA).
We have previously established that i) Androgen-induced AR nuclear translocation, DNA binding and interaction with transcription co-factors are all necessary steps towards neurodegeneration in SBMA; ii) Signaling pathways culminating in direct modification of AR affect its response to androgens, thereby resulting in major changes in protein structure, function, and toxicity; and iii) Peripheral tissues, such as skeletal muscle, play a key role in SBMA, indicating that AR expression in these tissues is important for disease pathogenesis. These findings imply that the toxic GOF underlying SBMA involves modification of the native function of AR, suggesting converging mechanisms with PC. Moreover, the observation that PTMs of AR affect its structure-folding, native function and toxicity offers the opportunity to identify agents that enhance PTMs suppressing toxicity and test these compounds for therapeutic purposes. Based on our results obtained in mice, two agents have been moved to phase II clinical trials for SBMA. We are currently exploring the molecular details of AR dysfunction and deregulation of androgen-responsive gene expression. Moreover, we are investigating what is the role of AR in peripheral tissues in health and disease.
Figure 1. Mutations in the AR cause different diseases. Loss of function (LOF) mutations cause androgen insensitivity syndrome. Gain of function (GOF) mutations can be hypermorphic if they enhance the native function of the disease-related proteins and neomorphic if they confer aberrant properties to the mutant protein. GOF mutations can either cause prostate cancer or spinobulbar muscular atrophy.
Figure 2. AR: From gene to protein function. The AR gene is composed of eight exons. A CAG tandem repeat is present in exon 1. AR is composed of three domains, the N-terminal transactivation domain that contains two activating function (AF) surfaces, AF-1 and AF-2, the DNA-binding domain (DBD), and the ligand-binding domain (LBD), which contains AF-2. In the absence of its natural ligands, testosterone (T) and its more potent derivative dihydrotestosterone (DHT), AR resides in the cytosol in association with heat shock proteins (HSPs). Upon ligand binding AR dissociates from HSPs, dimerizes and translocates to nucleus, where it binds to androgen-responsive elements (ARE) and regulates gene expression. GOF mutations responsible for PC and SBMA result in dysregulation of gene expression.
Figure 3. AR integrates androgen signaling and extracellular information by regulating gene expression. Signaling pathways initiated by extracellular molecules culminate in the post-translational modification of AR. Active AR translocates to nucleus, binds to chromatine, recruits transcription co-factors and interacts with the basal transcription machinery to regulate gene expression in response to androgen signaling and growth factors/neurotrophin-activated signal transduction pathways.
What is the molecular relationship between AR structure/function and disease?
Mutations in the AR gene can cause clinically distinct types of disease (Figure 1). Prostate Cancer (PC) is a fatal disease and the second leading cause of death in USA and Europe. Spinal and Bulbar Muscular Atrophy (SBMA) is a rare neuromuscular disease linked to expansions of the trinucleotide tandem repeat CAG encoding a polyglutamine (polyQ) tract in the first exon of the AR gene. While the final steps of PC and SBMA are different and diverge in their end-state, culminating in cell proliferation and cell death, respectively, these two diseases interestingly share several features. The primary events of both PC and SBMA are indeed strikingly androgen-dependent. Moreover, these disorders are age-related, with most of cases manifesting after the fourth/fifth decade of life. We have previously shown that phosphorylation of polyQ-AR by Akt blocks androgen binding and that this phosphorylation is regulated by the protein arginine methyltransferase 6 (PRMT6). We are currently investigating the role of other PTMs in health and disease.
What is the mechanism through which AR integrates androgen signaling with extracellular signaling and cell metabolism?
AR is the main effector of androgen signaling. AR is a transcription factor activated by androgens (Figure 2). Androgen binding results in nuclear translocation and binding to DNA at the level of androgen-responsive elements. AR recruits transcription co-factors to regulate (activate and repress) the expression of androgen-responsive genes. AR integrates the androgen signaling with that of extracellular signaling pathways initiated by binding of specific ligands to their receptors. AR is indeed highly phosphorylated, and phosphorylation by kinases, such as PKA and Akt, modifies AR stability, function and toxicity. In light of these results, we are now investigating the molecular logics of changes in gene expression resulting from activation of AR by androgens and growth factors and neurotrophin signaling. Moreover, we are investigating how cell metabolism affects AR function.
What is the pathophysiological role of AR in neurons and peripheral tissues?
AR is expressed in all tissues, with particularly high expression levels in skeletal and cardiac muscle, liver, adrenal glands, and testis. Moreover, AR is expressed in neurons, and within the central nervous system it is expressed at high levels in motor neurons. AR integrates androgen signaling and inputs from extracellular pathways to drive gene expression in a tissue- and time-specific manner (Figure 3). Alpha motor neurons (αMN) selectively degenerate in neuromuscular diseases, including amyotrophic lateral sclerosis (ALS), and SBMA. Distinct classes of αMNs (slow-fatigue resistant SFR-MNs, fast-fatigue resistant FFR-MNs, and fast-fatiguable FF-MNs) degenerate at different rate, with the FF-MNs degenerating first in aging and age-related diseases. The molecular mechanisms underlying this selective vulnerability of FF-MNs are poorly known. Building on our expertise in studying the molecular development of distinct neuronal classes, and leveraging on new technologies that we pioneer to purify and molecularly profile human and mouse MNs, we will identify the molecular landscapes of MNs in physiological and pathological conditions, informing on the logics that shape the selective susceptibility of αMNs to motor neuron disorder. Concerning peripheral tissues, IGF-1 overexpression selectively in the skeletal muscles of SBMA mice leads to increased polyQ-AR phosphorylation and reduced motor dysfunction, improved muscle and spinal cord pathology, and extended lifespan. These results provide proof-of-principle that intervention in muscle has remarkable effects on disease manifestations and indicate that muscle is a primary target of mutant AR toxicity. The molecular details of the role of AR in neurons and peripheral tissues remain to be elucidated.
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- 2017 Borgia D, Malena A, Spinazzi M, Andrea Desbats M, Salviati L, Russell AP, Miotto G, Tosatto L, Pegoraro E, Sorarù G, Pennuto M*, Vergani L*. Increased mitophagy in the skeletal muscle of spinal and bulbar muscular atrophy patients. Hum Mol Genet 26: 1087-103.
- 2017 Milioto C, Malena A, Maino E, Polanco MJ, Marchioretti C, Borgia D, Pereira MG, Blaauw B, Lieberman AP, Venturini R, Plebani M, Sambataro F, Vergani L, Pegoraro E, Sorarù G*, Pennuto M*. Beta-agonist stimulation ameliorates the phenotype of spinal and bulbar muscular atrophy mice and patient-derived myotubes. Sci Rep 7:41046.
- 2016 Polanco MJ, Parodi S, Piol D, Stack C, Chivet M, Contestabile A, Miranda HC, Lievens PMJ, Espinoza S, Jochum T, Rocchi A, Grunseich C, Gainetdinov RR, Cato ACB, Lieberman A, La Spada AR, Sambataro F, Fischbeck KH, Gozes I, Pennuto M*. CDK2 inhibition by PACAP/AC/PKA signaling reduces polyglutamine-expanded androgen receptor phosphorylation and toxicity in SBMA. Sci Transl Med 8:370ra181.
- 2016 Rocchi A, Milioto C, Parodi S, Armirotti A, Borgia D, Pellegrini M, Urciuolo A, Molon S, Morbidoni V, Marabita M, Romanello V, Gatto P, Blaauw B, Bonaldo P, Sambataro F, Robins DM, Lieberman AP, Sorarù G, Vergani L, Sandri M, Pennuto M*. Glycolytic-to-oxidative fiber-type switch and mTOR signaling activation are early-onset features of SBMA muscle modified by high-fat diet. Acta Neuropathol 132: 127-44.
- 2015 Scaramuzzino C, Casci I, Parodi S, Lievens PMJ, Polanco MJ, Milioto C, Chivet M, Monaghan J, Mishra A, Badders N, Aggarwal T, Grunseich C, Sambataro F, Basso M, Fackelmayer FO, Taylor JP, Pandey UB, Pennuto M*. Protein arginine methyltransferase 6 enhances polyglutamine-expanded androgen receptor function and toxicity in spinal and bulbar muscular atrophy. Neuron 85: 88-100.
- 2013 Malena A, Pennuto M, Tezze C, Querin G, D’Ascenzo C, Silani V, Cenacchi G, Scaramozza A, Romito S, Morandi L, Pegoraro E, Russell AP, Soraru` G, Vergani L. Androgen-dependent impairment of myogenesis in spinal and bulbar muscular atrophy. Acta Neuropathol 126: 109-21.
- 2012 Rinaldi C, Bott LC, Chen KL, Harmison GG, Katsuno M, Sobue G, Pennuto M, Fischbeck KH. IGF-1 administration ameliorates disease manifestations in a mouse model of spinal and bulbar muscular atrophy. Mol Med 18: 1261-8.
- 2010 Nedelsky NB, Pennuto M, Smith RB, Palazzolo I, Moore J, Nie Z, Neale G, Taylor JP. Native functions of the androgen receptor are essential to pathogenesis in a Drosophila model of spinobulbar muscular atrophy. Neuron 67: 936-52.
-Featured by Kratter and Finkbeiner, Neuron 67: 897-99.
- 2009 Palazzolo I, Stack C, Kong L, Musaro M, Adachi H, Katsuno M, Sobue G, Taylor JP, Sumner JC, Fischbeck HK, Pennuto M* Overexpression of muscle-specific isoform of IGF-1 in the skeletal muscle of SBMA mice extends life and attenuates disease manifestations. Neuron 63: 316-28.
-Featured by Papanikolau and Ellerby, Neuron 63: 277-78.
-Press coverage: Neurology Today, ScienceBX, MDA press release, KDA press release
- 2008 Pennuto M, Tinelli E, Malaguti M, Del Carro U, D'Antonio M, Ron D, Quattrini A, Feltri ML, Wrabetz L. Ablation of the UPR-mediator CHOP restores motor function and reduces demyelination in Charcot-Marie-Tooth 1B mice. Neuron 57: 393-405.
-Featured by Khajavi and Lupski, Neuron 57: 329-30.
- PhD: University of Milan, Italy (2000)
- Post-doc San Raffaele Scientific Institute, Milan, Italy (2001-2004)
- Post-doc NINDS, NIH, Bethesda MD, USA (2005-2007)
- Staff Scientist University of Pennsylvania, Philadelphia PA, USA (2008-2009)
- Group Leader Italian Institute of Technology Genoa, Italy (2009-2013)
- Professor: Assistant & Associate Professor, University of Trento, Italy (2013-2017)
- Professor: Associate Professor of Molecular Biology, University of Padua, Italy (2017-current)
- Group leader: Veneto Institute of Molecular Medicine, Padua, Italy (2018-current)
- 2017 Arimura Foundation State-of-Art Lecture Award, 13th International PACAP meeting, Hong Kong
- 2013 Dulbecco Telethon Institute Career Award
- 2011 IBRO selected Lecture “Woman in Neuroscience”, 10th International PACAP meeting, Israel
- 2003 Euresco Travel Award
- 1998 European Science Foundation Travel Award
- 1997 A. Marzullo National Award for Undergraduate Thesis, University of Trieste, Italy