AbstractsChemistry

Androgen receptor aggregates studies in vitro and in a transgenic mouse model of Spinal Bulbal Muscular Atrophpy (SMBA)

by Bahareh Eftekharzadeh




Institution: Universitat de Barcelona
Department:
Year: 2015
Keywords: Malalties neuromusculars; Enfermedades neuromusculares; Neuromuscular diseases; Atròfia muscular; Atrofia muscular; Muscular atrophy; Andrògens; Andrógenos; Androgens; Agregació (Química); Agregación (Química); Aggregation (Chemistry); Ciències de la Salut
Record ID: 1125736
Full text PDF: http://hdl.handle.net/10803/294596


Abstract

Spinal bulbar muscular atrophy (SBMA) is a rare hereditary neuromuscular disease caused by the elongation of a polymorphic polyglutamine (polyQ) tract in the N-terminal region of the transactivation domain (NTD) of androgen receptor (AR). Although the molecular basis of SBMA is not yet fully understood, the observation of nuclear inclusions containing AR fragments in specific tissues of SBMA patients has led to the suggestion that it is linked to AR aggregation. To characterize the molecular mechanism of this process we have investigated the structural properties of the polyQ tract present in AR as well as the early stages of its oligomerization in vitro by nuclear magnetic resonance (NMR) spectroscopy in solution. To study the structural property of the AR aggregates in tissue, the Seprion ligand was used for quantification of AR aggregate load in a SBMA mouse model. A combination of atomic force microscopy (AFM), transmission electron microscopy (TEM) and high-resolution microscopy was used to investigate the Seprion ligand captured aggregates from muscle and spinal cord tissue. The results indicated that aggregated structures from spinal cord extract differ remarkably from the fibrillar species isolated from muscle tissue. We found that the AR fibrils in the muscles accumulate and increase their length as the animals age. Our results indicate that there are differences between the androgen receptor variants in muscle and spinal cord, with more N-terminally truncated AR found in muscle compared to spinal cord. We propose that truncated AR forms aggregates and leads to AR fibrillar species in muscles and that mutant AR97Q plays a role in the recruitment of partner interacting proteins in an age-related fashion. Our studies into the elucidation of the early stages of oligomerization indicated that the polyQ tract is partially alpha-helical, a propensity that increases with its length. In addition, a specific region of the N-terminus of the NTD, distinct from the polyQ tract, appears to be responsible for the inter-molecular interactions that nucleate AR aggregation. Studying the interactions between AR and the molecular chaperones Hsp40 and Hsp72 respectively, by solution NMR spectroscopy we found that the Hsp72 and Hsp40 both bind to (23)FQNLF(27) motif, whereas the Hsp40 binds additionally to (54)LLLQQQQ(61). These findings provide a simple mechanism for the disassembly of the complex between AR and molecular chaperones required for androgen receptor function and emphasize the therapeutic potential of allosteric regulators of Hsp72 and Hsp40 and provide new insights into the role of the chaperone machinery in protein quality control in neurodegenerative diseases.; L'atròfia muscular espinobulbar (SBMA) és una malaltia neuromuscular hereditària causada per una elongació d'una regió de poliglutamines localitzada en el domini de transactivació del receptor d'andrògens (AR). Malgrat que la base molecular d'aquesta malaltia encara no es coneix del tot, l'observació d'inclusions nuclears que contenen fragments del…