Sequence Context Influences the Structure and Aggregation Behavior of a PolyQ Tract

Expansions of polyglutamine (polyQ) tracts in nine different proteins cause a family of neurodegenerative disorders called polyQ diseases. Because polyQ tracts are potential therapeutic targets for these pathologies there is great interest in characterizing the conformations that they adopt and in understanding how their aggregation behavior is influenced by the sequences flanking them. We used solution NMR to study at single-residue resolution a 156-residue proteolytic fragment of the androgen receptor that contains a polyQ tract associated with the disease spinobulbar muscular atrophy, also known as Kennedy disease. Our findings indicate that a Leu-rich region preceding the polyQ tract causes it to become α-helical and appears to protect the protein against aggregation, which represents a new, to our knowledge, mechanism by which sequence context can minimize the deleterious properties of these repetitive regions. Our results have implications for drug discovery for polyQ diseases because they suggest that the residues flanking these repetitive sequences may represent viable therapeutic targets

The effect of intrathecal delivery of bone marrow stromal cells on hippocampal neurons in rat model of Alzheimer's disease.

OBJECTIVES: Intracerebral injection of bone marrow stromal cells (BMSCs) is being investigated as a therapeutic tool to prevent Alzheimer's disease (AD). Our aim was to investigate the effects of BMSCs by intrathecal injection in AD rat model. MATERIALS AND METHODS: BMSCs were obtained from the bone marrow of Wistar rat and transplanted into AD rat model via intrathecal injection. The rat model had received an injection of β amyloid into the hippocampus for histological and immunohistochemical studies. RESULTS: Histological examination of the brains in transplanted rats compared to controls demonstrated the migration of BrdU-labeled BMSCs from the site of delivery, confirmed the differentiation of BMSCs transplanted cells into the cholinergic neurons, and increased number of healthy and decreased number of dark neurons. CONCLUSION: Our results showed that BMSCs intratechal administration could be a promising method for treatment of Alzheimer's disease in rat model

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

Side chain to main chain hydrogen bonds stabilize a polyglutamine helix in a transcription factor

Polyglutamine (polyQ) tracts are low-complexity regions and their expansion is linked to certain neurodegenerative diseases. Here the authors combine experimental and computational approaches to find that the length of the androgen receptor polyQ tract correlates with its helicity and show that the polyQ helical structure is stabilized by hydrogen bonds between the Gln side chains and main chain carbonyl groups

Tau protein liquid–liquid phase separation can initiate tau aggregation

Abstract The transition between soluble intrinsically disordered tau protein and aggregated tau in neurofibrillary tangles in Alzheimer's disease is unknown. Here, we propose that soluble tau species can undergo liquid–liquid phase separation (LLPS) under cellular conditions and that phase‐separated tau droplets can serve as an intermediate toward tau aggregate formation. We demonstrate that phosphorylated or mutant aggregation prone recombinant tau undergoes LLPS, as does high molecular weight soluble phospho‐tau isolated from human Alzheimer brain. Droplet‐like tau can also be observed in neurons and other cells. We found that tau droplets become gel‐like in minutes, and over days start to spontaneously form thioflavin‐S‐positive tau aggregates that are competent of seeding cellular tau aggregation. Since analogous LLPS observations have been made for FUS, hnRNPA1, and TDP43, which aggregate in the context of amyotrophic lateral sclerosis, we suggest that LLPS represents a biophysical process with a role in multiple different neurodegenerative diseases

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

[cat] 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 receptor dóna suport a la hipòtesi que està associada a l'agregació de l'AR. Per tal de caracteritzar el mecanisme molecular d'aquest procés hem investigat les propietats estructurals de la regió de poliglutamines del receptor així com els primers estadis de la seva oligomerització in vitro mitjançant espectroscòpia de ressonància magnètica nuclear (NMR) en solució. Per tal d'estudiar les propietats estructurals dels agregats que es formen en els teixits hem fet servir el lligand Seprion per aïllar els agregats que es formen en un model animal de SBMA. Mitjançant una combinació de microscòpia de força atòmica (AFM), microscòpia electrònica de transmissió (TEM) i microscòpia d'alta resolució hem caracteritzat els agregats formats tant en el múscul com en la medul·la espinal en aquest model animal. Els resultats indiquen que els agregats de l'AR que es formen en el múscul son clarament diferents d'aquells que es formen en la medul·la i, a més, que el fenotip dels animals empitjora a mesura que s'acumulen agregats en el primer d'aquests teixits. Els nostres resultats indiquen que les diferències que observem entre els agregats que es formen en el múscul i aquells que es formen en la medul·la estan associades a la presència de fragments d'AR en el primer d'aquest teixits. Proposem doncs, que formes truncades d'AR agreguen per formar espècies fibril·lars en el múscul del model animal i que aquestes provoquen el fenotip, que empitjora amb l'edat, perquè, en agregar, recluten proteïnes nuclears que altrament serien solubles. El nostre estudi dels primers estadis del mecanisme d'oligomerització indica clarament que la regió de poliglutamines és parcialment helicoïdal i que aquesta propensitat augmenta amb la seva longitud. A més hem identificat una regió del domini de transactivació, allunyada de la regió de poliglutamines, com a responsable de les primeres interaccions intermoleculars que tenen lloc durant el mecanisme d'oligomerització. En el nostre estudi de la interacció entre AR i les xaperones moleculars Hsp40 i Hsp72 hem descobert, mitjançant NMR, que totes dues proteïnes s'uneixen al motiu (23)FQNLF(27) del domini N-terminal i que l'Hsp40 s'uneix, a la vegada també al motiu (54)LLLLQQQQ(61) que hi ha a l'inici de la regió de poliglutamines. Aquestes descobertes suggereixen un senzill mecanisme per a desensamblatge del complex entre l'AR i les xaperones moleculars que té lloc durant l'activació del receptor per l'hormona testosterona, emfatitzen el potencial terapèutic de reguladors al·lostèrics de Hsp40 i Hsp72 i contribueixen a una millor comprensió del paper que les xaperones moleculars tenen en el control de qualitat de proteïnes en malalties neurodegeneratives.[eng] 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