Protein misfolding detected early in pathogenesis of transgenic mouse model of Huntington disease using amyloid seeding assay

Pleiotropic Nanostructures Built from l-Histidine Show Biologically Relevant Multicatalytic Activities

The essential amino acid histidine plays a central role in the manifestation of several metabolic processes, including protein synthesis, enzyme-catalysis, and key biomolecular interactions. However, excess accumulation of histidine causes histidinemia, which shows brain-related medical complications, and the molecular mechanism of such histidine-linked complications is largely unknown. Here, we show that histidine undergoes a self-assembly process, leading to the formation of amyloid-like cytotoxic and catalytically active nanofibers. The kinetics of histidine self-assembly was favored in the presence of Mg(II) and Co(II) ions. Molecular dynamics data showed that preferential noncovalent interactions dominated by H-bonds between histidine molecules facilitate the formation of histidine nanofibers. The histidine nanofibers induced amyloid cross-seeding reactions in several proteins and peptides including pathogenic Aβ1-42 and brain extract components. Further, the histidine nanofibers exhibited oxidase activity and enhanced the oxidation of neurotransmitters. Cell-based studies confirmed the cellular internalization of histidine nanofibers in SH-SY5Y cells and subsequent cytotoxic effects through necrosis and apoptosis-mediated cell death. Since several complications including behavioral abnormality, developmental delay, and neurological disabilities are directly linked to abnormal accumulation of histidine, our findings provide a foundational understanding of the mechanism of histidine-related complications. Further, the ability of histidine nanofibers to catalyze amyloid seeding and oxidation reactions is equally important for both biological and materials science research.

Initiation of Brain Extract Fibrillation and Effective Cellular Internalization of Tryptophan Fibrils Unveils Its Neurotoxicity Risk

Recent discoveries on the self-assembly of aromatic amino acids into amyloid-like neurotoxic nanostructures have initiated a quest to decode the molecular mechanisms for the initiation of neurodegeneration. Moreover, the multicomponent nature of the amyloid deposits still questions the existing and well-defined amyloid cascade hypothesis. Hence, deciphering the neurotoxicity of amyloid-like nanostructures of aromatic amino acids becomes crucial for understanding the etiology of amyloidogenesis. Here, we demonstrate the cellular internalization and consequential damaging effects of self-assembled amyloid-like tryptophan nanostructures on human neuroblastoma cells. The cell-damaging potential of tryptophan nanostructure seems to be facilitated via ROS generation, necrosis and apoptosis mediated cell death. Further, tryptophan nanostructures were found to be seeding competent conformers, which triggered aggressive aggregation of brain extract components. The early stage intermediate nanostructures possess a higher cross-seeding efficacy than the seeding potential of the matured tryptophan fibrils. In addition to the cell-damaging and cross-seeding effects, tryptophan fibrils were found to catalyze oxidation of neuromodulator dopamine. These findings add more insights into the specific role of tryptophan self-assembly during the pathogenesis of hypertryptophanemia and other amyloid-associated neurodegenerative complications.

Probing protein misfolding and dissociation with an infrared free-electron laser

Misfolding is observed in the mutant proteins that are causative for neurodegenerative disorders such as polyglutamine diseases. These proteins are prone to aggregate in the cytoplasm and nucleus of cells. To reproduce cells with the aggregated proteins, gene expression system is usually applied, in which the expression construct having the mutated DNA sequence of the interest is transfected into cells. The transfected DNA is finally converted into the mutant protein, which is gradually aggregated in the cells. In addition, a simple method to prepare the cells having aggregates inside has been recently applied. Peptides were first aggregated by incubating them in water. The aggregates are spontaneously taken up by cells because aggregated proteins generally transfer between cells. Peptides with different degrees of aggregation can be made by changing the incubation times and temperatures, which enables to examine contribution of aggregation to the toxicity to the recipient cells. Moreover, such cells can be used for therapeutic researches of diseases in which aggregates are involved. In this chapter, we show methods to induce aggregation of peptides. The functional analyses of the cells with aggregates are also described. Then, experimental dissociation of the aggregates produced using this method by mid infrared free electron laser irradiation and its theoretical support by molecular dynamics simulation are introduced as the therapeutic research for neurodegenerative disorders.

Genesis of Neurotoxic Hybrid Nanofibers from the Coassembly of Aromatic Amino Acids

Considering the relevance of accumulation and self-assembly of metabolites and aftermath of biological consequences, it is important to know whether they undergo coassembly and what properties the resultant hybrid higher-order structures would exhibit. This work reveals the inherent tendency of aromatic amino acids to undergo a spontaneous coassembly process under physiologically mimicked conditions, which yields neurotoxic hybrid nanofibers. Resultant hybrid nanostructures resembled the β-structured conformers stabilized by H-bonds and π-π stacking interactions, which were highly toxic to human neuroblastoma cells. The hybrid nanofibers also showed strong cross-seeding potential that triggered in vitro aggregation of diverse globular proteins and brain extract components, converting the native structures into cross-β-rich amyloid aggregates. The heterogenic nature of the hybrid nanofibers seems crucial for their higher toxicity and faster cross-seeding potential as compared to the homogeneous amino acid nanofibers. Our findings reveal the importance of aromaticity-driven optimized intermolecular arrangements for the coassembly of aromatic amino acids, and the results may provide important clues to the fundamental understanding of metabolite accumulation-related complications.

Structural insight into transmissive mutant huntingtin species by correlative light and electron microscopy and cryo-electron tomography

Aggregates of mutant huntingtin (mHTT) containing an expanded polyglutamine (polyQ) tract are hallmarks of Huntington's Disease (HD). Studies have shown that mHTT can spread between cells, leading to the propagation of misfolded protein pathology. However, the structure of transmissive mHTT species, and the molecular mechanisms underlying their transmission remain unknown. Using correlative light and electron microscopy (CLEM) and cryo-electron tomography (cryo-ET), we identified two types of aggregation-prone granules in conditioned medium from PC12 cells expressing a mHTT N-terminal fragment: densities enclosed by extracellular vesicles (EVs), and uncoated, amorphous meshworks of heterogeneous oligomers that co-localize with clusters of EVs. In vitro assays confirmed that liposomes induce condensation of polyQ oligomers into higher-order assemblies, resembling the uncoated meshworks observed in PC12 conditioned medium. Our findings provide novel insights into formation and architecture of transmissive mHTT proteins, and highlight the potential role of EVs as both carriers and modulators of transmissive mHTT proteins.

Huntington's disease: lessons from prion disorders

Decades of research on the prion protein and its associated diseases have caused a paradigm shift in our understanding of infectious agents. More recent years have been marked by a surge of studies supporting the application of these findings to a broad array of neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Here, we present evidence to suggest that Huntington's disease, a monogenic disorder of the central nervous system, shares features with prion disorders and that, it too, may be governed by similar mechanisms. We further posit that these similarities could suggest that, like other common neurodegenerative disorders, sporadic forms of Huntington's disease may exist.

Testing Amyloid Cross-Toxicity in the Vertebrate Brain

While amyloid proteins such as amyloid β (Aβ),α-synuclein, tau, and lysozyme are known to be prion-like; emerging data have revealed that they are also able to seed the misfolding of prion-like proteins differing in sequence. In the present study, we have developed a tool designed to test neurohistochemical outcomes associated with the entry of an amyloid protein into heterotypic neurons, i.e., neurons that do not express the invading amyloid and, instead, endogenously express amyloids differing in sequence. The stereotaxic introduction of Aβ into the rodent tegmental area of the mid-brain revealed that the foreign amyloid had infiltrated into nigral neurons. Furthermore, Aβ was found colocalized with α-synuclein, an amyloid endogenous to the substantia nigra and differing in sequence relative to Aβ. Disruption of α-synuclein status in the substantia nigra is associated with Parkinson's disease onset and progress. In addition to the study findings, a significant inroad to future neurodegenerative research was made via the stereotaxic introduction of the foreign amyloid. This technique limits the presence of confounding neurometabolic variables that may be prevalent in transgenic animal models of cross-toxicity and, thereby, better addresses the role of individual neuronal factors in cross-toxicity. Finally, the data from this work may help reconcile the high frequency of clinical comorbidity seen in neurodegenerative diseases.

Proteopathic Seed Amplification Assays for Neurodegenerative Disorders

The need for etiological biomarkers for neurodegenerative diseases involving protein aggregation has prompted development of ultrasensitive cellular and cell-free assays based on the prion-like seeding capacity of such aggregates. Among them, prion RT-QuIC assays allow accurate antemortem Creutzfeldt-Jakob disease diagnosis using cerebrospinal fluid and nasal brushings. Analogous assays for synucleinopathies (e.g., Parkinson disease and dementia with Lewy bodies) provide unprecedented diagnostic sensitivity using cerebrospinal fluid. Biosensor cell and tau RT-QuIC assays can detect and discriminate tau aggregates associated with multiple tauopathies (e.g., Alzheimer disease and frontotemporal degeneration). An expanding panel of seed amplification assays should improve diagnostics and therapeutics development.

Engineered Extracellular Vesicles/Exosomes as a New Tool against Neurodegenerative Diseases

Neurodegenerative diseases are commonly generated by intracellular accumulation of misfolded/aggregated mutated proteins. These abnormal protein aggregates impair the functions of mitochondria and induce oxidative stress, thereby resulting in neuronal cell death. In turn, neuronal damage induces chronic inflammation and neurodegeneration. Thus, reducing/eliminating these abnormal protein aggregates is a priority for any anti-neurodegenerative therapeutic approach. Although several antibodies against mutated neuronal proteins have been already developed, how to efficiently deliver them inside the target cells remains an unmet issue. Extracellular vesicles/exosomes incorporating intrabodies against the pathogenic products would be a tool for innovative therapeutic approaches. In this review/perspective article, we identify and describe the major molecular targets associated with neurodegenerative diseases, as well as the antibodies already developed against them. Finally, we propose a novel targeting strategy based on the endogenous engineering of extracellular vesicles/exosomes constitutively released by cells of the central nervous system.

mHTT Seeding Activity: A Marker of Disease Progression and Neurotoxicity in Models of Huntington's Disease

Self-propagating, amyloidogenic mutant huntingtin (mHTT) aggregates may drive progression of Huntington's disease (HD). Here, we report the development of a FRET-based mHTT aggregate seeding (FRASE) assay that enables the quantification of mHTT seeding activity (HSA) in complex biosamples from HD patients and disease models. Application of the FRASE assay revealed HSA in brain homogenates of presymptomatic HD transgenic and knockin mice and its progressive increase with phenotypic changes, suggesting that HSA quantitatively tracks disease progression. Biochemical investigations of mouse brain homogenates demonstrated that small, rather than large, mHTT structures are responsible for the HSA measured in FRASE assays. Finally, we assessed the neurotoxicity of mHTT seeds in an inducible Drosophila model transgenic for HTTex1. We found a strong correlation between the HSA measured in adult neurons and the increased mortality of transgenic HD flies, indicating that FRASE assays detect disease-relevant, neurotoxic, mHTT structures with severe phenotypic consequences in vivo.

Carbamylation promotes amyloidogenesis and induces structural changes in Tau-core hexapeptide fibrils

BACKGROUND

Carbamylation is a non-enzymatic post-translational modification (PTM), which involves the covalent modification of N-terminus of protein or ε-amino group of Lys. The role of carbamylation in several age-related disorders is well documented, however, the relationship between carbamylation and neurodegenerative disorders including Alzheimer's disease remains uncharted.

METHODS

In the present study, using aggregation-prone tau-core hexapeptide fragments ³⁰⁶VQIVYK³¹¹ (PHF6) and ²⁷⁵VQIINK²⁸⁰ (PHF6*) as models, we have elucidated the effect of carbamylation on aggregation kinetics and the changes occurring in the 3-dimensional architecture of fibrils using biophysical assays and molecular dynamics simulations.

RESULTS

We found that carbamylation aids in amyloid formation and can convert the unstructured off-pathway aggregates into robust amyloids, which were toxic to cells. Electron microscopy images and molecular dynamics simulations of PHF6 fibrils showed that carbamylated peptides can form excess hydrogen bonds and modulate the pitch length and twist of peptides fibrils. We have also compared N-terminal carbamylation to acetylation and further extended our finding to full length tau that exhibits aggregation upon carbamylation even in the absence of any external inducer.

CONCLUSION

Our in vitro and in silico results together suggest that carbamylation can modulate the aggregation pathway of the amyloidegenic sequences and cause structural changes in fibril assemblies.

GENERAL SIGNIFICANCE

Carbamylation acts as a switch, which triggers the aggregation in short amyloidogenic peptide fragments and modulate the structural changes in resulting amyloid fibrils.

Progress in developing transgenic monkey model for Huntington's disease

Huntington's disease (HD) is a complex neurodegenerative disorder that has no cure. Although treatments can often be given to relieve symptoms, the neuropathology associated with HD cannot be stopped or reversed. HD is characterized by degeneration of the striatum and associated pathways that leads to impairment in motor and cognitive functions as well as psychiatric disturbances. Although cell and rodent models for HD exist, longitudinal study in a transgenic HD nonhuman primate (i.e., rhesus macaque; HD monkeys) shows high similarity in its progression with human patients. Progressive brain atrophy and changes in white matter integrity examined by magnetic resonance imaging are coherent with the decline in cognitive behaviors related to corticostriatal functions and neuropathology. HD monkeys also express higher anxiety and irritability/aggression similar to human HD patients that other model systems have not yet replicated. While a comparative model approach is critical for advancing our understanding of HD pathogenesis, HD monkeys could provide a unique platform for preclinical studies and long-term assessment of translatable outcome measures. This review summarizes the progress in the development of the transgenic HD monkey model and the opportunities for advancing HD preclinical research.

Proteins Containing Expanded Polyglutamine Tracts and Neurodegenerative Disease

Several hereditary neurological and neuromuscular diseases are caused by an abnormal expansion of trinucleotide repeats. To date, there have been 10 of these trinucleotide repeat disorders associated with an expansion of the codon CAG encoding glutamine (Q). For these polyglutamine (polyQ) diseases, there is a critical threshold length of the CAG repeat required for disease, and further expansion beyond this threshold is correlated with age of onset and symptom severity. PolyQ expansion in the translated proteins promotes their self-assembly into a variety of oligomeric and fibrillar aggregate species that accumulate into the hallmark proteinaceous inclusion bodies associated with each disease. Here, we review aggregation mechanisms of proteins with expanded polyQ-tracts, structural consequences of expanded polyQ ranging from monomers to fibrillar aggregates, the impact of protein context and post-translational modifications on aggregation, and a potential role for lipid membranes in aggregation. As the pathogenic mechanisms that underlie these disorders are often classified as either a gain of toxic function or loss of normal protein function, some toxic mechanisms associated with mutant polyQ tracts will also be discussed.

Prions: Beyond a Single Protein

Since the term protein was first coined in 1838 and protein was discovered to be the essential component of fibrin and albumin, all cellular proteins were presumed to play beneficial roles in plants and mammals. However, in 1967, Griffith proposed that proteins could be infectious pathogens and postulated their involvement in scrapie, a universally fatal transmissible spongiform encephalopathy in goats and sheep. Nevertheless, this novel hypothesis had not been evidenced until 1982, when Prusiner and coworkers purified infectious particles from scrapie-infected hamster brains and demonstrated that they consisted of a specific protein that he called a "prion." Unprecedentedly, the infectious prion pathogen is actually derived from its endogenous cellular form in the central nervous system. Unlike other infectious agents, such as bacteria, viruses, and fungi, prions do not contain genetic materials such as DNA or RNA. The unique traits and genetic information of prions are believed to be encoded within the conformational structure and posttranslational modifications of the proteins. Remarkably, prion-like behavior has been recently observed in other cellular proteins-not only in pathogenic roles but also serving physiological functions. The significance of these fascinating developments in prion biology is far beyond the scope of a single cellular protein and its related disease.

Prefibrillar huntingtin oligomers isolated from HD brain potently seed amyloid formation

Many neurodegenerative diseases are associated with deposits of aggregated protein in the brain. The molecular pathways through which soluble proteins misfold to form amyloids and large protein aggregates often include diverse oligomeric species, only some of which progress to the amyloid state. Here we show that prefibrillar huntingtin (HTT) oligomers, isolated from Huntington's disease (HD) affected human brain samples or mouse models, stimulate polyglutamine amyloid formation. Fibrillar HTT oligomers have been shown to be unstable under denaturing conditions and appear not to lead to amyloid formation. Here we show that prefibrillar HTT oligomers are remarkably stable and are potent seeds of polyglutamine amyloid formation. Therefore, our findings help to dissect the complex molecular pathway of HTT misfolding.

Polyglutamine Aggregation in Huntington Disease: Does Structure Determine Toxicity?

Huntington disease is a dominantly inherited disease of the central nervous system. The mutational expansion of polyglutamine beyond a critical length produces a toxic gain of function in huntingtin and results in neuronal death. In the course of the disease, expanded huntingtin is proteolyzed, becomes abnormally folded, and accumulates in oligomers, fibrils, and microscopic inclusions. The aggregated forms of the expanded protein are structurally diverse. Structural heterogeneity may explain why polyglutamine-containing aggregates could paradoxically be either toxic or neuroprotective. When defined, the toxic structures could then specifically be targeted by prophylactic or therapeutic drugs aimed at inhibiting polyglutamine aggregation.

Comparative study of naturally occurring huntingtin fragments in Drosophila points to exon 1 as the most pathogenic species in Huntington's disease

Although Huntington's disease is caused by the expansion of a CAG triplet repeat within the context of the 3144-amino acid huntingtin protein (HTT), studies reveal that N-terminal fragments of HTT containing the expanded PolyQ region can be produced by proteolytic processing and/or aberrant splicing. N-terminal HTT fragments are also prevalent in postmortem tissue, and expression of some of these fragments in model organisms can cause pathology. This has led to the hypothesis that N-terminal peptides may be critical modulators of disease pathology, raising the possibility that targeting aberrant splicing or proteolytic processing may present attractive therapeutic targets. However, many factors can contribute to pathology, including genetic background and differential expression of transgenes, in addition to intrinsic differences between fragments and their cellular effects. We have used Drosophila as a model system to determine the relative toxicities of different naturally occurring huntingtin fragments in a system in which genetic background, transgene expression levels and post-translational proteolytic processing can be controlled. These studies reveal that among the naturally occurring N-terminal HTT peptides, the exon 1 peptide is exceptionally pathogenic and exhibits unique structural and biophysical behaviors that do not appear to be incremental changes compared with other fragments. If this proves correct, efforts to specifically reduce the levels of exon 1 peptides or to target toxicity-influencing post-translational modifications that occur with the exon 1 context are likely to have the greatest impact on pathology.

Proteopathic tau seeding predicts tauopathy in vivo

Transcellular propagation of protein aggregates, or proteopathic seeds, may drive the progression of neurodegenerative diseases in a prion-like manner. In tauopathies such as Alzheimer's disease, this model predicts that tau seeds propagate pathology through the brain via cell-cell transfer in neural networks. The critical role of tau seeding activity is untested, however. It is unknown whether seeding anticipates and correlates with subsequent development of pathology as predicted for a causal agent. One major limitation has been the lack of a robust assay to measure proteopathic seeding activity in biological specimens. We engineered an ultrasensitive, specific, and facile FRET-based flow cytometry biosensor assay based on expression of tau or synuclein fusions to CFP and YFP, and confirmed its sensitivity and specificity to tau (∼ 300 fM) and synuclein (∼ 300 pM) fibrils. This assay readily discriminates Alzheimer's disease vs. Huntington's disease and aged control brains. We then carried out a detailed time-course study in P301S tauopathy mice, comparing seeding activity versus histological markers of tau pathology, including MC1, AT8, PG5, and Thioflavin S. We detected robust seeding activity at 1.5 mo, >1 mo before the earliest histopathological stain. Proteopathic tau seeding is thus an early and robust marker of tauopathy, suggesting a proximal role for tau seeds in neurodegeneration.

Monomeric, oligomeric and polymeric proteins in huntington disease and other diseases of polyglutamine expansion

Huntington disease and other diseases of polyglutamine expansion are each caused by a different protein bearing an excessively long polyglutamine sequence and are associated with neuronal death. Although these diseases affect largely different brain regions, they all share a number of characteristics, and, therefore, are likely to possess a common mechanism. In all of the diseases, the causative protein is proteolyzed, becomes abnormally folded and accumulates in oligomers and larger aggregates. The aggregated and possibly the monomeric expanded polyglutamine are likely to play a critical role in the pathogenesis and there is increasing evidence that the secondary structure of the protein influences its toxicity. We describe here, with special attention to huntingtin, the mechanisms of polyglutamine aggregation and the modulation of aggregation by the sequences flanking the polyglutamine. We give a comprehensive picture of the characteristics of monomeric and aggregated polyglutamine, including morphology, composition, seeding ability, secondary structure, and toxicity. The structural heterogeneity of aggregated polyglutamine may explain why polyglutamine-containing aggregates could paradoxically be either toxic or neuroprotective.

The effects of flanking sequences in the interaction of polyglutamine peptides with a membrane bilayer

Huntington's disease (HD) is caused by the presence of an extended polyglutamine (polyQ) region at the N-terminus of the huntingtin (htt) protein. The presence of flanking sequences adjacent to the polyQ region has been reported to modulate the effects of potentially toxic protein-membrane interactions. In this study, we consider four peptide systems with various combinations of flanking sequences (KKQ35KK, KKQ35P11KK, N17Q35KK, N17Q35P11KK) and use atomistic molecular dynamics simulations to study the interactions with a DOPC lipid bilayer. We observe significant membrane thinning, disorderliness of lipid molecules, and compensation effects between the top and the bottom leaflets of the bilayer depending on the presence of particular flanking sequences. Overall, we find that the presence of the N-17 flanking sequence is crucial for membrane interactions. Polyproline decreases the interaction with the membrane in the absence of N-17, but enhances it when present along N-17.

Huntington's disease induced cardiac amyloidosis is reversed by modulating protein folding and oxidative stress pathways in the Drosophila heart

Amyloid-like inclusions have been associated with Huntington's disease (HD), which is caused by expanded polyglutamine repeats in the Huntingtin protein. HD patients exhibit a high incidence of cardiovascular events, presumably as a result of accumulation of toxic amyloid-like inclusions. We have generated a Drosophila model of cardiac amyloidosis that exhibits accumulation of PolyQ aggregates and oxidative stress in myocardial cells, upon heart-specific expression of Huntingtin protein fragments (Htt-PolyQ) with disease-causing poly-glutamine repeats (PolyQ-46, PolyQ-72, and PolyQ-102). Cardiac expression of GFP-tagged Htt-PolyQs resulted in PolyQ length-dependent functional defects that included increased incidence of arrhythmias and extreme cardiac dilation, accompanied by a significant decrease in contractility. Structural and ultrastructural analysis of the myocardial cells revealed reduced myofibrillar content, myofibrillar disorganization, mitochondrial defects and the presence of PolyQ-GFP positive aggregates. Cardiac-specific expression of disease causing Poly-Q also shortens lifespan of flies dramatically. To further confirm the involvement of oxidative stress or protein unfolding and to understand the mechanism of PolyQ induced cardiomyopathy, we co-expressed expanded PolyQ-72 with the antioxidant superoxide dismutase (SOD) or the myosin chaperone UNC-45. Co-expression of SOD suppressed PolyQ-72 induced mitochondrial defects and partially suppressed aggregation as well as myofibrillar disorganization. However, co-expression of UNC-45 dramatically suppressed PolyQ-72 induced aggregation and partially suppressed myofibrillar disorganization. Moreover, co-expression of both UNC-45 and SOD more efficiently suppressed GFP-positive aggregates, myofibrillar disorganization and physiological cardiac defects induced by PolyQ-72 than did either treatment alone. Our results demonstrate that mutant-PolyQ induces aggregates, disrupts the sarcomeric organization of contractile proteins, leads to mitochondrial dysfunction and increases oxidative stress in cardiomyocytes leading to abnormal cardiac function. We conclude that modulation of both protein unfolding and oxidative stress pathways in the Drosophila heart model can ameliorate the detrimental PolyQ effects, thus providing unique insights into the genetic mechanisms underlying amyloid-induced cardiac failure in HD patients.

Huntington's disease (HD) is associated with amyloid-like inclusions in the brain and heart, and accumulation of amyloid protein is associated with neurodegeneration and cardiomyopathy. Recent studies suggest that HD patients show increased susceptibility to cardiac failure. However, the mechanisms by which disease-causing poly-glutamine repeats (PolyQ) cause heart dysfunction in these patients are unclear. We have developed a novel Drosophila heart model that exhibits significant GFP-positive aggregates upon HD-causing PolyQ expression in myocardial cells resulting in PolyQ length-dependent physiological defects. Modulation of protein folding and oxidative stress pathways in this system reduced the number of aggregates and reversed the cardiac dysfunction in response to expression of disease-causing PolyQ. The ability to explore PolyQ-associated mechanisms of cardiomyopathy in a genetically tractable whole organism, Drosophila melanogaster, promises to provide novel insights into the relationship between amyloid accumulation and heart dysfunction. Our findings not only impact the understanding of PolyQ-induced cardiomyopathy but also other human cardiac diseases associated with oxidative stress, mitochondrial defects and protein homeostasis.

Intrabodies as neuroprotective therapeutics

The process of misfolding of proteins that can trigger a pathogenic cascade leading to neurodegenerative diseases largely originates intracellularly. It is possible to harness the specificity and affinity of antibodies to counteract either protein misfolding itself, or the aberrant interactions and excess stressors immediately downstream of the primary insult. This review covers the emerging field of engineering intracellular antibody fragments, intrabodies and nanobodies, in neurodegeneration. Huntington's disease has provided the clearest proof of concept for this approach. The model systems and readouts for this disorder power the studies, and the potential to intervene therapeutically at early stages in known carriers with projected ages of onset increases the chances of meaningful clinical trials. Both single-chain Fv and single-domain nanobodies have been identified against specific targets; data have allowed feedback for rational design of bifunctional constructs, as well as target validation. Intrabodies that can modulate the primary accumulating protein in Parkinson's disease, alpha-synuclein, are also reviewed, covering a range of domains and conformers. Recombinant antibody technology has become a major player in the therapeutic pipeline for cancer, infectious diseases, and autoimmunity. There is also tremendous potential for applying this powerful biotechnology to neurological diseases.

Kinetically competing huntingtin aggregation pathways control amyloid polymorphism and properties

In polyglutamine (polyQ) containing fragments of the Huntington's disease protein huntingtin (htt), the N-terminal 17 amino acid htt(NT) segment serves as the core of α-helical oligomers whose reversible assembly locally concentrates the polyQ segments, thereby facilitating polyQ amyloid nucleation. A variety of aggregation inhibitors have been described that achieve their effects by neutralizing this concentrating function of the htt(NT) segment. In this paper we characterize the nature and limits of this inhibition for three means of suppressing htt(NT)-mediated aggregation. We show that the previously described action of htt(NT) peptide-based inhibitors is solely due to their ability to suppress the htt(NT)-mediated aggregation pathway. That is, under htt(NT) inhibition, nucleation of polyQ amyloid formation by a previously described alternative nucleation mechanism proceeds unabated and transiently dominates the aggregation process. Removal of the bulk of the htt(NT) segment by proteolysis or mutagenesis also blocks the htt(NT)-mediated pathway, allowing the alternative nucleation pathway to dominate. In contrast, the previously described immunoglobulin-based inhibitor, the antihtt(NT) V(L) 12.3 protein, effectively blocks both amyloid pathways, leading to stable accumulation of nonamyloid oligomers. These data show that the htt(NT)-dependent and -independent pathways of amyloid nucleation in polyQ-containing htt fragments are in direct kinetic competition. The results illustrate how amyloid polymorphism depends on assembly mechanism and kinetics and have implications for how the intracellular environment can influence aggregation pathways.