Genetic Neurodegenerative Disease Research Articles

A complete overview of REEP1: old and new insights on its role in hereditary spastic paraplegia and neurodegeneration.

At the end of 19th century, Adolf von Strümpell and Sigmund Freud independently described the symptoms of a new pathology now known as hereditary spastic paraplegia (HSP). HSP is part of the group of genetic neurodegenerative diseases usually associated with slow progressive pyramidal syndrome, spasticity, weakness of the lower limbs, and distal-end degeneration of motor neuron long axons. Patients are typically characterized by gait symptoms (with or without other neurological disorders), which can appear both in young and adult ages depending on the different HSP forms. The disease prevalence is at 1.3-9.6 in 100 000 individuals in different areas of the world, making HSP part of the group of rare neurodegenerative diseases. Thus far, there are no specific clinical and paraclinical tests, and DNA analysis is still the only strategy to obtain a certain diagnosis. For these reasons, it is mandatory to extend the knowledge on genetic causes, pathology mechanism, and disease progression to give clinicians more tools to obtain early diagnosis, better therapeutic strategies, and examination tests. This review gives an overview of HSP pathologies and general insights to a specific HSP subtype called spastic paraplegia 31 (SPG31), which rises after mutation of REEP1 gene. In fact, recent findings discovered an interesting endoplasmic reticulum antistress function of REEP1 and a role of this protein in preventing τ accumulation in animal models. For this reason, this work tries to elucidate the main aspects of REEP1, which are described in the literature, to better understand its role in SPG31 HSP and other pathologies.

Inhibition of ER stress improves progressive motor deficits in a REEP1-null mouse model of hereditary spastic paraplegia.

ABSTRACTHereditary spastic paraplegias (HSPs) are genetic neurodegenerative diseases. HSPs are characterized by lower-extremity weakness and spasticity. However, there is no specific clinical treatment strategy to prevent or reverse nerve degeneration in HSPs. Mutations in receptor expression-enhancing protein 1 (REEP1) are well-recognized and relatively common causes of autosomal dominant HSPs. REEP1 modifies the endoplasmic reticulum (ER) shape, and is implicated in the ER stress response. Defects in the ER stress response seem to be crucial mechanisms underlying HSP neurodegeneration. Here, we report that REEP1−/− mice exhibit progressive motor deficits, along with denervation of neuromuscular junctions and increased ER stress. Moreover, marked axonal degeneration and morphological abnormalities are observed. In this study, we treated both REEP1−/− and wild-type (WT) mice with salubrinal, which is a specific inhibitor of ER stress, and we observed increased nerve-muscle connections and enhanced motor functions. Our data highlight the importance of ER homeostasis in HSPs, providing new opportunities for HSP treatment.

SUMOylation Prevents Huntingtin Fibrillization and Localization onto Lipid Membranes.

Huntington's disease (HD), a genetic neurodegenerative disease, is caused by an expanded polyglutamine (polyQ) domain in the first exon of the huntingtin protein (htt). PolyQ expansion destabilizes protein structure, resulting in aggregation into a variety of oligomers, protofibrils, and fibrils. Beyond the polyQ domain, adjacent protein sequences influence the aggregation process. Specifically, the first 17 N-terminal amino acids (Nt17) directly preceding the polyQ domain promote the formation of α-helix-rich oligomers that represent intermediate species associated with fibrillization. Due to its propensity to form an amphipathic α-helix, Nt17 also facilitates lipid binding. Three lysine residues (K6, K9, and K15) within Nt17 can be SUMOylated, which modifies htt's accumulation and toxicity within cells in a variety of HD models. The impact of SUMOylation on htt aggregation and direct interaction with lipid membranes was investigated. SUMOylation of htt-exon1 inhibited fibril formation while promoting larger, amorphous aggregate species. These amorphous aggregates were SDS soluble but nonetheless exhibited levels of β-sheet structure similar to that of htt-exon1 fibrils. In addition, SUMOylation prevented htt binding, aggregation, and accumulation on model lipid bilayers comprised of total brain lipid extract. Collectively, these observations demonstrate that SUMOylation promotes a distinct htt aggregation pathway that may affect htt toxicity.

Self-association of human beta-galactocerebrosidase: Dependence on pH, salt, and surfactant.

Krabbe disease, also known as globoid cell leukodystrophy, is a rare genetic neurodegenerative disease caused by a deficiency of the galactocerebrosidase enzyme. To understand the association status of human beta-galactocerebrosidase (hGALC) in solution, we employed analytical ultracentrifugation (AUC). Our AUC results show that hGALC has a tendency for reversible self-association. Self-association decreases as the concentration of sodium chloride increases from 50 to 500 mM. This indicates that ionic interactions are involved in the association. The association is also dependent on pH, and high order oligomerization decreases as the pH increases from 4.5 to 7.5. Taken together, our results indicate that hGALC has the highest tendency for oligomerization at physiological ionic strength and pH (lysosomal lumen). This is the first report describing the self-associating property of hGALC in solution.

CoA‐dependent activation of mitochondrial acyl carrier protein links four neurodegenerative diseases

PKAN, CoPAN, MePAN, and PDH‐E2 deficiency share key phenotypic features but harbor defects in distinct metabolic processes. Selective damage to the globus pallidus occurs in these genetic neurodegenerative diseases, which arise from defects in CoA biosynthesis (PKAN, CoPAN), protein lipoylation (MePAN), and pyruvate dehydrogenase activity (PDH‐E2 deficiency). Overlap of their clinical features suggests a common molecular etiology, the identification of which is required to understand their pathophysiology and design treatment strategies. We provide evidence that CoA‐dependent activation of mitochondrial acyl carrier protein (mtACP) is a possible process linking these diseases through its effect on PDH activity. CoA is the source for the 4′‐phosphopantetheine moiety required for the posttranslational 4′‐phosphopantetheinylation needed to activate specific proteins. We show that impaired CoA homeostasis leads to decreased 4′‐phosphopantetheinylation of mtACP. This results in a decrease of the active form of mtACP, and in turn a decrease in lipoylation with reduced activity of lipoylated proteins, including PDH. Defects in the steps of a linked CoA‐mtACP‐PDH pathway cause similar phenotypic abnormalities. By chemically and genetically re‐activating PDH, these phenotypes can be rescued, suggesting possible treatment strategies for these diseases.

A Deep Learning-Based Approach for Gait Analysis in Huntington Disease.

Huntington Disease (HD) is a genetic neurodegenerative disease which leads to involuntary movements and impaired balance. These changes have been quantified using footstep pressure sensor mats such as Protokinetics' Zeno Walkway. Drawing from distances between recorded footsteps, patients' disease severity have been measured in terms of high level gait characteristics such as gait width and stride length. However, little attention has been paid to the pressure data collected during formation of individual footsteps. This work investigates the potential of classifying patient disease severity based on individual footstep pressure data using deep learning techniques. Using the Motor Subscale of the Unified HD Rating Scale (UHDRS) as the gold standard, our experiments showed that using VGG16 and similar modules can achieve classification accuracy of 89%. Image pre-processing are key steps for better model performance. This classification accuracy is compared to results based on 3D CNN (82%) and SVM (86.9%).

Inhibition of the IGF-1-PI3K-Akt-mTORC2 pathway in lipid rafts increases neuronal vulnerability in a genetic lysosomal glycosphingolipidosis.

ABSTRACTGlycosphingolipid (GSL) accumulation is implicated in the neuropathology of several lysosomal conditions, such as Krabbe disease, and may also contribute to neuronal and glial dysfunction in adult-onset conditions such as Parkinson's disease, Alzheimer's disease and multiple sclerosis. GSLs accumulate in cellular membranes and disrupt their structure; however, how membrane disruption leads to cellular dysfunction remains unknown. Using authentic cellular and animal models for Krabbe disease, we provide a mechanism explaining the inactivation of lipid raft (LR)-associated IGF-1–PI3K–Akt–mTORC2, a pathway of crucial importance for neuronal function and survival. We show that psychosine, the GSL that accumulates in Krabbe disease, leads to a dose-dependent LR-mediated inhibition of this pathway by uncoupling IGF-1 receptor phosphorylation from downstream Akt activation. This occurs by interfering with the recruitment of PI3K and mTORC2 to LRs. Akt inhibition can be reversed by sustained IGF-1 stimulation, but only during a time window before psychosine accumulation reaches a threshold level. Our study shows a previously unknown connection between LR-dependent regulation of mTORC2 activity at the cell surface and a genetic neurodegenerative disease. Our results show that LR disruption by psychosine desensitizes cells to extracellular growth factors by inhibiting signal transmission from the plasma membrane to intracellular compartments. This mechanism serves also as a mechanistic model to understand how alterations of the membrane architecture by the progressive accumulation of lipids undermines cell function, with potential implications in other genetic sphingolipidoses and adult neurodegenerative conditions. This article has an associated First Person interview with the first author of the paper.

Specific patterns of brain alterations underlie distinct clinical profiles in Huntington's disease.

Huntington's disease (HD) is a genetic neurodegenerative disease which involves a triad of motor, cognitive and psychiatric disturbances. However, there is great variability in the prominence of each type of symptom across individuals. The neurobiological basis of such variability remains poorly understood but would be crucial for better tailored treatments. Multivariate multimodal neuroimaging approaches have been successful in disentangling these profiles in other disorders. Thus we applied for the first time such approach to HD. We studied the relationship between HD symptom domains and multimodal measures sensitive to grey and white matter structural alterations. Forty-three HD gene carriers (23 manifest and 20 premanifest individuals) were scanned and underwent behavioural assessments evaluating motor, cognitive and psychiatric domains. We conducted a multimodal analysis integrating different structural neuroimaging modalities measuring grey matter volume, cortical thickness and white matter diffusion indices – fractional anisotropy and radial diffusivity. All neuroimaging measures were entered into a linked independent component analysis in order to obtain multimodal components reflecting common inter-subject variation across imaging modalities. The relationship between multimodal neuroimaging independent components and behavioural measures was analysed using multiple linear regression. We found that cognitive and motor symptoms shared a common neurobiological basis, whereas the psychiatric domain presented a differentiated neural signature. Behavioural measures of different symptom domains correlated with different neuroimaging components, both the brain regions involved and the neuroimaging modalities most prominently associated with each type of symptom showing differences. More severe cognitive and motor signs together were associated with a multimodal component consisting in a pattern of reduced grey matter, cortical thickness and white matter integrity in cognitive and motor related networks. In contrast, depressive symptoms were associated with a component mainly characterised by reduced cortical thickness pattern in limbic and paralimbic regions. In conclusion, using a multivariate multimodal approach we were able to disentangle the neurobiological substrates of two distinct symptom profiles in HD: one characterised by cognitive and motor features dissociated from a psychiatric profile. These results open a new view on a disease classically considered as a uniform entity and initiates a new avenue for further research considering these qualitative individual differences.

Abstract SY39-03: Stem cell competition is central to leukemogenesis

Abstract Tissue stem cells regenerate the body and are the only cells that maintain self-renewal throughout life. When stem cells divide they give rise to stem cells (by self-renewal) and progenitors (by differentiation). Stem cell isolation and transplantation is the basis for regenerative medicine. We isolated mouse and then human hematopoietic stem cells (HSCs). Importantly, we demonstrated that transplantation of purified HSCs results in complete regeneration of the blood and immune systems without causing graft vs. host disease, and can induce permanent transplant tolerance of any organ or cell from the HSC donor. In a clinical trial in metastatic breast cancer patients, HSC purification made autologous transplantation to cancer patients possible, without including cancerous cells in the graft. The 15-year overall survival rate was ~7% in recipients of mobilized peripheral blood (MPB) autologous transplantation, and ~33% in recipients of cancer-free HSCs. We have also prospectively isolated human fetal brain CNS stem cells and found a method to propagate them without changing phenotype or normal regenerative functions upon transplantation. These are and have been used in clinical trials with children with genetic neurodegenerative diseases such as Batten and Pelizeus Mehrbacher, in patients with thoracic and cervical spinal cord injuries, and in patients with age-related macular degeneration. Self-renewal is strictly regulated and restricted to stem cells, because deregulation can lead to cancer. To study the relationship between stem cells and cancer, we followed the progression from hematopoietic stem cells (HSCs) to myelogenous leukemias. We found that the developing precancerous clones progress and accumulate mutations at the stage of HSCs, until they become fully malignant. At this point, the “leukemia” stem cell is a downstream oligolineage or multilineage progenitor that has evaded programmed cell death and programmed cell removal, and also acquired self-renewal. In the case of chronic myeloid leukemia (CML), bcr-abl+ HSC clones outcompete normal HSCs in the chronic phase. The transition from CML to myeloid blast crisis results in the leukemia stem cells appearing in the granulocyte-macrophage progenitor (GMP) stage, and is accompanied by cell intrinsic activation of β-catenin, endowing the already mutant progenitors with a self-renewal capacity. While there are many ways to defeat programmed cell death and senescence, there appears to be one dominant method that cancer cells use to avoid programmed cell removal—the elevated expression of the cell surface “don't eat me” protein CD47, the ligand for macrophage SIRPα. All cancers tested express CD47 to overcome expression of “eat me” signals such as calreticulin that is produced by macrophages and adheres to asialogylycoproteins on the surface of cancer cells. Antibodies that block the CD47-SIRPα interaction enable phagocytosis and killing of the tumor cells in vitro and in vivo. This includes human solid tumors and lymphomas/leukemias/myelomas. We showed that anti-CD47 antibodies or high-affinity SIRPα proteins synergize with anti-CD20 antibodies to eliminate human non-Hodgkin lymphoma in immune-deficient mice. We generated a humanized antibody of the IgG4 isotype, and these compounds are currently being tested in clinical trials. Citation Format: Irving L. Weissman. Stem cell competition is central to leukemogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr SY39-03.

Complex neuroprotective and neurotoxic effects of histone deacetylases.

By their ability to shatter quality of life for both patients and caregivers, neurodegenerative diseases are the most devastating of human disorders. Unfortunately, there are no effective or long-terms treatments capable of slowing down the relentless loss of neurons in any of these diseases. One impediment is the lack of detailed knowledge of the molecular mechanisms underlying the processes of neurodegeneration. While some neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, are mostly sporadic in nature, driven by both environment and genetic susceptibility, many others, including Huntington's disease, spinocerebellar ataxias, and spinal-bulbar muscular atrophy, are genetically inherited disorders. Surprisingly, given their different roots and etiologies, both sporadic and genetic neurodegenerative disorders have been linked to disease mechanisms involving histone deacetylase (HDAC) proteins, which consists of 18 family members with diverse functions. While most studies have implicated certain HDAC subtypes in promoting neurodegeneration, a substantial body of literature suggests that other HDAC proteins can preserve neuronal viability. Of particular interest, however, is the recent realization that a single HDAC subtype can have both neuroprotective and neurotoxic effects. Diverse mechanisms, beyond transcriptional regulation have been linked to these effects, including deacetylation of non-histone proteins, protein-protein interactions, post-translational modifications of the HDAC proteins themselves and direct interactions with disease proteins. The roles of these HDACs in both sporadic and genetic neurodegenerative diseases will be discussed in the current review.

Cerebrospinal fluid neurogranin and TREM2 in Huntington\u2019s disease

Biomarkers of Huntington’s disease (HD) in cerebrospinal fluid (CSF) could be of value in elucidating the biology of this genetic neurodegenerative disease, as well as in the development of novel therapeutics. Deranged synaptic and immune function have been reported in HD, and concentrations of the synaptic protein neurogranin and the microglial protein TREM2 are increased in other neurodegenerative diseases. We therefore used ELISAs to quantify neurogranin and TREM2 in CSF samples from HD mutation carriers and controls. CSF neurogranin concentration was not significantly altered in HD compared to controls, nor was it significantly associated with disease burden score, total functional capacity or motor score. An apparent increase in CSF TREM2 in manifest HD was determined to be due to increasing TREM2 with age. After age adjustment, there was no significant alteration of TREM2 in either HD group, nor any association with motor, functional or cognitive score, or brain volume quantified by MRI. Both analyses were well-powered, and sample size calculations indicated that several thousand samples per group would be needed to prove that disease-associated alterations do in fact exist. We conclude that neither neurogranin nor TREM2 is a useful biofluid biomarker for disease processes in Huntington’s disease.

The role of oxidative stress in Friedreich's ataxia.

Oxidative stress and an increase in the levels of free radicals are important markers associated with several pathologies, including Alzheimer's disease, cancer and diabetes. Friedreich's ataxia (FRDA) is an excellent paradigmatic example of a disease in which oxidative stress plays an important, albeit incompletely understood, role. FRDA is a rare genetic neurodegenerative disease that involves the partial silencing of frataxin, a small mitochondrial protein that was completely overlooked before being linked to FRDA. More than 20 years later, we now know how important this protein is in terms of being an essential and vital part of the machinery that produces iron‐sulfur clusters in the cell. In this review, we revisit the most important steps that have brought us to our current understanding of the function of frataxin and its role in disease. We discuss the current hypotheses on the role of oxidative stress in FRDA and review some of the existing animal and cellular models. We also evaluate new techniques that can assist in the study of the disease mechanisms, as well as in our understanding of the interplay between primary and secondary phenotypes.

Controlling futures? Online Genetic Testing and Neurodegenerative Disease : Comment on "Personal Genomic Testing, Genetic Inheritance, and Uncertainty".

Online personalized genetic testing services offer accessible and convenient options for satisfying personal curiosity about health and obtaining answers about one's genetic provenance. They are especially attractive to healthy people who wish to learn about their future risk of disease, as Paul Mason's (2017) case study of "Jordan" illustrates. In this response, we consider how online genetic testing services are used by people diagnosed with a common neurodegenerative disease, Parkinson's disease, to gain a sense of certainty regarding the future.

Compassionate Use of Simvastatin for a Patient with Juvenile Metachromatic Leukodystrophy

Background/Purpose: Juvenile metachromatic leukodystrophy (MLD) is a severe genetic neurodegenerative disease caused by deficiency of arylsulfatase A. Between the 3rd and the 16th year of life, demyelination causes motoric and cognitive disabilities. This leads to helplessness and early death. In early stages of the disease, hematopoietic stem cell transplant may positively influence the course of the disease. In later stages, only symptomatic treatment is possible. In 2015, it was reported that MLD mice receiving Simvastatin had less inflammatory cytokines and showed a better motor performance and less demyelination.

Unravelling Endogenous MicroRNA System Dysfunction as a New Pathophysiological Mechanism in Machado-Joseph Disease

Machado-Joseph disease (MJD) is a genetic neurodegenerative disease caused by an expanded polyglutamine tract within the protein ataxin-3 (ATXN3). Despite current efforts, MJD's mechanism of pathogenesis remains unclear and no disease-modifying treatment is available. Therefore, in this study, we investigated (1) the role of the 3' UTR of ATXN3, a putative microRNA (miRNA) target, (2) whether miRNA biogenesis and machinery are dysfunctional in MJD, and (3) which specific miRNAs target ATXN3-3' UTR and whether they can alleviate MJD neuropathology invivo. Our results demonstrate that endogenous miRNAs, by targeting sequences in the 3' UTR, robustly reduce ATXN3 expression and aggregation invitro and neurodegeneration and neuroinflammation invivo. Importantly, we found an abnormal MJD-associated downregulation of genes involved in miRNA biogenesis and silencing activity. Finally, we identified three miRNAs-mir-9, mir-181a, and mir-494-that interact with the ATXN3-3' UTR and whose expression is dysregulated in human MJD neurons and in other MJD cell and animal models. Furthermore, overexpression of these miRNAs in mice resulted in reduction of mutATXN3 levels, aggregate counts, and neuronal dysfunction. Altogether, these findings indicate that endogenous miRNAs and the 3'UTR of ATXN3 play a crucial role in MJD pathogenesis and provide a promising opportunity for MJD treatment.

E3 Ligase RNF126 Directly Ubiquitinates Frataxin, Promoting Its Degradation: Identification of a Potential Therapeutic Target for Friedreich Ataxia

SummaryFriedreich ataxia (FRDA) is a severe genetic neurodegenerative disease caused by reduced expression of the mitochondrial protein frataxin. To date, there is no therapy to treat this condition. The amount of residual frataxin critically affects the severity of the disease; thus, attempts to restore physiological frataxin levels are considered therapeutically relevant. Frataxin levels are controlled by the ubiquitin-proteasome system; therefore, inhibition of the frataxin E3 ligase may represent a strategy to achieve an increase in frataxin levels. Here, we report the identification of the RING E3 ligase RNF126 as the enzyme that specifically mediates frataxin ubiquitination and targets it for degradation. RNF126 interacts with frataxin and promotes its ubiquitination in a catalytic activity-dependent manner, both in vivo and in vitro. Most importantly, RNF126 depletion results in frataxin accumulation in cells derived from FRDA patients, highlighting the relevance of RNF126 as a new therapeutic target for Friedreich ataxia.

Exosome-Based Delivery of miR-124 in a Huntington's Disease Model.

Objective Huntington’s disease (HD) is a genetic neurodegenerative disease that is caused by abnormal CAG expansion. Altered microRNA (miRNA) expression also causes abnormal gene regulation in this neurodegenerative disease. The delivery of abnormally downregulated miRNAs might restore normal gene regulation and have a therapeutic effect. Methods We developed an exosome-based delivery method to treat this neurodegenerative disease. miR-124, one of the key miRNAs that is repressed in HD, was stably overexpressed in a stable cell line. Exosomes were then harvested from these cells using an optimized protocol. The exosomes (Exo-124) exhibited a high level of miR-124 expression and were taken up by recipient cells. Results When Exo-124 was injected into the striatum of R6/2 transgenic HD mice, expression of the target gene, RE1-Silencing Transcription Factor, was reduced. However, Exo-124 treatment did not produce significant behavioral improvement. Conclusion This study serves as a proof of concept for exosome-based delivery of miRNA in neurodegenerative diseases.

Mitochondrial malfunction in vanishing white matter disease: a disease of the cytosolic translation machinery.

Mitochondrial malfunction in vanishing white matter disease: a disease of the cytosolic translation machinery.

Azadiradione ameliorates polyglutamine expansion disease inDrosophilaby potentiating DNA binding activity of heat shock factor 1

Aggregation of proteins with the expansion of polyglutamine tracts in the brain underlies progressive genetic neurodegenerative diseases (NDs) like Huntington's disease and spinocerebellar ataxias (SCA). An insensitive cellular proteotoxic stress response to non-native protein oligomers is common in such conditions. Indeed, upregulation of heat shock factor 1 (HSF1) function and its target protein chaperone expression has shown promising results in animal models of NDs. Using an HSF1 sensitive cell based reporter screening, we have isolated azadiradione (AZD) from the methanolic extract of seeds of Azadirachta indica, a plant known for its multifarious medicinal properties. We show that AZD ameliorates toxicity due to protein aggregation in cell and fly models of polyglutamine expansion diseases to a great extent. All these effects are correlated with activation of HSF1 function and expression of its target protein chaperone genes. Notably, HSF1 activation by AZD is independent of cellular HSP90 or proteasome function. Furthermore, we show that AZD directly interacts with purified human HSF1 with high specificity, and facilitates binding of HSF1 to its recognition sequence with higher affinity. These unique findings qualify AZD as an ideal lead molecule for consideration for drug development against NDs that affect millions worldwide.

Factors Modulating the Interaction of Huntingtin with Lipid Membranes: Implications for Huntington's Disease

Huntington disease (HD) is a genetic neurodegenerative disease caused by an expanded polyglutamine (polyQ) domain in the first exon of the huntingtin (Htt) protein. This polyQ expansions leads directly to the formation of proteinaceous aggregates including oligomers and fibrils. Htt interacts with a variety of membraneous structures within the cell, and the first seventeen amino acids (Nt17) of Htt, which directly flanks the polyQ domain, is an amphiphathic α-helix (AH) lipid-binding domain. Here, the role that lipid/htt interactions play in aggregation was investigated with a specific emphasis on the role of Nt17 acetylation and membrane cholesterol content. N-terminal acetylation of htt has been implicated in the etiology of HD, and cholesterol homeostasis is altered in HD. A variety of aggregation assays, lipid binding assays, mass spectrometry, and atomic force microscopy were used. The model membrane systems were vesicles and supported bilayers comprised of total brain lipid extract (TBLE), and these were exposed to a variety of purified or synthetic peptides modeled after htt exon1. Acetylation of htt was achieved using a selective covalent label sulfo-N-hydroxysuccinimide (NHSA). Acetylation retarded fibril formation, promoted the formation of larger globular aggregates, and altered htt's ability to bind lipid membranes. Exogenous cholesterol was incorporated into our model TBLE membranes. As cholesterol content increased, morphological and mechanical changes in the bilayer associated with exposure to Htt were drastically altered. Collectively, these observations suggest that the acetylation and cholesterol content of bilayers play a critical role in htt binding to and aggregation on lipid membranes.