Early Alterations in Operant Performance and Prominent Huntingtin Aggregation in a Congenic F344 Rat Line of the Classical CAGn51trunc Model of Huntington Disease.
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ABSTRACT:
SUBMITTER: Plank AC
PROVIDER: S-EPMC5788972 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Huntington disease (HD) is caused by a polyglutamine-expansion mutation in huntingtin (HTT) that makes the protein toxic and aggregate-prone. The subcellular localisation of huntingtin and many of its interactors suggest a role in endocytosis, and recently it has been shown that huntingtin interacts indirectly with the early endosomal protein Rab5 through HAP40. Here we show that Rab5 inhibition enhanced polyglutamine toxicity, whereas Rab5 overexpression attenuated toxicity in our cell and fly models of HD. We tried to identify a mechanism for the Rab5 effects in our HD model systems, and our data suggest that Rab5 acts at an early stage of autophagosome formation in a macromolecular complex that contains beclin 1 (BECN1) and Vps34. Interestingly chemical or genetic inhibition of endocytosis also impeded macroautophagy, and enhanced aggregation and toxicity of mutant huntingtin. However, in contrast to Rab5, inhibition of endocytosis by various means suppressed autophagosome-lysosome fusion (the final step in the macroautophagy pathway) similar to bafilomycin A1. Thus, Rab5, which has previously been thought to be exclusively involved in endocytosis, has a new role in macroautophagy. We have previously shown that macroautophagy is an important clearance route for several aggregate-prone proteins including mutant huntingtin. Thus, better understanding of Rab5-regulated autophagy might lead to rational therapeutic targets for HD and other protein-conformation diseases.
| S-EPMC2635563 | biostudies-literature
Project description:In Huntington disease (HD), immune cells are activated before symptoms arise; however, it is unclear how the expression of mutant huntingtin (htt) compromises the normal functions of immune cells. Here we report that primary microglia from early postnatal HD mice were profoundly impaired in their migration to chemotactic stimuli, and expression of a mutant htt fragment in microglial cell lines was sufficient to reproduce these deficits. Microglia expressing mutant htt had a retarded response to a laser-induced brain injury in vivo. Leukocyte recruitment was defective upon induction of peritonitis in HD mice at early disease stages and was normalized upon genetic deletion of mutant htt in immune cells. Migration was also strongly impaired in peripheral immune cells from pre-manifest human HD patients. Defective actin remodeling in immune cells expressing mutant htt likely contributed to their migration deficit. Our results suggest that these functional changes may contribute to immune dysfunction and neurodegeneration in HD, and may have implications for other polyglutamine expansion diseases in which mutant proteins are ubiquitously expressed.
| S-EPMC3533551 | biostudies-literature
Project description:In Huntington's disease, a mutated version of the huntingtin protein leads to cell death. Mutant huntingtin is known to aggregate, a process that can be inhibited by the eukaryotic chaperonin TRiC (TCP1-ring complex) in vitro and in vivo. A structural understanding of the genesis of aggregates and their modulation by cellular chaperones could facilitate the development of therapies but has been hindered by the heterogeneity of amyloid aggregates. Using cryo-electron microscopy (cryoEM) and single particle cryo-electron tomography (SPT) we characterize the growth of fibrillar aggregates of mutant huntingtin exon 1 containing an expanded polyglutamine tract with 51 residues (mhttQ51), and resolve 3-D structures of the chaperonin TRiC interacting with mhttQ51. We find that TRiC caps mhttQ51 fibril tips via the apical domains of its subunits, and also encapsulates smaller mhtt oligomers within its chamber. These two complementary mechanisms provide a structural description for TRiC's inhibition of mhttQ51 aggregation in vitro. DOI:http://dx.doi.org/10.7554/eLife.00710.001.
| S-EPMC3707056 | biostudies-literature
Project description:Huntington disease (HD) is an autosomal dominant neurodegenerative disorder, characterized by motor, psychiatric and cognitive symptoms. HD is caused by a CAG repeat expansion in the first exon of the HTT gene, resulting in an expanded polyglutamine tract at the N-terminus of the huntingtin protein. Typical disease onset is around mid-life (adult-onset HD) whereas onset below 21 years is classified as juvenile HD. While much research has been done on the underlying HD disease mechanisms, little is known about regulation and expression levels of huntingtin RNA and protein.In this study we used 15 human post-mortem HD brain samples to investigate the expression of wild-type and mutant huntingtin mRNA and protein. In adult-onset HD brain samples, there was a small but significantly lower expression of mutant huntingtin mRNA compared to wild-type huntingtin mRNA, while wild-type and mutant huntingtin protein expression levels did not differ significantly. Juvenile HD subjects did show a lower expression of mutant huntingtin protein compared to wild-type huntingtin protein. Our results in HD brain and fibroblasts suggest that protein aggregation does not affect levels of huntingtin RNA and protein. Additionally, we did not find any evidence for a reduced expression of huntingtin antisense in fibroblasts derived from a homozygous HD patient.We found small differences in allelic huntingtin mRNA levels in adult-onset HD brain, with significantly lower mutant huntingtin mRNA levels. Wild-type and mutant huntingtin protein were not significantly different in adult-onset HD brain samples. Conversely, in juvenile HD brain samples mutant huntingtin protein levels were lower compared with wild-type huntingtin, showing subtle differences between juvenile HD and adult-onset HD. Since most HD model systems harbor juvenile repeat expansions, our results suggest caution with the interpretation of huntingtin mRNA and protein studies using HD cell and animal models with such long repeats. Furthermore, our huntingtin antisense results in homozygous HD cells do not support reduced huntingtin antisense expression due to an expanded CAG repeat.
| S-EPMC4411791 | biostudies-literature
Project description:Huntington's disease (HD) is a neurodegenerative disease caused by the expansion of a polyglutamine (polyQ) tract near the N-terminus of the huntingtin (htt) protein. Expanded polyQ tracts are prone to aggregate into oligomers and insoluble fibrils. Mutant htt (mhtt) localizes to variety of organelles, including mitochondria. Specifically, mitochondrial defects, morphological alteration, and dysfunction are observed in HD. Mitochondrial lipids, cardiolipin (CL) in particular, are essential in mitochondria function and have the potential to directly interact with htt, altering its aggregation. Here, the impact of mitochondrial membranes on htt aggregation was investigated using a combination of mitochondrial membrane mimics and tissue-derived mitochondrial-enriched fractions. The impact of exposure of outer and inner mitochondrial membrane mimics (OMM and IMM respectively) to mhtt was explored. OMM and IMM reduced mhtt fibrillization, with IMM having a larger effect. The role of CL in mhtt aggregation was investigated using a simple PC system with varying molar ratios of CL. Lower molar ratios of CL (<5%) promoted fibrillization; however, increased CL content retarded fibrillization. As revealed by in situ AFM, mhtt aggregation and associated membrane morphological changes at the surface of OMM mimics was markedly different compared to IMM mimics. While globular deposits of mhtt with few fibrillar aggregates were observed on OMM, plateau-like domains were observed on IMM. A similar impact on htt aggregation was observed with exposure to purified mitochondrial-enriched fractions. Collectively, these observations suggest mitochondrial membranes heavily influence htt aggregation with implication for HD.
| S-EPMC8328955 | biostudies-literature
Project description:Huntington's Disease is a fatal neurodegenerative disorder caused by expansion of a glutamine repeat region (polyQ) beyond a critical threshold within exon1 of the huntingtin protein (htt). As a consequence of polyQ expansion, htt associates into a variety of aggregate species that are thought to underlie cellular toxicity. Within cells, htt associates with numerous membranous organelles and surfaces that exert influence on the aggregation process. In particular, the first 17 amino acids at the N-terminus of htt (Nt17) serve as a lipid-binding domain that is intrinsically disordered in bulk solution but adopts an amphipathic α-helical structure upon binding membranes. Beyond this, Nt17 is implicated in initiating htt fibrillization. As the interaction between Nt17 and lipid membranes is likely influenced by lipid properties, the impact of lipid headgroups on htt-exon1 aggregation, membrane activity, and the ability to form protein:lipid complexes was determined. Htt-exon1 with a disease-length polyQ domain (46Q) was exposed to lipid vesicles comprised of lipids with either zwitterionic (POPC and POPE) or anionic (POPG and POPS) headgroups. With zwitterionic head groups, large lipid to peptide ratios were required to have a statistically significant impact on htt aggregation. Anionic lipids enhanced htt fibrillization, even at low lipid:protein ratios, and this was accompanied by changes in aggregate morphology. Despite the larger impact of anionic lipids, htt-exon1(46Q) was more membrane active with zwitterionic lipid systems. The ability of Nt17 to form complexes with lipids was also mediated by lipid headgroups as zwitterionic ionic lipids more readily associated with multimeric forms of Nt17 in comparison with anionic lipids. Collectively, these results highlight the complexity of htt/membrane interactions and the resulting impact on the aggregation process.
| S-EPMC7742038 | biostudies-literature
Project description:The precise degradation of dysfunctional mitochondria by mitophagy is essential for maintaining neuronal homeostasis. HTT (huntingtin) can interact with numerous other proteins and thereby perform multiple biological functions within the cell. In this study, we investigated the role of HTT during mitophagy and analyzed the impact of the expansion of its polyglutamine (polyQ) tract. HTT is involved in different mitophagy steps, promoting the physical proximity of different protein complexes during the initiation of mitophagy and recruiting mitophagy receptors essential for promoting the interaction between damaged mitochondria and the nascent autophagosome. The presence of the polyQ tract in mutant HTT affects the formation of these protein complexes and determines the negative consequences of mutant HTT on mitophagy, leading to the accumulation of damaged mitochondria and an increase in oxidative stress. These outcomes contribute to general mitochondrial dysfunction and neurodegeneration in Huntington disease.Abbreviations: AMPK: AMP-activated protein kinase; ATG13: autophagy related 13; BECN1: beclin 1, autophagy related; BNIP3: BCL2/adenovirus E1B interacting protein 3; BNIP3L/Nix: BCL2/adenovirus E1B interacting protein 3-like; CCCP: carbonyl cyanide 3-chlorophenyl hydrazone; DMEM: Dulbecco's modified eagle medium; EDTA: ethylene-diamine-tetra-acetic acid; EGFP: enhanced green fluorescent protein; EGTA: ethylene glycol bis(2-aminoethyl ether)tetraacetic acid; FUNDC1: FUN14 domain containing 1; HD: Huntington disease; HRP: horseradish peroxidase; HTT: huntingtin; LC3-II: lipidated form of MAP1LC3/LC3; mtDNA: mitochondrial deoxyribonucleic acid; MTDR: MitoTracker Deep Red; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin kinase complex 1; NBR1: NBR1, autophagy cargo receptor; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; OCR: oxygen consumption rate; OPTN: optineurin; OXPHOS: oxidative phosphorylation; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PIK3R4/VPS15: phosphoinositide-3-kinase regulatory subunit 4; PINK1: PTEN induced putative kinase 1; PLA: proximity ligation assay; PMSF: phenylmethylsulfonyl fluoride; polyQ: polyglutamine; PtdIns3K: phosphatidylinositol 3-kinase; ROS: reactive oxygen species; Rot: rotenone; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SEM: standard error of the mean; SQSTM1/p62: sequestosome 1; TMRM: tetramethylrhodamine methyl ester; UB: ubiquitin; ULK1: unc-51 like kinase 1.
| S-EPMC8032238 | biostudies-literature
Project description:Huntington disease (HD) is caused by an expansion of the polyglutamine (polyQ) repeat (>37Q) in huntingtin (htt), and age of onset is inversely correlated with the length of the polyQ repeat. Mutant htt with expanded polyQ is ubiquitously expressed in various types of cells, including glia, but causes selective neurodegeneration. Our recent study demonstrated that expression of the N-terminal mutant htt with a large polyQ repeat (160Q) in astrocytes is sufficient to induce neurological symptoms in mice (Bradford, J., Shin, J. Y., Roberts, M., Wang, C. E., Li, X.-J., and Li, S. H. (2009) Proc. Natl. Acad. Sci. U.S.A. 106, 22480-22485). Because glia-neuron interactions are critical for maintaining the normal function and survival of neurons in the brain and because mutant htt is more abundant in neurons than in glial cells, it is important to investigate whether glial htt can still contribute to HD pathology when mutant htt is abundantly expressed in neuronal cells. We generated transgenic mice that express mutant htt with 98Q in astrocytes. Unlike our recently generated htt-160Q transgenic mice, htt-98Q mice do not show obvious neurological phenotypes, suggesting that the length of the polyQ repeat determines the severity of glial dysfunction. However, htt-98Q mice show increased susceptibility to glutamate-induced seizure. Mice expressing mutant htt in astrocytes were mated with N171-82Q mice that express mutant htt primarily in neuronal cells. Double transgenic mice expressing mutant htt in both neuronal and glial cells display more severe neurological symptoms and earlier death than N171-82Q mice. These findings indicate a role of glial mutant htt in exacerbating HD neuropathology and underscore the importance of improving glial function in treating HD.
| S-EPMC2856273 | biostudies-literature
Project description:Animal personality and individuality are intensively researched in vertebrates and both concepts are increasingly applied to behavioral science in insects. However, only few studies have looked into individuality with respect to performance in learning and memory tasks. In vertebrates, individual learning capabilities vary considerably with respect to learning speed and learning rate. Likewise, honeybees express individual learning abilities in a wide range of classical conditioning protocols. Here, we study individuality in the learning and memory performance of cockroaches, both in classical and operant conditioning tasks. We implemented a novel classical (olfactory) conditioning paradigm where the conditioned response is established in the maxilla-labia response (MLR). Operant spatial learning was investigated in a forced two-choice task using a T-maze. Our results confirm individual learning abilities in classical conditioning of cockroaches that was reported for honeybees and vertebrates but contrast long-standing reports on stochastic learning behavior in fruit flies. In our experiments, most learners expressed a correct behavior after only a single learning trial showing a consistent high performance during training and test. We can further show that individual learning differences in insects are not limited to classical conditioning but equally appear in operant conditioning of the cockroach.
| S-EPMC6960104 | biostudies-literature
Project description:Quantitation of huntingtin protein in the brain is needed, both as a marker of Huntington disease (HD) progression and for use in clinical gene silencing trials. Measurement of huntingtin in cerebrospinal fluid could be a biomarker of brain huntingtin, but traditional protein quantitation methods have failed to detect huntingtin in cerebrospinal fluid. Using micro-bead based immunoprecipitation and flow cytometry (IP-FCM), we have developed a highly sensitive mutant huntingtin detection assay. The sensitivity of huntingtin IP-FCM enables accurate detection of mutant huntingtin protein in the cerebrospinal fluid of HD patients and model mice, demonstrating that mutant huntingtin levels in cerebrospinal fluid reflect brain levels, increasing with disease stage and decreasing following brain huntingtin suppression. This technique has potential applications as a research tool and as a clinical biomarker.
| S-EPMC4502413 | biostudies-literature