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Live-cell microscopy imaging typically involves the use of high-quality glass-bottom chambers that allow cell culture, gaseous buffer exchange and optical properties suitable for microscopy applications. However, commercial sources of these chambers can add significant annual costs to cell biology laboratories. Consumer products in three-dimensional printing technology, for both Filament Deposition Modeling (FDM) and Masked Stereo Lithography (MSLA), have resulted in more biomedical research labs adopting the use of these devices for prototyping and manufacturing of lab plastic-based items, but rarely consumables. Here we describe a modular, live-cell chamber with multiple design options that can be mixed per experiment. Single reusable carriers and the use of biodegradable plastics, in a hybrid of FDM and MSLA manufacturing methods, reduce plastic waste. The system is easy to adapt to bespoke designs, with concept-to-prototype in a single day, offers significant cost savings to the users over commercial sources, and no loss in dimensional quality or reliability.

Live-cell microscopy imaging typically involves the use of high-quality glass-bottom chambers that allow cell culture, gaseous buffer exchange and optical properties suitable for microscopy applications. However, commercial sources of these chambers can add significant annual costs to cell biology laboratories. Consumer products in three-dimensional printing technology, for both Filament Deposition Modeling (FDM) and Masked Stereo Lithography (MSLA), have resulted in more biomedical research labs adopting the use of these devices for prototyping and manufacturing of lab plastic-based items, but rarely consumables. Here we describe a modular, live-cell chamber with multiple design options that can be mixed per experiment. Single reusable carriers and the use of biodegradable plastics, in a hybrid of FDM and MSLA manufacturing methods, reduce plastic waste. The system is easy to adapt to bespoke designs, with concept-to-prototype in a single day, offers significant cost savings to the users over commercial sources, and no loss in dimensional quality or reliability.

Huntington’s disease results from expansion of a glutamine-coding CAG tract in the huntingtin (HTT) gene, producing an aberrantly functioning form of HTT. Both wildtype and disease-state HTT form a hetero-dimer with HAP40 of unknown functional relevance. We demonstrate in vivo and in cell models that HTT and HAP40 cellular abundance are coupled. Integrating data from a 2.6 Å cryo-electron microscopy structure, cross-linking mass spectrometry, small-angle X-ray scattering, and modeling, we provide a near-atomic-level view of HTT, its molecular interaction surfaces and compacted domain architecture, orchestrated by HAP40. Native mass spectrometry reveals a remarkably stable hetero-dimer, potentially explaining the cellular inter-dependence of HTT and HAP40. The exon 1 region of HTT is dynamic but shows greater conformational variety in the polyglutamine expanded mutant than wildtype exon 1. Our data provide a foundation for future functional and drug discovery studies targeting Huntington’s disease and illuminate the structural consequences of HTT polyglutamine expansion.Harding et al. present a biophysical and structural characterization of the complex between huntingtin (HTT) and HAP40 proteins. They show that the abundance of HAP40 is coupled with that of HTT and that there is greater conformational variety in the exon 1 of the mutant HTT than WT, important for the future drug discovery studies targeting Huntington’s disease.

Huntington disease (HD) is a genetic neurodegenerative disease caused by CAG expansion in the Huntingtin (HTT) gene, translating to an expanded polyglutamine tract in the huntingtin (HTT) protein. Age at disease onset correlates to CAG repeat length but varies by decades between individuals with identical repeat lengths. Genome-wide association studies link HD modification to DNA repair and mitochondrial health pathways. Clinical studies show elevated DNA damage in HD, even at the premanifest stage. A major DNA repair node influencing neurodegenerative disease is the PARP pathway. Accumulation of poly ADP-ribose (PAR) has been implicated in Alzheimer and Parkinson diseases, as well as cerebellar ataxia. We report that HD mutation carriers have lower cerebrospinal fluid PAR levels than healthy controls, starting at the premanifest stage. Human HD iPSC-derived neurons and patient- derived fibroblasts have diminished PAR response in the context of elevated DNA damage. We have defined a PAR-binding motif in huntingtin, detected huntingtin complexed with PARylated proteins in human cells during stress, and localized huntingtin to mitotic chromosomes upon inhibition of PAR degradation. Direct huntingtin PAR binding was measured by fluorescence polarization and visualized by atomic force microscopy at the single molecule level. While wild type and mutant huntingtin did not differ in their PAR binding ability, purified wild type huntingtin protein increased in vitro PARP1 activity while mutant huntingtin did not. These results provide insight into an early molecular mechanism of HD, suggesting possible targets for the design of early preventive therapies. A consensus on dysfunctional DNA repair has emerged in neurodegenerative disease research, with elevated poly ADP-ribose (PAR) signaling more recently implicated. In contrast, we have identified a deficient PAR response in Huntington’s disease (HD) patient spinal fluid samples and cells. This may be explained by the inability of huntingtin protein bearing the HD-causing mutation to stimulate production of PAR the way the wild type protein does. Since drugs that target PAR production and degradation have already been developed, these findings present an exciting avenue for therapeutic intervention for HD.

Huntington disease (HD) is an autosomal dominant genetic neurodegenerative disease caused by a CAG expansion in the Huntingtin (HTT) gene, translating to an expanded polyglutamine tract in the huntingtin (HTT) protein. Age at disease onset is correlated to CAG repeat length, but varies by decades between individuals with identical repeat lengths. Genome-wide association studies link HD modification to DNA repair and mitochondrial health pathways. Recent clinical studies show elevated DNA damage in HD, even at the premanifest stage of disease. One of the major DNA repair nodes influencing neurodegenerative disease is the PARP pathway. Accumulation of poly ADP-ribose (PAR), produced by PARP1 and PARP2, has been implicated in the pathology of Alzheimers and Parkinsons diseases, as well as autosomal recessive cerebellar ataxia. We report that HD mutation carriers have lower cerebrospinal fluid PAR levels than healthy controls, starting at the premanifest stage. Patient-derived fibroblasts have reduced PARP1/2 activity and elevated DNA damage, while elevated PAR levels are only revealed upon inhibition of PAR degradation. These phenotypes are rescued by moderate huntingtin level reduction via the huntingtin-lowering splice modulator drug, LMI070 (Branaplam). As a direct mechanism, we have defined a PAR-binding motif in huntingtin, detected huntingtin complexed with PARylated proteins in human cells during stress, and localized huntingtin to mitotic chromosomes upon inhibition of PAR degradation. Direct huntingtin PAR binding was measured by fluorescence polarization and visualized by atomic force microscopy. These results provide insight into a very early molecular mechanism of HD, suggesting possible targets in HD to design early preventive therapies.Competing Interest StatementRT is a consultant to Novartis AG. EJW reports consultancy / advisory board memberships with Annexon, Remix Therapeutics, Hoffman La Roche Ltd, Ionis Pharmaceuticals, PTC Therapeutics, Takeda, Teitur Trophics, Triplet Therapeutics and Vico Therapeutics. All honoraria for these consultancies were paid through the offices of UCL Consultants Ltd., a wholly owned subsidiary of University College London. FBR is a Medpace UK Ltd employee and was a University College London employee during the conduct of this study. FBR has provided consultancy services to G.L.G. and F. Hoffmann-La Roche Ltd.