Prion infections cause lethal neurodegeneration. This process requires the cellular prion protein (PrP(C); ref. 1), which contains a globular domain hinged to a long amino-proximal flexible tail. Here we describe rapid neurotoxicity in mice and cerebellar organotypic cultured slices exposed to ligands targeting the 1 and 3 helices of the PrP(C) globular domain. Ligands included seven distinct monoclonal antibodies, monovalent Fab1 fragments and recombinant single-chain variable fragment miniantibodies. Similar to prion infections, the toxicity of globular domain ligands required neuronal PrP(C), was exacerbated by PrP(C) overexpression, was associated with calpain activation and was antagonized by calpain inhibitors. Neurodegeneration was accompanied by a burst of reactive oxygen species, and was suppressed by antioxidants. Furthermore, genetic ablation of the superoxide-producing enzyme NOX2 (also known as CYBB) protected mice from globular domain ligand toxicity. We also found that neurotoxicity was prevented by deletions of the octapeptide repeats within the flexible tail. These deletions did not appreciably compromise globular domain antibody binding, suggesting that the flexible tail is required to transmit toxic signals that originate from the globular domain and trigger oxidative stress and calpain activation. Supporting this view, various octapeptide ligands were not only innocuous to both cerebellar organotypic cultured slices and mice, but also prevented the toxicity of globular domain ligands while not interfering with their binding. We conclude that PrP(C) consists of two functionally distinct modules, with the globular domain and the flexible tail exerting regulatory and executive functions, respectively. Octapeptide ligands also prolonged the life of mice expressing the toxic PrP(C) mutant, PrP(Δ94-134), indicating that the flexible tail mediates toxicity in two distinct PrP(C)-related conditions. Flexible tail-mediated toxicity may conceivably play a role in further prion pathologies, such as familial Creutzfeldt-Jakob disease in humans bearing supernumerary octapeptides. (Fig. 1b). None of three high-affinity antibodies to the octapeptide repeats (OR, residues 50-90 embedded within the FT) were neurotoxic (Fig. 1b). Antibodies POM3 and D13, which bind the "charged cluster-2" 11 (CC2, residues 95-110), were innocuous at 67 nM but neurotoxic at 200 nM (Fig. 1b). None of the tested antibodies were toxic to Prnp o/o COCS ( Supplementary Fig. 2a). The identity of the targeted epitopes appeared to be a better predictor of PrP C antibody toxicity than their affinity to PrP C , suggesting that neurotoxicity resulted from the interaction of antibodies with specific PrP C domains (Supplementary Table 2).The mechanisms of neurotoxicity were further explored using POM1, a highly toxic antibody targeting the GD. Wild-type (wt) and tga20 COCS lost most granule cells (CGC) within 28 and 14 days post-exposure (dpe) to POM1, respectively (Fig. 2a-c). Controls included POM1-treated Prnp o/o COCS 12 , t...
To expand the range of experiments that are accessible with optogenetics, we developed a photocleavable protein (PhoCl) that spontaneously dissociates into two fragments after violet-light-induced cleavage of a specific bond in the protein backbone. We demonstrated that PhoCl can be used to engineer light-activatable Cre recombinase, Gal4 transcription factor, and a viral protease that in turn was used to activate opening of the large-pore ion channel Pannexin-1.
Optical imaging probes have played a major role in detecting and monitoring a variety of diseases. In particular, nonlinear optical imaging probes, such as second harmonic generating (SHG) nanoprobes, hold great promise as clinical contrast agents, as they can be imaged with little background signal and unmatched long-term photostability. As their chemical composition often includes transition metals, the use of inorganic SHG nanoprobes can raise long-term health concerns. Ideally, contrast agents for biomedical applications should be degraded in vivo without any long-term toxicological consequences to the organism. Here, we developed biodegradable harmonophores (bioharmonophores) that consist of polymer-encapsulated, self-assembling peptides that generate a strong SHG signal. When functionalized with tumor cell surface markers, these reporters can target single cancer cells with high detection sensitivity in zebrafish embryos in vivo . Thus, bioharmonophores will enable an innovative approach to cancer treatment using targeted high-resolution optical imaging for diagnostics and therapy.
16Mechanosensing is a ubiquitous process to translate external mechanical 17 stimuli into biological responses during development, homeostasis, and disease. 18However, non-invasive investigation of cellular mechanosensing in complex and 19 intact live tissue remains challenging. Here, we developed GenEPi, a genetically-20 encoded fluorescent intensiometric reporter for mechanical stimuli based on 21Piezo1, an essential mechanosensitive ion channel found in vertebrates. We show 22that GenEPi has high specificity and spatiotemporal resolution for Piezo1-23 dependent mechanical stimuli, exemplified by resolving repetitive mechanical 24 stimuli of spontaneously contracting cardiomyocytes within microtissues, in a non-25 invasive manner. 26 27
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