α-Synuclein strains cause distinct synucleinopathies after local and systemic administration

W. Peelaerts, L. Bousset, A. Van der Perren, A. Moskalyuk, R. Pulizzi, M. Giugliano, C. Van den Haute, R. Melki and V. Baekelandt

Misfolded protein aggregates represent a continuum with overlapping features in neurodegenerative diseases, but differences in protein components and affected brain regions1. The molecular hallmark of synucleinopathies such as Parkinson’s disease, dementia with Lewy bodies and multiple system atrophy are megadalton α-synuclein-rich deposits suggestive of one molecular event causing distinct disease phenotypes. Glial α-synuclein (α-SYN) filamentous deposits are prominent in multiple system atrophy and neuronal α-SYN inclusions are found in Parkinson’s disease and dementia with Lewy bodies2. The discovery of α-SYN assemblies with different structural characteristics or ‘strains’ has led to the hypothesis that strains could account for the different clinico-pathological traits within synucleinopathies3, 4. In this study we show that α-SYN strain conformation and seeding propensity lead to distinct histopathological and behavioural phenotypes. We assess the properties of structurally well-defined α-SYN assemblies (oligomers, ribbons and fibrils) after injection in rat brain. We prove that α-SYN strains amplify in vivo. Fibrils seem to be the major toxic strain, resulting in progressive motor impairment and cell death, whereas ribbons cause a distinct histopathological phenotype displaying Parkinson’s disease and multiple system atrophy traits. Additionally, we show that α-SYN assemblies cross the blood–brain barrier and distribute to the central nervous system after intravenous injection. Our results demonstrate that distinct α-SYN strains display differential seeding capacities, inducing strain-specific pathology and neurotoxic phenotypes.

DOI

Journal:Nature

A DNA-based molecular probe for optically reporting cellular traction forces

Brandon L Blakely, Christoph E Dumelin, Britta Trappmann, Lynn M McGregor, Colin K Choi, Peter C Anthony, Van K Duesterberg, Brendon M Baker, Steven M Block, David R Liu, and Christopher S Chen

We developed molecular tension probes (TPs) that report traction forces of adherent cells with high spatial resolution, can in principle be linked to virtually any surface, and obviate monitoring deformations of elastic substrates. TPs consist of DNA hairpins conjugated to fluorophore-quencher pairs that unfold and fluoresce when subjected to specific forces. We applied TPs to reveal that cellular traction forces are heterogeneous within focal adhesions and localized at their distal edges.

DOI

Journal: Nature Methods

Protein folding: Turbo-charged crosslinking

David J. Craik

The efficient production of stable bioactive proteins often requires the selective formation of several disulfide crosslinks. Two recent studies have now shown that replacing cysteine with selenocysteine in the unfolded protein can autocatalyse the formation of the desired crosslinks.

DOI

Journal: Nature Chemistry

HSF-1–mediated cytoskeletal integrity determines thermotolerance and life span

Nathan A. Baird, Peter M. Douglas1, Milos S. Simic, Ana R. Grant, James J. Moresco, Suzanne C. Wolff, John R. Yates III, Gerard Manning, Andrew Dillin

The conserved heat shock transcription factor–1 (HSF-1) is essential to cellular stress resistance and life-span determination. The canonical function of HSF-1 is to regulate a network of genes encoding molecular chaperones that protect proteins from damage caused by extrinsic environmental stress or intrinsic age-related deterioration. In Caenorhabditis elegans, we engineered a modified HSF-1 strain that increased stress resistance and longevity without enhanced chaperone induction. This health assurance acted through the regulation of the calcium-binding protein PAT-10. Loss of pat-10 caused a collapse of the actin cytoskeleton, stress resistance, and life span. Furthermore, overexpression of pat-10 increased actin filament stability, thermotolerance, and longevity, indicating that in addition to chaperone regulation, HSF-1 has a prominent role in cytoskeletal integrity, ensuring cellular function during stress and aging.

DOI

Journal: Science

A long noncoding RNA protects the heart from pathological hypertrophy

Pei Han, Wei Li, Chiou-Hong Lin, Jin Yang, Ching Shang, Sylvia T. Nuernberg, Kevin Kai Jin, Weihong Xu, Chieh-Yu Lin, Chien-Jung Lin, Yiqin Xiong, Huan-Chieh Chien, Bin Zhou, Euan Ashley, Daniel Bernstein, Peng-Sheng Chen, Huei-Sheng Vincent Chen, Thomas Quertermous, and  Ching-Pin Chang

The role of long noncoding RNA (lncRNA) in adult hearts is unknown; also unclear is how lncRNA modulates nucleosome remodelling. An estimated 70% of mouse genes undergo antisense transcription1, including myosin heavy chain 7 (Myh7), which encodes molecular motor proteins for heart contraction2. Here we identify a cluster of lncRNA transcripts from Myh7 loci and demonstrate a new lncRNA–chromatin mechanism for heart failure. In mice, these transcripts, which we named myosin heavy-chain-associated RNA transcripts (Myheart, or Mhrt), are cardiac-specific and abundant in adult hearts. Pathological stress activates the Brg1–Hdac–Parp chromatin repressor complex3 to inhibit Mhrt transcription in the heart. Such stress-induced Mhrt repression is essential for cardiomyopathy to develop: restoring Mhrt to the pre-stress level protects the heart from hypertrophy and failure. Mhrt antagonizes the function of Brg1, a chromatin-remodelling factor that is activated by stress to trigger aberrant gene expression and cardiac myopathy3. Mhrt prevents Brg1 from recognizing its genomic DNA targets, thus inhibiting chromatin targeting and gene regulation by Brg1. It does so by binding to the helicase domain of Brg1, a domain that is crucial for tethering Brg1 to chromatinized DNA targets. Brg1 helicase has dual nucleic-acid-binding specificities: it is capable of binding lncRNA (Mhrt) and chromatinized—but not naked—DNA. This dual-binding feature of helicase enables a competitive inhibition mechanism by which Mhrt sequesters Brg1 from its genomic DNA targets to prevent chromatin remodelling. A Mhrt–Brg1 feedback circuit is thus crucial for heart function. Human MHRT also originates from MYH7 loci and is repressed in various types of myopathic hearts, suggesting a conserved lncRNA mechanism in human cardiomyopathy. Our studies identify a cardioprotective lncRNA, define a new targeting mechanism for ATP-dependent chromatin-remodelling factors, and establish a new paradigm for lncRNA–chromatin interaction.

DOI

Journal: Nature

DNA unwinding heterogeneity by RecBCD results from static molecules able to equilibrate

Bian Liu, Ronald J. Baskin, and Stephen C. Kowalczykowski

Single-molecule studies can overcome the complications of asynchrony and ensemble-averaging in bulk-phase measurements, provide mechanistic insights into molecular activities, and reveal interesting variations between individual molecules1, 2, 3. The application of these techniques to the RecBCD helicase of Escherichia coli has resolved some long-standing discrepancies, and has provided otherwise unattainable mechanistic insights into its enzymatic behaviour4, 5, 6. Enigmatically, the DNA unwinding rates of individual enzyme molecules are seen to vary considerably6, 7, 8, but the origin of this heterogeneity remains unknown. Here we investigate the physical basis for this behaviour. Although any individual RecBCD molecule unwound DNA at a constant rate for an average of approximately 30,000 steps, we discover that transiently halting a single enzyme–DNA complex by depleting Mg2+-ATP could change the subsequent rates of DNA unwinding by that enzyme after reintroduction to ligand. The proportion of molecules that changed rate increased exponentially with the duration of the interruption, with a half-life of approximately 1 second, suggesting that a conformational change occurred during the time that the molecule was arrested. The velocity after pausing an individual molecule was any velocity found in the starting distribution of the ensemble. We suggest that substrate binding stabilizes the enzyme in one of many equilibrium conformational sub-states that determine the rate-limiting translocation behaviour of each RecBCD molecule. Each stabilized sub-state can persist for the duration (approximately 1 minute) of processive unwinding of a DNA molecule, comprising tens of thousands of catalytic steps, each of which is much faster than the time needed for the conformational change required to alter kinetic behaviour. This ligand-dependent stabilization of rate-defining conformational sub-states results in seemingly static molecule-to-molecule variation in RecBCD helicase activity, but in fact reflects one microstate from the equilibrium ensemble that a single molecule manifests during an individual processive translocation event.

DOI

Journal: Nature

Ultrastable atomic force microscopy: Improved force and positional stability

Allison B. Churnside, Thomas T. Perkins

Atomic force microscopy (AFM) is an exciting technique for biophysical studies of single molecules, but its usefulness is limited by instrumental drift. We dramatically reduced positional drift by adding two lasers to track and thereby actively stabilize the tip and the surface. These lasers also enabled label-free optical images that were spatially aligned to the tip position. Finally, sub-pN force stability over 100 s was achieved by removing the gold coating from soft cantilevers. These enhancements to AFM instrumentation can immediately benefit research in biophysics and nanoscience.

DOI

Journal: Febs Letters