Pharmacological PINK1 activation ameliorates Pathology in Parkinson's Disease models

PINK1 loss-of-function mutations and exposure to mitochondrial toxins are causative for Parkinson's disease (PD) and Parkinsonism, respectively. We demonstrate that pathological α-synuclein deposition, the hallmark pathology of idiopathic PD, induces mitochondrial dysfunction, and impairs mitophagy as evidenced by the accumulation of the PINK1 substrate pS65-Ubiquitin (pUb). We discovered MTK458, a brain penetrant small molecule that binds to PINK1 and stabilizes its active complex, resulting in increased rates of mitophagy. Treatment with MTK458 mediates clearance of accumulated pUb and α-synuclein pathology in α-synuclein pathology models in vitro and in vivo. Our findings from preclinical PD models suggest that pharmacological activation of PINK1 warrants further clinical evaluation as a therapeutic strategy for disease modification in PD.

Pharmacological PINK1 activation ameliorates Pathology in Parkinson's Disease models

PINK1 loss-of-function mutations and exposure to mitochondrial toxins are causative for Parkinson's disease (PD) and Parkinsonism, respectively. We demonstrate that pathological α-synuclein deposition, the hallmark pathology of idiopathic PD, induces mitochondrial dysfunction and impairs mitophagy, driving accumulation of the PINK1 substrate pS65-Ubiquitin (pUb) in primary neurons and in vivo. We synthesized MTK458, a brain penetrant small molecule that binds to PINK1 and stabilizes an active heterocomplex, thereby increasing mitophagy. MTK458 mediates clearance of α-synuclein pathology in PFF seeding models in vitro and in vivo and reduces pUb. We developed an ultrasensitive assay to quantify pUb levels in plasma and observed an increase in pUb in PD subjects that correlates with disease progression, paralleling our observations in PD models. Our combined findings from preclinical PD models and patient biofluids suggest that pharmacological activation of PINK1 is worthy of further study as a therapeutic strategy for disease modification in PD.

Highlights

Discovery of a plasma Parkinson's Disease biomarker candidate, pS65-Ubiquitin (pUb)Plasma pUb levels correlate with disease status and progression in PD patients.Identification of a potent, brain penetrant PINK1 activator, MTK458MTK458 selectively activates PINK1 by stimulating dimerization and stabilization of the PINK1/TOM complexMTK458 drives clearance of α-synuclein pathology and normalizes pUb in in vivo Parkinson's models.

Optical ultrasound (OpUS): a novel concept for intravascular imaging

Aims

To evaluate whether Optical Ultrasound (OpUS), a novel method for performing ultrasound imaging, could provide compelling, real-time visualizations of coronary vasculature.

Methods and results

With current commercial intravascular ultrasound (IVUS) devices, piezoelectric transducers are used to electrically generate and receive Ultrasound (US). With this paradigm, there are several challenges that limit further improvement in image resolution. Firstly, with increasing miniaturization of these piezoelectric transducers it can be difficult to achieve adequate sensitivity and bandwidth for high resolution imaging. Secondly, the complexities associated with fabricating and electrically connectorising broadband piezocomposite transducers can result in high manufacturing costs. Lastly, with increasing interest in identifying the molecular composition of atherosclerotic plaque, it has been challenging to achieve high resolution and high imaging depths, whilst also allowing for hybrid imaging with photoacoustics (PA) or near-infrared spectroscopy (NIRS).

With OpUS, US is generated at the surface of a fibre optic transducer via the photoacoustic effect. Here, pulsed or modulated light from a laser source is transmitted along the fibre, absorbed in a coating on the fibre surface and converted to thermal energy. The subsequent heat rise leads to a corresponding pressure rise within the coating which propagates as ultrasound. This process is facilitated through the use of custom, engineered nanocomposite materials comprising an optical absorber with an elastomeric host. US reflections from tissue are received with optical interferometry in a method similar to optical coherence tomography (OCT) signal interrogation. For this study we included these elements into a probe and imaged ex-vivo coronary artery tissue. A novel, optically-selective nanocomposite coating enabled concurrent OpUS and PA imaging for molecular contrast using the same imaging probe.

Using OpUS we demonstrated high resolution imaging (<40 microns axial), large imaging depths (>2 cm) of coronary tissue and performed a comparison with histology. Numerous features of atherosclerotic plaque were identifiable, including a lipid pool, a calcified nodule, and the different layers comprising the vessel wall. The fiber-optic transducer generated ultra-high pressures and bandwidths: 21.5 MPa and 39.8 MHz respectively. Hybrid imaging using OpUS and PA was also demonstrated, highlighting regions with high lipid content.

Conclusion

This new platform for intravascular imaging offers high resolution equivalent to 60 Mhz high-definition IVUS whilst maintaining deep tissue penetration. Hybrid imaging with PA can be used for directly visualizing lipid plaque. OpUS transducers are highly flexible, with small diameters (<400 microns) and have low fabrication costs, making them well suited for incorporation into interventional devices.

Funding Acknowledgement

Type of funding source: Private grant(s) and/or Sponsorship. Main funding source(s): Wellcome Trust/EPSRC, National Institute for Health Research Biomedical Research Centre - University College London

Automated Spatially Targeted Optical Microproteomics (autoSTOMP) to Determine Protein Complexity of Subcellular Structures

Spatially targeted optical microproteomics (STOMP) is a method to study region-specific protein complexity in primary cells and tissue samples. STOMP uses a confocal microscope to visualize structures of interest and to tag the proteins within those structures by a photodriven cross-linking reaction so that they can be affinity purified and identified by mass spectrometry (eLife 2015, 4, e09579). However, the use of a custom photo-cross-linker and the requirement for extensive user intervention during sample tagging have posed barriers to the utilization of STOMP. To address these limitations, we built automated STOMP (autoSTOMP) which uses a customizable code in SikuliX to coordinate image capture and cross-linking functions in Zeiss Zen Black with image processing in FIJI. To increase protocol accessibility, we implemented a commercially available biotin-benzophenone photo-cross-linking and purification protocol. Here we demonstrate that autoSTOMP can efficiently label, purify, and identify proteins belonging to 1-2 μm structures in primary human foreskin fibroblasts or mouse bone marrow-derived dendritic cells infected with the protozoan parasite Toxoplasma gondii (Tg). AutoSTOMP can easily be adapted to address a range of research questions using Zeiss Zen Black microscopy systems and LC-MS protocols that are standard in many research cores.

1171Myocardial perfusion mapping in cardiac amyloidosis - exploring the spectrum from infiltration to ischaemia

Background

Cardiac involvement is the main driver of outcome in systemic amyloidosis, but the relationship between amyloid deposits and outcomes is not well understood. The simple explanation of physical, mechanical replacement of the interstitium by amyloid seems insufficient. Preliminary studies support the hypothesis that myocardial ischaemia could contribute to cell damage.

Purpose

(1) To assess myocardial ischaemia in cardiac amyloidosis. (2) To compare patients with cardiac amyloidosis to patients assessed on invasive coronary angiography (ICA) to have normal coronary physiology (NCP), microvascular dysfunction (MVD) and triple vessel coronary disease (3VD). (3) To assess correlation of perfusion mapping to markers of disease severity and prognosis.

Methods

86 patients and 20 healthy volunteers (HV) underwent CMR at 1.5T (Siemens) with standard cine, PSIR-LGE, T1, T2, Extracellular Volume (ECV) mapping and adenosine stress with myocardial blood flow (MBF) mapping. Thirty-eight patients also underwent ICA with 3 vessel assessment of Index of Microcirculatory Resistance and Fractional Flow Reserve: 7 had cardiac amyloidosis, 8 had NCP, 15 had MVD and 8 had 3VD.

Results

Cardiac amyloidosis patients had severe reduction in stress MBF and myocardial perfusion reserve (MPR) (1.22ml/g/min±0.70 and 1.62±0.63) compared to HV (3.21ml/g/min±0.64, p<0.001 and 4.17±0.78, p<0.001), NCP (2.66±0.56, p<0.001 and 2.51±0.43, p=0.036) and MVD (2.10±0.31, p<0.001 and 2.29±0.87, p=0.014) with the degree of reduction being similar only to patients with 3VD (1.44±0.54, p=1.000 and 1.64±0.68, p=1.000) (Figure 1). Rest MBF was also lower in amyloidosis than HV. Cardiac amyloidosis stress MBF and MPR inversely correlated with amyloid burden (ECV, r=−0.715, p<0.001, transmurality of LGE, p<0.01), systolic dysfunction (EF, r=0.405, p<0.01), and blood biomarkers (NT-proBNP (r=−0.678, p<0.001) and Troponin T (r=−0.628, p<0.001)). There was a correlation between stress MBF and native T1 (r=−0.588, p<0.001) but not T2 (p=0.591). Stress MBF and MPR were early disease markers, being elevated in patients with early cardiac amyloid infiltration (raised ECV, no LGE, P<0.01 vs HV).

Conclusion

Myocardial ischaemia is common in cardiac amyloidosis – with stress MBF and MPR similar to that of patients with 3VD. The reduction correlates with the degree of amyloid infiltration and markers of adverse prognosis, highlighting the potential role of myocardial ischaemia as a key mechanism in the pathophysiology of cardiac amyloidosis.

A Novel Destabilizing Domain Based on a Small-Molecule Dependent Fluorophore

Tools that can directly regulate the activity of any protein-of-interest are valuable in the study of complex biological processes. Herein, we describe the development of a novel protein domain that exhibits small molecule-dependent stability and fluorescence based on the bilirubin-inducible fluorescent protein, UnaG. When genetically fused to any protein-of-interest, this fluorescent destabilizing domain (FDD) confers its instability to the entire fusion protein, facilitating the rapid degradation of the fusion. In the presence of its cognate ligand bilirubin (BR), the FDD fusion becomes stable and fluorescent. This new chemical genetic tool allows for rapid, reversible, and tunable control over the stability and fluorescence of a wide range of protein targets.

Substoichiometric inhibition of transthyretin misfolding by immune-targeting sparsely populated misfolding intermediates: a potential diagnostic and therapeutic for TTR amyloidoses

Wild-type and mutant transthyretin (TTR) can misfold and deposit in the heart, peripheral nerves, and other sites causing amyloid disease. Pharmacological chaperones, Tafamidis^® and diflunisal, inhibit TTR misfolding by stabilizing native tetrameric TTR; however, their minimal effective concentration is in the micromolar range. By immune-targeting sparsely populated TTR misfolding intermediates (i.e. monomers), we achieved fibril inhibition at substoichiometric concentrations. We developed an antibody (misTTR) that targets TTR residues 89–97, an epitope buried in the tetramer but exposed in the monomer. Nanomolar misTTR inhibits fibrillogenesis of misfolded TTR under micromolar concentrations. Pan-specific TTR antibodies do not possess such fibril inhibiting properties. We show that selective targeting of misfolding intermediates is an alternative to native state stabilization and requires substoichiometric concentrations. MisTTR or its derivative may have both diagnostic and therapeutic potential.

Determining composition of micron-scale protein deposits in neurodegenerative disease by spatially targeted optical microproteomics

Spatially targeted optical microproteomics (STOMP) is a novel proteomics technique for interrogating micron-scale regions of interest (ROIs) in mammalian tissue, with no requirement for genetic manipulation. Methanol or formalin-fixed specimens are stained with fluorescent dyes or antibodies to visualize ROIs, then soaked in solutions containing the photo-tag: 4-benzoylbenzyl-glycyl-hexahistidine. Confocal imaging along with two photon excitation are used to covalently couple photo-tags to all proteins within each ROI, to a resolution of 0.67 µm in the xy-plane and 1.48 µm axially. After tissue solubilization, photo-tagged proteins are isolated and identified by mass spectrometry. As a test case, we examined amyloid plaques in an Alzheimer's disease (AD) mouse model and a post-mortem AD case, confirming known plaque constituents and discovering new ones. STOMP can be applied to various biological samples including cell lines, primary cell cultures, ex vivo specimens, biopsy samples, and fixed post-mortem tissue.

DOI:http://dx.doi.org/10.7554/eLife.09579.001

Neurodegenerative diseases such as Alzheimer's disease affect millions of people worldwide. In many of these diseases, toxic proteins accumulate in the brain and build up as small ‘plaques’ in the gaps, or synapses, that cells called neurons communicate across. Eventually, the plaques prevent the neurons signaling to each other correctly, leading to problems such as memory loss.

Identifying the proteins present in plaques is technically challenging, partly because the plaques are very small. Hadley, Rakhit et al. have now developed a new method called spatially targeted optical microproteomics (or STOMP) that can collect proteins from small areas of cells. In this method, plaques are identified under a light microscope, and their contents are attached to a molecule called a photo-affinity tag using lasers. The photo-tagged proteins are then pulled out using beads that specifically bind to the photo-affinity tag. The proteins can then be identified using a well-established method called mass spectrometry.

Hadley, Rakhit et al. used STOMP to analyze plaques present in the brains of mice that develop similar symptoms to those seen in humans with Alzheimer's disease. This revealed that these plaques contain more than 50 different proteins, some of which had not previously been found in plaques. In particular, several proteins from the ‘presynaptic’ neuron that sends signals across the synapse were found in the plaques. However, no proteins from the receiving (‘postsynaptic’) neuron on the other side of the synapse were present in the plaque.

Fixed human brain tissue is more difficult to analyze than mouse samples because it is modified for storage. In spite of these issues, Hadley, Rakhit et al. successfully also used STOMP to identify the proteins in human plaques. STOMP can be used to identify the proteins present in any area of a cell and thus has the potential to be widely used by scientists, not just those studying plaques.

DOI:http://dx.doi.org/10.7554/eLife.09579.002

General method for regulating protein stability with light

Post-translational regulation of protein abundance in cells is a powerful tool for studying protein function. Here, we describe a novel genetically encoded protein domain that is degraded upon exposure to nontoxic blue light. We demonstrate that fusion proteins containing this domain are rapidly degraded in cultured cells and in zebrafish upon illumination.

Ligand-switchable substrates for a ubiquitin-proteasome system

Cellular maintenance of protein homeostasis is essential for normal cellular function. The ubiquitin-proteasome system (UPS) plays a central role in processing cellular proteins destined for degradation, but little is currently known about how misfolded cytosolic proteins are recognized by protein quality control machinery and targeted to the UPS for degradation in mammalian cells. Destabilizing domains (DDs) are small protein domains that are unstable and degraded in the absence of ligand, but whose stability is rescued by binding to a high affinity cell-permeable ligand. In the work presented here, we investigate the biophysical properties and cellular fates of a panel of FKBP12 mutants displaying a range of stabilities when expressed in mammalian cells. Our findings correlate observed cellular instability to both the propensity of the protein domain to unfold in vitro and the extent of ubiquitination of the protein in the non-permissive (ligand-free) state. We propose a model in which removal of stabilizing ligand causes the DD to unfold and be rapidly ubiquitinated by the UPS for degradation at the proteasome. The conditional nature of DD stability allows a rapid and non-perturbing switch from stable protein to unstable UPS substrate unlike other methods currently used to interrogate protein quality control, providing tunable control of degradation rates.

Evaluation of FKBP and DHFR based destabilizing domains in Saccharomyces cerevisiae

Two orthogonal destabilizing domains have been developed based on mutants of human FKBP12 as well as bacterial DHFR and these engineered domains have been used to control protein concentration in a variety of contexts in vitro and in vivo. FKBP12 based destabilizing domains cannot be rescued in the yeast Saccharomyces cerevisiae; ecDHFR based destabilizing domains are not degraded as efficiently in S. cerevisiae as in mammalian cells or Plasmodium, but provide a starting point for the development of domains with increased signal-to-noise in S. cerevisiae.

An immunological epitope selective for pathological monomer-misfolded SOD1 in ALS

Misfolding of Cu/Zn-superoxide dismutase (SOD1) is emerging as a mechanism underlying motor neuron degeneration in individuals with amyotrophic lateral sclerosis (ALS) who carry a mutant SOD1 gene (SOD1 ALS). Here we describe a structure-guided approach to developing an antibody that specifically recognizes monomer-misfolded forms of SOD1. We raised this antibody to an epitope that is normally buried in the SOD1 native homodimer interface. The SOD1 exposed dimer interface (SEDI) antibody recognizes only those SOD1 conformations in which the native dimer is disrupted or misfolded and thereby exposes the hydrophobic dimer interface. Using the SEDI antibody, we established the presence of monomer-misfolded SOD1 in three ALS mouse models, with G37R, G85R and G93A SOD1 mutations, and in a human individual with an A4V SOD1 mutation. Despite ubiquitous expression, misfolded SOD1 was found primarily within degenerating motor neurons. Misfolded SOD1 appeared before the onset of symptoms and decreased at the end stage of the disease, concomitant with motor neuron loss.

Structure, folding, and misfolding of Cu,Zn superoxide dismutase in amyotrophic lateral sclerosis

Fourteen years after the discovery that mutations in Cu, Zn superoxide dismutase (SOD1) cause a subset of familial amyotrophic lateral sclerosis (fALS), the mechanism by which mutant SOD1 exerts toxicity remains unknown. The two principle hypotheses are (a) oxidative damage stemming from aberrant SOD1 redox chemistry, and (b) misfolding of the mutant protein. Here we review the structure and function of wild-type SOD1, as well as the changes to the structure and function in mutant SOD1. The relative merits of the two hypotheses are compared and a common unifying principle is outlined. Lastly, the potential for therapies targeting SOD1 misfolding is discussed.

Monomeric Cu,Zn-superoxide dismutase is a common misfolding intermediate in the oxidation models of sporadic and familial amyotrophic lateral sclerosis

Proteinacious intracellular aggregates in motor neurons are a key feature of both sporadic and familial amyotrophic lateral sclerosis (ALS). These inclusion bodies are often immunoreactive for Cu,Zn-superoxide dismutase (SOD1) and are implicated in the pathology of ALS. On the basis of this and a similar clinical presentation of symptoms in the familial (fALS) and sporadic forms of ALS, we sought to investigate the possibility that there exists a common disease-related aggregation pathway for fALS-associated mutant SODs and wild type SOD1. We have previously shown that oxidation of fALS-associated mutant SODs produces aggregates that have the same morphological, structural, and tinctorial features as those found in SOD1 inclusion bodies in ALS. Here, we show that oxidative damage of wild type SOD at physiological concentrations ( approximately 40 microm) results in destabilization and aggregation in vitro. Oxidation of either mutant or wild type SOD1 causes the enzyme to dissociate to monomers prior to aggregation. Only small changes in secondary and tertiary structure are associated with monomer formation. These results indicate a common aggregation prone monomeric intermediate for wild type and fALS-associated mutant SODs and provides a link between sporadic and familial ALS.

Oxidation-induced misfolding and aggregation of superoxide dismutase and its implications for amyotrophic lateral sclerosis

The presence of intracellular aggregates that contain Cu/Zn superoxide dismutase (SOD1) in spinal cord motor neurons is a pathological hallmark of amyotrophic lateral sclerosis (ALS). Although SOD1 is abundant in all cells, its half-life in motor neurons far exceeds that in any other cell type. On the basis of the premise that the long half-life of the protein increases the potential for oxidative damage, we investigated the effects of oxidation on misfolding/aggregation of SOD1 and ALS-associated SOD1 mutants. Zinc-deficient wild-type SOD1 and SOD1 mutants were extremely prone to form visible aggregates upon oxidation as compared with wild-type holo-protein. Oxidation of select histidine residues that bind metals in the active site mediates SOD1 aggregation. Our results provide a plausible model to explain the accumulation of SOD1 aggregates in motor neurons affected in ALS.

Raised factor VIII is associated with coronary thrombotic events

Coagulation is triggered during the onset of myocardial infarction, resulting in vascular occlusion. However, a causal role for individual haemostatic factors in the development of thrombotic occlusion is not established. Three cases (all relatively young women) are reported of raised factor VIII associated with myocardial infarction. Two patients presented acutely with myocardial infarction at a relatively young age with no preceding history of angina. The other patient had had venous thrombosis when young and activated protein C resistance (APCR), without the presence of factor V Leiden. A functional relation exists between APCR and factor VIII; therefore, raised factor VIII may contribute to APCR and the increased thrombotic risk in patients without factor V Leiden. Factor VIII is an important risk factor for atherothrombotic events, including sudden death, in patients with vascular disease. These cases support the association of raised factor VIII with acute thrombotic events, even in patients without significant underlying atheromatous disease.