A cell-based assay for rapid assessment of ACE2 catalytic function

Angiotensin-converting enzyme II (ACE2) is a monocarboxypeptidase expressed throughout multiple tissues and its catalysis of bioactive peptides regulates the renin-angiotensin system mediating blood pressure homeostasis. ACE2 is implicated in a variety of diseases, including obesity, diabetes, and cardiovascular diseases, and is the obligate entry receptor for SARS-CoV-2 infection. Disease-associated genetic variants of ACE2 are increasingly being identified but are poorly characterized. To aid this problem, we introduce a fluorometric cell-based assay for evaluating surface-expressed ACE2 catalytic activity that preserves the native glycosylation of the host environment and is amenable to high-throughput analysis of ACE2 variants in multi-well plates. We demonstrate sensitivity to detecting catalysis of the key ACE2 substrates, Angiotensin II, Apelin-13, and des-Arg9-bradykinin, and impact of a catalytically-deficient ACE2 variant. Normalizing catalytic measures to surface ACE2 expression accounts for variability in ACE2 variant transfection, surface delivery or stability. This assay provides a convenient and powerful approach for investigating the catalytic characteristics of ACE2 variants involved in cardiovascular peptide cascades and homeostasis of multiple organs.

CellPalmSeq: A curated RNAseq database of palmitoylating and de-palmitoylating enzyme expression in human cell types and laboratory cell lines

The reversible lipid modification protein S-palmitoylation can dynamically modify the localization, diffusion, function, conformation and physical interactions of substrate proteins. Dysregulated S-palmitoylation is associated with a multitude of human diseases including brain and metabolic disorders, viral infection and cancer. However, the diverse expression patterns of the genes that regulate palmitoylation in the broad range of human cell types are currently unexplored, and their expression in commonly used cell lines that are the workhorse of basic and preclinical research are often overlooked when studying palmitoylation dependent processes. We therefore created CellPalmSeq (https://cellpalmseq.med.ubc.ca), a curated RNAseq database and interactive webtool for visualization of the expression patterns of the genes that regulate palmitoylation across human single cell types, bulk tissue, cancer cell lines and commonly used laboratory non-human cell lines. This resource will allow exploration of these expression patterns, revealing important insights into cellular physiology and disease, and will aid with cell line selection and the interpretation of results when studying important cellular processes that depend on protein S-palmitoylation.

An Algorithm Based on a Cable-Nernst Planck Model Predicting Synaptic Activity throughout the Dendritic Arbor with Micron Specificity

Recent technological advances have enabled the recording of neurons in intact circuits with a high spatial and temporal resolution, creating the need for modeling with the same precision. In particular, the development of ultra-fast two-photon microscopy combined with fluorescence-based genetically-encoded Ca²⁺-indicators allows capture of full-dendritic arbor and somatic responses associated with synaptic input and action potential output. The complexity of dendritic arbor structures and distributed patterns of activity over time results in the generation of incredibly rich 4D datasets that are challenging to analyze (Sakaki et al. in Frontiers in Neural Circuits 14:33, 2020). Interpreting neural activity from fluorescence-based Ca²⁺ biosensors is challenging due to non-linear interactions between several factors influencing intracellular calcium ion concentration and its binding to sensors, including the ionic dynamics driven by diffusion, electrical gradients and voltage-gated conductances. To investigate those dynamics, we designed a model based on a Cable-like equation coupled to the Nernst-Planck equations for ionic fluxes in electrolytes. We employ this model to simulate signal propagation and ionic electrodiffusion across a dendritic arbor. Using these simulation results, we then designed an algorithm to detect synapses from Ca²⁺ imaging datasets. We finally apply this algorithm to experimental Ca²⁺-indicator datasets from neurons expressing jGCaMP7s (Dana et al. in Nature Methods 16:649-657, 2019), using full-dendritic arbor sampling in vivo in the Xenopus laevis optic tectum using fast random-access two-photon microscopy. Our model reproduces the dynamics of visual stimulus-evoked jGCaMP7s-mediated calcium signals observed experimentally, and the resulting algorithm allows prediction of the location of synapses across the dendritic arbor. Our study provides a way to predict synaptic activity and location on dendritic arbors, from fluorescence data in the full dendritic arbor of a neuron recorded in the intact and awake developing vertebrate brain.

Exploring the expression patterns of palmitoylating and de-palmitoylating enzymes in the mouse brain using the curated RNA-seq database BrainPalmSeq

Protein S-palmitoylation is a reversible post-translational lipid modification that plays a critical role in neuronal development and plasticity, while dysregulated S-palmitoylation underlies a number of severe neurological disorders. Dynamic S-palmitoylation is regulated by a large family of ZDHHC palmitoylating enzymes, their accessory proteins, and a small number of known de-palmitoylating enzymes. Here, we curated and analyzed expression data for the proteins that regulate S-palmitoylation from publicly available RNAseq datasets, providing a comprehensive overview of their distribution in the mouse nervous system. We developed a web-tool that enables interactive visualization of the expression patterns for these proteins in the nervous system (http://brainpalmseq.med.ubc.ca/), and explored this resource to find region and cell-type specific expression patterns that give insight into the function of palmitoylating and de-palmitoylating enzymes in the brain and neurological disorders. We found coordinated expression of ZDHHC enzymes with their accessory proteins, de-palmitoylating enzymes and other brain-expressed genes that included an enrichment of S-palmitoylation substrates. Finally, we utilized ZDHHC expression patterns to predict and validate palmitoylating enzyme-substrate interactions.

Bulk Dye Loading for In Vivo Calcium Imaging of Visual Responses in Populations of Xenopus Tectal Neurons

Bulk loading of neurons with fluorescent calcium indicators in transparent albino Xenopus tadpoles offers a rapid and easy method for tracking sensory-evoked activity in large numbers of neurons within an awake developing brain circuit. In vivo two-photon time-lapse imaging of an image plane through the optic tectum allows defining receptive field properties from visual-evoked responses for studies of single-neuron and network-level encoding and plasticity. Here, we describe loading the Xenopus tadpole optic tectum with the membrane-permeable AM ester of Oregon Green 488 BAPTA-1 (OGB-1 AM) for in vivo imaging experiments.

Quantifying neuronal structural changes over time using dynamic morphometrics

Brain circuit development involves tremendous structural formation and rearrangement of dendrites, axons, and the synaptic connections between them. Direct studies of neuronal morphogenesis are now possible through recent developments in multiple technologies, including single-neuron labeling, time-lapse imaging in intact tissues, and 4D rendering software capable of tracking neural growth over periods spanning minutes to days. These methods allow detailed quantification of structural changes of neurons over time, called dynamic morphometrics, providing new insights into fundamental growth patterns, underlying molecular mechanisms, and the intertwined influences of external factors, including neural activity, and intrinsic genetic programs. Here, we review the methods of dynamic morphometrics sampling and analyses, focusing on their applications to studies of activity-driven dendritogenesis in vertebrate systems.

[Ventilation Patients between Acute Care and Long-term Out-of-Hospital Ventilation - Routine Documentation based Analysis of the Care Situation]

BACKGROUND

 The number of invasive and non-invasive long-term out-of-hospital ventilations has been increasing rapidly for years. At the same time, there is poor information on the quality of care of out-of-hospital ventilated patients. The present investigation was conducted as part of the OVER-BEAS study. The aim of this study was to describe the care situation of weaning patients from admission to discharge from the weaning center using existing routine documentation.

MATERIAL AND METHODS

 In our retrospective analysis, we included all patients admitted in 2018 via the weaning ward of the Thorax Center Münnerstadt. Descriptive analysis of routine data collected as part of quality management was performed. Data sources were the WeanNet database, the discharge letter of the weaning center, and the transfer report of the referring hospital.

RESULTS

 In the studied weaning center, 50.8 % of the patients (n = 31) could be completely weaned from the respirator and extubated or decannulated (category 3aI). If complete weaning was not successful, 75.0 % (n = 21) required the constant presence of specially trained staff or a specialist nurse in the further course. In this case, further care was mostly provided in inpatient care facilities (e. g., ventilator shared living community).

CONCLUSION

 Based on routine documentation, the care situation of weaning patients can be presented and compared with known data. In this way, the outcome quality of a weaning center can be made comparable.

[Ventilation Patients between Acute Care and Long-term Out-of-Hospital Ventilation - Routine Documentation based Analysis of the Care Situation]

BACKGROUND

 The number of invasive and non-invasive long-term out-of-hospital ventilations has been increasing rapidly for years. At the same time, there is poor information on the quality of care of out-of-hospital ventilated patients. The present investigation was conducted as part of the OVER-BEAS study. The aim of this study was to describe the care situation of weaning patients from admission to discharge from the weaning center using existing routine documentation.

MATERIAL AND METHODS

 In our retrospective analysis, we included all patients admitted in 2018 via the weaning ward of the Thorax Center Münnerstadt. Descriptive analysis of routine data collected as part of quality management was performed. Data sources were the WeanNet database, the discharge letter of the weaning center, and the transfer report of the referring hospital.

RESULTS

 In the studied weaning center, 50.8 % of the patients (n = 31) could be completely weaned from the respirator and extubated or decannulated (category 3aI). If complete weaning was not successful, 75.0 % (n = 21) required the constant presence of specially trained staff or a specialist nurse in the further course. In this case, further care was mostly provided in inpatient care facilities (e. g., ventilator shared living community).

CONCLUSION

 Based on routine documentation, the care situation of weaning patients can be presented and compared with known data. In this way, the outcome quality of a weaning center can be made comparable.

Sentinel interaction mapping - a generic approach for the functional analysis of human disease gene variants using yeast

Advances in sequencing technology have led to an explosion in the number of known genetic variants of human genes. A major challenge is to now determine which of these variants contribute to diseases as a result of their effect on gene function. Here, we describe a generic approach using the yeast Saccharomyces cerevisiae to quickly develop gene-specific in vivo assays that can be used to quantify the level of function of a genetic variant. Using synthetic dosage lethality screening, 'sentinel' yeast strains are identified that are sensitive to overexpression of a human disease gene. Variants of the gene can then be functionalized in a high-throughput fashion through simple growth assays using solid or liquid media. Sentinel interaction mapping (SIM) has the potential to create functional assays for the large majority of human disease genes that do not have a yeast orthologue. Using the tumour suppressor gene PTEN as an example, we show that SIM assays can provide a fast and economical means to screen a large number of genetic variants.

Comprehensive Imaging of Sensory-Evoked Activity of Entire Neurons Within the Awake Developing Brain Using Ultrafast AOD-Based Random-Access Two-Photon Microscopy

Determining how neurons transform synaptic input and encode information in action potential (AP) firing output is required for understanding dendritic integration, neural transforms and encoding. Limitations in the speed of imaging 3D volumes of brain encompassing complex dendritic arbors in vivo using conventional galvanometer mirror-based laser-scanning microscopy has hampered fully capturing fluorescent sensors of activity throughout an individual neuron's entire complement of synaptic inputs and somatic APs. To address this problem, we have developed a two-photon microscope that achieves high-speed scanning by employing inertia-free acousto-optic deflectors (AODs) for laser beam positioning, enabling random-access sampling of hundreds to thousands of points-of-interest restricted to a predetermined neuronal structure, avoiding wasted scanning of surrounding extracellular tissue. This system is capable of comprehensive imaging of the activity of single neurons within the intact and awake vertebrate brain. Here, we demonstrate imaging of tectal neurons within the brains of albino Xenopus laevis tadpoles labeled using single-cell electroporation for expression of a red space-filling fluorophore to determine dendritic arbor morphology, and either the calcium sensor jGCaMP7s or the glutamate sensor iGluSnFR as indicators of neural activity. Using discrete, point-of-interest scanning we achieve sampling rates of 3 Hz for saturation sampling of entire arbors at 2 μm resolution, 6 Hz for sequentially sampling 3 volumes encompassing the dendritic arbor and soma, and 200–250 Hz for scanning individual planes through the dendritic arbor. This system allows investigations of sensory-evoked information input-output relationships of neurons within the intact and awake brain.

A Premalignant Cell-Based Model for Functionalization and Classification of PTEN Variants

As sequencing becomes more economical, we are identifying sequence variations in the population faster than ever. For disease-associated genes, it is imperative that we differentiate a sequence variant as either benign or pathogenic, such that the appropriate therapeutic interventions or surveillance can be implemented. PTEN is a frequently mutated tumor suppressor that has been linked to the PTEN hamartoma tumor syndrome. Although the domain structure of PTEN and the functional impact of a number of its most common tumor-linked mutations have been characterized, there is a lack of information about many recently identified clinical variants. To address this challenge, we developed a cell-based assay that utilizes a premalignant phenotype of normal mammary epithelial cells lacking PTEN. We measured the ability of PTEN variants to rescue the spheroid formation phenotype of PTEN^-/- MCF10A cells maintained in suspension. As proof of concept, we functionalized 47 missense variants using this assay, only 19 of which have clear classifications in ClinVar. We utilized a machine learning model trained with annotated genotypic data to classify variants as benign or pathogenic based on our functional scores. Our model predicted with high accuracy that loss of PTEN function was indicative of pathogenicity. We also determined that the pathogenicity of certain variants may have arisen from reduced stability of the protein product. Overall, this assay outperformed computational predictions, was scalable, and had a short run time, serving as an ideal alternative for annotating the clinical significance of cancer-associated PTEN variants. SIGNIFICANCE: Combined three-dimensional tumor spheroid modeling and machine learning classifies PTEN missense variants, over 70% of which are currently listed as variants of uncertain significance. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/13/2775/F1.large.jpg.

Evaluation of pulsed electric fields technology for the improvement of subsequent carotenoid extraction from dried Rhodotorula glutinis yeast

This research aims to evaluate whether the electroporation of Rhodotorula glutinis fresh biomass improved the subsequent extraction of carotenoids from dry biomass using supercritical CO2 and traditional solvent extraction. Supercritical CO2 extraction yields were low after all treatments assayed. Similarly, solvent extraction of carotenoids from untreated or PEF treated cells that were immediately freeze-dried after the pre-treatment was neither effective (extraction yield < 20% total content). Conversely, PEF-treatment and subsequent intermediate incubation in aqueous buffer for 24 h, followed by freeze-drying and extraction, led to a large improvement with the three solvents assayed (acetone, hexane, ethanol). Ethanol was the most efficient, reaching an extraction yield of 80% of total carotenoid, which represents a recovery of 267 µg/gdw. Torularhodin esters constituted the main carotenoid found in the extracts. This is of great interest, as ethanol is eco-friendly solvent and potential applications of torularhodin range from food to medical purposes.

Systematic phenomics analysis of autism-associated genes reveals parallel networks underlying reversible impairments in habituation

A major challenge facing the genetics of autism spectrum disorders (ASDs) is the large and growing number of candidate risk genes and gene variants of unknown functional significance. Here, we used Caenorhabditis elegans to systematically functionally characterize ASD-associated genes in vivo. Using our custom machine vision system, we quantified 26 phenotypes spanning morphology, locomotion, tactile sensitivity, and habituation learning in 135 strains each carrying a mutation in an ortholog of an ASD-associated gene. We identified hundreds of genotype-phenotype relationships ranging from severe developmental delays and uncoordinated movement to subtle deficits in sensory and learning behaviors. We clustered genes by similarity in phenomic profiles and used epistasis analysis to discover parallel networks centered on CHD8•chd-7 and NLGN3•nlg-1 that underlie mechanosensory hyperresponsivity and impaired habituation learning. We then leveraged our data for in vivo functional assays to gauge missense variant effect. Expression of wild-type NLG-1 in nlg-1 mutant C. elegans rescued their sensory and learning impairments. Testing the rescuing ability of conserved ASD-associated neuroligin variants revealed varied partial loss of function despite proper subcellular localization. Finally, we used CRISPR-Cas9 auxin-inducible degradation to determine that phenotypic abnormalities caused by developmental loss of NLG-1 can be reversed by adult expression. This work charts the phenotypic landscape of ASD-associated genes, offers in vivo variant functional assays, and potential therapeutic targets for ASD.

Muscle wasting and function after muscle activation and early protocol-based physiotherapy: an explorative trial

BACKGROUND

Early mobilization improves physical independency of critically ill patients at hospital discharge in a general intensive care unit (ICU)-cohort. We aimed to investigate clinical and molecular benefits or detriments of early mobilization and muscle activating measures in a high-risk ICU-acquired weakness cohort.

METHODS

Fifty patients with a SOFA score ≥9 within 72 h after ICU admission were randomized to muscle activating measures such as neuromuscular electrical stimulation or whole-body vibration in addition to early protocol-based physiotherapy (intervention) or early protocol-based physiotherapy alone (control). Muscle strength and function were assessed by Medical Research Council (MRC) score, handgrip strength and Functional Independence Measure at first awakening, ICU discharge, and 12 month follow-up. Patients underwent open surgical muscle biopsy on day 15. We investigated the impact of muscle activating measures in addition to early protocol-based physiotherapy on muscle strength and function as well as on muscle wasting, morphology, and homeostasis in patients with sepsis and ICU-acquired weakness. We compared the data with patients treated with common physiotherapeutic practice (CPP) earlier.

RESULTS

ICU-acquired weakness occurs within the entire cohort, and muscle activating measures did not improve muscle strength or function at first awakening (MRC median [IQR]: CPP 3.3 [3.0-4.3]; control 3.0 [2.7-3.4]; intervention 3.0 [2.1-3.8]; P > 0.05 for all), ICU discharge (MRC median [IQR]: CPP 3.8 [3.4-4.4]; control 3.9 [3.3-4.0]; intervention 3.6 [2.8-4.0]; P > 0.05 for all), and 12 month follow-up (MRC median [IQR]: control 5.0 [4.3-5.0]; intervention 4.8 [4.3-5.0]; P = 0.342 for all). No signs of necrosis or inflammatory infiltration were present in the histological analysis. Myocyte cross-sectional area in the intervention group was significantly larger in comparison with the control group (type I +10%; type IIa +13%; type IIb +3%; P < 0.001 for all) and CPP (type I +36%; type IIa +49%; type IIb +65%; P < 0.001 for all). This increase was accompanied by an up-regulated gene expression for myosin heavy chains (fold change median [IQR]: MYH1 2.3 [1.1-2.7]; MYH2 0.7 [0.2-1.8]; MYH4 5.1 [2.2-15.3]) and an unaffected gene expression for TRIM63, TRIM62, and FBXO32.

CONCLUSIONS

In our patients with sepsis syndrome at high risk for ICU-acquired weakness muscle activating measures in addition to early protocol-based physiotherapy did not improve muscle strength or function at first awakening, ICU discharge, or 12 month follow-up. Yet it prevented muscle atrophy.

The Effects of Colored Pigments on the Translucency of Experimental Dental Resin Composites

OBJECTIVE

Colored pigments are incorporated into dental resin composites to produce clinically acceptable shades for restorative materials but studies on their effects on translucency are rare. The aim of this study was to examine the effects of the addition of different colored pigments on the translucency of experimental dental resin composites.

MATERIALS AND METHODS

12 types of experimental dental resin composites containing different concentrations of red and yellow iron oxide pigments were formulated and light-cured. Total and diffuse translucency as well as CIE L*a*b* values were measured and the color differences were calculated.

RESULTS

There was a statistically significant difference in the translucency values between the composites with no pigments and the composites with increasing concentrations of the pigments (p<0.05). The translucency decreased as the concentration of the pigments increased. However at pigment concentrations greater than 0.02%, the translucency of the composites reached a plateau and ceased to be influenced by the addition of the pigments (p⟨0.05). All color differences were in the range of 3.62-16.00 ΔE*ab unit.

CONCLUSIONS

The pigments used in this study can influence the translucency of the experimental resin composites and should be considered as an important factor by clinicians to achieve optimal esthetic restorative outcome.

Automating Event-detection of Brain Neuron Synaptic Activity and Action Potential Firing in vivo using a Random-access Multiphoton Laser Scanning Microscope for Real-time Analysis

Determining how a neuron computes requires an understanding of the complex spatiotemporal relationship between its input (e.g. synaptic input as a result of external stimuli) and action potential output. Recent advances in in vivo, laser-scanning multiphoton technology, known as random-access microscopy (RAM), can capture this relationship by imaging fluorescent light, emitted from calcium-sensitive biosensors responding to synaptic and action potential firing in a neuron's full dendritic arbor and cell body. Ideally, a continuous output of fluorescent intensities from the neuron would be converted to a binary output (`event', 'or no-event'). These binary events can be used to correlate temporal and spatial associations between the input and output. However, neurons contain hundreds-to-thousands of synapses on the dendritic arbors generating an enormous quantity of data composed of physiological signals, which vary greatly in shape and size. Thus, automating data-processing tasks is essential to support high-throughput analysis for real-time/post-processing operations and to improve operators' comprehension of the data used to decipher neuron computations. Here, we describe an automated software algorithm to detect brain neuron events in real-time using an acousto-optic, multiphoton, laser scanning RAM developed in our laboratory. The fluorescent light intensities, from a genetically encoded, calcium biosensor (GCAMP 6m), are measured by our RAM system and are input to our 'event-detector', which converts them to a binary output meant for real-time applications. We evaluate three algorithms for this purpose: exponentially weighted moving average, cumulative sum, and template matching; present each algorithm's performance; and discuss user-feasibility of each. We validated our system in vivo, using the visual circuit of the Xenopus laevis.

Microbleeds in ischemic vs hemorrhagic strokes on novel oral anticoagulants

OBJECTIVES

To identify differences in clinical characteristics and severity of cerebral small vessel disease (CSVD) including cerebral microbleeds (CMBs), between patients suffering ischemic stroke (IS) or intracerebral hemorrhage (ICH) while taking novel (non-vitamin K antagonists) oral anticoagulants (NOACs).

METHODS

Multicenter, prospective, observational cohort study performed at 38 centers between 2012 and 2015. We compared demographics, comorbidity, and functional status (before and after stroke) between NOAC-IS and NOAC-ICH patients. Extent of white matter lesions (WML), and location and counts of CMBs were analyzed in a subgroup of patients for whom MRI including hemorrhage-sensitive sequences was available.

RESULTS

A total of 351 patients were included (290 NOAC-IS, 61 NOAC-ICH). Functional status was worse in NOAC-ICH patients before and after stroke. No significant differences were found for demographic variables and cardiovascular comorbidity. In the subgroup with available MRI (n = 116), the proportion of patients with at least one CMB was higher in NOAC-ICH than in NOAC-IS (15/19 [79%] vs 36/97 [37%], P < .001), as was the absolute number of CMBs (median 5 [IQR 1-24] vs 0 [0-1], P < .001). WML were more extensive in NOAC-ICH than in NOAC-IS patients. Adjusted for WML, logistic regression analysis showed higher odds of NOAC-ICH in patients with CMB than without (OR 5.60 [1.64-19.14], P = .006).

CONCLUSIONS

Patients with NOAC-ICH have similar clinical characteristics but a higher prevalent burden of CSVD compared to NOAC-IS. The role of neuroimaging in selection of patients for anticoagulation with NOAC requires further investigation in longitudinal studies.

Whole-body vibration to prevent intensive care unit-acquired weakness: safety, feasibility, and metabolic response

Background

Intensive care unit (ICU)-acquired weakness in critically ill patients is a common and significant complication affecting the course of critical illness. Whole-body vibration is known to be effective muscle training and may be an option in diminishing weakness and muscle wasting. Especially, patients who are immobilized and not available for active physiotherapy may benefit. Until now whole-body vibration was not investigated in mechanically ventilated ICU patients. We investigated the safety, feasibility, and metabolic response of whole-body vibration in critically ill patients.

Methods

We investigated 19 mechanically ventilated, immobilized ICU patients. Passive range of motion was performed prior to whole-body vibration therapy held in the supine position for 15 minutes. Continuous monitoring of vital signs, hemodynamics, and energy metabolism, as well as intermittent blood sampling, took place from the start of baseline measurements up to 1 hour post intervention. We performed comparative longitudinal analysis of the phases before, during, and after intervention.

Results

Vital signs and hemodynamic parameters remained stable with only minor changes resulting from the intervention. No application had to be interrupted. We did not observe any adverse event. Whole-body vibration did not significantly and/or clinically change vital signs and hemodynamics. A significant increase in energy expenditure during whole-body vibration could be observed.

Conclusions

In our study the application of whole-body vibration was safe and feasible. The technique leads to increased energy expenditure. This may offer the chance to treat patients in the ICU with whole-body vibration. Further investigations should focus on the efficacy of whole-body vibration in the prevention of ICU-acquired weakness.

Trial registration

Applicability and Safety of Vibration Therapy in Intensive Care Unit (ICU) Patients. ClinicalTrials.gov NCT01286610. Registered 28 January 2011.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1576-y) contains supplementary material, which is available to authorized users.

Critical illness polyneuropathy in ICU patients is related to reduced motor nerve excitability caused by reduced sodium permeability

Background

Reduced motor and sensory nerve amplitudes in critical illness polyneuropathy (CIP) are characteristic features described in electrophysiological studies and due to dysfunction of voltage-gated sodium channels. Yet, faulty membrane depolarization as reported in various tissues of critically ill patients may cause reduced membrane excitability as well. The aim of this study was to compare the pathophysiological differences in motor nerve membrane polarization and voltage-gated sodium channel function between CIP patients and critically ill patients not developing CIP during their ICU stay (ICU controls).

Methods

ICU patients underwent electrophysiological nerve conduction studies and were categorized as either ICU controls or CIP patients. Subsequently, excitability parameters were recorded as current-threshold relationship, stimulus-response behavior, threshold electrotonus, and recovery of excitability from the abductor pollicis brevis following median nerve stimulation.

Results

Twenty-six critically ill patients were enrolled and categorized as 12 ICU controls and 14 CIP patients. When compared to 31 healthy subjects, the ICU controls exhibited signs of membrane depolarization as shown by reduced superexcitability (p = 0.003), depolarized threshold electrotonus (p = 0.007), increased current-threshold relationship (p = 0.03), and slightly prolonged strength-duration time constant. In contrast, the CIP patients displayed a significantly reduced strength-duration time constant (p < 0.0001), which indicates an increased inactivation of voltage-gated sodium channels.

Conclusions

Abnormal motor nerve membrane depolarization is a general finding in critically ill patients whereas voltage-gated sodium channel dysfunction is a characteristic of CIP patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-016-0083-4) contains supplementary material, which is available to authorized users.

Interactions between mitochondria and the transcription factor myocyte enhancer factor 2 (MEF2) regulate neuronal structural and functional plasticity and metaplasticity

The classical view of mitochondria as housekeeping organelles acting in the background to simply maintain cellular energy demands has been challenged by mounting evidence of their direct and active participation in synaptic plasticity in neurons. Time-lapse imaging has revealed that mitochondria are motile in dendrites, with their localization and fusion and fission events regulated by synaptic activity. The positioning of mitochondria directly influences function of nearby synapses through multiple pathways including control over local concentrations of ATP, Ca(2+) and reactive oxygen species. Recent studies have also shown that mitochondrial protein cascades, classically associated with apoptosis, are involved in neural plasticity in healthy cells. These findings link mitochondria to the plasticity- and metaplasticity-associated activity-dependent transcription factor myocyte enhancer factor 2 (MEF2), further repositioning mitochondria as potential command centres for regulation of synaptic plasticity. Intriguingly, MEF2 and mitochondrial functions appear to be intricately intertwined, as MEF2 is a target of mitochondrial apoptotic caspases and, in turn, MEF2 regulates mitochondrial genome transcription essential for production of superoxidase and hydrogen peroxidase. Here, we review evidence supporting mitochondria as central organelles controlling the spatiotemporal expression of neuronal plasticity, and attempt to disentangle the MEF2-mitochondria relationship mediating these functions.

Long-term recovery In critical illness myopathy is complete, contrary to polyneuropathy

INTRODUCTION

Muscle weakness in critically ill patients after discharge varies. It is not known whether the electrophysiological distinction between critical illness myopathy (CIM) and critical illness polyneuropathy (CIP) during the early part of a patient's stay in the intensive care unit (ICU) predicts long-term prognosis.

METHODS

This was a prospective cohort study of mechanically ventilated ICU patients undergoing conventional nerve conduction studies and direct muscle stimulation in addition to neurological examination during their ICU stay and 1 year after ICU discharge.

RESULTS

Twenty-six patients (7 ICU controls, 8 CIM patients, and 11 CIM/CIP patients) were evaluated 1 year after discharge from the ICU. Eighty-eight percent (n = 7) of CIM patients recovered within 1 year compared with 55% (n = 6) of CIM/CIP patients. Thirty-six percent (n = 4) of CIM/CIP patients still needed assistance during their daily routine (P = 0.005).

CONCLUSIONS

Early electrophysiological testing predicts long-term outcome in ICU survivors. CIM has a significantly better prognosis than CIM/CIP.

Dynamics of myosin degradation in intensive care unit-acquired weakness during severe critical illness

IMPORTANCE

Intensive care unit (ICU)-acquired muscle wasting is a devastating complication leading to persistent weakness and functional disability. The mechanisms of this myopathy are unclear, but a disturbed balance of myosin heavy chain (MyHC) is implicated.

OBJECTIVE

To investigate pathways of myosin turnover in severe critically ill patients at high risk of ICU-acquired weakness.

DESIGN

Prospective, mechanistic, observational study.

SETTING

Interdisciplinary ICUs of a university hospital.

PARTICIPANTS

Twenty-nine patients with Sequential Organ Failure Assessment (SOFA) scores of at least 8 on three consecutive days within the first 5 days in ICU underwent two consecutive open skeletal muscle biopsies from the vastus lateralis at median days 5 and 15. Control biopsy specimens were from healthy subjects undergoing hip-replacement surgery.

INTERVENTIONS

None.

MAIN OUTCOME(S) AND MEASURE(S)

Time-dependent changes in myofiber architecture, MyHC synthesis, and degradation were determined and correlated with clinical data.

RESULTS

ICU-acquired muscle wasting was characterized by early, disrupted myofiber ultrastructure followed by atrophy of slow- and fast-twitch myofibers at later time points. A rapid decrease in MyHC mRNA and protein expression occurred by day 5 and persisted at day 15 (P < 0.05). Expression of the atrophy genes MuRF-1 and Atrogin1 was increased at day 5 (P < 0.05). Early MuRF-1 protein content was closely associated with late myofiber atrophy and the severity of weakness.

CONCLUSIONS AND RELEVANCE

Decreased synthesis and increased degradation of MyHCs contribute to ICU-acquired muscle wasting. The rates and time frames suggest that pathogenesis of muscle failure is initiated very early during critical illness. The persisting reduction of MyHC suggests that sustained treatment is required.

Fast non-negative temporal deconvolution for laser scanning microscopy

Laser scanning microscopy (LSM) is a common technique for high resolution fluorescent imaging. Here we describe a fast algorithm for non-negative deconvolution and apply it to readout of LSM detector photocurrents. By broadening photon impulses and deconvolving sampled photocurrent, effective quantum efficiency of the imaging system is increased. Using simulation and imaging with a custom-built two-photon microscope, we demonstrate improved fidelity of images acquired at short dwell times over a wide range of photon rates. Images formed show increased correlation-to-sample equivalent to a 25% increase in photon rate, lower noise, and reduced bleed-through compared to conventional image generation.

The transcription factor MEF2 directs developmental visually driven functional and structural metaplasticity

Natural sensory input shapes both structure and function of developing neurons, but how early experience-driven morphological and physiological plasticity are interrelated remains unclear. Using rapid time-lapse two-photon calcium imaging of network activity and single-neuron growth within the unanesthetized developing brain, we demonstrate that visual stimulation induces coordinated changes to neuronal responses and dendritogenesis. Further, we identify the transcription factor MEF2A/2D as a major regulator of neuronal response to plasticity-inducing stimuli directing both structural and functional changes. Unpatterned sensory stimuli that change plasticity thresholds induce rapid degradation of MEF2A/2D through a classical apoptotic pathway requiring NMDA receptors and caspases-9 and -3/7. Knockdown of MEF2A/2D alone is sufficient to induce a metaplastic shift in threshold of both functional and morphological plasticity. These findings demonstrate how sensory experience acting through altered levels of the transcription factor MEF2 fine-tunes the plasticity thresholds of brain neurons during neural circuit formation.

Functional clustering drives encoding improvement in a developing brain network during awake visual learning

Sensory experience drives dramatic structural and functional plasticity in developing neurons. However, for single-neuron plasticity to optimally improve whole-network encoding of sensory information, changes must be coordinated between neurons to ensure a full range of stimuli is efficiently represented. Using two-photon calcium imaging to monitor evoked activity in over 100 neurons simultaneously, we investigate network-level changes in the developing Xenopus laevis tectum during visual training with motion stimuli. Training causes stimulus-specific changes in neuronal responses and interactions, resulting in improved population encoding. This plasticity is spatially structured, increasing tuning curve similarity and interactions among nearby neurons, and decreasing interactions among distant neurons. Training does not improve encoding by single clusters of similarly responding neurons, but improves encoding across clusters, indicating coordinated plasticity across the network. NMDA receptor blockade prevents coordinated plasticity, reduces clustering, and abolishes whole-network encoding improvement. We conclude that NMDA receptors support experience-dependent network self-organization, allowing efficient population coding of a diverse range of stimuli.

Single-cell electroporation in Xenopus

Single-cell electroporation (SCE) is a versatile technique for delivering electrically charged macromolecules including DNA, RNA, synthetic oligonucleotides, peptides, dyes, and drugs to individual cells within intact tissues. Here, we describe methods for in vivo-targeted electroporation of single tectal neurons within the albino Xenopus laevis tadpole. Focal electroporation is achieved using a pipette electrode filled with a solution of the delivery molecules and with a tip diameter much smaller than the width of the target cell. The small tip allows for localization of an electric field, which restricts pore formation to only the individual cell in direct contact with the tip. Thus, the small tip permits focal delivery of the charged molecules within the pipette into individual cells. Factors affecting the efficiency of SCE, as well as various applications of this technique, are discussed. Particular focus is directed toward combining SCE with in vivo two-photon microscopy for three-dimensional (3D) imaging of neuron growth and cell-autonomous effects of altered protein function.

Single-cell electroporation of Xenopus tadpole tectal neurons

Single-cell electroporation (SCE) is a versatile technique for delivering electrically charged macromolecules, including DNA, RNA, synthetic oligonucleotides, peptides, dyes, and drugs, to individual cells within intact tissues. Here, we describe methods for SCE of single tectal neurons within the albino Xenopus laevis tadpole for delivery of plasmid DNA-expressing protein fluorophores or fluorescent dye. Individual neurons labeled by this technique can then be imaged in three dimensions (3D) within the intact and living brain using in vivo two-photon microscopy for studies of morphology and growth. The SCE protocol is relatively simple and requires minimal and common laboratory equipment, including a fluorescent stereomicroscope, micropipette puller, and electrical stimulator. Once equipment is set up, learning to label cells with fluorescent dyes is straightforward and usually quickly achieved, because direct visualization with fluorescent microscopy offers immediate feedback of success. The main challenges are positioning the pipette tip in a cell body layer and optimizing pipette tip shape and stimulation parameters. Once fluorescent dye loading has been achieved, transfecting neurons with DNA should follow by using the same pipette tip parameters, but extending the stimulation parameters, because plasmid DNA is larger than dye and requires formation of larger pores. Detectable expression of protein fluorophores from transfected DNA typically takes 6-12 h. SCE for dye loading or DNA transfection of tadpole tectal neurons is highly efficient and can be learned in 1 or 2 d by novice laboratory personnel.

Chondro/osteoblastic and cardiovascular gene modulation in human artery smooth muscle cells that calcify in the presence of phosphate and calcitriol or paricalcitol

Vitamin D sterol administration, a traditional treatment for secondary hyperparathyroidism, may increase serum calcium and phosphorus, and has been associated with increased vascular calcification (VC). In vitro studies suggest that in the presence of uremic concentrations of phosphorus, vitamin D sterols regulate gene expression associated with trans-differentiation of smooth muscle cells (SMCs) to a chondro/osteoblastic cell type. This study examined effects of vitamin D sterols on gene expression profiles associated with phosphate-enhanced human coronary artery SMC (CASMC) calcification. Cultured CASMCs were exposed to phosphate-containing differentiation medium (DM) with and without calcitriol, paricalcitol, or the calcimimetic R-568 (10(-11)-10(-7) M) for 7 days. Calcification of CASMCs, determined using colorimetry following acid extraction, was dose dependently increased (1.6- to 1.9-fold) by vitamin D sterols + DM. In contrast, R-568 did not increase calcification. Microarray analysis demonstrated that, compared with DM, calcitriol (10(-8) M) + DM or paricalcitol (10(-8) M) + DM similarly and significantly (P < 0.05) regulated genes of various pathways including: metabolism, CYP24A1; mineralization, ENPP1; apoptosis, GIP3; osteo/chondrogenesis, OPG, TGFB2, Dkk1, BMP4, BMP6; cardiovascular, HGF, DSP1, TNC; cell cycle, MAPK13; and ion channels, SLC22A3 KCNK3. R-568 had no effect on CASMC gene expression. Thus, SMC calcification observed in response to vitamin D sterol + DM may be partially mediated through targeting mineralization, apoptotic, osteo/chondrocytic, and cardiovascular pathway genes, although some gene changes may protect against calcification. Further studies to determine precise roles of these genes in development of, or protection against VC and cardiovascular disease are required.

Neurexin-neuroligin cell adhesion complexes contribute to synaptotropic dendritogenesis via growth stabilization mechanisms in vivo

Cell adhesion molecules are well characterized for mediating synapse initiation, specification, differentiation, and maturation, yet their contribution to directing dendritic arborization during early brain circuit formation remains unclear. Using two-photon time-lapse imaging of growing neurons within intact and awake embryonic Xenopus brain, we examine roles of β-neurexin (NRX) and neuroligin-1 (NLG1) in dendritic arbor development. Using methods of dynamic morphometrics for comprehensive 3D quantification of rapid dendritogenesis, we find initial trans-synaptic NRX-NLG1 adhesions confer transient morphologic stabilization independent of NMDA receptor activity, whereas persistent stabilization requires NMDA receptor-dependent synapse maturation. Disrupting NRX-NLG1 function destabilizes filopodia while reducing synaptic density and AMPA receptor mEPSC frequency. Altered dynamic growth culminates in reduced dendritic arbor complexity as neurons mature over days. These results expand the synaptotropic model of dendritogenesis to incorporate cell adhesion molecule-mediated morphological stabilization necessary for directing normal dendritic arborization, providing a potential morphological substrate for developmental cognitive impairment associated with cell adhesion molecule mutations.

[Photodynamic therapy with verteporfin combined with intravitreal injection of bevacizumab for occult and classic CNV in AMD]

PURPOSE

The aim of this study is to discuss the effect and outcome of a combined photodynamic therapy and intravitreal injection of bevacizumab (1.25 mg) in occult and classic choroidal neovascularisation (CNV) due to AMD. Especially cases of occult CNV with pigment epithelium detachment (PED) are not likely to respond positively to standard photodynamic therapy, often ending up in PED enlargement or tearing of the RPE.

METHODS

In a pilot study involving 23 patients, intravitreal injections of bevacizumab were administered within 12 to 24 hours after standard PDT to reduce the post-PDT increase of proangiogenic and inflammatory factors. Before and at 1, 3 and 6 month after treatment visual acuity and OCT examinations (retinal thickness) were performed.

RESULTS

Mean visual acuity was significantly improved compared to baseline. (VA baseline 20/125, after 1 month 20/80, after 3 months 20/80, and 20/80 after 6 months) and an enlargement of the PED in occult CNV was prevented. We found no RPE rip. OCT findings in patients with occult and classic choroidal neovascularisation 1, 3 and 6 months after combination therapy showed a reduced retinal thickness compared to baseline.

CONCLUSIONS

Photodynamic therapy combined with injection of intravitreal bevacizumab tends to be more effective compared to PDT monotherapy by reducing the post-PDT increase of vascular growth and inflammatory factors. Our short-term results are very promising. Further studies are necessary to show the long-term effect of PDT and anti-VEGF combination therapy.

Single cell electroporation in vivo within the intact developing brain

Single-cell electroporation (SCE) is a specialized technique allowing the delivery of DNA or other macromolecules into individual cells within intact tissue, including in vivo preparations. The distinct advantage of this technique is that experimental manipulations may be performed on individual cells while leaving the surrounding tissue unaltered, thereby distinguishing cell-autonomous effects from those resulting from global treatments. When combined with advanced in vivo imaging techniques, SCE of fluorescent markers permits direct visualization of cellular morphology, cell growth, and intracellular events over timescales ranging from seconds to days. While this technique is used in a variety of in vivo and ex vivo preparations, we have optimized this technique for use in Xenopus laevis tadpoles. In this video article, we detail the procedure for SCE of a fluorescent dye or plasmid DNA into neurons within the intact brain of the albino Xenopus tadpole. We also discuss methods to optimize yield, and show examples of live two-photon fluorescence imaging of neurons fluorescently labeled by SCE.