A method for objectively quantifying propidium iodide exclusion in organotypic hippocampal slice cultures

Slack K+ channels limit kainic acid-induced seizure severity in mice by modulating neuronal excitability and firing

Mutations of the Na+-activated K+ channel Slack (KCNT1) are associated with terrible epilepsy syndromes that already begin in infancy. Here we report increased severity of acute kainic acid-induced seizures in adult and juvenile Slack knockout mice (Slack-/-) in vivo. Fittingly, we find exacerbation of cell death following kainic acid exposure in organotypic hippocampal slices as well as dissociated hippocampal cultures from Slack-/- in vitro. Furthermore, in cultured Slack-/- neurons, kainic acid-triggered Ca2+ influx and K+ efflux as well as depolarization-induced tetrodotoxin-sensitive inward currents are higher compared to the respective controls. This apparent changes in ion homeostasis could possibly explain altered action potential kinetics of Slack-/- neurons: steeper rise slope, decreased threshold, and duration of afterhyperpolarization, which ultimately lead to higher action potential frequencies during kainic acid application or injection of depolarizing currents. Based on our data, we propose Slack as crucial gatekeeper of neuronal excitability to acutely limit seizure severity.

Thrombin-Induced Microglia Activation Modulated through Aryl Hydrocarbon Receptors

Thrombin is a multifunctional serine protein which is closely related to neurodegenerative disorders. The Aryl hydrocarbon receptor (AhR) is well expressed in microglia cells involving inflammatory disorders of the brain. However, it remains unclear as to how modulation of AhR expression by thrombin is related to the development of neurodegeneration disorders. In this study, we investigated the role of AhR in the development of thrombin-induced neurodegenerative processes, especially those concerning microglia. The primary culture of either wild type or AhR deleted microglia, as well as BV-2 cell lines, was used for an in vitro study. Hippocampal slice culture and animals with either wild type or with AhR deleted were used for the ex vivo and in vivo studies. Simulations of ligand protein docking showed a strong integration between the thrombin and AhR. In thrombin-triggered microglia cells, deleting AhR escalated both the NO release and iNOS expression. Such effects were abolished by the administration of the AhR agonist. In thrombin-activated microglia cells, downregulating AhR increased the following: vascular permeability, pro-inflammatory genetic expression, MMP-9 activity, and the ratio of M1/M2 phenotype. In the in vivo study, thrombin induced the activation of microglia and their volume, thereby contributing to the deterioration of neurobehavior. Deleting AhR furthermore aggravated the response in terms of impaired neurobehavior, increasing brain edema, aggregating microglia, and increasing neuronal death. In conclusion, thrombin caused the activation of microglia through increased vessel permeability, expression of inflammatory response, and phenotype of M1 microglia, as well the MMP activity. Deleting AhR augmented the above detrimental effects. These findings indicate that the modulation of AhR is essential for the regulation of thrombin-induced brain damages and that the AhR agonist may harbor the potentially therapeutic effect in thrombin-induced neurodegenerative disorder.

A living ex vivo platform for functional, personalized brain cancer diagnosis

Functional precision medicine platforms are emerging as promising strategies to improve pre-clinical drug testing and guide clinical decisions. We have developed an organotypic brain slice culture (OBSC)-based platform and multi-parametric algorithm that enable rapid engraftment, treatment, and analysis of uncultured patient brain tumor tissue and patient-derived cell lines. The platform has supported engraftment of every patient tumor tested to this point: high- and low-grade adult and pediatric tumor tissue rapidly establishes on OBSCs among endogenous astrocytes and microglia while maintaining the tumor's original DNA profile. Our algorithm calculates dose-response relationships of both tumor kill and OBSC toxicity, generating summarized drug sensitivity scores on the basis of therapeutic window and allowing us to normalize response profiles across a panel of U.S. Food and Drug Administration (FDA)-approved and exploratory agents. Summarized patient tumor scores after OBSC treatment show positive associations to clinical outcomes, suggesting that the OBSC platform can provide rapid, accurate, functional testing to ultimately guide patient care.

Potential Protective Function of Aβ42 Monomer on Tauopathies

While soluble forms of amyloid-β (Aβ) and Tau work together to drive healthy neurons into a disease state, how their interaction may control the prion-like propagation and neurotoxicity of Tau is not fully understood. The cross-linking via disulfide bond formation is crucial for Tau oligomers to obtain stable conformers and spread between cells. This work thus focuses on how Aβ₄₂ regulates this critical process. By studying the interactions between Aβ₄₂ and Tau_PHF43, a construct that mimics the Tau R3 isoform, has a similar length to Aβ42, and contains one cysteine (Cys-322), we discovered that fresh Aβ₄₂ could protect Tau against the formation of disulfide cross-linked dimers. We showed that the monomeric and small Aβ oligomers (the "nonamyloidogenic Aβ") efficiently disassembled tau dimers and heparin-induced Tau oligomers to recover Tau monomers. Interestingly, Aβ serves the role of an antioxidant to prevent disulfide bond formation, as supported by the experiments of Aβ with cystine. Furthermore, using cyclosporine A (CycA), a macrocyclic β-sheet disruptor, we demonstrated that targeting amyloidogenic Aβ with CycA does not affect the Tau_PHF43 disassembly driven by Aβ₄₂. Separately, we assessed the initial toxicity of Aβ₄₂ and Tau_PHF43 in acute brain slices and found that Aβ₄₂ is more toxic than Tau_PHF43 or the two peptides combined. Our work highlights a potential protective role of Aβ₄₂ monomers in AD that was previously overlooked while focusing on the mechanism behind Aβ₄₂ aggregation leading to tau dysfunction.

Selenium-Modified Chitosan Induces HepG2 Cell Apoptosis and Differential Protein Analysis

INTRODUCTION

Chitosan is the product of the natural polysaccharide chitin removing part of the acetyl group, and exhibits various physiological and bioactive functions. Selenium modification has been proved to further enhance the chitosan bioactivities, and has been a hot topic recently.

METHODS

The present study aimed to investigate the potential inhibitory mechanism of selenium-modified chitosan (SMC) on HepG2 cells through MTT assays, morphological observation, annexin V-FITC/PI double staining, mitochondrial membrane potential determination, cell-cycle detection, Western blotting, and two-dimensional gel electrophoresis (2-DE).

RESULTS

The results indicated that SMC can induce HepG2 cell apoptosis with the cell cycle arrested in the S and G2/M phases and gradual disruption of mitochondrial membrane potential, reduce the expression of Bcl2, and improve the expression of Bax, cytochrome C, cleaved caspase 9, and cleaved caspase 3. Also, 2-DE results showed that tubulin α1 B chain, myosin regulatory light chain 12A, calmodulin, UPF0568 protein chromosome 14 open reading frame 166, and the cytochrome C oxidase subunit 5B of HepG2 cells were downregulated in HepG2 cells after SMC treatment.

DISCUSSION

These data suggested that HepG2 cells induced apoptosis after SMC treatment via blocking the cell cycle in the S and G2/M phases, which might be mediated through the mitochondrial apoptotic pathway. These results could be of benefit to future practical applications of SMC in the food and drug fields.

Assessment of Neuronal Damage in Brain Slice Cultures Using Machine Learning Based on Spatial Features

Neuronal damage presents a major health issue necessitating extensive research to identify mechanisms of neuronal cell death and potential therapeutic targets. Commonly used models are slice cultures out of different brain regions extracted from mice or rats, excitotoxically, ischemic, or traumatically lesioned and subsequently treated with potential neuroprotective agents. Thereby cell death is regularly assessed by measuring the propidium iodide (PI) uptake or counting of PI-positive nuclei. The applied methods have a limited applicability, either in terms of objectivity and time consumption or regarding its applicability. Consequently, new tools for analysis are needed. Here, we present a framework to mimic manual counting using machine learning algorithms as tools for semantic segmentation of PI-positive dead cells in hippocampal slice cultures. Therefore, we trained a support vector machine (SVM) to classify images into either “high” or “low” neuronal damage and used naïve Bayes, discriminant analysis, random forest, and a multilayer perceptron (MLP) as classifiers for segmentation of dead cells. In our final models, pixel-wise accuracies of up to 0.97 were achieved using the MLP classifier. Furthermore, a SVM-based post-processing step was introduced to differentiate between false-positive and false-negative detections using morphological features. As only very few false-positive objects and thus training data remained when using the final model, this approach only mildly improved the results. A final object splitting step using Hough transformations was used to account for overlap, leading to a recall of up to 97.6% of the manually assigned PI-positive dead cells. Taken together, we present an analysis tool that can help to objectively and reproducibly analyze neuronal damage in brain-derived slice cultures, taking advantage of the morphology of pycnotic cells for segmentation, object splitting, and identification of false positives.

A microfluidic bubble perfusion device for brain slice culture

Ex vivo brain slice cultures are utilized as analytical models for studying neurophysiology. Common approaches to maintaining slice cultures include roller tube and membrane interface techniques. The rise of organ-on-chip technologies has demonstrated the value of microfluidic perfusion culture systems for sampling and analysis of complex biology under well-controlled in vitro or ex vivo conditions. A number of approaches to microfluidic brain slice culture have been developed, however these typically involve complex design, fabrication, or operational parameters in order to meet the high oxygen demands of brain slices. Here, we present proof-of-principle for a novel approach to microfluidic brain slice culture. In this system, which we term a microfluidic bubble perfusion device, principles of droplet microfluidics were employed to generate droplets of perfusion media dispersed between bubbles of carbogen gas, and brain tissue slices were perfused with the resulting monodispersed droplets and bubbles. The challenge of tissue immobilization in the flow system was addressed using a two-part cytocompatible carbohydrate-based tissue adhesive. Best practices are discussed for perfusion chamber designs that maintain segmented flow throughout the course of perfusion. Control of droplet and bubble volumes was possible across the range of ca. 4-15 μL, bubble generation frequency was well controlled in the range ca. 1-7 bubbles per min, and bubble duty cycle was well controlled across the range ca. 20-80%. Murine hypothalamic tissue slices containing the suprachiasmatic nuclei were successfully maintained for durations of 8-10 hours, with tissue remaining viable for the duration of perfusion as assessed by Ca²⁺ imaging and propidium iodide (PI) staining.

Kinin B2 Receptor Activation Prevents the Evolution of Alzheimer's Disease Pathological Characteristics in a Transgenic Mouse Model

Background: Alzheimer’s disease is mainly characterized by remarkable neurodegeneration in brain areas related to memory formation. This progressive neurodegeneration causes cognitive impairment, changes in behavior, functional disability, and even death. Our group has demonstrated changes in the kallikrein–kinin system (KKS) in Alzheimer’s disease (AD) experimental models, but there is a lack of evidence about the role of the KKS in Alzheimer’s disease. Aim: In order to answer this question, we evaluated the potential of the kinin B2 receptors (BKB2R) to modify AD characteristics, particularly memory impairment, neurodegeneration, and Aβ peptide deposition. Methods: To assess the effects of B2, we used transgenic Alzheimer’s disease mice treated with B2 receptor (B2R) agonists and antagonists, and performed behavioral and biochemical tests. In addition, we performed organotypic hippocampal culture of wild-type (WT) and transgenic (TG) animals, where the density of cytokines, neurotrophin BDNF, activated astrocyte marker S100B, and cell death were analyzed after treatments. Results: Treatment with the B2R agonist preserved the spatial memory of transgenic mice and decreased amyloid plaque deposition. In organotypic hippocampal culture, treatment with B2R agonist decreased cell death, neuroinflammation, and S100B levels, and increased BDNF release. Conclusions: Our results indicate that the kallikrein–kinin system plays a beneficial role in Alzheimer’s disease through B2R activation. The use of B2R agonists could, therefore, be a possible therapeutic option for patients diagnosed with Alzheimer’s disease.

Microdose Lithium Treatment Reduced Inflammatory Factors and Neurodegeneration in Organotypic Hippocampal Culture of Old SAMP-8 Mice

It was already shown that microdoses of lithium carbonate (Li₂CO₃) promoted memory stabilization in humans and mice. Prolonged treatment also reduced neuronal loss and increased the density of the neurotrophin BDNF in transgenic mice for Alzheimer's disease. The aim of this study was to evaluate whether lithium ions affect inflammatory profiles and neuronal integrity in an animal model of accelerated senescence (SAMP-8). Organotypic hippocampal cultures obtained from 11 to 12-month-old SAMP-8 mice were treated with 2 µM, 20 µM and 200 µM Li₂CO₃. 2 µM Li₂CO₃ promoted a significant reduction in propidium iodide uptake in the CA2 area of hippocampus, whereas 20 µM promoted neuroprotection in the CA3 and GrDG areas. 200 µM caused an increase in cellular death, showing toxicity. Measured with quantitative PCR, IL-1α, IL-6 and MIP-1B/CCL-4 gene expression was significantly reduced with 20 µM Li₂CO₃, whereas IL-10 gene expression was significantly increased with the same concentration. In addition, 2 µM and 20 µM Li₂CO₃ were also effective in reducing the activation of NFkB and inflammatory cytokines densities, as evaluated by ELISA. It is concluded that very low doses of Li₂CO₃ can play an important role in neuroprotection as it can reduce neuronal loss and neuroinflammation in older individuals.

Neuroprotective Effects of Kinin B2 Receptor in Organotypic Hippocampal Cultures of Middle-Aged Mice

Aging is a multifactorial phenomenon that results in several changes at cellular and molecular levels and is considered the main risk factor for some neurodegenerative diseases. Several evidence show the participation of the kallikrein-kinin system (KKS) in neurodegeneration and this system has been associated with inflammation and immunogenic responses in the central and peripheral systems by the activation of the B1 and B2 receptors. Previous work by our group showed that bradykinin (BK) and the B2 receptor played a possible role in neuroprotection. Therefore, the objective of this study was to evaluate the participation of B2 receptors in cell viability, neuroinflammatory response and neuroplasticity in organotypic hippocampal cultures (OHCs) of 6- and 12-month-old mice. It was observed that activation of the B2 receptor by bradykinin decreased the inflammatory response and increased plasticity in 12-month-old slices. Conversely, there was an increase in the inflammatory response and a decrease in neural plasticity in the 6-month-old slices. In both ages, an increase in cell viability was observed. This data suggests that the function of the kinin B2 receptor in the hippocampus is modulated by age, providing neuroprotective action in old age.