Functional differences in type I versus type III interferon mediated immunity

Intestinal epithelial cells (IECs) lining the surface of our gastrointestinal tract tolerate the presence of the commensal microbiota, while maintaining responsiveness against enteric pathogens. How IECs regulate their innate immune response to maintain this finely tuned balance and establish an immune-homeostatic state in the gut remains unclear. Interferons (IFNs) are cytokines produced upon viral infection. While type I IFN receptors are ubiquitously expressed, type III IFN receptors are preferentially expressed on epithelial cells. This epithelium specificity strongly suggests exclusive functions at epithelial surfaces, but the relative roles of type I and type III IFNs in the establishment of an antiviral response in human IECs are not clearly defined. Here, we utilized human mini-gut organoid cultures and human colon cell lines to delve into the antiviral properties of type I versus type III IFNs in the gut. We could show that although primary human IECs, produce transcript levels for both IFNs, they secrete only type III IFNs in the supernatant upon viral challenge. However, using genetic ablation of either type I or type III IFN receptors, we revealed that human IECs respond to both IFNs, by independently establishing an antiviral state, responsible for combating enteric viral infection. Importantly, we could identify differences in the establishment of each IFN antiviral activity. Contrary to type I IFN, the antiviral activity induced by type III IFN is strongly dependent on the mitogen- activated protein kinases signaling pathway, suggesting a pathway used by type III IFNs that non-redundantly contributes to the antiviral state. In addition, we showed that while type I IFN signaling is characterized by an acute strong induction of ISGs and confers fast antiviral protection, type III IFN mediated antiviral protection is characterized by a slow weak induction of ISGs. Combining data-driven mathematical modeling with experimental validation, we demonstrated that these kinetic differences are intrinsic to each signaling pathway and not due to different expression levels of the corresponding IFN receptors. In conclusion, our results strongly suggest that type III IFN is specifically tailored to act on epithelial cells not only due to the restriction of its receptor but also by providing IECs with a distinct antiviral environment compared to type I IFN, which allows for efficient protection against pathogens without producing excessive inflammatory signals. We propose that this specific antiviral environment is key for mucosal surfaces, which are often challenged with the extracellular environment, to maintain gut homeostasis

Bioinformatics and genetics analysis of experience dependent plasticity in the mouse barrel cortex

Formation of neuronal circuits represent memories, making synaptic plasticity the root of learning and memory (Buonomano and Merzenich 1998). Neuronal plasticity has been studied using facial vibrissae deprivation paradigm in rodents (Fox 1992). Whisker deprivation alters the balance of activity in cortical neurons and their responses to sensory input, providing good grounds to study experience dependent plasticity (Simons and Land 1987 Fox 1992). Alterations in gene expression underpinning changes in cortical activity have been investigated in this thesis. The molecular signature underlying the temporal effect of repeated anaesthesia was identified and provided a fertile area for future work, revealing the necessity to separate anaesthesia from deprivation induced changes. Changes in gene expression were gender specific, with the females exhibiting quicker neuronal organisation. Taking under consideration the two confounding factors anaesthesia and gender, a new normalisation protocol was developed underpinning investigations of plasticity dependent transcriptional alterations. The present study confirmed the two molecular mechanisms underlining synaptic plasticity (Shi et al. 1999) with early time points (Day 1) revealing alterations of existing synaptic proteins and later time points (Day 8 and 16) indicating neurotransmitter release regulating gene expression. Day 8 was identified as the critical time point for plasticity, exhibiting the peak of transcriptional changes. Gender specificity was evident, indicating a role for hormonal-dependent gene expression, which future studies should consider. Ontological analysis has confirmed the role of Ca2+ trafficking (via AMPARs and NMDARs) and calcium dependent binding (involving molecules like Calmodulin) in a variety of pathways, such as transporter activity, channel activity and neurogenesis, associated with gene transcription and regulation of plasticity. A significant up-regulation of the expression profiles of transcripts associated with plasticity, NOS1, NOS3 and Bassoon was observed at Day 8 in wild type mice. GluRl-/- mice revealed the direct relationship of these genes with the GluR 1 subunit of AMPA receptors. A delayed up-regulation was detected after 16 days, suggesting a plausible delayed compensatory mechanism in the absence of the GluRl subunit of the AMPA receptor. Gene ontology provided a functional footprint for plasticity even in the GluRl-/- mice, known to exhibit impaired post-synaptic plasticity (Schmitt et al. 2005)

Cardiac re-entry dynamics & self-termination in DT-MRI based model of Human Foetal Heart

The effect of heart geometry and anisotropy on cardiac re-entry dynamics and self-termination is studied here in anatomically realistic computer simulations of human foetal heart. 20 weeks of gestational age human foetal heart isotropic and anisotropic anatomy models from diffusion tensor MRI data sets are used in the computer simulations. The fibre orientation angles of the heart were obtained from the DT-MRI primary eigenvalues. In a spatially homogeneous electrophysiological mono domain model with the DT-MRI based heart geometries, we initiate simplified Fitz-Hugh-Nagumo kinetics cardiac re-entry at a prescribed location in a 2D slice, and in the full 3D anatomy model. In a slice of the heart, the MRI based fibre anisotropy changes the re-entry dynamics from pinned to anatomical re-entry. In the full 3D MRI based model, the foetal heart fibre anisotropy changes the re-entry dynamics from a persistent re-entry to the re-entry self-termination

Cardiac re-entry dynamics and self-termination in DT-MRI based model of Human Foetal Heart

The effect of human fetal heart geometry and anisotropy on anatomy induced drift and self-termination of cardiac re-entry is studied here in MRI based 2D slice and 3D whole heart computer simulations. Isotropic and anisotropic models of 20 weeks of gestational age human fetal heart obtained from 100 μm voxel diffusion tensor MRI data sets were used in the computer simulations. The fiber orientation angles of the heart were obtained from the orientation of the DT-MRI primary eigenvectors. In a spatially homogeneous electrophysiological monodomain model with the DT-MRI based heart geometries, cardiac re-entry was initiated at a prescribed location in a 2D slice, and in the 3D whole heart anatomy models. Excitation was described by simplified FitzHugh-Nagumo kinetics. In a slice of the heart, with propagation velocity twice as fast along the fibers than across the fibers, DT-MRI based fiber anisotropy changes the re-entry dynamics from pinned to an anatomical re-entry. In the 3D whole heart models, the fiber anisotropy changes cardiac re-entry dynamics from a persistent re-entry to the re-entry self-termination. The self-termination time depends on the re-entry's initial position. In all the simulations with the DT-MRI based cardiac geometry, the anisotropy of the myocardial tissue shortens the time to re-entry self-termination several folds. The numerical simulations depend on the validity of the DT-MRI data set used. The ventricular wall showed the characteristic transmural rotation of the helix angle of the developed mammalian heart, while the fiber orientation in the atria was irregula

Computational Modelling of Cardiac Electrophysiological Changes in Malarial Fever

Cardiac function is impaired in severe malarial fever, and ECGs show changes associated with repolarization. These could contribute to mortality via ventricular arrhythmia. The cardiac effects could be due to the malarial parasite load in the heart, specific cardio-toxic effects of the parasite or cardio-toxic effects of antimalarial agents. We construct a simple 1-dimensional electrophysiological model for the physico-chemical changes clinically observed during malarial fever: with temperature, pH and [ionic]plasma changes. The model can quantitatively reproduce the tachycardia and QTc prolongation seen in the adult, and shortening seen in the child during malarial fever

Dynamic Action Potential Restitution Contributes to Mechanical Restitution in Right Ventricular Myocytes From Pulmonary Hypertensive Rats

We investigated the steepened dynamic action potential duration (APD) restitution of rats with pulmonary artery hypertension (PAH) and right ventricular (RV) failure and tested whether the observed APD restitution properties were responsible for negative mechanical restitution in these myocytes. PAH and RV failure were provoked in male Wistar rats by a single injection of monocrotaline (MCT) and compared with saline-injected animals (CON). Action potentials were recorded from isolated RV myocytes at stimulation frequencies between 1 and 9 Hz. Action potential waveforms recorded at 1 Hz were used as voltage clamp profiles (action potential clamp) at stimulation frequencies between 1 and 7 Hz to evoke rate-dependent currents. Voltage clamp profiles mimicking typical CON and MCT APD restitution were applied and cell shortening simultaneously monitored. Compared with CON myocytes, MCT myocytes were hypertrophied; had less polarized diastolic membrane potentials; had action potentials that were triggered by decreased positive current density and shortened by decreased negative current density; APD was longer and APD restitution steeper. APD90 restitution was unchanged by exposure to the late Na⁺-channel blocker (5 μM) ranolazine or the intracellular Ca²⁺ buffer BAPTA. Under AP clamp, stimulation frequency-dependent inward currents were smaller in MCT myocytes and were abolished by BAPTA. In MCT myocytes, increasing stimulation frequency decreased contraction amplitude when depolarization duration was shortened, to mimic APD restitution, but not when depolarization duration was maintained. We present new evidence that the membrane potential of PAH myocytes is less stable than normal myocytes, being more easily perturbed by external currents. These observations can explain increased susceptibility to arrhythmias. We also present novel evidence that negative APD restitution is at least in part responsible for the negative mechanical restitution in PAH myocytes. Thus, our study links electrical restitution remodeling to a defining mechanical characteristic of heart failure, the reduced ability to respond to an increase in demand

Self-terminating re-entrant cardiac arrhythmias: quantitative characterization

Atrial and ventricular tachyarrhythmia are often sustained by re-entrant propagation, and explained by deterministic models. A quantitative, stochastic description of self-termination provides an alternative to the current paradigm for re-entrant tachyarrhythmia - that of triggers and a substrate, modelled by parametrically heterogeneous deterministic partial differential equations. Atrial and ventricular data was from recordings obtained during routine clinical monitoring and treatment, either noninvasively or invasively. Atrial and ventricular tachycardia are characterised by their initiation times and durations, re-presented as instantaneous rates, whose means estimate transition probabilities/s for onset and termination. These estimated probabilities range from 10(-9) to 10(-1)/s