Biology subjects

Smith, K. J.

Publications and source records attributed to Smith, K. J..

9 recordsLinked to original sources

bioRxiv2026

Common Genetic Variants of The Cardiac Sodium Channel Alter Patient Response to Class 1b Antiarrhythmics

Several common variants have been identified in SCN5A, which encodes the cardiac sodium channel -subunit Nav1.5 and is targeted by class I antiarrhythmics. Lidocaine and its analog mexiletine both have a primary amine that blocks Na+ current. While lidocaine is highly effective in terminating ventricular tachycardia after acute myocardial infarction, mexiletine has been shown to prevent arrhythmia induction in only [~]20% of patients. The factors underlying this inconsistent drug response are unclear. Here, we use cardiomyocytes that are derived from induced pluripotent stem cells to observe that a common polymorphism in the SCN5A gene, S1103Y, exhibits an altered pharmacological response to mexiletine, with enhanced use-dependent and tonic block of peak sodium current. In addition, an unexpected increase in late sodium current causes action potential prolongation. This paradoxical proarrhythmic phenotype shifts the paradigm of conventional antiarrhythmic therapy with mexiletine, suggesting that background variants may alter pharmacological responses leading to unanticipated consequences. Our results suggest that the unique genetic background of patients should inform therapeutic approaches to treat and prevent arrhythmias associated with common cardiac pathologies.

physiology↗

bioRxiv2024

Sodium channel inhibitors alter the progress of tangle development in a mouse model of dementia

Sodium channel inhibitors have been reported to protect against a range of neuroinflammatory and neurodegenerative diseases. Here the effect of chronic administration of two Na+ channel inhibitors with different mechanisms of action, phenytoin and GS967 are tested in mouse models of different stages of Alzheimers disease. Subtle changes in the distribution of plaque sizes were observed in AppNLGF/NLGF mouse at 3 months of age, after being fed control or drug-supplemented chow from weaning onwards, with phenytoin treatment resulting in a significant increase in the frequency of the smallest plaques and a decrease in large plaques. The later pathology of neurofibrillary tangles was studied, in old age, by supplementing the food of transgenic mice with a P301L mutation in Tau. Chronic administration of Na+ inhibitors from 15 months of age resulted in a decrease in the density of MC1-positive neurofibrillary tangles, possibly due to effects on microglial Na+ channels. The density of microglial cells was strongly correlated with the density of neurofibrillary tangles but only in mice treated with the Na+ inhibitors.

neuroscience↗

bioRxiv2024

Proteomic analysis reveals dysregulation of peripheral blood neutrophils in patients with Multiple Sclerosis

Multiple Sclerosis (MS) is a complex auto-inflammatory disease affecting the brain and spinal cord, which results in axonal de-myelination and symptoms including fatigue, pain, and difficulties with vision and mobility. The involvement of the immune system in the pathology of MS is well established, particularly the adaptive T cell response, and there has been a particular focus on the IL-17-producing subset of Th17 cells and their role in driving disease. However, the importance of innate immune cells has not been so well characterised. Here we focused on neutrophils, which are innate immune cells and rapid responders to inflammation, and which have recently been linked to other chronic autoimmune conditions. Multiple strands of evidence in patients with MS and in mice with the experimental autoimmune encephalomyelitis MS model suggest neutrophils may play a role in driving MS inflammation. Here, we performed proteomic analysis on neutrophils from patients with MS and healthy donors, revealing striking differences. In particular, granule proteins were significantly more abundant in the MS neutrophils compared to the healthy controls, with a particular over-abundance of proteins in primary and secondary granules. In addition, members of the MAVS signalling pathway were differently regulated compared to healthy donor cells. Finally, we find that MS neutrophils do not suppress T cell activation equivalently to healthy neutrophils, and in particular are unable to suppress expression of CD161 on the T cells, indicative of Th17 differentiation. We propose that neutrophil dysregulation in MS may contribute to dysfunctional T cell responses.

immunology↗

bioRxiv2022

Comparison of Transcranial Doppler Ultrasound with Computational Fluid Dynamics: Responses to Physiological Stimuli

Few studies have compared transcranial Doppler (TCD) ultrasound with independent techniques such as computational fluid dynamics (CFD) simulations, particularly in response to stimuli. We compared TCD cerebral blood flow velocity in healthy participants with subject-specific CFD simulations to determine differences in techniques. Twelve participants underwent head and neck imaging with 3 Tesla magnetic resonance angiography. Velocity waveforms in the middle cerebral artery (MCA) were measured with TCD while velocity and diameter in the neck arteries were measured with duplex ultrasound at rest, hypercapnia and exercise. Subject-specific CFD simulations were developed for each condition, with velocity waveforms extracted in the same region as TCD. We found that absolute TCD velocities were significantly higher than CFD data, and non-significantly correlated across all conditions (r range 0.030-0.377, all P>0.05). However, relative changes from rest to hypercapnia and exercise generally exhibited significant positive correlations (r range 0.448-0.770), with the strongest correlation being average velocity change from rest to exercise (r=0.770, P<0.01). We have found that although absolute MCA velocity measurements from different sources vary, relative velocity changes yield stronger correlations regardless of source. Our findings indicate relative responses to physiological stimuli, along with absolute data, should be considered for analyzing cerebral blood flow velocity.

bioengineering↗

bioRxiv2022

The antimicrobial peptide cathelicidin is critical for the development of Th17 responses in severe inflammatory disease

Multiple Sclerosis (MS) is a highly prevalent demyelinating autoimmune condition; the mechanisms regulating its severity and progression are unclear. The IL-17-producing Th17 subset of T cells has been widely implicated in MS and in the mouse model, experimental autoimmune encephalomyelitis (EAE). However, the differentiation and regulation of Th17 cells during EAE remain incompletely understood. Although evidence is mounting that the antimicrobial peptide cathelicidin profoundly affects early T cell differentiation, no studies have looked at its role in longer term T cell responses. Now, we report that cathelicidin drives severe EAE disease. It is released from neutrophils, microglia and endothelial cells throughout disease; its interaction with T cells potentiates Th17 differentiation in lymph nodes and Th17 to exTh17 plasticity and IFN-{gamma} production in the spinal cord. As a consequence, mice lacking cathelicidin are protected from severe EAE. In addition, we show that cathelicidin is produced by the same cell types in the active brain lesions in human MS disease. We propose that cathelicidin exposure results in highly activated, cytokine-producing T cells which drive autoimmunity; this is a mechanism through which neutrophils amplify inflammation in the central nervous system.

immunology↗

bioRxiv2021

The role of complex IV activity in the axonal response of mitochondria to demyelination in experimental disease models of multiple sclerosis

Axon loss is a cardinal neuropathological feature of multiple sclerosis (MS). Axonal injury in MS and experimental disease models is most frequently detected in acutely demyelinating regions. Furthermore, acute axonal injury consistently correlates with the extent of inflammatory demyelination. Following lysolecithin-induced demyelination, we recently reported a compensatory response in neurons, where mitochondria move from the cell body to the acutely demyelinated axon and increase the mitochondrial content. We termed this energetics phenomenon, that is also evident in MS, the axonal response of mitochondria to demyelination (ARMD). In the present study, we assessed axonal mitochondrial content as well as axonal mitochondrial respiratory chain complex IV activity (COX) of axons and related these to axonal injury in nine different experimental disease models. We consistently found ARMD in all experimental disease models. However, the increase in mitochondrial content within demyelinated axons was not always accompanied by a proportionate increase in COX activity, particularly in experimental autoimmune encephalomyelitis (EAE). Axonal COX activity inversely correlated with the extent of axonal injury in experimental disease models. Our findings indicate that ARMD is a consistent and prominent finding and emphasises the need to preserve axonal mitochondrial COX activity in inflammatory demyelination, paving the way for the development of novel neuroprotective therapies.

neuroscience↗

bioRxiv2020

The outcome of neutrophil-T cell contact differs depending on activation status of both cell types

Neutrophils and T cells exist in close proximity in lymph nodes and inflamed tissues during health and disease. They are able to form stable interactions, with profound effects on the phenotype and function of the T cells. However, the outcome of these effects are frequently contradictory; in some systems neutrophils suppress T cell proliferation, in others they are activatory or present antigen directly. Published protocols modelling these interactions in vitro do not reflect the full range of interactions found in vivo; they do not examine how activated and naive T cells differentially respond to neutrophils, or whether de-granulating or resting neutrophils induce different outcomes. Here, we established a culture protocol to ask these questions with human T cells and autologous neutrophils. We find that resting neutrophils suppress T cell proliferation, activation and cytokine production but that de-granulating neutrophils do not, and neutrophil released intracellular contents are pro-activatory. Strikingly, we also demonstrate that T cells early in the activation process are susceptible to suppression by neutrophils, while later-stage T cells are not, and naive T cells do not respond at all. Our protocol therefore allows nuanced analysis of the outcome of interaction of these cells and may explain contradictory results observed previously.

immunology↗

bioRxiv2020

The neutrophil antimicrobial peptide cathelicidin promotes Th17 differentiation

The host defence peptide cathelicidin (LL-37 in humans, mCRAMP in mice) is released from neutrophils by de-granulation, NETosis and necrotic cell death; it has potent antibacterial, antiviral and antifungal activity as well as being a powerful immunomodulator. It is released in proximity to CD4+ T cells during inflammatory and infectious disease but its impact on T cell phenotype is scarcely understood. Here we demonstrate that cathelicidin is a powerful Th17 potentiating factor which increases expression of the aryl hydrocarbon receptor (AHR) and the ROR{gamma}t transcription factor, in a TGF-{beta}1-dependent manner. We show that cathelicidin induces IL-17F production in particular, and that its induction of IL-17A+F+ double producing cells is dependent on AHR while its induction of IL-17F single producing cells is not. In the presence of TGF-{beta}1, cathelicidin profoundly suppressed IL-2 and down-regulated T-bet, specifically directing T cells away from Th1 and into a Th17 phenotype. Strikingly, Th17, but not Th1 cells were protected from apoptotic death by cathelicidin, in the first example of a neutrophil-released mediator inducing survival of a T cell subset. Finally, we show that cathelicidin is released by neutrophils in mouse lymph nodes following inoculation of heat-killed Salmonella typhimurium and that cathelicidin-deficient mice have suppressed Th17 responses during inflammation, but not at steady state. We propose that the release of cathelicidin by neutrophils is required for maximal Th17 differentiation and IL-17 production by CD4+ T cells, and that this is one method by which early neutrophilia directs subsequent adaptive immune responses with some sophistication.

immunology↗

bioRxiv2018

A TauP301L mouse model of dementia; development of pathology, synaptic transmission, microglial response and cognition throughout life

BackgroundLate stage Alzheimers disease and other dementias are associated with neurofibrillary tangles and neurodegeneration. Here we describe a mouse (TauD35) carrying human Tau with the P301L mutation that results in Tau hyperphosphorylation and tangles. Previously we have compared gene expression in TauD35 mice to mice which develop plaques but no tangles. A similar comparison of other pathological features throughout disease progression is made here between amyloid{beta} and Tau mice described in Parts I and II of this study.\n\nMethodsIn vitro CA1 patch clamp and field recordings were used to investigate synaptic transmission and plasticity. Plaque load and microglia were investigated with immunohistochemistry. Cognition, locomotor activity and anxiety-related behaviours were assessed with a forced-alternation T-maze, open field and light/dark box.\n\nResultsTransgene copy number in TauD35 mice fell into two groups (HighTAU and LowTAU), allowing assessment of dose-dependent effects of overexpression and resulting in tangle load increasing 100-fold for a 2-fold change in protein levels. Tangles were first detected at 8 (HighTAU) or 13 months (LowTAU) but the effects on synaptic transmission and plasticity and behaviour were subtle. However severe neurodegeneration occurred in HighTAU mice at around 17 months preceded by considerable proliferation but little additional activation of microglia. Proliferation only started as neurodegeneration began at 13 months. Similarly to HighTau mice at 13 months of age, LowTAU mice at 24 months of age showed a comparable tangle load and microglial proliferation. However, LowTAU mice showed no neurodegeneration at this stage and considerable microglial activation, stressing the dependence of these effects on overexpression and/or age.\n\nConclusionsComparison of the effects of amyloid{beta} and plaques without tangles in a model of preclinical Alzheimers disease to the effects of tangles without amyloid{beta} plaques in the late stage model described here may clarify the progressive stages of Alzheimers disease. While Tau hyperphosphorylation and neurofibrillary tangles are eventually sufficient to cause severe neurodegeneration, initial effects on synaptic transmission and the immune response are subtle. In contrast while even with a heavy plaque load little if any neurodegeneration occurs, considerable effects on synaptic transmission and the immune system result, even before plaques are detectable.

neuroscience↗