Biology subjects

Lockhart, A.

Publications and source records attributed to Lockhart, A..

7 recordsLinked to original sources

bioRxiv2024

Aberrant iron deposition in the multiple sclerosis spinal cord relates to neurodegeneration

BackgroundIron accumulates in microglia-macrophages at the edge of multiple sclerosis (MS) lesions in the brain. Iron-rimmed brain lesions strongly predict disability accumulation, supporting iron metabolism is crucial in MS pathology. Little is known about iron distribution in the spinal cord. MethodsAutopsy cervical, thoracic and lumbar spinal cord samples from 9 controls and 46 MS donors of whom a subset (n=36) had mesiofrontal motor cortical tissue available for study, were labelled and systematically assessed for iron (DAB-enhanced Turnbull), myelin (PLP), axons (Palmgren silver), microglia-macrophages (TMEM119, Iba1, CD68), astroglia (GFAP), oligodendroglia (OLIG2), acute axonal injury (B-APP, SMI-32, NPY-1R) and oxidative stress (E06). MS lesional and non-lesional areas were considered. Total non-haem iron was quantified by inductively coupled plasma optical emission spectroscopy (ICP-OES). ResultsIn controls, iron predominantly localised to oligodendrocytes with total non-haem iron relating to total myelin fraction, which markedly differed in MS where iron accumulated in microglia-macrophages, subpial astrocytes, and axons in non-lesional areas. Iron laden microglia-macrophages were over-represented relative to total microglial-macrophages and displayed dysmorphic features. Iron-positive axons showed a disto-proximal gradient (highest at lumbar level) with a predilection for the corticospinal tracts. The extent of iron axon positivity related to smaller spinal cord area, lower total axonal counts, and greater oxidative stress. Iron positivity in each cellular compartment (i.e. subpial astrocytes, microglia-macrophage and axons) related to one-another and total non-haem iron correlated with axonal counts in MS. No iron-rimmed lesions were detected in the spinal cord unlike in cortical grey and subcortical white matter of the same cases where 22% and 80% of iron-rimmed lesions, respectively, were seen. ConclusionsDespite the conspicuous absence of iron-rimmed lesions in the MS spinal cord, we demonstrate widespread aberrant iron distribution in the MS spinal cord that relates to oxidative stress and neurodegeneration independent of demyelination. The distal cord predominant and corticospinal tract specific accumulation of iron in axons mirrors the pattern of length-dependent motoric disability commonly encountered in progressive MS. These findings implicate aberrant iron accumulation as a novel, clinically relevant, feature of MS spinal cord pathology.

neuroscience↗

bioRxiv2023

Dietary protein shapes the profile and repertoire of intestinal CD4+ T cells

The intestinal immune system must tolerate food antigens to avoid allergy, a process requiring CD4+ T cells. Combining antigenically defined diets with gnotobiotic models, we show that food and microbiota distinctly influence the profile and T cell receptor repertoire of intestinal CD4+ T cells. Independent of the microbiota, dietary proteins contributed to accumulation and clonal selection of antigen-experienced CD4+ T cells at the intestinal epithelium, imprinting a tissue specialized transcriptional program including cytotoxic genes on both conventional and regulatory CD4+ T cells (Tregs). This steady state CD4+ T cell response to food was disrupted by inflammatory challenge, and protection against food allergy in this context was associated with Treg clonal expansion and decreased pro-inflammatory gene expression. Finally, we identified both steady state epithelium-adapted CD4+ T cells and tolerance-induced Tregs that recognize dietary antigens, suggesting that both cell types may be critical for preventing inappropriate immune responses to food.

immunology↗

bioRxiv2022

Identification of dendritic cell-T cell interactions driving immune responses to food

The intestinal immune system must concomitantly tolerate food and commensals and protect against pathogens. Dendritic cells (DCs) orchestrate these immune responses by presenting luminal antigens and inducing functional differentiation of CD4+ T cells into regulatory (pTreg) or pro-inflammatory (Th) subsets. However, the exact nature of the DCs inducing tolerance or inflammation to dietary antigens has been difficult to define. Using an intestine-adapted Labeling Immune Partnerships by SorTagging Intercellular Contacts (LIPSTIC) combined with single-cell transcriptomics, we characterized DCs presenting dietary antigens in the context of tolerance or infection. At steady-state, migratory cDC1 and cDC2 DCs, but not resident DCs, were found to present dietary antigen to cognate CD4+ T cells. Whereas cDC2s promoted T cell activation, only cDC1s induced their differentiation into pTregs. Infection with the helminth Strongyloides venezuelensis abrogated cDC1 presentation of dietary antigens, preventing pTreg and oral tolerance induction. In contrast, Heligmosomoides polygyrus infection only partially affected cDC1s, allowing oral tolerance to be maintained. An expanded population of cDC2s that induced type-2 immunity during both helminth infections did not present dietary antigens, demonstrating that compartmentalized presentation of luminal antigens can prevent food-specific Th2 responses during inflammatory conditions. Our data uncover novel cellular mechanisms by which tolerance to food is induced and can be disrupted during infections.

immunology↗

bioRxiv2022

Genetic requirements for repair of lesions caused by single genomic ribonucleotides in S phase

Single ribonucleoside monophosphates (rNMPs) are transiently present in eukaryotic genomes. The RNase H2-dependent ribonucleotide excision repair (RER) pathway ensures error-free genomic rNMP removal. In pathological conditions, genomic rNMP levels can rise and persist. If these rNMPs hydrolyse in, or prior to, S phase, toxic single-ended double-strand breaks (seDSBs) can occur upon an encounter with replication forks. How such rNMP-derived seDSB lesions are repaired is unclear. We employed a cell cycle phase restricted allele of RNase H2 as a genetic tool to induce nicks at rNMPs specifically in S phase to generate such lesions and study their repair. Here, we introduce a network of genes that maintain DNA integrity when rNMP-derived nick lesions arise during DNA replication. We use genetic methods to characterise the molecular requirements of a Top1-independent, rNMP-derived nick lesion repair (NLR). In NLR, the RAD52 epistasis group becomes essential for homology-directed repair (HDR). Moreover, the previously described Rtt101Mms1-Mms22 dependent ubiquitylation of histone H3 is essential for NLR in cells with high rNMP load, and loss of Rtt101Mms1-Mms22 combined with RNase H2 dysfunction leads to compromised cellular fitness. We discuss the genetic NLR network in the context of human disease, where cancer therapies may be able to exploit these synthetic lethalities.

genetics↗

bioRxiv2021

Vγ usage distinguishes pro- and anti-tumor intestinal γδ T cell subsets

{gamma}{delta} T cells physiologically scan the intestinal epithelium, representing a substantial fraction of infiltrating lymphocytes in colorectal cancer (CRC), albeit their role in CRC remains unclear. Using murine CRC models, we found that most {gamma}{delta} T cells in pre- or non-tumor colon express V{gamma}1+ or V{gamma}7+ and exhibit a cytotoxic profile. Targeting these {gamma}{delta} T cell subsets, as well as conditionally interfering with {gamma}{delta} T cell function at early stages of tumorigenesis led to heightened tumor development, suggesting anti-CRC functions for V{gamma}1+ and V{gamma}7+ subsets. In contrast, ROR{gamma}t+ {gamma}{delta} T cell subsets, including V{gamma}4+ and microbiotadependent V{gamma}6+, accumulated during CRC progression. Conditional deletion of ROR{gamma}t or V{gamma} chains revealed redundant roles for IL-17-producing V{gamma}4+ and V{gamma}6+ {gamma}{delta} T cells in promoting tumor growth. Our results uncover pro- and anti-tumor roles for {gamma}{delta} T cell subsets.

immunology↗

bioRxiv2019

RNase H1 and H2 are differentially regulated to eliminate RNA-DNA hybrids

RNA-DNA hybrids are tightly regulated to ensure genome integrity. The RNase H enzymes, RNase H1 and H2, contribute to chromosomal stability through the removal of RNA-DNA hybrids. Loss of RNase H2 function is implicated in human diseases of the nervous system and cancer. To better understand RNA-DNA hybrid dynamics, we have focused on elucidating the regulation of the RNase H enzymes themselves. Using yeast as a model system, we demonstrate that RNase H1 and H2 are controlled in different manners. RNase H2 is regulated in a strict cell cycle dependent manner, both in terms of its R-loop removal, and ribonucleotide excision repair functions. RNase H1, however, can function independent of cell cycle stage to remove R-loops, but appears to become activated in response to high R-loop loads. These results provide us with a more complete understanding of how and when RNA-DNA hybrids are acted upon by the RNase H enzymes.

molecular biology↗

bioRxiv2018

Compartmentalized lymph node drainage dictates intestinal adaptive immune responses

The intestinal immune system has the challenging task of tolerating foreign nutrients and the commensal microbiome, while excluding or eliminating ingested pathogens. Failure in such balance leads to a range of severe intestinal and systemic diseases such as inflammatory bowel diseases, food allergies or invasive gastrointestinal infections1,2. Multiple innate and adaptive immune mechanisms are therefore in place to maintain tissue integrity, including efficient peripheral generation of effector T (TH) cells and FOXP3+ regulatory T (pTreg) cells, which mediate resistance to pathogens and regulate excessive immune activation, respectively2-5. The gut-draining mesenteric lymph nodes (mLNs) are critical sites for orchestrating adaptive immunity to luminal perturbations6-8. However, how they manage to simultaneously support tolerogenic and inflammatory reactions is incompletely understood. Here we report that individual mLNs are anatomically and immunologically distinct according to the functional gut segment they drain. Dendritic cell gene signatures and adaptive T cell polarization against the same luminal antigen differed between mLNs along the intestine, the proximal small intestine-draining mLNs preferentially giving rise to tolerogenic and the distal mLNs to pro-inflammatory T cell responses. This compartmentalized dichotomy could be perturbed by duodenal infection, surgical removal of select distal mLNs, dysbiosis, or ectopic antigen delivery, impacting both lymphoid organ and tissue immune responses. Our findings reveal that the conflict between tolerogenic and inflammatory adaptive responses is in part resolved by discrete mLN drainage, and encourage gut segment-specific antigen targeting for therapeutic immune modulation.

immunology↗