Biology subjects

MacDonald, L.

Publications and source records attributed to MacDonald, L..

10 recordsLinked to original sources

bioRxiv2026

LIMK Inhibition and Metformin Block Mitochondrial Transfer Overcoming Macrophage Driven Therapy Resistance in Acute Myeloid Leukaemia

Chemoresistance is a major contributor to poor clinical outcomes in AML patients and can arise from interactions between AML cells and the bone marrow microenvironment (BME). How immune cells, particularly macrophages (M{varphi}s), facilitate this process requires better clarification. This study shows that M2-like M{varphi}s protect AML cells from apoptosis induced by daunorubicin (DNR) and cytarabine (Ara-C). This protection occurs via co-culture and is linked to enhanced mitochondrial transfer from M{varphi}s to AML cells. M{varphi}s interacted with AML cells via tunneling nanotube (TNT)-like structures. Furthermore, inhibition of mitochondrial transfer using cytochalasin B reduced the protective effect, indicating that mitochondria mediate this process. M{varphi}s transferred functional mitochondria to AML cells as evidenced by enhanced metabolic capacity and reduced reactive oxygen species levels in AML cells under chemotherapy stress. TH-257 (LIMK inhibitor) and metformin blocked mitochondrial transfer and M{varphi}-driven chemoprotection. Moreover, increased transcript expression levels of RhoC and cofilin correlate with inferior overall survival in AML patients. These findings suggest that M2-like M{varphi}s contribute to chemoresistance through TNT-mediated mitochondrial transfer and the LIMK-Cofilin pathway, identifying potential therapeutic targets to circumvent chemoresistance in AML.

cancer biology↗

bioRxiv2026

Synovial lining expressed mechanosensor PIEZO1 drives inflammation-permissive macrophage phenotypes and joint inflammation

Synovial tissue-resident macrophages regulate immune homeostasis within the joint, but can adopt an inflammation-permissive phenotype that promotes immune cell infiltration in rheumatoid arthritis (RA). Understanding the factors that drive this phenotypic switch may help prevent the localisation of inflammation in the joints of individuals at-risk of RA. We identified the mechanosensitive ion channel PIEZO1 as a potential regulator of lining-layer synovial tissue macrophage (STM) function. PIEZO1 was highly expressed in homeostatic, tissue resident TREM2pos lining-layer STMs and in its pathogenic chemokine producing TREM2low phenotype that characterises the hyperplastic lining-layer in active RA. Intra-articular injection of a PIEZO1 agonist in mice induced neutrophil and monocyte infiltration, whereas inhibition of PIEZO1 signalling restored the protective macrophage phenotype. Thus, mechanosensing via PIEZO1 is a defining feature of the joint lining-layer, and its aberrant activation by mechanical stress may lead to the localisation of inflammation within the joint, facilitating a transition from asymptomatic autoimmunity of at-risk RA to clinical disease.

immunology↗

bioRxiv2025

The ontogeny of myeloid-stromal synovial tissue niches in rheumatoid arthritis.

Recent single-cell multi-omic and spatial analyses of synovial biopsies have transformed our understanding of myeloid cell-driven mechanisms underlying human joint pathology and tissue homeostasis in Rheumatoid arthritis (RA). However, the developmental trajectories of synovial tissue macrophage (STM) subsets in humans remain poorly understood, due in part to the lack of models that faithfully replicate synovial tissue niches. This hinders the exploration of the therapeutic potential of targeting specific synovial myeloid cell clusters. Using multi-omics analyses of synovial tissue from an allogeneic bone marrow transplant recipient, we show that joint-specific tissue-resident STM subsets, including both health- and disease-associated clusters, can derive from peripheral blood monocytes. Analysis of embryonic synovial joints revealed that macrophage localization and maturation in the joints are preceded by local stromal niche specialisation, indicating that synovial fibroblasts (FLS) provide tissue-specific instructive cues to STM precursors. To elucidate human STM developmental trajectories, we established a SNP-based fate-tracking human synovial organoid system by embedding distinct blood-derived myeloid precursors, together with FLS clusters from RA synovial biopsies and endothelial cells, into 3D structures. These organoids reproduced key synovial tissue features, including lining and sublining architecture and stromal-myeloid cell cluster composition. Importantly, they supported differentiation of all resident STM subsets: homeostatic lining TREM2pos macrophages, their pathogenic TREM2lowSPP1pos counterparts that characterize the RA hyperplastic lining, and both homeostatic and RA-associated perivascular LYVE1pos STM clusters, all traced to monocytic precursors. In summary, we show that development of STM subsets is driven by fibroblast-conditioned spatial niches. We have established a novel, tractable ex vivo platform to dissect the niche-specific cues driving homeostatic versus pathogenic phenotypic clusters. One Sentence SummaryHuman tissue-resident STMs develop from monocytes under the guidance of cues from FLS within discrete spatial locations.

immunology↗

bioRxiv2025

The synovial lining macrophage layer develops in the first weeks of life in a CSF1- and TGFβ- dependent but monocyte-independent process.

Synovial joints harbor a protective lining layer, consisting of fibroblasts and macrophages, which form an epithelial-like barrier. In inflamed joints, lining macrophages regulate both early inflammatory cell influx and resolution. Despite these critical functions, it is currently unknown at what stage during development the synovial macrophage lining is established, and which signals drive this process. Here, we use a combination of genetic models and in vivo perturbations, single cell transcriptomics and imaging to delineate the process of lining formation in mice. We find that the synovial lining is immature at birth and becomes established within the first 3 weeks of life. In this window, the lining is gradually populated with macrophages that originate from fetal sources, proliferate and acquire the lining-specific transcriptional identity. In contrast, monocytes contribute only minimally to the developing lining, and their input remains limited in healthy adulthood. We identify CSF1 and TGF{beta} as key signals in this process, which also involves mechanosensing through PIEZO1. Our study thus identifies the early postnatal window as a critical period for lining macrophage development, with potential lifelong impact on joint health and disease.

immunology↗

bioRxiv2025

Human Fibroblast-Myeloid cell tissue atlas across lung, synovium, skin and heart

Single-cell RNA sequencing (scRNAseq) of human tissues has expanded our understanding of the complexity of cellular subsets and their changes in disease. The availability of scRNAseq data in different tissues and disease states provides an opportunity to compare cellular subsets and identify common and unique cellular activation. In this study, we aimed to characterize shared and tissue-specific myeloid and stromal phenotypes and uncover key cellular subtypes involved in pathogenic tissue activation. We analyzed scRNAseq data from 14 public datasets, comprising heart, lung, skin, and synovium in both healthy and diseased states. Our analysis identified distinct and overlapping myeloid and stromal cell populations in these tissues. Despite significant inter-individual variability, we were able to identify both shared and disease-specific changes in these cell populations. These findings provide insights into the conserved and tissue-specific roles of myeloid and stromal cells in health and disease and contribute to a better understanding of tissue pathology and potential therapeutic targets.

cell biology↗

bioRxiv2024

PROS1 released by human lung basal cells upon SARS-CoV-2 infection facilitates epithelial cell repair and limits inflammation.

Factors governing the coagulopathy and pneumonitis associated with severe viral infections remain unresolved. We previously found that the expression of protein S (PROS1) is increased in lung epithelium of patients with mild COVID-19 as compared to severe COVID-19. We hypothesised that PROS1 may exert a local effect that protects the upper airway against severe inflammation by modulating epithelial and myeloid cell responses. To test this, in vitro air-interface cultures, seeded from primary healthy human lung epithelial cells, were infected with different SARS-CoV-2 clades. This model, validated by single-cell RNAseq analysis, recapitulated the dynamic cell-profile and pathogenic changes of COVID-19. We showed that PROS1 was located in the basal cells of healthy pseudostratified epithelium. During SARS-Cov-2 infection, PROS1 was released by basal cells, which was partially mediated by interferon. Transcriptome analysis showed that SARS-CoV-2 infection induced proinflammatory phenotypes (CXCL10/11high, PTGS2posF3high, S100A8/A9high) of basal and transitional cells. PROS1 strongly downregulated these cells and transformed the proinflammatory CXCL10/11high basal cells into the regenerative S100A2posKRThigh basal cell phenotype. In addition, SARS-CoV-2 infection elevated M-CSF secretion from epithelium, which induced MERTK, a receptor for PROS1, on monocytes added into 3D lung epithelial culture. We demonstrated that SARS-CoV-2 drives monocyte phenotypes expressing coagulation (F13A1) and complement (C1O) genes. PROS1 significantly downregulated these phenotypes and induced higher expression of MHC class II. Overall, this study demonstrated that the epithelium-derived PROS1 during SARS-CoV-2 infection inhibits the proinflammatory epithelial phenotypes, favours basal cell regeneration, and inhibits myeloid inflammation while enhancing antigen presentation. These findings highlight the importance of basal epithelial cells and PROS1 protection from viral infection induced severe lung pathology. O_FIG O_LINKSMALLFIG WIDTH=193 HEIGHT=200 SRC="FIGDIR/small/612489v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@324deaorg.highwire.dtl.DTLVardef@994f30org.highwire.dtl.DTLVardef@11de2e0org.highwire.dtl.DTLVardef@11a0fe2_HPS_FORMAT_FIGEXP M_FIG 1) SARS-CoV2 infection of the epithelium results in release of IFN. 2) IFN secretion has an autocrine effect on epithelial cells 3) Infection and IFN cause release of PROS1 from the basal cells, as well as M-CSF from the epithelium 4) PROS1 acts on basal cells which express MERTK, a PROS1 receptor 5) PROS1 downregulated the proinflammatory phenotypes expanded by viral infection, while upregulating KRThigh basal cells with repair phenotypes 6) The secreted M-CSF drives MERTK expression on monocytes in cocultures with epithelium. 7) PROS1 induces downregulation of monocyte clusters characteristic of viral infection that express pro-coagulation and complement genes, while upregulating clusters with higher MHC class II. 8) In summary, PROS1 mediates phenotypic switch of SARS-Cov2 induced pathogenic myeloid clusters with complement and coagulation phenotypes into phenotype with efficient antigen presentation, reduces proinflammatory activation of epithelium and induces epithelial barrier repair, resulting in mild COVID-19. C_FIG

cell biology↗

bioRxiv2024

A multi-model approach defines function altering MECP2 missense variants identified in individuals with autism spectrum disorder

Pathogenic variants in MECP2 commonly lead to Rett syndrome, where MECP2s function as a DNA cytosine methylation reader is believed critical. MECP2 variants are also catalogued in individuals with autism spectrum disorder (ASD), including nine missense variants which had no known clinical significance at the start of this study. To assess these nine variants as risk alleles for ASD, we developed MECP2 variant functional assays using budding yeast and Drosophila. We calibrated these assays with known pathogenic and benign variants. Our data predict that four ASD variants are loss of function and five are functional. Protein destabilization offers insight into the altered function of some of these variants. Notably, yeast and Drosophila lack DNA methylation, yet all Rett pathogenic and ASD variants located in the methyl DNA binding domain that we analyzed proved to be loss of function, suggesting a clinically-relevant role for non-methyl DNA-binding by MECP2.

neuroscience↗

bioRxiv2024

Distinct tissue-niche localization and function of synovial tissue myeloid DC subsets in health, and in active and remission Rheumatoid Arthritis

Current rheumatoid arthritis (RA) treatments do not restore immune tolerance. Investigating dendritic cell (DC) populations in human synovial tissue (ST) may reveal pathways to re-instate tolerance in RA. With single-cell and spatial-transcriptomics of synovial tissue biopsies, validated by micro co-culture systems, we identified condition and niche-specific myeloid DC clusters with distinct differentiation trajectories and functions. Healthy synovium contains a unique tolerogenic AXLpos DC2 cluster in the superficial sublining layer. In active RA, a macrophage-rich lining-layer niche becomes populated with inflammatory DC3 clusters that specifically activate memory CCL5pos TEM and CCL5posCXCL13pos TPH, promoting synovitis. In the sublining lymphoid niche, CCR7pos DC2 mReg specifically interact with naive-T-cells, potentially driving the local expansion of new effector T-cells. Sustained remission sees the resolution of these niches but lacks the recovery of tolerogenic AXLpos DC2, indicating latent potential for disease flare. A human RA disease-flare model showed that the activation of blood predecessor of ST-DC3 clusters precedes the onset of inflammation in joints. Therapeutic strategies targeting pathogenic ST-DC3 clusters, or reinstating tolerogenic AXLpos DC2, may restore immune homeostasis in RA. In briefDeconstruction of human RA synovium, using single-cell spatial transcriptomics and micro-culture systems, reveals distinct neighbourhoods within the synovial architecture across health, and RA patients with active disease or sustained remission. Discrete niches are identified that contain distinct myeloid DC clusters that differ in frequency, differentiation trajectories, and effector functions. HighlightsO_LIHuman RA synovium exhibits condition and niche specific myeloid DC clusters that vary in their tissue differentiation trajectories and functions. C_LIO_LIST-CD14pos DC3 (iDC3) support inflammatory CCL5pos TEM and CCL5pos TPH cell activation in the hyperplastic lining layer. C_LIO_LIST-CCR7pos DC2 (mReg), driven by MIR155, interact with naive-T-cells in sublining lymphoid niches. C_LIO_LIA specific inflammatory signature of blood predecessors of ST-DC3s predict flare in RA. C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=199 HEIGHT=200 SRC="FIGDIR/small/600758v1_ufig1.gif" ALT="Figure 1"> View larger version (74K): org.highwire.dtl.DTLVardef@27ab01org.highwire.dtl.DTLVardef@4be238org.highwire.dtl.DTLVardef@1f10734org.highwire.dtl.DTLVardef@1102056_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2023

Primed to resolve: A single cell atlas of the shoulder capsule reveals a cellular basis for resolving inflammatory fibrosis

Fibrotic conditions are a significant global disease burden. While some therapies delay disease progression, none reverse fibrosis. To gain insights into how fibrosis might resolve, we developed a comparative single cell atlas of frozen shoulder capsule tissue; a chronic inflammatory fibrotic human disease that resolves spontaneously. We identified both a population of pro-inflammatory MERTKlowCD48+ macrophages (M{varphi}) and a population of MERTK+LYVE1+MRC1+M{varphi} enriched for negative regulators of inflammation. Micro-cultures of patient-derived cells identified cell-matrix interactions between MERTK+M{varphi} and DKK3+ and POSTN+ fibroblasts, suggesting that matrix remodelling plays a role in the resolution of frozen shoulder. Cross-tissue analysis revealed a shared gene expression cassette between MERTK+M{varphi} in the shoulder capsule and a similar cell population enriched in synovial tissues from rheumatoid arthritis patients in disease remi ssion, supporting the concept that MERTK+M{varphi} provide a cellular basis for the resolution of inflammation and fibrosis. Single-cell transcriptomic profiling and spatial analysis of human foetal shoulder tissues identified MERTK+LYVE1+MRC1+M{varphi} and DKK3+ and POSTN+ fibroblast populations analogous to those identified in adult shoulder capsule, suggesting that the template to resolve fibrosis is established during development. Therapeutic enhancement of crosstalk between MerTK+M{varphi} and pro-resolving DKK3+ and POSTN+ fibroblasts could accelerate resolution of frozen shoulder and resolve persistent inflammatory fibrotic disease in other tissues.

cell biology↗

bioRxiv2020

COVID-19 and Rheumatoid Arthritis share myeloid pathogenic and resolving pathways

BackgroundWe recently delineated the functional biology of pathogenic and inflammation resolving synovial tissue macrophage clusters in rheumatoid arthritis (RA). Whilst RA is not a viral respiratory syndrome, it represents a pro-inflammatory cytokine-driven chronic articular condition often accompanied by cardiovascular and lung pathologies. We hypothesised that functionally equivalent macrophage clusters in the lung might govern inflammation and resolution of COVID-19 pneumonitis. MethodsTo provide insight into the targetable functions of COVID-19 bronchoalveolar lavage (BALF) macrophage clusters, a comparative analysis of BALF macrophage single cell transcriptomics (scRNA-seq) with synovial tissue (ST) macrophage scRNA-seq and functional biology was performed. The function of shared BALF and ST MerTK inflammation-resolving pathway was confirmed with inhibitor in primary macrophage-synovial fibroblast co-cultures. Results. Distinct BALF FCNpos and FCNposSPP1pos macrophage clusters emerging in severe COVID-19 patients were closely related to ST CD48highS100A12pos and CD48posSPP1pos clusters driving synovitis in active RA. They shared transcriptomic profile and pathogenic mechanisms. Healthy lung resident alveolar FABP4pos macrophages shared a regulatory transcriptomic profile, including TAM (Tyro, Axl, MerTK) receptors pathway with synovial tissue TREM2pos macrophages that govern RA remission. This pathway was substantially altered in BALF macrophages of severe COVID-19. In vitro dexamethasone inhibited tissue inflammation via macrophages MerTK function. ConclusionPathogenesis and resolution of COVID-19 pneumonitis and RA synovitis might be driven by similar macrophage clusters and pathways. The MerTK-dependent anti-inflammatory mechanisms of dexamethasone, and the homeostatic function of TAM pathways that maintain RA in remission advocate the therapeutic MerTK agonism to ameliorate the cytokine storm and pneumonitis of severe COVID-19.

immunology↗