Biology subjects

Sullivan, M. A.

Publications and source records attributed to Sullivan, M. A..

6 recordsLinked to original sources

bioRxiv2025

Divergent ontogeny of Tissue Resident Memory and Tissue Resident Exhausted CD8+ T cells underlies distinct functional potential

Persistent antigen stimulation promotes differentiation of exhausted CD8+ T (TEX) cells. TEX cells are distinct from circulating memory T (TCIRCM) cells but share many features with tissue-resident memory (TRM) cells established following infection resolution. CD8+ T cells co-expressing residency- and exhaustion-associated molecules in chronic diseases often correlate with clinical outcomes. However, the relationship between these cells and conventional TRM or TEX cells remains unclear. Here, we show that chronic antigen stimulation drives development of tissue-resident TEX (TR-TEX) cells that are ontologically and functionally distinct from TRM cells generated after antigen clearance. TR-TEX phenotypically resembled TRM cells but were regulated by distinct transcriptional networks and were uniquely dependent on Tox for residency programming. Although TEX progenitor cells acquired residency features upon entering chronically infected tissues, they failed to generate conventional TRM cells after antigen withdrawal. Conversely, TRM cells were able to differentiate into TEX cells during chronic antigen stimulation. Deriving cell-state specific transcriptional signatures revealed a selective association of TR-TEX cells with patient responses to immune checkpoint blockade, and only TR-TEX but not TRM cells responded to PD-1 pathway inhibition in vivo. These data suggest that TR-TEX and TRM cells are developmentally distinct cell types that share a tissue-residency program but have distinct roles in disease control.

immunology↗

bioRxiv2022

iPSC-Derived PSEN2 (N141I) Astrocytes and Microglia Exhibit a Primed Inflammatory Phenotype

BackgroundWidescale evidence points to the involvement of glia and immune pathways in the progression of Alzheimers disease (AD). AD-associated iPSC-derived glial cells show a diverse range of AD-related phenotypic states encompassing cytokine/chemokine release, phagocytosis and morphological profiles, but to date studies are limited to cells derived from PSEN1, APOE and APP mutations or sporadic patients. The aim of the current study was to successfully differentiate iPSC-derived microglia and astrocytes from patients harbouring an AD-causative PSEN2 (N141I) mutation and characterise the inflammatory and morphological profile of these cells. MethodsiPSCs from three healthy control individuals and three familial AD patients harbouring a heterozygous PSEN2 (N141I) mutation were used to derive astrocytes and microglia-like cells and cell identity and morphology were characterised through immunofluorescent microscopy. Cellular characterisation involved the stimulation of these cells by LPS and A{beta}42 and analysis of cytokine/chemokine release was conducted through ELISAs and multi-cytokine arrays. The phagocytic capacity of these cells was then indexed by the uptake of fluorescently labelled fibrillar A{beta}42. ResultsAD-derived astrocytes and microglia-like cells exhibited an atrophied and less complex morphological appearance than healthy controls. AD-derived astrocytes showed increased basal expression of GFAP, S100{beta} and increased secretion and phagocytosis of A{beta}42 while AD-derived microglia-like cells showed decreased IL-8 secretion compared to healthy controls. Upon immunological challenge AD-derived astrocytes and microglia-like cells show exaggerated secretion of the pro-inflammatory IL-6, CXCL1, ICAM-1 and IL-8 from astrocytes and IL-18 and MIF from microglia. ConclusionOur study showed, for the first time, the differentiation and characterisation of iPSC-derived astrocytes and microglia-like cells harbouring a PSEN2 (N141I) mutation. PSEN2 (N141I)-mutant astrocytes and microglia-like cells presented with a primed phenotype characterised by reduced morphological complexity, exaggerated pro-inflammatory cytokine secretion and altered A{beta}42 production and phagocytosis.

neuroscience↗

bioRxiv2022

3D Bioprinting of Stem Cell-Derived Central Nervous System Cells Enables Astrocyte Growth, Vasculogenesis and Enhances Neural Differentiation/Function

Current research tools for pre-clinical drug development such as rodent models and 2D immortalised monocultures have failed to serve as effective translational models for human CNS disorders. Recent advancements in the development of iPSCs and 3D culturing can improve the in vivo-relevance of pre-clinical models, while generating 3D cultures though novel bioprinting technologies can offer increased scalability and replicability. As such, there is a need to develop platforms that combine iPSC-derived cells with 3D bioprinting to produce scalable, tunable and biomimetic cultures for preclinical drug discovery applications. We report a biocompatible PEG-based matrix which incorporates RGD and YIGSR peptide motifs and full length collagen IV at a stiffness similar to the human brain (1.5 kPa). Using a high-throughput commercial bioprinter we report the viable culture and morphological development of iPSC-derived astrocytes, brain microvascular endothelial cells, neural progenitors and neurons in our novel matrix. We also show that this system supports endothelial vasculogenesis and enhances neural differentiation and spontaneous activity. This platform forms a foundation for more complex, multicellular models to facilitate high-throughput translational drug discovery for CNS disorders.

neuroscience↗

bioRxiv2020

Perphenazine-macrocycle conjugates divert Aβ42 towards non-toxic aggregates by monomer sequestration.

Alzheimers disease is imposing a growing social and economic burden worldwide and effective therapies are required. Strategies aimed at the removal of fibrillar plaques formed by the amyloid-{beta} peptide have not proved therapeutic and the focus has shifted to approaches that target the cytotoxic oligomeric amyloid-{beta} species that are populated before fibrils are deposited. We have designed and synthesized perphenazine-cyclam conjugates that specifically and rapidly bind to the monomeric form of A{beta}42, reducing the production of both cytotoxic oligomers and amyloid fibrils. We have applied detailed kinetic analysis and NMR spectroscopy to show that the perphenazine-cyclam conjugates divert the A{beta}42 monomer into amorphous aggregates that are not toxic to differentiated SH-SY5Y cells in vitro. Unlike most other amyloid inhibitors studied to date, these conjugates inhibit oligomer and fibril assembly even in the presence of pre-formed fibrillar seeds, demonstrating that they act through a monomer sequestration mechanism. These modular, three-dimensional conjugates therefore effectively prevent monomer-dependent secondary nucleation, the autocatalytic process that generates the majority of toxic oligomers.

biophysics↗

bioRxiv2019

WDR76 promotes MLL-rearranged leukemia via selective recognition of 5-hydroxymethylcytosine in DNA

Although rare, the distribution of the 5-hydroxymethylcytosine (hmC) modification in mammalian DNA is tissue- and gene-specific, yet distinct from its transcriptionally-repressive methylcytosine (mC) precursor, suggesting unique signaling potential. To examine this possibility, we fractionated mammalian brain extracts to discover binding partners specific for oxidized states of mC. We demonstrate that one such factor, WDR76, is a highly hmC-specific binding protein that modulates gene expression within chromosomal regions enriched in hmC where it binds. We demonstrate direct transcriptional activation of several target genes in mouse embryonic stem cells as a function of hmC levels and contingent upon WDR76. In human cell lines and mouse models, WDR76 recruitment by hmC is critical for the initiation and maintenance of MLL-rearranged leukemias. Beyond its canonical role as an intermediate in mC remediation, we show that hmC can be an epigenetic mark whose recognition drives leukemogenesis, portending analogous signaling pathways for other rare DNA modifications.

biochemistry↗

bioRxiv2018

Deficiency of the E3 Ubiquitin Ligase RBCK1 Causes Diffuse Brain Polyglucosan Accumulation and Neurodegeneration

Glycogen synthesis is vital, malstructure resulting in precipitation and accumulation into neurotoxic polyglucosan bodies (PBs). One well-understood mechanism of PB generation is glycogen branching enzyme deficiency (GBED). Less understood is Lafora disease (LD), resulting from absence of the glycogen phosphatase laforin or the E3 ubiquitin ligase malin, and accumulation of hyperphosphorylated PBs. LD afforded first insight that glycogen sphericity depends on more than adequate branching activity. Unexpectedly, deficiencies of the Linear Ubiquitin Chain Assembly Complex (LUBAC) components RBCK1 and HOIP result in PBs in muscle tissues. Here we analyzed nervous system phenotypes of mice lacking RBCK1 and find profuse PB accumulations in brain and spinal cord with extensive neurodegeneration and neurobehavioral deficits. Brain glycogen in these mice is characterized by long chains and hyperphosphorylation, similar to LD. Like in LD, glycogen synthase and branching enzyme are unaltered. Regional PB distribution mirrors LD and not GBED. Perisynaptic PB localization is unlike LD or GBED. The results indicate that RBCK1 is part of a system supplementing laforin-malin in regulating glycogen architecture including in unique neuronal locales.

molecular biology↗