ORCID Profile
0000-0002-8056-5348
Current Organisations
Peter MacCallum Cancer Centre
,
Walter and Eliza Hall Institute of Medical Research
,
University of Melbourne
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Publisher: Cold Spring Harbor Laboratory
Date: 03-09-2023
Publisher: American Society of Hematology
Date: 09-09-2010
DOI: 10.1182/BLOOD-2009-12-259663
Abstract: The mechanisms responsible for the brief life span of blood platelets have been a subject of speculation since the 1950s. The most popular hypothesis to date has been the “multiple-hit” model, whereby damage inflicted by external “hits” triggers recognition and clearance by the reticuloendothelial system. Recently, it was demonstrated that platelets contain an apoptotic pathway that mediates their survival in vivo. Using a novel labeling technique to measure population and cohort survival in mice carrying mutations in this pathway, combined with mathematical modeling, we have studied the internal and external control of platelet fate. Our results cast doubt on the veracity of the multiple-hit model. An alternative model, under which platelets are born with an internal “timer,” provides a more parsimonious interpretation of the data. Thus, at steady state, platelet senescence is probably the product of internal processes rather than external hits.
Publisher: S. Karger AG
Date: 2019
DOI: 10.1159/000501297
Publisher: Public Library of Science (PLoS)
Date: 03-01-2014
Publisher: Frontiers Media SA
Date: 30-10-2018
Publisher: Wiley
Date: 06-09-2011
DOI: 10.1111/J.1365-2818.2011.03529.X
Abstract: Cell tracking is a key task in the high-throughput quantitative study of important biological processes, such as immune system regulation and neurogenesis. Variability in cell density and dynamics in different videos, h ers portability of existing trackers across videos. We address these potability challenges in order to develop a portable cell tracking algorithm. Our algorithm can handle noise in cell segmentation as well as isions and deaths of cells. We also propose a parameter-free variation of our tracker. In the tracker, we employ a novel method for recovering the distribution of cell displacements. Further, we present a mathematically justified procedure for determining the gating distance in relation to tracking performance. For the range of real videos tested, our tracker correctly recovers on average 96% of cell moves, and outperforms an advanced probabilistic tracker when the cell detection quality is high. The scalability of our tracker was tested on synthetic videos with up to 200 cells per frame. For more challenging tracking conditions, we propose a novel semi-automated framework that can increase the ratio of correctly recovered tracks by 12%, through selective manual inspection of only 10% of all frames in a video.
Publisher: Cold Spring Harbor Laboratory
Date: 27-10-2023
Publisher: Elsevier BV
Date: 09-2016
DOI: 10.1111/JTH.13397
Abstract: Essentials We examined platelet survival in models of absent or enhanced thrombopoietin (TPO) signaling. Platelet lifespan is normal in transgenic mice with chronically enhanced TPO signaling. Mpl deficiency does not negatively affect platelet lifespan in the absence of thrombocytopenia. We conclude that TPO and its receptor Mpl are dispensable for platelet survival in adult mice. Background It is well established that thrombopoietin (TPO), acting via its receptor Mpl, is the major cytokine regulator of platelet biogenesis. The primary mechanism by which TPO signaling stimulates thrombopoiesis is via stimulation of Mpl-expressing hematopoietic progenitors Mpl on megakaryocytes and platelets acts to control the amount of TPO available. TPO could potentially reduce platelet and/or megakaryocyte apoptosis, and therefore increase the platelet count. However, the effect of TPO receptor signaling on platelet survival is unresolved. Methods and results Here, we investigated platelet survival in mouse models of absent or enhanced TPO signaling. In the absence of thrombocytopenia, Mpl deficiency did not negatively influence platelet lifespan, and nor was platelet survival affected in transgenic mice with chronically increased TPO signaling. Conclusions We conclude that TPO and its receptor Mpl are dispensable for platelet survival in adult mice.
Publisher: Proceedings of the National Academy of Sciences
Date: 14-04-2014
Abstract: Cell ision is essential for an effective immune response. Estimates of rates of ision are often based on DNA measurements interpreted with an appropriate model for internal cell cycle steps. Here we use time-lapse microscopy and single cell tracking of T and B lymphocytes from reporter mice to measure times spent in cell cycle phases. These data led us to a stretched cell cycle model, a novel and improved mathematical description of cell cycle progression for proliferating lymphocytes. Our model can be used to deduce cell cycle parameters for lymphocytes from DNA and BrdU labeling and will be useful when comparing the effects of different stimuli, or therapeutic treatments on immune responses, or to understand molecular pathways controlling cell ision.
Publisher: American Society of Hematology
Date: 04-2020
DOI: 10.1182/BLOODADVANCES.2019001323
Abstract: In eukaryotic cells, messenger RNA (mRNA) molecules are exported from the nucleus to the cytoplasm, where they are translated. The highly conserved protein nuclear RNA export factor1 (Nxf1) is an important mediator of this process. Although studies in yeast and in human cell lines have shed light on the biochemical mechanisms of Nxf1 function, its contribution to mammalian physiology is less clear. Several groups have identified recurrent NXF1 mutations in chronic lymphocytic leukemia (CLL), placing it alongside several RNA-metabolism factors (including SF3B1, XPO, RPS15) whose dysregulation is thought to contribute to CLL pathogenesis. We report here an allelic series of germline point mutations in murine Nxf1. Mice heterozygous for these loss-of-function Nxf1 mutations exhibit thrombocytopenia and lymphopenia, together with milder hematological defects. This is primarily caused by cell-intrinsic defects in the survival of platelets and peripheral lymphocytes, which are sensitized to intrinsic apoptosis. In contrast, Nxf1 mutations have almost no effect on red blood cell homeostasis. Comparative transcriptome analysis of platelets, lymphocytes, and erythrocytes from Nxf1-mutant mice shows that, in response to impaired Nxf1 function, the cytoplasmic representation of transcripts encoding regulators of RNA metabolism is altered in a unique, lineage-specific way. Thus, blood cell lineages exhibit differential requirements for Nxf1-mediated global mRNA export.
Publisher: Cold Spring Harbor Laboratory
Date: 05-06-2023
DOI: 10.1101/2023.06.03.23290918
Abstract: Immune effector cell-associated neurotoxicity syndrome (ICANS) is a relatively common consequence of chimeric antigen receptor T-cell (CAR-T) therapy, with a wide range of possible cognitive presentations. The aim of this study was to characterise a real-word cognitive and psychological status of patients with advanced haematologic and solid organ malignancies planned for CAR-T. We also aimed to examine utility of two cognitive screening approaches. Patients underwent specialist cognitive assessment, including a self-report questionnaire of psychopathology and subjective cognitive function. A subset of in iduals also completed the Montreal Cognitive Assessment (MoCA). Of 60 patients included, 15-16 (25%-27%) presented with evidence of cognitive impairment, with six unique patterns of dysfunction. Impaired patients were more likely to have B-cell acute lymphoblastic leukaemia ( BF 10 =9.30), be younger ( BF 10 =7.76), have bone marrow involvement ( BF 10 =5.18), report history of anxiety ( BF 10 =4.85), or have evidence of psychopathology ( BF 10 =31.30). Analyses did not support the utility of cognitive screening. Of those patients who completed a self-report measure of psychopathology, nine (15.8%) were elevated on at least one symptom domain. The findings demonstrate a broad spectrum of dysfunction and psychopathology in this cohort, emphasising the importance of baseline evaluation for detecting cognitive neurotoxicity symptoms that might arise after CAR-T infusion.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 28-11-2014
Abstract: T cell responses are initiated by antigen and promoted by a range of costimulatory signals. Understanding how T cells integrate alternative signal combinations and make decisions affecting immune response strength or tolerance poses a considerable theoretical challenge. Here, we report that T cell receptor (TCR) and costimulatory signals imprint an early, cell-intrinsic, ision fate, whereby cells effectively count through generations before returning automatically to a quiescent state. This autonomous program can be extended by cytokines. Signals from the TCR, costimulatory receptors, and cytokines add together using a linear ision calculus, allowing the strength of a T cell response to be predicted from the sum of the underlying signal components. These data resolve a long-standing costimulation paradox and provide a quantitative paradigm for therapeutically manipulating immune response strength.
Publisher: Elsevier BV
Date: 07-2009
Abstract: Thymic involution remains a fundamental mystery in immunology. Here we present an argument that this seemingly counterproductive behavior may have evolved to allow for peripheral selection of a T-cell repertoire during young-adult life, optimized for fighting infections and avoiding reaction to self. Age-associated decline in immune function may be viewed as an unfortunate side effect of this selective process. Thus, the key to understanding thymic involution might lie in a more quantitative understanding of T-cell homeostasis in the periphery.
Publisher: Springer Science and Business Media LLC
Date: 06-09-2013
DOI: 10.1038/NCOMMS3406
Publisher: Rockefeller University Press
Date: 12-09-2011
DOI: 10.1084/JEM.20110750
Abstract: It is believed that megakaryocytes undergo a specialized form of apoptosis to shed platelets. Conversely, a range of pathophysiological insults, including chemotherapy, are thought to cause thrombocytopenia by inducing the apoptotic death of megakaryocytes and their progenitors. To resolve this paradox, we generated mice with hematopoietic- or megakaryocyte-specific deletions of the essential mediators of apoptosis, Bak and Bax. We found that platelet production was unperturbed. In stark contrast, deletion of the prosurvival protein Bcl-xL resulted in megakaryocyte apoptosis and a failure of platelet shedding. This could be rescued by deletion of Bak and Bax. We examined the effect on megakaryocytes of three agents that activate the intrinsic apoptosis pathway in other cell types: etoposide, staurosporine, and the BH3 mimetic ABT-737. All three triggered mitochondrial damage, caspase activation, and cell death. Deletion of Bak and Bax rendered megakaryocytes resistant to etoposide and ABT-737. In vivo, mice with a Bak−/− Bax−/− hematopoietic system were protected against thrombocytopenia induced by the chemotherapeutic agent carboplatin. Thus, megakaryocytes do not activate the intrinsic pathway to generate platelets rather, the opposite is true: they must restrain it to survive and progress safely through proplatelet formation and platelet shedding.
Publisher: Springer Science and Business Media LLC
Date: 12-09-2014
DOI: 10.1038/NRI3734-C1
Publisher: Springer Science and Business Media LLC
Date: 13-11-2017
DOI: 10.1038/BMT.2017.239
Abstract: Neurologic complications (NCs) may be a significant source of morbidity and mortality after hematopoietic cell transplantation (HCT). We performed a retrospective study of 263 consecutive patients undergoing allogeneic HCT for hematological malignancies to determine the incidence, risk factors and clinical impact of NCs in the first 5 years after HCT. We determined the incidence of central nervous system (CNS) infection, intracranial hemorrhage, ischemic stroke, metabolic encephalopathy, posterior reversal encephalopathy syndrome, seizure and peripheral neuropathy. In all, 50 patients experienced 63 NCs-37 early (⩽day +100), 21 late (day +101 to 2 years) and 5 very late (2 to 5 years). The 1- and 5-year cumulative incidences of all NCs were 15.6% and 19.2%, respectively, and of CNS complication (CNSC all of the above complications except peripheral neuropathy) were 12.2 and 14.5%. Risk factors for CNSC were age (hazard ratio (HR)=1.06 per year, P=0.0034), development of acute GvHD grade III-IV (HR=2.78, P=0.041), transfusion-dependent thrombocytopenia (HR=3.07, P=0.025) and delayed platelet engraftment (>90th centile HR=2.77, P=0.043). CNSCs negatively impacted progression-free survival (HR=2.29, P=0.0001), overall survival (HR=2.63, P<0.0001) and non-relapse mortality (HR=8.51, P<0.0001). NCs after HCT are associated with poor outcomes, and usually occur early after HCT.
Publisher: American Physical Society (APS)
Date: 06-04-2005
Publisher: Public Library of Science (PLoS)
Date: 07-03-2013
Publisher: Wiley
Date: 17-03-2009
DOI: 10.1038/ICB.2009.11
Abstract: Within an in idual, the population of mature naive T cells is maintained throughout life by both input from the thymus and homeostatic proliferation in the periphery. Here, we develop a mathematical model of this process of naive T-cell homeostasis, and use it to explore questions of lifespan, inheritance and receptor repertoire during ageing. By assuming lifespan is largely determined by a heritable trait reset on mitosis, we show that homeostatic proliferation leads naturally to a longer lived population with age. A plausible candidate for the heritable trait influencing lifespan is T-cell receptor affinity for major histocompatibility molecules loaded with self-peptides. Concurrently with increasing lifespan, receptor ersity decreases with age, thus quantitatively linking these two phenomena. These results depend on the thymus involuting with age so that homeostatic proliferation becomes the dominant mode of replacement of the naive T-cell repertoire.
Publisher: The Royal Society
Date: 16-08-2005
Abstract: In cell lifespan studies the exponential nature of cell survival curves is often interpreted as showing the rate of death is independent of the age of the cells within the population. Here we present an alternative model where cells that die are replaced and the age and lifespan of the population pool is monitored until a steady state is reached. In our model newly generated in idual cells are given a determined lifespan drawn from a number of known distributions including the lognormal, which is frequently found in nature. For lognormal lifespans the analytic steady-state survival curve obtained can be well-fit by a single or double exponential, depending on the mean and standard deviation. Thus, experimental evidence for exponential lifespans of one and/or two populations cannot be taken as definitive evidence for time and age independence of cell survival. A related model for a iding population in steady state is also developed. We propose that the common adoption of age-independent, constant rates of change in biological modelling may be responsible for significant errors, both of interpretation and of mathematical deduction. We suggest that additional mathematical and experimental methods must be used to resolve the relationship between time and behavioural changes by cells that are predominantly unsynchronized.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 20-01-2012
Abstract: During an adaptive immune response, B lymphocytes rapidly ide and differentiate into effector cell populations, including antibody-secreting plasmablasts and memory B cells. Many also change the class of antibody they secrete, through a process called isotype switching. During this process, some cells die. Whether cells acquire these different fates in a stochastic or programmed manner, however, is unclear. Duffy et al. (p. 338 , published online 5 January) used single-cell tracking to determine the times to ision, differentiation into a plasmablast, isotype switching, and death of stimulated B lymphocytes. Statistical analysis and mathematical modeling revealed that these cell-fate decisions appear to be the result of random clocks: Which clock went off first ( ision, differentiation, or death), determined the fate of the cell. Barnett et al. (p. 342 , published online 15 December) sought to determine whether asymmetrical cell ision, which is thought to contribute to effector cell-fate decisions in T cells, may be at work in B lymphocytes. Indeed, factors important for the initiation and maintenance of germinal center B lymphocyte identity, along with an ancestral polarity protein, were asymmetrically distributed and maintained their asymmetry during cell ision.
Publisher: Public Library of Science (PLoS)
Date: 07-01-2016
Publisher: Springer New York
Date: 17-11-2011
DOI: 10.1007/978-1-61779-307-3_5
Abstract: Like many nucleated mammalian cells, the life and death of the anucleate platelet is regulated by Bcl-2 family proteins. Platelets depend on Bcl-x(L) for survival. Bcl-x(L) maintains platelet viability by restraining the killer protein Bak. When Bak is unleashed, it triggers classical intrinsic apoptosis by causing mitochondrial damage. The latter leads to caspase activation and phosphatidylserine (PS) exposure. Platelet apoptosis can be blocked by caspase inhibitors, or by genetic deletion of Bak and its close relative Bax. Perturbations in the platelet apoptosis program lead to changes in platelet life span in vivo. Here, we describe methods to determine platelet life span, enumerate young platelets, and measure hallmarks of platelet apoptosis, such as PS exposure, caspase activation, and mitochondrial dysfunction.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 28-10-2022
DOI: 10.1126/SCIIMMUNOL.ABM8389
Abstract: Vaccines work largely by generating long-lived plasma cells (LLPCs), but knowledge of how such cells are recruited is sparse. Although it is clear that LLPCs preferentially originate in germinal centers (GCs) and relocate to survival niches in bone marrow where they can persist for decades, the issues of the timing of LLPC recruitment and the basis of their retention remain uncertain. Here, using a genetic timest ing system in mice, we show that persistent PCs accrue in bone marrow at an approximately constant rate of one cell per hour over a period spanning several weeks after a single immunization with a model antigen. Affinity-based selection was evident in persisting PCs, reflecting a relative and dynamic rather than absolute affinity threshold as evidenced by the changing pattern of V H gene somatic mutations conveying increased affinity for antigen. We conclude that the life span of persistent, antigen-specific PCs is in part intrinsic, preprogrammed, and varied and that their final number is related to the duration of the response in a predictable way. This implies that modulating vaccines to extend the duration of the GC reaction will enhance antibody-mediated protective immunity.
Location: Australia
No related grants have been discovered for Mark Dowling.