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Browsing by Author "Powell, Michael D."

Now showing 1 - 6 of 6
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    IL-12 signaling drives the differentiation and function of a T(H)1-derived T-FH1-like cell population
    Powell, Michael D.; Read, Kaitlin A.; Sreekumar, Bharath K.; Jones, Devin M.; Oestreich, Kenneth J. (Springer Nature, 2019-09-30)
    CD4(+) T follicular helper (T-FH) cells provide help to B cells and promote antibody-mediated immune responses. Increasing evidence supports the existence of T-FH populations that secrete cytokines typically associated with the effector functions of other CD4(+) T cell subsets. These include T helper 1 (T(H)1)-biased T-FH (T-FH(1)) cells that have recognized roles in both immune responses to pathogens and also the pathogenesis of autoimmune disease. Given their apparent importance to human health, there is interest in understanding the mechanisms that regulate T-FH1 cell formation and function. However, their origin and the molecular requirements for their differentiation are unclear. Here, we describe a population of murineT(H)1-derived,T-FH1-like cells that express the chemokine receptor Cxcr3 and produce both the T(H)1 cytokine interferon-gamma and the T-FH-associated cytokine interleu kin-21 (IL-21). Furthermore, these T-FH1-like cells promote B cell activation and antibody production at levels indistinguishable from conventional IL-6-derived T-FH-like cells. Regarding their regulatory requirements, we find that IL-12 signaling is necessary for the differentiation and function of this T-FH1-like cell population. Specifically, IL-12-dependent activation of STAT4, and unexpectedly STAT3, promotes increased expression of IL-21 and the T-FH lineage-defining transcription factor Bcl-6 in T-FH1-like cells. Taken together, these findings provide insight into the potential origin and differentiation requirements of T-FH1 cells.
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    IL-7 signalling represses Bcl-6 and the TFH gene Program
    McDonald, Paul W.; Read, Kaitlin A.; Baker, Chandra E.; Anderson, Ashlyn E.; Powell, Michael D.; Ballesteros-Tato, André; Oestreich, Kenneth J. (Nature, 2016-01-08)
    The transcriptional repressor Bcl-6 is linked to the development of both CD4⁺ T follicular helper (TFH) and central memory T (TCM) cells. Here, we demonstrate that in response to decreased IL-2 signalling, T helper 1 (TH1) cells upregulate Bcl-6 and co-initiate TFH- and TCM-like gene programs, including expression of the cytokine receptors IL-6R∝ and IL-7R. Exposure of this potentially bi-potent cell population to IL-6 favours the TFH gene program, whereas IL-7 signalling represses TFH-associated genes including Bcl6 and Cxcr5, but not the TCM-related genes Klf2 and Sell. Mechanistically, IL-7-dependent activation of STAT5 contributes to Bcl-6 repression. Importantly, antigen-specific IL-6R∝⁺IL-7R⁺ CD4⁺ T cells emerge from the effector population at late time points post influenza infection. These data support a novel role for IL-7 in the repression of the TFH gene program and evoke a divergent regulatory mechanism by which post-effector TH1 cells may contribute to long-term cell-mediated and humoral immunity.
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    Insights Into the Regulatory Requirements for T Follicular Helper Cell Development
    Powell, Michael D. (Virginia Tech, 2019-04-22)
    During the course of an immune response, CD4+ T helper cells differentiate into a number of subsets including: T helper 1 (TH1), TH2, TH17, and T follicular helper (TFH) populations. The functional diversity of CD4+ T effector cells results in a coordinated, pathogen-specific immune response. For example, the production of IFNγ by TH1 cells is vital for the clearance of intracellular pathogens, while TFH cell engagement with cognate B cells is required for germinal center (GC) formation and the generation of pathogen- and vaccine- induced antibody production. The development of CD4+ subsets is contingent on extracellular signals, in the form of cytokines, and downstream transcriptional networks responsible for promoting the unique gene expression profile for each subset while simultaneously suppressing alternative cell fates. However, the exact composition of, and stage-specific requirements for, these environmental cytokines and transcription factor networks in the governance of TFH cell differentiation remain incompletely understood. The work in this dissertation seeks to understand how cell-extrinsic cytokine signals and cell-intrinsic transcription factor activities are integrated to properly regulate TFH cell development. Here, we demonstrate that in response to decreased IL-2 and constant IL-12 signaling, T helper 1 (TH1) cells upregulate a TFH-like phenotype, including expression of the TFH lineage defining transcription factor Bcl-6. Intriguingly, our work established that signals from IL-12 were required for both the differentiation and function of this TFH-like population. Mechanistically, IL-12 signals are propagated through both STAT3 and STAT4, leading to the upregulation of the TFH associated genes Bcl6, Il21, and Icos, correlating with increased B cell helper activity. Conversely, exposure of these TFH-like cells to IL-7 results in the STAT5-dependent repression of Bcl-6 and subsequent inhibition of the TFH phenotype. Finally, we describe a novel regulatory mechanism wherein STAT3 and the Ikaros zinc finger transcription factors Ikaros and Aiolos cooperate to regulate Bcl-6 expression in these TFH-like cells. Collectively, the work in this dissertation significantly advances our understanding of the regulatory mechanisms that govern TFH cell differentiation, setting the basis for the rational design of novel immunotherapeutic strategies and increasingly effective vaccines.
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    Pericyte Progenitor Coupling to the Emerging Endothelium during Vasculogenesis via Connexin43
    Payne, Laura Beth; Tewari, Bhanu P.; Dunkenberger, Logan; Bond, Samantha; Savelli, Alyssa; Darden, Jordan; Zhao, Huaning; Willi, Caroline; Kanodia, Ronak; Gude, Rosalie; Powell, Michael D.; Oestreich, Kenneth J.; Sontheimer, Harald; Dal-Pra, Sophie; Chappell, John C. (Lippincott Williams & Wilkins, 2022-04-01)
    Background: Vascular pericytes stabilize blood vessels and contribute to their maturation, while playing other key roles in microvascular function. Nevertheless, relatively little is known about involvement of their precursors in the earliest stages of vascular development, specifically during vasculogenesis. Methods: We combined high-power, time-lapse imaging with transcriptional profiling of emerging pericytes and endothelial cells in reporter mouse and cell lines. We also analyzed conditional transgenic animals deficient in Cx43/Gja1 (connexin 43/gap junction alpha-1) expression within Ng2+ cells. Results: A subset of Ng2-DsRed+ cells, likely pericyte/mural cell precursors, arose alongside endothelial cell differentiation and organization and physically engaged vasculogenic endothelium in vivo and in vitro. We found no overlap between this population of differentiating pericyte/mural progenitors and other lineages including hemangiogenic and neuronal/glial cell types. We also observed cell-cell coupling and identified Cx43-based gap junctions contributing to pericyte-endothelial cell precursor communication during vascular assembly. Genetic loss of Cx43/Gja1 in Ng2+ pericyte progenitors compromised embryonic blood vessel formation in a subset of animals, while surviving mutants displayed little-to-no vessel abnormalities, suggesting a resilience to Cx43/Gja1 loss in Ng2+ cells or potential compensation by additional connexin isoforms. Conclusions: Together, our data suggest that a distinct pericyte lineage emerges alongside vasculogenesis and directly communicates with the nascent endothelium via Cx43 during early vessel formation. Cx43/Gja1 loss in pericyte/mural cell progenitors can induce embryonic vessel dysmorphogenesis, but alternate connexin isoforms may be able to compensate. These data provide insight that may reshape the current framework of vascular development and may also inform tissue revascularization/vascularization strategies.
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    Towards a Physiological Scale of Vocal Fold Agent-Based Models of Surgical Injury and Repair: Sensitivity Analysis, Calibration and Verification
    Garg, Aman; Yuen, Samson; Seekhao, Nuttiiya; Yu, Grace; Karwowski, Jeannie A. C.; Powell, Michael D.; Sakata, Jon T.; Mongeau, Luc; JaJa, Joseph; Li-Jessen, Nicole Y. K. (MDPI, 2019-07-25)
    Agent based models (ABM) were developed to numerically simulate the biological response to surgical vocal fold injury and repair at the physiological level. This study aimed to improve the representation of existing ABM through a combination of empirical and computational experiments. Empirical data of vocal fold cell populations including neutrophils, macrophages and fibroblasts were obtained using flow cytometry up to four weeks following surgical injury. Random Forests were used as a sensitivity analysis method to identify model parameters that were most influential to ABM outputs. Statistical Parameter Optimization Tool for Python was used to calibrate those parameter values to match the ABM-simulation data with the corresponding empirical data from Day 1 to Day 5 following surgery. Model performance was evaluated by verifying if the empirical data fell within the 95% confidence intervals of ABM outputs of cell quantities at Day 7, Week 2 and Week 4. For Day 7, all empirical data were within the ABM output ranges. The trends of ABM-simulated cell populations were also qualitatively comparable to those of the empirical data beyond Day 7. Exact values, however, fell outside of the 95% statistical confidence intervals. Parameters related to fibroblast proliferation were indicative to the ABM-simulation of fibroblast dynamics in final stages of wound healing.
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    Transcriptional Regulation of Amino Acid Transport in Glioblastoma Multiforme
    Umans, Robyn A.; Martin, Joelle; Harrigan, Megan E.; Patel, Dipan C.; Chaunsali, Lata; Roshandel, Aarash; Iyer, Kavya; Powell, Michael D.; Oestreich, Ken; Sontheimer, Harald (MDPI, 2021-12)
    Glioblastoma multiforme (GBM) is a highly invasive brain tumor that typically has poor patient outcomes. This is due in part to aggressive tumor expansion within the brain parenchyma. This process is aided by assiduous glutamate release via the System xc- (SXC) cystine-glutamate antiporter. SXC is over-expressed in roughly half of GBM tumors where it is responsible for glutamate-mediated neuronal cell death and provides excess glutamate to fuel tumor-associated epilepsy. Available pharmacological inhibitors have some promise, although they lack specificity and have poor bioavailability. Therefore, identifying regulators of SXC may provide a superior avenue to target GBM. In this study, we identify tumor protein 53 (TP53) as a molecular regulator of SXC in GBM. Glioblastoma multiforme (GBM) is a deadly brain tumor with a large unmet therapeutic need. Here, we tested the hypothesis that wild-type p53 is a negative transcriptional regulator of SLC7A11, the gene encoding the System xc- (SXC) catalytic subunit, xCT, in GBM. We demonstrate that xCT expression is inversely correlated with p53 expression in patient tissue. Using representative patient derived (PDX) tumor xenolines with wild-type, null, and mutant p53 we show that p53 expression negatively correlates with xCT expression. Using chromatin immunoprecipitation studies, we present a molecular interaction whereby p53 binds to the SLC7A11 promoter, suppressing gene expression in PDX GBM cells. Accordingly, genetic knockdown of p53 increases SLC7A11 transcript levels; conversely, over-expressing p53 in p53-null GBM cells downregulates xCT expression and glutamate release. Proof of principal studies in mice with flank gliomas demonstrate that daily treatment with the mutant p53 reactivator, PRIMA-1(Met), results in reduced tumor growth associated with reduced xCT expression. These findings suggest that p53 is a molecular switch for GBM glutamate biology, with potential therapeutic utility.