Browsing by Subject "Disease Models, Animal"
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Item Mechanisms controlling virulence thresholds of mixed viral populations and identification of novel host barriers to poliovirus neuropathogenesis(2012-07-20) Lancaster, Karen; Pfeiffer, Julie K.;Neurotropic viruses comprise some of the worlds most widespread and deadly pathogens, including West Nile virus, rabies virus, and poliovirus. Poliovirus, as a model neurotropic virus, is also an RNA virus. RNA viruses have high mutation rates and a propensity to revert attenuating mutations, contributing to disease and complicating treatment and vaccine development. Despite worldwide epidemics in the early nineteenth century, paralysis from poliovirus is a rare event occurring in less than 1% of poliovirus infections. This suggests the presence of viral and host barriers limiting disease. Here we examined viral barriers by exploring the concept of virulence thresholds using mixtures of virulent and attenuated viruses in a transgenic mouse model of poliovirus infection. We determined that 1000-fold excess of an attenuated strain of poliovirus was protective against disease induced by the virulent strain. Protection was induced locally, was a poliovirus specific effect, and inactivated virus conferred protection. Treatment with a poliovirus receptor-blocking antibody phenocopied the protective effect of inactivated viruses in vitro and in vivo, suggesting virulence thresholds may be modulated by competition for viral receptor. Furthermore, we found the attenuated virus became virulent in immune-deficient mice due to enhanced replication and reversion of attenuating mutations. We also identified additional host barriers limiting pathogenesis using a novel hybridization-based viral diversity assay to quantify the efficiency of poliovirus transport from the periphery to the central nervous system. We found viral replication in peripheral axons is limited and the type I interferon response limits viral replication in peripheral tissues, protecting against disease. Significantly, we discovered that retrograde axonal transport of poliovirus in the sciatic nerve was inefficient and only 20% of viral pool members reaching the brain. The efficiency of viral transport increased upon muscle damage, leading to increased viral diversity and pathogenesis. In summary, we identified a viral induced mechanism controlling virulence of mixed viral populations, and characterized three host barriers that restrict poliovirus pathogenesis in the nervous system. The identification of these barriers restricting virulence may help explain the rare incidence of neurological complications following poliovirus infection and aid in our understanding of viral population dynamics and pathogenesis. [Keywords: poliovirus, neurotropic, interferon, retrograde, axonal, transport, virulence, threshold, virus, barrier]Item Mucosal HIV-1 Transmission In Humanized Mice(2008-05-13) Denton, Paul Wesley; Garcia-Martinez, J. VictorHIV-1 infects ~6,800 people each and every day, transmitting predominantly through unprotected sexual contact. On a global scale, vaginal transmission now accounts for more than half of newly acquired HIV-1 infections. In developed countries intrarectal infection represents a major form of HIV-1 transmission. The social and economic toll of this disease has created an urgency to develop and implement novel approaches capable of preventing HIV-1 transmission. Yet this process has been hindered by the lack of adequate small animal models for pre-clinical efficacy and safety testing. Given the importance of mucosal HIV-1 transmission, the susceptibility of humanized mice to intrarectal and intravaginal HIV-1 infection was investigated. Human lymphocytes, including CD4+ T cells, generated in situ from hematopoietic stem cells reconstitute the gastrointestinal tract and the female reproductive tract of Bone marrow Liver Thymus (BLT) mice. The presence of human CD4+ T cells in these mucosal tissues renders BLT mice susceptible to both intrarectal and intravaginal HIV-1 transmission. Mucosally transmitted HIV-1 disseminates systemically in BLT mice. Effects of disseminated HIV-1 infection include a systemic loss of CD4+ T cells, particularly in gut associated lymphoid tissue, which closely mimics what happens in HIV-1 patients. The utility of humanized mice to study mucosal HIV-1 transmission is particularly highlighted by the demonstration herein that pre-exposure prophylaxis with antiretroviral drugs can prevent intravaginal HIV-1 transmission. This experimental finding has important implications for the clinical implementation of antiretroviral-based pre-exposure prophylactic measures to prevent the spread of AIDS. The goal of this dissertation project was to determine the suitability of the BLT mouse to serve as an animal model of HIV-1 transmission and as a model for assessing interventions aimed at preventing HIV-1 transmission. My conclusions are that BLT mice are susceptible to both intrarectal and intravaginal HIV-1 transmission and that pre-exposure prophylaxis with FDA approved antiretroviral drugs does prevent vaginal transmission in BLT mice. Thus, the BLT mouse system is an excellent candidate for pre-clinical evaluation of both microbicides and pre-exposure prophylactic regimens to prevent mucosal HIV-1 transmission.Item A Mutation in Alk6b Causes Impaired Germ Cell Differentation and Testicular Germ Cell Tumors in Zebrafish(2010-11-02T18:19:23Z) Neumann, Joanie; Amatruda, James F.Germ cell tumors (GCTs) affect infants, children and young adults and are increasing in incidence worldwide. GCTs arise from pluripotent germ cells and can exhibit differentiated and undifferentiated histologies, which vary in their malignant potential and response to treatment. The pathways that determine tumor cell differentiation are not known, impeding the development of new therapies. Thus, the treatment of GCTs has remained static since the introduction 30 years ago of cisplatin which, while effective, causes severe side effects including hearing loss, infertility and kidney damage. We identified a zebrafish mutant line with a high incidence of GCT during a forward genetic screen to identify cancer susceptibility loci. Homozygous adult males develop tumors consisting of undifferentiated spermatogonia by 4 months of age while heterozygous males develop tumors around 7 to 9 months of age. We used interval haplotype analysis and high-resolution recombinational mapping to localize the mutation to a 0.82 cM interval on zebrafish chromosome 10. We identified a premature termination codon in Alk6b (Activin Receptor-like Kinase 6b) in the mutant animals. Alk6b is a member of the TGF-beta/BMP superfamily of receptors. BMP signaling has diverse roles including regulation of cell proliferation, differentiation, embryonic development, germ cell specification and gonadogenesis. Misregulation of the BMP signaling pathway has been implicated in various human cancers. In agreement with a critical role for Alk6b in controlling germ cell differentiation, we find evidence of impaired BMP signal transduction in the zebrafish GCTs, as well as evidence of alterations in the expression level of BMP target genes. We have also examined BMP signaling in a series of 40 clinically-annotated human GCTs of diverse histologic subtypes. In agreement with the predictions made from our zebrafish model, we find that undifferentiated GCTs such as dysgerminomas lack BMP signaling activity, whereas signaling is maintained in the differentiated subtype of Yolk Sac Tumors. These results confirm the relevance of the zebrafish model for understanding germ cell tumorigenesis, and will foster the development of improved, targeted therapy of human GCTs.Item Vulnerability and Resilience to Social Defeat: The Role of Neuroplasticity Within the Mesolimbic Dopamine Circuit(2010-05-14) Krishnan, Vaishnav; Nester, Eric J.The pathophysiology of major depression and post-traumatic stress disorder are poorly understood. In particular, while stressful life events are an important cause of psychopathology, most individuals exposed to adversity maintain normal psychological functioning. The molecular mechanisms underlying this “resilience” are poorly understood. Here, we demonstrate that an inbred population of mice subjected to social defeat can be separated into susceptible and unsusceptible subpopulations which differ along several behavioral and physiological domains. Through a series of molecular and electrophysiological techniques, we identify signature adaptations within the mesolimbic dopamine circuit that are uniquely associated with vulnerability and, by a combination of viral-mediated gene transfer and genetic mouse models, we demonstrate how these adaptations are causally linked to a vulnerable phenotype. We also show that molecular recapitulations of adaptations associated with the unsusceptible phenotype are sufficient to promote resilient behavior. Our results validate a multidisciplinary approach to examine the neurobiological mechanisms of variations in stress resistance, and illustrate the importance of plasticity within the brain’s reward circuits in actively maintaining an emotional homeostasis.