The flavivirus dengue induces hypertrophy of white

Authors: Kim M Lee Kevin B Chiu Hope A Sansing Peter J Didier Andrew A Lackner Andrew G MacLean

Publish Date: 2016/06/06

Volume: 22, Issue: 6, Pages: 831-839

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Abstract

Flaviviruses including Zika and dengue DENV pose a serious global threat to human health Of the 50+ million humans infected with DENV annually approximately 1–3  progress to severe disease manifestations dengue hemorrhagic fever DHF or dengue shock syndrome DSS Several factors are suspected to mediate the course of infection and pathogenesis of DENV infection DHF and DSS are associated with vascular leakage and neurological sequelae Our hypothesis was that altered astrocyte activation and morphology would alter the dynamics of the extracellular space and hence neuronal and vascular function We investigated the mechanisms of neuropathogenesis DENV infection in rhesus macaques There were decreased numbers of GFAP immunopositive astrocytes per unit area although those that remained had increased arbor length and complexity This was combined with structural hypertrophy of white matter astrocytes in the absence of increased vascular leakage Combined these studies show how even lowgrade infection with DENV induces measurable changes within the parenchyma of infected individualsArboviruses infect over 100 million humans worldwide annually with 3 billion at risk for infection This family of viruses includes Chikungunya Zika and dengue DENV the last two of which are flaviviruses The increased risk for infection may be due in part to the spread of the mosquito vectors of DENV Aedes aegypti and Aedes albopictus WHO 2010The traditional focus on neurons has broadened to include astrocytes microglia and other cell types when examining neuropathogenesis Astrocyte activation is the fastest response in the brain to viral infection and often the only change observed Zlotnik 1968 We have recently observed dramatic changes in astrocyte microanatomy in animals infected with the togavirus Chikungunya Inglis et al 2015 the lentivirus simian immunodeficiency virus SIV Lee et al 2014 or the bacterium Brucella melitensis Lee et al 2013a We have also shown that the order of sequential activation has dramatic alterations in the physiology of astrocytes Renner et al 2013 Primates have six to seven subpopulations of astrocytes Oberheim et al 2009 compared with two types in rodents making the nonhuman primate the ideal model for neuropathological examination Recent evidence suggests that there is specific activation of astrocytes in different areas of brain depending on disease state Lee et al 2013b TorresPlatas et al 2011 As astrocytes are long established as sentinels for neuroinflammation Zlotnik 1968 it would be expected that astrocytes would be activated following infection with DENV Further astrocytes are known to remain in a phenotype associated with activation after virus is cleared from brain tissues Lee et al 2014 Zlotnik 1968 indicating longterm consequences of viral infectionA common sequela to flavivirus infection including infection with DENV is distorted capillaries Cassetti et al 2010 Talavera et al 2004 VelandiaRomero et al 2012 Zlotnik 1968 Zompi and Harris 2012 with downstream petechia and hematomas Onlamoon et al 2010 The mechanisms of these are however poorly understood Previous studies at Tulane National Primate Research Center TNPRC examined intravenous or subcutaneous inoculation of DENV to establish a model for DENV hemorrhagic fever which has been associated with neurological sequelae Maximova et al 2008 Ramos et al 1998 We have recently shown that in macaques with active lentiviral infection of brain there is astrogliosis Lee et al 2014 and increased vascular leakage as evidenced by increased parenchymal fibrinogen Renner et al 2012Our hypothesis was that DENV infection would induce vascular leakage and changes in the microanatomy of primate astrocytes associated with neuropathology To address this question we examined archived brain samples from macaques infected with DENV serotype 2 Our approach was to stain 6μm paraffin sections for fibrinogen ZO1 and glial fibrillary acidic protein GFAP During the acute phase of DENV infection we noted that cortical white matter astrocytes were significantly hypertrophied combined with increased complexity Therefore in the absence of apparent neuroinflammation or vascular leakage there was still immune activation of astrocytes and quantifiable changes to their microarchitectureAs has been described previously Lee et al 2015 animals were maintained in Animal Biosafety Level 2 housing with a 1212h lightdark cycle relative humidity 30 to 70  and a temperature of 178 to 289 °C as is routine at Tulane National Primate Research Center TNPRC is fully accredited by the Association for the Assessment and Accreditation of Laboratory Animal CareInternational Animal Welfare Assurance no A4499–01 All animalrelated protocols were overseen by veterinarians and their staff having been approved by the Institutional Animal Care and Use Committee IACUC and in accordance with to the guidelines prescribed by the NIH Guide to Laboratory Animal Care

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