Microglia from Mice Transgenic for a Provirus Encoding a Monocyte-Tropic HIV Type 1 Isolate Produce Infectious Virus and Display<i>in Vitro</i>and<i>in Vivo</i>Upregulation of Lipopolysaccharide-Induced Chemokine Gene Expression

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Inflammatory mediators and viral products produced by human immunodeficiency virus (HIV)-infected microglia and astrocytes perturb the function and viability of adjacent uninfected neuronal and glial cells and contribute to the pathogenesis of HIV-associated neurocognitive disorders (HAND). In vivo exposure to lipopolysaccharide (LPS) activates parenchymal microglia and astrocytes and induces cytokine and chemokine production in the brain. HIV-infected individuals display increased circulating LPS levels due to microbial translocation across a compromised mucosa barrier. We hypothesized that HIV-infected microglia and astrocytes display increased sensitivity to the proinflammatory effects of LPS, and this combines with the increased levels of systemic LPS in HIV-infected individuals to contribute to the development of HAND. To examine this possibility, we determined the in vivo responsiveness of HIV-infected microglia and astrocytes to LPS using our mouse model, JR-CSF/human cyclin T1 (JR-CSF/hu-cycT1) mice, which are transgenic for both an integrated full-length infectious HIV type 1 (HIV-1) provirus derived from the primary R5-tropic clinical isolate HIV-1 JR-CSF regulated by the endogenous HIV-1 long terminal repeat and the hu-cycT1 gene under the control of a CD4 promoter. In the current report, we demonstrated that in vivo-administered LPS more potently activated JR-CSF/hu-cycT1 mouse microglia and astrocytes and induced a significantly higher degree of monocyte chemoattractant protein production by JR-CSF/hu-cycT1 astrocytes compared to that of the in vivo LPS response of control littermate mouse microglia and astrocytes. These results indicate that HIV infection increases the sensitivity of microglia and astrocytes to inflammatory stimulation and support the use of these mice as a model to investigate various aspects of the in vivo mechanism of HIV-induced neuronal dysfunction.

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Increased In Vivo Activation of Microglia and Astrocytes in the Brains of Mice Transgenic for an Infectious R5 Human Immunodeficiency Virus Type 1 Provirus and for CD4-Specific Expression of Human Cyclin T1 in Response to Stimulation by Lipopolysaccharides

Sun

Zheng²,

Zhao

et al. 2008

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“…JR-CSF mice are transgenic for a full-length HIV-1 provirus that is expressed in the spleens, lymph nodes, thymuses, and brains of JR-CSF mice, and JR-CSF mouse T lymphocytes, monocytes, and microglia produce infectious HIV-1 (8,47,64). JR-CSF mouse splenocytes express Tat mRNA (data not shown), as determined by analysis using RT-PCR as described previously (31).…”

Section: Transgenic Expression Of Human Cyclin T1 Increases Hiv-1 Promentioning

confidence: 91%

“…HIV-1 infection of monocytes may induce chemokine production that facilitates the spread of infection by inappropriate induction of migration of T lymphocytes and inflammatory cells to the infected cells (62). We had previously demonstrated that MCP-1 gene expression in JR-CSF mouse microglia and brains was more responsive to in vitro and in vivo stimulation with LPS than that in microglia and brains from control mice (64). Therefore, we examined whether expression of the integrated HIV-1 provirus also affects chemokine production by stimulated JR-CSF bone marrow-derived mouse myeloid cells and whether Tat-mediated transactivation contributes to dysregulation of the chemokine response.…”

Section: Fig 4 Human Cyclin T1 Expression Increases the Infectiousnmentioning

confidence: 99%

CD4-Specific Transgenic Expression of Human Cyclin T1 Markedly Increases Human Immunodeficiency Virus Type 1 (HIV-1) Production by CD4⁺T Lymphocytes and Myeloid Cells in Mice Transgenic for a Provirus Encoding a Monocyte-Tropic HIV-1 Isolate

Sun¹,

Soos

KewalRamani

et al. 2006

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Human immunodeficiency virus type 1 (HIV-1)-encoded Tat provides transcriptional activation critical for efficient HIV-1 replication by interacting with cyclin T1 and recruiting P-TEFb to efficiently elongate the nascent HIV transcript. Tat-mediated transcriptional activation in mice is precluded by species-specific structural differences that prevent Tat interaction with mouse cyclin T1 and severely compromise HIV-1 replication in mouse cells. We investigated whether transgenic mice expressing human cyclin T1 under the control of a murine CD4 promoter/enhancer cassette that directs gene expression to CD4؉ T lymphocytes and monocytes/macrophages (hu-cycT1 mice) would display Tat responsiveness in their CD4-expressing mouse cells and selectively increase HIV-1 production in this cellular population, which is infected primarily in HIV-1-positive individuals. To this end, we crossed hu-cycT1 mice with JR-CSF transgenic mice carrying the full-length HIV-1 JR-CSF provirus under the control of the endogenous HIV-1 long terminal repeat and demonstrated that human cyclin T1 expression is sufficient to support Tat-mediated transactivation in primary mouse CD4 T lymphocytes and monocytes/macrophages and increases in vitro and in vivo HIV-1 production by these stimulated cells. Increased HIV-1 production by CD4 ؉ T lymphocytes was paralleled with their specific depletion in the peripheral blood of the JR-CSF/hu-cycT1 mice, which increased over time. In addition, increased HIV-1 transgene expression due to human cyclin T1 expression was associated with increased lipopolysaccharide-stimulated monocyte chemoattractant protein 1 production by JR-CSF mouse monocytes/ macrophages in vitro. Therefore, the JR-CSF/hu-cycT1 mice should provide an improved mouse system for investigating the pathogenesis of various aspects of HIV-1-mediated disease and the efficacies of therapeutic interventions.The transcriptional activator Tat, encoded by human immunodeficiency virus (HIV), is essential for efficient viral replication (13,19,54). Transcriptional activation by Tat is dependent upon its binding to the transactivation response element (TAR), an RNA stem-loop structure that is located downstream from the transcription initiation site in the 5Ј long terminal repeat (LTR) (5, 18, 45). TAR displays a secondary structure that includes a 5Ј bulge from position ϩ23 to position ϩ25 and a central loop at positions ϩ30 to ϩ35 (57). Although the 5Ј bulge and central loop are both required for Tat functional activity, the restricted binding of Tat to the 5Ј bulge and not to the central loop indicated that host cell factors were required to mediate the interaction between Tat and the central loop and subsequent transcriptional activation (32). The requirement for Tat to interact with a human-host-specific cell factor to mediate transactivation provided a rationale for the functional activity of Tat in human cells but not in mouse cells and for the capacity of transferred human chromosome 12 to confer mouse cells with the ability to support Tat tran...

“…Furthermore, infectious HIV-1 is produced by monocytes and microglia from the JR-CSF mice, and LPS-stimulated JR-CSF mouse monocytes and microglia produce higher levels of MCP-1 than monocytes and microglia from LPS-stimulated control mice (65). Because JR-CSF mouse monocytes and microglia carry an HIV-1 provirus regulated by the HIV-1 long terminal repeat, we used this model to investigate whether HIV-1 infection of monocytes increases their in vivo capacity to cross the intact and LPS-compromised BBB and migrate into the brain.…”

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confidence: 98%

Human Immunodeficiency Virus Type 1 Infection Increases the In Vivo Capacity of Peripheral Monocytes To Cross the Blood-Brain Barrier into the Brain and the In Vivo Sensitivity of the Blood-Brain Barrier to Disruption by Lipopolysaccharide

Wang¹,

Sun²,

Goldstein

2008

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Human immunodeficiency virus type 1 (HIV-1), introduced into the brain by HIV-1-infected monocytes which migrate across the blood-brain barrier (BBB), infects resident macrophages and microglia and initiates a process that causes HIV-1-associated neurocognitive disorders. The mechanism by which HIV-1 infection circumvents the BBB-restricted passage of systemic leukocytes into the brain and disrupts the integrity of the BBB is not known. Circulating lipopolysaccharide (LPS), which can compromise the integrity of the BBB, is significantly increased in HIV-1-infected individuals. We hypothesized that HIV-1 infection increases monocyte capacity to migrate across the BBB, which is further facilitated by a compromise of BBB integrity mediated by the increased systemic LPS levels present in HIV-1-infected individuals. To investigate this possibility, we examined the in vivo BBB migration of monocytes derived from our novel mouse model, JR-CSF/EYFP mice, which are transgenic for both a long terminal repeat-regulated full-length infectious HIV-1 provirus and ROSA-26-regulated enhanced yellow fluorescent protein. We demonstrated that JR-CSF/EYFP mouse monocytes displayed an increased capacity to enter the brain by crossing either an intact BBB or a BBB whose integrity was partially compromised by systemic LPS. We also demonstrated that the JR-CSF mouse BBB was more susceptible to disruption by systemic LPS than the control wild-type mouse BBB. These results demonstrated that HIV-1 infection increased the ability of monocytes to enter the brain and increased the sensitivity of the BBB to disruption by systemic LPS, which is elevated in HIV-1-infected individuals. These mice represent a new in vivo system for studying the mechanism by which HIV-1-infected monocytes migrate into the brain.