Daniel Cowley

Burnet Institute, Melbourne, Victoria, Australia

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Publications (10)40.17 Total impact

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    ABSTRACT: Human immunodeficiency virus type-1 (HIV-1) invades the central nervous system (CNS) during acute infection which can result in HIV-associated neurocognitive disorders in up to 50 % of patients, even in the presence of combination antiretroviral therapy (cART). Within the CNS, productive HIV-1 infection occurs in the perivascular macrophages and microglia. Astrocytes also become infected, although their infection is restricted and does not give rise to new viral particles. The major barrier to the elimination of HIV-1 is the establishment of viral reservoirs in different anatomical sites throughout the body and viral persistence during long-term treatment with cART. While the predominant viral reservoir is believed to be resting CD4(+) T cells in the blood, other anatomical compartments including the CNS, gut-associated lymphoid tissue, bone marrow, and genital tract can also harbour persistently infected cellular reservoirs of HIV-1. Viral latency is predominantly responsible for HIV-1 persistence and is most likely governed at the transcriptional level. Current clinical trials are testing transcriptional activators, in the background of cART, in an attempt to purge these viral reservoirs and reverse viral latency. These strategies aim to activate viral transcription in cells constituting the viral reservoir, so they can be recognised and cleared by the immune system, while new rounds of infection are blocked by co-administration of cART. The CNS has several unique characteristics that may result in differences in viral transcription and in the way latency is established. These include CNS-specific cell types, different transcription factors, altered immune surveillance, and reduced antiretroviral drug bioavailability. A comprehensive understanding of viral transcription and latency in the CNS is required in order to determine treatment outcomes when using transcriptional activators within the CNS.
    Journal of NeuroVirology 07/2014; · 2.85 Impact Factor
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    ABSTRACT: Abstract New evidence indicates that astrocytes of the central nervous system (CNS) are extensively infected with human immunodeficiency virus type 1 (HIV-1) in vivo. Although no new virus is produced, this nonproductive or restricted infection contributes to the pathogenesis of HIV-associated dementia (HAD) and compromises virus eradication strategies. The HIV-1 long terminal repeat (LTR) plays a critical role in regulating virus production from infected cells. Here, we determined whether LTRs derived from CNS and non-CNS compartments are genetically and functionally distinct and contribute to the restricted nature of astrocyte infection. CNS- and/or non-CNS-derived LTRs (n=82) were cloned from primary HIV-1 viruses isolated from autopsy tissues of seven patients who died with HAD. Phylogenetic analysis showed interpatient and intrapatient clustering of LTR nucleotide sequences. Functional analysis showed reduced basal transcriptional activity of CNS-derived LTRs in both astrocytes and T cells compared to that of non-CNS-derived LTRs. However, LTRs were heterogeneous in their responsiveness to activation by Tat. Therefore, using a relatively large, independent panel of primary HIV-1 LTRs derived from clinically well-characterized subjects, we show that LTRs segregate CNS- from non-CNS-derived tissues both genetically and functionally. The reduced basal transcriptional activity of LTRs derived from the CNS may contribute to the restricted HIV-1 infection of astrocytes and latent infection within the CNS. These findings have significance for understanding the molecular basis of HIV-1 persistence within cellular reservoirs of the CNS that need to be considered for strategies aimed at eradicating HIV-1.
    AIDS research and human retroviruses 08/2012; · 2.18 Impact Factor
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    ABSTRACT: Human immunodeficiency virus type 1 (HIV-1) nef undergoes adaptive evolution in the central nervous system (CNS), reflecting altered requirements for HIV-1 replication in macrophages/microglia and brain-specific immune selection pressures. The role of Nef in HIV-1 neurotropism and pathogenesis of HIV-associated dementia (HAD) is unclear. In this study, we characterized 82 nef alleles cloned from brain, cerebral spinal fluid, spinal cord, and blood/lymphoid tissue-derived HIV-1 isolates from seven subjects with HAD. CNS isolate-derived nef alleles were genetically compartmentalized and had reduced sequence diversity compared to those from lymphoid tissue isolates. Defective nef alleles predominated in a brain-derived isolate from one of the seven subjects (MACS2-br). The ability of Nef to down-modulate CD4 and MHC class 1 (MHC-1) was generally conserved among nef alleles from both CNS and lymphoid tissues. However, the potency of CD4 and MHC-1 down-modulation was variable, which was associated with sequence alterations known to influence these Nef functions. These results suggest that CD4 and MHC-1 down-modulations are highly conserved functions among nef alleles from CNS- and lymphoid tissue-derived HIV-1 isolates that may contribute to viral replication and escape from immune surveillance in the CNS.
    Journal of NeuroVirology 02/2011; 17(1):82-91. · 2.85 Impact Factor
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    ABSTRACT: Human immunodeficiency virus type 1 (HIV-1) demonstrates a high degree of viral diversity which has an impact on viral fitness. Genetic compartmentalization of HIV-1 proteins between central nervous system (CNS) and lymphoid tissues is well established and reflects altered requirements for HIV-1 replication in macrophages/microglia, brain-specific immune selection pressures and possibly the timing of virus invasion of the CNS. Tat-encoding mRNA has been detected in the CNS of HIV-1 infected individuals and its neurotoxic effects in the CNS are well documented. However, while CNS-derived tat sequences have demonstrated significant diversity, the effect of this molecular diversity on transcriptional regulation and its impact on the pathogenesis of HIV-associated dementia (HAD) remains unclear. In this study, we cloned and characterised 44 unique tat alleles from brain, cerebral spinal fluid, spinal cord and blood/lymphoid tissue-derived HIV-1 isolates from five subjects with HAD. While phylogenetic analyses revealed tissue-specific compartmentalization of Tat variants for two patients, broad compartmentalization across the panel of tissue-derived viruses was not observed. Despite the lack of consistent tissue-specific compartmentalization, sequence variations within patients segregated CNS and non-CNS tat alleles. These amino acid alterations predominated within the transactivation domain of Tat and could account for alterations in the ability of particular Tat proteins to transactivate the LTR. Although a subset of patients demonstrated reduced transactivation capacity among CNS-derived Tat proteins compared to those from matched lymphoid tissues, overall Tat proteins from the CNS to lymphoid compartments maintained similar levels of transactivation function. Together, these data suggest that despite the observed heterogeneity in tat alleles isolated from matched lymphoid to CNS compartments, Tat function is maintained, highlighting the importance of Tat function in HIV-1 neuropathogenesis.
    Journal of NeuroVirology 02/2011; 17(1):70-81. · 2.85 Impact Factor
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    ABSTRACT: While CCR5 is the principal coreceptor used by macrophage (M)-tropic HIV-1, not all primary CCR5-using (R5) viruses enter macrophages efficiently. Here, we used functionally-diverse R5 envelope (Env) clones to characterize virus-cell interactions important for efficient CCR5-mediated macrophage entry. The magnitude of macrophage entry by Env-pseudotyped reporter viruses correlated with increased immunoreactivity of CD4-induced gp120 epitopes, increased ability to scavenge low levels of cell-surface CCR5, reduced sensitivity to the CCR5 inhibitor maraviroc, and increased dependence on specific residues in the CCR5 ECL2 region. These results are consistent with an altered and more efficient mechanism of CCR5 engagement. Structural studies revealed potential alterations within the gp120 V3 loop, the gp41 interaction sites at the gp120 C- and N-termini, and within the gp120 CD4 binding site which may directly or indirectly lead to more efficient CCR5-usage. Thus, enhanced gp120-CCR5 interactions may contribute to M-tropism of R5 HIV-1 strains through different structural mechanisms.
    Virology 09/2010; 404(2):269-78. · 3.35 Impact Factor
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    ABSTRACT: CCR5-using (R5) human immunodeficiency virus type 1 (HIV-1) strains cause CD4+ T-cell loss in most infected individuals, but mechanisms underlying cytopathicity of R5 viruses are poorly understood. We investigated mechanisms contributing to R5 envelope glycoprotein (Env)-mediated cellular apoptosis by constructing a panel of retroviral vectors engineered to co-express GFP and R5 Envs derived from two HIV-1-infected subjects spanning asymptomatic (Early, E-R5 Envs) to late stages of infection (Late, L-R5 Envs). The L-R5 Envs induced significantly more cellular apoptosis than E-R5 Envs, but only in Env-expressing (GFP-positive) cells, and only in cells where CD4 and CCR5 levels were limiting. Studies with fusion-defective Env mutants showed induction of apoptosis required membrane-fusing events. Our results provide evidence for an intracellular mechanism of R5 Env-induced apoptosis of CD4+ cells that requires membrane fusion. Furthermore, they contribute to a better understanding of mechanisms involved in CD4+ T-cell loss in subjects experiencing progressive R5 HIV-1 infection.
    Virology 11/2009; 396(2):246-55. · 3.35 Impact Factor
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    ABSTRACT: Astrocyte infection with human immunodeficiency virus (HIV) is considered rare, so astrocytes are thought to play a secondary role in HIV neuropathogenesis. By combining double immunohistochemistry, laser capture microdissection, and highly sensitive multiplexed polymerase chain reaction to detect HIV DNA in single astrocytes in vivo, we showed that astrocyte infection is extensive in subjects with HIV-associated dementia, occurring in up to 19% of GFAP+ cells. In addition, astrocyte infection frequency correlated with the severity of neuropathological changes and proximity to perivascular macrophages. Our data indicate that astrocytes can be extensively infected with HIV, and suggest an important role for HIV-infected astrocytes in HIV neuropathogenesis.
    Annals of Neurology 04/2009; 66(2):253-8. · 11.19 Impact Factor
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    ABSTRACT: The authors studied the transcriptional activity of blood-and cerebrospinal fluid (CSF)-derived nef/long-terminal repeat (LTR) sequences isolated from a slow progressor infected with nef-deleted human immunodeficiency virus type 1 (HIV-1) who developed HIV-associated dementia (HIVD). The transcriptional activity of CSF-derived nef/LTR clones isolated during HIVD was up to 4.5-fold higher than blood-derived clones isolated before and during HIVD when tested under basal, phorbol 12-myristate 13-acetate-(PMA-), and Tat-activated conditions, and was associated with the presence of duplicated nuclear factor (NF)-kappaB and specificity factor-1 (Sp-1) binding sites coupled with a truncated nef sequence, increased replication capacity, and high CSF viral load. Thus, nef and LTR mutations that augment transcription may contribute to neuropathogenesis of nef-deleted HIV-1.
    Journal of NeuroVirology 07/2006; 12(3):219-28. · 2.85 Impact Factor
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    ABSTRACT: The importance of astrocytes as a reservoir of human immunodeficiency virus type 1 (HIV-1) in the brain remains elusive. By combining immunohistochemistry, laser capture microdissection, and triple-nested Alu-PCR, we demonstrate integrated HIV-1 in astrocytes and macrophages isolated directly from autopsy brain tissues of HIV-1-infected subjects. The ability of HIV-1 to integrate in terminally differentiated astrocytes suggests a permanent reservoir of provirus in brain that will impact the development and likely success of strategies aimed at eradicating HIV-1.
    Journal of NeuroVirology 05/2006; 12(2):146-52. · 2.85 Impact Factor
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    ABSTRACT: We studied the evolution and compartmentalization of nef/long terminal repeat (nef/LTR)-deleted human immunodeficiency virus type 1 (HIV-1) from a long-term survivor who developed HIV-associated dementia (HIVD). Analysis of sequential blood-derived HIV-1 isolated before and during HIVD revealed a persistent R5X4 phenotype and a progressive loss of nef/LTR sequence; in contrast, HIV-1 present in cerebrospinal fluid during HIVD had an R5 phenotype, distinct nef/LTR sequence of unique deletions and additional nuclear factor- kappa B sites and specificity factor-1 sites, and enhanced transcriptional activity, compared with the blood-derived isolates. Thus, nef/LTR-deleted HIV-1 strains may undergo compartmentalized evolution in long-term survivors and cause neurologic disease.
    The Journal of Infectious Diseases 01/2005; 190(12):2181-6. · 5.85 Impact Factor