CCL2 is required for initiation but not persistence of HIV infection mediated neurocognitive disease in mice

Abstract

HIV enters the brain within days of infection causing neurocognitive impairment (NCI) in up to half of infected people despite suppressive antiretroviral therapy. The virus is believed to enter the brain in infected monocytes through chemotaxis to the major monocyte chemokine, CCL2, but the roles of CCL2 in established NCI are not fully defined. We addressed this question during infection of conventional and CCL2 knockout mice with EcoHIV in which NCI can be verified in behavioral tests. EcoHIV enters mouse brain within 5 days of infection, but NCI develops gradually with established cognitive disease starting 25 days after infection. CCL2 knockout mice infected by intraperitoneal injection of virus failed to develop brain infection and NCI. However, when EcoHIV was directly injected into the brain, CCL2 knockout mice developed NCI. Knockout of CCL2 or its principal receptor, CCR2, slightly reduced macrophage infection in culture. Treatment of mice prior to and during EcoHIV infection with the CCL2 transcriptional inhibitor, bindarit, prevented brain infection and NCI and reduced macrophage infection. In contrast, bindarit treatment of mice 4 weeks after infection affected neither brain virus burden nor NCI. Based on these findings we propose that HIV enters the brain mainly through infected monocytes but that resident brain cells are sufficient to maintain NCI. These findings suggest that NCI therapy must act within the brain.

Innate immune responses reverse HIV cognitive disease in mice: Profile by RNAseq in the brain

“…2 ). EcoHIV infection impaired learning in the RAWM at the level of errors in finding a hidden platform or time to do so as we previously reported ( Gu et al, 2018 ; Jaureguiberry-Bravo et al, 2021 ; Kelschenbach et al, 2012 , 2019 ; Kim et al, 2019 , 2023 ; Murphy et al, 2022 ) but limited poly I:C administration restored cognitive function in infected mice ( Dong et al, 2020 ) ( Fig. 1A ).…”

“…All of the most significantly downregulated pathways involve neuronal gene expression indicating that the major effect of HIV in this analysis is loss of function as observed in previous studies of the brain transcriptome from PWH by others and ourselves ( Borjabad et al, 2011 ; Gelman et al, 2004 ). As previously reported and reproduced here, systemic infection induces behavioral defects ( Dong et al, 2020 ; Gu et al, 2018 ; Kim et al, 2019 , 2023 ), likewise it induces subtle changes in selected brain transcripts ( Kim et al, 2019 ) and as shown here, widespread alteration in gene expression in the striatum despite the very low virus burden present in the brain ( Kim et al, 2023 ; Murphy et al, 2022 ). The primary effect of poly I:C is to reduce HIV expression and spread of infection in macrophages and lymphocytes, presumably by its induction of IFN-I pathways ( Dong et al, 2020 ; Wang et al, 2011 ) as shown here, reducing the extent of HIV-associated pathogenic effects.…”

“…Results reported here demonstrate that during systemic EcoHIV infection of wildtype mice, animals exhibit defects in learning ( Dong et al, 2020 ; Gu et al, 2018 ; Kim et al, 2019 , 2023 ) and significantly downregulate roughly 800 genes in striatum. All of the most significantly downregulated pathways involve neuronal gene expression indicating that the major effect of HIV in this analysis is loss of function as observed in previous studies of the brain transcriptome from PWH by others and ourselves ( Borjabad et al, 2011 ; Gelman et al, 2004 ).…”

“…2E ). Systemic EcoHIV infection under the conditions reported here does not induce innate immune responses in the striatum, possibly because the virus burden in the brain at this time after IP injection is at the limit of detection ( Kim et al, 2023 ).…”

“…In brief, five-week-old mice were infected by EcoHIV/NDK at 10 6 pg p24, a dose yielding roughly10 3 copies of HIV gag DNA per 10 6 spleen cells during chronic infection ( Gu et al, 2018 ). Four weeks after infection 50 μg poly I:C was administered by IP injection to mice thrice weekly for two weeks, RAWM assay of learning was conducted during the last week of poly I:C treatment, at time when EcoHIV NCI was established, ( Kim et al, 2023 ). The assay was conducted until uninfected, PBS-treated mice achieve 0 or 1 error to find the hidden platform.…”