In situ analysis of neuronal injury and neuroinflammation during HIV-1 infection.

Background: Since the introduction of combination antiretroviral therapy (cART) the brain has become an important human immunodeficiency virus (HIV) reservoir due to the relatively low penetration of many drugs utilized in cART into the central nervous system (CNS). Given the inherent limitations of directly assessing acute HIV infection in the brains of people living with HIV (PLWH), animal models, such as humanized mouse models, offer the most effective means of studying the effects of different viral strains and their impact on HIV infection in the CNS. To evaluate CNS pathology during HIV-1 infection in the humanized bone marrow/liver/thymus (BLT) mouse model, a histological analysis was conducted on five CNS regions, including the frontal cortex, hippocampus, striatum, cerebellum, and spinal cord, to delineate the neuronal (MAP2ab, NeuN) and neuroinflammatory (GFAP, Iba-1) changes induced by two viral strains after 2 weeks and 8 weeks post-infection.

Results: Findings reveal HIV-infected human cells in the brain of HIV-infected BLT mice, demonstrating HIV neuroinvasion. Further, both viral strains, HIV-1_JR-CSF and HIV-1_CH040, induced neuronal injury and astrogliosis across all CNS regions following HIV infection at both time points, as demonstrated by decreases in MAP2ab and increases in GFAP fluorescence signal, respectively. Importantly, infection with HIV-1_JR-CSF had more prominent effects on neuronal health in specific CNS regions compared to HIV-1_CH040 infection, with decreasing number of NeuN⁺ neurons, specifically in the frontal cortex. On the other hand, infection with HIV-1_CH040 demonstrated more prominent effects on neuroinflammation, assessed by an increase in GFAP signal and/or an increase in number of Iba-1⁺ microglia, across CNS regions.

Conclusion: These findings demonstrate that CNS pathology is widespread during acute HIV infection. However, neuronal loss and the magnitude of neuroinflammation in the CNS is strain dependent indicating that strains of HIV cause differential CNS pathologies.