A Rat Model of EcoHIV Brain Infection

The Impact of Cannabis Use on Cognition in People with HIV: Evidence of Function-Dependent Effects and Mechanisms from Clinical and Preclinical Studies

PURPOSE OF REVIEW

Cannabis may have beneficial anti-inflammatory effects in people with HIV (PWH); however, given this population's high burden of persisting neurocognitive impairment (NCI), clinicians are concerned they may be particularly vulnerable to the deleterious effects of cannabis on cognition. Here, we present a systematic scoping review of clinical and preclinical studies evaluating the effects of cannabinoid exposure on cognition in HIV.

RECENT FINDINGS

Results revealed little evidence to support a harmful impact of cannabis use on cognition in HIV, with few eligible preclinical data existing. Furthermore, the beneficial/harmful effects of cannabis use observed on cognition were function-dependent and confounded by several factors (e.g., age, frequency of use). Results are discussed alongside potential mechanisms of cannabis effects on cognition in HIV (e.g., anti-inflammatory), and considerations are outlined for screening PWH that may benefit from cannabis interventions. We further highlight the value of accelerating research discoveries in this area by utilizing translatable cross-species tasks to facilitate comparisons across human and animal work.

Microglia Proliferation Underlies Synaptic Dysfunction in the Prefrontal Cortex: Implications for the Pathogenesis of HIV-1-Associated Neurocognitive and Affective Alterations

Microglia, which are productively infected by HIV-1, are critical for brain development and maturation, as well as synaptic plasticity. The pathophysiology of HIV-infected microglia and their role in the pathogenesis of HIV-1-associated neurocognitive and affective alterations, however, remains understudied. Three complementary aims were undertaken to critically address this knowledge gap. First, the predominant cell type expressing HIV-1 mRNA in the dorsolateral prefrontal cortex of postmortem HIV-1 seropositive individuals with HAND was investigated. Utilization of a combined RNAscope multiplex fluorescent and immunostaining assay revealed prominent HIV-1 mRNA in microglia of postmortem HIV-1 seropositive individuals with HAND. Second, measures of microglia proliferation and neuronal damage were evaluated in chimeric HIV (EcoHIV) rats. Eight weeks after EcoHIV innoculation, enhanced microglial proliferation was observed in the medial prefrontal cortex (mPFC) of EcoHIV rats, evidenced by an increased number of cells co-localized with both Iba1+ and Ki67+ relative to control animals. Neuronal damage in EcoHIV infected rats was evidenced by pronounced decreases in both synaptophysin and post synaptic density protein 95 (PSD-95), markers of pre-synaptic and post-synaptic damage, respectively. Third, regression analyses were conducted to evaluate whether microglia proliferation mechanistically underlies neuronal damage in EcoHIV and control animals. Indeed, microglia proliferation accounts for 42-68.6% of the variance in synaptic dysfunction. Collectively, microglia proliferation induced by chronic HIV-1 viral protein exposure may underlie the profound synaptodendritic alterations in HIV-1. Understanding how microglia are involved in the pathogenesis of HAND and HIV-1-associated affective disorders affords a key target for the development of novel therapeutics.

Disrupted Decision-Making: EcoHIV Inoculation in Cocaine Dependent Rats

Independently, chronic cocaine use and HIV-1 viral protein exposure induce neuroadaptations in the frontal-striatal circuit as evidenced by both clinical and preclinical studies; how the frontal-striatal circuit responds to HIV-1 infection following chronic drug use, however, has remained elusive. After establishing experience with both sucrose and cocaine self-administration, a pretest-posttest experimental design was utilized to evaluate preference judgment, a simple form of decision-making dependent upon the integrity of frontal-striatal circuit function. During the pretest assessment, male rats exhibited a clear preference for cocaine, whereas female animals preferred sucrose. Two posttest evaluations (3 days and 6 weeks post inoculation) revealed that, independent of biological sex, inoculation with chimeric HIV (EcoHIV), but not saline, disrupted decision-making. Prominent structural alterations in the frontal-striatal circuit were evidenced by synaptodendritic alterations in pyramidal neurons in the medial prefrontal cortex. Thus, the EcoHIV rat affords a valid animal model to critically investigate how the frontal-striatal circuit responds to HIV-1 infection following chronic drug use.

Humanized Mice for Infectious and Neurodegenerative disorders

Humanized mice model human disease and as such are used commonly for research studies of infectious, degenerative and cancer disorders. Recent models also reflect hematopoiesis, natural immunity, neurobiology, and molecular pathways that influence disease pathobiology. A spectrum of immunodeficient mouse strains permit long-lived human progenitor cell engraftments. The presence of both innate and adaptive immunity enables high levels of human hematolymphoid reconstitution with cell susceptibility to a broad range of microbial infections. These mice also facilitate investigations of human pathobiology, natural disease processes and therapeutic efficacy in a broad spectrum of human disorders. However, a bridge between humans and mice requires a complete understanding of pathogen dose, co-morbidities, disease progression, environment, and genetics which can be mirrored in these mice. These must be considered for understanding of microbial susceptibility, prevention, and disease progression. With known common limitations for access to human tissues, evaluation of metabolic and physiological changes and limitations in large animal numbers, studies in mice prove important in planning human clinical trials. To these ends, this review serves to outline how humanized mice can be used in viral and pharmacologic research emphasizing both current and future studies of viral and neurodegenerative diseases. In all, humanized mouse provides cost-effective, high throughput studies of infection or degeneration in natural pathogen host cells, and the ability to test transmission and eradication of disease.