Human immunodeficiency virus type 1 (HIV-1) is known to provoke microglial immune responses which likely play a paramount role in the development of chronic neuroinflammatory conditions and neuronal damage related to HIV-1 associated
neurocognitive disorders (HAND). In particular, HIV-1
Tat protein is a proinflammatory
neurotoxin which predisposes neurons to synaptodendritic injury. Drugs targeting the degradative
enzymes of endogenous
cannabinoids have shown promise in reducing
inflammation with minimal side effects in rodent models. Considering that markers of
neuroinflammation can predict the extent of neuronal injury in HAND patients, we evaluated the neurotoxic effect of HIV-1 Tat-exposed microglia following blockade of
fatty acid amid hydrolyze (FAAH), a catabolic
enzyme responsible for degradation of
endocannabinoids, e.g.
anandamide (AEA). In the present study, cultured murine microglia were incubated with Tat and/or a FAAH inhibitor (
PF3845). After 24 h, cells were imaged for morphological analysis and microglial
conditioned media (MCM) was collected. Frontal cortex neuron cultures (DIV 7-11) were then exposed to MCM, and neurotoxicity was assessed via live cell
calcium imaging and staining of actin positive dendritic structures. Results demonstrate a strong attenuation of microglial responses to Tat by
PF3845 pretreatment, which is indicated by 1) microglial changes in morphology to a less proinflammatory phenotype using fractal analysis, 2) a decrease in release of neurotoxic
cytokines/
chemokines (MCP-1/CCL2) and
matrix metalloproteinases (
MMPs;
MMP-9) using ELISA/multiplex assays, and 3) enhanced production of
endocannabinoids (AEA) using LC/MS/MS. Additionally,
PF3845's effects on Tat-induced microglial-mediated neurotoxicity, decreased dysregulation of neuronal intracellular
calcium and prevented the loss of actin-positive staining and punctate structure in frontal cortex neuron cultures. Interestingly, these observed
neuroprotective effects appeared to be independent of
cannabinoid receptor activity (CB1R & CB2R). We found that a purported GPR18 antagonist, CID-85469571, blocked the
neuroprotective effects of
PF3845 in all experiments. Collectively, these experiments increase understanding of the role of FAAH inhibition and Tat in mediating microglial neurotoxicity in the HAND condition.