Escalating morphine dosing in HIV-1 Tat transgenic mice with sustained Tat exposure reveals an allostatic shift in neuroinflammatory regulation accompanied by increased neuroprotective non-endocannabinoid lipid signaling molecules and amino acids

Abstract

Background Human immunodeficiency virus type-1 (HIV-1) and opiates cause long-term inflammatory insult to the central nervous system (CNS) and worsen disease progression and HIV-1-related neuropathology. The combination of these proinflammatory factors reflects a devastating problem as opioids have high abuse liability and continue to be prescribed for certain patients experiencing HIV-1-related pain. Methods Here, we examined the impact of chronic (3-month) HIV-1 transactivator of transcription (Tat) exposure to short-term (8-day), escalating morphine in HIV-1 Tat transgenic mice that express the HIV-1 Tat protein in a GFAP promoter-regulated, doxycycline (DOX)-inducible manner. In addition to assessing morphine-induced tolerance in nociceptive responses organized at spinal (i.e., tail-flick) and supraspinal (i.e., hot-plate) levels, we evaluated neuroinflammation via positron emission tomography (PET) imaging using the [18F]-PBR111 ligand, immunohistochemistry, and cytokine analyses. Further, we examined endocannabinoid (eCB) levels, related non-eCB lipids, and amino acids via mass spectrometry. Results Tat-expressing [Tat(+)] transgenic mice displayed antinociceptive tolerance in the tail withdrawal and hot-plate assays compared to control mice lacking Tat [Tat(−)]. This tolerance was accompanied by morphine-dependent increases in Iba-1 ± 3-nitrotryosine immunoreactive microglia, and alterations in pro- and anti-inflammatory cytokines, and chemokines in the spinal cord and striatum, while increases in neuroinflammation were absent by PET imaging of [18F]-PBR111 uptake. Tat and morphine exposure differentially affected eCB levels, non-eCB lipids, and specific amino acids in a region-dependent manner. In the striatum, non-eCB lipids were significantly increased by short-term, escalating morphine exposure, including peroxisome proliferator activator receptor alpha (PPAR-α) ligands N-oleoyl ethanolamide (OEA) and N-palmitoyl ethanolamide (PEA), as well as the amino acids phenylalanine and proline. In the spinal cord, Tat exposure increased amino acids leucine and valine, while morphine decreased levels of tyrosine and valine but did not affect eCBs or non-eCB lipids. Conclusion Overall results demonstrate that 3 months of Tat exposure increased morphine tolerance and potentially innate immune tolerance evidenced by reductions in specific cytokines (e.g., IL-1α, IL-12p40) and microglial reactivity. In contrast, short-term, escalating morphine exposure acted as a secondary stressor revealing an allostatic shift in CNS baseline inflammatory responsiveness from sustained Tat exposure.

HIV‐1 Tat and morphine interactions dynamically shift striatal monoamine levels and exploratory behaviors over time

“…For example, following 1-2 weeks of exposure to opioids, the expression of dopamine D2 receptors increases, and they become super-sensitized-markedly affecting striatal function (Strickland et al, 2022). With sustained Tat exposure and inflammation (1-10 months), key innate immune mechanisms appear to become tolerant, and there is an allostatic shift in a variety of metabolic and physiologic processes (Dickens et al, 2017;Hermes et al, 2020;Nass et al, 2023). F I G U R E 1 0 Tat increased the latency to interact with a novel mouse but did not affect the duration or number of social interactions.…”

“…(2018) expresses 3–7 copies of the tat gene (see Kim et al., 2003), whereas the mice used in the current study only express a single copy of the tat transgene and typically display a slower onset and less severe pathology (Dickens et al., 2017; Nass et al., 2020). Alternatively, we speculate that certain aspects of innate immune responsiveness become tolerant to Tat exposure in a time‐dependent manner (Hermes et al., 2020; Nass et al., 2023), though the reasons why specific innate immune responses become tolerant are not well understood (see Divangahi et al., 2021). Since there are deficits in dopamine in our model, but no decreases in TH‐positive neurons, we speculate that reductions in dopamine biosynthesis likely precede frank losses of TH neurons.…”

“…5-hydroxyindoleacetic acid (5-HIAA), dopamine, neuro-acquired human immunodeficiency virus (neuroHIV), norepinephrine, opioid use disorder, serotonin, tyrosine hydroxylase mice to examine behavioral (Nass et al, 2020(Nass et al, , 2021(Nass et al, , 2022(Nass et al, , 2023 and mass spectrometry analyses (Hermes et al, 2020;Kesby et al, 2017) were used to determine the sample sizes needed to sufficiently power our analyses. A posteriori power calculations were conducted using G*Power 3.1.9.7 (Faul et al, 2007) and suggest that the study was sufficiently powered to discern a medium effect size (d = 0.50) for three-way ANOVA neurochemistry and behavioral assays and a large effect size (d = 0.80) for two-way ANOVA 2-week monoamine metabolite data and dopamine cell data.…”

Depressive-like Behavior Is Accompanied by Prefrontal Cortical Innate Immune Fatigue and Dendritic Spine Losses after HIV-1 Tat and Morphine Exposure

“…However, surprisingly, control Tat(–) saline-treated mice exhibited decreased sucrose preference over time, which is normally stable—potentially due to injection stress [ 94 , 95 ]. Regardless, decreases in compensatory inflammatory cytokines and normalization of aberrant neuronal firing rates and behavior become more apparent with a longer duration of Tat exposure [ 27 , 55 , 59 , 96 , 97 ].…”

“…Further, in the amyloid precursor protein/presenilin 1 (AAP/PS1) model of Alzheimer’s disease, IL-10 knockout mice exhibit decreased amyloid-β deposits in their hippocampus and cortex [ 136 ]. Innate immune fatigue within the striatum, hippocampus, and spinal cord are seen after prolonged Tat (up to 3 months) exposure [ 27 , 97 , 137 ]. Expanding on our previous data showing that 48 h–8 weeks of Tat exposure increases PFC expression of the anti-inflammatory cytokine IL-10 [ 59 ], morphine exacerbated the Tat-induced increase of IL-10 expression in the PFC.…”