Prostaglandin E2 potentiates interferon-γ-induced nitric oxide production in cultured rat microglia

Association of Plasma Eicosanoid Levels With Immune, Viral, and Cognitive Outcomes in People With HIV

BACKGROUND AND OBJECTIVES

To determine whether plasma eicosanoid levels are associated with immune, viral, and cognitive outcomes in people with HIV (PWH).

METHODS

We measured 42 eicosanoids in a longitudinal study of 95 PWH and 25 demographically comparable uninfected participants. Routine clinical chemistry, virologic, immune markers, and a neuropsychological test battery assessing 7 cognitive domains were administered to all participants at 2 study visits over an average of 6.5 months.

RESULTS

Plasma eicosanoid concentrations were elevated in PWH (n = 95) compared with seronegative controls (n = 25) (100% prediction power at 5% false discovery rate [FDR], α = 0.0531) and were negatively associated with lower current and nadir CD4 lymphocyte counts. Higher levels of eicosanoids were associated with impairments in working memory, verbal fluency, and executive function. Higher plasma viral load was associated with elevated proinflammatory eicosanoids (24% prediction power at 5% FDR and 42.4% prediction power at 10% FDR, α = 0.10). Longitudinal analyses showed that eicosanoid levels were correlated with viral load and with plasma creatinine. Despite associations of eicosanoids with viral loads, elevated plasma eicosanoids were similar in virally suppressed and not fully suppressed PWH.

DISCUSSION

These data show that HIV infection is associated with a robust production of eicosanoids that are not substantially reduced by antiretroviral therapy (ART). The sustained elevation of these oxylipins in PWH despite ART may contribute to an accelerated aging phenotype that includes earlier than expected brain and peripheral organ damage.

3',4',7-Trihydroxyflavone Downregulates NO Production in LPS- or IFN-γ-Activated MG6 Microglial Cells by Attenuating the JNK-STAT1 Pathway

Neuroinflammation induced by activated microglia is a key feature of neurodegenerative diseases such as Alzheimer's disease. The natural flavonoid 3',4',7-trihydroxyflavone protects nerve cells from oxidative stress-mediated apoptosis and inhibits the aggregation of amyloid β protein in vitro. However, little is known about its effects on microglial activation. In this study, we investigated the effects of 3',4',7-trihydroxyflavone on lipopolysaccharide (LPS)- or interferon-γ (IFN-γ)-induced neuroinflammatory responses in MG6 microglial cells. 3',4',7-Trihydroxyflavone inhibited LPS- or IFN-γ-mediated nitric oxide (NO) generation and the upregulation of inducible NO synthase (iNOS) in MG6 cells. 3',4',7-Trihydroxyflavone also suppressed LPS- or IFN-γ-mediated phosphorylation of signal transducer and activator of transcription 1 (STAT1), which is crucial for iNOS expression. LPS stimulation induced rapid phosphorylation of c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), and extracellular signal-regulated kinase (ERK) in MG6 cells. 3',4',7-Trihydroxyflavone significantly inhibited the LPS-mediated phosphorylation of JNK, but not that of ERK and p38 MAPK. The inhibitory effect of 3',4',7-trihydroxyflavone on NO generation was mimicked by pharmacological inhibition of the JNK signaling pathway with SP600125. Furthermore, SP600125 significantly inhibited LPS- or IFN-γ-mediated phosphorylation of STAT1 in MG6 cells. These results suggest that 3',4',7-trihydroxyflavone exerts anti-neuroinflammatory effects via inhibition of the JNK-STAT1 pathway in microglia.

Prostaglandin E2 increases the expression of cyclooxygenase-2 in cultured rat microglia

Prostaglandin E₂ (PGE₂) plays pivotal roles in controlling microglial activation with the EP₂ receptor, a PGE₂ receptor subtype. Activated microglia are often reported to increase cyclooxygenase (COX)-2 expression, followed by PGE₂ production, but it is unclear whether extracellular PGE₂ is involved in microglial PGE₂ synthesis. In the present study, we report that PGE₂ increases COX-2 protein in microglia. In a culture system, PGE₂ at 10^-6 M for 3 h increased COX-2 and microsomal PGE synthase (mPGES)-1 mRNA levels, and reduced mPGES-2, but did not affect COX-1 or cytosolic PGE synthase (cPGES) in microglia. PGE₂ at 10^-6 M for 3 h also increased the COX-2 protein level, but did not affect COX-1, mPGES-1, mPGES-2, or cPGES. An EP₂ agonist, ONO-AE1-259-01, also increased COX-2 and mPGES-1 mRNA levels, and reduced mPGES-2, but did not affect COX-1 or cPGES, whereas an EP₁ agonist, ONO-DI-004, an EP₃ agonist, ONO-AE-248, and an EP₄ agonist, ONO-AE1-329, had no effect. Similar to PGE₂, ONO-AE1-259-01 increased the COX-2 protein level, but did not affect COX-1, mPGES-1, mPGES-2, or cPGES. In addition, the effects of PGE₂ were inhibited by an EP₂ antagonist, PF-04418948, but not by an EP₁ antagonist, ONO-8713, an EP₃ antagonist, ONO-AE3-240, or an EP₄ antagonist, ONO-AE3-208, at 10^-6 M. On the other hand, lipopolysaccharide (LPS) increased PGE₂ production, but the LPS-induced PGE₂ production was not affected by ONO-8713, PF-04418948, ONO-AE3-240, or ONO-AE3-208. These results indicate that PGE₂ increases COX-2 protein in microglia through the EP₂ receptor supporting the idea that extracellular PGE₂ has a triggering aspect for microglial activation.

Elevated Levels of Arachidonic Acid-Derived Lipids Including Prostaglandins and Endocannabinoids Are Present Throughout ABHD12 Knockout Brains: Novel Insights Into the Neurodegenerative Phenotype

Derived from arachidonic acid (AA), the endogenous cannabinoid (eCB) 2-arachidonoyl glycerol (2-AG) is a substrate for α/β hydrolase domain-12 (ABHD12). Loss-of-function mutations of ABHD12 are associated with the neurodegenerative disorder polyneuropathy, hearing loss, ataxia, retinitis pigmentosa, and cataract (PHARC). ABHD12 knockout (KO) mice show PHARC-like behaviors in older adulthood. Here, we test the hypothesis that ABHD12 deletion age-dependently regulates bioactive lipids in the CNS. Lipidomics analysis of the brainstem, cerebellum, cortex, hippocampus, hypothalamus, midbrain, striatum and thalamus from male young (3–4 months) and older (7 months) adult ABHD12 KO and age-matched wild-type (WT) mice was performed on over 80 lipids via HPLC/MS/MS, including eCBs, lipoamines, 2-acyl glycerols, free fatty acids, and prostaglandins (PGs). Aging and ABHD12 deletion drove widespread changes in the CNS lipidome; however, the effects of ABHD12 deletion were similar between old and young mice, meaning that many alterations in the lipidome precede PHARC-like symptoms. AA-derived lipids were particularly sensitive to ABHD12 deletion. 2-AG increased in the striatum, hippocampus, cerebellum, thalamus, midbrain, and brainstem, whereas the eCB N-arachidonoyl ethanolamine (AEA) increased in all 8 brain regions, along with at least 2-PGs. Aging also had a widespread effect on the lipidome and more age-related changes in bioactive lipids were found in ABHD12 KO mice than WT suggesting that ABHD12 deletion exacerbates the effects of age. The most robust effects of aging (independent of genotype) across the CNS were decreases in N-acyl GABAs and N-acyl glycines. In conclusion, levels of bioactive lipids are dynamic throughout adulthood and deleting ABHD12 disrupts the wider lipidome, modulating multiple AA-derived lipids with potential consequences for neuropathology.