ABSTRACT
The nucleotide-binding oligomerization domain-like receptor X1 (NLRX1) has been associated with various anti-inflammatory mechanisms. We investigated whether the NLRX1 ligand docosahexaenoic acid (DHA) ameliorates lipopolysaccharide (LPS)-induced inflammatory hyperalgesia by interacting with tumor necrosis factor receptor-associated factor 6 (TRAF6)/inhibitor of kB (IkB) kinase (IKK)/IkB-a/nuclear factor-κB (NF-κB) signaling pathway in the central nervous system. Reaction time to thermal stimuli within 30 seconds was measured in male mice injected with saline, lipopolysaccharide (LPS), and/or DHA after 6 hours using the hot plate test. Co-immunoprecipitation and immunoblotting studies were performed to determine the activation of the TRAF6/IKK/IkB-a/NF-kB pathway in the brains and spinal cords of animals. Latency to the thermal stimulus was reduced by 30% in LPS-injected endotoxemic mice compared with saline-injected mice. Treatment with DHA significantly improved latency compared with endotoxemic mice. In the brain and spinal cord of LPS-injected mice, treatment with DHA also prevented the increase in the expression and/or activity of (1) IKKa/IKKß, IKKg, and K63 U in the NLRX1-immunoprecipitated tissues, (2) IKKa/IKKß, K63 U, and K48 U in the IKKg-immunoprecipitated tissues, and (3) IkB-α, NF-kB p65, and interleukin-1ß associated with decreased IkB-α expression. These findings suggest that inhibition of IKK/IkB-a/NF-kB signaling by dissociation of NLRX1 from TRAF6 in response to LPS treatment contributes to the protective effect of DHA against inflammatory hyperalgesia.
Subject(s)
I-kappa B Kinase , NF-kappa B , Male , Mice , Animals , NF-kappa B/metabolism , I-kappa B Kinase/metabolism , I-kappa B Kinase/pharmacology , Lipopolysaccharides/pharmacology , TNF Receptor-Associated Factor 6/metabolism , Docosahexaenoic Acids/pharmacology , Docosahexaenoic Acids/therapeutic use , Hyperalgesia/chemically induced , Hyperalgesia/drug therapy , Ligands , Signal Transduction , Mitochondrial Proteins/metabolismABSTRACT
ABSTRACT: The orphan receptor, G protein-coupled receptor (GPR) 75, which has been shown to mediate various effects of 20-hydroxyeicosatetraenoic acid (20-HETE), is considered as a therapeutic target in the treatment of cardiovascular diseases in which changes in the production of 20-HETE play a key role in their pathogenesis. Our previous studies showed that 20-HETE mimetic, N -(20-hydroxyeicosa-5[Z],14[Z]-dienoyl)glycine (5,14-HEDGE), protects against vascular hyporeactivity, hypotension, tachycardia, and arterial inflammation induced by lipopolysaccharide (LPS) in rats. This study tested the hypothesis that the GPR75 signaling pathway mediates these effects of 5,14-HEDGE in response to systemic exposure to LPS. Mean arterial pressure reduced by 33 mm Hg, and heart rate increased by 102 beats/min at 4 hours following LPS injection. Coimmunoprecipitation studies demonstrated that (1) the dissociation of GPR75/Gα q/11 and GPR kinase interactor 1 (GIT1)/protein kinase C (PKC) α, the association of GPR75/GIT1, large conductance voltage and calcium-activated potassium subunit ß (MaxiKß)/PKCα, MaxiKß/proto-oncogene tyrosine-protein kinase (c-Src), and epidermal growth factor receptor (EGFR)/c-Src, MaxiKß, and EGFR tyrosine phosphorylation were decreased, and (2) the association of GIT1/c-Src was increased in the arterial tissues of rats treated with LPS. The LPS-induced changes were prevented by 5,14-HEDGE. N -[20-Hydroxyeicosa-6( Z ),15( Z )-dienoyl]glycine, a 20-HETE antagonist, reversed the effects of 5,14-HEDGE in the arterial tissues of LPS-treated rats. Thus, similar to 20-HETE, by binding to GPR75 and activating the Gα q/11 /PKCα/MaxiKß, GIT1/PKCα/MaxiKß, GIT1/c-Src/MaxiKß, and GIT1/c-Src/EGFR signaling pathways, 5,14-HEDGE may exert its protective effects against LPS-induced hypotension and tachycardia associated with vascular hyporeactivity and arterial inflammation.
