NLRX1 ligand, docosahexaenoic acid, ameliorates LPS-induced inflammatory hyperalgesia by decreasing TRAF6/IKK/IkB-a/NF-kB signaling pathway activity.

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.

Activation of GPR75 Signaling Pathway Contributes to the Effect of a 20-HETE Mimetic, 5,14-HEDGE, to Prevent Hypotensive and Tachycardic Responses to Lipopolysaccharide in a Rat Model of Septic Shock.

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.