Arachidonic Acid Metabolite 19(S)-HETE Induces Vasorelaxation and Platelet Inhibition by Activating Prostacyclin (IP) Receptor
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RESEARCH ARTICLE Arachidonic Acid Metabolite 19(S)-HETE Induces Vasorelaxation and Platelet Inhibition by Activating Prostacyclin (IP) Receptor Sorin Tunaru1*, Ramesh Chennupati1, Rolf M. NuÈ sing2, Stefan Offermanns1,3* 1 Max-Planck-Institute for Heart and Lung Research, Department of Pharmacology, Ludwigstr. 43, 61231 Bad Nauheim, Germany, 2 Institute for Clinical Pharmacology, J.W. Goethe University Frankfurt, Theodor- Stern-Kai 7, 60590 Frankfurt, Germany, 3 Medical Faculty, J.W. Goethe University Frankfurt, Theodor- Stern-Kai 7, 60590 Frankfurt, Germany a11111 * [email protected] (ST); [email protected] (SO) Abstract 19(S)-hydroxy-eicosatetraenoic acid (19(S)-HETE) belongs to a family of arachidonic acid OPEN ACCESS metabolites produced by cytochrome P450 enzymes, which play critical roles in the regula- Citation: Tunaru S, Chennupati R, NuÈsing RM, tion of cardiovascular, renal and pulmonary functions. Although it has been known for a Offermanns S (2016) Arachidonic Acid Metabolite long time that 19(S)-HETE has vascular effects, its mechanism of action has remained 19(S)-HETE Induces Vasorelaxation and Platelet unclear. In this study we show that 19(S)-HETE induces cAMP accumulation in the human Inhibition by Activating Prostacyclin (IP) Receptor. PLoS ONE 11(9): e0163633. doi:10.1371/journal. megakaryoblastic leukemia cell line MEG-01. This effect was concentration-dependent pone.0163633 with an EC50 of 520 nM, insensitive to pharmacological inhibition of COX-1/2 and required Editor: Bruno Lourenco Diaz, Universidade Federal the expression of the G-protein Gs. Systematic siRNA-mediated knock-down of each G- do Rio de Janeiro, BRAZIL protein coupled receptor (GPCR) expressed in MEG-01 followed by functional analysis Received: April 27, 2016 identified the prostacyclin receptor (IP) as the mediator of the effects of 19(S)-HETE, and the heterologously expressed IP receptor was also activated by 19(S)-HETE in a concen- Accepted: September 12, 2016 tration-dependent manner with an EC50 of 567 nM. Pretreatment of isolated murine plate- Published: September 23, 2016 lets with 19(S)-HETE blocked thrombin-induced platelets aggregation, an effect not seen in Copyright: © 2016 Tunaru et al. This is an open platelets from mice lacking the IP receptor. Furthermore, 19(S)-HETE was able to relax access article distributed under the terms of the mouse mesenteric artery- and thoracic aorta-derived vessel segments. While pharmaco- Creative Commons Attribution License, which permits unrestricted use, distribution, and logical inhibition of COX-1/2 enzymes had no effect on the vasodilatory activity of 19(S)- reproduction in any medium, provided the original HETE these effects were not observed in vessels from mice lacking the IP receptor. These author and source are credited. results identify a novel mechanism of action for the CYP450-dependent arachidonic acid Data Availability Statement: All relevant data are metabolite 19(S)-HETE and point to the existence of a broader spectrum of naturally occur- within the paper. ring prostanoid receptor agonists. Funding: This work was supported by the Collaborative Research Center 1039 of the German Research Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exists. PLOS ONE | DOI:10.1371/journal.pone.0163633 September 23, 2016 1 / 16 19(S)-HETE Is a Novel Prostacyclin Receptor Agonist Introduction Arachidonic acid is metabolized by cyclooxygenase (COX)-1 and -2 enzymes to prostanoids which regulate a plethora of physiological functions and contribute to various pathological states [1]. Their effects are mediated by specific plasma membrane receptors belonging to the superfamily of G-protein coupled receptors (GPCRs) [2]. An alternative pathway for the meta- bolization of arachidonic acid is mediated by cytochrome P450 (CYP450) enzyme family mem- bers which can convert arachidonic acid into epoxy-eicosatrienoic acids (EETs) and hydroxy- eicosatetraenoic acids such as 19- and 20-HETE [3–6]. Under basal conditions, 19(S)-HETE is the most abundant HETE produced by the rabbit kidney, its secretion being enhanced by angiotensin II [7]. In vitro studies show that multiple isoforms of class 2 CYP450 enzymes, such as isozymes 2E1, 2U1 and 2J9, can metabolize arachidonic acid to 19- and 20-HETE [8–10]. Experiments performed in perfused kidney from rabbits indicated that 19(S/R)-HETEs and 20-HETE are COX-1/2-dependent dilators of rabbit renal vasculature [7, 11]. Additional stud- ies, however, showed that 19(S/R)-HETEs and 20-HETE have pro-contractile effects on rat thoracic aortic rings, the latter being sensitive to COX-1/2 inhibition [12]. Nevertheless, it has also been described that 19(S)-HETE, but not its (R) isomer or arachidonic acid, functions as a stimulator of Na+ /K+-ATPase in a concentration-dependent manner, thereby contributing to increased volume absorption in the rabbit renal proximal straight tubes [13]. Although the gen- eral consensus appears to be that 19(S)-HETE has mainly vasodilatory effects, its biological role and the mechanism of action still remain unclear. Here we show that 19(S)-HETE is a full orthosteric agonist of the prostacyclin (IP) receptor and, by activating IP, can induce inhibition of platelet activation as well as relaxation of vessels from different vascular beds. Materials and Methods Reagents 19(S)-HETE and all related HETEs, cicaprost, arachidonic acid, PGE2, PGD2, cloprostenol, U46619, PGD2, Cay10441, were from Cayman Chemicals. FR122047 and NS398 were from Tocris. Forskolin, thrombin and sodium nitroprusside (SNP) were from Sigma-Aldrich and indomethacin from Alfa Aesar. [3H]-Iloprost (20 Ci/mmol) was from American Radiolabeled Chemicals. Intracellular cAMP determination MEG-01 or other indicated cell types, seeded in white walled, clear bottom 96-well plate were stimulated with test substances in Hanks’ balanced salt solution (HBSS) including 1.8 mM CaCl2 and 10 mM glucose for 15 min at 37°C. Intracellular cAMP concentrations were deter- mined by using an homogenous time-resolved fluorescence (HTRF)-based cAMP assay (Cis- bio) following manufacturer’s instructions. In case of heterologously expressed receptors, intracellular cAMP levels were measured by coexpression of a plasmid encoding a cytosolic cAMP-sensitive bioluminescent probe (GloSen- sorTM cAMP Assay, Promega). Forty-eight hours after transfection of receptors and cAMP probe, cells were removed from the incubator and medium was changed to HBSS containing TM 1.8 mM CaCl2, 10 mM glucose and 2% (v/v) of GloSensor cAMP reagent. Two hours after of incubation in dark at room temperature, intracellular cAMP was estimated in the “kinetic” mode by continuously recording the light produced over indicated time following ligand stim- ulation. For “end-point” determination, cells were stimulated with indicated ligands, and light PLOS ONE | DOI:10.1371/journal.pone.0163633 September 23, 2016 2 / 16 19(S)-HETE Is a Novel Prostacyclin Receptor Agonist generated was measured 15 minutes later with an integration time of 1250 ms. In both cases, light was recorded by a 96-well plate reader (Flexstation 3, Molecular Devices) and results were evaluated by SoftMaxPro software (Molecular Devices). 2+ Cell transfection and determination of [Ca ]i For studies of heterologously expressed receptors, COS-1 cells were seeded in white walls-clear bottom 96-well plates and transfected with plasmid containing cDNA for a calcium-sensitive bioluminescent fusion protein between aequorin and GFP[14] and plasmids containing the indicated receptors cDNA or control (empty vector, mock) at a concentration of 50 ng/well by using FuGENE 6 reagent (Promega) following manufacturer’s instructions. Forty eight hours later, cells were loaded with 5 μM coelenterazine h (Invitrogen) in HBSS containing 1.8 mM CaCl2 and 10 mM glucose for 2h at 37°C. Measurements were performed by using a lumino- metric plate reader (Flexstation 3). The area under each calcium transient was calculated by using SoftMaxPro software and expressed as area under the curve (AUC). Radioligand binding assay To measure the equilibrium binding of [15-3H]-iloprost (20 Ci/mmol; American Radiolabeled Chemicals, Inc.) to IP receptor, COS-1 cells were seeded in 24-well plates. Twenty-four hours later, they were transfected with a plasmid containing human IP receptor cDNA using Fugene 6 (Promega) transfection reagent, according to the manufacturer’s instructions. Two days later, cells were rinsed once with ice-cold binding buffer (PBS + 0.5% fatty-acid free BSA) and com- petition binding assays were carried out by incubating transfected cells in binding buffer con- taining 10 nM [3H]-iloprost and indicated concentrations of unlabeled substances for 90 min at +4°C. Binding was stopped by three washing steps with ice-cold binding buffer. Thereafter, cells were lysed in lysis buffer (0.1% Triton X-200, 2N NaOH) and transferred to vials contain- ing scintillation fluid (Ultima-Gold; Perkin-Elmer). Radioactivity was measured by a scintilla- tion counter (Hidex 300SL). siRNA transfection and screening MEG-01 cells seeded in 96 well plates were reverse transfected with pools consisting of four separate siRNAs against the indicated GPCR mRNAs at a concentration of 5 ng for each siRNA. Seventy-two hours later, 19(S)-HETE-induced cAMP increase was determined and ratios between effects on cells transfected with pools targeting a particular GPCR and effects on cells transfected with scrambled siRNA were determined. RNA isolation and quantitative RT-PCR RNA isolation and transcription from MEG-01 and HUVECs were performed by using the RNeasy kit (Qiagen) according to the manufacturer’s instructions. Quantitative RT-PCR was done by using primers designed with the Roche’s online tool reagents and a Universal Probe Library assay from Roche. Genetic mouse models IP-receptor deficient mice have been described elsewhere [15]. The mice used for experiments in this study were offspring of a breeding colony kept at the Institute for Clinical Pharmacology of the J.