Cytosolic phospholipase A2alpha contributes to blood pressure increases and endothelial dysfunction under chronic NO inhibition

2-Methoxyestradiol Ameliorates Angiotensin II-Induced Hypertension by Inhibiting Cytosolic Phospholipase A2α Activity in Female Mice

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We tested the hypothesis that CYP1B1 (cytochrome P450 1B1)-17β-estradiol metabolite 2-methoxyestradiol protects against Ang II (angiotensin II)–induced hypertension by inhibiting group IV cPLA₂α (cytosolic phospholipase A₂α) activity and production of prohypertensive eicosanoids in female mice. Ang II (700 ng/kg per minute, SC) increased mean arterial blood pressure (BP), systolic and diastolic BP measured by radiotelemetry, renal fibrosis, and reactive oxygen species production in wild-type mice (cPLA₂α^+/+/Cyp1b1^+/+) that were enhanced by ovariectomy and abolished in intact and ovariectomized-cPLA₂α^−/−/Cyp1b1^+/+ mice. Ang II–induced increase in SBP measured by tail-cuff, renal fibrosis, reactive oxygen species production, and cPLA₂α activity measured by its phosphorylation in the kidney, and urinary excretion of prostaglandin E₂ and thromboxane A₂ metabolites were enhanced in ovariectomized-cPLA₂α^+/+/Cyp1b1^+/+ and intact cPLA₂α^+/+/Cyp1b1^−/− mice. 2-Methoxyestradiol and arachidonic acid metabolism inhibitor 5,8,11,14-eicosatetraynoic acid attenuated the Ang II–induced increase in SBP, renal fibrosis, reactive oxygen species production, and urinary excretion of prostaglandin E₂, and thromboxane A₂ metabolites in ovariectomized-cPLA₂α^+/+/Cyp1b1^+/+ and intact cPLA₂α^+/+/Cyp1b1^−/− mice. Antagonists of prostaglandin E₂ and thromboxane A₂ receptors EP1 and EP3 and TP, respectively, inhibited Ang II–induced increases in SBP and reactive oxygen species production and renal fibrosis in ovariectomized-cPLA₂α^+/+/Cyp1b1^+/+ and intact cPLA₂α^+/+/Cyp1b1^−/− mice. These data suggest that CYP1B1-generated metabolite 2-methoxyestradiol mitigates Ang II–induced hypertension and renal fibrosis by inhibiting cPLA₂α activity, reducing prostaglandin E₂, and thromboxane A₂ production and stimulating EP1 and EP3 and TP receptors, respectively. Thus, 2-methoxyestradiol and the drugs that selectively block EP1 and EP3 and TP receptors could be useful in treating hypertension and its pathogenesis in females.

Enterococcus faecalis contributes to hypertension and renal injury in Sprague-Dawley rats by disturbing lipid metabolism

OBJECTIVE

Increasing studies have demonstrated that gut microbiota play vital roles in the development of hypertension. However, the underlying mechanism is not fully understood.

METHODS

The relative abundance of Enterococcus faecalis was determined in the faecal samples of angiotensin II or deoxycorticosterone acetate/salt-induced hypertensive rats. Then, E. faecalis culture was administered orally to rats for 6 weeks. Blood pressure (BP) was measured, renal injury was estimated and a serum metabolomic analysis was performed.

RESULTS

Compared with control, E. faecalis was markedly enriched in the faecal samples of hypertensive rats. The rats receiving live E. faecalis but not dead bacteria exhibited higher BP and enhanced renal injury. The serum metabolomic data showed that the E. faecalis treatment resulted in 35 variable metabolites including 16 (46%) lipid/lipid-like molecules, suggesting significant disturbance of lipid metabolism. Furthermore, the mRNA levels of 18 lipid metabolic enzymes in the renal medulla and cortex presented distinct and dynamic changes in response to 3 or 6-week E. faecalis treatment. Consistently, the protein levels of lysophospholipases A1 (LYPLA1) and phospholipase A2 group 4 A (PLA2G4) were enhanced only by live E. faecalis, which thus may have decreased the nitric oxide production in the renal medulla and elevated BP.

CONCLUSION

Our results suggest that E. faecalis in the gut contributes to hypertension and renal injury in rats by disturbing the lipid metabolism. The information provided here could shed new light on the pathologic mechanisms and potential intervention targets for the treatment of gut dysbiosis-induced hypertension.

TRPV4 activates cytosolic phospholipase A2 via Ca2+ -dependent PKC/ERK1/2 signalling in controlling hypertensive contraction

Activation of TRPV4 (transient receptor potential vanilloid 4) has been reported to result in endothelium-dependent contraction in the aortae of hypertensive mice. This contraction involved increased cPLA2 (cytosolic phospholipase A2 ) activity. The mechanism by which TRPV4 regulates cPLA2 activity to induce contraction in hypertension, however, is unknown. Through measurements of arterial tension and protein level, we showed that high-salt diet induced hypertension increases activity of PKC (protein kinase C) and ERK1/2 (extracellular signal-regulated kinase 1/2). GSK1016790A, a TRPV4 agonist and ACh (acetylcholine) induced contractions were suppressed by Go6983, a PKC inhibitor and PD98059, an ERK1/2 inhibitor. TRPV4 activation increased activity of PKC and ERK1/2 in endothelial cells from hypertensive mice and this response was suppressed by HC067047, a TRPV4 inhibitor and BAPTA/AM, a Ca2+ chelator. PLA2 assay and western blotting showed that blocking of PKC or ERK1/2 inhibited TRPV4 or ACh-induced cPLA2 activity. Enzyme immunoassay showed that GSK1016790A or ACh triggered the release of PGF2α (prostaglandin F2α ) was reduced by inhibition of PKC or ERK1/2. These data further suggest Ca2+ /PKC/ERK1/2 axis as a novel mechanism for TRPV4 in the activation of cPLA2 in hypertension.

Brain Cytosolic Phospholipase A2α Mediates Angiotensin II-Induced Hypertension and Reactive Oxygen Species Production in Male Mice

BACKGROUND

Recently, we reported that angiotensin II (Ang II)-induced hypertension is mediated by group IV cytosolic phospholipase A₂α (cPLA₂α) via production of prohypertensive eicosanoids. Since Ang II increases blood pressure (BP) via its action in the subfornical organ (SFO), it led us to investigate the expression and possible contribution of cPLA₂α to oxidative stress and development of hypertension in this brain area.

METHODS

Adenovirus (Ad)-green fluorescence protein (GFP) cPLA₂α short hairpin (sh) RNA (Ad-cPLA₂α shRNA) and its control Ad-scrambled shRNA (Ad-Scr shRNA) or Ad-enhanced cyan fluorescence protein cPLA₂α DNA (Ad-cPLA₂α DNA) and its control Ad-GFP DNA were transduced into SFO of cPLA₂α^+/+ and cPLA₂α^−/− male mice, respectively. Ang II (700 ng/kg/min) was infused for 14 days in these mice, and BP was measured by tail-cuff and radio telemetry. cPLA₂ activity, reactive oxygen species production, and endoplasmic reticulum stress were measured in the SFO.

RESULTS

Transduction of SFO with Ad-cPLA₂α shRNA, but not Ad-Scr shRNA in cPLA₂α^+/+ mice, minimized expression of cPLA₂α, Ang II-induced cPLA₂α activity and oxidative stress in the SFO, BP, and cardiac and renal fibrosis. In contrast, Ad-cPLA₂α DNA, but not its control Ad-GFP DNA in cPLA₂α^−/− mice, restored the expression of cPLA₂α, and Ang II-induced increase in cPLA₂ activity and oxidative stress in the SFO, BP, cardiac, and renal fibrosis.

CONCLUSIONS

These data suggest that cPLA₂α in the SFO is crucial in mediating Ang II-induced hypertension and associated pathogenesis. Therefore, development of selective cPLA₂α inhibitors could be useful in treating hypertension and its pathogenesis.

[Carboxyl-11 C]Labelling of Four High-Affinity cPLA2α Inhibitors and Their Evaluation as Radioligands in Mice by Positron Emission Tomography

Cytosolic phospholipase A2α (cPLA2α) may play a critical role in neuropsychiatric and neurodegenerative disorders associated with oxidative stress and neuroinflammation. An effective PET radioligand for imaging cPLA2α in living brain might prove useful for biomedical research, especially on neuroinflammation. We selected four high-affinity (IC₅₀ 2.1-12 nm) indole-5-carboxylic acid-based inhibitors of cPLA2α, namely 3-isobutyryl-1-(2-oxo-3-(4-phenoxyphenoxy)propyl)-1H-indole-5-carboxylic acid (1); 3-acetyl-1-(2-oxo-3-(4-(4-(trifluoromethyl)phenoxy)phenoxy)propyl)-1H-indole-5-carboxylic acid (2); 3-(3-methyl-1,2,4-oxadiazol-5-yl)-1-(2-oxo-3-(4-phenoxyphenoxy)propyl)-1H-indole-5-carboxylic acid (3); and 3-(3-methyl-1,2,4-oxadiazol-5-yl)-1-(3-(4-octylphenoxy)-2-oxopropyl)-1H-indole-5-carboxylic acid (4), for labelling in carboxyl position with carbon-11 (t_1/2 =20.4 min) to provide candidate PET radioligands for imaging brain cPLA2α. Compounds [¹¹ C]1-4 were obtained for intravenous injection in adequate overall yields (1.1-5.5 %) from cyclotron-produced [¹¹ C]carbon dioxide and with moderate molar activities (70-141 GBq μmol^-1 ) through the use of Pd⁰ -mediated [¹¹ C]carbon monoxide insertion on iodo precursors. Measured logD_7.4 values were within a narrow moderate range (1.9-2.4). After intravenous injection of [¹¹ C]1-4 in mice, radioactivity uptakes in brain peaked at low values (≤0.8 SUV) and decreased by about 90 % over 15 min. Pretreatments of the mice with high doses of the corresponding non-radioactive ligands did not alter brain time-activity curves. Brain uptakes of radioactivity after administration of [¹¹ C]1 to wild-type and P-gp/BCRP dual knock-out mice were similar (peak 0.4 vs. 0.5 SUV), indicating that [¹¹ C]1 and others in this structural class, are not substrates for efflux transporters.

Bone marrow-derived cPLA2α contributes to renal fibrosis progression

The group IVA calcium-dependent cytosolic phospholipase A2 (cPLA2α) enzyme directs a complex "eicosanoid storm" that accompanies the tissue response to injury. cPLA2α and its downstream eicosanoid mediators are also implicated in the pathogenesis of fibrosis in many organs, including the kidney. We aimed to determine the role of cPLA2α in bone marrow-derived cells in a murine model of renal fibrosis, unilateral ureteral obstruction (UUO). WT C57BL/6J mice were irradiated and engrafted with donor bone marrow from either WT mice [WT-bone marrow transplant (BMT)] or mice deficient in cPLA2α (KO-BMT). After full engraftment, mice underwent UUO and kidneys were collected 3, 7, and 14 days after injury. Using picrosirius red, collagen-3, and smooth muscle α actin staining, we determined that renal fibrosis was significantly attenuated in KO-BMT animals as compared with WT-BMT animals. Lipidomic analysis of homogenized kidneys demonstrated a time-dependent upregulation of pro-inflammatory eicosanoids after UUO; KO-BMT animals had lower levels of many of these eicosanoids. KO-BMT animals also had fewer infiltrating pro-inflammatory CD45+CD11b+Ly6C^hi macrophages and reduced message levels of pro-inflammatory cytokines. Our results indicate that cPLA2α and/or its downstream mediators, produced by bone marrow-derived cells, play a major role in eicosanoid production after renal injury and in renal fibrinogenesis.

Cytosolic phospholipase A₂: physiological function and role in disease

The group IV phospholipase A2 (PLA2) family is comprised of six intracellular enzymes (GIVA, -B, -C, -D, -E, and -F) commonly referred to as cytosolic PLA2 (cPLA2)α, -β, -γ, -δ, -ε, and -ζ. They contain a Ser-Asp catalytic dyad and all except cPLA2γ have a C2 domain, but differences in their catalytic activities and subcellular localization suggest unique regulation and function. With the exception of cPLA2α, the focus of this review, little is known about the in vivo function of group IV enzymes. cPLA2α catalyzes the hydrolysis of phospholipids to arachidonic acid and lysophospholipids that are precursors of numerous bioactive lipids. The regulation of cPLA2α is complex, involving transcriptional and posttranslational processes, particularly increases in calcium and phosphorylation. cPLA2α is a highly conserved widely expressed enzyme that promotes lipid mediator production in human and rodent cells from a variety of tissues. The diverse bioactive lipids produced as a result of cPLA2α activation regulate normal physiological processes and disease pathogenesis in many organ systems, as shown using cPLA2α KO mice. However, humans recently identified with cPLA2α deficiency exhibit more pronounced effects on health than observed in mice lacking cPLA2α, indicating that much remains to be learned about this interesting enzyme.

Cytosolic phospholipase A2α is critical for angiotensin II-induced hypertension and associated cardiovascular pathophysiology

Angiotensin II activates cytosolic phospholipase A(2)α (cPLA2α) and releases arachidonic acid from tissue phospholipids, which mediate or modulate ≥1 cardiovascular effects of angiotensin II and has been implicated in hypertension. Because arachidonic acid release is the rate limiting step in eicosanoid production, cPLA2α might play a central role in the development of angiotensin II-induced hypertension. To test this hypothesis, we investigated the effect of angiotensin II infusion for 13 days by micro-osmotic pumps on systolic blood pressure and associated pathogenesis in wild type (cPLA2α(+/+)) and cPLA2α(-/-) mice. Angiotensin II-induced increase in systolic blood pressure in cPLA2α(+/+) mice was abolished in cPLA2α(-/-) mice; increased systolic blood pressure was also abolished by the arachidonic acid metabolism inhibitor, 5,8,11,14-eicosatetraynoic acid in cPLA2α(+/+) mice. Angiotensin II in cPLA2α(+/+) mice increased cardiac cPLA2 activity and urinary eicosanoid excretion, decreased cardiac output, caused cardiovascular remodeling with endothelial dysfunction, and increased vascular reactivity in cPLA2α(+/+) mice; these changes were diminished in cPLA2α(-/-) mice. Angiotensin II also increased cardiac infiltration of F4/80(+) macrophages and CD3(+) T lymphocytes, cardiovascular oxidative stress, expression of endoplasmic reticulum stress markers p58(IPK), and CHOP in cPLA2α(+/+) but not cPLA2α(-/-) mice. Angiotensin II increased cardiac activity of ERK1/2 and cSrc in cPLA2α(+/+) but not cPLA2α(-/-) mice. These data suggest that angiotensin II-induced hypertension and associated cardiovascular pathophysiological changes are mediated by cPLA2α activation, most likely through the release of arachidonic acid and generation of eicosanoids with predominant prohypertensive effects and activation of ≥1 signaling molecules, including ERK1/2 and cSrc.

iPLA2β overexpression in smooth muscle exacerbates angiotensin II-induced hypertension and vascular remodeling

Objectives

Calcium independent group VIA phospholipase A₂ (iPLA₂β) is up-regulated in vascular smooth muscle cells in some diseases, but whether the up-regulated iPLA₂β affects vascular morphology and blood pressure is unknown. The current study addresses this question by evaluating the basal- and angiotensin II infusion-induced vascular remodeling and hypertension in smooth muscle specific iPLA₂β transgenic (iPLA₂β -Tg) mice.

Method and Results

Blood pressure was monitored by radiotelemetry and vascular remodeling was assessed by morphologic analysis. We found that the angiotensin II-induced increase in diastolic pressure was significantly higher in iPLA₂β-Tg than iPLA₂β-Wt mice, whereas, the basal blood pressure was not significantly different. The media thickness and media∶lumen ratio of the mesenteric arteries were significantly increased in angiotensin II-infused iPLA₂β-Tg mice. Analysis revealed no difference in vascular smooth muscle cell proliferation. In contrast, adenovirus-mediated iPLA₂β overexpression in cultured vascular smooth muscle cells promoted angiotensin II-induced [³H]-leucine incorporation, indicating enhanced hypertrophy. Moreover, angiotensin II infusion-induced c-Jun phosphorylation in vascular smooth muscle cells overexpressing iPLA2β to higher levels, which was abolished by inhibition of 12/15 lipoxygenase. In addition, we found that angiotensin II up-regulated the endogenous iPLA₂β protein in-vitro and in-vivo.

Conclusion

The present study reports that iPLA₂β up-regulation exacerbates angiotensin II-induced vascular smooth muscle cell hypertrophy, vascular remodeling and hypertension via the 12/15 lipoxygenase and c-Jun pathways.