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

Abstract

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.

Keywords: angiotensin II; cytosolic phospholipase A2α (cPLA2α); inflammation; mice; oxidative stress.

Figure 1. cPLA₂α contributes to the development of Ang II-induced hypertension in mice

cPLA₂α ^+/+ and cPLA₂α ^−/− mice were infused with either Ang II (700 ng/kg/min) or its vehicle (0.9% saline) with micro-osmotic pumps for 13 days, and SBP was measured by tail cuff (A) and radio telemetry (B). Diastolic (C) and mean arterial pressure (D) were also measured by telemetry *P< 0.05 cPLA₂α^+/+ vehicle vs. cPLA₂α^+/+Ang II, #P< 0.05 cPLA₂α^+/+Ang II vs. cPLA₂α^−/−Ang II (n = 4–6 for all experiments, and data are expressed as mean ± SEM, data was analyzed by RM two-way analysis of variance followed by Turkey’s multiple comparison tests)

Figure 2. Increased arachidonic acid metabolism to pro-hypertensive eicosanoids mediates Ang II induced hypertension in cPLA₂α^+/+ mice

Increase urinary excretion of PGE2 metabolites (A) TXB2 (B) and 20-HETE (C) was observed in cPLA₂α ^+/+ but not in cPLA₂α ^−/− mice infused with Ang II. *P< 0.05 cPLA₂α^+/+ vehicle vs. cPLA₂α^+/+Ang II, #P< 0.05 cPLA₂α^+/+Ang II vs. cPLA₂α^−/−Ang II, ϕ P< 0.05 cPLA₂α^+/+ vehicle vs. cPLA₂α^−/−vehicle (n = 4–6 for all experiments, and data are expressed as mean ± SEM)

Figure 3. cPLA₂α gene disruption attenuates cardiac dysfunction, hypertrophy and fibrosis associated with Ang II-induced hypertension in mice

Echocardiograms of the left ventricle in M mode, parasternal long-axis view (A), demonstrates increase in LVID in both systole (red) and diastole (green) suggesting dilated cardiomyopathy characterized by enlarged LV mass in Ang II-infused cPLA₂α^+/+ but not cPLA₂α^−/− mice. Various parameters of cardiac function were also measured (Table 1). Increased interstitial staining of α-SMA (B) and TGF-β (C) indicators of interstitial fibrosis and collagen accumulation (D) (intense blue staining) was observed in Ang II-infused cPLA₂α^+/+ but not cPLA₂α^−/− mice. (n=4–6 for each group; data are expressed as mean ± SEM)

Figure 4. cPLA₂α gene disruption protects against Ang II-induced vascular remodeling

Sections of aortas were stained and quantified for media:lumen ratio (A) α-smooth muscle actin (B), and collagen accumulation (C). *P< 0.05 vehicle vs. Ang II, #P< 0.05 cPLA₂α^+/+Ang II vs. cPLA₂α^−/−Ang II. (n=3–5 for each group; data are expressed as mean ± SEM)