sPLA(2) cooperates with cPLA(2)alpha to regulate prostacyclin synthesis in human endothelial cells

Effects of Statins and Xuezhikang on the Expression of Secretory Phospholipase A2, Group IIA in Rat Vascular Smooth Muscle Cells

Atherosclerosis is a multifactorial vascular disease characterized by formation of inflammatory lesions. Secretory phospholipase A2, group IIA (sPLA2-IIA) is involved in this process and plays a critical role. However, the exact role of sPLA2-IIA in cardiovascular inflammation is more complicated and remains unclear. Furthermore, both statins and Xuezhikang (XZK) are widely used in the prevention and treatment of cardiovascular disease risk because of their pleiotropic effects on the cardiovascular system. However, their effects on sPLA2-IIA are still controversial. We investigated the regulation of sPLA2-IIA by rat thoracic aorta smooth muscle cells (VSMCs) in culture. Cells were first incubated with IL-1β alone to induce expression of sPLA2-IIA and then treated with several concentrations of statins or XZK for different times in the absence or presence of IL-1β. We tested the expression of sPLA2-IIA, including sPLA2-IIA mRNA, protein, as well as activity. We found that statins or IL-1β increase the expression of sPLA2-IIA in VSMCs and the effect is based on a synergetic relationship between them. However, for the first time, we observed that XZK effectively reduces sPLA2-IIA expression in IL-1β-treated VSMCs. Our findings may shine a new light on the clinical use of XZK and statins in the prevention and treatment of atherosclerosis-related thrombosis.

Inherited human group IVA cytosolic phospholipase A2 deficiency abolishes platelet, endothelial, and leucocyte eicosanoid generation

Eicosanoids are important vascular regulators, but the phospholipase A₂ (PLA₂) isoforms supporting their production within the cardiovascular system are not fully understood. To address this, we have studied platelets, endothelial cells, and leukocytes from 2 siblings with a homozygous loss-of-function mutation in group IVA cytosolic phospholipase A₂ (cPLA₂α). Chromatography/mass spectrometry was used to determine levels of a broad range of eicosanoids produced by isolated vascular cells, and in plasma and urine. Eicosanoid release data were paired with studies of cellular function. Absence of cPLA₂α almost abolished eicosanoid synthesis in platelets (e.g., thromboxane A₂, control 20.5 ± 1.4 ng/ml vs. patient 0.1 ng/ml) and leukocytes [e.g., prostaglandin E₂ (PGE₂), control 21.9 ± 7.4 ng/ml vs. patient 1.9 ng/ml], and this was associated with impaired platelet activation and enhanced inflammatory responses. cPLA₂α-deficient endothelial cells showed reduced, but not absent, formation of prostaglandin I₂ (prostacyclin; control 956 ± 422 pg/ml vs. patient 196 pg/ml) and were primed for inflammation. In the urine, prostaglandin metabolites were selectively influenced by cPLA₂α deficiency. For example, prostacyclin metabolites were strongly reduced (18.4% of control) in patients lacking cPLA₂α, whereas PGE₂ metabolites (77.8% of control) were similar to healthy volunteer levels. These studies constitute a definitive account, demonstrating the fundamental role of cPLA₂α to eicosanoid formation and cellular responses within the human circulation.—Kirkby, N. S., Reed, D. M., Edin, M. L., Rauzi, F., Mataragka, S., Vojnovic, I., Bishop-Bailey, D., Milne, G. L., Longhurst, H., Zeldin, D. C., Mitchell, J. A., Warner, T. D. Inherited human group IVA cytosolic phospholipase A₂ deficiency abolishes platelet, endothelial, and leucocyte eicosanoid generation.

Secretory phospholipase A2, group IIA is a novel serum amyloid A target gene: activation of smooth muscle cell expression by an interleukin-1 receptor-independent mechanism

Atherosclerosis is a multifactorial vascular disease characterized by formation of inflammatory lesions. Elevated circulating acute phase proteins indicate disease risk. Serum amyloid A (SAA) is one such marker but its function remains unclear. To determine the role of SAA on aortic smooth muscle cell gene expression, a preliminary screen of a number of genes was performed and a strong up-regulation of expression of secretory phospholipase A(2), group IIA (sPLA(2)) was identified. The SAA-induced increase in sPLA(2) was validated by real time PCR, Western blot analysis, and enzyme activity assays. Demonstrating that SAA increased expression of sPLA(2) heteronuclear RNA and that inhibiting transcription eliminated the effect of SAA on sPLA(2) mRNA suggested that the increase was transcriptional. Transient transfections and electrophoretic mobility shift assays identified CAAT enhancer-binding protein (C/EBP) and nuclear factor kappaB (NFkappaB) as key regulatory sites mediating the induction of sPLA(2). Moreover, SAA activated the inhibitor of NF-kappaB kinase (IKK) in cultured smooth muscle cells. Previous reports showed that interleukin (IL)-1beta up-regulates Pla2g2a gene transcription via C/EBPbeta and NFkappaB. Interestingly, SAA activated smooth muscle cell IL-1beta mRNA expression, however, blocking IL-1 receptors had no effect on SAA-mediated activation of sPLA(2) expression. Thus, the observed changes in sPLA(2) expression were not secondary to SAA-induced IL-1 receptor activation. The association of SAA with high density lipoprotein abrogated the SAA-induced increase in sPLA(2) expression. These data suggest that during atherogenesis, SAA can amplify the involvement of smooth muscle cells in vascular inflammation and that this can lead to deposition of sPLA(2) and subsequent local changes in lipid homeostasis.

The pathophysiology of erectile dysfunction related to endothelial dysfunction and mediators of vascular function

The incidence of erectile dysfunction increases with diabetes, hypertension, hypercholesterolaemia, cardiovascular disease and renal failure. All these conditions are associated with endothelial dysfunction. This review addresses the pathophysiology of erectile dysfunction with a special focus on new insights into nitric oxide (NO)-mediated pathways, oxidative stress and parallels to endothelial dysfunction. NO appears to be the key mediator promoting endothelium-derived vasodilation and penile erection. The possibility is discussed that elevated plasma concentrations of asymmetrical dimethylarginine (ADMA), an endogenous NO synthase inhibitor, may provide an additional pathomechanism for various forms of erectile dysfunction associated with cardiovascular risk factors and disease. Likewise, the role of endothelium-derived factors mediating NO-independent pathways is evaluated.

Internalized group V secretory phospholipase A2 acts on the perinuclear membranes

Mammalian secretory phospholipases A(2) (sPLA(2)) have been implicated in cellular eicosanoid biosynthesis but the mechanism of their cellular action remains unknown. To elucidate the spatiotemporal dynamics of sPLA(2) mobilization and determine the site of its lipolytic action, we performed time-lapse confocal microscopic imaging of fluorescently labeled sPLA(2) acting on human embryonic kidney (HEK) 293 cells the membranes of which are labeled with a fluorogenic phospholipid, N-((6-(2,4-dinitrophenyl)amino)hexanoyl)-1-hexadecanoyl-2-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl)-sn-glycero-3-phosphoethanolamine. The Western blotting analysis of HEK293 cells treated with exogenous sPLA(2)s showed that not only the affinity for heparan sulfate proteoglycan but also other factors, such as sPLA(2) hydrolysis products or cytokines, are necessary for the internalization of sPLA(2) into HEK293 cells. Live cell imaging showed that the hydrolysis of fluorogenic phospholipids incorporated into HEK293 cell membranes was synchronized with the spatiotemporal dynamics of sPLA(2) internalization, detectable initially at the plasma membrane and then at the perinuclear region. Also, immunocytostaining showed that human group V sPLA(2) induced the translocation of 5-lipoxygenase to the nuclear envelope at which they were co-localized. Together, these studies provide the first experimental evidence that the internalized sPLA(2) acts on the nuclear envelope to provide arachidonate for other enzymes involved in the eicosanoid biosynthesis.