Expression of type V secretory phospholipase A in myocardial remodelling after infarction

The Link between Prostanoids and Cardiovascular Diseases

Cardiovascular diseases are the leading cause of global deaths, and many risk factors contribute to their pathogenesis. In this context, prostanoids, which derive from arachidonic acid, have attracted attention for their involvement in cardiovascular homeostasis and inflammatory processes. Prostanoids are the target of several drugs, but it has been shown that some of them increase the risk of thrombosis. Overall, many studies have shown that prostanoids are tightly associated with cardiovascular diseases and that several polymorphisms in genes involved in their synthesis and function increase the risk of developing these pathologies. In this review, we focus on molecular mechanisms linking prostanoids to cardiovascular diseases and we provide an overview of genetic polymorphisms that increase the risk for cardiovascular disease.

Harmful and protective roles of group V phospholipase A2: Current perspectives and future directions

Group V Phospholipase A₂ (Pla2g5) is a member of the PLA₂ family of lipid-generating enzymes. It is expressed in immune and non-immune cell types and is inducible during several pathologic conditions serving context-specific functions. In this review, we recapitulate the protective and detrimental functions of Pla2g5 investigated through preclinical and translational approaches. This article is part of a Special Issue entitled Novel functions of phospholipase A₂ Guest Editors: Makoto Murakami and Gerard Lambeau.

Cardioprotective Regimen of Adaptation to Chronic Hypoxia Diversely Alters Myocardial Gene Expression in SHR and SHR-mtBN Conplastic Rat Strains

Adaptation to continuous normobaric hypoxia (CNH) protects the heart against acute ischemia/reperfusion injury. Recently, we have demonstrated the infarct size-limiting effect of CNH also in hearts of spontaneously hypertensive rats (SHR) and in conplastic SHR-mt^BN strain characterized by the selective replacement of the mitochondrial genome of SHR with that of more ischemia-resistant Brown Norway rats. Importantly, cardioprotective effect of CNH was more pronounced in SHR-mt^BN than in SHR. Thus, here we aimed to identify candidate genes which may contribute to this difference between the strains. Rats were adapted to CNH (FiO₂ 0.1) for 3 weeks or kept at room air as normoxic controls. Screening of 45 transcripts was performed in left ventricles using Biomark Chip. Significant differences between the groups were analyzed by univariate analysis (ANOVA) and the genes contributing to the differences between the strains unmasked by CNH were identified by multivariate analyses (PCA, SOM). ANOVA with Bonferroni correction revealed that transcripts differently affected by CNH in SHR and SHR-mt^BN belong predominantly to lipid metabolism and antioxidant defense. PCA divided four experimental groups into two main clusters corresponding to chronically hypoxic and normoxic groups, and differences between the strains were more pronounced after CNH. Subsequently, the following 14 candidate transcripts were selected by PCA, and confirmed by SOM analyses, that can contribute to the strain differences in cardioprotective phenotype afforded by CNH: Alkaline ceramidase 2 (Acer2), Fatty acid translocase (Cd36), Aconitase 1 (Aco1), Peroxisome proliferator activated receptor gamma (Pparg), Hemoxygenase 2 (Hmox2), Phospholipase A2 group IIA (Ppla2g2a), Dynamin-related protein (Drp), Protein kinase C epsilon (Pkce), Hexokinase 2 (Hk2), Sphingomyelin synthase 2 (Sgms2), Caspase 3 (Casp3), Mitofussin 1 (Mfn1), Phospholipase A2 group V (Pla2g5), and Catalase (Cat). Our data suggest that the stronger cardioprotective phenotype of conplastic SHR-mt^BN strain afforded by CNH is associated with either preventing the drop or increasing the expression of transcripts related to energy metabolism, antioxidant response and mitochondrial dynamics.

Molecular and functional alterations in a mouse cardiac model of Friedreich ataxia: activation of the integrated stress response, eIF2α phosphorylation, and the induction of downstream targets

Friedreich ataxia (FA) is a neurodegenerative and cardiodegenerative disease resulting from marked frataxin deficiency. The condition is characterized by ataxia with fatal cardiomyopathy, but the pathogenic mechanisms are unclear. We investigated the association between gene expression and progressive histopathological and functional changes using the muscle creatine kinase conditional frataxin knockout (KO) mouse; this mouse develops a severe cardiac phenotype that resembles that of FA patients. We examined KO mice from 3 weeks of age, when they are asymptomatic, to 10 weeks of age, when they die of the disease. Positive iron staining was identified in KO mice from 5 weeks of age, with markedly reduced cardiac function from 6 weeks. We identified an early and marked up-regulation of a gene cohort responsible for stress-induced amino acid biosynthesis and observed markedly increased phosphorylation of eukaryotic translation initiation factor 2α (p-eIF2α), an activator of the integrated stress response, in KO mice at 3 weeks of age, relative to wild-type mice. Importantly, the eIF2α-mediated integrated stress response has been previously implicated in heart failure via downstream processes such as autophagy and apoptosis. Indeed, expression of a panel of autophagy and apoptosis markers was enhanced in KO mice. Thus, the pathogenesis of cardiomyopathy in FA correlates with the early and persistent eIF2α phosphorylation, which precedes activation of autophagy and apoptosis.

Group V secretory phospholipase A2 enhances the progression of angiotensin II-induced abdominal aortic aneurysms but confers protection against angiotensin II-induced cardiac fibrosis in apoE-deficient mice

Abdominal aortic aneurysms (AAAs) and heart failure are complex life-threatening diseases whose etiology is not completely understood. In this study, we investigated whether deficiency of group V secretory phospholipase A(2) (GV sPLA(2)) protects from experimental AAA. The impact of GV sPLA(2) deficiency on angiotensin (Ang) II-induced cardiac fibrosis was also investigated. Apolipoprotein E (apoE)(-/-) mice and apoE(-/-) mice lacking GV sPLA(2) (GV DKO) were infused with 1000 ng/kg per minute Ang II for up to 28 days. Increases in systolic blood pressure, plasma aldosterone level, and urinary and heart prostanoids were similar in apoE(-/-) and GV DKO mice after Ang II infusion. The incidence of aortic rupture in Ang II-infused GV DKO mice (10%) was significantly reduced compared with apoE(-/-) mice (29.4%). Although the incidence of AAA in GV DKO mice (81.3%) and apoE(-/-) mice (100%) was similar, the mean percentage increase in maximal luminal diameter of abdominal aortas was significantly smaller in GV DKO mice (68.5% ± 7.7%) compared with apoE(-/-) mice (92.6% ± 8.3%). Deficiency of GV sPLA(2) resulted in increased Ang II-induced cardiac fibrosis that was most pronounced in perivascular regions. Perivascular collagen, visualized by picrosirius red staining, was associated with increased TUNEL staining and increased immunopositivity for macrophages and myofibroblasts and nicotinamide adenine dinucleotide phosphate oxidase (NOX)-2 and NOX-4, respectively. Our findings indicate that GV sPLA(2) modulates pathological responses to Ang II, with different outcomes for AAA and cardiac fibrosis.

Endothelial progenitor cell transplantation decreases lymphangiogenesis and adverse myocardial remodeling in a mouse model of acute myocardial infarction

Cardiac lymphatic system in the remodeling after acute myocardial infarction (AMI) has been overlooked. We wanted to investigate the role of bone marrow-derived endothelial progenitor cells (EPCs) and their contribution to lymphatic distribution in myocardial remodeling after AMI. Mouse (C57bl/6J) MI models were created by ligation of the left anterior descending coronary artery and were treated with phosphate buffered saline (PBS) or EPCs. Real-time RT-PCR with 2- to 4-week myocardial tissue samples revealed that lymphangiogenetic factors such as vascular endothelial growth factor (VEGF)-C (8.5 fold, P < 0.05), VEGF-D (6.1 fold, P < 0.05), Lyve-1 (15 fold, P < 0.05), and Prox-1 (11 fold, P < 0.05) were expressed at significantly higher levels in the PBS group than the EPC group. The PBS group also showed a significantly higher density of lymphatic vessels in the peri-infarction area. Echocardiography showed that from 2 weeks after the treatment, left ventricle (LV) dimensions at both systole and diastole were significantly smaller in the EPC group than in the PBS group (P < 0.01) and LV fractional shortening was higher in the EPC group accordingly (P < 0.01). Lymphangiogenic markers increased in a mouse MI model. EPC transplantation decreased lymphangiogenesis and adverse ventricular remodeling after AMI. These novel findings suggest that new lymphatic vessels may be formed in severely damaged myocardium, and may be involved in adverse myocardial remodeling after AMI.

Transcoronary concentration gradients of circulating microRNAs

BACKGROUND

Circulating levels of microRNA (miR) have been proposed as biomarkers for cardiovascular disease. To identify the heart as a potential source for miRs released into the circulation, we measured concentration gradients across the coronary circulation for muscle-enriched (miR-133a, miR-499, miR-208a), vascular (miR-126, miR-92a), leukocyte-related (miR-155), and platelet-enriched (miR-223) miRs.

METHODS AND RESULTS

Circulating miRs were measured by TaqMan polymerase chain reaction in EDTA-plasma simultaneously obtained from the aorta and the coronary venous sinus in patients without coronary artery disease (n=7), with stable coronary artery disease (n=31), and with troponin-positive acute coronary syndromes (n=19). Circulating levels of the muscle-enriched miR-499 (>20-fold; P<0.01), miR-133a (11-fold; P<0.01), and miR-208a (5-fold; P<0.01) were significantly elevated in the aorta of troponin-positive acute coronary syndrome patients compared with patients with coronary artery disease. Importantly, there was a significant increase in circulating levels of miR-499 and miR-133a across the coronary circulation in troponin-positive acute coronary syndrome patients, suggestive of a release into the coronary circulation during myocardial injury. Indeed, miR-499 concentration gradients were significantly correlated with the extent of myocardial damage as measured by high-sensitivity troponin T (r=0.70, P<0.01). In contrast, circulating levels of miR-126 (P=0.16) decreased during transcoronary passage in patients with evidence of myocardial injury, suggesting consumption during transcoronary passage.

CONCLUSIONS

Muscle-enriched miR-499 and miR-133a are released from the heart into the coronary circulation on myocardial injury, whereas the vascular miR-126 is consumed during transcoronary passage. The differential regulation of circulating miRs during the transcoronary passage might provide important insights to exploit their role as cardiac biomarkers. Clinical Trial Registration- URL: http://www.germanctr.de. Unique identifier: DRKS00000207; in German Clinical Trials Registry.

Group V secretory phospholipase A2 plays a pathogenic role in myocardial ischaemia-reperfusion injury

AIMS

Group V secretory phospholipase A(2) (sPLA(2)-V) is highly expressed in the heart. This study examined (i) the role of sPLA(2)-V in myocardial ischaemia-reperfusion (I/R) injury and (ii) the cooperative action of sPLA(2)-V and cytosolic PLA(2) (cPLA(2)) in myocardial I/R injury, using sPLA(2)-V knockout (sPLA(2)V(-/-)) mice.

METHODS AND RESULTS

Myocardial I/R injury was created by 1 h ligation of the left anterior descending coronary artery, followed by 24 h of reperfusion. The sPLA(2)V(-/-) mice had a 44% decrease in myocardial infarct size, a preservation of echocardiographic LV function (%fractional shortening: 40 ± 3.5 vs. 21 ± 4.6, respectively), and lower content of leucotriene B(4) (LTB(4)) and thromboxane B(2) (TXB(2)) (40 and 37% lower, respectively) in the ischaemic myocardium after I/R compared with wild-type (WT) mice. Intraperitoneal administration of AACOCF3 or MAFP, inhibitors of cPLA(2) activity, decreased myocardial infarct size and myocardial content of LTB(4) and TXB(2) in both genotyped mice. The decrease in myocardial infarct size and content of LTB(4) and TXB(2) after cPLA(2) inhibitor administration was greater in WT mice than in sPLA(2)V(-/-) mice. I/R increased phosphorylation of extracellular signal-related kinase 1/2, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinases in the ischaemic myocardium in association with cPLA(2) phosphorylation. The I/R-induced increase in the phosphorylation of p38 and cPLA(2) was less in sPLA(2)-V(-/-) mice than in WT mice. Pretreatment with the p38 inhibitor SB202190 suppressed an increase in cPLA(2) phosphorylation after I/R in WT mice.

CONCLUSION

sPLA(2)-V plays an important role in the pathogenesis of myocardial I/R injury partly in concert with the activation of cPLA(2).

Deletion of secretory group V phospholipase A2 attenuates cell migration and airway hyperresponsiveness in immunosensitized mice

We investigated the role of group V phospholipase A2 (gVPLA2) in OVA-induced inflammatory cell migration and airway hyperresponsiveness (AHR) in C57BL/6 mice. Repeated allergen challenge induced biosynthesis of gVPLA2 in airways. By aerosol, gVPLA2 caused dose-related increase in airway resistance in saline-treated mice; in allergic mice, gVPLA2 caused persistent airway narrowing. Neither group IIa phospholipase A2, a close homolog of gVPLA2, nor W31A, an inactive gVPLA2 mutant with reduced activity, caused airway narrowing in immune-sensitized mice. Pretreatment with MCL-3G1, a blocking Ab against gVPLA2, before OVA challenge blocked fully gVPLA2-induced cell migration and airway narrowing as marked by reduction of migrating leukocytes in bronchoalveolar lavage fluid and decreased airway resistance. We also assessed whether nonspecific AHR caused by methacholine challenge was elicited by gVPLA2 secreted from resident airway cells of immune-sensitized mice. MCL-3G1 also blocked methacholine-induced airway bronchoconstriction in allergic mice. Blockade of bronchoconstriction by MCL-3G1 was replicated in allergic pla2g5-/- mice, which lack the gene encoding gVPLA2. Bronchoconstriction caused by gVPLA2 in pla2g4-/- mice was comparable to that in pla2g4+/+ mice. Our data demonstrate that gVPLA2 is a critical messenger enzyme in the development of AHR and regulation of cell migration during immunosensitization by a pathway that is independent of group IVa phospholipase A2.

Lymphangiogenesis in myocardial remodelling after infarction

Ishikawa Y, Akishima-Fukasawa Y, Ito K, Akasaka Y, Tanaka M, Shimokawa R, Kimura-Matsumoto M, Morita H, Sato S, Kamata I & Ishii T (2007) Histopathology51, 345–353

Lymphangiogenesis in myocardial remodelling after infarction

Postmortem cardiac troponin I and creatine kinase MB levels in the blood and pericardial fluid as markers of myocardial damage in medicolegal autopsy

The present study investigated cardiac troponin I (cTnI) and creatine kinase MB (CK-MB) in the blood and pericardial fluid from medicolegal autopsy cases (n=234, within 48h postmortem) with regard to the cause of death. The cTnI and CK-MB levels in cardiac, peripheral blood and pericardial fluid generally showed a mild and gradual postmortem time-dependent elevation (r=0.231-0.449, P<0.05-0.001). However, postmortem elevation of cTnI was larger for specific causes of death including acute myocardial infarction (AMI), cerebrovascular diseases (CVD), hyperthermia, fatal methamphetamine (MA) abuse and carbon monoxide (CO) intoxication and insignificant for recurrent myocardial infarction (RMI), chronic congestive heart diseases (CHD) and drowning, while that of CK-MB was greater for CO intoxication and insignificant for drowning. Cardiac blood and pericardial cTnI levels were relatively high for AMI, RMI, hyperthermia, MA abuse and CO intoxication, and was low for drowning. Elevated CK-MB level was observed for cardiac blood in asphyxiation and MA abuse cases and for peripheral blood in hyperthermia and MA abuse cases. When the cTnI/CK-MB ratio was estimated, it was independent of postmortem time, and the ratios for cardiac blood and pericardial fluid were significantly higher in cases of AMI, RMI, hyperthermia and CO intoxication but lower in cases of drowning. Elevations of cTnI levels in cardiac blood and pericardial fluid were related to the morphological severity of myocardial damage. These findings suggest that elevated cTnI and CK-MB levels in blood and pericardial fluid are related to ischemic, hypoxic and/or cytotoxic myocardial damage, which are characteristic of the cause of death, although the levels increase after death depending on myocardial damage at the time of death.

Expression of secretory phospholipase A2s in human atherosclerosis development

Secretory phospholipase A2s (sPLA2s) contribute to the hydrolysis of phospholipid. Among them, sPLA2-IIA, -V, and -X have been regarded as enhancers of lipid accumulation in arterial intima. However, the distribution and production of the other types of sPLA2 in human aortic wall remain unclear. Therefore, in this study, the distribution and production of seven types of sPLA2 including IIA, IID, IIE, IIF, III, V, and X in atherosclerosis development in the human aorta were comprehensively examined by immunohistochemistry and in situ hybridization (ISH). The extent of sPLA2s expression increased with atherosclerosis development, but only sPLA2-IIF was never observed in the normal aorta. Double-immunostaining demonstrated that sPLA2-V expression was limited to smooth muscle cells (SMCs), although the other sPLA2s were expressed in both macrophages and SMCs. ISH using sPLA2 cDNAs revealed that the expression pattern of each mRNA was consistent with the results of immunohistochemistry for each corresponding sPLA2. These results indicate that the seven types of sPLA2 are expressed with various patterns in all stages of atherosclerosis development and may play an atherogenic role through degradation of phospholipid.

Arachidonic Acid Metabolism as a Potential Mediator of Cardiac Fibrosis Associated with Inflammation

An increase in left ventricular collagen (cardiac fibrosis) is a detrimental process that adversely affects heart function. Strong evidence implicates the infiltration of inflammatory cells as a critical part of the process resulting in cardiac fibrosis. Inflammatory cells are capable of releasing arachidonic acid, which may be further metabolized by cyclooxygenase, lipoxygenase, and cytochrome P450 monooxygenase enzymes to biologically active products, including PGs, leukotrienes, epoxyeicosatrienoic acids, and hydroxyeicosatetraenoic acids. Some of these products have profibrotic properties and may represent a pathway by which inflammatory cells initiate and mediate the development of cardiac fibrosis. In this study, we critically review the current literature on the potential link between this pathway and cardiac fibrosis.

The proinflammatory mediator Platelet Activating Factor is an effective substrate for human group X secreted phospholipase A2

Platelet Activating Factor (PAF) is a potent mediator of inflammation whose biological activity depends on the acetyl group esterified at the sn-2 position of the molecule. PAF-acetylhydrolase (PAF-AH), a secreted calcium-independent phospholipase A(2), is known to inactivate PAF by formation of lyso-PAF and acetate. However, PAF-AH deficient patients are not susceptible to the biological effects of inhaled PAF in airway inflammation, suggesting that other enzymes may regulate extracellular levels of PAF. We therefore examined the hydrolytic activity of the recently described human group X secreted phospholipase A(2) (hGX sPLA(2)) towards PAF. Among different sPLA(2)s, hGX sPLA(2) has the highest affinity towards phosphatidylcholine (PC), the major phospholipid of cellular membranes and plasma lipoproteins. Our results show that unlike group IIA, group V, and the pancreatic group IB sPLA(2), recombinant hGX sPLA(2) can efficiently hydrolyze PAF. The hydrolysis of PAF by hGX sPLA(2) rises abruptly when the concentration of PAF passes through its critical micelle concentration suggesting that the enzyme undergoes interfacial binding and activation to PAF. In conclusion, our study shows that hGX sPLA(2) may be a novel player in PAF regulation during inflammatory processes.

Group V sPLA2: classical and novel functions

Group V sPLA(2) is unique among the family of secretory sPLA(2) enzymes in being able to bind to cell membranes through both interfacial-binding and through binding to proteoglycan. The function of group V sPLA(2) as an enzyme and its cross-talk with cPLA(2)alpha in initiating eicosanoid generation is well documented. Evidence, though, is emerging on the ability of this molecule to act as a regulator of several intracellular and extracellular pathways independently of its ability to provide arachidonic acid for eicosanoid generation, acting within the cell or as a secreted enzyme. In this article we will provide an overview of the properties of the enzyme and how they relate to our current understanding of its function.

Antifibrotic activity of an inhibitor of group IIA secretory phospholipase A2 in young spontaneously hypertensive rats

The development of fibrosis in the chronically hypertensive heart is associated with infiltration of inflammatory cells and cardiac hypertrophy. In this study, an inhibitor of the proinflammatory enzyme, group IIA human secretory phospholipase A2 (sPLA2-IIA), has been found to prevent collagen deposition as an important component of cardiovascular remodeling in a rat model of developing chronic hypertension. Daily treatment of young male spontaneously hypertensive rats (SHR) with an sPLA2-IIA inhibitor (KH064, 5-(4-benzyloxyphenyl)-4S-(phenyl-heptanoylamino)-pentanoic acid, 5 mg/kg/day p.o.) prevented increases in the content of perivascular (SHR 20.6 +/- 0.9%, n = 5; SHR+KH064 14.0 +/- 1.2%, n = 5) and interstitial (SHR 7.9 +/- 0.3%, n = 6; SHR+KH064 5.4 +/- 0.7%, n = 6) collagen in the left ventricle of rat hearts, but did not affect numbers of infiltrating monocytes/macrophages, left ventricular hypertrophy (SHR 2.88 +/- 0.08, n = 12; SHR+KH064 3.09 +/- 0.08 mg/g body weight, n = 9), increased systolic blood pressure, or thoracic aortic responses. This selective antifibrotic activity suggests that sPLA2-IIA may have an important but specific role in cardiac fibrosis, and that its inhibitors could be useful in dissecting molecular pathways leading to fibrotic conditions.

Oxidative stress and arachidonic acid mobilization

Reactive oxygen species are known to contribute to tissue damage during injury and inflammation. However, these species can also be sensed by the cells and trigger intracellular signaling cascades. This review examines recent evidence on the involvement of reactive oxygen species in lipid signaling. Attention is focused on activation of phospholipase A2s, enzymes whose action on membrane phospholipids can also render molecules with opposite effects on cells. The participation of Ca2+-dependent and Ca2+-independent phospholipase A2s in arachidonic acid mobilization from phospholipids is discussed, with particular attention to the interplay between cytosolic and secreted Ca2+-dependent forms. The involvement of alternative routes for arachidonic acid mobilization under oxidative stress is also considered.

Diverse cellular localizations of secretory phospholipase A2 enzymes in several human tissues

The secretory phospholipase A2 (sPLA2) family in mammals contains more than 10 enzymes. In this study, we examined by immunohistochemistry the localization of six sPLA2s (IIA, IID, IIE, IIF, V and X) in human heart, kidney, liver and stomach. In normal hearts, sPLA2-IIA was detected in coronary vascular smooth muscle cells (VSMC) and sPLA2-V in cardiomyocytes beneath the endocardium. In infarcted hearts, expression of these two enzymes was markedly increased in damaged cardiomyocytes, and expression of sPLA2-IID and-IIE, which was undetectable in normal hearts, was elevated in damaged cardiomyocytes and VSMC, respectively. In infarcted kidneys, sPLA2-IIA and-V were markedly induced in the uriniferous tubular epithelium. In livers affected by viral hepatitis, sPLA2-IIA and-V were expressed in hepatocytes with fatty degeneration. In the gastric glands exhibiting intestinal metaplasia, sPLA2-IIA was localized in the glandular base, sPLA2-IID and-V in the glandular body epithelium, sPLA2-IIE and-IIF in goblet cells in the foveolar epithelium, and sPLA2-X in both glandular body epithelial cells and foveolar epithelial goblet cells. In the gastric submucosal tissues, sPLA2-IIA and-IIE were located in VSMC and sPLA2-V was in the interstitial fibroblasts. In addition, sPLA2-IIA,-IIE,-IIF and-X were highly expressed in gastric signet ring cell carcinoma. Thus, individual sPLA2s exhibit unique cellular localizations in each tissue, suggesting their distinct roles in pathophysiology.