The Capacity of Group V sPLA ₂ to Increase Atherogenicity of ApoE ^−/− and LDLR ^−/− Mouse LDL In Vitro Predicts its Atherogenic Role In Vivo

Abstract

Objective-In vitro data indicate that human LDL modified by Group V secretory phospholipase A 2 (GV sPLA 2 ) is proatherogenic. Consistent with this, gain and loss of function studies demonstrated that GV sPLA 2 promotes atherosclerosis in LDLR Ϫ/Ϫ mice. The current study investigates whether GV sPLA 2 promotes atherosclerotic processes in apoE Ϫ/Ϫ mice. Methods and Results-LDL (dϭ1.019 to 1.063) from apoE Ϫ/Ϫ and LDLR Ϫ/Ϫ mice fed chow or Western diet were hydrolyzed by GV sPLA 2 . Phosphatidylcholine on LDL from LDLR Ϫ/Ϫ mice fed either a chow or Western diet was hydrolyzed to a greater extent (61.1Ϯ0.4% and 45.3Ϯ4.6%) than the corresponding fractions from apoE Ϫ/Ϫ mice (41.7Ϯ3.6% and 39.4Ϯ1.2%). ApoE Ϫ/Ϫ LDL induced macrophage foam cell formation in vitro without modification by GV sPLA 2 , whereas hydrolysis of LDLR Ϫ/Ϫ LDL was a prerequisite for foam cell formation. In contrast to findings in LDLR Ϫ/Ϫ mice, GV sPLA 2 deficiency did not significantly reduce atherosclerosis in apoE Ϫ/Ϫ mice, although collagen content was significantly reduced in lesions of apoE Ϫ/Ϫ mice lacking GV sPLA 2 . Conclusions-The ability of GV sPLA 2 to promote atherosclerotic lipid deposition in apoE Ϫ/Ϫ and LDLR Ϫ/Ϫ mice may be related to its ability to increase the atherogenic potential of LDL from these mice as assessed in vitro. Key Words: sphingomyelin Ⅲ foam cells Ⅲ cholesterol ester Ⅲ atherosclerosis S ecretory phospholipase A 2 (sPLA 2 ) 1 enzymes hydrolyze the fatty acid at the sn-2 position of glycerophospholipids. 1 Ten sPLA 2 isoforms have been described in mammals, and at least 7 of these can be detected in human atherosclerotic lesions. 2 These enzymes have been suggested to promote atherosclerosis through their hydrolyzing activities in the arterial intima. 3-5 GV, GX, and GIII sPLA 2 have been shown to effectively hydrolyze LDL. 6 -9 Our laboratory has shown that GV sPLA 2 hydrolysis of human LDL produces smaller LDL that are susceptible to aggregation, 7 modifications that enhance LDL retention in the vessel wall. In addition, GV sPLA 2 hydrolysis promotes LDL uptake by macrophages through a pathway that is independent of macrophage scavenger receptors and that involves cell surface proteoglycans. 10 Consistent with in vitro findings, overexpression of GV sPLA 2 in bone marrow-derived cells results in increased atherosclerosis in LDLR Ϫ/Ϫ mice, whereas deficiency of the enzyme results in reduced atherosclerosis. 11 However, several considerations led us to question whether GV sPLA 2 plays a major role in atherosclerotic lipid deposition in apoE Ϫ/Ϫ mice. First, in vitro studies have shown that LDL isolated from apoE Ϫ/Ϫ mice are oxidatively modified and hence induce macrophage foam cell formation in a CD36-dependent manner without the requirement for further modification. 12 Secondly, lipoprotein phospholipid (PL) content is altered in apoE Ϫ/Ϫ mice, such that the SM to PC ratio is relatively high because of increased SM production and decreased SM degradation. 13 Because previous in vitro data demonstrate that G...

Lipoprotein-Associated and Secreted Phospholipases A 2 in Cardiovascular Disease

“…However, the reduction in lesion area was not seen in apoE Ϫ/Ϫ mice lacking sPLA 2 -V, despite reduced collagen deposition in these mice. 84 In these studies, sPLA 2 -V did not alter foam cell formation in response to LDL from apoE Ϫ/Ϫ mice, whereas hydrolysis of LDL from LDLr Ϫ/Ϫ mice was a prerequisite for this process. These results suggest that the proatherogenic properties of sPLA 2 -V may depend in large part on its ability to enhance the proatherogenic potential of LDL.…”

“…These results suggest that the proatherogenic properties of sPLA 2 -V may depend in large part on its ability to enhance the proatherogenic potential of LDL. 84 Although sPLA 2 -X is the most efficient sPLA 2 to hydrolyze LDL and high-density lipoproteins 51 and to promote foam cell formation, 57 no direct evidence for a role of this isoform in atherosclerosis is currently available.…”

PLA2G10 Gene Variants, sPLA2 Activity, and Coronary Heart Disease Risk

“…We have had a long-standing interest in the sPLA2 enzymes 26,27 because they were identified as potential risk markers for CHD both from animal studies [10][11][12] and observational analyses. The aim of the present study was to investigate the contribution of sPLA2-X to the complex measure of sPLA2 activity, a marker of CHD risk, 28 by examining the association of PLA2G10 variants with sPLA2 activity.…”

“…12 Thus, by extrapolation, sPLA2-X, as the most potent of the 3 sPLA2s in hydrolyzing the most abundant phospholipid phosphotidylcholine, 13 could also be considered to be proatherogenic, and indeed it has been shown that PLA2G10 enhances foam cell formation in vitro by promoting atherogenic low-density lipoprotein (LDL) formation. 14 Transgenic mice overexpressing Pla2g10 have been shown to die neonatally because of severe lung pathology, suggesting a role for sPLA2-X overexpression in inflammatory airway diseases.…”

Group V Phospholipase A2 in Bone Marrow-derived Myeloid Cells and Bronchial Epithelial Cells Promotes Bacterial Clearance after Escherichia coli Pneumonia

“…Human low density lipoprotein modified by GV sPLA 2 is pro-atherogenic and promotes macrophage foam cell formation and overexpression of GV sPLA 2 increases, and targeted deletion of GV sPLA 2 decreases atherosclerotic plaque size in low density lipoprotein receptor-deficient mice (51,52). Based on these observations, pharmacologic inhibition of GV sPLA 2 has been identified as a possible therapeutic strategy for patients with atherosclerosis (21,53).…”