Introduction: Single nucleotide polymorphisms (SNP) in the gene encoding lipid phosphate phosphohydrolase 3 (PPAP2B/LPP3) are associated with susceptibility to atherosclerotic cardiovascular disease (ACVD) independently of classical risk factor. LPP3 inactivates lysophosphatidic acid (LPA), a pro-atherogenic, -inflammatory and -thrombotic lipid generated by phospholipase activity. Thus, changes in PPAP2B/LPP3 arterial expression levels may be associated to ACVD.
Hypothesis:PPAP2B/LPP3 and LPA receptors (LPAR1 to 6) differently expressed in human atherosclerotic lesions compared with normal arteries and co-localize with LPA
Methods: Immunohistochemistry, in situ hybridization and microarray gene analysis were used to investigate expression. Lipid species were detected with in situ lipid mass spectrometry imaging. Gene silencing in human endothelial cell were performed to investigate LPA-induced activation.
Results:PPAP2B/LPP3 mRNA was lower in carotid plaques compared to normal arteries. PPAP2B mRNA was lower in clinic symptomatic plaques compared with asymptomatic ones. PPAP2B protein co-localized with endothelial cells and smooth muscle cells. LPA and its precursors accumulated in the lesions fibrous cap and LPA co-localized with LPP3. LPAR 1 t-6 is expression profile was different in plaques compared with normal arteries. LPAR 2, 5, and 6 mRNA showed increased expression in plaques with highest expression of LPAR6 in endothelial cells and co-localizing with LPA. PPAP2B correlated negatively with LPAR2 and positively with LPAR6 mRNA expression levels. PPAP2B silencing increased LPA-induced endothelial cell adhesion molecules and cytokines mRNA expression. On the other hand, LPAR6 silencing inhibited LPA-induced cell activation, and increased LPAR1 expression, but not when silencing PPAP2B simultaneously.
Conclusions: Results show for the first time a comprehensive PPAP2B/LPP3 and LPAR1-6 expression in human atherosclerotic lesions supporting genetic findings implicating diminishing PPAP2B/LPP3 expression with ACVD. PPAP2B/LPP3 protects endothelial cells from LPA-induced activation. However, decrease PPAP2B/LPP3 expression, promote other non-LPAR6-LPA mediated cell-activation mechanism(s).