Differential Expression of Lipoprotein-Associated Phospholipase A2 in Monocyte Subsets: Impact of Uremia and Atherosclerosis.

Background: Monocytic products, such as lipoprotein-associated phospholipase A2 (Lp-PLA2), may participate in the development of atherosclerosis. Heterogeneity of monocytes is widely acknowledged. Classical, intermediate, and non-classical subsets can be discerned. Recently, an inflammatory, pro-atherogenic monocyte population could be identified in hemodialysis patients. In this study, we investigated the expression of Lp-PLA2 on leucocytes and different monocyte subpopulations and their possible role in uremia, inflammation, and atherosclerosis.
Methods: Chronic kidney disease stage 5-D (CKD5-D; n = 57), healthy control subjects with hs-C-reactive protein (CRP) levels ≤1 mg/L (CO-N, n = 22) and a control group with inflammatory activation (CRP levels >1 mg/L, CO-I, n = 29) were enrolled in this cross-sectional observation. The CKD5-D cohort was dichotomized into patients with (A+) and without subclinical atherosclerosis (A-) by carotid artery ultrasound measurement. Lp-PLA2 activity was determined in plasma samples, Lp-PLA2 mRNA expression analysis in leucocytes, and sorted monocyte subsets. Effects of Lp-PLA2 overexpression were studied in classical vs. intermediate and non-classical subsets.
Results: The classical monocytes expressed the highest Lp-PLA2 mRNA levels as compared to other subpopulations. CKD5-D patients revealed significantly higher Lp-PLA2 transcripts, as well as higher Lp-PLA2 plasma activity as compared to healthy and "inflammatory" controls. In vitro data confirmed that uremia significantly contributes to Lp-PLA2 mRNA upregulation. Non-classical monocytes of A+ patients revealed significant higher Lp-PLA2 mRNA compared to A-.
Conclusion: Uremic environment but not inflammation per se increases plasma Lp-PLA2 activity and upregulates monocytic Lp-PLA2 mRNA expression. The highest Lp-PLA2 levels were found in the classical and not in the inflammatory subsets. Atherosclerosis also contributes to a subset-specific increase in Lp-PLA2 mRNA expression.
(© 2016 S. Karger AG, Basel.)