Apolipoprotein (a)/Lipoprotein(a)-Induced Oxidative-Inflammatory a7-nAChR/p38 MAPK/IL-6/RhoA-GTP Signaling Axis and M1 Macrophage Polarization Modulate Inflammation-Associated Development of Coronary Artery Spasm

Objective. Apolipoprotein (a)/lipoprotein(a) (Lp(a)), a major carrier of oxidized phospholipids, and alpha 7-nicotinic acetylcholine receptor (alpha 7-nAChR) may play an important role in the development of coronary artery spasm (CAS). In CAS, the association between Lp(a) and the alpha 7-nAChR-modulated inflammatory macrophage polarization and activation and smooth muscle cell dysfunction remains unknown. Methods. We investigated the relevance of Lp(a)/alpha 7-nAChR signaling in patient monocyte-derived macrophages and human coronary artery smooth muscle cells (HCASMCs) using expression profile correlation analyses, fluorescence-assisted cell sorting flow cytometry, immunoblotting, quantitative real-time polymerase chain reaction, and clinicopathological analyses. Results. There are increased serum Lp(a) levels (3.98-fold, p=0.011) and macrophage population (3.30-fold, p=0.013) in patients with CAS compared with patients without CAS. Serum Lp(a) level was positively correlated with high-sensitivity C-reactive protein (r(2)=0.48, p < 0.01), IL-6 (r2=0.38, p=0.03), and alpha 7-nAChR (r2=0.45, p < 0.01) in patients with CAS, but not in patients without CAS. Compared with untreated or low-density lipoprotein- (LDL-) treated macrophages, Lp(a)-treated macrophages exhibited markedly enhanced alpha 7-nAChR mRNA expression (p < 0.01) and activity (p < 0.01), in vitro and ex vivo. Lp(a) but not LDL preferentially induced CD80+ macrophage (M1) polarization and reduced the inducible nitric oxide synthase expression and the subsequent NO production. While shRNA-mediated loss of alpha 7-nAChR function reduced the Lp(a)-induced CD80+ macrophage pool, both shRNA and anti-IL-6 receptor tocilizumab suppressed Lp(a)-upregulated alpha 7-nAChR, p-p38 MAPK, IL-6, and RhoA-GTP protein expression levels in cultures of patient monocyte-derived macrophages and HCASMCs. Conclusions. Elevated Lp(a) levels upregulate alpha 7-nAChR/IL-6/p38 MAPK signaling in macrophages of CAS patients and HCASMC, suggesting that Lp(a)-triggered inflammation mediates CAS through alpha 7-nAChR/p38 MAPK/IL-6/RhoA-GTP signaling induction, macrophage M1 polarization, and HCASMC activation.