Alternative C3 Complement System: Lipids and Atherosclerosis

Abstract

Familial hypercholesterolemia (FH) is increasingly associated with inflammation, a phenotype that persists despite treatment with lipid lowering therapies. The alternative C3 complement system (C3), as a key inflammatory mediator, seems to be involved in the atherosclerotic process; however, the relationship between C3 and lipids during plaque progression remains unknown. The aim of the study was to investigate by a systems biology approach the role of C3 in relation to lipoprotein levels during atherosclerosis (AT) progression and to gain a better understanding on the effects of C3 products on the phenotype and function of human lipid-loaded vascular smooth muscle cells (VSMCs). By mass spectrometry and differential proteomics, we found the extracellular matrix (ECM) of human aortas to be enriched in active components of the C3 complement system, with a significantly different proteomic signature in AT segments. Thus, C3 products were more abundant in AT-ECM than in macroscopically normal segments. Furthermore, circulating C3 levels were significantly elevated in FH patients with subclinical coronary AT, evidenced by computed tomographic angiography. However, no correlation was identified between circulating C3 levels and the increase in plaque burden, indicating a local regulation of the C3 in AT arteries. In cell culture studies of human VSMCs, we evidenced the expression of C3, C3aR (anaphylatoxin receptor) and the integrin αMβ2 receptor for C3b/iC3b (RT-PCR and Western blot). C3mRNA was up-regulated in lipid-loaded human VSMCs, and C3 protein significantly increased in cell culture supernatants, indicating that the C3 products in the AT-ECM have a local vessel-wall niche. Interestingly, C3a and iC3b (C3 active fragments) have functional effects on VSMCs, significantly reversing the inhibition of VSMC migration induced by aggregated LDL and stimulating cell spreading, organization of F-actin stress fibers and attachment during the adhesion of lipid-loaded human VSMCs. This study, by using a systems biology approach, identified molecular processes involving the C3 complement system in vascular remodeling and in the progression of advanced human atherosclerotic lesions.

Differentiation of human macrophages with anaphylatoxin C3a impairs alternative M2 polarization and decreases lipopolysaccharide‐induced cytokine secretion

“…In the early lesions (fatty streaks), monocytes migrate to the intima and differentiate into macrophages without any contact with proinflammatory cytokines including C3a. 41 The following lesion progression, however, leads to the macrophage activation and appearance of some cocktail of proinflammatory cytokines including C3a. 41 Therefore, in the early atherosclerotic lesions C3a acts on the mature macrophages.…”

“…41 The following lesion progression, however, leads to the macrophage activation and appearance of some cocktail of proinflammatory cytokines including C3a. 41 Therefore, in the early atherosclerotic lesions C3a acts on the mature macrophages. By contrast, the monocytes migrating to the intima of mature atherosclerotic plaques have to differentiate into macrophages being surrounded by the complicated cocktail of pro-and anti-inflammatory cytokines including C3a.…”

“…40 C3a has functional effects on vascular smooth muscle cells, significantly reversing the inhibition of vascular smooth muscle cell migration induced by aggregated LDL and stimulating cell spreading, organization of F-actin stress fibers and attachment during the adhesion of lipid-loaded human vascular smooth muscle cells. 41 Moreover, vascular smooth muscle cells may be the important source of C3a within atherosclerotic plaques. 41,42 In this study, we investigate the role of C3a in the M2 and M1 polarization of human macrophages.…”

“…41 Moreover, vascular smooth muscle cells may be the important source of C3a within atherosclerotic plaques. 41,42 In this study, we investigate the role of C3a in the M2 and M1 polarization of human macrophages. Our data provide a novel role of C3a in the regulation of macrophage polarization and suggest a crosstalk between C3a, TLR4 and PPARc signaling pathways.…”

Molecular Research in Cardiovascular Disease

“…Familial hypercholesterolemia (FC) represents one important risk factor for IHD; apart from lipid accumulation within the intima, another mechanism often encountered in FC is inflammation. By using a particular system biology, Garcia-Arguinzonis et al [7] investigated the role complement C3 plays in atherosclerosis on the phenotype and function of human lipid-loaded vascular smooth muscle cells (VSMCs). By spectrometry and differential proteomics, it was established that complement C3 was more abundantly expressed in atherosclerotic-extracellular matrix, compared with normal segments.…”