C-Reactive Protein Binds to Cholesterol Crystals and Co-Localizes with the Terminal Complement Complex in Human Atherosclerotic Plaques

Abstract

Inflammation is a part of the initial process leading to atherosclerosis and cholesterol crystals (CC), found in atherosclerotic plaques, which are known to induce complement activation. The pentraxins C-reactive protein (CRP), long pentraxin 3 (PTX3), and serum amyloid P component (SAP) are serum proteins associated with increased risk of cardiovascular events and these proteins have been shown to interact with the complement system. Whether the pentraxins binds to CC and mediate downstream complement-dependent inflammatory processes remains unknown. Binding of CRP, PTX3, and SAP to CC was investigated in vitro by flow cytometry and fluorescence microscopy. CRP, PTX3, and SAP bound to CC in a concentration-dependent manner. CRP and PTX3 interacted with the complement pattern recognition molecule C1q on CC by increasing the binding of both purified C1q and C1q in plasma. However, CRP was the strongest mediator of C1q binding and also the pentraxin that most potently elevated C1q-mediated complement activation. In a phagocytic assay using whole blood, we confirmed that phagocytosis of CC is complement dependent and initiated by C1q-mediated activation. The pathophysiological relevance of the in vitro observations was examined in vivo in human atherosclerotic plaques. CRP, PTX3, and SAP were all found in atherosclerotic plaques and were located mainly in the cholesterol-rich necrotic core, but co-localization with the terminal C5b-9 complement complex was only found for CRP. In conclusion, this study identifies CRP as a strong C1q recruiter and complement facilitator on CC, which may be highly relevant for the development of atherosclerosis.

C-reactive protein (CRP) recognizes uric acid crystals and recruits proteases C1 and MASP1

“…Similar to the preferential binding of CRP to the edges or specific sides of MSU crystals, we also found irregular binding of CRP to CPPD and it seems that the previously described binding of CRP to cholesterol crystals is also limited to certain areas of the crystals 34 .…”

“…Many other proteins in the list (Table S1a) are probably also MSU-binding proteins, but we only validated two more notable novel MSU-binding proteins: Thrombin (F2) and SAP (APCS), which both bound independently of CRP. Binding of both pentraxins CRP and SAP has also previously been shown for cholesterol crystals 34 . The third member of the pentraxin family PTX3 has been shown to inhibit calcium oxalate crystallization and nephrocalcinosis 35 , and to contribute to MSU-induced inflammation in mice 36 .…”

Zebrafish C-reactive protein isoforms inhibit SVCV replication by blocking autophagy through interactions with cell membrane cholesterol

“…In fact, the induction of ROS generation as a consequence of the interaction of the monomeric form of human CRP with lipid rafts in human and rat peripheral blood mononuclear cells has also been observed 89 . Thus, the high affinity for cholesterol described for MBCD 64,65 and CRPs 47,88,90 suggests that they may have cholesterol-sequestering faction that blocks the ROS-dependent autophagy. Furthermore, 25-HOC added to cells also changes the lipid raft composition with similar inhibition of autophagy.…”

The phagocytic state of brain myeloid cells after ischemia revealed by superresolution structured illumination microscopy

“…Phagocytosis is used by brain myeloid cells in different conditions, such as during brain development to prune synapses and model brain connectivity [42], or responding to altered homeostasis either in protective or detrimental ways [2]. Phagocytosis is mainly studied in vitro [11] or by FACS analysis [43] which requires tissue processing to sort macrophages thus loosing information on cell localization relative to an injured area. A few methods based on microscopy exist to assess phagocytosis in the brain [16, 44]; however, most of them lack enough resolution and perhaps sensitivity.…”