Complement anaphylatoxin C4a inhibits C5a-induced neointima formation following arterial injury

Abstract

Interactions between complement anaphylatoxins have been investigated in numerous fields; however, their functions during arterial remodeling following injury have not been studied. The inhibitory effect of complement anaphylatoxin C4a on neointima formation induced by C5a following arterial injury was investigated. Mice were subjected to wire-induced endothelial denudation of the femoral artery and treated with C5a alone or C5a + C4a for two weeks. C4a significantly inhibited C5a-induced neointima formation and the expression of CD68, F4/80, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and monocyte chemotactic protein-1 (MCP-1). In vitro, although C4a did not directly inhibit the migration, proliferation or the expression of vascular cell adhesion molecule-1 (VCAM-1) of C5a-induced vascular smooth muscle cells (VSMCs), C5a-pretreated conditioned medium-induced migration, proliferation and VCAM-1 expression of VSMCs were suppressed when VSMCs were exposed to conditioned medium from C4a-pretreated macrophages. In addition, C5a-induced TNF-α, IL-6 and MCP-1 expression, Ca2+ influx and extracellular signal-regulated kinase (ERK) activation in macrophages were suppressed by C4a. C4a inhibits C5a-induced neointima formation, not by acting directly on VSMCs, but via a macrophage-mediated reaction by inhibiting the Ca2+-dependent ERK pathway in macrophages.

C4a: An Anaphylatoxin in Name Only

“…The authors did not, however, assess for trace amounts of C3a and C5a in the C4a used in the study, which had been prepared using a method similar to that of Gorski et al [34], raising concerns about the purity of C4a and the validity of the data. In a study using recombinant C4a and C5a (thus overcoming the contamination issue), the ability of C4a to inhibit C5a-mediated neointima injury was assessed [55]. Coinfusion of C4a and C5a resulted in reduced neointima formation relative to infusion of C5a alone.…”

Complement-activation fragment C4a mediates effector functions by binding as untethered agonist to protease-activated receptors 1 and 4

“…It has to be noted that these early studies were typically performed with plasma-purified C4a, which may have contained small but physiologically relevant amounts of other anaphylatoxins. Recent studies using recombinant human C4a have shown that the protein can inhibit C3a-or C5a-mediated chemoattractant and secretagogue functions in mast cells, impair C5a-induced neointima formation, and protect against hyperoxic lung injury via a macrophage-dependent signaling pathway (8)(9)(10). Whereas these results may indicate a potential competition of C4a for the anaphylatoxin receptors, direct binding could not be confirmed to any of the receptors.…”

Adverse effects of BMPR2 suppression in macrophages in animal models of pulmonary hypertension

“…In PAH, monocytes/macrophages present in pulmonary vascular lesions and surrounding the remodeled pulmonary vessels are significantly increased. 74,77 Our lineage-tracing studies in the monocyte-specific BMPR2-KO mouse indicate that dysfunctional BMPR2 in macrophages accelerate the migration of these cells to pulmonary vessels following injury, which may influence pulmonary vessel remodeling; elimination of these cells by clodronate is shown to reverse this pulmonary vessel remodeling. Further, circulating and bone marrow-derived myeloid cells do not appear to directly influence macrophage infiltration and pulmonary vessel remodeling.…”