A Novel Role of Complement: Mice Deficient in the Fifth Component of Complement (C5) Exhibit Impaired Liver Regeneration

Abstract

Components of innate immunity have recently been implicated in the regulation of developmental processes. Most strikingly, complement factors appear to be involved in limb regeneration in certain urodele species. Prompted by these observations and anticipating a conserved role of complement in mammalian regeneration, we have now investigated the involvement of complement component C5 in liver regeneration, using a murine model of CCl4-induced liver toxicity and mice genetically deficient in C5. C5-deficient mice showed severely defective liver regeneration and persistent parenchymal necrosis after exposure to CCl4. In addition, these mice showed a marked delay in the re-entry of hepatocytes into the cell cycle (S phase) and diminished mitotic activity, as demonstrated, respectively, by the absence of 5-bromo-2′-deoxyuridine incorporation in hepatocytes, and the rare occurrence of mitoses in the liver parenchyma. Reconstitution of C5-deficient mice with murine C5 or C5a significantly restored hepatocyte regeneration after toxic injury. Furthermore, blockade of the C5a receptor (C5aR) abrogated the ability of hepatocytes to proliferate in response to liver injury, providing a mechanism by which C5 exerts its function, and establishing a critical role for C5aR signaling in the early events leading to hepatocyte proliferation. These results support a novel role for C5 in liver regeneration and strongly implicate the complement system as an important immunoregulatory component of hepatic homeostasis.

Evidence for non-traditional activation of complement factor C3 during murine liver regeneration

“…Taken together, the data reported here indicate that despite the established requirement for complement factors C3 and C5 during the hepatic regenerative response (Mastellos et al 2001;Strey et al 2003;Markiewski et al 2004), none of the traditional upstream complement activation pathways are absolutely necessary for normal liver regeneration. The most straightforward interpretation of these data is that proteolytic C3 activation during liver regeneration may occur via non-traditional mechanisms.…”

“…This link was established by studies demonstrating that liver regeneration is impaired in complement factor C3-null mice, and that such impairment is rescued by exogenous C3 or C3a supplementation (Strey et al 2003; Markiewski et al 2004). Similarly, complement factor C5-deficient mice exhibit abnormal hepatic regeneration which can be rescued by supplementation with exogenous C5 or C5a (Mastellos et al 2001; Strey et al 2003). These analyses also show that pharmacological C5 neutralization and C5a receptor blockade disrupt the hepatic regenerative response and that disruption of complement cascade activation is associated with suppression of TNFα-IL6, NFκB, and STAT3 activation (Strey et al 2003).…”

A Novel C5a Receptor-Tissue Factor Cross-Talk in Neutrophils Links Innate Immunity to Coagulation Pathways

“…2) SB-290152, a selective nonpeptide antagonist of the complement anaphylatoxin receptor C3aR, was used in this study to dissect the involvement of C3aR signaling in the generation of neutrophilderived TF (26). 3) To block C5aR stimulation on neutrophils, we used a small cyclic hexapeptide (AcF- [OPdChaWR]) that acts as a selective C5aR antagonist (27,28). 4) Recombinant human C5a (rhC5a) containing a Histag at the N terminus was expressed in Escherichia coli using the expression vector pQE30 (Qiagen).…”

Candidate inhibitors of porcine complement

“…C4b2a cleaves C3 to C3a and C3b and forms the C5 convertase The main function of the complement system is to detect and kill microorganisms, as well as maintain homeostasis through clearance of apoptotic cells and cell debris, and tissue regeneration (65)(66)(67)(68). Opsonization by C3b leading to phagocytosis is the most important mechanism, but for some pathogens like Neisseria-species, killing by direct lysis by the MAC is equally important (69).…”