Endothelial Oxidative Stress Activates the Lectin Complement Pathway

Abstract

Oxidative stress increases endothelial mannose-binding lectin (MBL) binding and activates the lectin complement pathway (LCP). However, the molecular mechanism of MBL binding to the endothelium after oxidative stress is unknown. Intermediate filaments have been previously reported to activate the classical complement pathway in an antibody-independent manner. We investigated whether oxidative stress increases human umbilical vein endothelial cell (HUVEC) cytokeratin 1 (CK1) expression and activates the LCP via MBL binding to CK1. Reoxygenation (3 hours, 21% O(2)) of hypoxic HUVECs (24 hours, 1% O(2)) significantly increased CK1 mRNA (in situ hybridization) and membrane protein expression [enzyme-linked immunosorbent assay (ELISA)/confocal microscopy]. Incubating human serum (HS) with N-acetyl-D-glucosamine or anti-human MBL monoclonal antibody attenuated MBL and C3 deposition on purified CK1 (ELISA). CK1 and MBL were co-immunoprecipitated from hypoxic HUVECs reoxygenated in HS. Treatment with anti-human cytokeratin Fab fragments attenuated endothelial MBL and C3 deposition after oxidative stress (ELISA/confocal microscopy). We conclude that: 1) endothelial oxidative stress increases CK1 expression, MBL binding, and C3 deposition; 2) inhibition of MBL attenuates purified CK1-induced complement activation; and 3) anti-human cytokeratin Fab fragments attenuate endothelial MBL and C3 deposition after oxidative stress. These results suggest that MBL binding to endothelial cytokeratins may mediate LCP activation after oxidative stress.

Genetically determined high serum levels of mannose-binding lectin and agalactosyl IgG are associated with ischemic heart disease in rheumatoid arthritis

“…MBL may enhance inflammation-mediated tissue injury during postischemic reperfusion by complement activation (14)(15)(16). MBL has also been suggested to be a mediator in the pathogenesis of microvascular complications in type 1 diabetes (36) as well as graft survival after kidney transplantation (37).…”

“…Lack of functional alleles in some populations is associated with increased risk of atherosclerosis and cardiovascular occlusion (9)(10)(11)(12)(13). However, experimental data and clinical observations suggest that MBL and the lectin pathway of complement may initiate the inflammatory reaction seen in relation to ischemia reperfusion injury (14)(15)(16). Moreover, subjects who are homozygous for the functional MBL2 genotype and have high serum levels of MBL have the highest rate of early restenosis after carotid eversion endarterectomy (17).…”

The complement system and age-related macular degeneration

“…Further studies using specific inhibitors of the classical, alternative or lectin pathway, in addition to using genetically modified mice will be needed to better comprehend the role of complements in oxidative stress. 32 The role of these pathways in AMD remains to be investigated.…”

Molecular cloning and expression analysis of Pleurodeles waltl complement component C3 under normal physiological conditions and environmental stresses

“…Furthermore, it has been shown that complement activation plays an important role in the inflammatory process after oxidative stress (Collard et al, 1999). There is increasing evidence that ROS activate the complement system and C3 is thought to provide protection against oxidative stress (Collard et al, 1999(Collard et al, , 2000Hart et al, 2004). Another possibility is that danger signals, such as HSP, that are induced by heat shock (Fig.…”

“…All complement activation pathways converge at the level of C3, the key component, which is processed into activation fragments C3a and C3b (Collard et al, 2000), with the assembly of C5 convertase and the further release of the C5a and C5b fragments. C3a and C5a are anaphylatoxins that exert a plethora of pro-inflammatory and immunoregulatory functions (Guo and Ward, 2005).…”