title: Protein load impairs factor H binding promoting complement-dependent dysfunction of proximal tubular cells.
abstract: Intrarenal complement activation plays an important role in the progression of chronic kidney disease. A key target of the activated complement cascade is the proximal tubule, a site where abnormally filtered plasma proteins and complement factors combine to promote injury. This study determined whether protein overloading of human proximal tubular cells (HK-2) in culture enhances complement activation by impairing complement regulation. Addition of albumin or transferrin to the cells incubated with diluted human serum as a source of complement caused increased apical C3 deposition. Soluble complement receptor-1 (an inhibitor of all 3 activation pathways) blocked complement deposition while the classical and lectin pathway inhibitor, magnesium chloride-EGTA, was, ineffective. Media containing albumin as well as complement had additive proinflammatory effects as shown by increased fractalkine and transforming growth factor-beta mRNA expression. This paralleled active C3 and C5b-9 generations, effects not shared by transferrin. Factor H, one of the main natural inhibitors of the alternative pathway, binds to heparan sulfate proteoglycans. Both the density of heparan sulfate and factor H binding were reduced with protein loading, thereby enhancing the albumin- and serum-dependent complement activation potential. Thus, protein overload reduces the ability of the tubule cell to bind factor H and counteract complement activation, effects instrumental to renal disease progression.
authors.affiliation: Mario Negri Institute for Pharmacological Research, Bergamo, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Buelli
authors.forename: Mauro
authors.initials: M
authors.lastname: Abbate
authors.forename: Marina
authors.initials: M
authors.lastname: Morigi
authors.forename: Daniela
authors.initials: D
authors.lastname: Moioli
authors.forename: Cristina
authors.initials: C
authors.lastname: Zanchi
authors.forename: Marina
authors.initials: M
authors.lastname: Noris
authors.forename: Carla
authors.initials: C
authors.lastname: Zoja
authors.forename: Charles D
authors.initials: CD
authors.lastname: Pusey
authors.forename: Peter F
authors.initials: PF
authors.lastname: Zipfel
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Remuzzi
mesh_terms: D002460:Cell Line; D003167:Complement Activation; D017242:Complement Factor H / Q000378:metabolism*; D003165:Complement System Proteins / Q000378:metabolism*; D018450:Disease Progression; D006801:Humans; D007674:Kidney Diseases / Q000209:etiology / Q000473:pathology; D007687:Kidney Tubules, Proximal / Q000473:pathology*; D011485:Protein Binding; D011506:Proteins / Q000494:pharmacology*; D012709:Serum Albumin / Q000494:pharmacology; D014168:Transferrin / Q000494:pharmacology
chemical_list: D011506:Proteins; D012709:Serum Albumin; D014168:Transferrin; D017242:Complement Factor H; D003165:Complement System Proteins