Factor H and Properdin Recognize Different Epitopes on Renal Tubular Epithelial Heparan Sulfate

Azadeh Zaferani,Romain R Vivès,Pieter Van Der Pol,Gerjan J Navis,Mohamed R Daha,Cees Van Kooten,Hugues Lortat-Jacob,Marc A Seelen,Jacob Van Den Born

doi:10.1074/jbc.m112.380386

Abstract

During proteinuria, renal tubular epithelial cells become exposed to ultrafiltrate-derived serum proteins, including complement factors. Recently, we showed that properdin binds to tubular heparan sulfates (HS). We now document that factor H also binds to tubular HS, although to a different epitope than properdin. Factor H was present on the urinary side of renal tubular cells in proteinuric, but not in normal renal tissues and colocalized with properdin in proteinuric kidneys. Factor H dose-dependently bound to proximal tubular epithelial cells (PTEC) in vitro. Preincubation of factor H with exogenous heparin and pretreatment of PTECs with heparitinase abolished the binding to PTECs. Surface plasmon resonance experiments showed high affinity of factor H for heparin and HS (K(D) values of 32 and 93 nm, respectively). Using a library of HS-like polysaccharides, we showed that chain length and high sulfation density are the most important determinants for glycosaminoglycan-factor H interaction and clearly differ from properdin-heparinoid interaction. Coincubation of properdin and factor H did not hamper HS/heparin binding of one another, indicating recognition of different nonoverlapping epitopes on HS/heparin by factor H and properdin. Finally we showed that certain low anticoagulant heparinoids can inhibit properdin binding to tubular HS, with a minor effect on factor H binding to tubular HS. As a result, these heparinoids can control the alternative complement pathway. In conclusion, factor H and properdin interact with different HS epitopes of PTECs. These interactions can be manipulated with some low anticoagulant heparinoids, which can be important for preventing complement-derived tubular injury in proteinuric renal diseases.

Highlights

Alternative pathway (AP) of complement is involved in proteinuria-derived tubular injury
Factor H Binds to Tubular Epithelial Cells via Heparan Sulfates—Because under proteinuric conditions, renal tubular cells become exposed to serum proteins including complement factors, and factor H has been found in the urines of proteinuric patients [33,34,35], we evaluated whether renal tubular cells can bind factor H
Mutations in the complement control protein (CCP) 7–9 GAG-binding domain of factor H have been associated with increased AP activation in age-related macular degeneration [39], whereas mutations in the CCP 19 –20 GAG-binding domain of factor H have been associated to increased AP activation in atypical hemolytic uremic syndrome [40]

Summary

Background

Alternative pathway (AP) of complement is involved in proteinuria-derived tubular injury. PGs can be found on almost all mammalian cell surfaces and within extracellular matrices, whereas HS proteoglycans (HSPG) are predominantly found in basement membranes They play an important role in cell activities via their interaction with chemokines, growth factors, and cytokines [13]. We demonstrate selective inhibition of properdin binding to proximal tubular epithelial cells, without loss of factor H binding to these cells by some heparinoids with low anticoagulant activity. This finding might be of great importance for potential therapeutic interventions

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION