heparitin-sulfate and Atypical-Hemolytic-Uremic-Syndrome

The complement system plays a key role in the pathophysiology of kidney thrombotic microangiopathies (TMA), as illustrated by atypical hemolytic uremic syndrome. But complement abnormalities are not the only drivers of TMA lesions. Among other potential pathophysiological actors, we hypothesized that alteration of heparan sulfate (HS) in the endothelial glycocalyx could be important. To evaluate this, we analyzed clinical and histological features of kidney biopsies from a monocentric, retrospective cohort of 72 patients with TMA, particularly for HS integrity and markers of local complement activation. The role of heme (a major product of hemolysis) as an HS-degrading agent in vitro, and the impact of altering endothelial cell (ECs) HS on their ability to locally activate complement were studied. Compared with a positive control, glomerular HS staining was lower in 57 (79%) patients with TMA, moderately reduced in 20 (28%), and strongly reduced in 37 (51%) of these 57 cases. Strongly reduced HS density was significantly associated with both hemolysis at the time of biopsy and local complement activation (C3 and/or C5b-9 deposits). Using primary endothelial cells (HUVECs, Glomerular ECs), we observed decreased HS expression after short-term exposure to heme, and that artificial HS degradation by exposure to heparinase was associated with local complement activation. Further, prolonged exposure to heme modulated expression of several key genes of glycocalyx metabolism involved in coagulation regulation (C5-EPI, HS6ST1, HS3ST1). Thus, our study highlights the impact of hemolysis on the integrity of endothelial HS, both in patients and in endothelial cell models. Hence, acute alteration of HS may be a mechanism of heme-induced complement activation.

Topics: Atypical Hemolytic Uremic Syndrome; Complement Activation; Complement System Proteins; Endothelial Cells; Glycocalyx; Heme; Hemolysis; Heparitin Sulfate; Humans; Kidney Diseases; Retrospective Studies; Thrombotic Microangiopathies

Complement factor H (CFH) regulates complement activation in host tissues through its recognition of polyanions, which mediate CFH binding to host cell surfaces and extracellular matrix, promoting the deactivation of deposited C3b. These polyanions include heparan sulfate (HS), a glycosaminoglycan with a highly diverse range of structures, for which two regions of CFH (CCP6-8 and CCP19-20) have been implicated in HS binding. Mutations/polymorphisms within these glycosaminoglycan-binding sites have been associated with age-related macular degeneration (AMD) and atypical hemolytic uremic syndrome. In this study, we demonstrate that CFH has tissue-specific binding properties mediated through its two HS-binding regions. Our data show that the CCP6-8 region of CFH binds more strongly to heparin (a highly sulfated form of HS) than CCP19-20, and that their sulfate specificities are different. Furthermore, the HS binding site in CCP6-8, which is affected by the AMD-associated Y402H polymorphism, plays the principal role in host tissue recognition in the human eye, whereas the CCP19-20 region makes the major contribution to the binding of CFH in the human kidney. This helps provide a biochemical explanation for the genetic basis of tissue-specific diseases such as AMD and atypical hemolytic uremic syndrome, and leads to a better understanding of the pathogenic mechanisms for these diseases of complement dysregulation.

Topics: Adult; Aged; Aged, 80 and over; Amino Acid Substitution; Atypical Hemolytic Uremic Syndrome; Autopsy; Binding Sites; Complement Activation; Complement Factor H; Escherichia coli; Eye; Female; Hemolytic-Uremic Syndrome; Heparitin Sulfate; Humans; Kidney; Macular Degeneration; Male; Middle Aged; Mutation; Organ Specificity; Protein Binding; Recombinant Proteins