Contribution of Chondroitin Sulfate A to the Binding of Complement Proteins to Activated Platelets

PLoS One. 2010 Sep 23;5(9):e12889. doi: 10.1371/journal.pone.0012889.

Abstract

Background: Exposure of chondroitin sulfate A (CS-A) on the surface of activated platelets is well established. The aim of the present study was to investigate to what extent CS-A contributes to the binding of the complement recognition molecule C1q and the complement regulators C1 inhibitor (C1INH), C4b-binding protein (C4BP), and factor H to platelets.

Principal findings: Human blood serum was passed over Sepharose conjugated with CS-A, and CS-A-specific binding proteins were identified by Western blotting and mass spectrometric analysis. C1q was shown to be the main protein that specifically bound to CS-A, but C4BP and factor H were also shown to interact. Binding of C1INH was dependent of the presence of C1q and then not bound to CS-A from C1q-depleted serum. The specific interactions observed of these proteins with CS-A were subsequently confirmed by surface plasmon resonance analysis using purified proteins. Importantly, C1q, C4BP, and factor H were also shown to bind to activated platelets and this interaction was inhibited by a CS-A-specific monoclonal antibody, thereby linking the binding of C1q, C4BP, and factor H to exposure of CS-A on activated platelets. CS-A-bound C1q was also shown to amplify the binding of model immune complexes to both microtiter plate-bound CS-A and to activated platelets.

Conclusions: This study supports the concept that CS-A contributes to the binding of C1q, C4BP, and factor H to platelets, thereby adding CS-A to the previously reported binding sites for these proteins on the platelet surface. CS-A-bound C1q also seems to amplify the binding of immune complexes to activated platelets, suggesting a role for this molecule in immune complex diseases.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Blood Platelets / drug effects
  • Blood Platelets / metabolism*
  • Chondroitin Sulfates / pharmacology*
  • Complement C1 Inactivator Proteins / metabolism
  • Complement C1 Inhibitor Protein
  • Complement C1q / metabolism
  • Complement C4b-Binding Protein / metabolism
  • Complement Factor H / metabolism
  • Complement System Proteins / metabolism*
  • Humans
  • Platelet Activation / drug effects*
  • Protein Binding / drug effects

Substances

  • Complement C1 Inactivator Proteins
  • Complement C1 Inhibitor Protein
  • Complement C4b-Binding Protein
  • SERPING1 protein, human
  • Complement C1q
  • Complement Factor H
  • Chondroitin Sulfates
  • Complement System Proteins