Heparan sulfate proteoglycans mediate factor XIIa binding to the cell surface

Area of Science:

• Biochemistry
• Cell Biology
• Medical Research

Background:

• Hageman factor (FXIIa) initiates coagulation and activates other systems.
• FXIIa also acts as a growth factor, but its cell surface binding mechanisms are unclear.
• FXIIa interacts with various cell types, including human lung fibroblasts (HLF).

Purpose of the Study:

• To elucidate the mechanisms of FXIIa cell surface binding.
• To investigate the role of glycosaminoglycans in FXIIa-HLF interactions.
• To explore FXIIa binding in idiopathic pulmonary fibrosis (IPF) and its potential contribution to fibrogenesis.

Main Methods:

• Enzymatic, inhibitory, and overexpression approaches to identify FXIIa binding determinants.
• Cell-free assays and competition experiments to assess binding preferences.
• Analysis of fibroblasts from IPF patients, including gene expression and functional assays.
• RNA interference and intracellular sulfation inhibitors to study FXIIa accumulation.

Main Results:

• FXIIa binds to HLF through cell membrane-bound heparan sulfate (HS), a component of proteoglycans.
• FXIIa shows preferential binding to HS and heparin over other sulfated glycosaminoglycans.
• Fibroblasts from IPF patients exhibit increased FXIIa binding due to enhanced HS sulfation.
• FXIIa stimulates HLF migration, an effect inhibited by heparinase I.

Conclusions:

• Heparan sulfate glycosaminoglycans mediate the local accumulation of FXIIa on the cell membrane.
• Enhanced FXIIa binding to IPF fibroblasts suggests a role in fibrogenesis.
• Targeting HS-FXIIa interactions may offer therapeutic strategies for IPF.