Epithelial Heparan Sulfate Promotes Staphylococcus aureus Corneal Infection by Inhibiting Cathelicidins

Area of Science:

• Immunology
• Microbiology
• Biochemistry

Background:

• Cathelicidins are vital antimicrobial peptides in innate immunity, primarily active against bacteria.
• Mechanisms regulating cathelicidin activity in vivo are less understood than in vitro bacterial killing.
• Bacterial pathogens may exploit host extracellular matrix components to evade immune defenses like cathelicidins.

Purpose of the Study:

• To investigate how host heparan sulfate (HS) inhibits cathelicidins, specifically the murine cathelicidin CRAMP.
• To elucidate the role of HS-cathelicidin interactions in bacterial infections, particularly Staphylococcus aureus corneal infections.
• To determine the structural and chemical basis for HS inhibition of cathelicidin activity.

Main Methods:

• Murine models of Staphylococcus aureus corneal infection with CRAMP deletion.
• Biochemical assays to determine HS binding affinity and structural requirements for CRAMP.
• Investigating the effect of heparan compounds on cathelicidin-mediated bacterial killing.
• Conditional deletion of HS2ST in corneal epithelial cells to assess the role of HS 2-O-sulfation.

Main Results:

• Deletion of CRAMP increased susceptibility to S. aureus corneal infection.
• Heparan compounds bind CRAMP with high affinity, requiring CRAMP's secondary structure, and inhibiting bacterial binding.
• Heparan compounds inhibited S. aureus killing by multiple mammalian cathelicidins in a 2-O-sulfate-dependent manner.
• Conditional deletion of HS2ST in corneal epithelial cells reduced susceptibility to corneal infection.

Conclusions:

• Epithelial heparan sulfate acts as an endogenous inhibitor of cathelicidins.
• 2-O-sulfated HS neutralizes cathelicidin antibacterial activity by binding and preventing bacterial cell interaction.
• This HS-mediated inhibition mechanism plays a significant role in susceptibility to bacterial infections.