Role of HSPGs in Systemic Bacterial Infections

Abstract

Heparan sulfate proteoglycans (HSPGs) are at the forefront of host-microbe interactions. Cell surface HSPGs are thought to promote infection as attachment and internalization receptors for many bacterial pathogens and as soluble inhibitors of host immunity when released from the cell surface by ectodomain shedding. However, the importance of HSPG-pathogen interactions in vivo has yet to be clearly established. Here we describe several representative methods to study the role of HSPGs in systemic bacterial infections, such as bacteremia and sepsis. The overall experimental strategy is to use mouse models to establish the physiological significance of HSPGs, to determine the identity of HSPGs that specifically promote infection, and to define key structural features of HSPGs that enhance bacterial virulence in systemic infections.

Keywords: Bacteremia; Heparan sulfate; Heparin; Host defense; Proteoglycan; Sepsis; Syndecans.

Fig. 1

Systemic S. aureus infection induces Sdc1 shedding. Wt mice on the C57BL/6J background were infected i.v. or i.p. with 5 × 10⁷ cfu of S. aureus USA300, and their livers were isolated at 24 h post-infection. Paraffin-embedded liver sections of unchallenged mice and infected mice were immunostained for Sdc1 with Alexa 647-conjugated 281.2 rat anti-mouse Sdc1 monoclonal antibodies (original magnification, ×200)

Fig. 2

Comparison of i.v. and i.p. S. aureus infection. Wt mice on C57BL/6J were infected i.v. or i.p. with 5 × 10⁷ cfu of S. aureus USA300, and their tissues were isolated at 24 h post-infection. A) Liver, lung, and spleen bacterial burden were determined by extracting live bacteria from tissues, plating serial dilutions onto TSA plates, and counting the number of colonies (n = 5). B) Liver sections (5 μm) were immunostained with human anti-PNAG antibodies and Alexa 647-conjugated rat anti-human monoclonal antibodies (original magnification, ×200). C) Liver sections were immunostained with Alexa 488-conjugated rat anti-mouse Ly6G monoclonal antibodies (original magnification, ×200)

Fig. 3

O-sulfated motifs in heparin promote i.v. S. aureus infection. Wt mice on BL/6J were infected i.v. with 5 × 10⁷ cfu of S. aureus USA300, injected i.v. with 5 μg of porcine mucosal heparin (HP) or completely de-O-sulfated porcine heparin (deOS-HP) 6 h after infection, and the liver and lung bacterial burden were determined at 24 h post-infection (n = 5, *p < 0.05, ANOVA)