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Exploitation of syndecan-1 shedding by Pseudomonas aeruginosa enhances virulence

Nature volume 411, pages 98–102 (2001)Cite this article

Abstract

Cell-surface heparan sulphate proteoglycans (HSPGs) are ubiquitous and abundant receptors/co-receptors of extracellular ligands1,2, including many microbes3,4,5,6,7,8,9,10. Their role in microbial infections is poorly defined, however, because no cell-surface HSPG has been clearly connected to the pathogenesis of a particular microbe. We have previously shown that Pseudomonas aeruginosa, through its virulence factor LasA, enhances the in vitro shedding of syndecan-1—the predominant cell-surface HSPG of epithelia11. Here we show that shedding of syndecan-1 is also activated by P. aeruginosa in vivo, and that the resulting syndecan-1 ectodomains enhance bacterial virulence in newborn mice. Newborn mice deficient in syndecan-1 resist P. aeruginosa lung infection but become susceptible when given purified syndecan-1 ectodomains or heparin, but not when given ectodomain core protein, indicating that the ectodomain's heparan sulphate chains are the effectors. In wild-type newborn mice, inhibition of syndecan-1 shedding or inactivation of the shed ectodomain's heparan sulphate chains prevents lung infection. Our findings uncover a pathogenetic mechanism in which a host response to tissue injury—syndecan-1 shedding—is exploited to enhance microbial virulence apparently by modulating host defences.

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Figure 1: Synd-1-/- mice resist intranasally induced P. aeruginosa infection.
Figure 2: Resistance of the synd-1-/- mice to P. aeruginosa infection can be reversed by administering purified shed syndecan-1 ectodomains or heparin.
Figure 3: P. aeruginosa specifically increases the amount of shed syndecan-1 ectodomains in the lung.
Figure 4: Inhibition of shedding or neutralization of HS prevents intranasally induced P. aeruginosa lung infection.

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Acknowledgements

We thank A. Drummond and P. Kincade for the peptide hydroxamate (BB1101) and the Ky 8.2 monoclonal antibody, respectively. This work was supported by the Parker B. Francis Foundation (P.W.P.) and the NIH (G.B.P. and M.B.).

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Author notes

  1. Pyong Woo Park

    Present address: Section of Infectious Diseases, Baylor College of Medicine, One Baylor Plaza, BCM 286, Room N1319, Houston, Texas, 77030, USA

Authors and Affiliations

  1. Division of Newborn Medicine, Department of Pediatrics, Children's Hospital and,

    Pyong Woo Park, Michael T. Hinkes & Merton Bernfield

  2. Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, 02115, Massachusetts, USA

    Gerald B. Pier

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Corresponding author

Correspondence to Merton Bernfield.

Supplementary information

Figure 1.

(GIF 11.3 kb)

For 35S-labeled syndecan-1, 9050 cpm (2 ng) was incubated with 5x109 cfus of P. aeruginosa strains (PAO1, BL2, or 6077) in 300 µl of TSB with or without heparin or HS-free ectodomain core protein (both 40 µg) at room temperature. After 1 h, the mixtures were spun down, washed once with buffer, and the amount of radioactivity associated with P. aeruginosa was quantified by scintillationcounting. The binding assay using 125I-labeled syndecan-1 followed the same protocol except that 105,500 cpm (67 ng) of the labeled syndecan-1 was incubated with 1x1010 cfus of P. aeruginosa strain BL2, and binding was quantified by counting in a g counter.P. aeruginosa strains did not bind syndecan-1 labeled by either 35S or 125I significantly above background levels (23 cpm & 900 cpm, respectively). Results are shown as mean±SD from triplicate measurements.

Figure 2.

(GIF 13.1 kb)

For the pre-treatment experiments, P. aeruginosa strain PAO1 was incubated with 5 ng/µl of heparin in 50 µl of TSB for 30 min at room temperature, then washed (2x) with 1 ml of TSB. The inoculum for the non-treated control groups was 2.1x109 cfus/7 µl, whereasthose for the pre-treated bacteria/wild type synd-1+/+ and pre-treated bacteria/synd-1-/- mice were 1.4x109 cfus/7 µl and 1.9x109 cfus/7 µl, respectively. The extent of infection was assessed by quantifying lung (pneumonia) and spleen (bacteremia)colonization, and by observing mortality as described in our manuscript.

Figure 3.

(GIF 7.09 kb)

Early log growth phase bacteria (E. coli, JM101) were incubated in 500 µl of TSB with or without the neutrophil-derived antimicrobial peptide bactenecin-7 (10 µg), shed syndecan-1 ectodomain (5 µg), or heparin (5 µg) as indicated at 37°C with agitation. After 8 h, bacterial viability was measured by the tetrazolium salt conversion assay, in which only live cells will convert the tetrazolium salt (MTT) to insoluble formazan (purple). Formazan is solubilized by DMSO and the samples are read at OD550nm. Results shown are mean±SD from triplicate measurements.

Figure 4.

(GIF 5.05 kb)

Bactenecin-7 was radioiodinated by the IODOGEN method, and approximately 500 ng (177,000 cpm) of the iodinated antimicrobial was incubated with 8x109 cfus of bacteria (E. coli, JM101) with or without heparin or chondroitin sulfate C (both 20 µg) in 300 µl of TSB. After 30 min, cells were washed once with TSB and radioactivity associated with the cell pellet was quantified in a g counter.Background was determined in the absence of bacteria and glycosaminoglycans. Data shown are mean±SD of triplicate measurements.

Figure 5.

(GIF 5.4 kb)

Early log growth phase bacteria (E. coli, JM101) were incubated in 500 µl of TSB with bactenecin-7, PR-39, or cecropin B (all at 1.5 mM) with or without heparin (5 µg). After 3 h, bacterial viability was measured by the tetrazolium salt conversion assay as described in Appendix 3. Results shown are mean±SD of triplicate measurements.

Figure 6.

(GIF 9.6 kb)

Mice were inoculated intraperitoneally with P. aeruginosa strain PAO1 in 100 µl of TSB. After 20 h, lungs were harvested, strained through a stainless steel mesh, incubated in TSB containing 0.1% (v/v) Triton X-100, diluted in TSB, and plated out on TSB agar plates. Lung colonization (bacteremia) values shown are mean±SE, and mortality values are shown in parentheses above the bar graphs.

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Park, P., Pier, G., Hinkes, M. et al. Exploitation of syndecan-1 shedding by Pseudomonas aeruginosa enhances virulence. Nature 411, 98–102 (2001). https://doi.org/10.1038/35075100

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