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A streptococcal lipid toxin induces membrane permeabilization and pyroptosis leading to fetal injury.

Whidbey C, Vornhagen J, Gendrin C, Boldenow E, Samson JM, Doering K, Ngo L, Ezekwe EA, Gundlach JH, Elovitz MA, Liggitt D, Duncan JA, Adams Waldorf KM, Rajagopal L - EMBO Mol Med (2015)

Bottom Line: Here, we show that the GBS pigment induces membrane permeability in artificial lipid bilayers and host cells.Macrophages lacking the NLRP3 inflammasome recovered from pigment-induced cell damage.These results demonstrate that the dual mechanism of action of the bacterial pigment/lipid toxin leading to hemolysis or pyroptosis exacerbates fetal injury and suggest that preventing both activities of the hemolytic lipid is likely critical to reduce GBS fetal injury and preterm birth.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatric Infectious Diseases, University of Washington and Seattle Children's Research Institute, Seattle, WA, USA Department of Global Health, University of Washington, Seattle, WA, USA.

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Proposed model on GBS pigment-mediated host cell lysis and preterm birthThe GBS pigment intercalates into host cell membranes leading to membrane permeability and ion flux. In RBC, this leads to colloidal osmotic lysis. In macrophages, the loss of intracellular potassium serves as a trigger for NLRP3 inflammasome formation. The activated inflammasome then activates caspase 1, which cleaves pro-IL-1β and pro-IL-18 to their active forms. Finally, caspase 1 activation causes cell death by pyroptosis. While NLRP3-dependent pyroptosis is the major form of cell death observed in macrophages exposed to purified pigment and hemolytic/pigmented GBS strains, hyperpigmented GBS strains induced low levels of cell death in NLRP3-deficient and ASC-deficient macrophages that were independent of inflammasome and caspase 3/7. In host cells that are either resistant or recover from pigment-induced membrane damage (e.g., NLRP3-deficient macrophages), we predict that lysosomal degradation of pigment or shedding of vesicles that contain pigment–membrane complexes and the turnover of plasma membrane prevents cell death. The GBS pigment exacerbates fetal injury and preterm birth through the combined action of colloidal osmotic lysis and pyroptosis.
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fig08: Proposed model on GBS pigment-mediated host cell lysis and preterm birthThe GBS pigment intercalates into host cell membranes leading to membrane permeability and ion flux. In RBC, this leads to colloidal osmotic lysis. In macrophages, the loss of intracellular potassium serves as a trigger for NLRP3 inflammasome formation. The activated inflammasome then activates caspase 1, which cleaves pro-IL-1β and pro-IL-18 to their active forms. Finally, caspase 1 activation causes cell death by pyroptosis. While NLRP3-dependent pyroptosis is the major form of cell death observed in macrophages exposed to purified pigment and hemolytic/pigmented GBS strains, hyperpigmented GBS strains induced low levels of cell death in NLRP3-deficient and ASC-deficient macrophages that were independent of inflammasome and caspase 3/7. In host cells that are either resistant or recover from pigment-induced membrane damage (e.g., NLRP3-deficient macrophages), we predict that lysosomal degradation of pigment or shedding of vesicles that contain pigment–membrane complexes and the turnover of plasma membrane prevents cell death. The GBS pigment exacerbates fetal injury and preterm birth through the combined action of colloidal osmotic lysis and pyroptosis.

Mentions: This study demonstrates how the GBS hemolytic pigment/lipid toxin causes cell death, triggers inflammation, and promotes fetal injury. Although the hemolytic nature of GBS was described almost a century ago (Brown, 1920; Rosa-Fraile et al, 2014) and is associated with virulence of the pathogen (Pritzlaff et al, 2001; Doran et al, 2003; Liu et al, 2004; Hensler et al, 2005; Lembo et al, 2010), mechanistic insight into this potent virulence factor was lacking. We recently showed that the molecular basis of hemolytic activity in GBS is the pigment/lipid toxin (Whidbey et al, 2013). In the current study, we utilized artificial lipid bilayers, RBC, and macrophages to understand how a bacterial pigment/lipid toxin disrupts these host cells. The trans-membrane conductance observed in artificial lipid bilayers suggests that the pigment/lipid toxin does not induce the formation of large, multimeric pores (commonly observed with protein toxins) but rather induces membrane permeabilization by forming variably sized membrane defects similar to those previously observed with the cyclic antimicrobial peptide, Gramicidin S (Ashrafuzzaman et al, 2008). The predicted length of the polyene moiety of the GBS pigment is approximately 32 Å (determined using a molecular model generated by the National Cancer Institute's Online SMILES Translator and modeled using PyMol), which is similar to the average thickness of the plasma membrane at 30–40 Å (Schrodinger, 2010). Thus, we predict that insertion of the GBS hemolytic pigment may span the host cell membrane, with the rhamnose and ornithine moieties acting as polar head groups. Insertion of the GBS pigment into RBC membranes triggers membrane disruption leading to colloidal osmotic lysis (see proposed model in Fig8).


A streptococcal lipid toxin induces membrane permeabilization and pyroptosis leading to fetal injury.

Whidbey C, Vornhagen J, Gendrin C, Boldenow E, Samson JM, Doering K, Ngo L, Ezekwe EA, Gundlach JH, Elovitz MA, Liggitt D, Duncan JA, Adams Waldorf KM, Rajagopal L - EMBO Mol Med (2015)

Proposed model on GBS pigment-mediated host cell lysis and preterm birthThe GBS pigment intercalates into host cell membranes leading to membrane permeability and ion flux. In RBC, this leads to colloidal osmotic lysis. In macrophages, the loss of intracellular potassium serves as a trigger for NLRP3 inflammasome formation. The activated inflammasome then activates caspase 1, which cleaves pro-IL-1β and pro-IL-18 to their active forms. Finally, caspase 1 activation causes cell death by pyroptosis. While NLRP3-dependent pyroptosis is the major form of cell death observed in macrophages exposed to purified pigment and hemolytic/pigmented GBS strains, hyperpigmented GBS strains induced low levels of cell death in NLRP3-deficient and ASC-deficient macrophages that were independent of inflammasome and caspase 3/7. In host cells that are either resistant or recover from pigment-induced membrane damage (e.g., NLRP3-deficient macrophages), we predict that lysosomal degradation of pigment or shedding of vesicles that contain pigment–membrane complexes and the turnover of plasma membrane prevents cell death. The GBS pigment exacerbates fetal injury and preterm birth through the combined action of colloidal osmotic lysis and pyroptosis.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4403049&req=5

fig08: Proposed model on GBS pigment-mediated host cell lysis and preterm birthThe GBS pigment intercalates into host cell membranes leading to membrane permeability and ion flux. In RBC, this leads to colloidal osmotic lysis. In macrophages, the loss of intracellular potassium serves as a trigger for NLRP3 inflammasome formation. The activated inflammasome then activates caspase 1, which cleaves pro-IL-1β and pro-IL-18 to their active forms. Finally, caspase 1 activation causes cell death by pyroptosis. While NLRP3-dependent pyroptosis is the major form of cell death observed in macrophages exposed to purified pigment and hemolytic/pigmented GBS strains, hyperpigmented GBS strains induced low levels of cell death in NLRP3-deficient and ASC-deficient macrophages that were independent of inflammasome and caspase 3/7. In host cells that are either resistant or recover from pigment-induced membrane damage (e.g., NLRP3-deficient macrophages), we predict that lysosomal degradation of pigment or shedding of vesicles that contain pigment–membrane complexes and the turnover of plasma membrane prevents cell death. The GBS pigment exacerbates fetal injury and preterm birth through the combined action of colloidal osmotic lysis and pyroptosis.
Mentions: This study demonstrates how the GBS hemolytic pigment/lipid toxin causes cell death, triggers inflammation, and promotes fetal injury. Although the hemolytic nature of GBS was described almost a century ago (Brown, 1920; Rosa-Fraile et al, 2014) and is associated with virulence of the pathogen (Pritzlaff et al, 2001; Doran et al, 2003; Liu et al, 2004; Hensler et al, 2005; Lembo et al, 2010), mechanistic insight into this potent virulence factor was lacking. We recently showed that the molecular basis of hemolytic activity in GBS is the pigment/lipid toxin (Whidbey et al, 2013). In the current study, we utilized artificial lipid bilayers, RBC, and macrophages to understand how a bacterial pigment/lipid toxin disrupts these host cells. The trans-membrane conductance observed in artificial lipid bilayers suggests that the pigment/lipid toxin does not induce the formation of large, multimeric pores (commonly observed with protein toxins) but rather induces membrane permeabilization by forming variably sized membrane defects similar to those previously observed with the cyclic antimicrobial peptide, Gramicidin S (Ashrafuzzaman et al, 2008). The predicted length of the polyene moiety of the GBS pigment is approximately 32 Å (determined using a molecular model generated by the National Cancer Institute's Online SMILES Translator and modeled using PyMol), which is similar to the average thickness of the plasma membrane at 30–40 Å (Schrodinger, 2010). Thus, we predict that insertion of the GBS hemolytic pigment may span the host cell membrane, with the rhamnose and ornithine moieties acting as polar head groups. Insertion of the GBS pigment into RBC membranes triggers membrane disruption leading to colloidal osmotic lysis (see proposed model in Fig8).

Bottom Line: Here, we show that the GBS pigment induces membrane permeability in artificial lipid bilayers and host cells.Macrophages lacking the NLRP3 inflammasome recovered from pigment-induced cell damage.These results demonstrate that the dual mechanism of action of the bacterial pigment/lipid toxin leading to hemolysis or pyroptosis exacerbates fetal injury and suggest that preventing both activities of the hemolytic lipid is likely critical to reduce GBS fetal injury and preterm birth.

View Article: PubMed Central - PubMed

Affiliation: Department of Pediatric Infectious Diseases, University of Washington and Seattle Children's Research Institute, Seattle, WA, USA Department of Global Health, University of Washington, Seattle, WA, USA.

Show MeSH
Related in: MedlinePlus