title: Circulating Pneumolysin Is a Potent Inducer of Cardiac Injury during Pneumococcal Infection.
abstract: Streptococcus pneumoniae accounts for more deaths worldwide than any other single pathogen through diverse disease manifestations including pneumonia, sepsis and meningitis. Life-threatening acute cardiac complications are more common in pneumococcal infection compared to other bacterial infections. Distinctively, these arise despite effective antibiotic therapy. Here, we describe a novel mechanism of myocardial injury, which is triggered and sustained by circulating pneumolysin (PLY). Using a mouse model of invasive pneumococcal disease (IPD), we demonstrate that wild type PLY-expressing pneumococci but not PLY-deficient mutants induced elevation of circulating cardiac troponins (cTns), well-recognized biomarkers of cardiac injury. Furthermore, elevated cTn levels linearly correlated with pneumococcal blood counts (r=0.688, p=0.001) and levels were significantly higher in non-surviving than in surviving mice. These cTn levels were significantly reduced by administration of PLY-sequestering liposomes. Intravenous injection of purified PLY, but not a non-pore forming mutant (PdB), induced substantial increase in cardiac troponins to suggest that the pore-forming activity of circulating PLY is essential for myocardial injury in vivo. Purified PLY and PLY-expressing pneumococci also caused myocardial inflammatory changes but apoptosis was not detected. Exposure of cultured cardiomyocytes to PLY-expressing pneumococci caused dose-dependent cardiomyocyte contractile dysfunction and death, which was exacerbated by further PLY release following antibiotic treatment. We found that high PLY doses induced extensive cardiomyocyte lysis, but more interestingly, sub-lytic PLY concentrations triggered profound calcium influx and overload with subsequent membrane depolarization and progressive reduction in intracellular calcium transient amplitude, a key determinant of contractile force. This was coupled to activation of signalling pathways commonly associated with cardiac dysfunction in clinical and experimental sepsis and ultimately resulted in depressed cardiomyocyte contractile performance along with rhythm disturbance. Our study proposes a detailed molecular mechanism of pneumococcal toxin-induced cardiac injury and highlights the major translational potential of targeting circulating PLY to protect against cardiac complications during pneumococcal infections.
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Yasir
authors.initials: Y
authors.lastname: Alhamdi
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Neill
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Simon T
authors.initials: ST
authors.lastname: Abrams
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Hesham A
authors.initials: HA
authors.lastname: Malak
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Reham
authors.initials: R
authors.lastname: Yahya
authors.affiliation: Department of Musculoskeletal Biology, Institute of Aging and Chronic Diseases, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Barrett-Jolley
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Guozheng
authors.initials: G
authors.lastname: Wang
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom.
authors.forename: Aras
authors.initials: A
authors.lastname: Kadioglu
authors.affiliation: Department of Clinical Infection, Microbiology and Immunology, Institute of Infection and Global Health, University of Liverpool, Liverpool, United Kingdom; Roald Dahl Haemostasis & Thrombosis Centre, Royal Liverpool University Hospital, Liverpool, United Kingdom.
authors.forename: Cheng-Hock
authors.initials: CH
authors.lastname: Toh
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism; D006331:Heart Diseases / Q000209:etiology*; D051379:Mice; D011008:Pneumococcal Infections / Q000150:complications* / Q000175:diagnosis / Q000188:drug therapy; D022242:Pneumococcal Vaccines / Q000627:therapeutic use*; D013296:Streptococcus pneumoniae / Q000276:immunology*; D013301:Streptolysins / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D022242:Pneumococcal Vaccines; D013301:Streptolysins; C032290:plY protein, Streptococcus pneumoniae