title: The mechanism of pneumolysin-induced cochlear hair cell death in the rat.
abstract: Streptoccocus pneumoniae infection can result in local and systemic diseases such as otitis media, pneumonia and meningitis. Sensorineural hearing loss associated with this infection is mediated by the release of an exotoxin, pneumolysin. The goal of the present study was to characterize the mechanisms of pneumolysin toxicity in cochlear hair cells in vitro. Pneumolysin induced severe damage in cochlear hair cells, ranging from stereocilia disorganization to total cell loss. Surprisingly, pneumolysin-induced cell death preferentially targeted inner hair cells. Pneumolysin triggered in vitro cell death by an influx of calcium. Extracellular calcium appeared to enter the cell through a pore formed by the toxin. Buffering intracellular calcium with BAPTA improved hair cell survival. The mitochondrial apoptotic pathway involved in pneumolysin-induced cell death was demonstrated by the use of bongkrekic acid. Binding of pneumolysin to the hair cell plasma membrane was required to induce cell death. Increasing external calcium reduced cell toxicity by preventing the binding of pneumolysin to hair cell membranes. These results showed the significant role of calcium both in triggering pneumolysin-induced hair cell apoptosis and in preventing the toxin from binding to its cellular target.
authors.affiliation: EA-3665 Université Victor Segalen Bordeaux 2, Laboratoire de Biologie Cellulaire et Moléculaire de l'Audition, Hôpital Pellegrin, Bat PQR, 33076 Bordeaux, France. maryline.beurg@bordeaux.inserm.fr
authors.forename: Maryline
authors.initials: M
authors.lastname: Beurg
authors.forename: Aziz
authors.initials: A
authors.lastname: Hafidi
authors.forename: Liam
authors.initials: L
authors.lastname: Skinner
authors.forename: Graeme
authors.initials: G
authors.lastname: Cowan
authors.forename: Yannick
authors.initials: Y
authors.lastname: Hondarrague
authors.forename: Tim J
authors.initials: TJ
authors.lastname: Mitchell
authors.forename: Didier
authors.initials: D
authors.lastname: Dulon
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects; D001426:Bacterial Proteins / Q000235:genetics / Q000633:toxicity; D001865:Bongkrekic Acid / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D002614:Chelating Agents / Q000494:pharmacology; D003051:Cochlea / Q000187:drug effects* / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics; D006199:Hair Cells, Auditory, Inner / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D018072:Hair Cells, Auditory, Outer / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D000226:Mitochondrial ADP, ATP Translocases / Q000037:antagonists & inhibitors; D009924:Organ Culture Techniques; D051381:Rats; D017208:Rats, Wistar; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013301:Streptolysins / Q000235:genetics / Q000633:toxicity*; D013997:Time Factors
chemical_list: D001426:Bacterial Proteins; D015220:Calcium Channels; D002614:Chelating Agents; D011993:Recombinant Fusion Proteins; D013301:Streptolysins; C032290:plY protein, Streptococcus pneumoniae; D001865:Bongkrekic Acid; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D049452:Green Fluorescent Proteins; D004533:Egtazic Acid; D000226:Mitochondrial ADP, ATP Translocases; D002118:Calcium