title: The novel PMCA2 pump mutation Tommy impairs cytosolic calcium clearance in hair cells and links to deafness in mice.
abstract: The mechanotransduction process in hair cells in the inner ear is associated with the influx of calcium from the endolymph. Calcium is exported back to the endolymph via the splice variant w/a of the PMCA2 of the stereocilia membrane. To further investigate the role of the pump, we have identified and characterized a novel ENU-induced mouse mutation, Tommy, in the PMCA2 gene. The mutation causes a non-conservative E629K change in the second intracellular loop of the pump that harbors the active site. Tommy mice show profound hearing impairment from P18, with significant differences in hearing thresholds between wild type and heterozygotes. Expression of mutant PMCA2 in CHO cells shows calcium extrusion impairment; specifically, the long term, non-stimulated calcium extrusion activity of the pump is inhibited. Calcium extrusion was investigated directly in neonatal organotypic cultures of the utricle sensory epithelium in Tommy mice. Confocal imaging combined with flash photolysis of caged calcium showed impairment of calcium export in both Tommy heterozygotes and homozygotes. Immunofluorescence studies of the organ of Corti in homozygous Tommy mice showed a progressive base to apex degeneration of hair cells after P40. Our results on the Tommy mutation along with previously observed interactions between cadherin-23 and PMCA2 mutations in mouse and humans underline the importance of maintaining the appropriate calcium concentrations in the endolymph to control the rigidity of cadherin and ensure the function of interstereocilia links, including tip links, of the stereocilia bundle.
authors.affiliation: Department of Physics G Galilei, University of Padua, Padua 35131, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Bortolozzi
authors.forename: Marisa
authors.initials: M
authors.lastname: Brini
authors.forename: Nick
authors.initials: N
authors.lastname: Parkinson
authors.forename: Giulia
authors.initials: G
authors.lastname: Crispino
authors.forename: Pietro
authors.initials: P
authors.lastname: Scimemi
authors.forename: Romolo Daniele
authors.initials: RD
authors.lastname: De Siati
authors.forename: Francesca
authors.initials: F
authors.lastname: Di Leva
authors.forename: Andrew
authors.initials: A
authors.lastname: Parker
authors.forename: Saida
authors.initials: S
authors.lastname: Ortolano
authors.forename: Edoardo
authors.initials: E
authors.lastname: Arslan
authors.forename: Steve D
authors.initials: SD
authors.lastname: Brown
authors.forename: Ernesto
authors.initials: E
authors.lastname: Carafoli
authors.forename: Fabio
authors.initials: F
authors.lastname: Mammano
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism*; D003638:Deafness / Q000235:genetics* / Q000378:metabolism*; D004195:Disease Models, Animal; D007758:Ear, Inner / Q000378:metabolism; D006198:Hair Cells, Auditory / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D053499:Plasma Membrane Calcium-Transporting ATPases; C506959:Atp2b2 protein, mouse; D002118:Calcium
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