Regulation of the cardiac sodium channel Nav1.5 by utrophin in dystrophin-deficient mice.
OBJECTIVE
Duchenne muscular dystrophy (DMD) is a severe striated muscle disease due to the absence of dystrophin. Dystrophin deficiency results in dysfunctional sodium channels and conduction abnormalities in hearts of mdx mice. Disease progression in the mdx mouse only modestly reflects that of DMD patients, possibly due to utrophin up-regulation. Here, we investigated mice deficient in both dystrophin and utrophin [double knockout (DKO)] to assess the role of utrophin in the regulation of the cardiac sodium channel (Na(v)1.5) in mdx mice.


RESULTS
Co-immunoprecipitation studies in HEK293 cells showed that utrophin interacts with Na(v)1.5 via syntrophin proteins, an interaction abolished by deletion of the PDZ (PSD-95, Dlg, and Zona occludens) domain-binding motif of Na(v)1.5. We also provide evidence for such interaction in mouse heart using Na(v)1.5 C-terminus fusion proteins. In hearts of DKO mice, Na(v)1.5 protein levels were decreased by 25 ± 8%, together with a 42 ± 12% reduction of syntrophins compared with mdx, where utrophin was up-regulated by 52 ± 9% compared with C57BL/10 control mice. Sodium current was found to be reduced by 41 ± 5% in DKO cardiomyocytes compared with mdx, representing a loss of 63 ± 3% when compared with C57BL/10 wild-type control mice. Decreased Na(v)1.5 protein and current in DKO were reflected in a significant slowing of 27 ± 6% of maximal upstroke velocity of the cardiac action potential compared with mdx.


CONCLUSIONS
Utrophin plays a central role in the regulation of Na(v)1.5 in mdx mice. These findings provide support for therapeutic strategies aimed at overexpressing utrophin in the hopes of reducing cardiac pathology in DMD patients.
Department of Clinical Research, University of Bern, Murtenstrasse 35, 3010 Bern, Switzerland.
Maxime
M
Albesa
Jakob
J
Ogrodnik
Jean-Sébastien
JS
Rougier
Hugues
H
Abriel
D000200:Action Potentials; D020816:Amino Acid Motifs; D000818:Animals; D001665:Binding Sites; D004195:Disease Models, Animal; D016189:Dystrophin / Q000172:deficiency* / Q000235:genetics; D049029:Dystrophin-Associated Proteins / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D047468:Immunoprecipitation; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018101:Mice, Inbred mdx; D018345:Mice, Knockout; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D020388:Muscular Dystrophy, Duchenne / Q000235:genetics / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D062554:NAV1.5 Voltage-Gated Sodium Channel; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D049411:Utrophin / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
D016189:Dystrophin; D049029:Dystrophin-Associated Proteins; D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; D011993:Recombinant Fusion Proteins; C568320:SCN5A protein, human; C568321:Scn5a protein, mouse; D015222:Sodium Channels; C483599:UTRN protein, human; D049411:Utrophin; C091824:syntrophin; D012964:Sodium