title: Parvalbumin corrects slowed relaxation in adult cardiac myocytes expressing hypertrophic cardiomyopathy-linked alpha-tropomyosin mutations.
abstract: Hypertrophic cardiomyopathy mutations A63V and E180G in alpha-tropomyosin (alpha-Tm) have been shown to cause slow cardiac muscle relaxation. In this study, we used two complementary genetic strategies, gene transfer in isolated rat myocytes and transgenesis in mice, to ascertain whether parvalbumin (Parv), a myoplasmic calcium buffer, could correct the diastolic dysfunction caused by these mutations. Sarcomere shortening measurements in rat cardiac myocytes expressing the alpha-Tm A63V mutant revealed a slower time to 50% relengthening (T50R: 44.2+/-1.4 ms in A63V, 36.8+/-1.0 ms in controls; n=96 to 108; P<0.001) when compared with controls. Dual gene transfer of alpha-Tm A63V and Parv caused a marked decrease in T50R (29.8+/-1.0 ms). However, this increase in relaxation rate was accompanied with a decrease in shortening amplitude (114.6+/-4.4 nm in A63+Parv, 137.8+/-5.3 nm in controls). Using an asynchronous gene transfer strategy, Parv expression was reduced (from approximately 0.12 to approximately 0.016 mmol/L), slow relaxation redressed, and shortening amplitude maintained (T50R=33.9+/-1.6 ms, sarcomere shortening amplitude=132.2+/-7.0 nm in A63V+PVdelayed; n=56). Transgenic mice expressing the E180G alpha-Tm mutation and mice expressing Parv in the heart were crossed. In isolated adult myocytes, the alpha-Tm mutation alone (E180G+/PV-) had slower sarcomere relengthening kinetics than the controls (T90R: 199+/-7 ms in E180G+/PV-, 130+/-4 ms in E180G-/PV-; n=71 to 72), but when coexpressed with Parv, cellular relaxation was faster (T90R: 36+/-4 ms in E180G+/PV+). Collectively, these findings show that slow relaxation caused by alpha-Tm mutants can be corrected by modifying calcium handling with Parv.
authors.affiliation: Department of Biomedical Engineering , University of Michigan, Ann Arbor, Mich 48109-0622, USA.
authors.forename: Pierre
authors.initials: P
authors.lastname: Coutu
authors.forename: Christina N
authors.initials: CN
authors.lastname: Bennett
authors.forename: Elizabeth G
authors.initials: EG
authors.lastname: Favre
authors.forename: Sharlene M
authors.initials: SM
authors.lastname: Day
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Metzger
mesh_terms: D008841:Actin Cytoskeleton / Q000648:ultrastructure; D019943:Amino Acid Substitution; D000818:Animals; D020013:Calcium Signaling / Q000235:genetics / Q000502:physiology*; D002312:Cardiomyopathy, Hypertrophic / Q000235:genetics*; D003433:Crosses, Genetic; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D020125:Mutation, Missense; D009200:Myocardial Contraction / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010320:Parvalbumins / Q000235:genetics / Q000502:physiology*; D017354:Point Mutation; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012518:Sarcomeres / Q000648:ultrastructure; D013329:Structure-Activity Relationship; D013997:Time Factors; D014161:Transduction, Genetic; D014335:Tropomyosin / Q000737:chemistry / Q000235:genetics*
chemical_list: D010320:Parvalbumins; D011993:Recombinant Fusion Proteins; D014335:Tropomyosin