title: Fetal cardiac troponin isoforms rescue the increased Ca2+ sensitivity produced by a novel double deletion in cardiac troponin T linked to restrictive cardiomyopathy: a clinical, genetic, and functional approach.
abstract: A novel double deletion in cardiac troponin T (cTnT) of two highly conserved amino acids (Asn-100 and Glu-101) was found in a restrictive cardiomyopathic (RCM) pediatric patient. Clinical evaluation revealed the presence of left atrial enlargement and marked left ventricle diastolic dysfunction. The explanted heart examined by electron microscopy revealed myofibrillar disarray and mild fibrosis. Pedigree analysis established that this mutation arose de novo. The patient tested negative for six other sarcomeric genes. The single and double recombinant cTnT mutants were generated, and their functional consequences were analyzed in porcine skinned cardiac muscle. In the adult Tn environment (cTnT3 + cardiac troponin I), the single cTnT3-ΔN100 and cTnT3-ΔE101 mutations had opposing effects on the Ca(2+) sensitivity of force development compared with WT, whereas the double deletion cTnT3-ΔN100/ΔE101 increased the Ca(2+) sensitivity + 0.19 pCa units. In addition, cTnT3-ΔN100/ΔE101 decreased the cooperativity of force development, suggesting alterations in intrafilament protein-protein interactions. In the fetal Tn environment, (cTnT1 + slow skeletal troponin I), the single (cTnT1-ΔN110) and double (cTnT1-ΔN110/ΔE111) deletions did not change the Ca(2+) sensitivity compared with control. To recreate the patient's heterozygous genotype, we performed a reconstituted ATPase activity assay. Thin filaments containing 50:50 cTnT3-ΔN100/ΔE101:cTnT3-WT also increased the myofilament Ca(2+) sensitivity compared with WT. Co-sedimentation of thin filament proteins indicated that no significant changes occurred in the binding of Tn containing the RCM cTnT mutation to actin-Tm. This report reveals the protective role of Tn fetal isoforms as they rescue the increased Ca(2+) sensitivity produced by a cTnT-RCM mutation and may account for the lack of lethality during gestation.
authors.affiliation: University of Miami Miller School of Medicine, Miami, Florida 33136, USA.
authors.forename: Jose Renato
authors.initials: JR
authors.lastname: Pinto
authors.forename: Shi Wei
authors.initials: SW
authors.lastname: Yang
authors.forename: Marc-Phillip
authors.initials: MP
authors.lastname: Hitz
authors.forename: Michelle S
authors.initials: MS
authors.lastname: Parvatiyar
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Jones
authors.forename: Jingsheng
authors.initials: J
authors.lastname: Liang
authors.forename: Victor
authors.initials: V
authors.lastname: Kokta
authors.forename: Mario
authors.initials: M
authors.lastname: Talajic
authors.forename: Nicolas
authors.initials: N
authors.lastname: Tremblay
authors.forename: Michelle
authors.initials: M
authors.lastname: Jaeggi
authors.forename: Gregor
authors.initials: G
authors.lastname: Andelfinger
authors.forename: James D
authors.initials: JD
authors.lastname: Potter
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D000328:Adult; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002313:Cardiomyopathy, Restrictive / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002648:Child; D002675:Child, Preschool; D005260:Female; D005838:Genotype; D006801:Humans; D054643:INDEL Mutation; D008297:Male; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D010375:Pedigree; D011994:Recombinant Proteins; D013552:Swine; D020107:Troponin T / Q000235:genetics / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D020107:Troponin T; D002118:Calcium