Martins Adriano S, Parvatiyar Michelle S, Feng Han-Zhong, Bos J Martijn, Gonzalez-Martinez David, Vukmirovic Milica, Turna Rajdeep S, Sanchez-Gonzalez Marcos A, Badger Crystal-Dawn, Zorio Diego A R, Singh Rakesh K, Wang Yingcai, Jin J-P, Ackerman Michael J, Pinto Jose R
Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee.
Department of Molecular and Cellular Pharmacology, University of Miami, Miller School of Medicine, Miami, FL.
Circ Cardiovasc Genet. 2015 Oct;8(5):653-664. doi: 10.1161/CIRCGENETICS.114.000957. Epub 2015 Aug 24.
Mutations in thin-filament proteins have been linked to hypertrophic cardiomyopathy, but it has never been demonstrated that variants identified in the TNNC1 (gene encoding troponin C) can evoke cardiac remodeling in vivo. The goal of this study was to determine whether TNNC1 can be categorized as an hypertrophic cardiomyopathy susceptibility gene, such that a mouse model can recapitulate the clinical presentation of the proband.
The TNNC1-A8V proband diagnosed with severe obstructive hypertrophic cardiomyopathy at 34 years of age exhibited mild-to-moderate thickening in left and right ventricular walls, decreased left ventricular dimensions, left atrial enlargement, and hyperdynamic left ventricular systolic function. Genetically engineered knock-in (KI) mice containing the A8V mutation (heterozygote=KI-TnC-A8V(+/-); homozygote=KI-TnC-A8V(+/+)) were characterized by echocardiography and pressure-volume studies. Three-month-old KI-TnC-A8V(+/+) mice displayed decreased ventricular dimensions, mild diastolic dysfunction, and enhanced systolic function, whereas KI-TnC-A8V(+/-) mice displayed cardiac restriction at 14 months of age. KI hearts exhibited atrial enlargement, papillary muscle hypertrophy, and fibrosis. Liquid chromatography-mass spectroscopy was used to determine incorporation of mutant cardiac troponin C (≈ 21%) into the KI-TnC-A8V(+/-) cardiac myofilament. Reduced diastolic sarcomeric length, increased shortening, and prolonged Ca(2+) and contractile transients were recorded in intact KI-TnC-A8V(+/-) and KI-TnC-A8V(+/+) cardiomyocytes. Ca(2+) sensitivity of contraction in skinned fibers increased with mutant gene dose: KI-TnC-A8V(+/+)>KI-TnC-A8V(+/-)>wild-type, whereas KI-TnC-A8V(+/+) relaxed more slowly on flash photolysis of diazo-2.
The TNNC1-A8V mutant increases the Ca(2+)-binding affinity of the thin filament and elicits changes in Ca(2+) homeostasis and cellular remodeling, which leads to diastolic dysfunction. These in vivo alterations further implicate the role of TNNC1 mutations in the development of cardiomyopathy.
细肌丝蛋白突变与肥厚型心肌病有关，但从未有研究证明在TNNC1（编码肌钙蛋白C的基因）中鉴定出的变异体可在体内引发心脏重塑。本研究的目的是确定TNNC1是否可归类为肥厚型心肌病易感基因，以便小鼠模型能够重现先证者的临床表现。
一名34岁被诊断为严重梗阻性肥厚型心肌病的TNNC1-A8V先证者，表现出左、右心室壁轻度至中度增厚，左心室尺寸减小，左心房扩大，以及左心室收缩功能亢进。通过超声心动图和压力-容积研究对含有A8V突变的基因工程敲入（KI）小鼠（杂合子=KI-TnC-A8V(+/-)；纯合子=KI-TnC-A8V(+/+)）进行了表征。3个月大的KI-TnC-A8V(+/+)小鼠心室尺寸减小，轻度舒张功能障碍，收缩功能增强，而KI-TnC-A8V(+/-)小鼠在14个月大时出现心脏受限。KI心脏表现出心房扩大、乳头肌肥大和纤维化。采用液相色谱-质谱法测定突变型心肌肌钙蛋白C（约21%）掺入KI-TnC-A8V(+/-)心肌肌丝中的情况。在完整的KI-TnC-A8V(+/-)和KI-TnC-A8V(+/+)心肌细胞中记录到舒张期肌节长度缩短、缩短增加以及Ca(2+)和收缩瞬变延长。在脱细胞纤维中，收缩的Ca(2+)敏感性随突变基因剂量增加而增加：KI-TnC-A8V(+/+)>KI-TnC-A8V(+/-)>野生型，而在重氮-2闪光光解后，KI-TnC-A8V(+/+)舒张更慢。
TNNC1-A8V突变体增加了细肌丝的Ca(2+)结合亲和力，并引发Ca(2+)稳态和细胞重塑的变化，从而导致舒张功能障碍。这些体内改变进一步表明TNNC1突变在心肌病发展中的作用。
