Molecular and Functional Characterization of a Novel Cardiac-Specific Human Tropomyosin Isoform

Abstract

Background-Tropomyosin (TM), an essential actin-binding protein, is central to the control of calcium-regulated striated muscle contraction. Although TPM1␣ (also called ␣-TM) is the predominant TM isoform in human hearts, the precise TM isoform composition remains unclear. Methods and Results-In this study, we quantified for the first time the levels of striated muscle TM isoforms in human heart, including a novel isoform called TPM1. By developing a TPM1-specific antibody, we found that the TPM1 protein is expressed and incorporated into organized myofibrils in hearts and that its level is increased in human dilated cardiomyopathy and heart failure. To investigate the role of TPM1 in sarcomeric function, we generated transgenic mice overexpressing cardiac-specific TPM1. Incorporation of increased levels of TPM1 protein in myofilaments leads to dilated cardiomyopathy. Physiological alterations include decreased fractional shortening, systolic and diastolic dysfunction, and decreased myofilament calcium sensitivity with no change in maximum developed tension. Additional biophysical studies demonstrate less structural stability and weaker actin-binding affinity of TPM1 compared with TPM1␣. Conclusions-This functional analysis of TPM1 provides a possible mechanism for the consequences of the TM isoform switch observed in dilated cardiomyopathy and heart failure patients. (Circulation. 2010;121:410-418.)Key Words: cardiomyopathy Ⅲ contractility Ⅲ heart failure Ⅲ myocardial contraction T he heart adapts to different challenges presented by an array of mechanical, hormonal, and nutritional signals in the process of maintaining its circulatory function. Isoform switching of sarcomeric proteins is 1 mode the heart uses to adapt to those challenges, along with alterations in the relative abundance and phosphorylation status of contractile and regulatory proteins. 1 These changes in isoform expression and phosphorylation status also play an essential role during cardiac development and in response to cardiac hypertrophy and heart failure (HF). Although sarcomeric protein isoforms are subject to developmental regulation, cardiomyopathy and HF primarily elicit changes in thick filament protein isoforms. 2 The only thin filament protein to change isoform expression in the failing human heart is troponin T. 3,4 Furthermore, altered phosphorylation of troponin I, myosin binding protein C, and other sarcomeric proteins has dramatic effects on cardiac function in the failing human myocardium. 5 Editorial see p 351 Clinical Perspective on p 418To understand the specific role of another thin filament protein, tropomyosin (TM), in the normal and the pathological heart, it is essential to define the TM isoform expression profile. Tropomyosins comprise a family of actin-binding proteins encoded by 4 different genes (TPM1, TPM2, TPM3, and TPM4). Each gene uses alternative splicing, alternative promoters, and differential processing to encode multiple striated muscle, smooth muscle, and cytoskeletal transcripts. For example, the TPM1...

MicroRNA-21 Regulates Vascular Smooth Muscle Cell Function via Targeting Tropomyosin 1 in Arteriosclerosis Obliterans of Lower Extremities

“…It has been shown that transcriptional loss of TPM1 in hearts results in cardiomyopathy. 27,47 Our findings indicate that posttranscriptional loss of TPM1 in arteries may contribute to ASO.…”

“…It has been shown that transcriptional loss of TPM1 in hearts results in cardiomyopathy. 27,47 Our findings indicate that posttranscriptional loss of TPM1 in arteries may contribute to ASO.TPM1 expression occurs later than that of SM ␣-actin and smooth muscle myosin heavy chain in smooth muscle cell development, and it has been suggested to be a better phenotypic marker for quiescent smooth muscle cells. 48 In the present study, we found that both TPM1 and SM ␣-actin were abundantly expressed in normal arteries.…”

“…27 Members of this family take up multiple positions on actin filaments and function as universal regulators of cytoskeleton. 28 -30 Changes of TPMs and actin proportion could induce cytoskeleton reorganization and consequently induce cell shape alteration.…”

Tropomyosin Dephosphorylation Results in Compensated Cardiac Hypertrophy

“…Echocardiographic and Pressure Overload MeasurementsEchocardiographic measurements were performed utilizing a 30-MHz high resolution transducer (Vevo 770 high resolution imaging system) after anesthetization of 3-month-old mice as previously described (24). Echocardiographic dimensions and thicknesses were taken from two-dimensional guided M-Mode from the parasternal long axis view in triplicate on NTG and TG 12-16-week-old mice.…”

Effects of nicotine administration in a mouse model of familial hypertrophic cardiomyopathy, α-tropomyosin D175N

“…HR was also monitored continuously. Transthoracic echocardiographic recordings were then obtained using a 30-MHz high resolution transducer and an integrated rail system (Vevo 770 High-Resolution Imaging System; Visualsonics, Toronto, ON, Canada) as previously described (48).…”