Background-The role of the giant protein titin in patients with heart failure is not well established. We investigated titin expression in patients with end-stage heart failure resulting from nonischemic dilated cardiomyopathy, in particular as it relates to left ventricular (LV) myocardial stiffness and LV function. Methods and Results-SDS-agarose gels revealed small N2B (stiff) and large N2BA (compliant) cardiac titin isoforms with a mean N2BA:N2B expression ratio that was significantly (PϽ0.003) increased in 20 heart failure patients versus 6 controls. However, total titin was unchanged. The coexpression ratio was highest in a subsample of patients with an impaired LV relaxation pattern (nϭ7), intermediate in those with pseudonormal filling (nϭ6), and lowest in the group with restrictive filling (nϭ7). Mechanical measurements on LV muscle strips dissected from these hearts (nϭ8) revealed that passive muscle stiffness was significantly reduced in patients with a high N2BA:N2B expression ratio. Clinical correlations support the relevance of these changes for LV function (assessed by invasive hemodynamics and Doppler echocardiography). A positive correlation between the N2BA:N2B titin isoform ratio and deceleration time of mitral E velocity, A wave transit time, and end diastolic volume/pressure ratio was found. These changes affect exercise tolerance, as indicated by the positive correlation between the N2BA:N2B isoform ratio and peak O 2 consumption (nϭ10). Upregulated N2BA expression was accompanied by increased expression levels of titin-binding proteins (cardiac ankyrin repeat protein, ankrd2, and diabetes ankyrin repeat protein) that bind to the N2A element of N2BA titin (studied in 13 patients). Conclusions-Total titin content was unchanged in end-stage failing hearts and the more compliant N2BA isoform comprised a greater percentage of titin in these hearts. Changes in titin isoform expression in heart failure patients with dilated cardiomyopathy significantly impact diastolic filling by lowering myocardial stiffness. Upregulation of titin-binding proteins indicates that the importance of altered titin expression might extend to cell signaling and regulation of gene expression.

GLDH appears to be more useful than miR-122 in identifying DILI patients, and K18, OPN, and MCSFR are promising candidates for prediction of prognosis during an acute DILI event. Serial assessment of these biomarkers in large prospective studies will help further delineate their role in DILI diagnosis and management. (Hepatology 2018).

Rationale: The giant protein titin plays key roles in myofilament assembly and determines the passive mechanical properties of the sarcomere. The cardiac titin molecule has 2 mayor elastic elements, the N2B and the PEVK region. Both have been suggested to determine the elastic properties of the heart with loss of function data only available for the N2B region. Objective: The purpose of this study was to investigate the contribution of titin's proline-glutamate-valine-lysine (PEVK) region to biomechanics and growth of the heart. Methods and Results: We removed a portion of the PEVK segment (exons 219 to 225; 282 aa) that corresponds to the PEVK element of N2B titin, the main cardiac titin isoform. Adult homozygous PEVK knockout (KO) mice developed diastolic dysfunction, as determined by pressure-volume loops, echocardiography, isolated heart experiments, and muscle mechanics. Immunoelectron microscopy revealed increased strain of the N2B element, a spring region retained in the PEVK-KO. Interestingly, the PEVK-KO mice had hypertrophied hearts with an induction of the hypertrophy and fetal gene response that includes upregulation of FHL proteins. This contrasts the cardiac atrophy phenotype with decreased FHL2 levels that result from the deletion of the N2B element. Key Words: diastole Ⅲ connectin Ⅲ hypertrophy Ⅲ compliance Ⅲ FHL T itin is the largest protein in mammals and forms a continuous elastic filament along the myofibril (reviewed in 1 ). Because of its enormous size, titin is a prominent target for mutations that give rise to diseases such as familial dilated cardiomyopathy and muscular dystrophy. 2,3 Titin's extensible region resides in the I-band of the sarcomere and consists of immunoglobulin (Ig)-like domains arranged in tandem, the heart specific N2B element, and the prolineglutamate-valine-lysine (PEVK) element. 4 The PEVK element is thought to function as a largely unfolded polypeptide that extends at low force levels and that thereby provides an important source of elasticity at physiological sarcomere lengths. [5][6][7] Unlike the 1-exon heart specific N2B element, the titin gene contains 112 PEVK exons that are differentially expressed between muscle types. 8 Of these PEVK exons, 219 to 225 are expressed in the so-called N2B titin isoform, that constitutes the dominant cardiac isoform in the left ventricle of a wide range of species, including rodents and human. 9 Here we generated a mouse deficient in titin's exons 219 to 225 that results in a deletion of the c-terminal PEVK region (282 aa) and determined its role in cardiac function using echocardiography, in vivo pressure-volume loops, isolated heart physiology, muscle mechanics, immunoelectron microscopy, and expression analysis. We investigated the hypertrophy phenotype and studied members of the four-and-a-half LIM family involved in atrophy/hypertrophy signaling-FHL1 and FHL2. 10,11 Our results reveal the strong effect of the PEVK element on diastolic function but also that the role of the PEVK extends beyond that of a mechanical spr...