Deficiency in Nebulin Repeats of Sarcomeric Nebulette is Detrimental for Cardiomyocyte Tolerance to Exercise and Biomechanical Stress

The actin-binding sarcomeric nebulette (NEBL) protein provides efficient contractile flexibility via interaction with desmin intermediate filaments. gene mutations affecting the nebulin repeat (NR) domain are known to induce cardiomyopathy. The study aimed to explore the roles of NEBL in exercise and biomechanical stress response. We ablated exon3 encoding the first NR of and created global Nebl knockout mice. Cardiac function, structure, and transcriptome were assessed before and after a 4-wk treadmill regimen. A -based exercise signaling network was constructed using systems genetics methods. H9C2 and neonatal rat cardiomyocytes (NRCs) expressing wild-type or mutant NEBL underwent cyclic mechanical strain. Nebl mice demonstrated diastolic dysfunction with preserved systolic function at 6 mo of age. After treadmill running, 4-mo-old Nebl mice developed concentric cardiac hypertrophy and left ventricular dilation compared with running Nebl and sedentary Nebl mice. Disturbance of sarcomeric Z-disks and thin filaments architecture and disruption of intercalated disks and mitochondria were found in exercised Nebl mice. A -based exercise signaling network included , , , , , and . Disturbed expression of TM1, DES, JUP, β-catenin, MLP, α-actinin2, and vinculin proteins was demonstrated. In H9C2 cells, NEBL was recruited into focal adhesions at 24-h poststrain and redistributed along with F-actin at 72-h poststrain, suggesting time-dependent redistribution of NEBL in response to strain. mutations cause desmin disorganization in NRCs upon stretch. We conclude that Nebl's NR ablation causes disturbed sarcomere, Z-disks, and desmin organization, and prevents NEBL redistribution to focal adhesions in cardiomyocytes, weakening cardiac tolerance to biomechanical stress. We demonstrate that ablation of first nebulin-repeats of sarcomeric nebulette () causes diastolic dysfunction in Nebl mice. Exercise-induced development of diastolic dysfunction, cardiac hypertrophy and ventricular dilation in knockouts. This was associated with sarcomere disturbance, intercalated disks disruption, and mitochondrial distortion upon stress and altered expression of genes involved in -based stress network. We demonstrate that G202R and A592 mutations alter actin and desmin expression causing disorganization of desmin filaments upon cyclic strain.