Background: The actin-binding sarcomeric nebulette (NEBL) protein provides efficient contractile flexibility via interaction with desmin intermediate filaments. NEBL gene mutations affecting the nebulin repeat (NR) domain is known to induce cardiomyopathy. Objective: The study aimed to explore the roles of NEBL in exercise and biomechanical stress response. Methods: We ablated exon3 encoding the first NR of Nebl and created global Nebl3ex-/3ex- knockout mice. Cardiac function, structure and transcriptome was assessed before and after a 4-week treadmill regimen. A Nebl-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. Results: Nebl3ex-/3ex- mice demonstrated diastolic dysfunction with preserved systolic function at 6-months of age. After treadmill running, 4-month-old Nebl3ex-/3ex- mice developed concentric cardiac hypertrophy and left ventricular dilation compared to running Nebl+/+ and sedentary Nebl3ex-/3ex- mice. Disturbance of sarcomeric Z-disks and thin filaments architecture, disruption of intercalated disks and mitochondria were found in exercised Nebl3ex-/3ex- mice. A Nebl-based exercise signaling network included Csrp3, Des, Fbox32, Jup, Myh6, and Myh7. Disturbed expression of TM1, DES, JUP, b-catenin, MLP, α-actinin2 and vinculin proteins was demonstrated. In H9C2 cells, NEBL was recruited into focal adhesions at 24-hours post-strain and redistributed along with F-actin at 72-hours post-strain, suggesting time-dependent redistribution of NEBL in response to strain. NEBL mutations cause desmin disorganization in NRCs upon stretch. Conclusions: Upon stretch, NEBL deficiency causes disturbed sarcomere, Z-disks and desmin organization, and prevents NEBL redistribution to focal adhesions in cardiomyocytes, weakening cardiac tolerance to stress.
Author response: A Rho signaling network links microtubules to PKD controlled carrier transport to focal adhesions
