Deleting full length titin versus the titin M-band region leads to differential mechanosignaling and cardiac phenotypes

Background: Titin is a giant elastic protein that spans the half-sarcomere from Z-disk to M-band. It acts as a molecular spring and mechanosensor and has been linked to striated muscle disease. The pathways that govern titin dependent cardiac growth and contribute to disease are diverse and difficult to dissect. Methods: To study titin deficiency versus dysfunction, we generated and compared striated muscle specific knockouts with progressive postnatal loss of the complete titin protein by removing exon 2 (E2-KO) or an M-band truncation that eliminates proper sarcomeric integration but retains all other functional domains (M1/2-KO). We evaluated cardiac function, cardiomyocyte mechanics, and the molecular basis of the phenotype. Results: Skeletal muscle atrophy with reduced strength, severe sarcomere disassembly, and lethality from 2 weeks of age were shared between the models. Cardiac phenotypes differed considerably: loss of titin leads to dilated cardiomyopathy (DCM) with combined systolic and diastoli...