Force Generation via β-Cardiac Myosin, Titin, and α-Actinin Drives Cardiac Sarcomere Assembly from Cell-Matrix Adhesions

Publication date: 8 January 2018
Source:Developmental Cell, Volume 44, Issue 1
Author(s): Anant Chopra, Matthew L. Kutys, Kehan Zhang, William J. Polacheck, Calvin C. Sheng, Rebeccah J. Luu, Jeroen Eyckmans, J. Travis Hinson, Jonathan G. Seidman, Christine E. Seidman, Christopher S. Chen
Truncating mutations in the sarcomere protein titin cause dilated cardiomyopathy due to sarcomere insufficiency. However, it remains mechanistically unclear how these mutations decrease sarcomere content in cardiomyocytes. Utilizing human induced pluripotent stem cell-derived cardiomyocytes, CRISPR/Cas9, and live microscopy, we characterize the fundamental mechanisms of human cardiac sarcomere formation. We observe that sarcomerogenesis initiates at protocostameres, sites of cell-extracellular matrix adhesion, where nucleation and centripetal assembly of α-actinin-2-containing fibers provide a template for the fusion of Z-disk precursors, Z bodies, and subsequent striation. We identify that β-cardiac myosin-titin-protocostamere form an essential mechanical connection that transmits forces required to direct α-actinin-2 centripetal fiber assembly and sarcomere formation. Titin propagates diastolic traction stresses from β-cardiac myosin, but not α-cardiac myosin or non-muscle myosin II, to protocostameres during sarcomerogenesis. Ablating protocostameres or decoupling titin from protocostameres abolishes sarcomere assembly. Together these results identify the mechanical and molecular components critical for human cardiac sarcomerogenesis.

Graphical abstract

Teaser

Chopra, Kutys, Zhang, et al. identify that dilated cardiomyopathy-causing titin truncation mutations impair early-stage sarcomerogenesis in a model of dynamic human cardiac sarcomere assembly. This work uncovers fundamental mechanisms driving sarcomere assembly and reveals a critical role for titin in connecting β-cardiac myosin-generated tension to protocostameres to initiate sarcomerogenesis.


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