Microtubule-Mediated Defects in Junctophilin-2 Trafficking Contribute to Myocyte T-Tubule Remodeling and Ca2+ Handling Dysfunction in Heart Failure
Background—Cardiac dysfunction in failing hearts of human patients and animal models is associated with both microtubule densification and T-tubule remodeling. Our objective was to investigate whether microtubule densification contributes to T-tubule remodeling and excitation-contraction coupling dysfunction in heart disease.
Methods and Results—In a mouse model of pressure overload-induced cardiomyopathy by transaortic banding (TAB), colchicine, a microtubule depolymerizer, significantly ameliorated T-tubule remodeling and cardiac dysfunction. In cultured cardiomyocytes, microtubule depolymerization with nocodazole or colchicine profoundly attenuated T-tubule impairment, whereas microtubule polymerization/stabilization with taxol accelerated T-tubule remodeling. In situ immunofluorescence of heart tissue sections demonstrated significant disorganization of JP2, a protein that bridges the T-tubule and sarcoplasmic reticulum membranes, in TAB hearts as well as in human failing hearts, while colchicine injection significantly preserved the distribution of JP2 in TAB hearts. In isolated mouse cardiomyocytes, prolonged culture or treatment with taxol resulted in pronounced redistribution of JP2 from T-tubules to the peripheral plasma membrane, without changing total JP2 expression. Nocodazole treatment antagonized JP2 redistribution. Moreover, overexpression of a dominant-negative mutant of Kinesin 1, a microtubule motor protein responsible for anterograde trafficking of proteins, protected against JP2 redistribution and T-tubule remodeling in culture. Finally, nocodazole treatment improved Ca2+ handling in cultured myocytes by increasing the amplitude of Ca2+ transients and reducing the frequency of Ca2+ sparks.
Conclusions—Our data identify a mechanistic link between microtubule densification and T-tubule remodeling and reveal microtubule-mediated JP2 redistribution as a novel mechanism for T-tubule disruption, loss of E-C coupling, and heart failure.
- Received December 30, 2013.
- Revision received January 28, 2014.
- Accepted January 31, 2014.