Abstract 13: Suppressing Microtubule Detyrosination Reduces Stiffness and Improves Contractility in Human Cardiomyocytes

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The microtubule contribution to myocyte mechanics has been a controversial topic over the years. Utilizing high-speed, super-resolution imaging, we were recently able to directly observe microtubule behavior in working myocytes (Robison et al., Science 2016). Strikingly, we found that microtubules buckle like springs between sarcomeric attachment points, providing a mechanical resistance that limits sarcomere shortening and stretch. Further, we identified that post-translational “detyrosination” of microtubules regulates their attachment to the sarcomere, and thus the microtubule contribution to both passive and active mechanics. Here we present new data identifying microtubule detyrosination as a compelling therapeutic target for the treatment of human heart failure. Using quantitative mass spectrometry, we have probed the cytoskeletal changes that occur during the progression of human heart failure in over 40 patient samples at different stages and etiologies of disease. We find that progressive upregulation and stabilization of the structural cytoskeleton, particularly microtubules and intermediate filaments, is a robust hallmark of human heart failure. Next, we have performed detailed biophysical studies on isolated myocytes from explanted failing and non-failing human hearts. Using advanced imaging, single myocyte tensile tests and atomic force microscopy (e.g. Prosser et al., Science 2011; Robison et al. Science 2016), we have interrogated the contribution of detyrosinated microtubules to the active and passive mechanics of human myocytes. We find that by reducing microtubule detyrosination, we can robustly improve contractile function. Suppressing detyrosination significantly lowers passive stiffness at physiologic rates, while robustly improving contraction velocity, fractional shortening, and relaxation speed. Of note, the improvement in mechanics correlates with the severity of disease, as myocytes from end-stage patients show greater benefits than those from non-failing or compensated hypertrophic hearts. In conclusion, our work demonstrates pre-clinical efficacy for suppressing detyrosinated microtubules to improve myocyte mechanics in human heart failure.