Detyrosinated microtubules in cardiomyocyte mechanics

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Project Summary A common and currently intractable feature of heart failure is the stiffening of cardiac tissue that impairs the heart's ability to relax. The microtubule cytoskeleton contributes to the internal stiffness of heart muscle cells, and under certain conditions can impede the ability of cardiomyocytes to both contract and relax. Over the first five years of this R01, we found that cardiomyocyte stiffness is tightly regulated by post-translational detyrosination of microtubules, and that detyrosinated microtubules are consistently elevated in human heart failure, concomitant with increased myocardial stiffness. We also found that reducing detyrosinated microtubules is sufficient to lower stiffness and improve contraction and relaxation in cardiomyocytes and myocardial tissue from patients with diverse forms of heart failure. We further identified the enzyme responsible for detyrosination in the heart, and showed that targeting this enzyme is sufficient to robustly improve relaxation in failing human heart cells. As such, detyrosination forms a promising new therapeutic target for the treatment of heart failure. The proposed research will test the hypothesis that genetic or small molecule targeting of the “tyrosination cycle” can stably improve both systolic and diastolic function in different small and large animal models of heart failure. Studies under three aims will address several components of this hypothesis. In Aim 1, we will explore whether a gene therapy approach overexpressing the tyrosinating enzyme (TTL) is sufficient to improve systolic function in a genetic mouse model of heart failure, and to improve diastolic function in surgical model of heart failure with preserved ejection fraction. Aim 2 experiments will focus on a different therapeutic modality consisting of novel and highly potent small molecule inhibitors of the detyrosinating enzyme (VASH). We will evaluate the pharmacokinetics of these novel inhibitors and test their tolerability and efficacy for reducing detyrosination and improving cardiac function in both rodent and human cells and tissues. In Aim 3, we will move our exploration to larger animal studies and test whether targeting detyrosination is sufficient to improve myocyte and myocardial function in cats with hypertrophic cardiomyopathy and with heart failure with preserved ejection fraction. Our cross-species, multi-scale and multi-pronged approach will balance our goals of reductionist rigor and integrative relevance that ultimately furthers clinical translation. Together, this work will determine if targeting detyrosinated microtubules can stably improve cardiac function in heart failure, and identify therapeutic compounds that may be suitable for progression into a clinical pipeline.