Targeting Troponin I Phosphorylation for Precision Treatment of Diastolic Dysfunction

Abstract

Background: Defective cardiac relaxation (diastolic dysfunction) is common in heart failure, especially with diabetes, obesity, hypertension, and ageing, and is linked to increased mortality. No effective therapy specifically targets this dysfunction. Phosphorylation of troponin I by cAMP-dependent protein kinase A (PKA) promotes relaxation, but global PKA activation affects numerous downstream targets. Here we investigated whether selective enhancement of troponin I phosphorylation could improve relaxation without widespread PKA activation. Methods: To investigate cAMP signalling with subcellular resolution we used real-time detection of cAMP levels and FRET based genetically encoded reporters targeted to specific locations combined with biochemical and genetic approaches. We applied peptide array technology to study protein-protein interaction surfaces and develop a protein-protein interaction disruptor peptide. The impact of such peptide on cardiac myocyte function was investigated in vitro, using both mouse and human primary cardiac myocytes and biochemical approaches, real-time imaging, work-loop analysis. In vivo analysis involved echocardiography and hemodynamics measurements. Results: We discovered that the cAMP-hydrolysing enzyme PDE4D9 binds troponin I and locally degrades cAMP within a nanometre-scale domain, thereby selectively regulating troponin I phosphorylation. The association of PDE4D9 with troponin I is markedly increased in cardiac disease in rodents and humans. A peptide displacing PDE4D9 from troponin I selectively elevates troponin I phosphorylation, enhances cardiomyocyte relaxation, and prevents diastolic dysfunction in a mouse heart failure model. Conclusions: Our findings define a first-in-class, mechanism-based therapeutic approach to a major, unmet contributor to heart failure.