Chronic Rho-kinase inhibition improves left ventricular contractile dysfunction in early type-1 diabetes by increasing myosin cross-bridge extension.

Mark T Waddingham,Yutaka Fujii,James T Pearson,Dong-Yun Zhan,Naoto Yagi,Darren J Kelly,Tadakatsu Inagaki,Alberto Astolfo,Cheng-Kun Du,Mikiyasu Shirai,Hirotsugu Tsuchimochi,Amanda J Edgley

doi:10.1186/s12933-015-0256-6

Abstract

BackgroundImpaired actin–myosin cross-bridge (CB) dynamics correlate with impaired left ventricular (LV) function in early diabetic cardiomyopathy (DCM). Elevated expression and activity of Rho kinase (ROCK) contributes to the development of DCM. ROCK targets several sarcomeric proteins including myosin light chain 2, myosin binding protein-C (MyBP-C), troponin I (TnI) and troponin T that all have important roles in regulating CB dynamics and contractility of the myocardium. Our aim was to examine if chronic ROCK inhibition prevents impaired CB dynamics and LV dysfunction in a rat model of early diabetes, and whether these changes are associated with changes in myofilament phosphorylation state.MethodsSeven days post-diabetes induction (65 mg/kg ip, streptozotocin), diabetic rats received the ROCK inhibitor, fasudil (10 mg/kg/day ip) or vehicle for 14 days. Rats underwent cardiac catheterization to assess LV function simultaneous with X-ray diffraction using synchrotron radiation to assess in situ CB dynamics.ResultsCompared to controls, diabetic rats developed mild systolic and diastolic dysfunction, which was attenuated by fasudil. End-diastolic and systolic myosin proximity to actin filaments were significantly reduced in diabetic rats (P < 0.05). In all rats there was an inverse correlation between ROCK1 expression and the extension of myosin CB in diastole, with the lowest ROCK expression in control and fasudil-treated diabetic rats. In diabetic and fasudil-treated diabetic rats changes in relative phosphorylation of TnI and MyBP-C were not significant from controls.ConclusionsOur results demonstrate a clear role for ROCK in the development of LV dysfunction and impaired CB dynamics in early DCM.Electronic supplementary materialThe online version of this article (doi:10.1186/s12933-015-0256-6) contains supplementary material, which is available to authorized users.

Highlights

Impaired actin–myosin cross-bridge (CB) dynamics correlate with impaired left ventricular (LV) func‐ tion in early diabetic cardiomyopathy (DCM)
Given that myosin interfilament spacing did not differ between the groups, we speculated that LV contractile dysfunction driven by impaired CB dynamics in early diabetes might be attributed to a reduction in the activity of myosin accessory proteins, myosin light chain-2 (MLC-2) or cardiac myosin binding protein-C (MyBP-C), which meticulously regulate myosin head extension on a beat-to-beat basis [9,10,11,12,13]
In experiments 1 and 2, LV weights tended to be lower in diabetic rats compared to their control counterparts

Summary

Introduction

Impaired actin–myosin cross-bridge (CB) dynamics correlate with impaired left ventricular (LV) func‐ tion in early diabetic cardiomyopathy (DCM). We demonstrated that in the hearts of diabetic rats, myosin heads are displaced away from the actin thin-filament during diastole, leading to suppressed systolic myosin transfer to actin, and an assumed reduction in strong CB formation as the rate of pressure development was decreased [8]. Given that myosin interfilament spacing did not differ between the groups, we speculated that LV contractile dysfunction driven by impaired CB dynamics in early diabetes might be attributed to a reduction in the activity of myosin accessory proteins, myosin light chain-2 (MLC-2) or cardiac myosin binding protein-C (MyBP-C), which meticulously regulate myosin head extension on a beat-to-beat basis [9,10,11,12,13]

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