RVF occurs when mechanisms compensating an increased RV afterload e.g. caused by PH, pulmonary vascular stenosis, etc. are exhausted. We hypothesized that transition from compensation to decompensation of the RV may be promoted by changes in cardiomyocytes calcium dynamics, release of ROS and metabolism. Therefore, we investigated the role of mitochondrial uncoupling protein 2 (UCP2) in a murine model of RV hypertrophy and failure. Pressure overload was induced by PAB in UCP2 deficient mice (UCP2-/-) and in C57BL/6J mice. Three weeks after PAB or sham operation, right heart hypertrophy and function were determined by invasive hemodynamics and echocardiography. Contraction and relaxation of cardiomyocytes isolated from these mice, as well as cellular calcium dynamics and mitochondrial superoxide release were measured by fluorescence microscopy. Expression of the cardiac calcium handling proteins SERCA2a, PLB and the NCX, as well as MFN2, which is a mitochondrial protein that has been shown to influence mitochondrial-SR interaction, were determined by immunoblotting. Mitochondrial superoxide release and respiration were determined by the fluorescent dye MitoSOX, and high resolution respirometry, respectively. Echocardiographic and hemodynamic assessments revealed that: PAB induced increased right ventricular systolic pressure (RVSP) and right heart hypertrophy in C57BL/6J and UCP2-/- mice PAB induced a decrease of CO and RV dilation as signs of RV decompensation in C57BL/6J mice Right ventricular function was preserved after PAB in UCP2-/- mice in contrast to C57BL/6J mice Functional studies in cardiomyocytes revealed that: Cardiomyocytes isolated from the RV of both, C57BL/6J and UCP2-/- mice, showed increased contractility, despite decrease of CO in C57BL/6J mice Cardiomyocytes isolated from the RV of UCP2-/- mice showed further improved function after PAB compared to C57BL/6J mice Cardiomyocytes isolated from the RV of UCP2-/- mice showed improved contraction and relaxation after PAB compared to C57BL/6J mice Analysis of calcium dynamics in isolated cardiomyocytes revealed that: Calcium transients were increased in cardiomyocytes from UCP2-/- mice after PAB compared to C57BL/6J mice The time of calcium to reach 50% of the basal value was decreased in cardiomyocytes from UCP2-/- mice after PAB compared to C57BL/6J mice Expression of calcium handling proteins in cardiomyocytes revealed that: SERCA2a expression was increased in RV cardiomyocytes from UCP2-/- mice after PAB compared to C57BL/6J mice MFN2 expression was increased in RV cardiomyocytes from UCP2-/- mice after PAB compared to C57BL/6J mice NCX expression and PLB expression were unchanged in cardiomyocytes from UCP2-/- mice after PAB compared to C57BL/6J mice ROS studies in cardiomyocytes and mitochondrial respiration in muscle fibers revealed that: Isolated cardiomyocytes from UCP2-/- mice after PAB showed increased mitochondrial superoxide concentration under stimulation compared to C57BL/6J mice ROS inhibition by superoxide scavenger tempol decreased cardiomyocyte function and contractility Mitochondrial respiration in permeabilized muscle fibers remained unchanged independent of genotype and treatment We conclude that UCP2 deficiency may protect from pressure overload-induced RV dysfunction via improved cardiomyocyte calcium dynamics due to increased SERCA2a expression. Regulation of calcium dynamics due to increased SERCA2a may be regulated by increased ROS release. Therefore, UCP2 deletion and SERCA2a may be considered as novel therapeutic targets to inhibit transition from compensated RV hypertrophy to RVF.
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