Dataset Information

Contractile Function During Angiotensin-II Activation: Increased Nox2 Activity Modulates Cardiac Calcium Handling via Phospholamban Phosphorylation.

ABSTRACT:

Background

Renin-angiotensin system activation is a feature of many cardiovascular conditions. Activity of myocardial reduced nicotinamide adenine dinucleotide phosphate oxidase 2 (NADPH oxidase 2 or Nox2) is enhanced by angiotensin II (Ang II) and contributes to increased hypertrophy, fibrosis, and adverse remodeling. Recent studies found that Nox2-mediated reactive oxygen species production modulates physiological cardiomyocyte function.

Objectives

This study sought to investigate the effects of cardiomyocyte Nox2 on contractile function during increased Ang II activation.

Methods

We generated a cardiomyocyte-targeted Nox2-transgenic mouse model and studied the effects of in vivo and ex vivo Ang II stimulation, as well as chronic aortic banding.

Results

Chronic subpressor Ang II infusion induced greater cardiac hypertrophy in transgenic than wild-type mice but unexpectedly enhanced contractile function. Acute Ang II treatment also enhanced contractile function in transgenic hearts in vivo and transgenic cardiomyocytes ex vivo. Ang II-stimulated Nox2 activity increased sarcoplasmic reticulum (SR) Ca(2+) uptake in transgenic mice, increased the Ca(2+) transient and contractile amplitude, and accelerated cardiomyocyte contraction and relaxation. Elevated Nox2 activity increased phospholamban phosphorylation in both hearts and cardiomyocytes, related to inhibition of protein phosphatase 1 activity. In a model of aortic banding-induced chronic pressure overload, heart function was similarly depressed in transgenic and wild-type mice.

Conclusions

We identified a novel mechanism in which Nox2 modulates cardiomyocyte SR Ca(2+) uptake and contractile function through redox-regulated changes in phospholamban phosphorylation. This mechanism can drive increased contractility in the short term in disease states characterized by enhanced renin-angiotensin system activation.

SUBMITTER: Zhang M

PROVIDER: S-EPMC4509515 | biostudies-literature |

REPOSITORIES: biostudies-literature

ACCESS DATA

Similar Datasets

Project description:Aims:PKN1 is a stress-responsive protein kinase acting downstream of small GTP-binding proteins of the Rho/Rac family. The aim was to determine its role in endogenous cardioprotection. Methods and results:Hearts from PKN1 knockout (KO) or wild type (WT) littermate control mice were perfused in Langendorff mode and subjected to global ischaemia and reperfusion (I/R). Myocardial infarct size was doubled in PKN1 KO hearts compared to WT hearts. PKN1 was basally phosphorylated on the activation loop Thr778 PDK1 target site which was unchanged during I/R. However, phosphorylation of p42/p44-MAPK was decreased in KO hearts at baseline and during I/R. In cultured neonatal rat ventricular cardiomyocytes (NRVM) and NRVM transduced with kinase dead (KD) PKN1 K644R mutant subjected to simulated ischaemia/reperfusion (sI/R), PhosTag® gel analysis showed net dephosphorylation of PKN1 during sI and early R despite Thr778 phosphorylation. siRNA knockdown of PKN1 in NRVM significantly decreased cell survival and increased cell injury by sI/R which was reversed by WT- or KD-PKN1 expression. Confocal immunofluorescence analysis of PKN1 in NRVM showed increased localization to the sarcoplasmic reticulum (SR) during sI. GC-MS/MS and immunoblot analysis of PKN1 immunoprecipitates following sI/R confirmed interaction with CamKII?. Co-translocation of PKN1 and CamKII? to the SR/membrane fraction during sI correlated with phospholamban (PLB) Thr17 phosphorylation. siRNA knockdown of PKN1 in NRVM resulted in increased basal CamKII? activation and increased PLB Thr17 phosphorylation only during sI. In vivo PLB Thr17 phosphorylation, Sarco-Endoplasmic Reticulum Ca2+ ATPase (SERCA2) expression and Junctophilin-2 (Jph2) expression were also basally increased in PKN1 KO hearts. Furthermore, in vivo P-V loop analysis of the beat-to-beat relationship between rate of LV pressure development or relaxation and end diastolic P (EDP) showed mild but significant systolic and diastolic dysfunction with preserved ejection fraction in PKN1 KO hearts. Conclusion:Loss of PKN1 in vivo significantly reduces endogenous cardioprotection and increases myocardial infarct size following I/R injury. Cardioprotection by PKN1 is associated with reduced CamKII?-dependent PLB Thr17 phosphorylation at the SR and therefore may stabilize the coupling of SR Ca2+ handling and contractile function, independent of its kinase activity.