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Overexpression of the Na+/K+ ATPase ?2 but not ?1 isoform attenuates pathological cardiac hypertrophy and remodeling.

ABSTRACT: RATIONALE:The Na+ / K+ ATPase (NKA) directly regulates intracellular Na+ levels, which in turn indirectly regulates Ca2+ levels by proximally controlling flux through the Na+ / Ca2+ exchanger (NCX1). Elevated Na+ levels have been reported during heart failure, which permits some degree of reverse-mode Ca2+ entry through NCX1, as well as less efficient Ca2+ clearance. OBJECTIVE:To determine whether maintaining lower intracellular Na+ levels by NKA overexpression in the heart would enhance forward-mode Ca2+ clearance and prevent reverse-mode Ca2+ entry through NCX1 to protect the heart. METHODS AND RESULTS:Cardiac-specific transgenic mice overexpressing either NKA-?1 or NKA-?2 were generated and subjected to pressure overload hypertrophic stimulation. We found that although increased expression of NKA-?1 had no protective effect, overexpression of NKA-?2 significantly decreased cardiac hypertrophy after pressure overload in mice at 2, 10, and 16 weeks of stimulation. Remarkably, total NKA protein expression and activity were not altered in either of these 2 transgenic models because increased expression of one isoform led to a concomitant decrease in the other endogenous isoform. NKA-?2 overexpression but not NKA-?1 led to significantly faster removal of bulk Ca2+ from the cytosol in a manner requiring NCX1 activity. Mechanistically, overexpressed NKA-?2 showed greater affinity for Na+ compared with NKA-?1, leading to more efficient clearance of this ion. Furthermore, overexpression of NKA-?2 but not NKA-?1 was coupled to a decrease in phospholemman expression and phosphorylation, which would favor greater NKA activity, NCX1 activity, and Ca2+ removal. CONCLUSIONS:Our results suggest that the protective effect produced by increased expression of NKA-?2 on the heart after pressure overload is due to more efficient Ca2+ clearance because this isoform of NKA preferentially enhances NCX1 activity compared with NKA-?1.

SUBMITTER: Correll RN

PROVIDER: S-EPMC4001807 | biostudies-literature | 2014 Jan

REPOSITORIES: biostudies-literature

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Overexpression of the Na+/K+ ATPase α2 but not α1 isoform attenuates pathological cardiac hypertrophy and remodeling.

Correll Robert N RN Eder Petra P Burr Adam R AR Despa Sanda S Davis Jennifer J Bers Donald M DM Molkentin Jeffery D JD

Circulation research 20131111 2

<h4>Rationale</h4>The Na+ / K+ ATPase (NKA) directly regulates intracellular Na+ levels, which in turn indirectly regulates Ca2+ levels by proximally controlling flux through the Na+ / Ca2+ exchanger (NCX1). Elevated Na+ levels have been reported during heart failure, which permits some degree of reverse-mode Ca2+ entry through NCX1, as well as less efficient Ca2+ clearance.<h4>Objective</h4>To determine whether maintaining lower intracellular Na+ levels by NKA overexpression in the heart would ...[more]

PMID: 24218169

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Project description:Heart failure (HF) is a functional lack of myocardial performance due to a loss of molecular control over increases in calcium and ROS, resulting in proteolytic degradative advances and cardiac remodeling. Mitochondria are the molecular powerhouse of cells, shifting the sphere of cardiomyocyte stability and performance. Functional mitochondria rely on the molecular abilities of safety factors such as TFAM to maintain physiological parameters. Mitochondrial transcription factor A (TFAM) creates a mitochondrial nucleoid structure around mtDNA, protecting it from mutation, inhibiting NFAT (ROS activator/hypertrophic stimulator), and transcriptionally activates Serca2a to decrease calcium mishandling. Calpain1 and MMP9 are proteolytic degratory factors that play a major role in cardiomyocyte decline in HF. Current literature depicts major decreases in TFAM as HF progresses. We aim to assess TFAM function against Calpain1 and MMP9 proteolytic activity and its role in cardiac remodeling. To this date, no publication has surfaced describing the effects of aortic banding (AB) as a surgical HF model in TFAM-TG mice. HF models were created via AB in TFAM transgenic (TFAM-TG) and C57BLJ-6 (WT) mice. Eight weeks post AB, functional analysis revealed a successful banding procedure, resulting in cardiac hypertrophy as observed via echocardiography. Pulse wave and color doppler show increased aortic flow rates as well as turbulent flow at the banding site. Preliminary results of cardiac tissue immuno-histochemistry of HF-control mice show decreased TFAM and compensatory increases in Serca2a fluorescent expression, along with increased Calpain1 and MMP9 expression. Protein, RNA, and IHC analysis will further assess TFAM-TG results post-banding. Echocardiography shows more cardiac stability and functionality in HF-induced TFAM-TG mice than the control counterpart. These findings complement our published in vitro results. Overall, this suggests that TFAM has molecular therapeutic potential to reduce protease expression.

Project description:BackgroundThe Ca2+/calmodulin-dependent phosphatase calcineurin is a key regulator of cardiac myocyte hypertrophy in disease. An unexplained paradox is how the β isoform of the calcineurin catalytic A-subunit (CaNAβ) is required for induction of pathological myocyte hypertrophy, despite calcineurin Aα expression in the same cells. It is unclear how the pleiotropic second messenger Ca2+ drives excitation-contraction coupling while not stimulating hypertrophy by calcineurin in the normal heart. Elucidation of the mechanisms conferring this selectivity in calcineurin signaling should reveal new strategies for targeting the phosphatase in disease.MethodsPrimary adult rat ventricular myocytes were studied for morphology and intracellular signaling. New Förster resonance energy transfer reporters were used to assay Ca2+ and calcineurin activity in living cells. Conditional gene deletion and adeno-associated virus-mediated gene delivery in the mouse were used to study calcineurin signaling after transverse aortic constriction in vivo.ResultsCIP4 (Cdc42-interacting protein 4)/TRIP10 (thyroid hormone receptor interactor 10) was identified as a new polyproline domain-dependent scaffold for CaNAβ2 by yeast 2-hybrid screen. Cardiac myocyte-specific CIP4 gene deletion in mice attenuated pressure overload-induced pathological cardiac remodeling and heart failure. Blockade of CaNAβ polyproline-dependent anchoring using a competing peptide inhibited concentric hypertrophy in cultured myocytes; disruption of anchoring in vivo using an adeno-associated virus gene therapy vector inhibited cardiac hypertrophy and improved systolic function after pressure overload. Live cell Förster resonance energy transfer biosensor imaging of cultured myocytes revealed that Ca2+ levels and calcineurin activity associated with the CIP4 compartment were increased by neurohormonal stimulation, but minimally by pacing. Conversely, Ca2+ levels and calcineurin activity detected by nonlocalized Förster resonance energy transfer sensors were induced by pacing and minimally by neurohormonal stimulation, providing functional evidence for differential intracellular compartmentation of Ca2+ and calcineurin signal transduction.ConclusionsThese results support a structural model for Ca2+ and CaNAβ compartmentation in cells based on an isoform-specific mechanism for calcineurin protein-protein interaction and localization. This mechanism provides an explanation for the specific role of CaNAβ in hypertrophy and its selective activation under conditions of pathologic stress. Disruption of CaNAβ polyproline-dependent anchoring constitutes a rational strategy for therapeutic targeting of CaNAβ-specific signaling responsible for pathological cardiac remodeling in cardiovascular disease deserving of further preclinical investigation.

Dataset Information

Overexpression of the Na+/K+ ATPase ?2 but not ?1 isoform attenuates pathological cardiac hypertrophy and remodeling.

Publications

Overexpression of the Na+/K+ ATPase α2 but not α1 isoform attenuates pathological cardiac hypertrophy and remodeling.

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