Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA046

Poster Communications

Cardiac specific overexpression of PGC-1α isoform 4 in mice causes distinct changes in postnatal cardiomyocyte Na+/K+ ATPase function and leads to early death by dilating heart failure

T. Tuomainen1, N. Naumenko1, M. Mutikainen1, A. Shakirzyanova1, J. Ruas2, P. Tavi1,2

1. A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Kuopio, Finland. 2. Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.

  • Figure 1. MTC stained cardiac cross sections from control (ctrl) and Pgc-1α4 overexpressing (α4+) mice. Scale 1 mm.

  • Figure 2. Representative relative Na+/K+ ATPase current traces under consecutive applications of 10 µM and 1 mM ouabain in neonatal (left) and 4-week-old (right) cardiomyocytes isolated from control (ctrl) and Pgc-1α4 overexpressing (α4+) mice.

Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), a transcriptional coactivator, is a master regulator of cellular energy metabolism. In cardiac myocytes, PGC-1α contributes also to expression of many proteins involved in the processes of contractile function (1). PGC-1α isoform 4 (PGC-1α4) has been shown to regulate skeletal muscle growth and its transgenic overexpression in mice induced skeletal muscle hypertrophy (2). In this study, we aimed to investigate the effects of PGC-1α4 on heart muscle by using a transgenic mouse model where PGC-1α4 expression is restricted to cardiac myocytes with Cre-Lox recombination system. PGC-1α4 overexpressing mice (α4+) died by the age of five weeks (n=9) and histological analysis showed severe cardiac dilation at the age of four weeks (Fig.1). Calcium handling and electrophysiological traits (action potential, sodium and calcium currents) were drastically changed in cardiomyocytes isolated from 4-week-old α4+ mice. To pinpoint initial actions of PGC-1α4 in our model, we performed RNA sequencing from ventricular tissue of α4+ mice at neonatal stage when their survival was yet unaffected by the overexpression. As expected, neonatal α4+ hearts had only 202 differentially expressed genes (DEG) compared to control hearts whereas 4-week-old α4+ hearts had 1554 DEGs (threshold for DEG: adjP<0.01, absolute logFC>1; n=4). Interestingly, at both time points gene enrichment analysis indicated notable changes in processes involved with plasmalemmal ion transport. One of the most prominent expressional changes was increase in Na+/K+ ATPase (NKA) subunit alpha-3, which at both time points translated into increased protein expression as assessed with western blot (n=4). In addition, expression of NKA subunit alpha-2 increased in neonatal, but not in four-week old α4+ hearts. Next, we examined NKA current in isolated cardiomyocytes with patch clamping under exposure to its pharmacological inhibitor ouabain at saturating concentration (1 mM) and at concentration that blocks only the more sensitive alpha-2 and -3 isoforms (10 µM) (3). Proportion of more ouabain sensitive component of the total pump current was increased in both neonatal (26.6%±3.3% in control [n=7] vs 40.9%±4.5% in α4+ [n=9], p<0.05) and 4-week-old (20.5%±2.5% in control [n=12] vs 40.7%±3.5% in α4+ [n=8], p<0.001) cardiomyocytes (Fig.2). Increased NKA expression leading to its overt activity will increase the cardiomyocyte energy consumption, which might be one of the causative changes inducing heart failure in this model. In conclusion, the present study proposes role for PGC-1α4 in the regulation of cardiomyocyte ion homeostasis and its overexpression during cardiac development lethally impairs the heart growth in the immediate postnatal stage.

Where applicable, experiments conform with Society ethical requirements