Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA044

Poster Communications

Iron deficiency reduces cardiac contraction by downregulating RyR2 channels and suppressing SERCA pump activity

Y. Chung1, A. Luo1, A. Loonat1, S. Lakhal-Littleton1, P. A. Robbins1, P. Swietach1

1. Department of Physiology, Anatomy & Genetics, University of Oxford, Oxford, United Kingdom.

Introduction: Iron deficiency, irrespective of anemia, has been shown to be detrimental to cardiac function in chronic heart failure patients. Clinical trials have consistently demonstrated a beneficial effect of intravenous iron supplementation on cardiac function (1). However, the mechanisms of this effect are unknown. We investigated the link between iron deficiency (anemia), cardiac dysfunction and iron supplementation in mice fed an iron-deficient diet. Methods: Mice were weaned on an iron-deficient diet for 6 weeks; some received intravenous iron as ferric carboxymaltose (FCM) after 3 weeks on the diet. In vivo cardiac function was assessed by CINE-MR imaging at the end of weeks 3, 4 and 5 of diet. To investigate the effect of iron deficiency (anemia) on gene expression, animals were sacrificed at the end of week 6 of diet, and their cardiac mRNA was subject to RNA-seq (Illumina HiSeq 4000) and analyzed for differential gene expression and altered pathways. The dynamics of cardiac calcium handling were interrogated using a variety of methods, including electrophysiology and live-cell fluorescence Ca2+-imaging of electrically evoked Ca2+ transients in enzymatically isolated cardiac myocytes loaded with the dyes Fluo-3 or FuraRed. Results: Following 5-weeks of an iron-deficient diet, animals became anemic (Hb (g/L): Control 147.7 vs Deficient 63.6). By week 3 of diet, ejection fraction of iron-deficient anemic animals was significantly decreased to 64% (compared to 70% Control). Whole-transcriptome sequencing (RNA-seq) suggested altered gene expression in several pathways, including cardiac Ca2+ signalling. Western blotting of cardiac lysates indicated a remodeling of proteins associated with the sarcoplasmic (SR) Ca2+ store: a two-fold downregulation of RyR2 channels and phospholamban phosphorylation at Thr17. Ventricular myocytes from iron-deficient anemic animals had reduced CaT amplitude (by 33%), with no change in diastolic SR Ca2+ load, L-type current or Ca2+ buffering. Reduced fractional Ca2+ release was attributable to downregulated RyR2 channel activity. The constancy of diastolic SR Ca2+ load was maintained by the combination of reduced RyR2 permeability and right-shifted SERCA pump activity. Intravenous injections of FCM were able to reverse the anemia and iron deficiency and restore CaT amplitude and cardiac ejection fraction. Conclusion: Herein, we present a molecular mechanism underpinning cardiac remodeling in iron deficiency anemia and confirm the efficacy of intravenous iron supplementation in restoring normal function at the cellular and whole-organ level.

Where applicable, experiments conform with Society ethical requirements