Abstract P2081: Defective Translation Of Mitochondrial Proteins Impairs Cardiac Metabolism In HFpEF

Abstract

We recently reported that heart failure with preserved ejection fraction (HFpEF) in human myocardium has broadly reduced acylcarnitines and Krebs cycle intermediates, and that transcriptomics shows increased gene expression of oxidative-phosphorylation (OxPhos) related pathways. However, new preliminary data finds protein expression related to OxPhos is decreased. Here, we explored a key mechanism that could drive depressed mitochondrial protein translation in HFpEF. Elongation factor 5A (EIF5A) is a ribosomal subunit that is post-translationally modified on lysine 50 by the transfer of an aminobutyryl moiety from spermidine, called hypusination (Hyp). We find EIF5A Hyp and the mitochondrial proteome are diminished despite elevated gene transcripts in the myocardium of human and a mouse model of HFpEF (latter high-fat diet +L-NAME). Inhibiting EIF5A hypusination in neonatal rat cardiomyocytes results in ribosome stalling, disruption of OxPhos, and increased glycolysis.Proteomics of adult cardiomyocytes with inhibition of the rate-limiting hypusination enzyme deoxyhypusine synthase (DHPS) phenocopies depressed mitochondria as in human HFpEF. Cardiomyocyte-specific knockout of DHPS is lethal in pups within 24hrs after birth. These mice have significantly less myocardial EIF5A Hyp . Cardiac-specific DHPS+/- are viable and have no heart phenotype in unstressed situations, but display marked cardiac dilation with low ejection fraction with failure to hypertrophy in response to transverse aortic constriction.Four weeks following tamoxifen-inducible homozygous knockout of DHPS in cardiomyocytes of 8-week-old mice, we find impaired diastolic function (increased E/E’) with preserved ejection fraction and reduced exercise tolerance. Despite reduced hypusination in HFpEF, ornithine levels are elevated suggesting inhibition of hypusination at the hypusinating enzymes. Interestingly, DHPS levels are decreased in human HFpEF hearts.In summary, we have uncovered a novel role of polyamines in cardiomyocytes: the facilitation of translation of mitochondrial proteins by EIF5A hypusination. We find reduced hypusination resulting from defects in hypusine synthesizing enzymes contributes to mitochondrial defects in HFpEF.