The role of Eukaryotic elongation factor 1 α in cardiac homeostasis

Abel Martin Garrido (Mannheim)1, J. Heineke (Mannheim)2, F. A. Trogisch (Mannheim)3, S. Hemanna (Mannheim)1, M. Keles (Mannheim)4, N. Weinzierl (Mannheim)1

1Medizinische Fakultät Mannheim der Universität Heidelberg Abteilung für Herz- Kreislaufforschung Mannheim, Deutschland; 2Medizinische Fakultät Mannheim der Universität Heidelberg Kardiovaskuläre Physiologie Mannheim, Deutschland; 3Medizinische Fakultät Mannheim der Universität Heidelberg Abteilung für kardiovaskuläre Physiologie Mannheim, Deutschland; 4ECAS (European Center for Angioscience), Mannheim Faculty of Medicine, Heidelberg University Department of Cardiovascular Physiology Mannheim, Deutschland


Background: The canonical function of Eukaryotic elongation factor 1 α (Eef1a) is the translocation of tRNA from the cytosol to the ribosome during translational elongation. In addition, Eef1a is linked to F-actin formation, proteasome activity, aggresome assembly and microtubules formation. In mammalian cells, there are two paralogs of Eef1a: Eef1a1 and Eef1a2. Whereas Eef1a1 is ubiquitously expressed in every cell type, the expression of Eef1a2 is restricted to adult cardiomyocytes, skeletal myocytes and neurons.  Recently, it was shown that patients with mutations in Eef1a2 develop cardiomyopathies; however, the mechanism involved is completely unknown.

Methods and Results: Here we generated cardiomyocyte specific, tamoxifen induced adult onset knock-out mice for Eef1a1 (eEf1a1 cKO), Eef1a2 (eEf1a2 cKO), and for Eef1a1 and Eef1a2 in combination (eEf1a1/a2 cKO).  We analyzed cardiac dimensions and function by echocardiography, morphometry and conducted histological analyses of heart tissue. In addition, we started to analyze how Eef1a2 acts in cardiomyocytes on the molecular level. Our result show that Eef1a2 cKO exert decreased cardiac function after 2 months post gene-deletion, but not at 1-month post deletion. This decrease was accompanied by an increase in ventricular weight, cardiomyocyte cross-sectional area and interstitial fibrosis. 40% of Eef1a2 cKO mice died within 2 months post deletion. By contrast, Eef1a1 cKO had normal cardiac function after 2 months of gene-deletion and no premature mortality. The Eef1a1/a2 cKO mice exerted an early mortality (40 days post deletion), however, the cardiac function remained unaltered, suggesting sudden death at that time point. A combined RNA sequencing and proteomics analysis from isolated ventricles of Eef1a2 cKO and eEf1a1/a2 cKO versus WT mice revealed an increase in the mRNA levels of genes involved in cardiac hypertrophy, fibrosis and dysfunction. By contrast, in the proteomics analysis we observed an upregulation of ribosomal proteins. In both analyses, the response was exacerbated in Eef1a1/a2 cKO compared with Eef1a2 cKO. Surprisingly, the global cardiac protein synthesis rate, assessed by Puromycin incorporation, was similar between Eef1a2 cKO and WT mice, and was only reduced by 30% in eEf1a1/a2 cKO mice 1-month post deletion.  On the other hand, we observed an increase in protein expression of the autophagy marker p62 in heart tissue of eEF1A2-cKO mice after 2-months post tamoxifen. Accordingly, immunofluorescence analyses show an increase of p62 punctate positive cells, broadly overlapping with proteins labelled for degradation by ubiquitin. Hence, the lack of functional eEF1A2 appears to trigger the activation of protein degradation pathways, while maintaining global protein synthesis capability potentially by upregulation of ribosomal proteins in cardiomyocytes.

Conclusions:  Our result demonstrate for the first time that eEF1A levels regulate the homeostasis of ribosome subunits expression in cardiomyocytes, and that eEF1A1 functions are partially redundant with eEF1A2. Future directions will answer whether cellular stress upon loss of functional eEF1A2 is induced by the dysregulation of ribogenesis, by disturbed protein synthesis fidelity and/or the increased induction of protein degradation pathways.

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