The canonical function of Eukaryotic elongation factor 1 α (Eef1a) is the translocation of tRNA from the cytosol to ribosomes during translational elongation. In addition, Eef1a was linked to F-actin formation, proteasome activity 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. Although it was shown that patients with mutations in EEF1A2 develop cardiomyopathies, the mechanism involved is completely unknown.
To study the role of cardiac Eef1a2 in adult mice, we generated adult induced, cardiomyocyte specific Eef1a2 knock-out (Eef1a2 cKO) and Eef1a1/Eef1a2 double KO (Eef1a1/a2 cKO) mice. We found that Eef1a cKO exert decreased survival (60%) and cardiac dysfunction 2 months after tamoxifen induced gene-deletion. The Eef1a1/a2 cKO mice exhibit an early mortality (40 days post gene deletion), however, the cardiac function remained unaltered before sudden death occurred. Surprisingly, the global cardiac protein synthesis rate was similar between Eef1a2 cKO and WT mice, and was only reduced by 30% in Eef1a1/a2 cKO mice.
A combined RNA sequencing and proteomics analysis from hearts of eEf1a2 cKO and eEf1a1/a2 cKO mice at one month post gene deletion versus WT mice revealed an increase in ribosomal proteins and elongation factors post-transcriptionally. Ribo-Seq analysis of cardiac samples showed that ribosomal proteins and elongation factors are translated more efficiently in Eef1a2-cKO and Eef1a1/a2-cKO mice.
We also demonstrated that Eef1a2 acts as functional chaperone using two independent methods. First, Luciferase activity was strongly reduced (by>90%) in isolated cardiomyocytes from Eef1a2 cKO and double Eef1a1/a2-cKO mice despite unchanged Luciferase mRNA levels. Conversely, Eef1a2 overexpression in HEK cells conferred resistance to heat shock-induced loss of Luciferase activity.
Analyses of cardiac tissue two months after gene deletion revealed an increase of LC3-I, Beclin1, Atg7, p62 and aggresome bodies in heart tissue of Eef1a2-cKO mice, suggesting that Eef1a2 regulates autophagy in adult cardiomyocytes. More importantly, we found that daily administration of Rapamycin (mTORC1 inhibitor) for one month starting one month after deletion of eEf1a2 reverts cardiac dysfunction, reduced p62 and aggresome body formation and normalized the survival of Eef1a2 cKO mice.
Our data demonstrate that Eef1a2 maintains cardiac proteostasis by controlling ribosomal protein synthesis, by ensuring proper protein folding, and by promoting autophagic flux. Loss of Eef1a2 in cardiomyocytes leads to proteotoxic stress and cardiac dysfunction, which can be reversed by mTORC1 inhibition with Rapamycin. Here, we show for the first time a link between the translational elongation machinery and cardiac proteostasis, offering new therapeutic possibilities for EEF1A2-associated cardiomyopathies.
