TOR pathway regulates calcium handling in heart tissue through eIF-4E and 4E-BP

SANTALLA M; MATTIAZZI A; VALVERDE CA; FERRERO P; HERNÁNDEZ G

Ciudad Autónoma de Buenos Aires

Congreso; XXII ISHR WORLD CONGRESS 2016; 2016

International Society for Heart Research

The target of rapamycin (TOR) pathway regulates growth, survival and aging. It senses environmental cues to control metabolism, protein synthesis and autophagy, and its dysregulation has been implicated in cardiac diseases. Protein synthesis is the best characterized process controlled by TOR. Initiation of translation occurs when the eukaryotic initiation factor (eIF4E) promotes mRNA recruitment to the ribosome. This step takes place when eIF4E recognizes the cap structure of mRNAs. The eIF4E-binding protein (4E-BP) inhibits cap recognition by associating with eIF4E. TOR phosphorylates and inhibits 4E-BP, thus promoting translation. Changes in expression of eIF4E and 4E-BP alter cardiac stress-response during aging, but the molecular mechanisms associated to cardiac calcium handling remains not understood. In this report, we studied the effect of genetic up and downregulation of eIF4E and 4EBP on cardiac calciumhandling using Drosophila melanogaster as genetic model. We assessed the intracellular calcium level by registering the fluorescent signal of a cardiac reporter system (TinC-Gal4-UASGCaMP3) in semi-intact preparation of 7 days-old flies. Overexpression of 4E-BP incremented the Ca2+-transient amplitude (125%) and relaxation (100%), and the sarcoplasmic reticulum (SR) calcium load (20%). These effects were linked to a higher SR Ca2+ reuptake through the Ca+2-ATPase pump (SERCA). Downregulation of 4E-BP prevented these changes. Accordingly, interference of eIF4E mimicked the effects of 4E-BP overexpression on cardiac performance. Likewise, a 48 hs period of starvation provoked an increment in the amplitude of Ca2+ transients and SR-Ca2+ load. TOR inactivation, and therefore 4EBP derepression, on flies overexpressing eIF4E is consistent with the phenotypes observed in flies overexpressing 4E-BP. eIF4E downregulation and TOR inactivation mimicked these effects. Altogether, our results provide evidence for a critical role of the TOR pathway, via eIF4E and E-BP,on cardiac Ca2+handling, SERCA activity and contractility.