MTORC1 regulates cardiac function and myocyte survival through 4E-BP1 inhibition in mice
Denghong Zhang, … , Nahum Sonenberg, Gianluigi Condorelli
Denghong Zhang, … , Nahum Sonenberg, Gianluigi Condorelli
Published July 19, 2010
Citation Information: J Clin Invest. 2010;120(8):2805-2816. https://doi.org/10.1172/JCI43008.
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Research Article Cardiology

MTORC1 regulates cardiac function and myocyte survival through 4E-BP1 inhibition in mice

Abstract

Mechanistic target of rapamycin (MTOR) plays a critical role in the regulation of cell growth and in the response to energy state changes. Drugs inhibiting MTOR are increasingly used in antineoplastic therapies. Myocardial MTOR activity changes during hypertrophy and heart failure (HF). However, whether MTOR exerts a positive or a negative effect on myocardial function remains to be fully elucidated. Here, we show that ablation of Mtor in the adult mouse myocardium results in a fatal, dilated cardiomyopathy that is characterized by apoptosis, autophagy, altered mitochondrial structure, and accumulation of eukaryotic translation initiation factor 4E–binding protein 1 (4E-BP1). 4E-BP1 is an MTOR-containing multiprotein complex-1 (MTORC1) substrate that inhibits translation initiation. When subjected to pressure overload, Mtor-ablated mice demonstrated an impaired hypertrophic response and accelerated HF progression. When the gene encoding 4E-BP1 was ablated together with Mtor, marked improvements were observed in apoptosis, heart function, and survival. Our results demonstrate a role for the MTORC1 signaling network in the myocardial response to stress. In particular, they highlight the role of 4E-BP1 in regulating cardiomyocyte viability and in HF. Because the effects of reduced MTOR activity were mediated through increased 4E-BP1 inhibitory activity, blunting this mechanism may represent a novel therapeutic strategy for improving cardiac function in clinical HF.

Authors

Denghong Zhang, Riccardo Contu, Michael V.G. Latronico, Jianlin Zhang, Roberto Rizzi, Daniele Catalucci, Shigeki Miyamoto, Katherine Huang, Marcello Ceci, Yusu Gu, Nancy D. Dalton, Kirk L. Peterson, Kun-Liang Guan, Joan Heller Brown, Ju Chen, Nahum Sonenberg, Gianluigi Condorelli

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Figure 3

Western blot analysis of MTORC1- and MTORC2-associated proteins.

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Western blot analysis of MTORC1- and MTORC2-associated proteins. (A) Blo...
(A) Blots of total and phosphorylated (p) MTORC1-associated proteins from myocardial extracts from WT-Cre controls at 4 weeks after TMX administration (post-TMX) and from Mtor-cKO mice at 1, 2, and 4 weeks after TMX administration (above). Densitometry (arbitrary units, mean ± SD) of nonphosphorylated and total 4E-BP1 and S6 protein phosphorylated at Ser240 (below). Phosphorylation of downstream targets of MTORC1 is reduced by 2 weeks after TMX administration. Accumulation of 4E-BP1 is a striking characteristic of myocardium lacking Mtor expression. Gapdh was used as an internal loading control. (B) Blots of total and phosphorylated MTORC2-associated proteins and of Foxo proteins in myocardial extracts from WT-Cre controls at 4 weeks after TMX administration and from Mtor-cKO mice at 1, 2, and 4 weeks after TMX administration (top). Phosphorylation of Akt at sites independent of MTORC2 (Thr308 and Thr450) was also analyzed. Densitometry (arbitrary units, mean ± SD) of phosphorylation levels of Akt (bottom). (C) Representative blot of myocardial extracts from sham- and TAC-operated wild-type mice. The MTORC1 downstream proteins S6 kinase and S6 become less expressed when hearts are failing (8 weeks after TAC). Note the accumulation of 4E-BP1 bound to eIF4E at 8 weeks in TAC-operated mice. (D) Representative blot of myocardial extracts from wild-type littermates and MLP-KO mice, a genetic model of dilated cardiomyopathy. Similarly to Mtor-cKO (A) and failing pressure-overloaded wild-type myocardium (C), 4E-BP1 becomes dephosphorylated at Ser65 and more bound to eIF4E also in this model.