Abstract 15786: Ddit4L: A Novel Differential Regulator of mTor and Autophagy in Cardiomyocytes
DNA-Damage-Inducible Transcript 4-Like (DDiT4L) protein regulates mTOR signaling in skeletal muscle, however its role in the heart is unknown. Here we investigated the role of DDiT4L in regulating mTOR signaling in cardiomyocytes. We show that DDiT4L differentially regulates mTORC1 and mTORC2 signaling in cardiomyocytes and regulates autophagy in an mTOR dependent, TSC2 independent manner. We studied DDiT4L regulation in the heart using murine models of cardiomyopathy and isolated rat neonatal cardiomyocytes (NRVMs). The functional role of DDiT4L was assessed with loss and gain of function approaches in NRVMs, and an HA-DDiT4L cardiac specific conditional transgenic mouse using Western blotting, PCR, ECHO and confocal imaging. DDiT4L expression increased in mouse models of pathological (pressure overload hypertrophy and dilated cardiomyopathy (myosin heavy chain F764L knock in) n=3-5, p<0.001) but not physiological hypertrophy (swim model) compared to WT. In NRVMs, DDiT4L mRNA increased with the pathological stressors; stretch, oxidative stress and glucose deprivation (n=3-5, p<0.05-0.01). We found DDiT4L localized to lysosomes in NRVMs, and adenoviral overexpression or siRNA knockdown of DDiT4L show that DDiT4L is necessary and sufficient for glucose deprivation induced autophagy in an mTOR dependent, AMPK and TSC2 independent manner (n=3-5, p <0.05-0.001). DDiT4L also inhibits ‘non-lysosomal’ mTORC1 signaling (P-S6K levels) and activates mTORC2 signaling (P-Akt levels) in a TSC2 dependent manner (n=3-5, p<0.01). Mice with conditional cardiac specific overexpression of DDiT4L show mild systolic dysfunction with baseline inhibition of mTORC1 and increased autophagy with mTORC2 activation (n=6-9, p<0.05-0.001). This phenotype is completely reversed with suppression of transgene expression (n=3-9). Our data show that DDiT4L expression is altered during models of pathological hypertrophy and plays a central role in regulating mTOR signaling and autophagy in the heart via mTORC1 in a novel TSC2 independent manner. DDiT4L also appears to be a new activator of mTORC2 signaling. Due to the central role of mTOR signaling and autophagy in cardiovascular diseases, DDiT4L may represent a previously unexplored, novel therapeutic target.
Author Disclosures: B. Simonson: None. V. Subramanya: None. C. Xiao: None. M. Mishra: None. T. Khurana: None. J. Seidman: None. C. Seidman: None. A. Rosenzweig: None. S. Das: None.
- © 2014 by American Heart Association, Inc.