Abstract 151: A Novel Role for DDiT4L in Regulation of mTOR and Autophagy in the Heart
Introduction: DDiT4L is a known negative regulator of mTOR signaling in skeletal muscle; however its role in the heart is unknown. We have recently showed increased DDiT4L mRNA in a murine transgenic model of pathological but not physiological hypertrophy. Here we test the hypothesis that DDiT4L is a regulator of mTOR signaling in the heart and may play a role in pathological hypertrophy and heart failure.
Methods: We investigated the regulation of DDiT4L in murine models of hypertrophy and in cultured neonatal rat ventricular cardiomyocytes (NRVMs). Loss and gain of function of DDiT4L in mTOR regulation and autophagy was investigated using confocal imaging, immunoblotting, and qRT-PCR in NRVMs.
Results: DDiT4L gene and protein expression was increased four-fold in pressure overload hypertrophy (n = 4-6, p<0.001), but not in a swim model of physiological hypertrophy. DDiT4L gene expression also significantly increased in a genetic model of dilated cardiomyopathy model (n = 4, p<0.001). In NRVMs, DDiT4L was induced by cardiac stressors such as pathological stretch, hypoxia, and glucose deprivation (n = 3-5 in duplicate, p<0.05-0.01). Increased DDiT4L expression correlated with inhibition of mTOR signaling, and an increase in autophagy markers. siRNA ablation of DDiT4L revealed that inhibition of mTOR signaling by DDiT4L was necessary for glucose deprivation induced autophagy, as determined by imaging of GFP-LC3 autophagosomes (n = 3 in duplicate, p<0.01), and immunoblotting of autophagy markers. Conversely, adenoviral-driven overexpression of DDiT4L inhibited mTOR signaling and significantly increased basal autophagy (n = 3 in duplicate, p<0.05). In TAC mice, the increase in DDiT4L protein expression correlated to inhibition of mTOR signaling, increases in autophagy markers (p<0.01), and preceded the transition to LV dilation and HF.
Conclusion: Our data suggests that DDiT4L expression is altered in diverse models of pathological hypertrophy and precedes the development of LV dilatation and overt heart failure. DDiT4L inhibition of mTOR and modulation of autophagy may play a role in the progression to heart failure. DDiT4L may represent a novel therapeutic target to prevent this transition.
- © 2013 by American Heart Association, Inc.