Abstract 14792: Suppression of Autophagy by Mst1-mediated Phosphorylation of Beclin1 Compromises Protein Quality Control in Failing Hearts
We have shown previously that mammalian Ste20-like kinase 1(Mst1)-mediated Thr108 phosphorylation of Beclin1, a key mediator of autophagy, negatively regulates autophagy in the heart. Mst1 is activated during cardiac remodeling after myocardial infarction (MI) whereas suppression of endogenous Mst1 attenuates left ventricular (LV) remodeling and dysfunction. In order to test whether the beneficial effect of Mst1 suppression during cardiac remodeling is mediated through stimulation of autophagy, transgenic mice with cardiac specific overexpression of dominant negative Mst1 (Tg-DN-Mst1) were crossed with beclin1+/- mice and the mice were subjected to permanent coronary artery ligation. At Day-42, LV dysfunction was milder (LV ejection fraction 52±4 vs 43±4%, p<0.05) in Tg-DN-Mst1 than in NTg mice. The beneficial effects of DN-Mst1 were reversed in beclin1-/+-Tg-DN-Mst1 mice (32±2%). Although the LV scar size at Day-42 was significantly smaller in Tg-DN-Mst1 than in NTg mice, it was increased in beclin1-/+-Tg-DN-Mst1 mice (21±3, 34±4, 48±5%, p<0.05). Autophagosome formation in the MI border zone, evaluated by GFP-LC3 dots on Day 42, was significantly increased in NTg mice (Sham vs MI: 18±4 vs 78±9 counts/HPF, p<0.01, n=6). The number of GFP-LC3 dots was significantly greater in Tg-DN-Mst1 than in NTg (180±16, 78±9 counts/HPF, p<0.05). Conversely, the increase in GFP-LC3 dots was attenuated in beclin1-/+-Tg-DN-Mst1 (31±9 counts/HPF, p<0.05). Mst1 activity was significantly higher (3-fold) and Thr108-phosphorylated Beclin1 was significantly accumulated (4-fold) in failing hearts from patients with end-stage dilated cardiomyopathy compared to in normal hearts. The amount of p62 was significantly increased (3.5-fold), the LC3-II amount was significantly lower (0.3-fold), and aggresomes colocalized with p62 in the perinuclear region of cardiomyocytes accumulated more prominently in the failing hearts than in normal hearts. Collectively, these results suggest that the beneficial effects of suppressing endogenous Mst1 are mediated through alleviation of Beclin1 phosphorylation and stimulation of autophagy, thereby maintaining protein quality control, which, in turn, reduces cardiac dysfunction.
- © 2012 by American Heart Association, Inc.