Abstract 16391: Constitutively Active GSK-3β Attenuates Cardiac Aging Through Ulk1-Dependent Stimulation of Autophagy
Phosphorylation of glycogen synthase kinase-3β (GSK-3β) at S9 increases during aging or cellular senescence. However, it is unknown whether the phosphorylation is beneficial or detrimental, and mechanisms through which GSK-3β affects aging remain to be elucidated. Autophagy, which protects organs against aging, decreases with aging. We hypothesize that GSK-3β mediates its effects via Ulk1, a regulator of autophagy, and studied unphosphorylatable/constitutively active (CA) GSK-3βS9A knock-in mice (βKI) and GSK-3βS9A/Ulk1+/- bigenic mice (Bigenic) up to 24 months (M) of age. From 6M to 24M, left ventricular (LV) weight/body weight (LVW/BW, mg/g) increased in wild-type mice (WT, 3.2±0.2 vs 3.8±0.2) but decreased in βKI (3.2±0.3 vs 2.4±0.1), and was lower (p<0.005) in βKI than in WT at 24M. Cardiac myocyte cross-sectional area (CSA, μm2) was smaller in βKI than in WT at 24M (376±5 vs 501±8, p<0.001). The LVW/BW was higher (3.5±0.2, p<0.001) and the CSA was bigger (527±4, p<0.001) in Bigenic than in βKI at 24M. These data suggest that CA GSK-3β attenuates aging-related cardiac hypertrophy via Ulk1. Cardiac fibrosis (%) increased at 24M in WT (3.5±0.2 vs 1.1±0.1, p<0.001), but was less in βKI (2.4±0.1) than in WT (p<0.001) or Bigenic (5.5±0.6, p<0.001). The TUNEL-positive nuclei (%) increased at 24M in WT (0.17±0.02 vs 0.03±0.01, p<0.001), but there were fewer in βKI (0.04±0.01) than in WT (p<0.005) or Bigenic (0.19±0.03, p<0.005). These data demonstrate that CA GSK-3β decreases aging-associated cardiac fibrosis and apoptosis via Ulk1. The LV end-systolic elastance (mmHg/μl) decreased in WT (5±1 vs 16 ±2, p<0.005) but not in βKI, while the LV chamber stiffness constant (μl-1) increased in WT (0.13±0.0 vs 0.04±0.01, p<0.001) but not in βKI, and these effects of CA GSK-3β were abolished in Bigenic. These data suggest that CA GSK-3β preserves cardiac function via Ulk1. The numbers of autophagosomes and autolysosomes, determined using tandem fluorescent mRFP-GFP-LC3 transgenic mice (tfLC3), were significantly higher in βKI/tfLC3 mice than in tfLC3 or βKI/tfLC3/Ulk1+/- mice, indicating that CA GSK-3β activates autophagy via Ulk1. In conclusion, S9 phosphorylation of GSK-3β is detrimental during aging, and CA GSK-3β beneficially enhances Ulk1-dependent autophagy.
Author Disclosures: P. Zhai: None. Y. Ikeda: None. A. Shirakabe: None. T. Yamamoto: None. B. Magrys: None. X. Cheng: None. J. Sadoshima: None.
- © 2014 by American Heart Association, Inc.