Abstract 13089: Constitutively Active GSK-3β Attenuates Cardiac Aging through Ulk1
The phosphorylation of glycogen synthase kinase-3β (GSK-3β) at S9 is reportedly increased during aging or cellular senescence. However, it is unknown whether the phosphorylation of GSK-3β is protective or detrimental, and the mechanism through which GSK-3β modulates aging remains to be elucidated. We hypothesize that the effect of GSK-3β is mediated through Ulk1, a regulator of autophagy. Therefore, we studied unphosphorylatable GSK-3βS9A knock-in mice (βKI) and GSK-3βS9A/Ulk1+/- bigenic mice (Bigenic). Left ventricular (LV) weight/body weight (LVW/BW, mg/g) increased in wild-type mice (WT, 3.2±0.2 vs 3.4±0.2) but decreased in βKI (3.2±0.3 vs 2.8±0.1) from 6 months (M) to 13 M, with LVW/BW at 13 M being significantly (p<0.01) lower in βKI. The cardiac myocyte cross-sectional area (CSA, μm2) was also significantly smaller in βKI (318±5 vs 359±9) at 13 M. The LVW/BW was significantly higher (3.25±0.11) and the CSA was significantly bigger (388±12) in Bigenic than in βKI at 13 M. These data suggest that GSK-3β attenuates age-dependent cardiac hypertrophy through Ulk1. Cardiac fibrosis (%) increased significantly and age-dependently in WT (1.1±0.1 vs 2.3±0.2) but not in βKI (1.1±0.1 vs 1.3±0.1), and it was significantly higher in Bigenic (3.1±0.3) than in βKI at 13 M. The TUNEL-positive nuclei (%) significantly increased in aging WT (0.03±0.01 vs 0.09±0.02) but not in βKI, while it was significantly higher in Bigenic (0.09±0.02) than in βKI (0.02±0.01) at 13 M. These results indicate that GSK-3β prevents aging-associated cardiac fibrosis and apoptosis through Ulk1. There were age-dependent decreases in LV ejection fraction (EF, %) and fractional shortening (FS, %) in WT (EF 75±3 vs 66±2; FS 38±3 vs 30±1) but not βKI (EF 74±2 vs 75±2; FS 36±2 vs 37±2). LVEF (60±3) and LVFS (26±2) were significantly lower in Bigenic than in βKI at 13 M. The higher LV end-systolic elastance and lower LV chamber stiffness constant in βKI were abolished in Bigenic at 13M. These data suggest that GSK-3β maintains cardiac function through Ulk1 during aging. An in vitro kinase assay revealed that GSK-3β directly phosphorylated Ulk1. In conclusion, S9 phosphorylation of GSK-3β is detrimental during aging, and constitutively active GSK-3β exerts its protective effects by phosphorylating Ulk1.
- © 2013 by American Heart Association, Inc.