Abstract 15693: GSK-3β Mitigates Cardiac Hypertrophy by Phosphorylating Foxo1 During Pressure Overload
Introduction: Both GSK-3β and FoxO1 negatively regulate cardiac hypertrophy. GSK-3β promotes nuclear translocation of FoxO1 and transcription of its targets by phosphorylating FoxO1 in cardiomyocytes (CMs) in vitro. Mice with knock-in of GSK-3β-S9A (S9A), a constitutively active form of GSK-3β, (β-KI) exhibit less severe cardiac hypertrophy in response to pressure overload (PO) than wild type (WT) mice. The role of FoxO1 in mediating the anti-hypertrophic effect of GSK-3β is currently unknown.
Hypothesis: S9A alleviates PO-induced cardiac hypertrophy through phosphorylation of FoxO1 in vivo.
Methods & Results: β-KI mice were crossed with cardiac-specific FoxO1-knockout (c-FoxO1-KO) mice. Mice were subjected to transverse aortic constriction (TAC). Cardiac hypertrophy in response to PO was significantly attenuated in β-KI mice compared to in wild type mice (WT), as indicated by LV weight (LVW) / tibial length (TL) (mg/mm, 6.8 ± 0.4 vs 7.4 ± 0.3, P < 0.05). S9A-induced suppression of cardiac hypertrophy was completely reversed in β-KI / c-FoxO1-KO mice (7.6 ± 0.6, P < 0.05 vs β-KI). Although FoxO1 is localized primarily in the cytosol of CMs after TAC in WT mice, it was localized in the nucleus after TAC in β-KI mice. To identify whether GSK-3β-induced phosphorylation of FoxO1 is critical for the suppression of cardiac hypertrophy, we generated adenovirus harboring a GFP-tagged phosphorylation resistant (PR) mutant of FoxO1, in which the GSK-3β phosphorylation site is replaced with alanine (Ad-GFP-PRmutFoxO1). Although Ad-S9A induced prominent nuclear localization of Ad-GFP-FoxO1-WT, it failed to induce nuclear localization of Ad-GFP-PRmutFoxO1. Although Ad-GFP-FoxO1-WT significantly suppressed phenylephrine (PE)-induced increases in CM cell size compared to Ad-LacZ (Relative CM size after PE treatment: 0.76 vs 1, P < 0.05), Ad-GFP-PRmutFoxO1 failed to suppress them (1.14 vs 1, N.S.).
Conclusion: An active form of GSK-3β phosphorylates FoxO1, thereby inducing nuclear translocation of FoxO1. FoxO1, in turn, plays an important role in mediating the anti-hypertrophic actions of GSK-3β. Serine 9 phosphorylation and inactivation of GSK-3β in response to PO promotes cardiac hypertrophy by inhibiting the nuclear action of FoxO1.
Author Disclosures: Y. Maejima: None. N. Nagarajan: None. P. Zhai: None. M. Isobe: None. J. Sadoshima: None.
- © 2016 by American Heart Association, Inc.