Abstract 17221: AMPK Regulation of Microtubule Dynamics in Cardiac Hypertrophy
Cardiomyocyte hypertrophy requires increased protein synthesis as well as remodeling/growth of the cytoskeletal networks necessary to support cell enlargement. AMPK is a metabolic sensor that couples cell growth to ATP levels. Whether AMPK regulates cardiomyocyte cytoskeletal dynamics and how this influences hypertrophy is not known. Here we used cultured neonatal cardiomyocytes and AMPK KO mice to examine the role of AMPK in cytoskeletal remodeling that occurs during hypertrophy. In cardiomyocytes exposed to hypertrophic stress (phenylephrine or constitutively active Raf), AMPK activation (AICAR 0.1-0.2 mM) or constitutively active AMPK had little effect on intermediate filaments or myofilaments, but did attenuate accumulation and stabilization of microtubules (AICAR reduced MT levels to 38% +/- 3.6 % and detyrosinated MTs to 14% +/- 11% of PE treated; p<.001). Importantly, AMPK reduction of microtubule stability occurred at low doses of AICAR that did not block mTOR/p70S6k signaling or translation, suggesting microtubule dynamics are an extremely sensitive target of AMPK. Interestingly, AMPK reduction of microtubules limited cardiomyocyte elongation, suggesting a mechanism by which AMPK influences cell morphology. In mice exposed to pressure overload (transverse aortic constriction;TAC), microtubule levels were exacerbated by AMPK alpha 2 KO as compared to WT mice (202 % +/- 42%; p=.047). Furthermore, microtubule levels exhibited a significant inverse correlation with LV ejection fraction (R2=.752; p<.001), suggesting microtubule densification may contribute to reduced contractile function in AMPK KO mice. Mechanistically, AMPK activation increased phosphorylation of Microtubule Associated Protein 4 (MAP4) at serine 768, which prevents its ability to stabilize microtubules. Phosphorylation of MAP4Ser768 was reduced in AMPK KO mice, but increased in WT mice exposed to metformin, which also reduced MT stability. RNAi depletion of MAP4 in isolated cardiomyocytes further confirmed its important role in stabilizing microtubules during hypertrophy. Together, our data identify a novel protective role for AMPK in preventing aberrant stabilization and accumulation of cardiac microtubules in response to hypertrophic stress.
- © 2011 by American Heart Association, Inc.