title: AMPK attenuates microtubule proliferation in cardiac hypertrophy.
abstract: Cell hypertrophy requires increased protein synthesis and expansion of the cytoskeletal networks that support cell enlargement. AMPK limits anabolic processes, such as protein synthesis, when energy supply is insufficient, but its role in cytoskeletal remodeling is not known. Here, we examined the influence of AMPK in cytoskeletal remodeling during cardiomyocyte hypertrophy, a clinically relevant condition in which cardiomyocytes enlarge but do not divide. In neonatal cardiomyocytes, activation of AMPK with 5-aminoimidazole carboxamide ribonucleotide (AICAR) or expression of constitutively active AMPK (CA-AMPK) attenuated cell area increase by hypertrophic stimuli (phenylephrine). AMPK activation had little effect on intermediate filaments or myofilaments but dramatically reduced microtubule stability, as measured by detyrosinated tubulin levels and cytoskeletal tubulin accumulation. Importantly, low-level AMPK activation limited cell expansion and microtubule growth independent of mTORC1 or protein synthesis repression, identifying a new mechanism by which AMPK regulates cell growth. Mechanistically, AICAR treatment increased Ser-915 phosphorylation of microtubule-associated protein 4 (MAP4), which reduces affinity for tubulin and prevents stabilization of microtubules (MTs). RNAi knockdown of MAP4 confirmed its critical role in cardiomyocyte MT stabilization. In support of a pathophysiological role for AMPK regulation of cardiac microtubules, AMPK α2 KO mice exposed to pressure overload (transverse aortic constriction; TAC) demonstrated reduced MAP4 phosphorylation and increased microtubule accumulation that correlated with the severity of contractile dysfunction. Together, our data identify the microtubule cytoskeleton as a sensitive target of AMPK activity, and the data suggest a novel role for AMPK in limiting accumulation and densification of microtubules that occurs in response to hypertrophic stress.
authors: Cardiovascular Division, University of Minnesota Medical School, Minneapolis, MN, USA.
authors: John T
authors: JT
authors: Fassett
authors: Xinli
authors: X
authors: Hu
authors: Xin
authors: X
authors: Xu
authors: Zhongbing
authors: Z
authors: Lu
authors: Ping
authors: P
authors: Zhang
authors: Yingjie
authors: Y
authors: Chen
authors: Robert J
authors: RJ
authors: Bache
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D006332:Cardiomegaly / Q000378:metabolism* / Q000473:pathology*; D002478:Cells, Cultured; D004195:Disease Models, Animal; D051379:Mice; D018345:Mice, Knockout; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D032383:Myocytes, Cardiac / Q000166:cytology / Q000201:enzymology*; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D014404:Tubulin / Q000378:metabolism; D017725:Ventricular Pressure / Q000502:physiology
chemical_list: D008869:Microtubule-Associated Proteins; D034741:RNA, Small Interfering; D014404:Tubulin; C534978:Prkaa2 protein, mouse; C543928:Prkaa2 protein, rat; D055372:AMP-Activated Protein Kinases