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Edward J Miller

Publications and source records attributed to Edward J Miller.

4 recordsLinked to original sources
PubMed2006

Activation of AMPK alpha- and gamma-isoform complexes in the intact ischemic rat heart.

AMP-activated protein kinase (AMPK) plays a key role in modulating cellular metabolic processes. AMPK, a serine-threonine kinase, is a heterotrimeric complex of catalytic alpha-subunits and regulatory beta- and gamma-subunits with multiple isoforms. Mutations in the cardiac gamma(2)-isoform have been associated with hypertrophic cardiomyopathy and pre-excitation syndromes. However, physiological regulation of AMPK complexes containing different subunit isoforms is not well defined and is important for an understanding of the function of this signaling pathway in the intact heart. We evaluated the kinase activity associated with heart AMPK complexes containing specific alpha- and gamma-subunit isoforms of AMPK in an in vivo rat model of regional ischemia. Left coronary artery occlusion activated the immunoprecipitated alpha(1)-isoform (6-fold, P < 0.01) and alpha(2)-isoform (9-fold, P < 0.01) in the ischemic left ventricle compared with sham controls. The degree of alpha-subunit activation depended on the extent of ischemia and paralleled echocardiographic contractile dysfunction. The regulatory gamma(1)- and gamma(2)-isoforms were expressed in the heart. The gamma(1)- and gamma(2)-isoforms coimmunoprecipitated with alpha(1)- and alpha(2)-isoforms in proportion to alpha-subunit content. gamma(1)-Isoform immunocomplexes accounted for 70% of AMPK activity and AMPK phosphorylation (Thr(172)) in hearts. Ischemia similarly increased AMPK activity associated with the gamma(1)- and gamma(2)-isoform complexes threefold (P < 0.01 for each). Thus AMPK catalytic alpha(1)- and alpha(2)-isoforms are activated by regional ischemia in vivo in the heart, irrespective of the regulatory gamma(1)- or gamma(2)-isoforms to which they are complexed. Despite the pathophysiological importance of gamma(2)-isoform mutations, gamma(1)-isoform complexes account for most of the AMPK activity in the ischemic heart.

AMP-Activated Protein Kinases↗
PubMed2005

AMP-activated protein kinase activates p38 mitogen-activated protein kinase by increasing recruitment of p38 MAPK to TAB1 in the ischemic heart.

AMP-activated protein kinase (AMPK) promotes glucose transport, maintains ATP stores, and prevents injury and apoptosis during ischemia. AMPK has several direct molecular targets in the heart but also may interact with other stress-signaling pathways. This study examined the role of AMPK in the activation of the p38 mitogen-activated protein kinase (MAPK). In isolated heart muscles, the AMPK activator 5-aminoimidazole-4-carboxy-amide-1-beta-D-ribofuranoside (AICAR) increased p38 MAPK activation. In AMPK-deficient mouse hearts, expressing a kinase-dead (KD) alpha2 catalytic subunit, p38 MAPK activation was markedly reduced during low-flow ischemia (2.3- versus 7-fold in wild-type hearts, P<0.01) and was similarly reduced during severe no-flow ischemia in KD hearts (P<0.01 versus ischemic wild type). Knockout of the p38 MAPK upstream kinase, MAPK kinase 3 (MKK3), did not affect ischemic activation of either AMPK or p38 MAPK in transgenic mkk3(-/-) mouse hearts. Ischemia increased p38 MAPK recruitment to transforming growth factor-beta-activated protein kinase 1-binding protein 1 (TAB1), a scaffold protein that promotes p38 MAPK autophosphorylation. Moreover, TAB1 was associated with the alpha2 catalytic subunit of AMPK. p38 MAPK recruitment to TAB1/AMPK complexes required AMPK activation and was reduced in ischemic AMPK-deficient transgenic mouse hearts. The potential role of p38 MAPK in mediating the downstream action of AMPK to promote glucose transport was also assessed. The p38 MAPK inhibitor SB203580 partially inhibited both AICAR- and hypoxia-stimulated glucose uptake and GLUT4 translocation. Activation of p38 MAPK by anisomycin also increased glucose transport in heart muscles. Thus, AMPK has an important role in promoting p38 MAPK activation in the ischemic heart by inducing p38 MAPK autophosphorylation through interaction with the scaffold protein TAB1.

AMP-Activated Protein Kinases↗
PubMed2005

Dual mechanisms regulating AMPK kinase action in the ischemic heart.

AMP-activated protein kinase (AMPK) is emerging as an important signaling protein during myocardial ischemia. AMPK is a heterotrimeric complex containing an alpha catalytic subunit and beta and gamma regulatory subunits. Phosphorylation of Thr172 in the activation loop of the alpha subunit by upstream AMPK kinase(s) (AMPKK) is a critical determinant of AMPK activity. However, the mechanisms regulating AMPK phosphorylation in the ischemic heart remain uncertain and were therefore investigated. In the isolated working rat heart, low-flow ischemia rapidly activated AMPKK activity when measured using recombinant AMPK (rAMPK) as substrate. The addition of AMP (10 to 200 micromol/L) augmented the ability of heterotrimeric alpha1beta1gamma1 or alpha2beta1gamma1 rAMPK to be phosphorylated by heart AMPKK in vitro, whereas physiologic concentrations of ATP inhibited rAMPK phosphorylation. However, neither AMP nor ATP directly influenced AMPKK activity: they had no effect on AMPKK-mediated phosphorylation of rAMPK substrates lacking normal AMP-binding gamma subunits (isolated truncated alpha1(1-312) or alpha1beta1gamma1 rAMPK containing an R70Q mutation in the gamma1 AMP-binding site). Regional ischemia in vivo also increased AMPKK activity and AMPK phosphorylation in the rat heart. AMPK phosphorylation could also be induced in vivo without activating AMPKK: AICAR infusion increased AMPK phosphorylation without activating AMPKK; however, the AMP-mimetic AICAR metabolite ZMP enhanced the ability of heterotrimeric rAMPK to be phosphorylated by AMPKK. Thus, heart AMPKK activity is increased by ischemia and its ability to phosphorylate AMPK is highly modulated by the interaction of AMP and ATP with the heterotrimeric AMPK complex, indicating that dual mechanisms regulate AMPKK action in the ischemic heart.

AMP-Activated Protein Kinase Kinases↗