Abstract 3954: Changes in Subunit Composition of AMPK in the Developmental and Diseased Hearts
AMP-activated protein kinase (AMPK) is a heterotrimeric complex composed of catalytic α-subunit and regulatory β- and γ-subunits with multiple isoforms for each subunit. Recently, point mutations in the regulatory γ2-subunit have been shown to cause glycogen storage cardiomyopathy in humans suggesting an unique role of γ2-AMPK in the heart. Thus, knowledge of subunit composition of the AMPK will provide important insights into the understanding of the AMPK function in the intact heart, and will ultimately benefit the pharmacological targeting of AMPK. Using antibodies specific to each subunit isoform, we determined the protein expression pattern of AMPK subunit isoforms during cardiac development as well as during the progression of cardiac hypertrophy to failure in mouse and human hearts. In mouse developmental hearts, AMPK was highly expressed in the fetal stage and fell ~2-fold to adult expression level after birth. In hypertrophied and failing hearts, we found that the expression levels of β-subunit shifted from β1 (2-fold down) to β2 (2–3 fold up) in both mice and humans. However, in failing mouse hearts the γ2-subunit increased by 2.5 fold while the human failing hearts switched to γ1 isoforms (γ1 8.8 fold up and γ2 5.7 fold down, p<0.01). By combining immunoprecipitation and AMPK activity assay, we found that both mouse and human hearts have all 12 heterotrimeric AMPK complexes in contrary to human skeletal muscle in which only 3 different AMPK complexes were reported. In normal mouse hearts, the α2-AMPK accounts for 78% of total AMPK activity with the α1-AMPK accounts for the remaining (22%) activity. In human hearts, however, α1 and α2 complexes each account for 50% of the total AMPK activity. These results demonstrate that isoform composition of AMPK subunit in the heart changes during both physiological and pathological conditions. There are significant differences in the isoform-specific activity of AMPK between mice and humans. These observations provide a basis for future development of organ-selective strategies for AMPK activation.