Common and distinct roles of AMPKγ isoforms in small-molecule activator-stimulated glucose uptake in mouse skeletal muscle

Abstract

ObjectiveSmall-molecule activators targeting the allosteric drug and metabolite (ADaM) site of AMPK enhance insulin-independent glucose uptake in skeletal muscle and lower glucose in preclinical models of hyperglycemia. The regulatory AMPK{gamma} subunit plays a central role in energy sensing. While the skeletal muscle-selective {gamma}3 isoform is essential for AMP/ZMP-induced glucose uptake, it is dispensable for ADaM site-binding activators. We hypothesized that the predominant {gamma}1 isoform is required for ADaM site activator-stimulated glucose uptake in skeletal muscle. MethodsSingle-nucleus RNA sequencing (snRNA-seq) was performed on mouse and human skeletal muscle mapping AMPK subunit isoform distribution across resident cell types. To determine {gamma} isoform-specific requirements for activator-stimulated glucose uptake, skeletal muscle-specific inducible AMPK{gamma}1/{gamma}3 double knockout (im{gamma}1-/-/{gamma}3-/-) and single knockout (im{gamma}1-/- and im{gamma}3-/-) mice were generated. Ex vivo glucose uptake was measured following treatment with AICAR (AMP-mimetic) or MK-8722 (ADaM site activator), and in vivo MK-8722-induced blood glucose lowering was assessed. ResultssnRNA-seq revealed distinct AMPK isoform distribution: {gamma}1 was ubiquitously expressed, whereas {gamma}3 was enriched in glycolytic myofibers in both mouse and human skeletal muscle. Ex vivo, glucose uptake stimulated by either AICAR or MK-8722 was abolished in im{gamma}1-/-/{gamma}3-/- muscle, and MK-8722-induced blood glucose lowering was significantly blunted in vivo. AICAR but not MK-8722-stimulated muscle glucose uptake was abolished in im{gamma}3-/-, whereas both activators fully retained effects on glucose uptake and glucose lowering in im{gamma}1-/- mice. ConclusionsWhile {gamma}1 predominates in stabilizing the AMPK2{beta}2{gamma}1 complex, it is dispensable for AMPK activator-stimulated glucose uptake in skeletal muscle, whether mediated via the nucleotide-binding or ADaM site.