The human AMPKgamma3 R225W mutation does neither enhance basal AMPKgamma3-associated activity nor glycogen in human or mouse skeletal muscle

BackgroundAMP-activated protein kinase (AMPK) is activated during cellular energy perturbation. AMPK is composed of three subunits and several variants of AMPK complexes are expressed in skeletal muscle. The regulatory AMPK{gamma}3 subunit is predominantly expressed in fast-twitch muscle fibers. A human AMPK{gamma}3 R225W mutation has been described in two families. In cultured cells derived from R225W carrier muscle, the mutation was reported to increase total AMPK activity. In addition, elevated glycogen levels were observed in skeletal muscle. This led to the idea of AMPK{gamma}3 being involved in glycogen levels in skeletal muscle. Evidence for such a causative link has never been provided. ResultsWe studied newly obtained muscle biopsies from three human carriers of the AMPK{gamma}3 R225W mutation and matched controls and we developed a novel knock-in mouse model carrying the AMPK{gamma}3 R225W mutation (KI HOM). In all three human pairs, the basal AMPK{gamma}3-associated activity was reduced when assayed in the absence of exogenous AMP. No difference was observed when assayed under AMP saturation, which was supported by findings in muscle of KI HOM mice. Furthermore, the well-established stimulatory effects of AICAR/muscle contraction on AMPK{gamma}3-associated activity were absent in muscle from KI HOM mice. Muscle glycogen levels were not affected by the mutation in human carriers or in KI HOM mice. ConclusionsThe AMPK{gamma}3 R225W mutation does not impact AMPK-associated activity in mature human skeletal muscle and the mutation is not linked to glycogen accumulation. The R225W mutation ablates AMPK{gamma}3-associated activation by AICAR/muscle contractions, presumably through loss of nucleotide binding.