The human AMPKγ3 R225W mutation does neither enhance basal AMPKγ3-associated activity nor glycogen in human or mouse skeletal muscle

Abstract Background AMP-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 AMPKγ3 subunit is predominantly expressed in fast-twitch muscle fibers. A human AMPKγ3 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 AMPKγ3 being involved in glycogen levels in skeletal muscle. Evidence for such a causative link has never been provided. Results We studied newly obtained muscle biopsies from three human carriers of the AMPKγ3 R225W mutation and matched controls and we developed a novel knock-in mouse model carrying the AMPKγ3 R225W mutation (KI HOM). In all three human pairs, the basal AMPKγ3-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 AMPKγ3-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. Conclusions The AMPKγ3 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 AMPKγ3-associated activation by AICAR/muscle contractions, presumably through loss of nucleotide binding.