Gain of function AMP?￠????activated protein kinase ???3 3 mutation (AMPK ???3 3 R200Q ) in pig muscle increases glycogen storage regardless of AMPK activation

摘要

Chronic activation of AMP?￠????activated protein kinase (AMPK) increases glycogen content in skeletal muscle. Previously, we demonstrated that a mutation in the ryanodine receptor (RyR1 R615C ) blunts AMPK phosphorylation in longissimus muscle of pigs with a gain of function mutation in the AMPK ???3 3 subunit (AMPK ???3 3 R200Q ); this may decrease the glycogen storage capacity of AMPK ???3 3 R200Q ????+????RyR1 R615C muscle. Therefore, our aim in this study was to utilize our pig model to understand how AMPK ???3 3 R200Q and AMPK activation contribute to glycogen storage and metabolism in muscle. We selected and bred pigs in order to generate offspring with naturally occurring AMPK ???3 3 R200Q , RyR1 R615C , and AMPK ???3 3 R200Q ????+????RyR1 R615C mutations, and also retained wild?￠????type littermates (control). We assessed glycogen content and parameters of glycogen metabolism in longissimus muscle. Regardless of RyR1 R615C , AMPK ???3 3 R200Q increased the glycogen content by approximately 70%. Activity of glycogen synthase (GS) without the allosteric activator glucose 6?￠????phosphate (G6P) was decreased in AMPK ???3 3 R200Q relative to all other genotypes, whereas both AMPK ???3 3 R200Q and AMPK ???3 3 R200Q ????+????RyR1 R615C muscle exhibited increased GS activity with G6P. Increased activity of GS with G6P was not associated with increased abundance of GS or hexokinase 2. However, AMPK ???3 3 R200Q enhanced UDP?￠????glucose pyrophosphorylase 2 (UGP2) expression approximately threefold. Although UGP2 is not generally considered a rate?￠????limiting enzyme for glycogen synthesis, our model suggests that UGP2 plays an important role in increasing flux to glycogen synthase. Moreover, we have shown that the capacity for glycogen storage is more closely related to the AMPK ???3 3 R200Q mutation than activity.