Davis, Patrick R.Miller, Spencer G.Verhoeven, Nicolas A.Morgan, Joshua S.Tulis, David A.Witczak, Carol A.Brault, Jeffrey J.2023-02-022023-02-022020-07Davis PR, Miller SG, Verhoeven NA, et al. Increased AMP deaminase activity decreases ATP content and slows protein degradation in cultured skeletal muscle. Metabolism. 2020;108:154257. doi:10.1016/j.metabol.2020.154257https://hdl.handle.net/1805/31089Background: Protein degradation is an energy-dependent process, requiring ATP at multiple steps. However, reports conflict as to the relationship between intracellular energetics and the rate of proteasome-mediated protein degradation. Methods: To determine whether the concentration of the adenine nucleotide pool (ATP + ADP + AMP) affects protein degradation in muscle cells, we overexpressed an AMP degrading enzyme, AMP deaminase 3 (AMPD3), via adenovirus in C2C12 myotubes. Results: Overexpression of AMPD3 resulted in a dose- and time-dependent reduction of total adenine nucleotides (ATP, ADP and AMP) without increasing the ADP/ATP or AMP/ATP ratios. In agreement, the reduction of total adenine nucleotide concentration did not result in increased Thr172 phosphorylation of AMP-activated protein kinase (AMPK), a common indicator of intracellular energetic state. Furthermore, LC3 protein accumulation and ULK1 (Ser 555) phosphorylation were not induced. However, overall protein degradation and ubiquitin-dependent proteolysis were slowed by overexpression of AMPD3, despite unchanged content of several proteasome subunit proteins and proteasome activity in vitro under standard conditions. Conclusions: Altogether, these findings indicate that a physiologically relevant decrease in ATP content, without a concomitant increase in ADP or AMP, is sufficient to decrease the rate of protein degradation and activity of the ubiquitin-proteasome system in muscle cells. This suggests that adenine nucleotide degrading enzymes, such as AMPD3, may be a viable target to control muscle protein degradation and perhaps muscle mass.en-USPublisher PolicyAdenine nucleotidesC2C12 myoblastsEnergeticsProtein degradationUbiquitin-proteasome systemArticle