AMP Deaminase 3 Knockout Does Not Reduce Mitochondrial Content Loss in Denervation Induced Inactivity

Abstract

Muscle atrophy leads to decrements in muscle function, partly attributable to reductions in mitochondrial content. One controller of mitochondrial content is AMP‐activated protein kinase (AMPK), which when bound by AMP stimulates PGC‐1α leading to mitochondrial biogenesis, keeping mitochondrial content elevated. AMP Deaminase 1 is the dominant isoform of AMPD in skeletal muscle, yet AMP Deaminase 3 (AMPD3) is robustly upregulated during atrophy conditions in skeletal muscle, and degrades AMP (AMP à IMP + NH3). The purpose of this study is to determine if loss of AMPD3 gene will reduce mitochondrial content loss typically seen with atrophy.MethodsWhole body AMPD3 knock out mice on a C57BL6 strain background were surgically denervated on the left hind limb by removal of ~2 mm of the sciatic nerve. A sham surgery was performed on the right hind limb. Two weeks later, mice were weighed, and extensor digitorum longus (EDL) muscles were collected, weighed, and analyzed for citrate synthase enzyme activity as a measure of mitochondrial content. ANOVA analyses were made between three genotypes (Wild Type ‐ WT, AMPD3 heterozygous ‐ HET, and AMPD3 knockout ‐ KO) of 12 week old littermate female mice (n = 5–8).ResultsBody weights were not significantly different among genotypes (22.9 ± 0.7 g WT, 22.3 ± 0.4 HET, 22.0 ± 1.0 KO)(p = .74). Likewise, non‐denervated EDL muscle weights were not significantly different among genotypes (8.75 ± 0.2 mg WT, 8.47 ± 0.2 HET, 8.77 ± 0.3 KO)(p = 0.67). As expected, surgical denervation for two weeks led to substantial muscle atrophy versus innervated muscle (22.07 ± 1.42% WT, 23.69 ± 4.84 HET, 19.2 ± 3.67 KO), which was not different among genotypes (p = 0.68). Finally, citrate synthase activity in innervated EDL was not significantly different among genotypes (10.27 ± 0.36 WT, 9.3 ± 0.77 HET, 8.93 ± 0.38 KO)(p = 0.16). The decrease in citrate synthase activity due to denervation was not significantly different between wild type and heterozygous, but there was a trend for heterozygous group to have less activity (20.32 ± 2.02% WT, 4.38 ± 5.83 HET)(p = 0.059).ConclusionThese data suggest AMPD3 does not affect mitochondrial content loss in this atrophy model. However, since AMPD3 was not present during development in our AMPD3 knockout mice, we cannot exclude compensation from other AMPD isoforms. Therefore, future research should investigate either inducible muscle specific AMPD3 knockouts or loss of both AMPD1 and AMPD3.Support or Funding InformationNIH R01 AR 070200This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.