NO production results in suspension-induced muscle atrophy through dislocation of neuronal NOS
Naoki Suzuki, Norio Motohashi, Akiyoshi Uezumi, So-ichiro Fukada, Tetsuhiko Yoshimura, Yasuto Itoyama, Masashi Aoki, Yuko Miyagoe-Suzuki, Shin’ichi Takeda
Naoki Suzuki, Norio Motohashi, Akiyoshi Uezumi, So-ichiro Fukada, Tetsuhiko Yoshimura, Yasuto Itoyama, Masashi Aoki, Yuko Miyagoe-Suzuki, Shin’ichi Takeda
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Research Article

NO production results in suspension-induced muscle atrophy through dislocation of neuronal NOS

Abstract

Forkhead box O (Foxo) transcription factors induce muscle atrophy by upregulating the muscle-specific E3 ubiquitin ligases MuRF-1 and atrogin-1/MAFbx, but other than Akt, the upstream regulators of Foxos during muscle atrophy are largely unknown. To examine the involvement of the dystrophin glycoprotein complex (DGC) in regulation of Foxo activities and muscle atrophy, we analyzed the expression of DGC members during tail suspension, a model of unloading-induced muscle atrophy. Among several DGC members, only neuronal NOS (nNOS) quickly dislocated from the sarcolemma to the cytoplasm during tail suspension. Electron paramagnetic resonance spectrometry revealed production of NO in atrophying muscle. nNOS-null mice showed much milder muscle atrophy after tail suspension than did wild-type mice. Importantly, nuclear accumulation of dephosphorylated Foxo3a was not evident in nNOS-null muscle, and neither MuRF-1 nor atrogin-1/MAFbx were upregulated during tail suspension. Furthermore, an nNOS-specific inhibitor, 7-nitroindazole, significantly prevented suspension-induced muscle atrophy. The NF-κB pathway was activated in both wild-type and nNOS-null muscle during tail suspension. We also show that nNOS was involved in the mechanism of denervation-induced atrophy. We conclude that nNOS/NO mediates muscle atrophy via regulation of Foxo transcription factors and is a new therapeutic target for disuse-induced muscle atrophy.

Authors

Naoki Suzuki, Norio Motohashi, Akiyoshi Uezumi, So-ichiro Fukada, Tetsuhiko Yoshimura, Yasuto Itoyama, Masashi Aoki, Yuko Miyagoe-Suzuki, Shin’ichi Takeda

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Figure 3

Measurement of NO in muscle and NOS activity during tail suspension.

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Measurement of NO in muscle and NOS activity during tail suspension. (A)...
(A) EPR spectra of the NO adduct of Fe-MGD complex observed in skeletal muscle at room temperature. The NO-trapping agent was injected 30 minutes before measurements were taken. The EPR spectra of ground control and tail-suspended wild-type and nNOS-null mice were shown. Each spectrum represents the average of 5 accumulations. The signal height was obtained by measuring the peak-to-peak height of the lower field side signal (vertical arrows) in the 3-line spectrum. (B) NO levels of the skeletal muscle with and without tail suspension for 7 or 14 days were analyzed in EPR spectrometry (n = 6; *P < 0.05, Mann-Whitney). Note that NO level in muscle is elevated in wild-type tail-suspended mice at 14 days but not in nNOS-null tail-suspended mice. 7NI was used as a selective nNOS inhibitor. (C) NOS catalytic activity in soluble and particulate fractions (n = 5; Mann-Whitney). [3H]-citrulline, converted from [3H]-arginine in vitro by NOS, was quantified by liquid scintillation spectroscopy. Note higher NOS activities in the soluble fraction than in the particulate fraction for suspended wild-type mice.