Inducible Rpt3, a Proteasome Component, Knockout in Adult Skeletal Muscle Results in Muscle Atrophy

Yasuo Kitajima; Naoki Suzuki; Kiyoshi Yoshioka; Rumiko Izumi; Maki Tateyama; Yoshitaka Tashiro; Ryosuke Takahashi; Masashi Aoki; Yusuke Ono

doi:10.3389/fcell.2020.00859

Inducible Rpt3, a Proteasome Component, Knockout in Adult Skeletal Muscle Results in Muscle Atrophy

Front Cell Dev Biol. 2020 Sep 2:8:859. doi: 10.3389/fcell.2020.00859. eCollection 2020.

Authors

Yasuo Kitajima¹, Naoki Suzuki^{2

3}, Kiyoshi Yoshioka¹, Rumiko Izumi², Maki Tateyama^{2

4}, Yoshitaka Tashiro⁵, Ryosuke Takahashi⁶, Masashi Aoki², Yusuke Ono¹

Affiliations

¹ Department of Muscle Development and Regeneration, Institute of Molecular Embryology and Genetics, Kumamoto University, Kumamoto, Japan.
² Department of Neurology, Tohoku University School of Medicine, Sendai, Japan.
³ Department of Neurology, Shodo-kai Southern Tohoku General Hospital, Iwanuma, Japan.
⁴ National Hospital Organization Iwate National Hospital, Hanamaki, Japan.
⁵ Department of Aging Neurobiology, National Center for Geriatrics and Gerontology, Obu, Japan.
⁶ Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto University, Kyoto, Japan.

Abstract

The ubiquitin-proteasome system has the capacity to degrade polyubiquitinated proteins and plays an important role in many cellular processes. However, the role of Rpt3, a crucial proteasomal gene, has not been investigated in adult muscles in vivo. Herein, we generated skeletal-muscle-specific Rpt3 knockout mice, in which genetic inactivation of Rpt3 could be induced by doxycycline administration. The Rpt3-knockout mice showed a significant reduction by more than 90% in the expression of Rpt3 in adult muscles. Using this model, we found that proteasome dysfunction in adult muscles resulted in muscle wasting and a decrease in the myofiber size. Immunoblotting analysis showed that the amounts of ubiquitinated proteins were markedly higher in muscles of Rpt3-deficient mice than in those of the control mice. Analysis of the autophagy pathway in the Rpt3-deficient mice showed that the upregulation of LC3II, p62, Atg5, Atg7, and Beclin-1 in protein levels, which supposed to be compensatory proteolysis activation. Our results suggest that the proteasome inhibition in adult muscle severely deteriorates myofiber integrity and results in muscle atrophy.

Keywords: Rpt3; adult skeletal muscle; muscle atrophy; muscle homeostasis; sarcopenia; ubiquitin proteasome system.