Seungmin Lee ‡ § 1 , Seon-Yong Jeong ¶ 1 , Won-Chung Lim ‡ , Sujeong Kim‡ § , Yong-Yea Park‡ § , Xuejun Sun∥ , Richard J. Youle** and Hyeseong Cho‡ § 2
‡Department of Biochemistry and ¶Department of Medical Genetics, Ajou University School of Medicine and §Graduate School of Molecular Science and Technology, Ajou University, 5 Wonchon-dong, Yeongtong-gu, Suwon 443-721, Korea, ∥Molecular Imaging Facility, Cross Cancer Institute, Edmonton T6G 1Z2, Alberta, Canada, and**Biochemistry Section, SNB, NINDS, National Institutes of Health, Bethesda, Maryland 20892
2 To whom correspondence should be addressed: Dept. of Biochemistry, Ajou University School of Medicine, 5 Wonchon-dong, Yeongtong-gu, Suwon 443-721, Korea.
Abstract
The number and morphology of mitochondria within a cell are precisely regulated by the mitochondrial fission and fusion machinery. The human protein, hFis1, participates in mitochondrial fission by recruiting the Drp1 into the mitochondria. Using short hairpin RNA, we reduced the expression levels of hFis1 in mammalian cells. Cells lacking hFis1 showed sustained elongation of mitochondria and underwent significant cellular morphological changes, including enlargement, flattening, and increased cellular granularity. In these cells, staining for acidic senescence-associated β-galactosidase activity was elevated, and the rate of cell proliferation was greatly reduced, indicating that cells lacking hFis1 undergo senescence-associated phenotypic changes. Reintroduction of the hFis1 gene into hFis1-depleted cells restored mitochondrial fragmentation and suppressed senescence-associated β-galactosidase activity. Moreover, depletion of both hFis1 and OPA1, a critical component of mitochondrial fusion, resulted in extensive mitochondrial fragmentation and markedly rescued cells from senescence-associated phenotypic changes. Intriguingly, sustained elongation of mitochondria was associated with decreased mitochondrial membrane potential, increased reactive oxygen species production, and DNA damage. The data indicate that sustained mitochondrial elongation induces senescence-associated phenotypic changes that can be neutralized by mitochondrial fragmentation. Thus, one of the key functions of mitochondrial fission might be prevention of the sustained extensive mitochondrial elongation that triggers cellular senescence.
1 Both authors contributed equally to this work.