UPRmt scales mitochondrial network expansion with protein synthesis via mitochondrial import in Caenorhabditis elegans

• Published in: Nature communications Vol. 12; no. 1; p. 479
• Main Authors: Shpilka, Tomer, Du, YunGuang, Yang, Qiyuan, Melber, Andrew, Uma Naresh, Nandhitha, Lavelle, Joshua, Kim, Sookyung, Liu, Pengpeng, Weidberg, Hilla, Li, Rui, Yu, Jun, Zhu, Lihua Julie, Strittmatter, Lara, Haynes, Cole M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 20-01-2021; Nature Publishing Group; Nature Portfolio
• Subjects: 14; 14/19; 14/28; 14/34; 14/35; 14/63; 38/15; 38/89; 49/88; 49/91; 631/136/334/1582/712; 631/337/470/1981; 631/80/642/333; 631/80/642/333/1465; 64/11; 82/1; 96/106; Caenorhabditis elegans; Cell growth; Humanities and Social Sciences; Imports; Mitochondria; multidisciplinary; Muscles; Nematodes; Protein biosynthesis; Protein folding; Protein synthesis; Protein transport; Proteins; Science; Science (multidisciplinary); Signal transduction; Transcription factors
• DOI: 10.1038/s41467-020-20784-y
• EISSN: 2041-1723

As organisms develop, individual cells generate mitochondria to fulfill physiological requirements. However, it remains unknown how mitochondrial network expansion is scaled to cell growth. The mitochondrial unfolded protein response (UPR
mt
) is a signaling pathway mediated by the transcription factor ATFS-1 which harbors a mitochondrial targeting sequence (MTS). Here, using the model organism
Caenorhabditis elegans
we demonstrate that ATFS-1 mediates an adaptable mitochondrial network expansion program that is active throughout normal development. Mitochondrial network expansion requires the relatively inefficient MTS in ATFS-1, which allows the transcription factor to be responsive to parameters that impact protein import capacity of the mitochondrial network. Increasing the strength of the ATFS-1 MTS impairs UPR
mt
activity by increasing accumulation within mitochondria. Manipulations of TORC1 activity increase or decrease ATFS-1 activity in a manner that correlates with protein synthesis. Lastly, expression of mitochondrial-targeted GFP is sufficient to expand the muscle cell mitochondrial network in an ATFS-1-dependent manner. We propose that mitochondrial network expansion during development is an emergent property of the synthesis of highly expressed mitochondrial proteins that exclude ATFS-1 from mitochondrial import, causing UPR
mt
activation.
The mitochondrial network expands to accommodate cell growth, but how scaling occurs is unclear. Here, the authors show in
C. elegans
that ATFS-1 mitochondrial import is reduced when mitochondrial proteins are highly expressed, activating the unfolded protein response and causing expansion.