Sci Adv. 2025 Aug 15. 11(33): eadr6012
Roopasingam Kugapreethan,
Sheik Nadeem Elahee Doomun,
Joanna Sacharz,
Ann E Frazier,
Tanavi Sharma,
Yau Chung Low,
Shuai Nie,
Michael G Leeming,
Linden Muellner-Wong,
Karena Last,
Tegan Stait,
David P De Souza,
David R Thorburn,
Malcolm J McConville,
David A Stroud.
During acute oxidative phosphorylation (OXPHOS) dysfunction, reversal of succinate dehydrogenase (complex II) maintains the redox state of the Coenzyme Q (Q)-pool by using fumarate as terminal electron acceptor in certain tissues and cell lines. We identified the action of SDHAF2 protein, a complex II assembly factor, as critical for metabolic adaptation during complex III dysfunction in HEK293T cells. SDHAF2 loss during complex III inhibition led to a net reductive TCA cycle from loss of succinate oxidation, loss of SDHA active site-derived reactive oxygen species (ROS) signaling, insufficient glycolytic adaptation, and a severe growth impairment. Glycolysis adapted cells, however, did not accumulate SDHAF2 upon Q-pool stress, exhibited a net reductive TCA cycle and mild growth phenotypes regardless of SDHAF2 presence. Thus, our study reveals how complex II assembly controls a balance between dynamics of TCA cycle directionality, protection from Q-pool stress, and an ability to use ROS-meditated signaling to overcome acute OXPHOS dysfunction in cells reliant on mitochondrial respiration.