bims-resufa 2024-01-14 papers

Issue of 2024‒01‒14
two papers selected by
Gavin McStay, Liverpool John Moores University

Proc Natl Acad Sci U S A. 2024 Jan 16. 121(3): e2307904121

Systems-level analyses dissociate genetic regulators of reactive oxygen species and energy production.

Neal K Bennett, Megan Lee, Adam L Orr, Ken Nakamura.

Respiratory chain dysfunction can decrease ATP and increase reactive oxygen species (ROS) levels. Despite the importance of these metabolic parameters to a wide range of cellular functions and disease, we lack an integrated understanding of how they are differentially regulated. To address this question, we adapted a CRISPRi- and FACS-based platform to compare the effects of respiratory gene knockdown on ROS to their effects on ATP. Focusing on genes whose knockdown is known to decrease mitochondria-derived ATP, we showed that knockdown of genes in specific respiratory chain complexes (I, III, and CoQ10 biosynthesis) increased ROS, whereas knockdown of other low ATP hits either had no impact (mitochondrial ribosomal proteins) or actually decreased ROS (complex IV). Moreover, although shifting metabolic conditions profoundly altered mitochondria-derived ATP levels, it had little impact on mitochondrial or cytosolic ROS. In addition, knockdown of a subset of complex I subunits-including NDUFA8, NDUFB4, and NDUFS8-decreased complex I activity, mitochondria-derived ATP, and supercomplex level, but knockdown of these genes had differential effects on ROS. Conversely, we found an essential role for ether lipids in the dynamic regulation of mitochondrial ROS levels independent of ATP. Thus, our results identify specific metabolic regulators of cellular ATP and ROS balance that may help dissect the roles of these processes in disease and identify therapeutic strategies to independently target energy failure and oxidative stress.

Keywords: ATP; CRISPRi; ROS; metabolism; mitochondria

DOI: https://doi.org/10.1073/pnas.2307904121

J Biol Chem. 2024 Jan 08. pii: S0021-9258(24)00002-4. [Epub ahead of print] 105626

Accessory subunit NDUFB4 participates in mitochondrial complex I supercomplex formation.

Gaganvir Parmar, Claire Fong-McMaster, Chantal Pileggi, David A Patten, Alexanne Cuillerier, Stephanie Myers, Ying Wang, Siegfried Hekimi, Miroslava Cuperlovic-Culf, Mary-Ellen Harper.

Mitochondrial electron transport chain (ETC) complexes organize into supramolecular structures called respiratory supercomplexes (SCs). The role of respiratory SC remains largely unconfirmed despite evidence supporting their necessity for mitochondrial respiratory function. The mechanisms underlying the formation of the I1III2IV1 "respirasome" SC are also not fully understood, further limiting insights into these processes in physiology and diseases, including neurodegeneration and metabolic syndromes. NDUFB4 is a complex I accessory subunit that contains residues that interact with the subunit UQCRC1 from complex III, suggesting that NDUFB4 is integral for I1III2IV1 respirasome integrity. Here, we introduced specific point mutations to Asn24 (N24) and Arg30 (R30) residues on NDUFB4 to decipher the role of I1III2-containing respiratory SCs in cellular metabolism while minimizing the functional consequences to complex I assembly. Our results demonstrate that NDUFB4 point mutations N24A and R30A impair I1III2IV1 respirasome assembly and reduce mitochondrial respiratory flux. Steady-state metabolomics also revealed a global decrease in TCA cycle metabolites, affecting NADH-generating substrates. Taken together, our findings highlight an integral role of NDUFB4 in respirasome assembly and demonstrate the functional significance of SCs in regulating mammalian cell bioenergetics.

Keywords: Mitochondria; NDUFB4; electron transport chain; oxidative phosphorylation; respirasome; steady-state metabolomics; supercomplexes

DOI: https://doi.org/10.1016/j.jbc.2024.105626