bims-smemid 2026-03-01 papers

Nat Struct Mol Biol. 2026 Feb 27.

Stress adaptation of mitochondrial protein import by OMA1-mediated degradation of DNAJC15.

Lara Kroczek, Hendrik Nolte, Yvonne Lasarzewski, Ishita Agrawal, Thibaut Molinié, Daniel Curbelo Piñero, Kathrin Lemke, Elena Rugarli, Thomas Langer.

Mitochondria dynamically adapt to cellular stress to ensure cell survival. The stress-regulated mitochondrial peptidase OMA1 orchestrates these adaptive responses, which limit mitochondrial fusion and promote mitochondrial stress signaling and metabolic rewiring. Here, we show that cellular stress adaptation involves OMA1-mediated regulation of mitochondrial protein import and OXPHOS biogenesis. OMA1 cleaves the mitochondrial chaperone DNAJC15 and promotes its degradation by the m-AAA protease AFG3L2. Loss of DNAJC15 impairs mitochondrial protein import and restricts OXPHOS biogenesis under conditions of mitochondrial dysfunction. Non-imported mitochondrial preproteins accumulate at the endoplasmic reticulum, inducing an unfolded protein response. Our results demonstrate stress-dependent changes in mitochondrial protein import as part of the OMA1-mediated mitochondrial stress response and highlight the interdependence of proteostasis regulation between different organelles.

DOI: https://doi.org/10.1038/s41594-026-01756-0

Mol Cell. 2026 Feb 26. pii: S1097-2765(26)00099-7. [Epub ahead of print]

Aspartate availability drives differential engagement of the malate-aspartate shuttle.

Julia S Brunner, Anna E Bridgeman, Benjamin T Jackson, Sangita Chakraborty, Maider Fagoaga-Eugui, Katrina I Paras, Abigail Xie, Paige K Arnold, Julia Losner, Lydia W S Finley.

The malate-aspartate shuttle is a major electron shuttle that transfers reducing equivalents from the cytosol to the mitochondria, where they can be safely deposited onto the electron transport chain. Nevertheless, many proliferating cells discard reducing equivalents in the form of lactate, raising the question of what factors limit electron shuttle use. Here, we show that aspartate availability determines engagement of the malate-aspartate shuttle. In proliferating cells, increasing aspartate availability enhances use of the malate-aspartate shuttle and increases metabolism of glucose-derived pyruvate in mitochondria, a process that requires regeneration of oxidized electron carriers in the cytosol. During differentiation, elevated flux through the malate-aspartate shuttle cells enables cells to fuel mitochondrial networks from glucose-derived carbon. Engineering aspartate demand reverses this metabolic signature of differentiated cells. Together, these results demonstrate that cell-state-specific demand for aspartate is sufficient to determine use of the malate-aspartate shuttle and drives changing mitochondrial substrate preferences during differentiation.

Keywords: GOT1; GOT2; TCA cycle; Warburg effect; aspartate; differentiation; electron shuttles; malate-aspartate shuttle; metabolism; proliferation

DOI: https://doi.org/10.1016/j.molcel.2026.02.004

medRxiv. 2026 Feb 09. pii: 2026.02.06.26345691. [Epub ahead of print]

Cooperative Architecture of Mitochondrial Proteome Homeostasis.

Patrick Forny, Merima Forny, Andrew J Smith, Andrew Y Sung, Kaixian Liu, David J Pagliarini.

Mitochondria are semi-autonomous organelles whose generation and maintenance demand precise expression, processing, and assembly of >1,000 proteins encoded across two genomes. To explore this cooperativity, we performed multiomic analyses on >200 cell lines harboring mitochondrial gene perturbations, generating >26M molecular measurements. Our data reveal that mitochondrial proteome homeostasis is heavily influenced by post-transcriptional processes. Through nearest neighbor analyses, we reveal diverse protein activities undergirding this regulation, including MDH2's regulation of MT-ND3 transcription via FASTKD1 binding and CLPP's processing of the mitoribosomal assembly factor MALSU1, which we establish as a disease gene. Through entropy analysis, we reveal unexpectedly heterogeneous protein-level variability across complexes and use complexome profiling to identify new complex-specific membership, including C15orf61's association with complex V. We further observe substantial mtDNA copy number variation, notably upon disruption of the disease-related cobalamin biosynthesis protein MMADHC. Together, we establish new protein functions and provide a multilayered view into mitochondrial proteome regulation.
Highlights: Multiomic signatures across perturbations reveal extensive post-transcriptional regulationThe TCA cycle enzyme MDH2 binds FASTKD1 to modulate MT-ND3 transcript levelsMALSU1 is a CLPP protease substrate whose deficiency causes a mitochondrial diseaseC15orf61 binds ATP synthase and negatively regulates its higher order assemblyMMADHC inversely affects mtDNA levels potentially mediated through LONP1.

DOI: https://doi.org/10.64898/2026.02.06.26345691

Nat Commun. 2026 Feb 23.

PRMT5 in mitochondria regulates mtDNA stability through TFAM arginine methylation.

Sangheeta Bhattacharjee, Sayan Das, Banhi Chowdhury, Benu Brata Das.

Protein arginine methyltransferase 5 (PRMT5) catalyzes arginine methylation and regulates cellular functions such as proliferation, RNA splicing, and nuclear DNA damage response. This study uncovers that a fraction of nuclear-encoded PRMT5 localizes to the mitochondria, which is critical for maintaining mitochondrial DNA (mtDNA) homeostasis. PRMT5 knockout (PRMT5-/-) cells had reduced nucleoid counts, diminished mtDNA copy numbers, disrupted the balance of the mitochondrial fission-fusion cycle, impaired mitochondrial plasticity, and nucleoid trafficking. PRMT5-/- cells are hypersensitive to mtDNA-damaging agents, exhibit reduced mitochondrial transcripts, oxidative phosphorylation, and respiratory capacity that triggers cell death. We identify TFAM as a previously unrecognized interacting partner of PRMT5, which catalyzes symmetric dimethylation of TFAM at R82 residue, which is crucial for mtDNA binding and protection. Defective R82-methylation destabilizes TFAM, which is then degraded by LonP1. Together, we establish that PRMT5 is a mitochondrial enzyme and a key regulator of TFAM in mtDNA maintenance.

DOI: https://doi.org/10.1038/s41467-026-69676-7

bioRxiv. 2026 Feb 12. pii: 2026.02.10.705117. [Epub ahead of print]

4,5-dihydroxyhexanoic acid is a robust circulating and urine marker of mitochondrial disease and its severity.

Owen S Skinner, Maria Miranda, Fangcong Dong, Tessa Struhl, Melissa A Walker, Grigorij Schleifer, Matthew T Henke, Jon Clardy, Michio Hirano, Darryl C De Vivo, Eric A Schon, Kristin Engelstad, Stephanie E Siegmund, Catherine Laprise, Christine Des Rosiers, Vamsi K Mootha, Rohit Sharma.

Management of patients with mitochondrial respiratory chain diseases is challenging, in part because of our incomplete understanding of pathogenesis and a lack of biomarkers. Unknown metabolites account for >90% of detected features in modern metabolomics experiments and hold immense untapped promise for new basic and biomedical research. We recently used mass spectrometry-based metabolomics to identify and validate 19 circulating blood-based biomarkers for patients with the mitochondrial DNA (mtDNA) m.3243A>G pathogenic variant, which is the most frequent cause of the mitochondrial disorder MELAS ( m itochondrial e ncephalomyopathy, lactic a cidosis, and s troke-like episodes). However, the most significantly changing biomarker corresponded to an "unknown" metabolite. Here, we combine cheminformatics with analytical chemistry and identify that feature as 4,5-dihydroxyhexanoic acid (4,5-DHHA), a metabolite previously associated with inherited defects of gamma-aminobutyric acid (GABA) catabolism, but with no prior links to mitochondrial respiratory chain disorders. We validate this finding in an independent MELAS cohort and further show that 4,5-DHHA levels correlate with disease severity and are elevated in patients with other forms of mitochondrial disease and sepsis. Furthermore, brain 4,5-DHHA levels were elevated in two genetic mouse models of mitochondrial disease. In vitro and tissue culture experiments indicate that 4,5-DHHA is generated when the GABA catabolite succinic semialdehyde reacts with an intermediate of the pyruvate dehydrogenase reaction and is sensitive to mitochondrial complex I function. Our work identifies 4,5-DHHA as a robust plasma and urine marker of mitochondrial dysfunction in humans and reveals new connections between the respiratory chain and GABA metabolism.
Significance Statement: Inborn errors of the mitochondrial respiratory chain cause severe, progressive diseases, yet effective treatments and biomarkers remain limited. Modern metabolomics detects thousands of molecules in biofluids, but the vast majority are unidentified. In this study, we investigate the most significantly altered blood metabolite in patients with the most common mitochondrial disease - MELAS ( m itochondrial e ncephalomyopathy, lactic a cidosis, and s troke-like episodes) - and identify it as an 4,5-dihydroxyhexanoic acid (4,5-DHHA). We show that 4,5-DHHA is reproducibly elevated and correlates with severity. Levels are increased across multiple mitochondrial disorders as well as in sepsis and rise when respiratory chain function is impaired. These findings establish 4,5-DHHA as a promising biomarker of mitochondrial dysfunction and reveal a link to dysregulated GABA metabolism.

DOI: https://doi.org/10.64898/2026.02.10.705117