bims-smemid Biomed News
on Stress metabolism in mitochondrial dysfunction
Issue of 2024–11–10
two papers selected by
Deepti Mudartha, The International Institute of Molecular Mechanisms and Machines
  1. Cellular ATP demand creates metabolically distinct subpopulations of mitochondria.
  2. Methods to analyze the mitochondrial unfolded protein response (UPRmt).
  1. Nature. 2024 Nov 06.
    Cellular ATP demand creates metabolically distinct subpopulations of mitochondria.
    Keun Woo Ryu, Tak Shun Fung, Daphne C Baker, Michelle Saoi, Jinsung Park, Christopher A Febres-Aldana, Rania G Aly, Ruobing Cui, Anurag Sharma, Yi Fu, Olivia L Jones, Xin Cai, H Amalia Pasolli, Justin R Cross, Charles M Rudin, Craig B Thompson.
      Mitochondria serve a crucial role in cell growth and proliferation by supporting both ATP synthesis and the production of macromolecular precursors. Whereas oxidative phosphorylation (OXPHOS) depends mainly on the oxidation of intermediates from the tricarboxylic acid cycle, the mitochondrial production of proline and ornithine relies on reductive synthesis1. How these competing metabolic pathways take place in the same organelle is not clear. Here we show that when cellular dependence on OXPHOS increases, pyrroline-5-carboxylate synthase (P5CS)-the rate-limiting enzyme in the reductive synthesis of proline and ornithine-becomes sequestered in a subset of mitochondria that lack cristae and ATP synthase. This sequestration is driven by both the intrinsic ability of P5CS to form filaments and the mitochondrial fusion and fission cycle. Disruption of mitochondrial dynamics, by impeding mitofusin-mediated fusion or dynamin-like-protein-1-mediated fission, impairs the separation of P5CS-containing mitochondria from mitochondria that are enriched in cristae and ATP synthase. Failure to segregate these metabolic pathways through mitochondrial fusion and fission results in cells either sacrificing the capacity for OXPHOS while sustaining the reductive synthesis of proline, or foregoing proline synthesis while preserving adaptive OXPHOS. These findings provide evidence of the key role of mitochondrial fission and fusion in maintaining both oxidative and reductive biosyntheses in response to changing nutrient availability and bioenergetic demand.
    DOI:  https://doi.org/10.1038/s41586-024-08146-w
  2. Methods Enzymol. 2024 ;pii: S0076-6879(24)00365-3. [Epub ahead of print]707 543-564
    Methods to analyze the mitochondrial unfolded protein response (UPRmt).
    Avijit Mallick, Cole M Haynes.
      The mitochondrial unfolded protein response (UPRmt) is a mitochondria-to-nuclear signaling pathway that mediates the transcription of genes required to maintain mitochondrial function during development as well as during aging. In this chapter, we describe the approaches and techniques that we and others have used to elucidate the mechanism(s) by which cells detect mitochondrial stress or dysfunction and communicate with the nucleus to induce transcription of a protective stress response. We also describe approaches to evaluate the impact of UPRmt activation on mitochondrial function and mitochondrial biogenesis including imaging-based approaches as well as approaches to evaluate mitochondrial genome (mtDNA) copy number.
    Keywords:  Deleterious mtDNA heteroplasmy; Mito-nuclear communication; Mitochondrial biogenesis; Mitochondrial unfolded protein response; Molecular chaperones; MtDNA replication
    DOI:  https://doi.org/10.1016/bs.mie.2024.07.029
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