bims-mikwok 2022-09-11 papers

Issue of 2022‒09‒11
three papers selected by
Avinash N. Mukkala, University of Toronto

J Cell Biol. 2022 Oct 03. pii: e202205104. [Epub ahead of print]221(10):

DarT-mediated mtDNA damage induces dynamic reorganization and selective segregation of mitochondria.

Nitish Dua, Akshaya Seshadri, Anjana Badrinarayanan.

Mitochondria are dynamic organelles that play essential roles in cell growth and survival. Processes of fission and fusion are critical for the distribution, segregation, and maintenance of mitochondria and their genomes (mtDNA). While recent work has revealed the significance of mitochondrial organization for mtDNA maintenance, the impact of mtDNA perturbations on mitochondrial dynamics remains less understood. Here, we develop a tool to induce mitochondria-specific DNA damage using a mitochondrial-targeted base modifying bacterial toxin, DarT. Following damage, we observe dynamic reorganization of mitochondrial networks, likely driven by mitochondrial dysfunction. Changes in the organization are associated with the loss of mtDNA, independent of mitophagy. Unexpectedly, perturbation to exonuclease function of mtDNA replicative polymerase, Mip1, results in rapid loss of mtDNA. Our data suggest that, under damage, partitioning of defective mtDNA and organelle are de-coupled, with emphasis on mitochondrial segregation independent of its DNA. Together, our work underscores the importance of genome maintenance on mitochondrial function, which can act as a modulator of organelle organization and segregation.

DOI: https://doi.org/10.1083/jcb.202205104

Biochim Biophys Acta Bioenerg. 2022 Sep 02. pii: S0005-2728(22)00384-X. [Epub ahead of print] 148914

Non-conventional mitochondrial permeability transition: Its regulation by mitochondrial dynamics.

Yisang Yoon, Hakjoo Lee, Marilen Federico, Shey-Shing Sheu.

Mitochondrial permeability transition (MPT) is a phenomenon that the inner mitochondrial membrane (IMM) loses its selective permeability, leading to mitochondrial dysfunction and cell injury. Electrophysiological evidence indicates the presence of a mega-channel commonly called permeability transition pore (PTP) whose opening is responsible for MPT. However, the molecular identity of the PTP is still under intensive investigations and debates, although cyclophilin D that is inhibited by cyclosporine A (CsA) is the established regulatory component of the PTP. PTP can also open transiently and functions as a rapid mitochondrial Ca2+ releasing mechanism. Mitochondrial fission and fusion, the main components of mitochondrial dynamics, control the number and size of mitochondria, and have been shown to play a role in regulating MPT directly or indirectly. Studies by us and others have indicated the potential existence of a form of transient MPT that is insensitive to CsA. This "non-conventional" MPT is regulated by mitochondrial dynamics and may serve a protective role possibly by decreasing the susceptibility for a frequent or sustained PTP opening; hence, it may have a therapeutic value in many disease conditions involving MPT.

Keywords: Mitochondrial dynamics; Mitochondrial permeability transition; Non-conventional mitochondrial permeability transition; Permeability transition pore

DOI: https://doi.org/10.1016/j.bbabio.2022.148914

iScience. 2022 Sep 16. 25(9): 104923

STAT6 in mitochondrial outer membrane impairs mitochondrial fusion by inhibiting MFN2 dimerization.

Hyunmi Kim, Soo Jung Park, Ilo Jou.

Although it is reported that mitochondria-localized nuclear transcription factors (TFs) regulate mitochondrial processes such as apoptosis and mitochondrial transcription/respiration, the functions and mechanisms of mitochondrial dynamics regulated by mitochondria-localized nuclear TFs are yet to be fully characterized. Here, we identify STAT6 as a mitochondrial protein that is localized in the outer membrane of mitochondria (OMM). STAT6 in OMM inhibits mitochondrial fusion by blocking MFN2 dimerization. This implies that STAT6 has a critical role in mitochondrial dynamics. Moreover, mitochondrial accumulation of STAT6 in response to hypoxic conditions reveals that STAT6 is a regulator of mitochondrial processes including fusion/fission mechanisms.

Keywords: Biological sciences; Molecular biology; Molecular interaction; Natural sciences

DOI: https://doi.org/10.1016/j.isci.2022.104923