bims-mitper Biomed News
on Mitochondrial Permeabilization
Issue of 2022‒11‒20
ten papers selected by
Bradley Irizarry
Thomas Jefferson University

  1. iScience. 2022 Nov 18. 25(11): 105447
      An increase in permeability of the mitochondrial inner membrane, mitochondrial permeability transition (PT), is the central event responsible for cell death and tissue damage in conditions such as stroke and heart attack. PT is caused by the cyclosporin A (CSA)-dependent calcium-induced pore, the permeability transition pore (PTP). The molecular details of PTP are incompletely understood. We utilized holographic and fluorescent microscopy to assess the contribution of ATP synthase and adenine nucleotide translocator (ANT) toward PTP. In cells lacking either ATP synthase or ANT, we observed CSA-sensitive membrane depolarization, but not high-conductance PTP. In wild-type cells, calcium-induced CSA-sensitive depolarization preceded opening of PTP, which occurred only after nearly complete mitochondrial membrane depolarization. We propose that both ATP synthase and ANT are required for high-conductance PTP but not depolarization, which presumably occurs through activation of the low-conductance PT, which has a molecular nature that is different from both complexes.
    Keywords:  Cell biology; Functional aspects of cell biology; Molecular biology
  2. EMBO J. 2022 Nov 18. e112920
      Mitochondria are key signaling hubs for innate immune responses. In this issue, Wu et al (2022) report that remodeling of the outer mitochondrial membrane by the linear ubiquiting chain assembly complex (LUBAC) facilitates transport of activated NF-κB to the nucleus in response to TNF signaling.
  3. Cell Death Differ. 2022 Nov 14.
      Apoptosis is a regulated cellular pathway that ensures that a cell dies in a structured fashion to prevent negative consequences for the tissue or the organism. Dysfunctional apoptosis is a hallmark of numerous pathologies, and treatments for various diseases are successful based on the induction of apoptosis. Under homeostatic conditions, apoptosis is a non-inflammatory event, as the activation of caspases ensures that inflammatory pathways are disabled. However, there is an increasing understanding that under specific conditions, such as caspase inhibition, apoptosis and the apoptotic machinery can be re-wired into a process which is inflammatory. In this review we discuss how the death receptor and mitochondrial pathways of apoptosis can activate inflammation. Furthermore, we will highlight how cell death due to mitotic stress might be a special case when it comes to cell death and the induction of inflammation.
  4. EMBO Rep. 2022 Nov 16. e51800
      Cyclic GMP-AMP synthase (cGAS) is a double-stranded DNA (dsDNA) sensor that functions in the innate immune system. Upon binding dsDNA, cGAS and dsDNA form phase-separated condensates in which cGAS catalyzes the synthesis of 2'3'-cyclic GMP-AMP that subsequently triggers a STING-dependent, type I interferon (IFN-I) response. Here, we show that cytoplasmic RNAs regulate cGAS activity. We discover that RNAs do not activate cGAS but rather promote phase separation of cGAS in vitro. In cells, cGAS colocalizes with RNA and forms complexes with RNA. In the presence of cytoplasmic dsDNA, RNAs colocalize with phase-separated condensates of cGAS and dsDNA. Further in vitro assays showed that RNAs promote the formation of cGAS-containing phase separations and enhance cGAS activity when the dsDNA concentration is low. Cotransfection of RNA with a small amount of dsDNA into THP1 cells significantly enhances the production of the downstream signaling molecule interferon beta (IFNB). This enhancement can be blocked by a cGAS-specific inhibitor. Thus, cytoplasmic RNAs could regulate cGAS activity by modulating the formation of cGAS-containing condensates.
    Keywords:  RNA; cGAS; innate immunity; phase separation; regulation
  5. Int Immunopharmacol. 2022 Nov 11. pii: S1567-5769(22)00917-1. [Epub ahead of print]113(Pt B): 109432
      Occupational medicamentose-like dermatitis due to trichloroethylene (OMDT) is a systemic allergic disease similar to drug eruption-like dermatitis that occurs in workers after exposure to trichloroethylene. In addition to skin and mucosa damage, OMDT patients often accompanied by severe multiorgan damage, including kidney injury. However, the mechanism remains unclear. The aim of our research was to explore the role of increased cytosolic mitochondrial DNA in the activation of cGAS-STING signaling and in the kidney injury of trichloroethylene sensitization mice using a mouse model and an in vitro model. By analyzing the kidneys of TCE-sensitized mice, we found obvious tubular mitochondrial damage, decreased expression of COX-IV and TFAM proteins and increased cytosolic mitochondrial DNA in TCE-sensitized-positive mice. Further study found that cytosolic mitochondrial DNA activated cGAS-STING signaling, resulting in the nuclear translocation of P-IRF3 and NF-κB P65 and the transcription and synthesis of type Ⅰ interferons and cytokines, which ultimately led to immune kidney injury in trichloroethylene-sensitized mice. Interestingly, pretreatment with C-176, a STING inhibitor, not only blocked the nuclear translocation of P-IRF3 and NF-κB P65, but also alleviated the kidney injury induced by TCE sensitization. Consistently, in vitro studies also found that mitochondrial DNA pretreatment can activate the cGAS-STING pathway, causing the nuclear translocation of P-IRF3 and NF-κB P65 and the transcription of type Ⅰ interferons and cytokines in HK-2 cells. Overall, our results suggested that cytosolic mitochondrial DNA plays an important role in the activation of the cGAS-STING pathway and TCE sensitization-induced immune kidney injury.
    Keywords:  Immune kidney injury; Mitochondrial DNA; OMDT; Trichloroethylene sensitization; cGAS-STING
  6. PeerJ. 2022 ;10 e14350
      Mitochondria play essential cellular roles in Adenosine triphosphate (ATP) synthesis, calcium homeostasis, and metabolism, but these vital processes have potentially deadly side effects. The production of the reactive oxygen species (ROS) and the aggregation of misfolded mitochondrial proteins can lead to severe mitochondrial damage and even cell death. The accumulation of mitochondrial damage is strongly implicated in aging and several incurable diseases, including neurodegenerative disorders and cancer. To oppose this, metazoans utilize a variety of quality control strategies, including the degradation of the damaged mitochondrial proteins by the mitochondrial-resident proteases of the ATPase Associated with the diverse cellular Activities (AAA+) family. This mini-review focuses on the quality control mediated by the mitochondrial-resident proteases of the AAA+ family used to combat the accumulation of damaged mitochondria and on how the failure of this mitochondrial quality control contributes to diseases.
    Keywords:  AAA+ Protease; Mitochondria in neurological disorders; Mitochondrial Translation; Mitochondrial Unfolded Protein Response; Mitochondrial quality control
  7. Cell Death Differ. 2022 Nov 14.
      How BAK and BAX induce mitochondrial outer membrane (MOM) permeabilization (MOMP) during apoptosis is incompletely understood. Here we have used molecular dynamics simulations, surface plasmon resonance, and assays for membrane permeabilization in vitro and in vivo to assess the structure and function of selected BAK subdomains and their derivatives. Results of these studies demonstrate that BAK helical regions α5 and α6 bind the MOM lipid cardiolipin. While individual peptides corresponding to these helical regions lack the full biological activity of BAK, tandem peptides corresponding to α4-α5, α5-α6, or α6-α7/8 can localize exogenous proteins to mitochondria, permeabilize liposomes composed of MOM lipids, and cause MOMP in the absence of the remainder of the BAK protein. Importantly, the ability of these tandem helices to induce MOMP under cell-free conditions is diminished by mutations that disrupt the U-shaped helix-turn-helix structure of the tandem peptides or decrease their lipid binding. Likewise, BAK-induced apoptosis in intact cells is diminished by CLS1 gene interruption, which decreases mitochondrial cardiolipin content, or by BAK mutations that disrupt the U-shaped tandem peptide structure or diminish lipid binding. Collectively, these results suggest that BAK structural rearrangements during apoptosis might mobilize helices involved in specific protein-lipid interactions that are critical for MOMP.
  8. Front Cell Dev Biol. 2022 ;10 1044672
      Mitochondrial dysfunction is strongly implicated in neurodegenerative diseases including age-related macular degeneration (AMD), which causes irreversible blindness in over 50 million older adults worldwide. A key site of insult in AMD is the retinal pigment epithelium (RPE), a monolayer of postmitotic polarized cells that performs essential functions for photoreceptor health and vision. Recent studies from our group and others have identified several features of mitochondrial dysfunction in AMD including mitochondrial fragmentation and bioenergetic defects. While these studies provide valuable insight at fixed points in time, high-resolution, high-speed live imaging is essential for following mitochondrial injury in real time and identifying disease mechanisms. Here, we demonstrate the advantages of live imaging to investigate RPE mitochondrial dynamics in cell-based and mouse models. We show that mitochondria in the RPE form extensive networks that are destroyed by fixation and discuss important live imaging considerations that can interfere with accurate evaluation of mitochondrial integrity such as RPE differentiation status and acquisition parameters. Our data demonstrate that RPE mitochondria show localized heterogeneities in membrane potential and ATP production that could reflect focal changes in metabolism and oxidative stress. Contacts between the mitochondria and organelles such as the ER and lysosomes mediate calcium flux and mitochondrial fission. Live imaging of mouse RPE flatmounts revealed a striking loss of mitochondrial integrity in albino mouse RPE compared to pigmented mice that could have significant functional consequences for cellular metabolism. Our studies lay a framework to guide experimental design and selection of model systems for evaluating mitochondrial health and function in the RPE.
    Keywords:  RPE; live imaging; mitochondria; pigmented and albino mice; retina
  9. DNA (Basel). 2022 Jun;2(2): 131-148
      In the course of its short history, mitochondrial DNA (mtDNA) has made a long journey from obscurity to the forefront of research on major biological processes. mtDNA alterations have been found in all major disease groups, and their significance remains the subject of intense research. Despite remarkable progress, our understanding of the major aspects of mtDNA biology, such as its replication, damage, repair, transcription, maintenance, etc., is frustratingly limited. The path to better understanding mtDNA and its role in cells, however, remains torturous and not without errors, which sometimes leave a long trail of controversy behind them. This review aims to provide a brief summary of our current knowledge of mtDNA and highlight some of the controversies that require attention from the mitochondrial research community.
    Keywords:  extramitochondrial mtDNA; mitochondrial theory of aging; mtDNA; mtDNA repair; mtDNA replication; mtDNA transcription
  10. Brain Res Bull. 2022 Nov 10. pii: S0361-9230(22)00316-1. [Epub ahead of print]
      Caspases, a family of cysteine proteases is a renowned regulator of apoptosis. Members of this family are responsible for the proteolytic dismantling of numerous cellular structures. Apart from apoptosis, caspases remarkably contribute to a diverse range of molecular processes. Being the imperative members of several cellular cascades their abnormal activation/deactivation has severe implications and also leads to various diseased conditions. Similar aberrant activation of caspases is one of the several causes of neuropathologies associated with Alzheimer's disease (AD), a form of dementia severely affecting neuropsychiatric and cognitive functions. Emerging studies are providing deeper insights into the mechanisms of caspase action in the progression of AD. Current article is an attempt to review these studies and present the action mechanisms of different mammalian caspases in the advancement of AD associated neuropathologies.
    Keywords:  Alzheimer disease; Amyloid beta; Apoptosis; Caspases; Microglial activation; Tau