bims-mitpro Biomed News
on Mitochondrial proteostasis
Issue of 2023–11–12
seven papers selected by
Andreas Kohler, Umeå University
  1. Mitochondrial AAA+ proteases.
  2. Cristae formation is a mechanical buckling event controlled by the inner mitochondrial membrane lipidome.
  3. Mitochondrial Inherited Disorders and their Correlation with Neurodegenerative Diseases.
  4. Aggregation of alpha-synuclein disrupts mitochondrial metabolism and induce mitophagy via cardiolipin externalization.
  5. Pharmacologic activation of a compensatory integrated stress response kinase promotes mitochondrial remodeling in PERK-deficient cells.
  6. FUNDC1 collaborates with PINK1 in regulating mitochondrial Fission and compensating for PINK1 deficiency.
  7. Modulating mitochondrial calcium channels (TRPM2/MCU/NCX) as a therapeutic strategy for neurodegenerative disorders.
  1. Enzymes. 2023 ;pii: S1874-6047(23)00028-8. [Epub ahead of print]54 205-220
    Mitochondrial AAA+ proteases.
    Yuichi Matsushima.
      Mitochondria are multifunctional organelles that play a central role in a wide range of life-sustaining tasks in eukaryotic cells, including adenosine triphosphate (ATP) production, calcium storage and coenzyme generation pathways such as iron-sulfur cluster biosynthesis. The wide range of mitochondrial functions is carried out by a diverse array of proteins comprising approximately 1500 proteins or polypeptides. Degradation of these proteins is mainly performed by four AAA+ proteases localized in mitochondria. These AAA+ proteases play a quality control role in degrading damaged or misfolded proteins and perform various other functions. This chapter describes previously identified roles for these AAA+ proteases that are localized in the mitochondria of animal cells.
    Keywords:  AAA+ protease; ClpXP; Lon; Mitochondria; i-AAA; m-AAA
    DOI:  https://doi.org/10.1016/bs.enz.2023.09.002
  2. EMBO J. 2023 Nov 07. e114054
    Cristae formation is a mechanical buckling event controlled by the inner mitochondrial membrane lipidome.
    Kailash Venkatraman, Christopher T Lee, Guadalupe C Garcia, Arijit Mahapatra, Daniel Milshteyn, Guy Perkins, Keun-Young Kim, H Amalia Pasolli, Sebastien Phan, Jennifer Lippincott-Schwartz, Mark H Ellisman, Padmini Rangamani, Itay Budin.
      Cristae are high-curvature structures in the inner mitochondrial membrane (IMM) that are crucial for ATP production. While cristae-shaping proteins have been defined, analogous lipid-based mechanisms have yet to be elucidated. Here, we combine experimental lipidome dissection with multi-scale modeling to investigate how lipid interactions dictate IMM morphology and ATP generation. When modulating phospholipid (PL) saturation in engineered yeast strains, we observed a surprisingly abrupt breakpoint in IMM topology driven by a continuous loss of ATP synthase organization at cristae ridges. We found that cardiolipin (CL) specifically buffers the inner mitochondrial membrane against curvature loss, an effect that is independent of ATP synthase dimerization. To explain this interaction, we developed a continuum model for cristae tubule formation that integrates both lipid and protein-mediated curvatures. This model highlighted a snapthrough instability, which drives IMM collapse upon small changes in membrane properties. We also showed that cardiolipin is essential in low-oxygen conditions that promote PL saturation. These results demonstrate that the mechanical function of cardiolipin is dependent on the surrounding lipid and protein components of the IMM.
    Keywords:  cardiolipin; cristae; lipids; mechanics; mitochondria
    DOI:  https://doi.org/10.15252/embj.2023114054
  3. Endocr Metab Immune Disord Drug Targets. 2023 Nov 01.
    Mitochondrial Inherited Disorders and their Correlation with Neurodegenerative Diseases.
    Sofjana Gushi, Dr Vasileios Balis PhD Mrsb.
      Mitochondria are essential organelles for the survival of a cell because they produce energy. The cells that need more mitochondria are neurons because they perform a variety of tasks that are necessary to support brain homeostasis. The build-up of abnormal proteins in neurons, as well as their interactions with mitochondrial proteins, or MAM proteins, cause serious health issues. As a result, mitochondrial functions, such as mitophagy, are impaired, resulting in the disorders described in this review. They are also due to mtDNA mutations, which alter the heritability of diseases. The topic of disease prevention, as well as the diagnosis, requires further explanation and exploration. Finally, there are treatments that are quite promising, but more detailed research is needed.
    Keywords:  Mitochondria; diagnosis; heritability.; mitochondrial DNA; mitophagy; neurodegeneration; prevention; treatment
    DOI:  https://doi.org/10.2174/0118715303250271231018103202
  4. Cell Death Dis. 2023 Nov 10. 14(11): 729
    Aggregation of alpha-synuclein disrupts mitochondrial metabolism and induce mitophagy via cardiolipin externalization.
    Olivier Lurette, Rebeca Martín-Jiménez, Mehtab Khan, Razan Sheta, Stéphanie Jean, Mia Schofield, Maxime Teixeira, Raquel Rodriguez-Aller, Isabelle Perron, Abid Oueslati, Etienne Hebert-Chatelain.
      Accumulation of α-synuclein aggregates in the substantia nigra pars compacta is central in the pathophysiology of Parkinson's disease, leading to the degeneration of dopaminergic neurons and the manifestation of motor symptoms. Although several PD models mimic the pathological accumulation of α-synuclein after overexpression, they do not allow for controlling and monitoring its aggregation. We recently generated a new optogenetic tool by which we can spatiotemporally control the aggregation of α-synuclein using a light-induced protein aggregation system. Using this innovative tool, we aimed to characterize the impact of α-synuclein clustering on mitochondria, whose activity is crucial to maintain neuronal survival. We observed that aggregates of α-synuclein transiently and dynamically interact with mitochondria, leading to mitochondrial depolarization, lower ATP production, mitochondrial fragmentation and degradation via cardiolipin externalization-dependent mitophagy. Aggregation of α-synuclein also leads to lower mitochondrial content in human dopaminergic neurons and in mouse midbrain. Interestingly, overexpression of α-synuclein alone did not induce mitochondrial degradation. This work is among the first to clearly discriminate between the impact of α-synuclein overexpression and aggregation on mitochondria. This study thus represents a new framework to characterize the role of mitochondria in PD.
    DOI:  https://doi.org/10.1038/s41419-023-06251-8
  5. Cell Chem Biol. 2023 Oct 26. pii: S2451-9456(23)00367-7. [Epub ahead of print]
    Pharmacologic activation of a compensatory integrated stress response kinase promotes mitochondrial remodeling in PERK-deficient cells.
    Valerie Perea, Kelsey R Baron, Vivian Dolina, Giovanni Aviles, Grace Kim, Jessica D Rosarda, Xiaoyan Guo, Martin Kampmann, R Luke Wiseman.
      The integrated stress response (ISR) comprises the eIF2α kinases PERK, GCN2, HRI, and PKR, which induce translational and transcriptional signaling in response to diverse insults. Deficiencies in PERK signaling lead to mitochondrial dysfunction and contribute to the pathogenesis of numerous diseases. We define the potential for pharmacologic activation of compensatory eIF2α kinases to rescue ISR signaling and promote mitochondrial adaptation in PERK-deficient cells. We show that the HRI activator BtdCPU and GCN2 activator halofuginone promote ISR signaling and rescue ER stress sensitivity in PERK-deficient cells. However, BtdCPU induces mitochondrial depolarization, leading to mitochondrial fragmentation and activation of the OMA1-DELE1-HRI signaling axis. In contrast, halofuginone promotes mitochondrial elongation and adaptive mitochondrial respiration, mimicking regulation induced by PERK. This shows halofuginone can compensate for deficiencies in PERK signaling and promote adaptive mitochondrial remodeling, highlighting the potential for pharmacologic ISR activation to mitigate mitochondrial dysfunction and motivating the pursuit of highly selective ISR activators.
    Keywords:  ISR; UPR; integrated stress response; pharmacologic activator; stress-responsive signaling pathway; unfolded protein response
    DOI:  https://doi.org/10.1016/j.chembiol.2023.10.006
  6. Biochem Biophys Res Commun. 2023 Nov 01. pii: S0006-291X(23)01304-9. [Epub ahead of print]687 149210
    FUNDC1 collaborates with PINK1 in regulating mitochondrial Fission and compensating for PINK1 deficiency.
    Jing Xu, Zhouyang Deng, Shuai Shang, Caifang Wang, Hailong Han.
      Parkinson's disease is presently thought to have its molecular roots in the alteration of PINK1-mediated mitophagy and mitochondrial dynamics. Finding new suppressors of the pathway is essential for developing cutting-edge treatment approaches. Our study shows that FUNDC1 suppressed PINK1 mutant phenotypes in Drosophila. The restoration of PINK1-deficient phenotypes through FUNDC1 is not reliant on its LC3-binding motif Y (18)L (21) or autophagy-related pathway. Moreover, the absence of Drp1 affects the phenotypic restoration of PINK1 mediated by FUNDC1 in flies. In summary, our findings have unveiled a fresh mechanism through which FUNDC1 compensates for the loss of PINK1, operating independently of autophagy but exerting its influence via interaction with Drp1.
    Keywords:  Autophagy receptor; Drp1; Mitochondrial dynamics; PD; Ubiquitin-independent mitophagy
    DOI:  https://doi.org/10.1016/j.bbrc.2023.149210
  7. Front Neurosci. 2023 ;17 1202167
    Modulating mitochondrial calcium channels (TRPM2/MCU/NCX) as a therapeutic strategy for neurodegenerative disorders.
    Gretchen A Johnson, Raghu R Krishnamoorthy, Dorota L Stankowska.
      Efficient cellular communication is essential for the brain to regulate diverse functions like muscle contractions, memory formation and recall, decision-making, and task execution. This communication is facilitated by rapid signaling through electrical and chemical messengers, including voltage-gated ion channels and neurotransmitters. These messengers elicit broad responses by propagating action potentials and mediating synaptic transmission. Calcium influx and efflux are essential for releasing neurotransmitters and regulating synaptic transmission. Mitochondria, which are involved in oxidative phosphorylation, and the energy generation process, also interact with the endoplasmic reticulum to store and regulate cytoplasmic calcium levels. The number, morphology, and distribution of mitochondria in different cell types vary based on energy demands. Mitochondrial damage can cause excess reactive oxygen species (ROS) generation. Mitophagy is a selective process that targets and degrades damaged mitochondria via autophagosome-lysosome fusion. Defects in mitophagy can lead to a buildup of ROS and cell death. Numerous studies have attempted to characterize the relationship between mitochondrial dysfunction and calcium dysregulation in neurodegenerative diseases such as Alzheimer's Disease, Parkinson's Disease, Huntington's Disease, Amyotrophic lateral sclerosis, spinocerebellar ataxia, and aging. Interventional strategies to reduce mitochondrial damage and accumulation could serve as a therapeutic target, but further research is needed to unravel this potential. This review offers an overview of calcium signaling related to mitochondria in various neuronal cells. It critically examines recent findings, exploring the potential roles that mitochondrial dysfunction might play in multiple neurodegenerative diseases and aging. Furthermore, the review identifies existing gaps in knowledge to guide the direction of future research.
    Keywords:  ROS; aging; calcium; mitochondria; neurodegeneration
    DOI:  https://doi.org/10.3389/fnins.2023.1202167
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