bims-nenemi 2024-08-11 papers

bims-nenemi

Biomed News

on Neuroinflammation, neurodegeneration and mitochondria

Issue of 2024‒08‒11
ten papers selected by
Marco Tigano, Thomas Jefferson University

Structures of the mitochondrial single-stranded DNA binding protein with DNA and DNA polymerase γ.
Real-time assessment of mitochondrial DNA heteroplasmy dynamics at the single-cell level.
Multiple unfolded protein response pathways cooperate to link cytosolic dsDNA release to stimulator of interferon gene activation.
Heterozygous de novo dominant negative mutation of REXO2 results in interferonopathy.
PERK-ATAD3A interaction provides a subcellular safe haven for protein synthesis during ER stress.
Real-Time Monitoring of mtDNA Aggregation and Mitophagy Induced by a Fluorescent Platinum Complex in Living Cells.
A Comprehensive Review of Leber Hereditary Optic Neuropathy and Its Association with Multiple Sclerosis-Like Phenotypes Known as Harding's Disease.
Discovery of novel disease-causing mutation in SSBP1 and its correction using adenine base editor to improve mitochondrial function.
Mitochondrial Dysfunction is a Crucial Immune Checkpoint for Neuroinflammation and Neurodegeneration: mtDAMPs in Focus.
Placental mitochondrial impairment and its association with maternal metabolic dysfunction.

Nucleic Acids Res. 2024 Aug 06. pii: gkae670. [Epub ahead of print]

Structures of the mitochondrial single-stranded DNA binding protein with DNA and DNA polymerase γ.

Amanda A Riccio, Jonathan Bouvette, Lars C Pedersen, Shruti Somai, Robert C Dutcher, Mario J Borgnia, William C Copeland.

The mitochondrial single-stranded DNA (ssDNA) binding protein, mtSSB or SSBP1, binds to ssDNA to prevent secondary structures of DNA that could impede downstream replication or repair processes. Clinical mutations in the SSBP1 gene have been linked to a range of mitochondrial disorders affecting nearly all organs and systems. Yet, the molecular determinants governing the interaction between mtSSB and ssDNA have remained elusive. Similarly, the structural interaction between mtSSB and other replisome components, such as the mitochondrial DNA polymerase, Polγ, has been minimally explored. Here, we determined a 1.9-Å X-ray crystallography structure of the human mtSSB bound to ssDNA. This structure uncovered two distinct DNA binding sites, a low-affinity site and a high-affinity site, confirmed through site-directed mutagenesis. The high-affinity binding site encompasses a clinically relevant residue, R38, and a highly conserved DNA base stacking residue, W84. Employing cryo-electron microscopy, we confirmed the tetrameric assembly in solution and capture its interaction with Polγ. Finally, we derived a model depicting modes of ssDNA wrapping around mtSSB and a region within Polγ that mtSSB binds.

DOI: https://doi.org/10.1093/nar/gkae670
EMBO J. 2024 Aug 05.

Real-time assessment of mitochondrial DNA heteroplasmy dynamics at the single-cell level.

Rodaria Roussou, Dirk Metzler, Francesco Padovani, Felix Thoma, Rebecca Schwarz, Boris Shraiman, Kurt M Schmoller, Christof Osman.

  Mitochondrial DNA (mtDNA) is present in multiple copies within cells and is required for mitochondrial ATP generation. Even within individual cells, mtDNA copies can differ in their sequence, a state known as heteroplasmy. The principles underlying dynamic changes in the degree of heteroplasmy remain incompletely understood, due to the inability to monitor this phenomenon in real time. Here, we employ mtDNA-based fluorescent markers, microfluidics, and automated cell tracking, to follow mtDNA variants in live heteroplasmic yeast populations at the single-cell level. This approach, in combination with direct mtDNA tracking and data-driven mathematical modeling reveals asymmetric partitioning of mtDNA copies during cell division, as well as limited mitochondrial fusion and fission frequencies, as critical driving forces for mtDNA variant segregation. Given that our approach also facilitates assessment of segregation between intact and mutant mtDNA, we anticipate that it will be instrumental in elucidating the mechanisms underlying the purifying selection of mtDNA.

Keywords:  Heteroplasmy; Mathematical Modeling; Mitochondria; Mitochondrial Fission; mtDNA

DOI:  https://doi.org/10.1038/s44318-024-00183-5
Front Immunol. 2024 ;15 1358462

Multiple unfolded protein response pathways cooperate to link cytosolic dsDNA release to stimulator of interferon gene activation.

Tiancheng Hu, Yiping Liu, Jeremy Fleck, Cason King, Elaine Schalk, Zhenyu Zhang, Andrew Mehle, Judith A Smith.

  The double-stranded DNA (dsDNA) sensor STING has been increasingly implicated in responses to "sterile" endogenous threats and pathogens without nominal DNA or cyclic di-nucleotide stimuli. Previous work showed an endoplasmic reticulum (ER) stress response, known as the unfolded protein response (UPR), activates STING. Herein, we sought to determine if ER stress generated a STING ligand, and to identify the UPR pathways involved. Induction of IFN-β expression following stimulation with the UPR inducer thapsigargin (TPG) or oxygen glucose deprivation required both STING and the dsDNA-sensing cyclic GMP-AMP synthase (cGAS). Furthermore, TPG increased cytosolic mitochondrial DNA, and immunofluorescence visualized dsDNA punctae in murine and human cells, providing a cGAS stimulus. N-acetylcysteine decreased IFN-β induction by TPG, implicating reactive oxygen species (ROS). However, mitoTEMPO, a mitochondrial oxidative stress inhibitor did not impact TPG-induced IFN. On the other hand, inhibiting the inositol requiring enzyme 1 (IRE1) ER stress sensor and its target transcription factor XBP1 decreased the generation of cytosolic dsDNA. iNOS upregulation was XBP1-dependent, and an iNOS inhibitor decreased cytosolic dsDNA and IFN-β, implicating ROS downstream of the IRE1-XBP1 pathway. Inhibition of the PKR-like ER kinase (PERK) pathway also attenuated cytoplasmic dsDNA release. The PERK-regulated apoptotic factor Bim was required for both dsDNA release and IFN-β mRNA induction. Finally, XBP1 and PERK pathways contributed to cytosolic dsDNA release and IFN-induction by the RNA virus, Vesicular Stomatitis Virus (VSV). Together, our findings suggest that ER stressors, including viral pathogens without nominal STING or cGAS ligands such as RNA viruses, trigger multiple canonical UPR pathways that cooperate to activate STING and downstream IFN-β via mitochondrial dsDNA release.

Keywords:  PERK; STING; VSV; XBP1; mitochondria; unfolded protein response

DOI:  https://doi.org/10.3389/fimmu.2024.1358462
Nat Commun. 2024 Aug 06. 15(1): 6685

Heterozygous de novo dominant negative mutation of REXO2 results in interferonopathy.

Elina Idiiatullina, Mahmoud Al-Azab, Meng Lin, Katja Hrovat-Schaale, Ziyang Liu, Xiaotian Li, Caiqin Guo, Xixi Chen, Yaoying Li, Song Gao, Jun Cui, Wenhao Zhou, Li Liu, Yuxia Zhang, Seth L Masters.

Mitochondrial RNA (mtRNA) in the cytosol can trigger the innate immune sensor MDA5, and autoinflammatory disease due to type I IFN. Here, we show that a dominant negative mutation in the gene encoding the mitochondrial exonuclease REXO2 may cause interferonopathy by triggering the MDA5 pathway. A patient characterized by this heterozygous de novo mutation (p.T132A) presented with persistent skin rash featuring hyperkeratosis, parakeratosis and acanthosis, with infiltration of lymphocytes and eosinophils around small blood vessels. In addition, circulating IgE levels and inflammatory cytokines, including IFNα, are found consistently elevated. Transcriptional analysis highlights a type I IFN gene signature in PBMC. Mechanistically, REXO2 (T132A) lacks the ability to cleave RNA and inhibits the activity of wild-type REXO2. This leads to an accumulation of mitochondrial dsRNA in the cytosol, which is recognized by MDA5, leading to the associated type I IFN gene signature. These results demonstrate that in the absence of appropriate regulation by REXO2, aberrant cellular nucleic acids may accumulate and continuously trigger innate sensors, resulting in an inborn error of immunity.

DOI: https://doi.org/10.1038/s41467-024-50878-w
Science. 2024 Aug 08. eadp7114

PERK-ATAD3A interaction provides a subcellular safe haven for protein synthesis during ER stress.

Karinder K Brar, Daniel T Hughes, Jordan L Morris, Kelly Subramanian, Shivaani Krishna, Fei Gao, Lara-Sophie Rieder, Sebastian Uhrig, Joshua Freeman, Heather L Smith, Rebekkah Jukes-Jones, Edward Avezov, Jodi Nunnari, Julien Prudent, Adrian J Butcher, Giovanna R Mallucci.

Endoplasmic Reticulum (ER) stress induces repression of protein synthesis throughout the cell. Attempts to understand how localized stress leads to widespread repression have been limited by difficulties in resolving translation rates at the subcellular level. Here, using live-cell imaging of reporter mRNA translation, we unexpectedly found that during ER stress active translation at mitochondria was significantly protected. The mitochondrial protein, ATAD3A, interacted with PERK and mediated this effect on localized translation by competing for binding with PERK's target, eIF2. PERK-ATAD3A interactions increased during ER stress, forming mitochondria-ER contact sites. Furthermore, ATAD3A binding attenuated local PERK signaling and rescued the expression of some mitochondrial proteins. Thus, PERK-ATAD3A interactions can control translational repression at a subcellular level, mitigating the impact of ER stress on the cell.

DOI: https://doi.org/10.1126/science.adp7114
Anal Chem. 2024 Aug 07.

Real-Time Monitoring of mtDNA Aggregation and Mitophagy Induced by a Fluorescent Platinum Complex in Living Cells.

Bing Liu, Ting Sun, Yumeng Wang, Xiao-Yu Xia, Shixian Cao, Kang-Nan Wang, Qixin Chen, Zong-Wan Mao.

Mitochondrial DNA (mtDNA) is pivotal for mitochondrial morphology and function. Upon mtDNA damage, mitochondria undergo quality control mechanisms, including fusion, fission, and mitophagy. Real-time monitoring of mtDNA enables a deeper understanding of its effect on mitochondrial function and morphology. Controllable induction and real-time tracking of mtDNA dynamics and behavior are of paramount significance for studying mitochondrial function and morphology, facilitating a deeper understanding of mitochondria-related diseases. In this work, a fluorescent platinum complex was designed and developed that not only induces mitochondrial DNA (mtDNA) aggregation but also triggers mitochondrial autophagy (mitophagy) through the MDV pathway for damaged mtDNA clearance in living cells. Additionally, this complex allows for the real-time monitoring of these processes. This complex may serve as a valuable tool for studying mitochondrial microautophagy and holds promise for broader applications in cellular imaging and disease research.

DOI: https://doi.org/10.1021/acs.analchem.4c01128
Eye Brain. 2024 ;16 17-24

A Comprehensive Review of Leber Hereditary Optic Neuropathy and Its Association with Multiple Sclerosis-Like Phenotypes Known as Harding's Disease.

Jehad Alorainy, Yara Alorfi, Rustum Karanjia, Nooran Badeeb.

  Leber Hereditary Optic Neuropathy (LHON) stands as a distinctive maternally inherited mitochondrial disorder marked by painless, subacute central vision loss, primarily affecting young males. This review covers the possible relationship between LHON and multiple sclerosis (MS), covering genetic mutations, clinical presentations, imaging findings, and treatment options. LHON is associated with mutations in mitochondrial DNA (mtDNA), notably m.11778G>A, m.3460G>A, and m.14484T>C, affecting complex I subunits. Beyond ocular manifestations, LHON can go beyond the eye into a multi-systemic disorder, showcasing extraocular abnormalities. Clinical presentations, varying in gender prevalence and outcomes, underscore the nature of mitochondrial optic neuropathies. Hypotheses exploring the connection between LHON and MS encompass mitochondrial DNA mutations triggering neurological diseases, immunologically mediated responses inducing demyelination, and the possibility of coincidental diseases. The research on mtDNA mutations among MS patients sheds light on potential associations with specific clinical subgroups, offering a unique perspective into the broader landscape of MS. Imaging findings, ranging from white matter alterations to cerebrospinal fluid biomarkers, further emphasize shared pathological processes between LHON-MS and classical MS. This comprehensive review contributes to the understanding of the complex relationship between LHON and MS.

Keywords:  demyelination diseases; mitochondrial DNA; neuro-ophthalmology; visual impairment

DOI:  https://doi.org/10.2147/EB.S470184
Mol Ther Nucleic Acids. 2024 Sep 10. 35(3): 102257

Discovery of novel disease-causing mutation in SSBP1 and its correction using adenine base editor to improve mitochondrial function.

Ju Hyuen Cha, Seok-Hoon Lee, Yejin Yun, Won Hoon Choi, Hansol Koo, Sung Ho Jung, Ho Byung Chae, Dae Hee Lee, Seok Jae Lee, Dong Hyun Jo, Jeong Hun Kim, Jae-Jin Song, Jong-Hee Chae, Jun Ho Lee, Jiho Park, Jin Young Kang, Sangsu Bae, Sang-Yeon Lee.

  Mutations in nuclear genes regulating mitochondrial DNA (mtDNA) replication are associated with mtDNA depletion syndromes. Using whole-genome sequencing, we identified a heterozygous mutation (c.272G>A:p.Arg91Gln) in single-stranded DNA-binding protein 1 (SSBP1), a crucial protein involved in mtDNA replisome. The proband manifested symptoms including sensorineural deafness, congenital cataract, optic atrophy, macular dystrophy, and myopathy. This mutation impeded multimer formation and DNA-binding affinity, leading to reduced efficiency of mtDNA replication, altered mitochondria dynamics, and compromised mitochondrial function. To correct this mutation, we tested two adenine base editor (ABE) variants on patient-derived fibroblasts. One variant, NG-Cas9-based ABE8e (NG-ABE8e), showed higher editing efficacy (≤30%) and enhanced mitochondrial replication and function, despite off-target editing frequencies; however, risks from bystander editing were limited due to silent mutations and off-target sites in non-translated regions. The other variant, NG-Cas9-based ABE8eWQ (NG-ABE8eWQ), had a safer therapeutic profile with very few off-target effects, but this came at the cost of lower editing efficacy (≤10% editing). Despite this, NG-ABE8eWQ-edited cells still restored replication and improved mtDNA copy number, which in turn recovery of compromised mitochondrial function. Taken together, base editing-based gene therapies may be a promising treatment for mitochondrial diseases, including those associated with SSBP1 mutations.

Keywords:  MT: RNA/ DNA editing; NG-ABE8e; NG-ABE8eWQ; NG-Cas9-based ABE8e; NG-Cas9-based ABE8eWQ; SSBP1; editing efficacy; mitochondrial diseases; myopathy; off-target effects; optic atrophy; sensorineural deafness; single-stranded binding protein 1

DOI:  https://doi.org/10.1016/j.omtn.2024.102257
Mol Neurobiol. 2024 Aug 08.

Mitochondrial Dysfunction is a Crucial Immune Checkpoint for Neuroinflammation and Neurodegeneration: mtDAMPs in Focus.

Yogesh Mishra, Ashutosh Kumar, Ravinder Kumar Kaundal.

  Neuroinflammation is a pivotal factor in the progression of both age-related and acute neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and stroke. Mitochondria, essential for neuronal health due to their roles in energy production, calcium buffering, and oxidative stress regulation, become increasingly susceptible to dysfunction under conditions of metabolic stress, aging, or injury. Impaired mitophagy in aged or injured neurons leads to the accumulation of dysfunctional mitochondria, which release mitochondrial-derived damage-associated molecular patterns (mtDAMPs). These mtDAMPs act as immune checkpoints, activating pattern recognition receptors (PRRs) and triggering innate immune signaling pathways. This activation initiates inflammatory responses in neurons and brain-resident immune cells, releasing cytokines and chemokines that damage adjacent healthy neurons and recruit peripheral immune cells, further amplifying neuroinflammation and neurodegeneration. Long-term mitochondrial dysfunction perpetuates a chronic inflammatory state, exacerbating neuronal injury and contributing additional immunogenic components to the extracellular environment. Emerging evidence highlights the critical role of mtDAMPs in initiating and sustaining neuroinflammation, with circulating levels of these molecules potentially serving as biomarkers for disease progression. This review explores the mechanisms of mtDAMP release due to mitochondrial dysfunction, their interaction with PRRs, and the subsequent activation of inflammatory pathways. We also discuss the role of mtDAMP-triggered innate immune responses in exacerbating both acute and chronic neuroinflammation and neurodegeneration. Targeting dysfunctional mitochondria and mtDAMPs with pharmacological agents presents a promising strategy for mitigating the initiation and progression of neuropathological conditions.

Keywords:  Inflammatory signaling; Mitochondrial dysfunction; Neurodegenerative disorders; Sterile neuroinflammation; mtDAMPs

DOI:  https://doi.org/10.1007/s12035-024-04412-0
J Physiol. 2024 Aug 08.

Placental mitochondrial impairment and its association with maternal metabolic dysfunction.

Adriana Grismaldo R, Luis A Luévano-Martínez, Monserrat Reyes, Grecia García-Márquez, Gerardo García-Rivas, Luis Sobrevia.

  The placenta plays an essential role in pregnancy, leading to proper fetal development and growth. As an organ with multiple physiological functions for both mother and fetus, it is a highly energetic and metabolically demanding tissue. Mitochondrial physiology plays a crucial role in the metabolism of this organ and thus any alteration leading to mitochondrial dysfunction has a severe outcome in the development of the fetus. Pregnancy-related pathological states with a mitochondrial dysfunction outcome include preeclampsia and gestational diabetes mellitus. In this review, we address the role of mitochondrial morphology, metabolism and physiology of the placenta during pregnancy, highlighting the roles of the cytotrophoblast and syncytiotrophoblast. We also describe the relationship between preeclampsia, gestational diabetes, gestational diabesity and pre-pregnancy maternal obesity with mitochondrial dysfunction.

Keywords:  gestational diabetes; metabolic dysfunction; mitochondria; obesity; placenta; preeclampsia; pregnancy

DOI:  https://doi.org/10.1113/JP285935