bims-minimp 2022-06-05 papers

on Mitochondria, innate immunity, proteostasis

Issue of 2022‒06‒05
sixteen papers selected by
Hanna Salmonowicz
International Institute of Molecular Mechanisms and Machines of the Polish Academy of Sciences

Genome Replication Is Associated With Release of Immunogenic DNA Waste.
Nuclear antiviral innate responses at the intersection of DNA sensing and DNA repair.
Mitochondrial matrix-localized Src kinase regulates mitochondrial morphology.
MAPK15 protects from oxidative stress-dependent cellular senescence by inducing the mitophagic process.
A mitochondrial unfolded protein response inhibitor suppresses prostate cancer growth in mice via HSP60.
TNF-α/IFN-γ synergy amplifies senescence-associated inflammation and SARS-CoV-2 receptor expression via hyper-activated JAK/STAT1.
Mistargeting of aggregation prone mitochondrial proteins activates a nucleus-mediated posttranscriptional quality control pathway in trypanosomes.
Sex-Biased Control of Inflammation and Metabolism by a Mitochondrial Nod-Like Receptor.
Leukocyte cytokine responses in adult patients with mitochondrial DNA defects.
Intracellular localization of the proteasome in response to stress conditions.
ER-lysosome lipid transfer protein VPS13C/PARK23 prevents aberrant mtDNA-dependent STING signaling.
Binding of SARS-CoV-2 protein ORF9b to mitochondrial translocase TOM70 prevents its interaction with chaperone HSP90.
Depletion of Toxoplasma adenine nucleotide translocator leads to defects in mitochondrial morphology.
Presynaptic Mitochondria Communicate With Release Sites for Spatio-Temporal Regulation of Exocytosis at the Motor Nerve Terminal.
Ribosomal protein eL39 is important for maturation of the nascent polypeptide exit tunnel and proper protein folding during translation.
Plant mitochondrial FMT and its mammalian homolog CLUH controls development and behavior in Arabidopsis and locomotion in mice.

Front Immunol. 2022 ;13 880413

Genome Replication Is Associated With Release of Immunogenic DNA Waste.

Nadja Schubert, Tina Schumann, Elena Daum, Karolin Flade, Yan Ge, Lara Hagedorn, Winfried Edelmann, Luise Müller, Marc Schmitz, Gunnar Kuut, Veit Hornung, Rayk Behrendt, Axel Roers.

  Innate DNA sensors detect foreign and endogenous DNA to induce responses to infection and cellular stress or damage. Inappropriate activation by self-DNA triggers severe autoinflammatory conditions, including Aicardi-Goutières syndrome (AGS) that can be caused by defects of the cytosolic DNase 3'repair exonuclease 1 (TREX1). TREX1 loss-of-function alleles are also associated with systemic lupus erythematosus (SLE). Chronic activation of innate antiviral immunity in TREX1-deficient cells depends on the DNA sensor cGAS, implying that accumulating TREX1 DNA substrates cause the inflammatory pathology. Retrotransposon-derived cDNAs were shown to activate cGAS in TREX1-deficient neuronal cells. We addressed other endogenous sources of cGAS ligands in cells lacking TREX1. We find that induced loss of TREX1 in primary cells induces a rapid IFN response that requires ongoing proliferation. The inflammatory phenotype of Trex1-/- mice was partially rescued by additional knock out of exonuclease 1, a multifunctional enzyme providing 5' flap endonuclease activity for Okazaki fragment processing and postreplicative ribonucleotide excision repair. Our data imply genome replication as a source of DNA waste with pathogenic potential that is efficiently degraded by TREX1.

Keywords:  Exo1; Trex1; cytosolic DNA; interferonopathy; replication; type I interferon

DOI:  https://doi.org/10.3389/fimmu.2022.880413
Trends Microbiol. 2022 May 28. pii: S0966-842X(22)00116-0. [Epub ahead of print]

Nuclear antiviral innate responses at the intersection of DNA sensing and DNA repair.

Joshua L Justice, Ileana M Cristea.

  The coevolution of vertebrate and mammalian hosts with DNA viruses has driven the ability of host cells to distinguish viral from cellular DNA in the nucleus to induce intrinsic immune responses. Concomitant viral mechanisms have arisen to inhibit DNA sensing. At this virus-host interface, emerging evidence links cytokine responses and cellular homeostasis pathways, particularly the DNA damage response (DDR). Nuclear DNA sensors, such as the interferon (IFN)-γ inducible protein 16 (IFI16), functionally intersect with the DDR regulators ataxia telangiectasia mutated (ATM) and DNA-dependent protein kinase (DNA-PK). Here, we discuss accumulating knowledge for the DDR-innate immunity signaling axis. Through the lens of this infection-driven signaling axis, we present host and viral molecular strategies acquired to regulate autoinflammation and antiviral responses.

Keywords:  DNA damage response; DNA virus infection; antiviral response; interferon; nuclear DNA sensing

DOI:  https://doi.org/10.1016/j.tim.2022.05.004
Cell Mol Life Sci. 2022 May 30. 79(6): 327

Mitochondrial matrix-localized Src kinase regulates mitochondrial morphology.

Olivier Lurette, Hala Guedouari, Jordan L Morris, Rebeca Martín-Jiménez, Julie-Pier Robichaud, Geneviève Hamel-Côté, Mehtab Khan, Nicholas Dauphinee, Nicolas Pichaud, Julien Prudent, Etienne Hebert-Chatelain.

  The architecture of mitochondria adapts to physiological contexts: while mitochondrial fragmentation is usually associated to quality control and cell death, mitochondrial elongation often enhances cell survival during stress. Understanding how these events are regulated is important to elucidate how mitochondrial dynamics control cell fate. Here, we show that the tyrosine kinase Src regulates mitochondrial morphology. Deletion of Src increased mitochondrial size and reduced cellular respiration independently of mitochondrial mass, mitochondrial membrane potential or ATP levels. Re-expression of Src targeted to the mitochondrial matrix, but not of Src targeted to the plasma membrane, rescued mitochondrial morphology in a kinase activity-dependent manner. These findings highlight a novel function for Src in the control of mitochondrial dynamics.

Keywords:  Cellular respiration; Mitochondria-shaping protein; Mitochondrial dynamics; Oxidative phosphorylation

DOI:  https://doi.org/10.1007/s00018-022-04325-y
Aging Cell. 2022 Jun 01. e13620

MAPK15 protects from oxidative stress-dependent cellular senescence by inducing the mitophagic process.

Lorenzo Franci, Alessandro Tubita, Franca Maria Bertolino, Alessandro Palma, Giuseppe Cannino, Carmine Settembre, Andrea Rasola, Elisabetta Rovida, Mario Chiariello.

  Mitochondria are the major source of reactive oxygen species (ROS), whose aberrant production by dysfunctional mitochondria leads to oxidative stress, thus contributing to aging as well as neurodegenerative disorders and cancer. Cells efficiently eliminate damaged mitochondria through a selective type of autophagy, named mitophagy. Here, we demonstrate the involvement of the atypical MAP kinase family member MAPK15 in cellular senescence, by preserving mitochondrial quality, thanks to its ability to control mitophagy and, therefore, prevent oxidative stress. We indeed demonstrate that reduced MAPK15 expression strongly decreases mitochondrial respiration and ATP production, while increasing mitochondrial ROS levels. We show that MAPK15 controls the mitophagic process by stimulating ULK1-dependent PRKN Ser108 phosphorylation and inducing the recruitment of damaged mitochondria to autophagosomal and lysosomal compartments, thus leading to a reduction of their mass, but also by participating in the reorganization of the mitochondrial network that usually anticipates their disposal. Consequently, MAPK15-dependent mitophagy protects cells from accumulating nuclear DNA damage due to mitochondrial ROS and, consequently, from senescence deriving from this chronic DNA insult. Indeed, we ultimately demonstrate that MAPK15 protects primary human airway epithelial cells from senescence, establishing a new specific role for MAPK15 in controlling mitochondrial fitness by efficient disposal of old and damaged organelles and suggesting this kinase as a new potential therapeutic target in diverse age-associated human diseases.

Keywords:  MAP kinases; Oxidative DNA damage; autophagy; cellular senescence; mitophagy; signal transduction

DOI:  https://doi.org/10.1111/acel.13620
J Clin Invest. 2022 Jun 02. pii: e149906. [Epub ahead of print]

A mitochondrial unfolded protein response inhibitor suppresses prostate cancer growth in mice via HSP60.

Rahul Kumar, Ajay Kumar Chaudhary, Jordan Woytash, Joseph R Inigo, Abhiram A Gokhale, Wiam Bshara, Kristopher Attwood, Jianmin Wang, Joseph A Spernyak, Eva Rath, Neelu Yadav, Dirk Haller, David W Goodrich, Dean G Tang, Dhyan Chandra.

  Mitochondrial proteostasis, regulated by the mitochondrial unfolded protein response (UPRmt), is crucial for maintenance of cellular functions and survival. Elevated oxidative and proteotoxic stress in mitochondria must be attenuated by the activation of ubiquitous UPRmt to promote prostate cancer (PCa) growth. Here we show that the two key components of the UPRmt, heat shock protein 60 (HSP60, a mitochondrial chaperonin) and caseinolytic protease (ClpP, a mitochondrial protease) were required for the development of advanced PCa. HSP60 regulated ClpP expression via c-Myc and physically interacted with ClpP to restore mitochondrial functions promoting cancer cell survival. HSP60 maintained the ATP-producing functions of mitochondria, which activated β-catenin pathway leading to the upregulation of c-Myc. We identified an UPRmt inhibitor that blocked HSP60 interaction with ClpP and abrogated survival signaling without altering HSP60 chaperonin function. Disruption of HSP60-ClpP interaction by UPRmt inhibitor triggered metabolic stress and impeded PCa promoting signaling. Treatment with UPRmt inhibitor, or genetic ablation of Hsp60, inhibited PCa growth and progression. Together, our findings identify that HSP60-ClpP mediated UPRmt is essential for prostate tumorigenesis and HSP60-ClpP interaction represents a therapeutic vulnerability in PCa.

Keywords:  Cell Biology; Cell stress; Mitochondria; Oncology; Prostate cancer

DOI:  https://doi.org/10.1172/JCI149906
Aging Cell. 2022 May 30. e13646

TNF-α/IFN-γ synergy amplifies senescence-associated inflammation and SARS-CoV-2 receptor expression via hyper-activated JAK/STAT1.

Renuka Kandhaya-Pillai, Xiaomeng Yang, Tamar Tchkonia, George M Martin, James L Kirkland, Junko Oshima.

  Older age and underlying conditions such as diabetes/obesity or immunosuppression are leading host risk factors for developing severe complications from COVID-19 infection. The pathogenesis of COVID-19-related cytokine storm, tissue damage, and fibrosis may be interconnected with fundamental aging processes, including dysregulated immune responses and cellular senescence. Here, we examined effects of key cytokines linked to cellular senescence on expression of SARS-CoV-2 viral entry receptors. We found exposure of human umbilical vein endothelial cells (HUVECs) to the inflammatory cytokines, TNF-α + IFN-γ or a cocktail of TNF-α + IFN-γ + IL-6, increased expression of ACE2/DPP4, accentuated the pro-inflammatory senescence-associated secretory phenotype (SASP), and decreased cellular proliferative capacity, consistent with progression towards a cellular senescence-like state. IL-6 by itself failed to induce substantial effects on viral entry receptors or SASP-related genes, while synergy between TNF-α and IFN-γ initiated a positive feedback loop via hyper-activation of the JAK/STAT1 pathway, causing SASP amplification. Breaking the interactive loop between senescence and cytokine secretion with JAK inhibitor ruxolitinib or antiviral drug remdesivir prevented hyper-inflammation, normalized SARS-CoV-2 entry receptor expression, and restored HUVECs proliferative capacity. This loop appears to underlie cytokine-mediated viral entry receptor activation and links with senescence and hyper-inflammation.

Keywords:  ACE2; COVID-19; DPP4; JAK-STAT; SARS-COV-2 receptor; cytokines; inflammation; senescence

DOI:  https://doi.org/10.1111/acel.13646
Nat Commun. 2022 Jun 02. 13(1): 3084

Mistargeting of aggregation prone mitochondrial proteins activates a nucleus-mediated posttranscriptional quality control pathway in trypanosomes.

Caroline E Dewar, Silke Oeljeklaus, Jan Mani, Wignand W D Mühlhäuser, Corinne von Känel, Johannes Zimmermann, Torsten Ochsenreiter, Bettina Warscheid, André Schneider.

Mitochondrial protein import in the parasitic protozoan Trypanosoma brucei is mediated by the atypical outer membrane translocase, ATOM. It consists of seven subunits including ATOM69, the import receptor for hydrophobic proteins. Ablation of ATOM69, but not of any other subunit, triggers a unique quality control pathway resulting in the proteasomal degradation of non-imported mitochondrial proteins. The process requires a protein of unknown function, an E3 ubiquitin ligase and the ubiquitin-like protein (TbUbL1), which all are recruited to the mitochondrion upon ATOM69 depletion. TbUbL1 is a nuclear protein, a fraction of which is released to the cytosol upon triggering of the pathway. Nuclear release is essential as cytosolic TbUbL1 can bind mislocalised mitochondrial proteins and likely transfers them to the proteasome. Mitochondrial quality control has previously been studied in yeast and metazoans. Finding such a pathway in the highly diverged trypanosomes suggests such pathways are an obligate feature of all eukaryotes.

DOI: https://doi.org/10.1038/s41467-022-30748-z
Front Immunol. 2022 ;13 882867

Sex-Biased Control of Inflammation and Metabolism by a Mitochondrial Nod-Like Receptor.

Tiia Snäkä, Amel Bekkar, Chantal Desponds, Florence Prével, Stéphanie Claudinot, Nathalie Isorce, Filipa Teixeira, Coline Grasset, Ioannis Xenarios, Isabel C Lopez-Mejia, Lluis Fajas, Nicolas Fasel.

  Mitochondria regulate steroid hormone synthesis, and in turn sex hormones regulate mitochondrial function for maintaining cellular homeostasis and controlling inflammation. This crosstalk can explain sex differences observed in several pathologies such as in metabolic or inflammatory disorders. Nod-like receptor X1 (NLRX1) is a mitochondria-associated innate receptor that could modulate metabolic functions and attenuates inflammatory responses. Here, we showed that in an infectious model with the human protozoan parasite, Leishmania guyanensis, NLRX1 attenuated inflammation in females but not in male mice. Analysis of infected female and male bone marrow derived macrophages showed both sex- and genotype-specific differences in both inflammatory and metabolic profiles with increased type I interferon production, mitochondrial respiration, and glycolytic rate in Nlrx1-deficient female BMDMs in comparison to wild-type cells, while no differences were observed between males. Transcriptomics of female and male BMDMs revealed an altered steroid hormone signaling in Nlrx1-deficient cells, and a "masculinization" of Nlrx1-deficient female BMDMs. Thus, our findings suggest that NLRX1 prevents uncontrolled inflammation and metabolism in females and therefore may contribute to the sex differences observed in infectious and inflammatory diseases.

Keywords:  inflammation; innate immunity; metabolism; nod-like receptor X1; sex

DOI:  https://doi.org/10.3389/fimmu.2022.882867
J Mol Med (Berl). 2022 Jun;100(6): 963-971

Leukocyte cytokine responses in adult patients with mitochondrial DNA defects.

Kalpita R Karan, Caroline Trumpff, Marissa Cross, Kristin M Engelstad, Anna L Marsland, Peter J McGuire, Michio Hirano, Martin Picard.

  Patients with oxidative phosphorylation (OxPhos) defects causing mitochondrial diseases appear particularly vulnerable to infections. Although OxPhos defects modulate cytokine production in vitro and in animal models, little is known about how circulating leukocytes of patients with inherited mitochondrial DNA (mtDNA) defects respond to acute immune challenges. In a small cohort of healthy controls (n = 21) and patients (n = 12) with either the m.3243A > G mutation or single, large-scale mtDNA deletions, we examined (i) cytokine responses (IL-6, TNF-α, IL-1β) in response to acute lipopolysaccharide (LPS) exposure and (ii) sensitivity to the immunosuppressive effects of glucocorticoid signaling (dexamethasone) on cytokine production. In dose-response experiments to determine the half-maximal effective LPS concentration (EC50), relative to controls, leukocytes from patients with mtDNA deletions showed 74-79% lower responses for IL-6 and IL-1β (pIL-6 = 0.031, pIL-1β = 0.009). Moreover, whole blood from patients with mtDNA deletions (pIL-6 = 0.006), but not patients with the m.3243A > G mutation, showed greater sensitivity to the immunosuppressive effects of dexamethasone. Together, these ex vivo data provide preliminary evidence that some systemic OxPhos defects may compromise immune cytokine responses and increase the sensitivity to immune cytokine suppression by glucocorticoids. Further work in larger cohorts is needed to define the nature of immune dysregulation in patients with mitochondrial disease, and their potential implications for disease phenotypes. KEY MESSAGES: Little is known about leukocyte cytokine responses in patients with mitochondrial diseases. Leukocytes of patients with mtDNA deletions show blunted LPS sensitivity and cytokine responses. Leukocytes of patients with mtDNA deletions are more sensitive to glucocorticoid-mediated IL-6 suppression. Work in larger cohorts is needed to delineate potential immune alterations in mitochondrial diseases.

Keywords:  3243A > G; Cytokine; Glucocorticoid; Inflammation; Inflammation Suppression; Interleukin; Mitochondrial disease; mtDNA deletion

DOI:  https://doi.org/10.1007/s00109-022-02206-2
J Biol Chem. 2022 May 27. pii: S0021-9258(22)00524-5. [Epub ahead of print] 102083

Intracellular localization of the proteasome in response to stress conditions.

Cordula Enenkel, Ryu Won Kang, Florian Wilfling, Oliver P Ernst.

  The ubiquitin-proteasome-system (UPS) fulfills an essential role in regulating protein homeostasis by spatially and temporally controlling proteolysis in an ATP- and ubiquitin-dependent manner. However, the localization of proteasomes is highly variable under diverse cellular conditions. In yeast, newly synthesized proteasomes are primarily localized to the nucleus during cell proliferation. Yeast proteasomes are transported into the nucleus through the nuclear pore either as immature subcomplexes or as mature enzymes via adaptor proteins Sts1 and Blm10, while in mammalian cells, post-mitotic uptake of proteasomes into the nucleus is mediated by AKIRIN2, an adaptor protein essentially required for nuclear protein degradation. Stressful growth conditions and the reversible halt of proliferation, i.e. quiescence, are associated with a decline in ATP and the re-organization of proteasome localization. Cellular stress leads to proteasome accumulation in membraneless granules either in the nucleus or in the cytoplasm. In quiescence, yeast proteasomes are sequestered in a ubiquitin-dependent manner into motile and reversible proteasome storage granules (PSGs) in the cytoplasm. In cancer cells upon amino acid deprivation, heat shock, osmotic stress, oxidative stress, or the inhibition of either proteasome activity or nuclear export, reversible proteasome foci containing poly-ubiquitinated substrates are formed by liquid-liquid phase separation in the nucleus. In this review, we summarize recent literature revealing new links between nuclear transport, ubiquitin signaling and the intracellular organization of proteasomes during cellular stress conditions.

Keywords:  liquid-liquid phase separation; nuclear transport; proteasome foci; proteasome storage granule; protein quality control; stress response; ubiquitin-proteasome-system

DOI:  https://doi.org/10.1016/j.jbc.2022.102083
J Cell Biol. 2022 Jul 04. pii: e202106046. [Epub ahead of print]221(7):

ER-lysosome lipid transfer protein VPS13C/PARK23 prevents aberrant mtDNA-dependent STING signaling.

William Hancock-Cerutti, Zheng Wu, Peng Xu, Narayana Yadavalli, Marianna Leonzino, Arun Kumar Tharkeshwar, Shawn M Ferguson, Gerald S Shadel, Pietro De Camilli.

Mutations in VPS13C cause early-onset, autosomal recessive Parkinson's disease (PD). We have established that VPS13C encodes a lipid transfer protein localized to contact sites between the ER and late endosomes/lysosomes. In the current study, we demonstrate that depleting VPS13C in HeLa cells causes an accumulation of lysosomes with an altered lipid profile, including an accumulation of di-22:6-BMP, a biomarker of the PD-associated leucine-rich repeat kinase 2 (LRRK2) G2019S mutation. In addition, the DNA-sensing cGAS-STING pathway, which was recently implicated in PD pathogenesis, is activated in these cells. This activation results from a combination of elevated mitochondrial DNA in the cytosol and a defect in the degradation of activated STING, a lysosome-dependent process. These results suggest a link between ER-lysosome lipid transfer and innate immune activation in a model human cell line and place VPS13C in pathways relevant to PD pathogenesis.

DOI: https://doi.org/10.1083/jcb.202106046
Biochimie. 2022 May 25. pii: S0300-9084(22)00146-8. [Epub ahead of print]

Binding of SARS-CoV-2 protein ORF9b to mitochondrial translocase TOM70 prevents its interaction with chaperone HSP90.

Kehinde S Ayinde, Glaucia M S Pinheiro, Carlos H I Ramos.

  The emergence of the COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), remains a great threat to global health. ORF9b, an important accessory protein of SARS-CoV-2, plays a critical role in the viral host interaction, targeting TOM70, a member of the mitochondrial translocase of the outer membrane complex. The assembly between ORF9b and TOM70 is implicated in disrupting mitochondrial antiviral signaling, leading to immune evasion. We describe the expression, purification, and characterization of ORF9b alone or coexpressed with the cytosolic domain of human TOM70 in E. coli. ORF9b has 97 residues and was purified as a homodimer with an molecular mass of 22 kDa as determined by SEC-MALS. Circular dichroism experiments showed that Orf9b alone exhibits a random conformation. The ORF9b-TOM70 complex characterized by CD and differential scanning calorimetry showed that the complex is folded and more thermally stable than free TOM70, indicating strong binding. Importantly, protein-protein interaction assays demonstrated that full-length human Hsp90 is capable of binding to free TOM70 but not to the ORF9b-TOM70 complex. To narrow down the nature of this inhibition, the isolated C-terminal domain of Hsp90 was also tested. These results were used to build a model of the mechanism of inhibition, in which ORF9b efficiently targets two sites of interaction between TOM70 and Hsp90. The findings showed that ORF9b complexed with TOM70 prevents the interaction with Hsp90, and this is one major explanation for SARS-CoV-2 evasion of host innate immunity via the inhibition of the interferon activation pathway.

Keywords:  COVID-19; HSP90; Immune evasion; Protein–protein interaction; SARS-CoV-2; TOM70

DOI:  https://doi.org/10.1016/j.biochi.2022.05.016
Parasit Vectors. 2022 May 31. 15(1): 185

Depletion of Toxoplasma adenine nucleotide translocator leads to defects in mitochondrial morphology.

Yihan Wu, Zhu Ying, Jing Liu, Zhepeng Sun, Shuang Li, Qun Liu.

  BACKGROUND: Adenine nucleotide translocase (ANT) is a protein that catalyzes the exchange of ADP/ATP across the inner mitochondrial membrane. Beyond this, ANT is closely associated with cell death pathways and mitochondrial dysfunction. It is a potential therapeutic target for many diseases. The function of the ANT in Toxoplasma gondii is poorly understood.METHODS: The CRISPR/CAS9 gene editing tool was used to identify and study the function of the ANT protein in T. gondii. We constructed T. gondii ANT transgenic parasite lines, including endogenous tag strain, knockout strain and gene complement strain, to clarify the function and location of TgANT. Mitochondrial morphology was observed by immunofluorescence and transmission electron microscopy.
RESULTS: Toxoplasma gondii was found to encode an ANT protein, which was designated TgANT. TgANT localized to the inner mitochondrial membrane. The proliferation of the Δant strain was significantly reduced. More important, depletion of TgANT resulted in significant changes in the morphology and ultrastructure of mitochondria, abnormal apicoplast division and abnormal cytoskeletal daughter budding. In addition, the pathogenicity of the Δant strain to mice was significantly reduced.
CONCLUSIONS: Altogether, we identified and characterized the ANT protein of T. gondii. Depletion of TgANT inhibited parasite growth and impaired apicoplast and mitochondrial biogenesis, as well as abnormal parasite division, suggesting TgANT is important for parasite growth.

Keywords:  Adenine nucleotide translocase; Mitochondria; Toxoplasma gondii

DOI:  https://doi.org/10.1186/s13071-022-05295-7
Front Synaptic Neurosci. 2022 ;14 858340

Presynaptic Mitochondria Communicate With Release Sites for Spatio-Temporal Regulation of Exocytosis at the Motor Nerve Terminal.

Mario Lopez-Manzaneda, Andrea Fuentes-Moliz, Lucia Tabares.

  Presynaptic Ca2+ regulation is critical for accurate neurotransmitter release, vesicle reloading of release sites, and plastic changes in response to electrical activity. One of the main players in the regulation of cytosolic Ca2+ in nerve terminals is mitochondria, which control the size and spread of the Ca2+ wave during sustained electrical activity. However, the role of mitochondria in Ca2+ signaling during high-frequency short bursts of action potentials (APs) is not well known. Here, we studied spatial and temporal relationships between mitochondrial Ca2+ (mCa2+) and exocytosis by live imaging and electrophysiology in adult motor nerve terminals of transgenic mice expressing synaptophysin-pHluorin (SypHy). Our results show that hot spots of exocytosis and mitochondria are organized in subsynaptic functional regions and that mitochondria start to uptake Ca2+ after a few APs. We also show that mitochondria contribute to the regulation of the mode of fusion (synchronous and asynchronous) and the kinetics of release and replenishment of the readily releasable pool (RRP) of vesicles. We propose that mitochondria modulate the timing and reliability of neurotransmission in motor nerve terminals during brief AP trains.

Keywords:  active zones; asynchronous release; calcium; exocytosis; mitochondria; neuromuscular junction; synapse; synchronous release

DOI:  https://doi.org/10.3389/fnsyn.2022.858340
Nucleic Acids Res. 2022 May 27. pii: gkac366. [Epub ahead of print]

Ribosomal protein eL39 is important for maturation of the nascent polypeptide exit tunnel and proper protein folding during translation.

Jelena Micic, Olga Rodríguez-Galán, Reyes Babiano, Fiona Fitzgerald, José Fernández-Fernández, Yunyang Zhang, Ning Gao, John L Woolford, Jesús de la Cruz.

During translation, nascent polypeptide chains travel from the peptidyl transferase center through the nascent polypeptide exit tunnel (NPET) to emerge from 60S subunits. The NPET includes portions of five of the six 25S/5.8S rRNA domains and ribosomal proteins uL4, uL22, and eL39. Internal loops of uL4 and uL22 form the constriction sites of the NPET and are important for both assembly and function of ribosomes. Here, we investigated the roles of eL39 in tunnel construction, 60S biogenesis, and protein synthesis. We show that eL39 is important for proper protein folding during translation. Consistent with a delay in processing of 27S and 7S pre-rRNAs, eL39 functions in pre-60S assembly during middle nucleolar stages. Our biochemical assays suggest the presence of eL39 in particles at these stages, although it is not visualized in them by cryo-electron microscopy. This indicates that eL39 takes part in assembly even when it is not fully accommodated into the body of pre-60S particles. eL39 is also important for later steps of assembly, rotation of the 5S ribonucleoprotein complex, likely through long range rRNA interactions. Finally, our data strongly suggest the presence of alternative pathways of ribosome assembly, previously observed in the biogenesis of bacterial ribosomal subunits.

DOI: https://doi.org/10.1093/nar/gkac366
Cell Mol Life Sci. 2022 Jun 02. 79(6): 334

Plant mitochondrial FMT and its mammalian homolog CLUH controls development and behavior in Arabidopsis and locomotion in mice.

Alexandra Ralevski, Federico Apelt, Justyna J Olas, Bernd Mueller-Roeber, Elena I Rugarli, Friedrich Kragler, Tamas L Horvath.

  Mitochondria in animals are associated with development, as well as physiological and pathological behaviors. Several conserved mitochondrial genes exist between plants and higher eukaryotes. Yet, the similarities in mitochondrial function between plant and animal species is poorly understood. Here, we show that FMT (FRIENDLY MITOCHONDRIA) from Arabidopsis thaliana, a highly conserved homolog of the mammalian CLUH (CLUSTERED MITOCHONDRIA) gene family encoding mitochondrial proteins associated with developmental alterations and adult physiological and pathological behaviors, affects whole plant morphology and development under both stressed and normal growth conditions. FMT was found to regulate mitochondrial morphology and dynamics, germination, and flowering time. It also affects leaf expansion growth, salt stress responses and hyponastic behavior, including changes in speed of hyponastic movements. Strikingly, Cluh± heterozygous knockout mice also displayed altered locomotive movements, traveling for shorter distances and had slower average and maximum speeds in the open field test. These observations indicate that homologous mitochondrial genes may play similar roles and affect homologous functions in both plants and animals.

Keywords:  Arabidopsis thaliana; CLUH; FMT; Hyponasty; Locomotion; Mice; Mitochondria

DOI:  https://doi.org/10.1007/s00018-022-04382-3