bims-mitmed 2023-03-26 papers

bims-mitmed

Biomed News

on Mitochondrial medicine

Issue of 2023–03–26
35 papers selected by
Dario Brunetti, Fondazione IRCCS Istituto Neurologico

A shared pattern of altered gene expression in human embryos affected by mitochondrial diseases.
Research development and the prospect of animal models of mitochondrial DNA-related mitochondrial diseases.
A quantitative fluorescence-based approach to study mitochondrial protein import.
Loss of respiratory complex I subunit NDUFB10 affects complex I assembly and supercomplex formation.
Mitochondria in reproduction.
Identification of two novel RRM2B variants associated with autosomal recessive progressive external ophthalmoplegia in a family with pseudodominant inheritance pattern.
Tetracycline-dependent inhibition of mitoribosome protein elongation in mitochondrial disease mutant cells suppresses IRE1α to promote cell survival.
Hypertrophic cardiomyopathy as the initial presentation of mitochondrial disease in an infant born to a diabetic mother.
Mitochondrial network structure controls cell-to-cell mtDNA variability generated by cell divisions.
NSUN3-mediated mitochondrial tRNA 5-formylcytidine modification is essential for embryonic development and respiratory complexes in mice.
Pharmacologic Activation of an Integrated Stress Response Kinase Promotes Mitochondrial Remodeling.
Mitochondrial Membrane Potential Independent Near-Infrared Mitochondrial Viscosity Probes for Real-Time Tracking Mitophagy.
Resistance training improves hypertrophic and mitochondrial adaptation in skeletal muscle.
MFN1 augmentation prevents retinal degeneration in a Charcot-Marie-Tooth type 2A mouse model.
Increased mitochondrial Ca2+ contributes to health decline with age and Duchene muscular dystrophy in C. elegans.
Mitochondrial dysfunction and calcium dysregulation in COQ8A-ataxia Purkinje neurons are rescued by CoQ10 treatment.
Mitochondrial damage activates the NLRP10 inflammasome.
Resting mitochondrial complex I from Drosophila melanogaster adopts a helix-locked state.
Structural basis of mitochondrial membrane bending by the I-II-III2-IV2 supercomplex.
Mitochondrial haplotype and mito-nuclear matching drive somatic mutation and selection throughout aging.
Mitochondrial dysfunction rapidly modulates the abundance and thermal stability of cellular proteins.
Sirtuin 3 mutation- induced mitochondrial dysfunction and optic neuropathy: a case report.
Knockout of cardiolipin synthase disrupts postnatal cardiac development by inhibiting the maturation of mitochondrial cristae.
Structure-based design and characterization of Parkin-activating mutations.
Molecular mechanisms of mitochondrial DNA release and activation of the cGAS-STING pathway.
Rapamycin encourages the maintenance of mitochondrial dynamic balance and mitophagy activity for improving developmental competence of blastocysts in porcine embryos in vitro.
Intrathecal AAV9/AP4M1 gene therapy for hereditary spastic paraplegia 50 shows safety and efficacy in preclinical studies.
Loss of fatty acid degradation by astrocytic mitochondria triggers neuroinflammation and neurodegeneration.
Peroxisome proliferator-activated receptor-α (PPARα) regulates wound healing and mitochondrial metabolism in the cornea.
Muscle PARP1 inhibition extends lifespan through AMPKα PARylation and activation in Drosophila.
Editorial: Altered bioenergetics, mitochondrial quality control, and calcium signaling in the brain: Implications to age-related diseases.
Molecular and metabolic heterogeneity of astrocytes and microglia.
Switching ubiquitous and muscle-specific isoforms of mitochondrial respiratory complex IV in skeletal muscle fine-tunes complex IV activity.
Neuronal loss of NCLX-dependent mitochondrial calcium efflux mediates age-associated cognitive decline.
A defect in mitochondrial protein translation influences mitonuclear communication in the heart.

Hum Reprod. 2023 Mar 23. pii: dead052. [Epub ahead of print]

A shared pattern of altered gene expression in human embryos affected by mitochondrial diseases.

Kalliopi Chatzovoulou, Anne Mayeur, Nicolas Cagnard, Mohammed Zarhrate, Christine Bole, Patrick Nitschke, Fabienne Jabot-Hanin, Agnès Rötig, Sophie Monnot, Arnold Munnich, Nelly Frydman, Julie Steffann.

   STUDY QUESTION: Does mitochondrial deficiency affect human embryonic preimplantation development?
SUMMARY ANSWER: The presence of a pathogenic mitochondrial variant triggers changes in the gene expression of preimplantation human embryos, compromising their development, cell differentiation, and survival.
WHAT IS KNOWN ALREADY: Quantitative and qualitative anomalies of mitochondrial DNA (mtDNA) are reportedly associated with impaired human embryonic development, but the underlying mechanisms remain unexplained.
STUDY DESIGN, SIZE, DURATION: Taking advantage of the preimplantation genetic testing for mitochondrial disorders in at-risk couples, we have compared gene expression of 9 human embryos carrying pathogenic variants in either mtDNA genes or nuclear genes encoding mitochondrial protein to 33 age-matched control embryos.
PARTICIPANTS/MATERIALS, SETTING, METHODS: Single-embryo transcriptomic analysis was performed on whole human blastocyst embryos donated to research.
MAIN RESULTS AND THE ROLE OF CHANCE: Specific pathogenic mitochondrial variants downregulate gene expression in preimplantation human embryos [566 genes in oxidative phosphorylation (OXPHOS)-deficient embryos], impacting transcriptional regulators, differentiation factors, and nuclear genes encoding mitochondrial proteins. These changes in gene expression primarily alter OXPHOS and cell survival pathways.
LIMITATIONS, REASONS FOR CAUTION: The number of OXPHOS-deficient embryos available for the study was limited owing to the rarity of this material. However, the molecular signature shared by all these embryos supports the relevance of the findings.
WIDER IMPLICATIONS OF THE FINDINGS: While identification of reliable markers of normal embryonic development is urgently needed in ART, our study prompts us to consider under-expression of the targeted genes reported here, as predictive biomarkers of mitochondrial dysfunction during preimplantation development.
STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the 'Association Française contre les Myopathies (AFM-Téléthon)' and the 'La Fondation Maladies Rares'. No competing interests to declare.
TRIAL REGISTRATION NUMBER: N/A.

Keywords:  RNA sequencing; differential gene expression; human embryo development; mitochondrial metabolism; mitochondrial mutation; transcriptome

DOI:  https://doi.org/10.1093/humrep/dead052
Anal Biochem. 2023 Mar 20. pii: S0003-2697(23)00087-8. [Epub ahead of print] 115122

Research development and the prospect of animal models of mitochondrial DNA-related mitochondrial diseases.

Xiaolei Wang, Hedong Lu, Min Li, Zhiguo Zhang, Zhaolian Wei, Ping Zhou, Yunxia Cao, Dongmei Ji, Weiwei Zou.

  Mitochondrial diseases (MDs) are genetic and clinical heterogeneous diseases caused by mitochondrial oxidative phosphorylation defects. It is not only one of the most common genetic diseases, but also the only genetic disease involving two different genomes in humans. As a result of the complicated genetic condition, the pathogenesis of MDs is not entirely elucidated at present, and there is a lack of effective treatment in the clinic. Establishing the ideal animal models is the critical preclinical platform to explore the pathogenesis of MDs and to verify new therapeutic strategies. However, the development of animal modeling of mitochondrial DNA (mtDNA)-related MDs is time-consuming due to the limitations of physiological structure and technology. A small number of animal models of mtDNA mutations have been constructed using cell hybridization and other methods. However, the diversity of mtDNA mutation sites and clinical phenotypes make establishing relevant animal models tricky. The development of gene editing technology has become a new hope for establishing animal models of mtDNA-related mitochondrial diseases.

Keywords:  Animal models; Mitochondrial DNA; Mitochondrial diseases; MtDNA mutation

DOI:  https://doi.org/10.1016/j.ab.2023.115122
EMBO Rep. 2023 Mar 20. e55760

A quantitative fluorescence-based approach to study mitochondrial protein import.

Naintara Jain, Ridhima Gomkale, Olaf Bernhard, Peter Rehling, Luis Daniel Cruz-Zaragoza.

  Mitochondria play central roles in cellular energy production and metabolism. Most proteins required to carry out these functions are synthesized in the cytosol and imported into mitochondria. A growing number of metabolic disorders arising from mitochondrial dysfunction can be traced to errors in mitochondrial protein import. The mechanisms underlying the import of precursor proteins are commonly studied using radioactively labeled precursor proteins imported into purified mitochondria. Here, we establish a fluorescence-based import assay to analyze protein import into mitochondria. We show that fluorescently labeled precursors enable import analysis with similar sensitivity to those using radioactive precursors, yet they provide the advantage of quantifying import with picomole resolution. We adapted the import assay to a 96-well plate format allowing for fast analysis in a screening-compatible format. Moreover, we show that fluorescently labeled precursors can be used to monitor the assembly of the F1 F0 ATP synthase in purified mitochondria. Thus, we provide a sensitive fluorescence-based import assay that enables quantitative and fast import analysis.

Keywords:  fluorescent precursor; in vitro import; mitochondria; presequence pathway; protein import

DOI:  https://doi.org/10.15252/embr.202255760
Biol Chem. 2023 Mar 24.

Loss of respiratory complex I subunit NDUFB10 affects complex I assembly and supercomplex formation.

Tasnim Arroum, Marie-Theres Borowski, Nico Marx, Frank Schmelter, Martin Scholz, Olympia Ekaterini Psathaki, Michael Hippler, José Antonio Enriquez, Karin B Busch.

  The orchestrated activity of the mitochondrial respiratory or electron transport chain (ETC) and ATP synthase convert reduction power (NADH, FADH2) into ATP, the cell's energy currency in a process named oxidative phosphorylation (OXPHOS). Three out of the four ETC complexes are found in supramolecular assemblies: complex I, III, and IV form the respiratory supercomplexes (SC). The plasticity model suggests that SC formation is a form of adaptation to changing conditions such as energy supply, redox state, and stress. Complex I, the NADH-dehydrogenase, is part of the largest supercomplex (CI + CIII2 + CIVn). Here, we demonstrate the role of NDUFB10, a subunit of the membrane arm of complex I, in complex I and supercomplex assembly on the one hand and bioenergetics function on the other. NDUFB10 knockout was correlated with a decrease of SCAF1, a supercomplex assembly factor, and a reduction of respiration and mitochondrial membrane potential. This likely is due to loss of proton pumping since the CI P P -module is downregulated and the P D -module is completely abolished in NDUFB10 knock outs.

Keywords:  NDUFB10; OXPHOS; complex I; mitochondria; respiratory chain supercomplexes

DOI:  https://doi.org/10.1515/hsz-2022-0309
Clin Exp Reprod Med. 2023 Mar;50(1): 1-11

Mitochondria in reproduction.

Min-Hee Kang, Yu Jin Kim, Jae Ho Lee.

  In reproduction, mitochondria produce bioenergy, help to synthesize biomolecules, and support the ovaries, oogenesis, and preimplantation embryos, thereby facilitating healthy live births. However, the regulatory mechanism of mitochondria in oocytes and embryos during oogenesis and embryo development has not been clearly elucidated. The functional activity of mitochondria is crucial for determining the quality of oocytes and embryos; therefore, the underlying mechanism must be better understood. In this review, we summarize the specific role of mitochondria in reproduction in oocytes and embryos. We also briefly discuss the recovery of mitochondrial function in gametes and zygotes. First, we introduce the general characteristics of mitochondria in cells, including their roles in adenosine triphosphate and reactive oxygen species production, calcium homeostasis, and programmed cell death. Second, we present the unique characteristics of mitochondria in female reproduction, covering the bottleneck theory, mitochondrial shape, and mitochondrial metabolic pathways during oogenesis and preimplantation embryo development. Mitochondrial dysfunction is associated with ovarian aging, a diminished ovarian reserve, a poor ovarian response, and several reproduction problems in gametes and zygotes, such as aneuploidy and genetic disorders. Finally, we briefly describe which factors are involved in mitochondrial dysfunction and how mitochondrial function can be recovered in reproduction. We hope to provide a new viewpoint regarding factors that can overcome mitochondrial dysfunction in the field of reproductive medicine.

Keywords:  Dysfunction; Mechanism; Mitochondria; Recovery; Reproduction

DOI:  https://doi.org/10.5653/cerm.2022.05659
J Hum Genet. 2023 Mar 23.

Identification of two novel RRM2B variants associated with autosomal recessive progressive external ophthalmoplegia in a family with pseudodominant inheritance pattern.

Juan Luis Restrepo-Vera, Eulàlia Rovira-Moreno, Javier Ramón, Marta Codina-Sola, Arnau Llauradó, Maria Salvadó, Daniel Sánchez-Tejerina, Javier Sotoca, Elena Martínez-Sáez, Ramon Martí, Elena García-Arumí, Raul Juntas-Morales.

RRM2B encodes the p53-inducible small subunit (p53R2) of ribonucleotide reductase, a key protein for mitochondrial DNA (mtDNA) synthesis. Pathogenic variants in this gene result in familial mitochondrial disease in adults and children, secondary to a maintenance disorder of mtDNA. This study describes two patients, mother and son, with early-onset chronic progressive external ophthalmoplegia (PEO). Skeletal muscle biopsy from the latter was examined: cytochrome c oxidase (COX)-negative fibres were shown, and molecular studies revealed multiple mtDNA deletions. A next-generation sequencing gene panel for nuclear-encoded mitochondrial maintenance genes identified two unreported heterozygous missense variants (c.514 G > A and c.682 G > A) in the clinically affected son. The clinically affected mother harboured the first variant in homozygous state, and the clinically unaffected father harboured the remaining variant in heterozygous state. In silico analyses predicted both variants as deleterious. Cell culture studies revealed that patients' skin fibroblasts, but not fibroblasts from healthy controls, responded to nucleoside supplementation with enhanced mtDNA repopulation, thus suggesting an in vitro functional difference in patients' cells. Our results support the pathogenicity of two novel RRM2B variants found in two patients with autosomal recessive PEO with multiple mtDNA deletions inherited with a pseudodominant pattern.

DOI: https://doi.org/10.1038/s10038-023-01144-2
bioRxiv. 2023 Mar 09. pii: 2023.03.09.531795. [Epub ahead of print]

Tetracycline-dependent inhibition of mitoribosome protein elongation in mitochondrial disease mutant cells suppresses IRE1α to promote cell survival.

Conor T Ronayne, Christopher F Bennett, Elizabeth A Perry, Noa Kantorovic, Pere Puigserver.

Mitochondrial diseases are a group of disorders defined by defects in oxidative phosphorylation caused by nuclear- or mitochondrial-encoded gene mutations. A main cellular phenotype of mitochondrial disease mutations are redox imbalances and inflammatory signaling underlying pathogenic signatures of these patients. Depending on the type of mitochondrial mutation, certain mechanisms can efficiently rescue cell death vulnerability. One method is the inhibition of mitochondrial translation elongation using tetracyclines, potent suppressors of cell death in mitochondrial disease mutant cells. However, the mechanisms whereby tetracyclines promote cell survival are unknown. Here, we show that in mitochondrial mutant disease cells, tetracycline-mediated inhibition of mitoribosome elongation promotes survival through suppression of the ER stress IRE1α protein. Tetracyclines increased levels of the splitting factor MALSU1 (Mitochondrial Assembly of Ribosomal Large Subunit 1) at the mitochondria with recruitment to the mitochondrial ribosome (mitoribosome) large subunit. MALSU1, but not other quality control factors, was required for tetracycline-induced cell survival in mitochondrial disease mutant cells during glucose starvation. In these cells, nutrient stress induced cell death through IRE1α activation associated with a strong protein loading in the ER lumen. Notably, tetracyclines rescued cell death through suppression of IRE1α oligomerization and activity. Consistent with MALSU1 requirement, MALSU1 deficient mitochondrial mutant cells were sensitive to glucose-deprivation and exhibited increased ER stress and activation of IRE1α that was not reversed by tetracyclines. These studies show that inhibition of mitoribosome elongation signals to the ER to promote survival, establishing a new interorganelle communication between the mitoribosome and ER with implications in basic mechanisms of cell survival and treatment of mitochondrial diseases.
Significance Statement: Mitochondrial diseases are a rare and heterogenous class of diseases that result from mutations in mitochondrial genes. Currently, there are no curative therapies due to a lack of mechanistic insights into pathological transformation and signaling. Our lab has discovered that the class of mitochondrial ribosome targeting antibiotics, tetracyclines, promote survival and fitness in models of mitochondrial disease, establishing a new paradigm of cell survival under nutrient stress conditions. In the current study, we present mechanistic insights into tetracyclines ability to rescue mitochondrial disease cells, detailing an interorganelle communication between mitochondrial protein translation and the unfolded protein response during endoplasmic reticulum stress.

DOI: https://doi.org/10.1101/2023.03.09.531795
Cardiol Young. 2023 Mar 23. 1-3

Hypertrophic cardiomyopathy as the initial presentation of mitochondrial disease in an infant born to a diabetic mother.

Jun Chul Byun, Hee Joung Choi.

  In contrast to hypertrophic cardiomyopathy caused by maternal diabetes, neonatal mitochondrial cardiomyopathy is rare and has a poor prognosis. We report an infant born to a mother with maternal diabetes with persistent ventricular hypertrophy, who was diagnosed with mitochondrial disease associated with m.3243A>G mutation in a mitochondrial tRNA leucine 1 gene. The hypertrophic cardiomyopathy was his initial and only clinical presentation.

Keywords:  Hypertrophic cardiomyopathy; MT-TL1 mutation; infant of a diabetic mother; mitochondrial cardiomyopathy

DOI:  https://doi.org/10.1017/S1047951123000392
PLoS Comput Biol. 2023 Mar 23. 19(3): e1010953

Mitochondrial network structure controls cell-to-cell mtDNA variability generated by cell divisions.

Robert C Glastad, Iain G Johnston.

Mitochondria are highly dynamic organelles, containing vital populations of mitochondrial DNA (mtDNA) distributed throughout the cell. Mitochondria form diverse physical structures in different cells, from cell-wide reticulated networks to fragmented individual organelles. These physical structures are known to influence the genetic makeup of mtDNA populations between cell divisions, but their influence on the inheritance of mtDNA at divisions remains less understood. Here, we use statistical and computational models of mtDNA content inside and outside the reticulated network to quantify how mitochondrial network structure can control the variances of inherited mtDNA copy number and mutant load. We assess the use of moment-based approximations to describe heteroplasmy variance and identify several cases where such an approach has shortcomings. We show that biased inclusion of one mtDNA type in the network can substantially increase heteroplasmy variance (acting as a genetic bottleneck), and controlled distribution of network mass and mtDNA through the cell can conversely reduce heteroplasmy variance below a binomial inheritance picture. Network structure also allows the generation of heteroplasmy variance while controlling copy number inheritance to sub-binomial levels, reconciling several observations from the experimental literature. Overall, different network structures and mtDNA arrangements within them can control the variances of key variables to suit a palette of different inheritance priorities.

DOI: https://doi.org/10.1371/journal.pcbi.1010953
Commun Biol. 2023 Mar 22. 6(1): 307

NSUN3-mediated mitochondrial tRNA 5-formylcytidine modification is essential for embryonic development and respiratory complexes in mice.

Yoshitaka Murakami, Fan-Yan Wei, Yoshimi Kawamura, Haruki Horiguchi, Tsuyoshi Kadomatsu, Keishi Miyata, Kyoko Miura, Yuichi Oike, Yukio Ando, Mitsuharu Ueda, Kazuhito Tomizawa, Takeshi Chujo.

In mammalian mitochondria, translation of the AUA codon is supported by 5-formylcytidine (f5C) modification in the mitochondrial methionine tRNA anticodon. The 5-formylation is initiated by NSUN3 methylase. Human NSUN3 mutations are associated with mitochondrial diseases. Here we show that Nsun3 is essential for embryonic development in mice with whole-body Nsun3 knockout embryos dying between E10.5 and E12.5. To determine the functions of NSUN3 in adult tissue, we generated heart-specific Nsun3 knockout (Nsun3HKO) mice. Nsun3HKO heart mitochondria were enlarged and contained fragmented cristae. Nsun3HKO resulted in enhanced heart contraction and age-associated mild heart enlargement. In the Nsun3HKO hearts, mitochondrial mRNAs that encode respiratory complex subunits were not down regulated, but the enzymatic activities of the respiratory complexes decreased, especially in older mice. Our study emphasizes that mitochondrial tRNA anticodon modification is essential for mammalian embryonic development and shows that tissue-specific loss of a single mitochondrial tRNA modification can induce tissue aberration that worsens in later adulthood.

DOI: https://doi.org/10.1038/s42003-023-04680-x
bioRxiv. 2023 Mar 12. pii: 2023.03.11.532186. [Epub ahead of print]

Pharmacologic Activation of an Integrated Stress Response Kinase Promotes Mitochondrial Remodeling.

Valerie Perea, Kelsey R Baron, Vivian Dolina, Giovanni Aviles, Jessica D Rosarda, Xiaoyan Guo, Martin Kampmann, R Luke Wiseman.

The integrated stress response (ISR) is a network of eIF2 α kinases, comprising PERK, GCN2, HRI, and PKR, that induce translational and transcriptional signaling in response to diverse insults. The PERK ISR kinase regulates mitochondria in response to endoplasmic reticulum (ER) stress. Deficiencies in PERK signaling lead to mitochondrial dysfunction and contribute to the pathogenesis of numerous diseases. We define the potential for pharmacologic activators of other ISR kinases to rescue ISR signaling and promote mitochondrial adaptation in cells lacking PERK. We show that the HRI activator BtdCPU and the GCN2 activator halofuginone activate ISR signaling and restore ER stress sensitivity in Perk- deficient cells. However, these compounds differentially impact mitochondria. BtdCPU induces mitochondrial depolarization, leading to mitochondrial fragmentation and ISR activation through the OMA1-DELE1-HRI signaling axis. In contrast, halofuginone promotes mitochondrial elongation and altered mitochondrial respiration, mimicking the regulation induced by PERK. This shows halofuginone can compensate for deficiencies in PERK activity 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.

DOI: https://doi.org/10.1101/2023.03.11.532186
Anal Chem. 2023 Mar 20.

Mitochondrial Membrane Potential Independent Near-Infrared Mitochondrial Viscosity Probes for Real-Time Tracking Mitophagy.

Jiaxin Hong, Xiaogang Guan, Yao Chen, Xiaodong Tan, Shiya Zhang, Guoqiang Feng.

Mitophagy is a vital cellular process playing vital roles in regulating cellular metabolism and mitochondrial quality control. Mitochondrial viscosity is a key microenvironmental index, closely associated with mitochondrial status. To monitor mitophagy and mitochondrial viscosity, three molecular rotors (Mito-1, Mito-2, and Mito-3) were developed. All probes contain a cationic quinolinium unit and a C12 chain so that they can tightly bind mitochondria and are not affected by the mitochondrial membrane potential. Optical studies showed that all probes are sensitive to viscosity changes with an off-on fluorescence response, and Mito-3 shows the best fluorescence enhancement. Bioimaging studies showed that all these probes can not only tightly locate and visualize mitochondria with near-infrared fluorescence but also effectively monitor the mitochondrial viscosity changes in cells. Moreover, Mito-3 was successfully applied to visualize the mitophagy process induced by starvation, and mitochondrial viscosity was found to show an increase during mitophagy. We expect Mito-3 to become a useful imaging tool for studying mitochondrial viscosity and mitophagy.

DOI: https://doi.org/10.1021/acs.analchem.2c05568
Int J Sports Med. 2023 Mar 21.

Resistance training improves hypertrophic and mitochondrial adaptation in skeletal muscle.

Yong-Cai Zhao, Yan-Yan Wu.

Resistance training is employed for pursuing muscle strength characterized by activation of mammalian target of rapamycin (mTOR)-mediated hypertrophic signaling for protein production. Endurance training elevates peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) signaling of mitochondrial adaptations for oxidative phosphorylation. Now, emerging evidence suggests that, like endurance training, resistance training also elicits profound effects on mitochondrial adaptations in skeletal muscle, which means that resistance training yields both strength and endurance phenotypes in myofibers, which has treatment value for the muscle loss and poor aerobic capacity in humans. Our review outlines a brief overview of muscle hypertrophic signals with resistance training and focused on the effects of resistance training on mitochondrial biogenesis and respiration in skeletal muscle, providing novel insights into the therapeutic strategy of resistance training for the metabolically dysfunctional individuals with declined mitochondrial function.

DOI: https://doi.org/10.1055/a-2059-9175
iScience. 2023 Mar 17. 26(3): 106270

MFN1 augmentation prevents retinal degeneration in a Charcot-Marie-Tooth type 2A mouse model.

Saba Shahin, Bin Lu, Yueqin Zhou, Hui Xu, Jason Chetsawang, Robert H Baloh, Shaomei Wang.

  Charcot-Marie-Tooth disease type 2A (CMT2A), the most common inherited peripheral axonal neuropathy, is associated with more than 100 dominant mutations, including R94Q as the most abundant mutation in the Mitofusin2 (MFN2) gene. CMT2A is characterized by progressive motor and sensory loss, color-vision defects, and progressive loss of visual acuity. We used a well-established transgenic mouse model of CMT2A with R94Q mutation on MFN2 gene (MFN2 R94Q ) to investigate the functional and morphological changes in retina. We documented extensive vision loss due to photoreceptor degeneration, retinal ganglion cell and their axonal loss, retinal secondary neuronal and synaptic alternation, and Müller cell gliosis in the retina of MFN2 R94Q mice. Imbalanced MFN1/MFN2 ratio and dysregulated mitochondrial fusion/fission result in retinal degeneration via P62/LC3B-mediated mitophagy/autophagy in MFN2 R94Q mice. Finally, transgenic MFN1 augmentation (MFN2 R94Q :MFN1) rescued vision and retinal morphology to wild-type level via restoring homeostasis in mitochondrial MFN1/MFN2 ratio, fusion/fission cycle, and PINK1-dependent, Parkin-independent mitophagy.

Keywords:  Biological sciences; Molecular neuroscience; Neuroscience; Sensory neuroscience

DOI:  https://doi.org/10.1016/j.isci.2023.106270
FASEB J. 2023 Apr;37(4): e22851

Increased mitochondrial Ca2+ contributes to health decline with age and Duchene muscular dystrophy in C. elegans.

Atsushi Higashitani, Mika Teranishi, Yui Nakagawa, Yukou Itoh, Surabhi Sudevan, Nathaniel J Szewczyk, Yukihiko Kubota, Takaaki Abe, Takeshi Kobayashi.

  Sarcopenia is a geriatric syndrome characterized by an age-related decline in skeletal muscle mass and strength. Here, we show that suppression of mitochondrial calcium uniporter (MCU)-mediated Ca2+ influx into mitochondria in the body wall muscles of the nematode Caenorhabditis elegans improved the sarcopenic phenotypes, blunting movement and mitochondrial structural and functional decline with age. We found that normally aged muscle cells exhibited elevated resting mitochondrial Ca2+ levels and increased mitophagy to eliminate damaged mitochondria. Similar to aging muscle, we found that suppressing MCU function in muscular dystrophy improved movement via reducing elevated resting mitochondrial Ca2+ levels. Taken together, our results reveal that elevated resting mitochondrial Ca2+ levels contribute to muscle decline with age and muscular dystrophy. Further, modulation of MCU activity may act as a potential pharmacological target in various conditions involving muscle loss.

Keywords:  MCU; aging; calcium; dystrophy; mitophagy; sarcopenia

DOI:  https://doi.org/10.1096/fj.202201489RR
Brain. 2023 Mar 24. pii: awad099. [Epub ahead of print]

Mitochondrial dysfunction and calcium dysregulation in COQ8A-ataxia Purkinje neurons are rescued by CoQ10 treatment.

Ioannis Manolaras, Andrea Del Bondio, Olivier Griso, Laurence Reutenauer, Aurélie Eisenmann, Bianca H Habermann, Hélène Puccio.

  COQ8A-Ataxia is a rare form of neurodegenerative disorder due to mutations in the COQ8A gene. The encoded mitochondrial protein is involved in the regulation of Coenzyme Q10 biosynthesis. Previous studies on the constitutive Coq8a-/-mice indicated specific alterations of cerebellar Purkinje neurons involving altered electrophysiological function and dark cell degeneration. In the present manuscript, we extend our understanding of the contribution of Purkinje neuron dysfunction to the pathology. By generating a Purkinje specific conditional COQ8A knockout, we demonstrate that loss of COQ8A in Purkinje neurons is the main cause of cerebellar ataxia. Furthermore, through in vivo and in vitro approaches, we show that COQ8A-depleted Purkinje neurons have abnormal dendritic arborizations, altered mitochondria function and intracellular calcium dysregulation. Furthermore, we demonstrate that oxidative phosphorylation, in particular Complex IV, is primarily altered at pre-symptomatic stages of the disease. Finally, the morphology of primary Purkinje neurons as well as the mitochondrial dysfunction and calcium dysregulation could be rescued by CoQ10 treatment, suggesting that CoQ10 could be a beneficial treatment for COQ8A-Ataxia.

Keywords:  Purkinje neurons; ataxia; calcium; coenzyme Q10; mitochondria

DOI:  https://doi.org/10.1093/brain/awad099
Nat Immunol. 2023 Mar 20.

Mitochondrial damage activates the NLRP10 inflammasome.

Tomasz Próchnicki, Matilde B Vasconcelos, Kim S Robinson, Matthew S J Mangan, Dennis De Graaf, Kateryna Shkarina, Marta Lovotti, Lena Standke, Romina Kaiser, Rainer Stahl, Fraser G Duthie, Maximilian Rothe, Kateryna Antonova, Lea-Marie Jenster, Zhi Heng Lau, Sarah Rösing, Nora Mirza, Clarissa Gottschild, Dagmar Wachten, Claudia Günther, Thomas A Kufer, Florian I Schmidt, Franklin L Zhong, Eicke Latz.

Upon detecting pathogens or cell stress, several NOD-like receptors (NLRs) form inflammasome complexes with the adapter ASC and caspase-1, inducing gasdermin D (GSDMD)-dependent cell death and maturation and release of IL-1β and IL-18. The triggers and activation mechanisms of several inflammasome-forming sensors are not well understood. Here we show that mitochondrial damage activates the NLRP10 inflammasome, leading to ASC speck formation and caspase-1-dependent cytokine release. While the AIM2 inflammasome can also sense mitochondrial demise by detecting mitochondrial DNA (mtDNA) in the cytosol, NLRP10 monitors mitochondrial integrity in an mtDNA-independent manner, suggesting the recognition of distinct molecular entities displayed by the damaged organelles. NLRP10 is highly expressed in differentiated human keratinocytes, in which it can also assemble an inflammasome. Our study shows that this inflammasome surveils mitochondrial integrity. These findings might also lead to a better understanding of mitochondria-linked inflammatory diseases.

DOI: https://doi.org/10.1038/s41590-023-01451-y
Elife. 2023 Mar 23. pii: e84415. [Epub ahead of print]12

Resting mitochondrial complex I from Drosophila melanogaster adopts a helix-locked state.

Abhilash Padavannil, Anjaneyulu Murari, Shauna-Kay Rhooms, Edward Owusu-Ansah, James A Letts.

  Respiratory complex I is a proton-pumping oxidoreductase key to bioenergetic metabolism. Biochemical studies have found a divide in the behavior of complex I in metazoans that aligns with the evolutionary split between Protostomia and Deuterostomia. Complex I from Deuterostomia including mammals can adopt a biochemically defined off-pathway 'deactive' state, whereas complex I from Protostomia cannot. The presence of off-pathway states complicates the interpretation of structural results and has led to considerable mechanistic debate. Here, we report the structure of mitochondrial complex I from the thoracic muscles of the model protostome Drosophila melanogaster. We show that although D. melanogaster complex I (Dm-CI) does not have a NEM-sensitive deactive state, it does show slow activation kinetics indicative of an off-pathway resting state. The resting-state structure of Dm-CI from the thoracic muscle reveals multiple conformations. We identify a helix-locked state in which an N-terminal α-helix on the NDUFS4 subunit wedges between the peripheral and membrane arms. Comparison of the Dm-CI structure and conformational states to those observed in bacteria, yeast, and mammals provides insight into the roles of subunits across organisms, explains why the Dm-CI off-pathway resting state is NEM insensitive, and raises questions regarding current mechanistic models of complex I turnover.

Keywords:  complex I; drosophila melanogaster; electron transport chain; mitochondria; molecular biophysics; respiration; single particle cryoEM; structural biology

DOI:  https://doi.org/10.7554/eLife.84415
Nature. 2023 Mar 22.

Structural basis of mitochondrial membrane bending by the I-II-III2-IV2 supercomplex.

Alexander Mühleip, Rasmus Kock Flygaard, Rozbeh Baradaran, Outi Haapanen, Thomas Gruhl, Victor Tobiasson, Amandine Maréchal, Vivek Sharma, Alexey Amunts.

Mitochondrial energy conversion requires an intricate architecture of the inner mitochondrial membrane1. Here we show that a supercomplex containing all four respiratory chain components contributes to membrane curvature induction in ciliates. We report cryo-electron microscopy and cryo-tomography structures of the supercomplex that comprises 150 different proteins and 311 bound lipids, forming a stable 5.8-MDa assembly. Owing to subunit acquisition and extension, complex I associates with a complex IV dimer, generating a wedge-shaped gap that serves as a binding site for complex II. Together with a tilted complex III dimer association, it results in a curved membrane region. Using molecular dynamics simulations, we demonstrate that the divergent supercomplex actively contributes to the membrane curvature induction and tubulation of cristae. Our findings highlight how the evolution of protein subunits of respiratory complexes has led to the I-II-III2-IV2 supercomplex that contributes to the shaping of the bioenergetic membrane, thereby enabling its functional specialization.

DOI: https://doi.org/10.1038/s41586-023-05817-y
bioRxiv. 2023 Mar 08. pii: 2023.03.06.531392. [Epub ahead of print]

Mitochondrial haplotype and mito-nuclear matching drive somatic mutation and selection throughout aging.

Isabel M Serrano, Misa Hirose, Clint Valentine, Sharie Austin, Elizabeth Schmidt, Gabriel Pratt, Lindsey Williams, Jesse Salk, Saleh Ibrahim, Peter H Sudmant.

Mitochondrial genomes co-evolve with the nuclear genome over evolutionary timescales and are shaped by selection in the female germline. Here, we investigate how mismatching between nuclear and mitochondrial ancestry impacts the somatic evolution of the mt-genome in different tissues throughout aging. We used ultra-sensitive Duplex Sequencing to profile ∼2.5 million mt-genomes across five mitochondrial haplotypes and three tissues in young and aged mice, cataloging ∼1.2 million mitochondrial somatic mutations. We identify haplotype-specific mutational patterns and several mutational hotspots, including at the Light Strand Origin of Replication, which consistently exhibits the highest mutation frequency. We show that rodents exhibit a distinct mitochondrial somatic mutational spectrum compared to primates with a surfeit of reactive oxygen species-associated G>T/C>A mutations and that somatic mutations in protein coding genes exhibit strong signatures of positive selection. Lastly, we identify an extensive enrichment in somatic reversion mutations that "re-align" mito-nuclear ancestry within an organism's lifespan. Together, our findings demonstrate that mitochondrial genomes are a dynamically evolving subcellular population shaped by somatic mutation and selection throughout organismal lifetimes.

DOI: https://doi.org/10.1101/2023.03.06.531392
Life Sci Alliance. 2023 Jun;pii: e202201805. [Epub ahead of print]6(6):

Mitochondrial dysfunction rapidly modulates the abundance and thermal stability of cellular proteins.

Carina Groh, Per Haberkant, Frank Stein, Sebastian Filbeck, Stefan Pfeffer, Mikhail M Savitski, Felix Boos, Johannes M Herrmann.

Cellular functionality relies on a well-balanced, but highly dynamic proteome. Dysfunction of mitochondrial protein import leads to the cytosolic accumulation of mitochondrial precursor proteins which compromise cellular proteostasis and trigger a mitoprotein-induced stress response. To dissect the effects of mitochondrial dysfunction on the cellular proteome as a whole, we developed pre-post thermal proteome profiling. This multiplexed time-resolved proteome-wide thermal stability profiling approach with isobaric peptide tags in combination with a pulsed SILAC labelling elucidated dynamic proteostasis changes in several dimensions: In addition to adaptations in protein abundance, we observed rapid modulations of the thermal stability of individual cellular proteins. Different functional groups of proteins showed characteristic response patterns and reacted with group-specific kinetics, allowing the identification of functional modules that are relevant for mitoprotein-induced stress. Thus, our new pre-post thermal proteome profiling approach uncovered a complex response network that orchestrates proteome homeostasis in eukaryotic cells by time-controlled adaptations of the abundance and the conformation of proteins.

DOI: https://doi.org/10.26508/lsa.202201805
BMC Ophthalmol. 2023 Mar 24. 23(1): 118

Sirtuin 3 mutation- induced mitochondrial dysfunction and optic neuropathy: a case report.

Bo Young Chun, Jung Moon Choi, Su-Kyeong Hwang, Soolienah Rhiu.

   BACKGROUND: Mitochondrial optic neuropathy is characterized by painless, progressive, symmetrical central vision loss, and dyschromatopsia owing to mitochondrial dysfunction. This report documents a rare case of mitochondrial optic neuropathy due to the SIRT3 gene mutation.
CASE PRESENTATION: This report describes a case of a 17-year-old boy who presented with symptoms of bilateral painless, progressive vision decline over several years. Fundus examination revealed temporal pallor of the optic nerve head in both the eyes and an OCT showed considerable thinning of the retinal nerve fiber and ganglion cell layers. Pathogenicity was confirmed by decreased mitochondrial function measured by bioenergetic health index and oxygen consumption rate in this patient. Subsequent NGS revealed a missense mutation of the SIRT3 gene (c.1137G > C, p.Trp379Cys) in the patient.
CONCLUSIONS: This case describes the clinical manifestation of mitochondrial optic neuropathy due to the SIRT3 gene mutation.

Keywords:  Case report; Mitochondrial dysfunction; Mitochondrial optic neuropathy; SIRT3 gene mutation

DOI:  https://doi.org/10.1186/s12886-023-02872-x
bioRxiv. 2023 Mar 10. pii: 2023.03.09.531996. [Epub ahead of print]

Knockout of cardiolipin synthase disrupts postnatal cardiac development by inhibiting the maturation of mitochondrial cristae.

Mindong Ren, Yang Xu, Colin K L Phoon, Hediye Erdjument-Bromage, Thomas A Neubert, Michael Schlame.

Background: Cardiomyocyte maturation requires a massive increase in respiratory enzymes and their assembly into long-lived complexes of oxidative phosphorylation (OXPHOS). The molecular mechanisms underlying the maturation of cardiac mitochondria have not been established.
Methods: To determine whether the mitochondria-specific lipid cardiolipin is involved in cardiac maturation, we created a cardiomyocyte-restricted knockout (KO) of cardiolipin synthase ( Crls1 ) in mice and studied the postnatal development of the heart. We also measured the turnover rates of proteins and lipids in cardiolipin-deficient flight muscle from Drosophila, a tissue that has mitochondria with high OXPHOS activity like the heart.
Results: Crls1KO mice survived the prenatal period but failed to accumulate OXPHOS proteins during postnatal maturation and succumbed to heart failure at the age of 2 weeks. Turnover measurements showed that the exceptionally long half-life of OXPHOS proteins is critically dependent on cardiolipin.
Conclusions: Cardiolipin is essential for the postnatal maturation of cardiomyocytes because it allows mitochondrial cristae to accumulate OXPHOS proteins to a high concentration and to shield them from degradation.

DOI: https://doi.org/10.1101/2023.03.09.531996
Life Sci Alliance. 2023 Jun;pii: e202201419. [Epub ahead of print]6(6):

Structure-based design and characterization of Parkin-activating mutations.

Michael U Stevens, Nathalie Croteau, Mohamed A Eldeeb, Odetta Antico, Zhi Wei Zeng, Rachel Toth, Thomas M Durcan, Wolfdieter Springer, Edward A Fon, Miratul Mk Muqit, Jean-François Trempe.

Autosomal recessive mutations in the Parkin gene cause Parkinson's disease. Parkin encodes an ubiquitin E3 ligase that functions together with the kinase PINK1 in a mitochondrial quality control pathway. Parkin exists in an inactive conformation mediated by autoinhibitory domain interfaces. Thus, Parkin has become a target for the development of therapeutics that activate its ligase activity. Yet, the extent to which different regions of Parkin can be targeted for activation remained unknown. Here, we have used a rational structure-based approach to design new activating mutations in both human and rat Parkin across interdomain interfaces. Out of 31 mutations tested, we identified 11 activating mutations that all cluster near the RING0:RING2 or REP:RING1 interfaces. The activity of these mutants correlates with reduced thermal stability. Furthermore, three mutations V393D, A401D, and W403A rescue a Parkin S65A mutant, defective in mitophagy, in cell-based studies. Overall our data extend previous analysis of Parkin activation mutants and suggests that small molecules that would mimic RING0:RING2 or REP:RING1 destabilisation offer therapeutic potential for Parkinson's disease patients harbouring select Parkin mutations.

DOI: https://doi.org/10.26508/lsa.202201419
Exp Mol Med. 2023 Mar 24.

Molecular mechanisms of mitochondrial DNA release and activation of the cGAS-STING pathway.

Jeonghan Kim, Ho-Shik Kim, Jay H Chung.

In addition to constituting the genetic material of an organism, DNA is a tracer for the recognition of foreign pathogens and a trigger of the innate immune system. cGAS functions as a sensor of double-stranded DNA fragments and initiates an immune response via the adaptor protein STING. The cGAS-STING pathway not only defends cells against various DNA-containing pathogens but also modulates many pathological processes caused by the immune response to the ectopic localization of self-DNA, such as cytosolic mitochondrial DNA (mtDNA) and extranuclear chromatin. In addition, macrophages can cause inflammation by forming a class of protein complexes called inflammasomes, and the activation of the NLRP3 inflammasome requires the release of oxidized mtDNA. In innate immunity related to inflammasomes, mtDNA release is mediated by macropores that are formed on the outer membrane of mitochondria via VDAC oligomerization. These macropores are specifically formed in response to mitochondrial stress and tissue damage, and the inhibition of VDAC oligomerization mitigates this inflammatory response. The rapidly expanding area of research on the mechanisms by which mtDNA is released and triggers inflammation has revealed new treatment strategies not only for inflammation but also, surprisingly, for neurodegenerative diseases such as amyotrophic lateral sclerosis.

DOI: https://doi.org/10.1038/s12276-023-00965-7
Mol Reprod Dev. 2023 Mar 21.

Rapamycin encourages the maintenance of mitochondrial dynamic balance and mitophagy activity for improving developmental competence of blastocysts in porcine embryos in vitro.

Hyo-Jin Park, Gyeong-Deok Heo, Seul-Gi Yang, Deog-Bon Koo.

  Rapamycin induces autophagosome formation and activity during oocyte maturation, improved fertilization ability of matured oocytes, and early embryonic developmental competence. However, potential changes in mitochondrial fission and mitophagy via regulation of autophagy in early porcine embryonic development have not been previously studied. Here, we investigated embryonic developmental ability and quality of porcine embryos 2 days after in vitro fertilization and following treatment with 1 and 10 nM rapamycin. As a results, 1 nM rapamycin exposure significantly improved (p < 0.05) blastocyst developmental competence compared to that in nontreated embryos (nontreated: 26.2 ± 5.7% vs. 1 nM rapamycin: 35.3 ± 5.1%). We observed autophagic (LC3B) and mitochondrial fission protein expression (dynamin-related protein-1 [DRP1] and pDRP1-Ser616) at the cleavage stage of 1 and 10 nM rapamycin-treated porcine embryos, using Western blot and immunofluorescence analyses. Interestingly, 1 nM rapamycin treatment significantly improved autophagy formation, mitochondrial activation, and mitochondrial fission protein levels (p < 0.05; p-DRP1 [Ser616]) at the cleavage stage of porcine embryos. Additionally, mitophagy was significantly increased in blastocysts treated with 1 nM rapamycin. In conclusion, our results suggest that rapamycin promotes blastocyst development ability in porcine embryos through mitochondrial fission, activation, and mitophagy in in vitro culture.

Keywords:  in vitro culture; mitochondrial fission; mitophagy; porcine embryos; rapamycin

DOI:  https://doi.org/10.1002/mrd.23681
J Clin Invest. 2023 Mar 23. pii: e164575. [Epub ahead of print]

Intrathecal AAV9/AP4M1 gene therapy for hereditary spastic paraplegia 50 shows safety and efficacy in preclinical studies.

Xin Chen, Thomas Dong, Yuhui Hu, Raffaella De Pace, Rafael Mattera, Kathrin Eberhardt, Marvin Ziegler, Terry Pirovolakis, Mustafa Sahin, Juan S Bonifacino, Darius Ebrahimi-Fakhari, Steven J Gray.

  Spastic paraplegia 50 (SPG50) is an ultrarare childhood-onset neurological disorder caused by biallelic loss-of-function variants in the AP4M1 gene. SPG50 is characterized by progressive spastic paraplegia, global developmental delay and subsequent intellectual disability, secondary microcephaly, and epilepsy. Preclinical studies evaluated an adeno-associated virus (AAV)/AP4M1 gene therapy for SPG50. In vitro studies demonstrated that transduction of patient-derived fibroblasts with AAV2/AP4M1 resulted in phenotypic rescue. To evaluate efficacy in vivo, Ap4m1 knockout mice were intrathecally (IT) injected with 5E11, 2.5E11, or 1.25E11 vg doses of AAV9/AP4M1 at postnatal day p7-10 (pre-manifesting cohorts) or p90 (early manifesting cohorts). Age- and dose-dependent effects were observed, with early intervention and higher doses achieving the best therapeutic benefits. In parallel, three toxicology studies in wild-type mice, rats, and non-human primates (NHPs) demonstrated that AAV9/AP4M1 had an acceptable safety profile up to a target human dose of 1E15 vg. Of note, similar degrees of minimal to mild dorsal root ganglia (DRG) toxicity were observed in both rats and NHPs, supporting the use of rats to monitor DRG toxicity in future IT AAV studies. These preclinical results identify an acceptably safe and efficacious dose of IT-administered AAV9/AP4M1, supporting an investigational gene transfer clinical trial to treat SPG50.

Keywords:  Neurological disorders; Neuroscience

DOI:  https://doi.org/10.1172/JCI164575
Nat Metab. 2023 Mar 23.

Loss of fatty acid degradation by astrocytic mitochondria triggers neuroinflammation and neurodegeneration.

Yashi Mi, Guoyuan Qi, Francesca Vitali, Yuan Shang, Adam C Raikes, Tian Wang, Yan Jin, Roberta D Brinton, Haiwei Gu, Fei Yin.

Astrocytes provide key neuronal support, and their phenotypic transformation is implicated in neurodegenerative diseases. Metabolically, astrocytes possess low mitochondrial oxidative phosphorylation (OxPhos) activity, but its pathophysiological role in neurodegeneration remains unclear. Here, we show that the brain critically depends on astrocytic OxPhos to degrade fatty acids (FAs) and maintain lipid homeostasis. Aberrant astrocytic OxPhos induces lipid droplet (LD) accumulation followed by neurodegeneration that recapitulates key features of Alzheimer's disease (AD), including synaptic loss, neuroinflammation, demyelination and cognitive impairment. Mechanistically, when FA load overwhelms astrocytic OxPhos capacity, elevated acetyl-CoA levels induce astrocyte reactivity by enhancing STAT3 acetylation and activation. Intercellularly, lipid-laden reactive astrocytes stimulate neuronal FA oxidation and oxidative stress, activate microglia through IL-3 signalling, and inhibit the biosynthesis of FAs and phospholipids required for myelin replenishment. Along with LD accumulation and impaired FA degradation manifested in an AD mouse model, we reveal a lipid-centric, AD-resembling mechanism by which astrocytic mitochondrial dysfunction progressively induces neuroinflammation and neurodegeneration.

DOI: https://doi.org/10.1038/s42255-023-00756-4
Proc Natl Acad Sci U S A. 2023 Mar 28. 120(13): e2217576120

Peroxisome proliferator-activated receptor-α (PPARα) regulates wound healing and mitochondrial metabolism in the cornea.

Wentao Liang, Li Huang, Amy Whelchel, Tian Yuan, Xiang Ma, Rui Cheng, Yusuke Takahashi, Dimitrios Karamichos, Jian-Xing Ma.

  Diabetes can result in impaired corneal wound healing. Mitochondrial dysfunction plays an important role in diabetic complications. However, the regulation of mitochondria function in the diabetic cornea and its impacts on wound healing remain elusive. The present study aimed to explore the molecular basis for the disturbed mitochondrial metabolism and subsequent wound healing impairment in the diabetic cornea. Seahorse analysis showed that mitochondrial oxidative phosphorylation is a major source of ATP production in human corneal epithelial cells. Live corneal biopsy punches from type 1 and type 2 diabetic mouse models showed impaired mitochondrial functions, correlating with impaired corneal wound healing, compared to nondiabetic controls. To approach the molecular basis for the impaired mitochondrial function, we found that Peroxisome Proliferator-Activated Receptor-α (PPARα) expression was downregulated in diabetic human corneas. Even without diabetes, global PPARα knockout mice and corneal epithelium-specific PPARα conditional knockout mice showed disturbed mitochondrial function and delayed wound healing in the cornea, similar to that in diabetic corneas. In contrast, fenofibrate, a PPARα agonist, ameliorated mitochondrial dysfunction and enhanced wound healing in the corneas of diabetic mice. Similarly, corneal epithelium-specific PPARα transgenic overexpression improved mitochondrial function and enhanced wound healing in the cornea. Furthermore, PPARα agonist ameliorated the mitochondrial dysfunction in primary human corneal epithelial cells exposed to diabetic stressors, which was impeded by siRNA knockdown of PPARα, suggesting a PPARα-dependent mechanism. These findings suggest that downregulation of PPARα plays an important role in the impaired mitochondrial function in the corneal epithelium and delayed corneal wound healing in diabetes.

Keywords:  PPARα; cornea; epithelium; mitochondria; wound healing

DOI:  https://doi.org/10.1073/pnas.2217576120
Proc Natl Acad Sci U S A. 2023 Mar 28. 120(13): e2213857120

Muscle PARP1 inhibition extends lifespan through AMPKα PARylation and activation in Drosophila.

Shanshan Guo, Shuang Zhang, Yixiao Zhuang, Famin Xie, Ruwen Wang, Xingyu Kong, Qiongyue Zhang, Yonghao Feng, Huanqing Gao, Xingxing Kong, Tiemin Liu.

  Poly(ADP-ribose) polymerase-1 (PARP1) has been reported to play an important role in longevity. Here, we showed that the knockdown of the PARP1 extended the lifespan of Drosophila, with particular emphasis on the skeletal muscle. The muscle-specific mutant Drosophila exhibited resistance to starvation and oxidative stress, as well as an increased ability to climb, with enhanced mitochondrial biogenesis and activity at an older age. Mechanistically, the inhibition of PARP1 increases the activity of AMP-activated protein kinase alpha (AMPKα) and mitochondrial turnover. PARP1 could interact with AMPKα and then regulate it via poly(ADP ribosyl)ation (PARylation) at residues E155 and E195. Double knockdown of PARP1 and AMPKα, specifically in muscle, could counteract the effects of PARP1 inhibition in Drosophila. Finally, we showed that increasing lifespan via maintaining mitochondrial network homeostasis required intact PTEN induced kinase 1 (PINK1). Taken together, these data indicate that the interplay between PARP1 and AMPKα can manipulate mitochondrial turnover, and be targeted to promote longevity.

Keywords:  PARP1; PARylation; longevity; mitochondria

DOI:  https://doi.org/10.1073/pnas.2213857120
Front Aging. 2023 ;4 1171221

Editorial: Altered bioenergetics, mitochondrial quality control, and calcium signaling in the brain: Implications to age-related diseases.

Smijin K Soman, Bridget Martinez, Ruben K Dagda.



Keywords:  2-deoxyglucose; d-Glyceric acid; diabetes mellitus; mitochondria; retinal degeneration

DOI:  https://doi.org/10.3389/fragi.2023.1171221
Cell Metab. 2023 Mar 17. pii: S1550-4131(23)00084-0. [Epub ahead of print]

Molecular and metabolic heterogeneity of astrocytes and microglia.

Philip Hasel, William H Aisenberg, F Chris Bennett, Shane A Liddelow.

Astrocytes and microglia are central players in a myriad of processes in the healthy and diseased brain, ranging from metabolism to immunity. The crosstalk between these two cell types contributes to pathology in many if not all neuroinflammatory and neurodegenerative diseases. Recent advancements in integrative multimodal sequencing techniques have begun to highlight how heterogeneous both cell types are and the importance of metabolism to their regulation. We discuss here the transcriptomic, metabolic, and functional heterogeneity of astrocytes and microglia and highlight their interaction in health and disease.

DOI: https://doi.org/10.1016/j.cmet.2023.03.006
FASEB J. 2023 Apr;37(4): e22891

Switching ubiquitous and muscle-specific isoforms of mitochondrial respiratory complex IV in skeletal muscle fine-tunes complex IV activity.

Xianglai Ye, Yaojun Xie, Yu Shi, Bo Wang, Xinyu Han, Xiaoxuan Zhou, Kexin Pan, Maofeng Wang, Hezhi Fang.

  Respiratory complex IV (CIV, cytochrome c oxidase) is the terminal enzyme of the mitochondrial electron transport chain. Some CIV subunits have two or more isoforms, which are ubiquitously expressed or are expressed in specific tissues like the lung, muscle, and testis. Among the tissue-specific CIV isoforms, the muscle-specific isoforms are expressed in adult cardiac and skeletal muscles. To date, the physiological and biochemical association between the muscle-specific CIV isoforms and aerobic respiration in muscles remains unclear. In this study, we profiled the CIV organization and expression pattern of muscle-specific CIV isoforms in different mouse muscle tissues. We found extensive CIV-containing supramolecular organization in murine musculature at advanced developmental stages, while a switch in the expression from ubiquitous to muscle-specific isoforms of CIV was also detected. Such a switch was confirmed during the in vitro differentiation of mouse C2C12 myoblasts. Unexpectedly, a CIV expression decrease was observed during C2C12 differentiation, which was probably due to a small increase in the expression of muscle-specific isoforms coupled with a dramatic decrease in the ubiquitous isoforms. We also found that the enzymatic activity of CIV containing the muscle-specific isoform COX6A2 was higher than that with COX6A1 in engineered HEK293T cells. Overall, our results indicate that switching the expression from ubiquitous to muscle-specific CIV isoforms is indispensable for optimized oxidative phosphorylation in mature skeletal muscles. We also note that the in vitro C2C12 differentiation model is not suitable for the study of muscular aerobic respiration due to insufficient expression of muscle-specific CIV isoforms.

Keywords:  electron transport complex IV; myoblasts; oxidative phosphorylation; protein isoforms; skeletal muscle

DOI:  https://doi.org/10.1096/fj.202201223RR
iScience. 2023 Mar 17. 26(3): 106296

Neuronal loss of NCLX-dependent mitochondrial calcium efflux mediates age-associated cognitive decline.

Pooja Jadiya, Henry M Cohen, Devin W Kolmetzky, Ashlesha A Kadam, Dhanendra Tomar, John W Elrod.

  Mitochondrial calcium overload contributes to neurodegenerative disease development and progression. We recently reported that loss of the mitochondrial sodium/calcium exchanger (NCLX), the primary mechanism of mCa2+ efflux, promotes mCa2+ overload, metabolic derangement, redox stress, and cognitive decline in models of Alzheimer's disease (AD). However, whether disrupted mCa2+ signaling contributes to neuronal pathology and cognitive decline independent of pre-existing amyloid or tau pathology remains unknown. Here, we generated mice with neuronal deletion of the mitochondrial sodium/calcium exchanger (NCLX, Slc8b1 gene), and evaluated age-associated changes in cognitive function and neuropathology. Neuronal loss of NCLX resulted in an age-dependent decline in spatial and cued recall memory, moderate amyloid deposition, mild tau pathology, synaptic remodeling, and indications of cell death. These results demonstrate that loss of NCLX-dependent mCa2+ efflux alone is sufficient to induce an Alzheimer's disease-like pathology and highlights the promise of therapies targeting mCa2+ exchange.

Keywords:  Behavioral neuroscience; Cellular neuroscience; Cognitive neuroscience; Molecular neuroscience

DOI:  https://doi.org/10.1016/j.isci.2023.106296
Nat Commun. 2023 Mar 22. 14(1): 1595

A defect in mitochondrial protein translation influences mitonuclear communication in the heart.

Feng Gao, Tian Liang, Yao Wei Lu, Xuyang Fu, Xiaoxuan Dong, Linbin Pu, Tingting Hong, Yuxia Zhou, Yu Zhang, Ning Liu, Feng Zhang, Jianming Liu, Andrea P Malizia, Hong Yu, Wei Zhu, Douglas B Cowan, Hong Chen, Xinyang Hu, John D Mably, Jian'an Wang, Da-Zhi Wang, Jinghai Chen.

The regulation of the informational flow from the mitochondria to the nucleus (mitonuclear communication) is not fully characterized in the heart. We have determined that mitochondrial ribosomal protein S5 (MRPS5/uS5m) can regulate cardiac function and key pathways to coordinate this process during cardiac stress. We demonstrate that loss of Mrps5 in the developing heart leads to cardiac defects and embryonic lethality while postnatal loss induces cardiac hypertrophy and heart failure. The structure and function of mitochondria is disrupted in Mrps5 mutant cardiomyocytes, impairing mitochondrial protein translation and OXPHOS. We identify Klf15 as a Mrps5 downstream target and demonstrate that exogenous Klf15 is able to rescue the overt defects and re-balance the cardiac metabolome. We further show that Mrps5 represses Klf15 expression through c-myc, together with the metabolite L-phenylalanine. This critical role for Mrps5 in cardiac metabolism and mitonuclear communication highlights its potential as a target for heart failure therapies.

DOI: https://doi.org/10.1038/s41467-023-37291-5