bims-mitmed 2024-03-03 papers

bims-mitmed

Biomed News

on Mitochondrial medicine

Issue of 2024–03–03
thirty-two papers selected by
Dario Brunetti, Fondazione IRCCS Istituto Neurologico

FBXL4: safeguarding against mitochondrial depletion through suppression of mitophagy.
Lack of mitochondrial complex I assembly factor NDUFAF2 results in a distinctive infantile-onset brainstem neurodegenerative disease with early lethality.
Optic atrophy 1 mediates muscle differentiation by promoting a metabolic switch via the supercomplex assembly factor SCAF1.
mitoTALEN reduces the mutant mtDNA load in neurons.
Mitochondrial derived vesicles- Quo Vadis?
Gene editing improves endoplasmic reticulum-mitochondrial contacts and unfolded protein response in Friedreich's ataxia iPSC-derived neurons.
Mitochondrial DNA leakage triggers inflammation in age-related cardiovascular diseases.
Aging STINGs: mitophagy at the crossroads of neuroinflammation.
Tom20 gates PINK1 activity and mediates its tethering of the TOM and TIM23 translocases upon mitochondrial stress.
Mitochondria in disease: changes in shapes and dynamics.
MtDNA deletions and aging.
Prophylactic nicotinamide treatment protects from rotenone-induced neurodegeneration by increasing mitochondrial content and volume.
NEMF-mediated Listerin-independent mitochondrial translational surveillance by E3 ligase Pirh2 and mitochondrial protease ClpXP.
Mitochondrial dysfunction in lipid processing and gastrointestinal disorders.
The Application of Brain Organoid for Drug Discovery in Mitochondrial Diseases.
Mitochondrial stress in the spaceflight environment.
ATF4-dependent increase in mitochondrial-endoplasmic reticulum tethering following OPA1 deletion in skeletal muscle.
Characterization of Cardiac-Onset Initial Presentation in Friedreich Ataxia.
Therapeutic benefit of idebenone in patients with Leber hereditary optic neuropathy: The LEROS nonrandomized controlled trial.
PMF-seq: a highly scalable screening strategy for linking genetics to mitochondrial bioenergetics.
In utero pulse injection of isotopic amino acids quantifies protein turnover rates during murine fetal development.
Reorganization of mitochondria-organelle interactions during postnatal development in skeletal muscle.
'Epigenetic' editing cuts cholesterol in mice.
Miro1 improves the exogenous engraftment efficiency and therapeutic potential of mitochondria transfer using Wharton's jelly mesenchymal stem cells.
Human Platelet Derived Mitochondrial OPA-1 Isoforms and Interaction With TDP-43 in Neurodegenerative Diseases.
Phage-assisted evolution of highly active cytosine base editors with enhanced selectivity and minimal sequence context preference.
Mitochondrial DNA integrity and metabolome profile are preserved in the human induced pluripotent stem cell reference line KOLF2.1J.
Placental inflammation, oxidative stress, and fetal outcomes in maternal obesity.
Human neural stem cells promote mitochondrial genesis to alleviate neuronal damage in MPTP-induced cynomolgus monkey models.
Morphological diversification and functional maturation of human astrocytes in glia-enriched cortical organoid transplanted in mouse brain.
Mitochondrial fusion and altered beta-oxidation drive muscle wasting in a Drosophila cachexia model.
Cellular reprogramming in vivo initiated by SOX4 pioneer factor activity.

Autophagy. 2024 Feb 29. 1-3

FBXL4: safeguarding against mitochondrial depletion through suppression of mitophagy.

Prajakta Kulkarni, Giang Thanh Nguyen-Dien, Keri-Lyn Kozul, Julia K Pagan.

  Mitophagy is a critical mitochondrial quality control process that selectively removes dysfunctional or excess mitochondria through the autophagy-lysosome system. The process is tightly controlled to ensure cellular and physiological homeostasis. Insufficient mitophagy can result in failure to remove damaged mitochondria and consequent cellular degeneration, but it is equally important to appropriately restrain mitophagy to prevent excessive mitochondrial depletion. Here, we discuss our recent discovery that the SKP1-CUL1-F-box (SCF)-FBXL4 (F-box and leucine-rich repeat protein 4) E3 ubiquitin ligase localizes to the mitochondrial outer membrane, where it constitutively mediates the ubiquitination and degradation of BNIP3L/NIX and BNIP3 mitophagy receptors to suppress mitophagy. The post-translational regulation of BNIP3L and BNIP3 is disrupted in mitochondrial DNA depletion syndrome 13 (MTDPS13), a multi-systemic disorder caused by mutations in the FBXL4 gene and characterized by elevated mitophagy and mitochondrial DNA/mtDNA depletion in patient fibroblasts. Our results demonstrate that mitophagy is not solely stimulated in response to specific conditions but is instead also actively suppressed through the continuous degradation of BNIP3L and BNIP3 mediated by the SCF-FBXL4 ubiquitin ligase. Thus, cellular conditions or signaling events that prevent the FBXL4-mediated turnover of BNIP3L and BNIP3 on specific mitochondria are expected to facilitate their selective removal.

Keywords:  BNIP3; BNIP3L/NIX; FBXL4; MTDPS13; mitophagy; ubiquitin ligase

DOI:  https://doi.org/10.1080/15548627.2024.2318077
Orphanet J Rare Dis. 2024 Feb 28. 19(1): 92

Lack of mitochondrial complex I assembly factor NDUFAF2 results in a distinctive infantile-onset brainstem neurodegenerative disease with early lethality.

Firas Abu Hanna, Yoav Zehavi, Eran Cohen-Barak, Morad Khayat, Nasim Warwar, Roni Shreter, Richard J Rodenburg, Ronen Spiegel.

   BACKGROUND: Congenital disorders of the mitochondrial respiratory chain are a heterogeneous group of inborn errors of metabolism. Among them, NADH:ubiquinone oxidoreductase (complex I, CI) deficiency is the most common. Biallelic pathogenic variants in NDUFAF2, encoding the nuclear assembly CI factor NDUFAF2, were initially reported to cause progressive encephalopathy beginning in infancy. Since the initial report in 2005, less than a dozen patients with NDUFAF2-related disease have been reported.
METHODS: Clinical, biochemical, and neuroradiological features of four new patients residing in Northern Israel were collected during 2016-2022 at Emek Medical Center. Enzymatic activities of the five respiratory-chain complexes were determined in isolated fibroblast mitochondria by spectrophotometric methods. Western blot analyses were conducted with anti-human NDUFAF2 antibody; antibody against the mitochondrial marker VDAC1 was used as a loading control. Genetic studies were performed by chromosome microarray analysis using Affymetrix CytoScan 750 K arrays.
RESULTS: All four patients presented with infantile-onset growth retardation, ophthalmological impairments with nystagmus, strabismus (starting between 5 and 9 months), and further progressed to life-threatening episodes of apnea usually triggered by trivial febrile illnesses (between 10 and 18 months) with gradual loss of acquired developmental milestones (3 of 4 patients). Serial magnetic-resonance imaging studies in two of the four patients showed a progressive pattern of abnormal T2-weighted hyperintense signals involving primarily the brainstem, the upper cervical cord, and later, the basal ganglia and thalami. Magnetic-resonance spectroscopy in one patient showed an increased lactate peak. Disease progression was marked by ventilatory dependency and early lethality. 3 of the 4 patients tested, harbored a homozygous 142-kb partial interstitial deletion that omits exons 2-4 of NDUFAF2. Mitochondrial CI activity was significantly decreased in the only patient tested. Western blot analysis disclosed the absence of NDUFAF2 protein compared to normal controls. In addition, we reviewed all 10 previously reported NDUFAF2-deficient cases to better characterize the disease.
CONCLUSIONS: Biallelic loss-of-function mutations in NDUFAF2 result in a distinctive phenotype in the spectrum of Leigh syndrome with clinical and neuroradiological features that are primarily attributed to progressive brainstem damage.

Keywords:   NDUFAF2 gene; Leigh syndrome; Mitochondrial disease; Optic neuropathy; Oxidative phosphorylation

DOI:  https://doi.org/10.1186/s13023-024-03094-0
iScience. 2024 Mar 15. 27(3): 109164

Optic atrophy 1 mediates muscle differentiation by promoting a metabolic switch via the supercomplex assembly factor SCAF1.

Matthew Triolo, Nicole Baker, Soniya Agarwal, Nikita Larionov, Tina Podinić, Mireille Khacho.

  Myogenic differentiation is integral for the regeneration of skeletal muscle following tissue damage. Though high-energy post-mitotic muscle relies predominantly on mitochondrial respiration, the importance of mitochondrial remodeling in enabling muscle differentiation and the players involved are not fully known. Here we show that the mitochondrial fusion protein OPA1 is essential for muscle differentiation. Our study demonstrates that OPA1 loss or inhibition, through genetic and pharmacological means, abolishes in vivo muscle regeneration and in vitro myotube formation. We show that both the inhibition and genetic deletion of OPA1 prevent the early onset metabolic switch required to drive myoblast differentiation. In addition, we observe an OPA1-dependent upregulation of the supercomplex assembly factor, SCAF1, at the onset of differentiation. Importantly, preventing the upregulation of SCAF1, through OPA1 loss or siRNA-mediated SCAF1 knockdown, impairs metabolic reprogramming and muscle differentiation. These findings reveal the integral role of OPA1 and mitochondrial reprogramming at the onset of myogenic differentiation.

Keywords:  Molecular biology; Physiology

DOI:  https://doi.org/10.1016/j.isci.2024.109164
Mol Ther Nucleic Acids. 2024 Mar 12. 35(1): 102132

mitoTALEN reduces the mutant mtDNA load in neurons.

Sandra R Bacman, Jose Domingo Barrera-Paez, Milena Pinto, Derek Van Booven, James B Stewart, Anthony J Griswold, Carlos T Moraes.

  Mutations within mtDNA frequently give rise to severe encephalopathies. Given that a majority of these mtDNA defects exist in a heteroplasmic state, we harnessed the precision of mitochondrial-targeted TALEN (mitoTALEN) to selectively eliminate mutant mtDNA within the CNS of a murine model harboring a heteroplasmic mutation in the mitochondrial tRNA alanine gene (m.5024C>T). This targeted approach was accomplished by the use of AAV-PHP.eB and a neuron-specific synapsin promoter for effective neuronal delivery and expression of mitoTALEN. We found that most CNS regions were effectively transduced and showed a significant reduction in mutant mtDNA. This reduction was accompanied by an increase in mitochondrial tRNA alanine levels, which are drastically reduced by the m.5024C>T mutation. These results showed that mitochondrial-targeted gene editing can be effective in reducing CNS-mutant mtDNA in vivo, paving the way for clinical trials in patients with mitochondrial encephalopathies.

Keywords:  AAV-PHPeB; CNS; MT: RNA/DNA editing; TALEN; gene therapy; heteroplasmy; mitochondria

DOI:  https://doi.org/10.1016/j.omtn.2024.102132
FEBS J. 2024 Feb 27.

Mitochondrial derived vesicles- Quo Vadis?

Reut Hazan Ben-Menachem, Ophry Pines, Ann Saada.

  Mitochondria are dynamic, intracellular organelles with a separate genome originating from prokaryotes. They perform numerous functions essential for cellular metabolism and energy production. Mitochondrial-derived vesicles (MDVs) are single or double membrane-enclosed vesicles, formed and released from the mitochondrial sub-compartments into the cytosol, in response to various triggers. MDVs interact with other organelles such as lysosomes and peroxisomes or may be incorporated and excreted via extracellular vesicles (EVs). MDVs selectively incorporate diverse protein and lipid cargoes and are involved in various functions such as mitochondrial quality control, immunomodulation, energy complementation, and compartmentalization and transport. This review aims to provide a summary of the current knowledge of MDVs biogenesis, release, cargoes, and roles.

Keywords:  membrane; mitochondria; mitochondrial-derived vesicles

DOI:  https://doi.org/10.1111/febs.17103
Front Pharmacol. 2024 ;15 1323491

Gene editing improves endoplasmic reticulum-mitochondrial contacts and unfolded protein response in Friedreich's ataxia iPSC-derived neurons.

Priyanka Mishra, Anusha Sivakumar, Avalon Johnson, Carla Pernaci, Anna S Warden, Lilas Rony El-Hachem, Emily Hansen, Rafael A Badell-Grau, Veenita Khare, Gabriela Ramirez, Sydney Gillette, Angelyn B Solis, Peng Guo, Nicole Coufal, Stephanie Cherqui.

  Friedreich ataxia (FRDA) is a multisystemic, autosomal recessive disorder caused by homozygous GAA expansion mutation in the first intron of frataxin (FXN) gene. FXN is a mitochondrial protein critical for iron-sulfur cluster biosynthesis and deficiency impairs mitochondrial electron transport chain functions and iron homeostasis within the organelle. Currently, there is no effective treatment for FRDA. We have previously demonstrated that single infusion of wild-type hematopoietic stem and progenitor cells (HSPCs) resulted in prevention of neurologic and cardiac complications of FRDA in YG8R mice, and rescue was mediated by FXN transfer from tissue engrafted, HSPC-derived microglia/macrophages to diseased neurons/myocytes. For a future clinical translation, we developed an autologous stem cell transplantation approach using CRISPR/Cas9 for the excision of the GAA repeats in FRDA patients' CD34+ HSPCs; this strategy leading to increased FXN expression and improved mitochondrial functions. The aim of the current study is to validate the efficiency and safety of our gene editing approach in a disease-relevant model. We generated a cohort of FRDA patient-derived iPSCs and isogenic lines that were gene edited with our CRISPR/Cas9 approach. iPSC derived FRDA neurons displayed characteristic apoptotic and mitochondrial phenotype of the disease, such as non-homogenous microtubule staining in neurites, increased caspase-3 expression, mitochondrial superoxide levels, mitochondrial fragmentation, and partial degradation of the cristae compared to healthy controls. These defects were fully prevented in the gene edited neurons. RNASeq analysis of FRDA and gene edited neurons demonstrated striking improvement in gene clusters associated with endoplasmic reticulum (ER) stress in the isogenic lines. Gene edited neurons demonstrated improved ER-calcium release, normalization of ER stress response gene, XBP-1, and significantly increased ER-mitochondrial contacts that are critical for functional homeostasis of both organelles, as compared to FRDA neurons. Ultrastructural analysis for these contact sites displayed severe ER structural damage in FRDA neurons, that was undetected in gene edited neurons. Taken together, these results represent a novel finding for disease pathogenesis showing dramatic ER structural damage in FRDA, validate the efficacy profile of our FXN gene editing approach in a disease relevant model, and support our approach as an effective strategy for therapeutic intervention for Friedreich's ataxia.

Keywords:  Friedreich’s ataxia; calcium homeostasis; endoplasmic reticulum-mitochondrial contacts; gene editing; induced pluripotent stem cells; neuronal apoptosis; neurons; unfolded protein response

DOI:  https://doi.org/10.3389/fphar.2024.1323491
Front Cell Dev Biol. 2024 ;12 1287447

Mitochondrial DNA leakage triggers inflammation in age-related cardiovascular diseases.

Wanyue Ding, Jingyu Chen, Lei Zhao, Shuang Wu, Xiaomei Chen, Hong Chen.

  Mitochondrial dysfunction is one of the hallmarks of cardiovascular aging. The leakage of mitochondrial DNA (mtDNA) is increased in senescent cells, which are resistant to programmed cell death such as apoptosis. Due to its similarity to prokaryotic DNA, mtDNA could be recognized by cellular DNA sensors and trigger innate immune responses, resulting in chronic inflammatory conditions during aging. The mechanisms include cGAS-STING signaling, TLR-9 and inflammasomes activation. Mitochondrial quality controls such as mitophagy could prevent mitochondria from triggering harmful inflammatory responses, but when this homeostasis is out of balance, mtDNA-induced inflammation could become pathogenic and contribute to age-related cardiovascular diseases. Here, we summarize recent studies on mechanisms by which mtDNA promotes inflammation and aging-related cardiovascular diseases, and discuss the potential value of mtDNA in early screening and as therapeutic targets.

Keywords:  cardiovasuclar diseases; inflammation; innate immunity; mitochondrial DNA; senescence

DOI:  https://doi.org/10.3389/fcell.2024.1287447
Autophagy. 2024 Feb 27.

Aging STINGs: mitophagy at the crossroads of neuroinflammation.

Juan Ignacio Jiménez-Loygorri, Patricia Boya.

  Loss of proteostasis and dysregulated mitochondrial function are part of the traditional hallmarks of aging, and in their last revision impaired macroautophagy and chronic inflammation are also included. Mitophagy is at the intersection of all these processes but whether it undergoes age-associated perturbations was not known. In our recent work, we performed a systematic and systemic analysis of mitolysosome levels in mice and found that, despite the already-known decrease in non-selective macroautophagy, mitophagy remains stable or increases upon aging in all tissues analyzed and is mediated by the PINK1-PRKN-dependent pathway. Further analyses revealed a concomitant increase in mtDNA leakage into the cytosol and activation of the CGAS-STING1 inflammation axis. Notably, both phenomena are also observed in primary fibroblasts from aged human donors. We hypothesized that mitophagy might be selectively upregulated during aging to improve mitochondrial fitness and reduce mtDNA-induced inflammation. Treatment with the mitophagy inducer urolithin A alleviates age-associated neurological decline, including improved synaptic connectivity, cognitive memory and visual function. Supporting our initial hypothesis, urolithin A reduces the levels of cytosolic mtDNA, CGAS-STING1 activation and neuroinflammation. Finally, using an in vitro model of mitochondrial membrane permeabilization we validated that PINK1-PRKN-mediated mitophagy is essential to resolve cytosolic mtDNA-triggered inflammation. These findings open up an integrative approach to tackle aging and increase healthspan via mitophagy induction.

Keywords:  Inflammation; PINK1; Parkin; mitochondria; mtDNA; retina

DOI:  https://doi.org/10.1080/15548627.2024.2322421
Proc Natl Acad Sci U S A. 2024 Mar 05. 121(10): e2313540121

Tom20 gates PINK1 activity and mediates its tethering of the TOM and TIM23 translocases upon mitochondrial stress.

Mohamed A Eldeeb, Andrew N Bayne, Armaan Fallahi, Thomas Goiran, Emma J MacDougall, Andrea Soumbasis, Cornelia E Zorca, Jace-Jones Tabah, Rhalena A Thomas, Nathan Karpilovsky, Meghna Mathur, Thomas M Durcan, Jean-François Trempe, Edward A Fon.

  Mutations in PTEN-induced putative kinase 1 (PINK1) cause autosomal recessive early-onset Parkinson's disease (PD). PINK1 is a Ser/Thr kinase that regulates mitochondrial quality control by triggering mitophagy mediated by the ubiquitin (Ub) ligase Parkin. Upon mitochondrial damage, PINK1 accumulates on the outer mitochondrial membrane forming a high-molecular-weight complex with the translocase of the outer membrane (TOM). PINK1 then phosphorylates Ub, which enables recruitment and activation of Parkin followed by autophagic clearance of the damaged mitochondrion. Thus, Parkin-dependent mitophagy hinges on the stable accumulation of PINK1 on the TOM complex. Yet, the mechanism linking mitochondrial stressors to PINK1 accumulation and whether the translocases of the inner membrane (TIMs) are also involved remain unclear. Herein, we demonstrate that mitochondrial stress induces the formation of a PINK1-TOM-TIM23 supercomplex in human cultured cell lines, dopamine neurons, and midbrain organoids. Moreover, we show that PINK1 is required to stably tether the TOM to TIM23 complexes in response to stress such that the supercomplex fails to accumulate in cells lacking PINK1. This tethering is dependent on an interaction between the PINK1 N-terminal-C-terminal extension module and the cytosolic domain of the Tom20 subunit of the TOM complex, the disruption of which, by either designer or PD-associated PINK1 mutations, inhibits downstream mitophagy. Together, the findings provide key insight into how PINK1 interfaces with the mitochondrial import machinery, with important implications for the mechanisms of mitochondrial quality control and PD pathogenesis.

Keywords:  PINK1; mitochondrial import; mitochondrial quality control; mitophagy; proteolysis

DOI:  https://doi.org/10.1073/pnas.2313540121
Trends Biochem Sci. 2024 Feb 23. pii: S0968-0004(24)00031-8. [Epub ahead of print]

Mitochondria in disease: changes in shapes and dynamics.

Brenita C Jenkins, Kit Neikirk, Prasanna Katti, Steven M Claypool, Annet Kirabo, Melanie R McReynolds, Antentor Hinton.

  Mitochondrial structure often determines the function of these highly dynamic, multifunctional, eukaryotic organelles, which are essential for maintaining cellular health. The dynamic nature of mitochondria is apparent in descriptions of different mitochondrial shapes [e.g., donuts, megamitochondria (MGs), and nanotunnels] and crista dynamics. This review explores the significance of dynamic alterations in mitochondrial morphology and regulators of mitochondrial and cristae shape. We focus on studies across tissue types and also describe new microscopy techniques for detecting mitochondrial morphologies both in vivo and in vitro that can improve understanding of mitochondrial structure. We highlight the potential therapeutic benefits of regulating mitochondrial morphology and discuss prospective avenues to restore mitochondrial bioenergetics to manage diseases related to mitochondrial dysfunction.

Keywords:  clinical diagnostics; contact sites; cristae dynamics; microscopy; mitochondrial morphology; mitochondrial shapes

DOI:  https://doi.org/10.1016/j.tibs.2024.01.011
Front Aging. 2024 ;5 1359638

MtDNA deletions and aging.

Charlotte Sprason, Trudy Tucker, David Clancy.

  Aging is the major risk factor in most of the leading causes of mortality worldwide, yet its fundamental causes mostly remain unclear. One of the clear hallmarks of aging is mitochondrial dysfunction. Mitochondria are best known for their roles in cellular energy generation, but they are also critical biosynthetic and signaling organelles. They also undergo multiple changes with organismal age, including increased genetic errors in their independent, circular genome. A key group of studies looking at mice with increased mtDNA mutations showed that premature aging phenotypes correlated with increased deletions but not point mutations. This generated an interest in mitochondrial deletions as a potential fundamental cause of aging. However, subsequent studies in different models have yielded diverse results. This review summarizes the research on mitochondrial deletions in various organisms to understand their possible roles in causing aging while identifying the key complications in quantifying deletions across all models.

Keywords:  aging; mitochondria; mitochondrial DNA; mitochondrial DNA deletions; mitochondrial dysfunction

DOI:  https://doi.org/10.3389/fragi.2024.1359638
Acta Neuropathol Commun. 2024 Mar 01. 12(1): 37

Prophylactic nicotinamide treatment protects from rotenone-induced neurodegeneration by increasing mitochondrial content and volume.

Amin Otmani, Gauti Jóhannesson, Rune Brautaset, James R Tribble, Pete A Williams.

  Leber's hereditary optic neuropathy (LHON) is driven by mtDNA mutations affecting Complex I presenting as progressive retinal ganglion cell dysfunction usually in the absence of extra-ophthalmic symptoms. There are no long-term neuroprotective agents for LHON. Oral nicotinamide provides a robust neuroprotective effect against mitochondrial and metabolic dysfunction in other retinal injuries. We explored the potential for nicotinamide to protect mitochondria in LHON by modelling the disease in mice through intravitreal injection of the Complex I inhibitor rotenone. Using MitoV mice expressing a mitochondrial-tagged YFP in retinal ganglion cells we assessed mitochondrial morphology through super-resolution imaging and digital reconstruction. Rotenone induced Complex I inhibition resulted in retinal ganglion cell wide mitochondrial loss and fragmentation. This was prevented by oral nicotinamide treatment. Mitochondrial ultrastructure was quantified by transition electron microscopy, demonstrating a loss of cristae density following rotenone injection, which was also prevented by nicotinamide treatment. These results demonstrate that nicotinamide protects mitochondria during Complex I dysfunction. Nicotinamide has the potential to be a useful treatment strategy for LHON to limit retinal ganglion cell degeneration.

Keywords:  Mitochondria; Neurodegeneration; Nicotinamide; Optic nerve; Retina; Retina ganglion cells

DOI:  https://doi.org/10.1186/s40478-024-01724-z
Cell Rep. 2024 Feb 26. pii: S2211-1247(24)00188-8. [Epub ahead of print]43(3): 113860

NEMF-mediated Listerin-independent mitochondrial translational surveillance by E3 ligase Pirh2 and mitochondrial protease ClpXP.

Liang Lv, Jinyou Mo, Yumin Qing, Shuchao Wang, Leijie Chen, Anna Mei, Ru Xu, Hualin Huang, Jieqiong Tan, Yifu Li, Jia Liu.

  The ribosome-associated protein quality control (RQC) pathway acts as a translational surveillance mechanism to maintain proteostasis. In mammalian cells, the cytoplasmic RQC pathway involves nuclear export mediator factor (NEMF)-dependent recruitment of the E3 ligase Listerin to ubiquitinate ribosome-stalled nascent polypeptides on the lysine residue for degradation. However, the quality control of ribosome-stalled nuclear-encoded mitochondrial nascent polypeptides remains elusive, as these peptides can be partially imported into mitochondria through translocons, restricting accessibility to the lysine by Listerin. Here, we identify a Listerin-independent organelle-specific mitochondrial RQC pathway that acts on NEMF-mediated carboxy-terminal poly-alanine modification. In the pathway, mitochondrial proteins carrying C-end poly-Ala tails are recognized by the cytosolic E3 ligase Pirh2 and the ClpXP protease in the mitochondria, which coordinately clear ribosome-stalled mitochondrial nascent polypeptides. Defects in this elimination pathway result in NEMF-mediated aggregates and mitochondrial integrity failure, thus providing a potential molecular mechanism of the RQC pathway in mitochondrial-associated human diseases.

Keywords:  CP: Microbiology; CP: Molecular biology; ClpXP; Listerin; NEMF; Pirh2; mitochondrion

DOI:  https://doi.org/10.1016/j.celrep.2024.113860
Trends Endocrinol Metab. 2024 Feb 27. pii: S1043-2760(24)00038-9. [Epub ahead of print]

Mitochondrial dysfunction in lipid processing and gastrointestinal disorders.

Yan Hu, Hao Huang, Rong Xiang.

  Mitochondrial dysfunctions predominantly cause encephalomyopathies with muscle atrophy and neurodegeneration. However, their impact on other tissues, particularly the gastrointestinal tract, requires further investigation. In a recent report in Nature, Moschandrea et al. used mice deficient in the mitochondrial aminoacyl-tRNA synthetase DARS2 to investigate the role of enterocytic mitochondria in dietary lipid processing and transport. Their work sheds light on the development of gastrointestinal disorders as a result of mitochondrial dysfunction.

Keywords:  DARS2; gastrointestinal disorders; lipid processing; mitochondria; mitochondrial aminoacyl-tRNA synthetases (mt-AaRSs)

DOI:  https://doi.org/10.1016/j.tem.2024.02.009
Int J Biochem Cell Biol. 2024 Feb 27. pii: S1357-2725(24)00047-5. [Epub ahead of print] 106556

The Application of Brain Organoid for Drug Discovery in Mitochondrial Diseases.

Kristina Xiao Liang.

  Mitochondrial diseases are difficult to treat due to the complexity and multifaceted nature of mitochondrial dysfunction. Brain organoids are three-dimensional (3D) structures derived from human pluripotent stem cells designed to mimic brain-like development and function. Brain organoids have received a lot of attention in recent years as powerful tools for modeling human diseases, brain development, and drug screening. Screening compounds for mitochondrial diseases using brain organoids could provide a more physiologically relevant platform for drug discovery. Brain organoids offer the possibility of personalized medicine because they can be derived from patient-specific cells, allowing testing of drugs tailored to specific genetic mutations. In this article, we highlight how brain organoids offer a promising avenue for screening compounds for mitochondrial diseases and address the challenges and limitations associated with their use. We hope this review will provide new insights into the further progress of brain organoids for mitochondrial screening studies.

Keywords:  Brain organoid; drug discovery; drug screening; iPSCs; mitochondrial diseases

DOI:  https://doi.org/10.1016/j.biocel.2024.106556
Mitochondrion. 2024 Feb 23. pii: S1567-7249(24)00013-8. [Epub ahead of print]76 101855

Mitochondrial stress in the spaceflight environment.

Agata M Rudolf, Wendy R Hood.

  Space is a challenging environment that deregulates individual homeostasis. The main external hazards associated with spaceflight include ionizing space radiation, microgravity, isolation and confinement, distance from Earth, and hostile environment. Characterizing the biological responses to spaceflight environment is essential to validate the health risks, and to develop effective protection strategies. Mitochondria energetics is a key mechanism underpinning many physiological, ecological and evolutionary processes. Moreover, mitochondrial stress can be considered one of the fundamental features of space travel. So, we attempt to synthesize key information regarding the extensive effects of spaceflight on mitochondria. In summary, mitochondria are affected by all of the five main hazards of spaceflight at multiple levels, including their morphology, respiratory function, protein, and genetics, in various tissues and organ systems. We emphasize that investigating mitochondrial biology in spaceflight conditions should become the central focus of research on the impacts of spaceflight on human health, as this approach will help resolve numerous challenges of space health and combat several health disorders associated with mitochondrial dysfunction.

Keywords:  Microgravity; Mitochondria; Oxidative stress; Radiation; Spaceflight

DOI:  https://doi.org/10.1016/j.mito.2024.101855
J Cell Physiol. 2024 Feb 28.

ATF4-dependent increase in mitochondrial-endoplasmic reticulum tethering following OPA1 deletion in skeletal muscle.

Antentor Hinton, Prasanna Katti, Margaret Mungai, Duane D Hall, Olha Koval, Jianqiang Shao, Zer Vue, Edgar Garza Lopez, Rahmati Rostami, Kit Neikirk, Jessica Ponce, Jennifer Streeter, Brandon Schickling, Serif Bacevac, Chad Grueter, Andrea Marshall, Heather K Beasley, Young Do Koo, Sue C Bodine, Nayeli G Reyes Nava, Anita M Quintana, Long-Sheng Song, Isabella M Grumbach, Renata O Pereira, Brian Glancy, E Dale Abel.

  Mitochondria and endoplasmic reticulum (ER) contact sites (MERCs) are protein- and lipid-enriched hubs that mediate interorganellar communication by contributing to the dynamic transfer of Ca2+ , lipid, and other metabolites between these organelles. Defective MERCs are associated with cellular oxidative stress, neurodegenerative disease, and cardiac and skeletal muscle pathology via mechanisms that are poorly understood. We previously demonstrated that skeletal muscle-specific knockdown (KD) of the mitochondrial fusion mediator optic atrophy 1 (OPA1) induced ER stress and correlated with an induction of Mitofusin-2, a known MERC protein. In the present study, we tested the hypothesis that Opa1 downregulation in skeletal muscle cells alters MERC formation by evaluating multiple myocyte systems, including from mice and Drosophila, and in primary myotubes. Our results revealed that OPA1 deficiency induced tighter and more frequent MERCs in concert with a greater abundance of MERC proteins involved in calcium exchange. Additionally, loss of OPA1 increased the expression of activating transcription factor 4 (ATF4), an integrated stress response (ISR) pathway effector. Reducing Atf4 expression prevented the OPA1-loss-induced tightening of MERC structures. OPA1 reduction was associated with decreased mitochondrial and sarcoplasmic reticulum, a specialized form of ER, calcium, which was reversed following ATF4 repression. These data suggest that mitochondrial stress, induced by OPA1 deficiency, regulates skeletal muscle MERC formation in an ATF4-dependent manner.

Keywords:  activating transcription factor 4; endoplasmic reticulum; integrated stress response; interorganelle communication; mitochondria

DOI:  https://doi.org/10.1002/jcp.31204
Pediatr Cardiol. 2024 Mar 01.

Characterization of Cardiac-Onset Initial Presentation in Friedreich Ataxia.

David R Lynch, Sub Subramony, Kimberly Y Lin, Katherine Mathews, Susan Perlman, Grace Yoon, Christian Rummey.

  We examined the clinical features of Friedreich ataxia (FRDA) patients who present first with cardiac disease in order to understand the earliest features of the diagnostic journey in FRDA. We identified a group of subjects in the FACOMS natural history study whose first identified clinical feature was cardiac. Only 0.5% of the total cohort belonged to this group, which was younger on average at the time of presentation. Their cardiac symptoms ranged from asymptomatic features to heart failure with severe systolic dysfunction. Two of those individuals with severe dysfunction proceeded to heart transplantation, but others spontaneously recovered. In most cases, diagnosis of FRDA was not made until well after cardiac presentation. The present study shows that some FRDA patients present based on cardiac features, suggesting that earlier identification of FRDA might occur through enhancing awareness of FRDA among pediatric cardiologists who see such patients. This is important in the context of newly identified therapies for FRDA.

Keywords:  Cardiomyopathy; Hypertrophy; Mitochondria; Omaveloxolone

DOI:  https://doi.org/10.1007/s00246-024-03429-5
Cell Rep Med. 2024 Feb 28. pii: S2666-3791(24)00060-0. [Epub ahead of print] 101437

Therapeutic benefit of idebenone in patients with Leber hereditary optic neuropathy: The LEROS nonrandomized controlled trial.

LEROS Study Group

  Leber hereditary optic neuropathy (LHON) is a mitochondrial disease leading to rapid and severe bilateral vision loss. Idebenone has been shown to be effective in stabilizing and restoring vision in patients treated within 1 year of onset of vision loss. The open-label, international, multicenter, natural history-controlled LEROS study (ClinicalTrials.gov NCT02774005) assesses the efficacy and safety of idebenone treatment (900 mg/day) in patients with LHON up to 5 years after symptom onset (N = 199) and over a treatment period of 24 months, compared to an external natural history control cohort (N = 372), matched by time since symptom onset. LEROS meets its primary endpoint and confirms the long-term efficacy of idebenone in the subacute/dynamic and chronic phases; the treatment effect varies depending on disease phase and the causative mtDNA mutation. The findings of the LEROS study will help guide the clinical management of patients with LHON.

Keywords:  LHON; Leber hereditary optic neuropathy; idebenone; mitochondrial disease; mtDNA; neuro-ophthalmology; optic atrophy; optic neuropathy; retinal ganglion cells

DOI:  https://doi.org/10.1016/j.xcrm.2024.101437
Nat Metab. 2024 Feb 27.

PMF-seq: a highly scalable screening strategy for linking genetics to mitochondrial bioenergetics.

Tsz-Leung To, Jason G McCoy, Naomi K Ostriker, Lev S Sandler, Carmen A Mannella, Vamsi K Mootha.

Our current understanding of mitochondrial organelle physiology has benefited from two broad approaches: classically, cuvette-based measurements with suspensions of isolated mitochondria, in which bioenergetic parameters are monitored acutely in response to respiratory chain substrates and inhibitors1-4, and more recently, highly scalable genetic screens for fitness phenotypes associated with coarse-grained properties of the mitochondrial state5-10. Here we introduce permeabilized-cell mitochondrial function sequencing (PMF-seq) to combine strengths of these two approaches to connect genes to detailed bioenergetic phenotypes. In PMF-seq, the plasma membranes within a pool of CRISPR mutagenized cells are gently permeabilized under conditions that preserve mitochondrial physiology, where detailed bioenergetics can be probed in the same way as with isolated organelles. Cells with desired bioenergetic parameters are selected optically using flow cytometry and subjected to next-generation sequencing. Using PMF-seq, we recover genes differentially required for mitochondrial respiratory chain branching and reversibility. We demonstrate that human D-lactate dehydrogenase specifically conveys electrons from D-lactate into cytochrome c to support mitochondrial membrane polarization. Finally, we screen for genetic modifiers of tBID, a pro-apoptotic protein that acts directly and acutely on mitochondria. We find the loss of the complex V assembly factor ATPAF2 acts as a genetic sensitizer of tBID's acute action. We anticipate that PMF-seq will be valuable for defining genes critical to the physiology of mitochondria and other organelles.

DOI: https://doi.org/10.1038/s42255-024-00994-0
Cell Rep Methods. 2024 Feb 26. pii: S2667-2375(24)00028-6. [Epub ahead of print]4(2): 100713

In utero pulse injection of isotopic amino acids quantifies protein turnover rates during murine fetal development.

Josue Baeza, Barbara E Coons, Zongtao Lin, John Riley, Mariel Mendoza, William H Peranteau, Benjamin A Garcia.

  Protein translational control is critical for ensuring that the fetus develops correctly and that necessary organs and tissues are formed and functional. We developed an in utero method to quantify tissue-specific protein dynamics by monitoring amino acid incorporation into the proteome after pulse injection. Fetuses of pregnant mice were injected with isotopically labeled lysine and arginine via the vitelline vein at various embyonic days, and organs and tissues were harvested. By analyzing the nascent proteome, unique signatures of each tissue were identified by hierarchical clustering. In addition, the quantified proteome-wide turnover rates were calculated between 3.81E-5 and 0.424 h-1. We observed similar protein turnover profiles for analyzed organs (e.g., liver vs. brain); however, their distributions of turnover rates vary significantly. The translational kinetic profiles of developing organs displayed differentially expressed protein pathways and synthesis rates, which correlated with known physiological changes during mouse development.

Keywords:  CP: Developmental biology; CP: Molecular biology; fetal development; in utero injection; protein turnover; proteomics; pulse labeling

DOI:  https://doi.org/10.1016/j.crmeth.2024.100713
J Physiol. 2024 Mar 01.

Reorganization of mitochondria-organelle interactions during postnatal development in skeletal muscle.

Yuho Kim, Hailey A Parry, T Bradley Willingham, Greg Alspaugh, Eric Lindberg, Christian A Combs, Jay R Knutson, Christopher K E Bleck, Brian Glancy.

  Skeletal muscle cellular development requires the integrated assembly of mitochondria and other organelles adjacent to the sarcomere in support of muscle contractile performance. However, it remains unclear how interactions among organelles and with the sarcomere relates to the development of muscle cell function. Here, we combine 3D volume electron microscopy, proteomic analyses, and live cell functional imaging to investigate the postnatal reorganization of mitochondria-organelle interactions in skeletal muscle. We show that while mitochondrial networks are disorganized and loosely associated with the contractile apparatus at birth, contact sites among mitochondria, lipid droplets and the sarcoplasmic reticulum are highly abundant in neonatal muscles. The maturation process is characterized by a transition to highly organized mitochondrial networks wrapped tightly around the muscle sarcomere but also to less frequent interactions with both lipid droplets and the sarcoplasmic reticulum. Concomitantly, expression of proteins involved in mitochondria-organelle membrane contact sites decreases during postnatal development in tandem with a decrease in abundance of proteins associated with sarcomere assembly despite an overall increase in contractile protein abundance. Functionally, parallel measures of mitochondrial membrane potential, NADH redox status, and NADH flux within intact cells revealed that mitochondria in adult skeletal muscle fibres maintain a more activated electron transport chain compared with neonatal muscle mitochondria. These data demonstrate a developmental redesign reflecting a shift from muscle cell assembly and frequent inter-organelle communication toward a muscle fibre with mitochondrial structure, interactions, composition and function specialized to support contractile function. KEY POINTS: Mitochondrial network organization is remodelled during skeletal muscle postnatal development. The mitochondrial outer membrane is in frequent contact with other organelles at birth and transitions to more close associations with the contractile apparatus in mature muscles. Mitochondrial energy metabolism becomes more activated during postnatal development. Understanding the developmental redesign process within skeletal muscle cells may help pinpoint specific areas of deficit in muscles with developmental disorders.

Keywords:  3D mitochondrial structure; functional cellular imaging; organelle interactions; postnatal muscle development; volume electron microscopy

DOI:  https://doi.org/10.1113/JP285014
Nature. 2024 Feb 28.

'Epigenetic' editing cuts cholesterol in mice.

Heidi Ledford.



Keywords:  Cardiovascular biology; Diseases; Epigenetics; Gene therapy

DOI:  https://doi.org/10.1038/d41586-024-00563-1
Mitochondrion. 2024 Feb 24. pii: S1567-7249(24)00014-X. [Epub ahead of print] 101856

Miro1 improves the exogenous engraftment efficiency and therapeutic potential of mitochondria transfer using Wharton's jelly mesenchymal stem cells.

Yu-Han Lin, Kai-Lieh Lin, Xiao-Wen Wang, Jong-Jer Lee, Feng-Sheng Wang, Pei-Wen Wang, Min-Yu Lan, Chia-Wei Liou, Tsu-Kung Lin.

  Mitochondria are important for maintaining cellular energy metabolism and regulating cellular senescence. Mitochondrial DNA (mtDNA) encodes subunits of the OXPHOS complexes which are essential for cellular respiration and energy production. Meanwhile, mtDNA variants have been associated with the pathogenesis of neurodegenerative diseases, including MELAS, for which no effective treatment has been developed. To alleviate the pathological conditions involved in mitochondrial disorders, mitochondria transfer therapy has shown promise. Wharton's jelly mesenchymal stem cells (WJMSCs) have been identified as suitable mitochondria donors for mitochondria-defective cells, wherein mitochondrial functions can be rescued. Miro1 participates in mitochondria trafficking by anchoring mitochondria to microtubules. In this study, we identified Miro1 over-expression as a factor that could help to enhance the efficiency of mitochondrial delivery. More specifically, we reveal that Miro1 over-expressed WJMSCs significantly improved intercellular communications, cell proliferation rates, and mitochondrial membrane potential, while restoring mitochondrial bioenergetics in mitochondria-defective fibroblasts. Furthermore, Miro1 over-expressed WJMSCs decreased rates of induced apoptosis and ROS production in MELAS fibroblasts; although, Miro1 over-expression did not rescue mtDNA mutation ratios nor mitochondrial biogenesis. This study presents a potentially novel therapeutic strategy for treating mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS), and other diseases associated with dysfunctional mitochondria, while the pathophysiological relevance of our results should be further verified by animal models and clinical studies.

Keywords:  MELAS; Miro1; Mitochondria; Mitochondrial bioenergetics; WJMSCs

DOI:  https://doi.org/10.1016/j.mito.2024.101856
Mo Med. 2024 Jan-Feb;121(1):121(1): 87-92

Human Platelet Derived Mitochondrial OPA-1 Isoforms and Interaction With TDP-43 in Neurodegenerative Diseases.

Su Han Lee, Duyen Pham, Edina Kosa, Abdulbaki Agbas.

Optic atrophy 1(OPA1) is a GTPase protein that controls mitochondrial fusion, cristae integrity, and mtDNA maintenance. In neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), the mitochondrial network morphology is compromised. Studies on TAR-DNA binding protein 43 (TDP-43) has been the focus in our lab. OPA1 and TDP-43 interaction may shed a light on how aberrant TDP-43 interacts with OPA1, which will lead to mitochondrial dysfunction. The preliminary study tested the idea of whether OPA1 and TDP-43 are physically interacting in human platelet derived mitochondria obtained from healthy human subjects.
Nat Commun. 2024 Feb 24. 15(1): 1697

Phage-assisted evolution of highly active cytosine base editors with enhanced selectivity and minimal sequence context preference.

Emily Zhang, Monica E Neugebauer, Nicholas A Krasnow, David R Liu.

TadA-derived cytosine base editors (TadCBEs) enable programmable C•G-to-T•A editing while retaining the small size, high on-target activity, and low off-target activity of TadA deaminases. Existing TadCBEs, however, exhibit residual A•T-to-G•C editing at certain positions and lower editing efficiencies at some sequence contexts and with non-SpCas9 targeting domains. To address these limitations, we use phage-assisted evolution to evolve CBE6s from a TadA-mediated dual cytosine and adenine base editor, discovering mutations at N46 and Y73 in TadA that prevent A•T-to-G•C editing and improve C•G-to-T•A editing with expanded sequence-context compatibility, respectively. In E. coli, CBE6 variants offer high C•G-to-T•A editing and no detected A•T-to-G•C editing in any sequence context. In human cells, CBE6 variants exhibit broad Cas domain compatibility and retain low off-target editing despite exceeding BE4max and previous TadCBEs in on-target editing efficiency. Finally, we show that the high selectivity of CBE6 variants is well-suited for therapeutically relevant stop codon installation without creating unwanted missense mutations from residual A•T-to-G•C editing.

DOI: https://doi.org/10.1038/s41467-024-45969-7
Stem Cell Reports. 2024 Feb 12. pii: S2213-6711(24)00012-2. [Epub ahead of print]

Mitochondrial DNA integrity and metabolome profile are preserved in the human induced pluripotent stem cell reference line KOLF2.1J.

Jochen Dobner, Thach Nguyen, Andreas Dunkel, Alessandro Prigione, Jean Krutmann, Andrea Rossi.

  Quality control of human induced pluripotent stem cells (iPSCs) is critical to ensure reproducibility of research. Recently, KOLF2.1J was characterized and published as a male iPSC reference line to study neurological disorders. Emerging evidence suggests potential negative effects of mtDNA mutations, but its integrity was not analyzed in the original publication. To assess mtDNA integrity, we conducted a targeted mtDNA analysis followed by untargeted metabolomics analysis. We found that KOLF2.1J mtDNA integrity was intact at the time of publication and is still preserved in the commercially distributed cell line. In addition, the basal KOLF2.1J metabolome profile was similar to that of the two commercially available iPSC lines IMR90 and iPSC12, but clearly distinct from an in-house-generated ERCC6R683X/R683X iPSC line modeling Cockayne syndrome. Conclusively, we validate KOLF2.1J as a reference iPSC line, and encourage scientists to conduct mtDNA analysis and unbiased metabolomics whenever feasible.

Keywords:  Cockayne syndrome; ERCC6; KOLF2.1J; Oxford Nanopore sequencing; iPSC reference line; iPSCs quality control; mtDNA analysis; mtDNA integrity

DOI:  https://doi.org/10.1016/j.stemcr.2024.01.009
Trends Endocrinol Metab. 2024 Feb 28. pii: S1043-2760(24)00031-6. [Epub ahead of print]

Placental inflammation, oxidative stress, and fetal outcomes in maternal obesity.

Cindy X W Zhang, Alejandro A Candia, Amanda N Sferruzzi-Perri.

  The obesity epidemic has led to a growing body of research investigating the consequences of maternal obesity on pregnancy and offspring health. The placenta, traditionally viewed as a passive intermediary between mother and fetus, is known to play a critical role in modulating the intrauterine environment and fetal development, and we now know that maternal obesity leads to increased inflammation, oxidative stress, and altered placental function. Here, we review recent research exploring the involvement of inflammation and oxidative stress as mechanisms impacting the placenta and fetus during obese pregnancy. Understanding them is crucial for informing strategies that can mitigate the adverse health effects of maternal obesity on offspring development and disease risk.

Keywords:  ROS; diet; fetus; immune; inflammation; obese; obesity; oxidant; oxidative; placenta; programming

DOI:  https://doi.org/10.1016/j.tem.2024.02.002
Neurochem Int. 2024 Feb 26. pii: S0197-0186(24)00027-5. [Epub ahead of print] 105700

Human neural stem cells promote mitochondrial genesis to alleviate neuronal damage in MPTP-induced cynomolgus monkey models.

Ying He, Ruicheng Li, Yuxi Yu, Chusheng Huang, Zhiran Xu, Tianbao Wang, Chen Ming, Hongri Huang, Zhongquan Qi.

  Currently, there is no effective treatment for Parkinson's disease (PD), and the regenerative treatment of neural stem cells (NSCs) is considered the most promising method. This study aimed to investigate the protective effect and mechanism of NSCs on neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP)-induced cynomolgus monkey (Macaca fascicularis) model of PD. We first found that injecting NSCs into the subarachnoid space relieved motor dysfunction in PD cynomolgus monkeys, as well as reduced dopaminergic neuron loss and neuronal damage in the substantia nigra (SN) and striatum. Besides, NSCs decreased 17-estradiol(E2) level, an estrogen, in the cerebrospinal fluid (CSF) of PD cynomolgus monkeys, which shows NSCs may provide neuro-protection by controlling estrogen levels in the CSF. Furthermore, NSCs elevated proliferator-activated receptor gamma coactivator-1 alpha(PGC-1a), mitofusin 2(MFN2), and optic atrophy 1(OPA1) expression, three genes mediating mitochondrial biogenesis, in the SN and striatum of PD monkeys. In addition, NSCs suppress reactive oxygen species (ROS) production caused by MPTP, as well as mitochondrial autophagy, therefore preserving dopaminergic neurons. In summary, our findings show that NSCs may preserve dopaminergic and neuronal cells in an MPTP-induced PD cynomolgus monkey model. These protective benefits might be attributed to NSCs' ability of modulating estrogen balance, increasing mitochondrial biogenesis, and limiting oxidative stress and mitochondrial autophagy. These findings add to our understanding of the mechanism of NSC treatment and shed light on further clinical treatment options.

Keywords:  Cynomolgus monkeys; MPTP; Mitochondria; Neural stem cells; Parkinson's disease

DOI:  https://doi.org/10.1016/j.neuint.2024.105700
Nat Biotechnol. 2024 Feb 28.

Morphological diversification and functional maturation of human astrocytes in glia-enriched cortical organoid transplanted in mouse brain.

Meiyan Wang, Lei Zhang, Sammy Weiser Novak, Jingting Yu, Iryna S Gallina, Lynne L Xu, Christina K Lim, Sarah Fernandes, Maxim N Shokhirev, April E Williams, Monisha D Saxena, Shashank Coorapati, Sarah L Parylak, Cristian Quintero, Elsa Molina, Leonardo R Andrade, Uri Manor, Fred H Gage.

Astrocytes, the most abundant glial cell type in the brain, are underrepresented in traditional cortical organoid models due to the delayed onset of cortical gliogenesis. Here we introduce a new glia-enriched cortical organoid model that exhibits accelerated astrogliogenesis. We demonstrated that induction of a gliogenic switch in a subset of progenitors enabled the rapid derivation of astroglial cells, which account for 25-31% of the cell population within 8-10 weeks of differentiation. Intracerebral transplantation of these organoids reliably generated a diverse repertoire of cortical neurons and anatomical subclasses of human astrocytes. Spatial transcriptome profiling identified layer-specific expression patterns among distinct subclasses of astrocytes within organoid transplants. Using an in vivo acute neuroinflammation model, we identified a subpopulation of astrocytes that rapidly activates pro-inflammatory pathways upon cytokine stimulation. Additionally, we demonstrated that CD38 signaling has a crucial role in mediating metabolic and mitochondrial stress in reactive astrocytes. This model provides a robust platform for investigating human astrocyte function.

DOI: https://doi.org/10.1038/s41587-024-02157-8
EMBO Rep. 2024 Mar 01.

Mitochondrial fusion and altered beta-oxidation drive muscle wasting in a Drosophila cachexia model.

Callum Dark, Nashia Ali, Sofya Golenkina, Vaibhav Dhyani, Ronnie Blazev, Benjamin L Parker, Kate T Murphy, Gordon S Lynch, Tarosi Senapati, S Sean Millard, Sarah M Judge, Andrew R Judge, Lopamudra Giri, Sarah M Russell, Louise Y Cheng.

  Cancer cachexia is a tumour-induced wasting syndrome, characterised by extreme loss of skeletal muscle. Defective mitochondria can contribute to muscle wasting; however, the underlying mechanisms remain unclear. Using a Drosophila larval model of cancer cachexia, we observed enlarged and dysfunctional muscle mitochondria. Morphological changes were accompanied by upregulation of beta-oxidation proteins and depletion of muscle glycogen and lipid stores. Muscle lipid stores were also decreased in Colon-26 adenocarcinoma mouse muscle samples, and expression of the beta-oxidation gene CPT1A was negatively associated with muscle quality in cachectic patients. Mechanistically, mitochondrial defects result from reduced muscle insulin signalling, downstream of tumour-secreted insulin growth factor binding protein (IGFBP) homologue ImpL2. Strikingly, muscle-specific inhibition of Forkhead box O (FOXO), mitochondrial fusion, or beta-oxidation in tumour-bearing animals preserved muscle integrity. Finally, dietary supplementation with nicotinamide or lipids, improved muscle health in tumour-bearing animals. Overall, our work demonstrates that muscle FOXO, mitochondria dynamics/beta-oxidation and lipid utilisation are key regulators of muscle wasting in cancer cachexia.

Keywords:   Drosophila ; Cachexia; Lipid Metabolism; Muscle

DOI:  https://doi.org/10.1038/s44319-024-00102-z
Nat Commun. 2024 Feb 26. 15(1): 1761

Cellular reprogramming in vivo initiated by SOX4 pioneer factor activity.

Takeshi Katsuda, Jonathan H Sussman, Kenji Ito, Andrew Katznelson, Salina Yuan, Naomi Takenaka, Jinyang Li, Allyson J Merrell, Hector Cure, Qinglan Li, Reyaz Ur Rasool, Irfan A Asangani, Kenneth S Zaret, Ben Z Stanger.

Tissue damage elicits cell fate switching through a process called metaplasia, but how the starting cell fate is silenced and the new cell fate is activated has not been investigated in animals. In cell culture, pioneer transcription factors mediate "reprogramming" by opening new chromatin sites for expression that can attract transcription factors from the starting cell's enhancers. Here we report that SOX4 is sufficient to initiate hepatobiliary metaplasia in the adult mouse liver, closely mimicking metaplasia initiated by toxic damage to the liver. In lineage-traced cells, we assessed the timing of SOX4-mediated opening of enhancer chromatin versus enhancer decommissioning. Initially, SOX4 directly binds to and closes hepatocyte regulatory sequences via an overlapping motif with HNF4A, a hepatocyte master regulatory transcription factor. Subsequently, SOX4 exerts pioneer factor activity to open biliary regulatory sequences. The results delineate a hierarchy by which gene networks become reprogrammed under physiological conditions, providing deeper insight into the basis for cell fate transitions in animals.

DOI: https://doi.org/10.1038/s41467-024-45939-z