Zebrafish lacking functional DNA polymerase gamma survive to juvenile stage, despite rapid and sustained mitochondrial DNA depletion, altered energetics and growth

Zebrafish polg2 knock-out recapitulates human POLG-disorders; implications for drug treatment

The human mitochondrial DNA polymerase gamma is a holoenzyme, involved in mitochondrial DNA (mtDNA) replication and maintenance, composed of a catalytic subunit (POLG) and a dimeric accessory subunit (POLG2) conferring processivity. Mutations in POLG or POLG2 cause POLG-related diseases in humans, leading to a subset of Mendelian-inherited mitochondrial disorders characterized by mtDNA depletion (MDD) or accumulation of multiple deletions, presenting multi-organ defects and often leading to premature death at a young age. Considering the paucity of POLG2 models, we have generated a stable zebrafish polg2 mutant line (polg2ia304) by CRISPR/Cas9 technology, carrying a 10-nucleotide deletion with frameshift mutation and premature stop codon. Zebrafish polg2 homozygous mutants present slower development and decreased viability compared to wild type siblings, dying before the juvenile stage. Mutants display a set of POLG-related phenotypes comparable to the symptoms of human patients affected by POLG-related diseases, including remarkable MDD, altered mitochondrial network and dynamics, and reduced mitochondrial respiration. Histological analyses detected morphological alterations in high-energy demanding tissues, along with a significant disorganization of skeletal muscle fibres. Consistent with the last finding, locomotor assays highlighted a decreased larval motility. Of note, treatment with the Clofilium tosylate drug, previously shown to be effective in POLG models, could partially rescue MDD in Polg2 mutant animals. Altogether, our results point at zebrafish as an effective model to study the etiopathology of human POLG-related disorders linked to POLG2, and a suitable platform to screen the efficacy of POLG-directed drugs in POLG2-associated forms.

PRRG4 regulates mitochondrial function and promotes migratory behaviors of breast cancer cells through the Src-STAT3-POLG axis

BACKGROUND

Breast cancer is the leading cause of cancer death for women worldwide. Most of the breast cancer death are due to disease recurrence and metastasis. Increasingly accumulating evidence indicates that mitochondria play key roles in cancer progression and metastasis. Our recent study revealed that transmembrane protein PRRG4 promotes the metastasis of breast cancer. However, it is not clear whether PRRG4 can affect the migration and invasion of breast cancer cells through regulating mitochondria function.

METHODS

RNA-seq analyses were performed on breast cancer cells expressing control and PRRG4 shRNAs. Quantitative PCR analysis and measurements of mitochondrial ATP content and oxygen consumption were carried out to explore the roles of PRRG4 in regulating mitochondrial function. Luciferase reporter plasmids containing different lengths of promoter fragments were constructed. Luciferase activities in breast cancer cells transiently transfected with these reporter plasmids were analyzed to examine the effects of PRRG4 overexpression on promoter activity. Transwell assays were performed to determine the effects of PRRG4-regulated pathway on migratory behaviors of breast cancer cells.

RESULTS

Analysis of the RNA-seq data revealed that PRRG4 knockdown decreased the transcript levels of all the mitochondrial protein-encoding genes. Subsequently, studies with PRRG4 knockdown and overexpression showed that PRRG4 expression increased mitochondrial DNA (mtDNA) content. Mechanistically, PRRG4 via Src activated STAT3 in breast cancer cells. Activated STAT3 in turn promoted the transcription of mtDNA polymerase POLG through a STAT3 DNA binding site present in the POLG promoter region, and increased mtDNA content as well as mitochondrial ATP production and oxygen consumption. In addition, PRRG4-mediated activation of STAT3 also enhanced filopodia formation, migration, and invasion of breast cancer cells. Moreover, PRRG4 elevated migratory behaviors and mitochondrial function of breast cancer cells through POLG.

CONCLUSION

Our results indicate that PRRG4 via the Src-STAT3-POLG axis enhances mitochondrial function and promotes migratory behaviors of breast cancer cells.

Model systems informing mechanisms and drug discovery: a systematic review of POLG-related disease models

Introduction Pathogenic variants in the gene encoding the catalytic subunit of DNA polymerase gamma (POLG), comprise an important single-gene cause of inherited mitochondrial disorders. Clinical manifestations are now recognised as an array of overlapping clinical features rather than discrete syndromes as originally conceptualised. Animal and cellular models have been used to address numerous scientific questions, from basic science to the development and assessment of novel therapies. Here, we sought to perform a systematic review of the existing models used in mitochondrial research and their effectiveness in recapitulating POLG-related disease. Methods Four databases were searched from inception to May 31, 2022: MEDLINE, Scopus, Web of Science, and Cochrane Review. Original articles available in English, reporting the use of a model system designed to recapitulate POLG­-related disease, or related pathogenicity, were eligible for inclusion. Risk of bias and the methodological quality of articles were assessed by an adapted version of the Cochrane Risk of Bias Tool, with the quality of evidence synthesized across each model. Results A total of 55 articles, including seven model organisms (Human, yeast [Saccharomyces cerevisiae and Schizosaccharomyces pombe], Drosophila, Mouse, Nematoda, and Zebrafish) with 258 distinct variants were included. Of these, 66% (N=38) of articles recapitulated mitochondrial DNA (mtDNA) depletion and 42% (N=23) recapitulated POLG-related disease. Thirty-three percent of articles (N=18/55) utilised tissue-specific models of POLG-related dysfunction, while 13% (N=7) investigated the effect of potential therapeutics in POLG-related mitochondrial disorders. Discussion The available evidence supporting the ability of models for POLG-related disease to recapitulate molecular mechanisms and phenotype is limited, inconsistent and of poor methodologic quality.  Further success in examining and translating novel therapies into effective treatments will be enhanced by the availability of more robust models that better recapitulate the entire spectrum of POLG-related disease. PROSPERO registration: CRD42021234883

Mapping Adverse Outcome Pathways for Kidney Injury as a Basis for the Development of Mechanism-Based Animal-Sparing Approaches to Assessment of Nephrotoxicity

In line with recent OECD activities on the use of AOPs in developing Integrated Approaches to Testing and Assessment (IATAs), it is expected that systematic mapping of AOPs leading to systemic toxicity may provide a mechanistic framework for the development and implementation of mechanism-based in vitro endpoints. These may form part of an integrated testing strategy to reduce the need for repeated dose toxicity studies. Focusing on kidney and in particular the proximal tubule epithelium as a key target site of chemical-induced injury, the overall aim of this work is to contribute to building a network of AOPs leading to nephrotoxicity. Current mechanistic understanding of kidney injury initiated by 1) inhibition of mitochondrial DNA polymerase γ (mtDNA Polγ), 2) receptor mediated endocytosis and lysosomal overload, and 3) covalent protein binding, which all present fairly well established, common mechanisms by which certain chemicals or drugs may cause nephrotoxicity, is presented and systematically captured in a formal description of AOPs in line with the OECD AOP development programme and in accordance with the harmonized terminology provided by the Collaborative Adverse Outcome Pathway Wiki. The relative level of confidence in the established AOPs is assessed based on evolved Bradford-Hill weight of evidence considerations of biological plausibility, essentiality and empirical support (temporal and dose-response concordance).

Mitochondrial damage and activation of the cytosolic DNA sensor cGAS-STING pathway lead to cardiac pyroptosis and hypertrophy in diabetic cardiomyopathy mice

Diabetic cardiomyopathy (DCM) is a serious cardiac complication of diabetes that currently lacks specific treatment. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has been suggested to contribute to the pathogenesis of cardiovascular diseases. However, whether cGAS-STING is involved in the development of DCM has not been established. Our study aimed to determine the role of cGAS-STING in the initiation of nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (NLRP3) inflammasome-induced cardiac pyroptosis and chronic inflammation during the pathogenesis of DCM. C57BL/6J mice were preinjected with adeno-associated virus 9 (AAV9) intravenously via the tail vein to specifically knock down myocardial STING. After four weeks, mice with myocardium-specific knockdown of STING received injections of streptozotocin (STZ; 50 mg/kg) and a high-fat diet to induce diabetes. Measurements included echocardiography, immunohistochemical analyses, wheat germ agglutinin (WGA) staining, and western blotting. Here, we showed that the cGAS-STING signaling pathway was activated in diabetic hearts, which was indicated by the increased phosphorylation of TANK-binding kinase 1 (TBK1) and interferon (IFN) regulatory factor 3 (IRF3), leading to the activation of the NLRP3 inflammasome in the hearts of diabetic mice and proinflammatory cytokine release into serum. Moreover, STING knockdown via adeno-associated virus-9 (AAV9) in diabetic mouse heart alleviated cardiac pyroptosis and the inflammatory response, prevented diabetes-induced hypertrophy, and restored cardiac function. Mechanistically, we showed that palmitic acid (PA)-induced lipotoxicity impairs mitochondrial homeostasis, producing excessive mitochondrial reactive oxygen species (mtROS), which results in oxidative damage to mitochondrial DNA (mtDNA) and its release into the cytoplasm while switching on cGAS-STING-mediated pyroptosis in cardiomyocytes, thereby worsening the progression of diabetic cardiomyopathy. Our study demonstrated that activation of the cGAS-STING pathway caused by mitochondrial oxidative damage and mtDNA escape induced by free fatty acids promoted pyroptosis and proinflammatory responses in cardiomyocytes in a NLRP3 inflammasome-dependent manner, thus promoting myocardial hypertrophy during the progression of DCM.

DTYMK is essential for genome integrity and neuronal survival

Nucleotide metabolism is a complex pathway regulating crucial cellular processes such as nucleic acid synthesis, DNA repair and proliferation. This study shows that impairment of the biosynthesis of one of the building blocks of DNA, dTTP, causes a severe, early-onset neurodegenerative disease. Here, we describe two unrelated children with bi-allelic variants in DTYMK, encoding dTMPK, which catalyzes the penultimate step in dTTP biosynthesis. The affected children show severe microcephaly and growth retardation with minimal neurodevelopment. Brain imaging revealed severe cerebral atrophy and disappearance of the basal ganglia. In cells of affected individuals, dTMPK enzyme activity was minimal, along with impaired DNA replication. In addition, we generated dtymk mutant zebrafish that replicate this phenotype of microcephaly, neuronal cell death and early lethality. An increase of ribonucleotide incorporation in the genome as well as impaired responses to DNA damage were observed in dtymk mutant zebrafish, providing novel pathophysiological insights. It is highly remarkable that this deficiency is viable as an essential component for DNA cannot be generated, since the metabolic pathway for dTTP synthesis is completely blocked. In summary, by combining genetic and biochemical approaches in multiple models we identified loss-of-function of DTYMK as the cause of a severe postnatal neurodegenerative disease and highlight the essential nature of dTTP synthesis in the maintenance of genome stability and neuronal survival.

Sirt1 promotes tissue regeneration in zebrafish through regulating the mitochondrial unfolded protein response

The mitochondrial unfolded protein response (UPRmt) is an organellar stress signaling pathway that functions to detect and restore disruption of mitochondrial proteostasis. The UPRmt is involved in a wide range of physiological and disease conditions, including aging, stem cell maintenance, innate immunity, neurodegeneration, and cancer. Here we report that the UPRmt is integral to zebrafish fin regeneration. Taking advantage of a novel zebrafish UPRmt reporter, we observed that UPRmt activation occurs in regenerating fin tissue shortly after injury. Through chemical and genetic approaches, we discovered that the Sirt1-UPRmt pathway, best known for its role in promoting lifespan extension, is crucial for fin regeneration. The metabolism of NAD+ is an important contributor to Sirt1 activity in this context. We propose that Sirt1 activation induces mitochondrial biogenesis in injured fin tissue, which leads to UPRmt activation and promotes tissue regeneration.

Therapy Prospects for Mitochondrial DNA Maintenance Disorders

Mitochondrial DNA depletion and multiple deletions syndromes (MDDS) constitute a group of mitochondrial diseases defined by dysfunctional mitochondrial DNA (mtDNA) replication and maintenance. As is the case for many other mitochondrial diseases, the options for the treatment of these disorders are rather limited today. Some aggressive treatments such as liver transplantation or allogeneic stem cell transplantation are among the few available options for patients with some forms of MDDS. However, in recent years, significant advances in our knowledge of the biochemical pathomechanisms accounting for dysfunctional mtDNA replication have been achieved, which has opened new prospects for the treatment of these often fatal diseases. Current strategies under investigation to treat MDDS range from small molecule substrate enhancement approaches to more complex treatments, such as lentiviral or adenoassociated vector-mediated gene therapy. Some of these experimental therapies have already reached the clinical phase with very promising results, however, they are hampered by the fact that these are all rare disorders and so the patient recruitment potential for clinical trials is very limited.

Zebrafish Models of Autosomal Recessive Ataxias

Autosomal recessive ataxias are much less well studied than autosomal dominant ataxias and there are no clearly defined systems to classify them. Autosomal recessive ataxias, which are characterized by neuronal and multisystemic features, have significant overlapping symptoms with other complex multisystemic recessive disorders. The generation of animal models of neurodegenerative disorders increases our knowledge of their cellular and molecular mechanisms and helps in the search for new therapies. Among animal models, the zebrafish, which shares 70% of its genome with humans, offer the advantages of being small in size and demonstrating rapid development, making them optimal for high throughput drug and genetic screening. Furthermore, embryo and larval transparency allows to visualize cellular processes and central nervous system development in vivo. In this review, we discuss the contributions of zebrafish models to the study of autosomal recessive ataxias characteristic phenotypes, behavior, and gene function, in addition to commenting on possible treatments found in these models. Most of the zebrafish models generated to date recapitulate the main features of recessive ataxias.

Efficient clofilium tosylate-mediated rescue of POLG-related disease phenotypes in zebrafish

The DNA polymerase gamma (Polg) is a nuclear-encoded enzyme involved in DNA replication in animal mitochondria. In humans, mutations in the POLG gene underlie a set of mitochondrial diseases characterized by mitochondrial DNA (mtDNA) depletion or deletion and multiorgan defects, named POLG disorders, for which an effective therapy is still needed. By applying antisense strategies, ENU- and CRISPR/Cas9-based mutagenesis, we have generated embryonic, larval-lethal and adult-viable zebrafish Polg models. Morphological and functional characterizations detected a set of phenotypes remarkably associated to POLG disorders, including cardiac, skeletal muscle, hepatic and gonadal defects, as well as mitochondrial dysfunctions and, notably, a perturbed mitochondria-to-nucleus retrograde signaling (CREB and Hypoxia pathways). Next, taking advantage of preliminary evidence on the candidate molecule Clofilium tosylate (CLO), we tested CLO toxicity and then its efficacy in our zebrafish lines. Interestingly, at well tolerated doses, the CLO drug could successfully rescue mtDNA and Complex I respiratory activity to normal levels, even in mutant phenotypes worsened by treatment with Ethidium Bromide. In addition, the CLO drug could efficiently restore cardio-skeletal parameters and mitochondrial mass back to normal values. Altogether, these evidences point to zebrafish as a valuable vertebrate organism to faithfully phenocopy multiple defects detected in POLG patients. Moreover, this model represents an excellent platform to screen, at the whole-animal level, candidate molecules with therapeutic effects in POLG disorders.

The zebrafish orthologue of the human hepatocerebral disease gene MPV17 plays pleiotropic roles in mitochondria

Mitochondrial DNA depletion syndromes (MDS) are a group of rare autosomal recessive disorders with early onset and no cure available. MDS are caused by mutations in nuclear genes involved in mitochondrial DNA (mtDNA) maintenance, and characterized by both a strong reduction in mtDNA content and severe mitochondrial defects in affected tissues. Mutations in MPV17, a nuclear gene encoding a mitochondrial inner membrane protein, have been associated with hepatocerebral forms of MDS. The zebrafish mpv17 null mutant lacks the guanine-based reflective skin cells named iridophores and represents a promising model to clarify the role of Mpv17. In this study, we characterized the mitochondrial phenotype of mpv17^−/− larvae and found early and severe ultrastructural alterations in liver mitochondria, as well as significant impairment of the respiratory chain, leading to activation of the mitochondrial quality control. Our results provide evidence for zebrafish Mpv17 being essential for maintaining mitochondrial structure and functionality, while its effects on mtDNA copy number seem to be subordinate. Considering that a role in nucleotide availability had already been postulated for MPV17, that embryos blocked in pyrimidine synthesis do phenocopy mpv17^−/− knockouts (KOs) and that mpv17^−/− KOs have impaired Dihydroorotate dehydrogenase activity, we provided mpv17 mutants with the pyrimidine precursor orotic acid (OA). Treatment with OA, an easily available food supplement, significantly increased both iridophore number and mtDNA content in mpv17^−/− mutants, thus linking the loss of Mpv17 to pyrimidine de novo synthesis and opening a new simple therapeutic approach for MPV17-related MDS.

Summary: The zebrafish mpv17^−/− mutant shows a severe mitochondrial phenotype with ultrastructural alterations and oxidative phosphorylation impairment. The pyrimidine precursor orotic acid ameliorates mpv17^−/− phenotype and increases mitochondrial DNA content, linking the loss of Mpv17 to pyrimidine de novo synthesis.

Nucleoside supplementation modulates mitochondrial DNA copy number in the dguok -/- zebrafish

Deoxyguanosine kinase (dGK) is an essential rate-limiting component of the mitochondrial purine nucleotide salvage pathway, encoded by the nuclear gene encoding deoxyguanosine kinase (DGUOK). Mutations in DGUOK lead to mitochondrial DNA (mtDNA) depletion typically in the liver and brain, causing a hepatocerebral phenotype. Previous work has shown that in cultured DGUOK patient cells it is possible to rescue mtDNA depletion by increasing substrate amounts for dGK. In this study we developed a mutant dguok zebrafish (Danio rerio) line using CRISPR/Cas9 mediated mutagenesis; dguok-/- fish have significantly reduced mtDNA levels compared with wild-type (wt) fish. When supplemented with only one purine nucleoside (dGuo), mtDNA copy number in both mutant and wt juvenile animals was significantly reduced, contrasting with previous cell culture studies, possibly because of nucleotide pool imbalance. However, in adult dguok-/- fish we detected a significant increase in liver mtDNA copy number when supplemented with both purine nucleosides. This study further supports the idea that nucleoside supplementation has a potential therapeutic benefit in mtDNA depletion syndromes by substrate enhancement of the purine nucleoside salvage pathway and might improve the liver pathology in patients.

Dissecting metabolism using zebrafish models of disease

Zebrafish (Danio rerio) are becoming an increasingly powerful model organism to study the role of metabolism in disease. Since its inception, the zebrafish model has relied on unique attributes such as the transparency of embryos, high fecundity and conservation with higher vertebrates, to perform phenotype-driven chemical and genetic screens. In this review, we describe how zebrafish have been used to reveal novel mechanisms by which metabolism regulates embryonic development, obesity, fatty liver disease and cancer. In addition, we will highlight how new approaches in advanced microscopy, transcriptomics and metabolomics using zebrafish as a model system have yielded fundamental insights into the mechanistic underpinnings of disease.

Loss of the Mia40a oxidoreductase leads to hepato-pancreatic insufficiency in zebrafish

Development and function of tissues and organs are powered by the activity of mitochondria. In humans, inherited genetic mutations that lead to progressive mitochondrial pathology often manifest during infancy and can lead to death, reflecting the indispensable nature of mitochondrial biogenesis and function. Here, we describe a zebrafish mutant for the gene mia40a (chchd4a), the life-essential homologue of the evolutionarily conserved Mia40 oxidoreductase which drives the biogenesis of cysteine-rich mitochondrial proteins. We report that mia40a mutant animals undergo progressive cellular respiration defects and develop enlarged mitochondria in skeletal muscles before their ultimate death at the larval stage. We generated a deep transcriptomic and proteomic resource that allowed us to identify abnormalities in the development and physiology of endodermal organs, in particular the liver and pancreas. We identify the acinar cells of the exocrine pancreas to be severely affected by mutations in the MIA pathway. Our data contribute to a better understanding of the molecular, cellular and organismal effects of mitochondrial deficiency, important for the accurate diagnosis and future treatment strategies of mitochondrial diseases.

Mitochondrial pathologies which result from mutations in the nuclear DNA remain incurable and often lead to death. As mitochondria play various roles in cellular and tissue-specific contexts, the symptoms of mitochondrial pathologies can differ between patients. Thus, diagnosis and treatment of mitochondrial disorders remain challenging. To enhance this, the generation of new models that explore and define the consequences of mitochondria insufficiencies is of central importance. Here, we present a mia40a zebrafish mutant as a model for mitochondrial dysfunction, caused by an imbalance in mitochondrial protein biogenesis. This mutant shares characteristics with existing reports on mitochondria dysfunction, and has led us to identify novel phenotypes such as enlarged mitochondrial clusters in skeletal muscles. In addition, our transcriptomics and proteomics data contribute important findings to the existing knowledge on how faulty mitochondria impinge on vertebrate development in molecular, tissue and organ specific contexts.

Metabolic etiologies in West syndrome

West syndrome (WS) is an early life epileptic encephalopathy associated with infantile spasms, interictal electroencephalography (EEG) abnormalities including high amplitude, disorganized background with multifocal epileptic spikes (hypsarrhythmia), and often neurodevelopmental impairments. Approximately 64% of the patients have structural, metabolic, genetic, or infectious etiologies and, in the rest, the etiology is unknown. Here we review the contribution of etiologies due to various metabolic disorders in the pathology of WS. These may include metabolic errors in organic molecules involved in amino acid and glucose metabolism, fatty acid oxidation, metal metabolism, pyridoxine deficiency or dependency, or acidurias in organelles such as mitochondria and lysosomes. We discuss the biochemical, clinical, and EEG features of these disorders as well as the evidence of how they may be implicated in the pathogenesis and treatment of WS. The early recognition of these etiologies in some cases may permit early interventions that may improve the course of the disease.

Inherited mitochondrial genomic instability and chemical exposures

There are approximately 1500 proteins that are needed for mitochondrial structure and function, most of which are encoded in the nuclear genome (Calvo et al., 2006). Each mitochondrion has its own genome (mtDNA), which in humans encodes 13 polypeptides, 22 tRNAs and 2 rRNAs required for oxidative phosphorylation. The mitochondrial genome of humans and most vertebrates is approximately 16.5kbp, double-stranded, circular, with few non-coding bases. Thus, maintaining mtDNA stability, that is, the ability of the cell to maintain adequate levels of mtDNA template for oxidative phosphorylation is essential and can be impacted by the level of mtDNA mutation currently within the cell or mitochondrion, but also from errors made during normal mtDNA replication, defects in mitochondrial quality control mechanisms, and exacerbated by exposures to exogenous and/or endogenous genotoxic agents. In this review, we expand on the origins and consequences of mtDNA instability, the current state of research regarding the mechanisms by which mtDNA instability can be overcome by cellular and chemical interventions, and the future of research and treatments for mtDNA instability.

Genome-wide analysis of facial skeletal regionalization in zebrafish

Patterning of the facial skeleton involves the precise deployment of thousands of genes in distinct regions of the pharyngeal arches. Despite the significance for craniofacial development, how genetic programs drive this regionalization remains incompletely understood. Here we use combinatorial labeling of zebrafish cranial neural crest-derived cells (CNCCs) to define global gene expression along the dorsoventral axis of the developing arches. Intersection of region-specific transcriptomes with expression changes in response to signaling perturbations demonstrates complex roles for Endothelin 1 (Edn1) signaling in the intermediate joint-forming region, yet a surprisingly minor role in ventralmost regions. Analysis of co-variance across multiple sequencing experiments further reveals clusters of co-regulated genes, with in situ hybridization confirming the domain-specific expression of novel genes. We then created loss-of-function alleles for 12 genes and uncovered antagonistic functions of two new Edn1 targets, follistatin a (fsta) and emx2, in regulating cartilaginous joints in the hyoid arch. Our unbiased discovery and functional analysis of genes with regional expression in zebrafish arch CNCCs reveals complex regulation by Edn1 and points to novel candidates for craniofacial disorders.

Wars2 is a determinant of angiogenesis

Coronary flow (CF) measured ex vivo is largely determined by capillary density that reflects angiogenic vessel formation in the heart in vivo. Here we exploit this relationship and show that CF in the rat is influenced by a locus on rat chromosome 2 that is also associated with cardiac capillary density. Mitochondrial tryptophanyl-tRNA synthetase (Wars2), encoding an L53F protein variant within the ATP-binding motif, is prioritized as the candidate at the locus by integrating genomic data sets. WARS2(L53F) has low enzyme activity and inhibition of WARS2 in endothelial cells reduces angiogenesis. In the zebrafish, inhibition of wars2 results in trunk vessel deficiencies, disordered endocardial-myocardial contact and impaired heart function. Inhibition of Wars2 in the rat causes cardiac angiogenesis defects and diminished cardiac capillary density. Our data demonstrate a pro-angiogenic function for Wars2 both within and outside the heart that may have translational relevance given the association of WARS2 with common human diseases.

Blood supply to the heart is crucial for cardiac function. Here, the authors show that the mitochondrial tryptophanyl-tRNA synthetase, WARS2, drives blood vessel generation in zebrafish and rats and that inhibition of Wars2 diminishes blood vessel growth both within and outside in the heart, suggesting a new target for manipulating angiogenesis.