Phenotypic rescue of aDrosophilamodel of mitochondrial ANT1 disease

Abstract

A point mutation in the Drosophila gene that codes for the major adult isoform of adenine nuclear translocase (ANT) represents a model for human diseases that are associated with ANT insufficiency [stress-sensitive B1 (sesB1)]. We characterized the organismal, bioenergetic and molecular phenotype of sesB1 flies then tested strategies to compensate the mutant phenotype. In addition to developmental delay and mechanical-stress-induced seizures, sesB1 flies have an impaired response to sound, defective male courtship, female sterility and curtailed lifespan. These phenotypes, excluding the latter two, are shared with the mitoribosomal protein S12 mutant, tko25t. Mitochondria from sesB1 adults showed a decreased respiratory control ratio and downregulation of cytochrome oxidase. sesB1 adults exhibited ATP depletion, lactate accumulation and changes in gene expression that were consistent with a metabolic shift towards glycolysis, characterized by activation of lactate dehydrogenase and anaplerotic pathways. Females also showed downregulation of many genes that are required for oogenesis, and their eggs, although fertilized, failed to develop to the larval stages. The sesB1 phenotypes of developmental delay and mechanical-stress-induced seizures were alleviated by an altered mitochondrial DNA background. Female sterility was substantially rescued by somatic expression of alternative oxidase (AOX) from the sea squirt Ciona intestinalis, whereas AOX did not alleviate developmental delay. Our findings illustrate the potential of different therapeutic strategies for ANT-linked diseases, based on alleviating metabolic stress.

Glial lipid droplets and neurodegeneration in a Drosophila model of complex I deficiency

“…As suggested by studies in mice or flies, cells with defective mitochondria could shift from metabolic activity of the respiratory chain to other types of energetic pathways. Indeed, metabolomic analysis of mitochondrial disease models associated with cytochrome oxidase deficiency (Vartiainen et al, 2014;Kemppainen et al, 2016), or ATP synthase mutation (Celotto et al, 2011) that are impacting respiratory complexes shows a switch to glycolysis for ATP production. Indeed, metabolomic analysis of mitochondrial disease models associated with cytochrome oxidase deficiency (Vartiainen et al, 2014;Kemppainen et al, 2016), or ATP synthase mutation (Celotto et al, 2011) that are impacting respiratory complexes shows a switch to glycolysis for ATP production.…”

“…They use fatty acid b-oxidation, glycolysis or protein catabolism due to transcriptional dysregulation of genes affecting the diverse metabolic processes (Crimi et al, 2005;Fern andez-Ayala et al, 2010;Celotto, Chiu, Voorhies, & Palladino, 2011). Indeed, metabolomic analysis of mitochondrial disease models associated with cytochrome oxidase deficiency (Vartiainen et al, 2014;Kemppainen et al, 2016), or ATP synthase mutation (Celotto et al, 2011) that are impacting respiratory complexes shows a switch to glycolysis for ATP production. In ND23 knockdown, the increased glucose entry due to transporter overexpression may likely trigger a compensatory metabolic pathway.…”

Risks inherent to mitochondrial replacement

“…Lack of evidence from small-scale proof-of-principle experiments for MR effects should not be used to conclude mito-nuclear incompatibilities are unlikely to manifest post-MR, because these experiments cover few mito-nuclear combinations and their statistical inferences, in some cases, appear open to question. In fact, there is actually an extensive, but largely overlooked, body of experimental evidence that indicates mito-nuclear interactions are important in determining health outcomes in humans 30–42 , as well evidence for mito-nuclear incompatibilities following the similar procedure of somatic cell nuclear transfer in cattle 43,44 . Furthermore, the only previous attempt of using pronuclear transfer in humans was not successful 45 .…”

Mitochondrial diseases: Drosophila melanogaster as a model to evaluate potential therapeutics

“…They often exhibit common phenotypic features, although with different levels of severity, such as shortened lifespan or lethality, developmental delay, muscle weakness, neuronal dysfunction and degeneration, seizures, and a decreased activity of the specific targeted complex, all of which are phenotypes commonly observed in patients. In Drosophila, multiple techniques and assays are available to assess these and related systemic defects, such as locomotors tests (e.g., monitoring of activity and movements, flight, and climbing assays) (Walker et al, 2006;Fernandez-Ayala et al, 2009;Ghezzi et al, 2011) sensitivity tests (seizures) (Royden et al, 1987;Zhang et al, 1999;Vartiainen et al, 2014).…”

“…Ultimately, it illustrates that not all patients with mutations in subunits of complex I will benefit from the same treatment. Similarly, while the phenotypes of fly models for two different mitochondrial proteins, the tko 25t and the sesB 1 (a mutant allele of the Adenine Nucleotide Translocase) largely overlap (Vartiainen et al, 2014), only one could be rescued by the Zhang et al, 1999;Vartiainen et al, 2014 Abbreviations: MARF, mitochondrial assembly regulatory factor. somatic expression of an alternative oxidase (Kemppainen et al, 2014).…”