Method of carrier-free delivery of therapeutic RNA importable into human mitochondria: Lipophilic conjugates with cleavable bonds:

Defects in mitochondrial DNA often cause neuromuscular pathologies, for which no efficient therapy has yet been developed. MtDNA targeting nucleic acids might therefore be promising therapeutic candidates. Nevertheless, mitochondrial gene therapy has never been achieved because DNA molecules can not penetrate inside mitochondria in vivo. In contrast, some small non-coding RNAs are imported into mitochondrial matrix, and we recently designed mitochondrial RNA vectors that can be used to address therapeutic oligoribonucleotides into human mitochondria. Here we describe an approach of carrier-free targeting of the mitochondrially importable RNA into living human cells. For this purpose, we developed the protocol of chemical synthesis of oligoribonucleotides conjugated with cholesterol residue through cleavable covalent bonds. Conjugates containing pH-triggered hydrazone bond were stable during the cell transfection procedure and rapidly cleaved in acidic endosomal cellular compartments. RNAs conjugated to cholesterol through a hydrazone bond were characterized by efficient carrier-free cellular uptake and partial co-localization with mitochondrial network. Moreover, the imported oligoribonucleotide designed to target a pathogenic point mutation in mitochondrial DNA was able to induce a decrease in the proportion of mutant mitochondrial genomes. This newly developed approach can be useful for a carrier-free delivery of therapeutic RNA into mitochondria of living human cells

Induced tRNA import into human mitochondria: implication of a host aminoacyl-tRNA-synthetase:

In human cell, a subset of small non-coding RNAs is imported into mitochondria from the cytosol. Analysis of the tRNA import pathway allowing targeting of the yeast tRNA(Lys)(CUU) into human mitochondria demonstrates a similarity between the RNA import mechanisms in yeast and human cells. We show that the cytosolic precursor of human mitochondrial lysyl-tRNA synthetase (preKARS2) interacts with the yeast tRNA(Lys)(CUU) and small artificial RNAs which contain the structural elements determining the tRNA mitochondrial import, and facilitates their internalization by isolated human mitochondria. The tRNA import efficiency increased upon addition of the glycolytic enzyme enolase, previously found to be an actor of the yeast RNA import machinery. Finally, the role of preKARS2 in the RNA mitochondrial import has been directly demonstrated in vivo, in cultured human cells transfected with the yeast tRNA and artificial importable RNA molecules, in combination with preKARS2 overexpression or downregulation by RNA interference. These findings suggest that the requirement of protein factors for the RNA mitochondrial targeting might be a conserved feature of the RNA import pathway in different organisms

Biological significance of 5S rRNA import into human mitochondria: role of ribosomal protein MRP-L18:

5S rRNA is an essential component of ribosomes of all living organisms, the only known exceptions being mitochondrial ribosomes of fungi, animals, and some protists. An intriguing situation distinguishes mammalian cells: Although the mitochondrial genome contains no 5S rRNA genes, abundant import of the nuclear DNA-encoded 5S rRNA into mitochondria was reported. Neither the detailed mechanism of this pathway nor its rationale was clarified to date. In this study, we describe an elegant molecular conveyor composed of a previously identified human 5S rRNA import factor, rhodanese, and mitochondrial ribosomal protein L18, thanks to which 5S rRNA molecules can be specifically withdrawn from the cytosolic pool and redirected to mitochondria, bypassing the classic nucleolar reimport pathway. Inside mitochondria, the cytosolic 5S rRNA is shown to be associated with mitochondrial ribosomes

A Moonlighting Human Protein Is Involved in Mitochondrial Import of tRNA

In yeast Saccharomyces cerevisiae, ~3% of the lysine transfer RNA acceptor 1 (tRK1) pool is imported into mitochondria while the second isoacceptor, tRK2, fully remains in the cytosol. The mitochondrial function of tRK1 is suggested to boost mitochondrial translation under stress conditions. Strikingly, yeast tRK1 can also be imported into human mitochondria in vivo, and can thus be potentially used as a vector to address RNAs with therapeutic anti-replicative capacity into mitochondria of sick cells. Better understanding of the targeting mechanism in yeast and human is thus critical. Mitochondrial import of tRK1 in yeast proceeds first through a drastic conformational rearrangement of tRK1 induced by enolase 2, which carries this freight to the mitochondrial pre-lysyl-tRNA synthetase (preMSK). The latter may cross the mitochondrial membranes to reach the matrix where imported tRK1 could be used by the mitochondrial translation apparatus. This work focuses on the characterization of the complex that tRK1 forms with human enolases and their role on the interaction between tRK1 and human pre-lysyl-tRNA synthetase (preKARS2)

Modeling of antigenomic therapy of mitochondrial diseases by mitochondrially addressed RNA targeting a pathogenic point mutation in mitochondrial DNA

Defects in mitochondrial genome can cause a wide range of clinical disorders, mainly neuromuscular diseases. Presently, no efficient therapeutic treatment has been developed against this class of pathologies. Because most of deleterious mitochondrial mutations are heteroplasmic, meaning that wild type and mutated forms of mitochondrial DNA (mtDNA) coexist in the same cell, the shift in proportion between mutant and wild type molecules could restore mitochondrial functions. Recently, we developed mitochondrial RNA vectors that can be used to address anti-replicative oligoribonucleotides into human mitochondria and thus impact heteroplasmy level in cells bearing a large deletion in mtDNA. Here, we show that this strategy can be also applied to point mutations in mtDNA. We demonstrate that specifically designed RNA molecules containing structural determinants for mitochondrial import and 20-nucleotide sequence corresponding to the mutated region of mtDNA, are able to anneal selectively to the mutated mitochondrial genomes. After being imported into mitochondria of living human cells in culture, these RNA induced a decrease of the proportion of mtDNA molecules bearing a pathogenic point mutation in the mtDNA ND5 gene

Mitochondrial targeting of recombinant RNAs modulates the level of a heteroplasmic mutation in human mitochondrial DNA associated with Kearns Sayre Syndrome

Mitochondrial mutations, an important cause of incurable human neuromuscular diseases, are mostly heteroplasmic: mutated mitochondrial DNA is present in cells simultaneously with wild-type genomes, the pathogenic threshold being generally >70% of mutant mtDNA. We studied whether heteroplasmy level could be decreased by specifically designed oligoribonucleotides, targeted into mitochondria by the pathway delivering RNA molecules in vivo. Using mitochondrially imported RNAs as vectors, we demonstrated that oligoribonucleotides complementary to mutant mtDNA region can specifically reduce the proportion of mtDNA bearing a large deletion associated with the Kearns Sayre Syndrome in cultured transmitochondrial cybrid cells. These findings may be relevant to developing of a new tool for therapy of mtDNA associated diseases

Pathologies de l’ADN mitochondrial et stratégies thérapeutiques

De multiples altérations peuvent affecter le génome mitochondrial et entraîner l’apparition de nombreuses maladies, pour la plupart neuromusculaires. Bien qu’à ce jour il n’existe aucun traitement efficace pour de telles affections, diverses stratégies sont envisagées. Nous décrivons ici les principales affections liées à une altération de l’ADN mitochondrial (ADNmt), les systèmes expérimentaux utilisés pour étudier les mécanismes moléculaires de ces dysfonctionnements (levures, cellules cybrides, souris, etc.) et faisons un tour d’horizon des progrès récents dans le développement de différentes approches thérapeutiques

Caractérisation d ARN artificiels importables dans les mitochondries humaines à des fins thérapeutiques

Les mutations dans l ADN mitochondrial (ADNmt) sont la cause de nombreuses pathologies, pour la plupart des myopathies et des maladies neurodégénératives. La majorité de ces mutations sont hétéroplasmiques, signifiant que les molécules d ADNmt muté coexistent au sein de la même cellule avec des molécules d ADNmt sauvage. Ce n est cependant en général qu à partir d un seuil d hétéroplasmie de l ordre de 70% que les symptômes de la maladie apparaissent. L objectif de cette thèse a été de tester si le taux d hétéroplasmie pouvait être diminué en adressant des oligonucléotides complémentaires à l ADNmt muté dans les mitochondries par la voie d import des ARN afin d inhiber leur réplication. Pour ce faire, nous avons utilisé un petit ARN artificiel construit sur la base des déterminants d importation de l ARNt Lys CUU importé dans les mitochondries de levure. Les résultats obtenus ont permis de montrer que cet ARN pouvait servir de vecteur pour importer dans les mitochondries humaines les oligonucléotides au potentiel anti-réplicatif et que ces derniers étaient capables d inhiber la réplication des molécules d ADNmt muté sans affecter celles des molécules d ADNmt sauvage. C est la première fois que la validité de cette stratégie dite anti-génomique a pu être testée dans un modèle de cellules humaines en culture, ce qui pourrait aboutir à une alternative prometteuse pour traiter les maladies mitochondriales causées par des mutations dans l ADNmt.Mitochondrial DNA mutations, important cause of incurable human neuromuscular diseases, are mostly heteroplasmic: mutated mtDNA is present in cells simultaneously with wild-type genomes, the pathogenic threshold being generally > 70% of mutant mtDNA. We studied if heteroplasmy level could be decreased by RNAs complementary to mutant mtDNA regions. To target specifically designed oligoribonucleotides into the organelle, mitochondrial import of RNA was exploited, the pathway delivering nucleic acids into mitochondria in vivo. Using mitochondrially targeted RNAs as mitochondrial vectors we demonstrated, in cultured transmitochondrial cybrid cells, that RNAs complementary to the mutant mtDNA region can specifically reduce the proportion of mtDNA bearing a large deletion associated with the Kearns Sayre Syndrome. These findings may be relevant to developing of a new tool for therapy of mtDNA associated diseases.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Study of the interactome of mitochondrial protein YBEY in human cells by FLIM-FRET

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