Résumé :
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Over the last decade, the significant advances made in the understanding of the molecular mechanisms responsible for debilitating muscle loss lead us to envision new pharmaceutical approaches suitable for in vivo inhibition of putative therapeutic targets. MAFbx/Atrogin-1, a major atrophy-related F-box protein found in various species, including human patients, is specifically up-regulated during muscle disuse or immobilization, fasting, chronic diseases (diabetes, cardiovascular diseases...) or cachectic states such as cancer. The E3 ligase complex associated with MAFbx (SCFMAFbx for Skp1/Cul1/F-box) is a trigger of muscle atrophy responsible for the targeting of i) the transcription factor MyoD that inhibits muscle protein expression in both differentiated fibers and committed progenitors and ii) the ubiquitination and degradation of eIF3-f that dramatically decreases muscle protein synthesis via inhibition of the IGF-1/Akt/mTOR pathway. In cellulo and in vivo inhibition of MAFbx protects muscle cells from atrophy and mice, in which the MAFbx gene has been removed, show a resistance to atrophy induction. We propose an alternative strategy to prevent the rapid activation of MAFbx gene upon atrophy with a newly developed nucleic acid carrier (Aonys®) designed for in vivo use. Aonys® technology consists of a natural micellar structure of pharmacopeia products permitting non-invasive and protective delivery of nucleic acids. These untargeted nanodroplets provide a highly efficient delivery mechanism increasing cellular bioavailability without toxic effects (siRNA: 300 ?g/kg/day). The aim of our study was to evaluate the inhibition of the MAFbx gene expression in an induced model of muscle atrophy (food deprivation) after a 2-Day rectal mucosa administration (1mL/kg/day) of siRNA vectorized with Aonys®. Accumulation of MAFbx mRNA and protein was respectively measured by QRT-PCR and immuno-detection in mouse muscles (TA, Soleus, EDL) and heart extracts (3 cohorts/57 rodents). The two different MAFbx siRNA duplexes (in cellulo validated) used in this study respectively down-regulated MAFbx mRNA accumulation with a 4.5 fold (78% decrease) and a 5.7 fold (82%) reduction compared to mice that received Aonys®/scrambled siRNA or i.v. injection of MAFbx siRNA saline solution. Therefore, Aonys®technology appears to be a promising alternative to intravenous, intramuscular or subcutaneous administration for siRNA silencing of MAFbx mRNA under muscle wasting conditions.
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