IRES-Mediated Translation of Utrophin A Is Enhanced by Glucocorticoid Treatment in Skeletal Muscle Cells

Glucocorticoids are currently the only drug treatment recognized to benefit Duchenne muscular dystrophy (DMD) patients. The nature of the mechanisms underlying the beneficial effects remains incompletely understood but may involve an increase in the expression of utrophin. Here, we show that treatment of myotubes with 6α−methylprednisolone-21 sodium succinate (PDN) results in enhanced expression of utrophin A without concomitant increases in mRNA levels thereby suggesting that translational regulation contributes to the increase. In agreement with this, we show that PDN treatment of cells transfected with monocistronic reporter constructs harbouring the utrophin A 5′UTR, causes an increase in reporter protein expression while leaving levels of reporter mRNAs unchanged. Using bicistronic reporter assays, we further demonstrate that PDN enhances activity of an Internal Ribosome Entry Site (IRES) located within the utrophin A 5′UTR. Analysis of polysomes demonstrate that PDN causes an overall reduction in polysome-associated mRNAs indicating that global translation rates are depressed under these conditions. Importantly, PDN causes an increase in the polysome association of endogenous utrophin A mRNAs and reporter mRNAs harbouring the utrophin A 5′UTR. Additional experiments identified a distinct region within the utrophin A 5′UTR that contains the inducible IRES activity. Together, these studies demonstrate that a translational regulatory mechanism involving increased IRES activation mediates, at least partially, the enhanced expression of utrophin A in muscle cells treated with glucocorticoids. Targeting the utrophin A IRES may thus offer an important and novel therapeutic avenue for developing drugs appropriate for DMD patients

NQO1-Dependent Redox Cycling of Idebenone: Effects on Cellular Redox Potential and Energy Levels

Short-chain quinones are described as potent antioxidants and in the case of idebenone have already been under clinical investigation for the treatment of neuromuscular disorders. Due to their analogy to coenzyme Q10 (CoQ10), a long-chain quinone, they are widely regarded as a substitute for CoQ10. However, apart from their antioxidant function, this provides no clear rationale for their use in disorders with normal CoQ10 levels. Using recombinant NAD(P)H:quinone oxidoreductase (NQO) enzymes, we observed that contrary to CoQ10 short-chain quinones such as idebenone are good substrates for both NQO1 and NQO2. Furthermore, the reduction of short-chain quinones by NQOs enabled an antimycin A-sensitive transfer of electrons from cytosolic NAD(P)H to the mitochondrial respiratory chain in both human hepatoma cells (HepG2) and freshly isolated mouse hepatocytes. Consistent with the substrate selectivity of NQOs, both idebenone and CoQ1, but not CoQ10, partially restored cellular ATP levels under conditions of impaired complex I function. The observed cytosolic-mitochondrial shuttling of idebenone and CoQ1 was also associated with reduced lactate production by cybrid cells from mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) patients. Thus, the observed activities separate the effectiveness of short-chain quinones from the related long-chain CoQ10 and provide the rationale for the use of short-chain quinones such as idebenone for the treatment of mitochondrial disorders

Facteurs et expression du polycyclisme juvénile chez le chêne rouge d'Amérique (Quercus rubra L) planté en conditions naturelles

II est montré, dans un essai installé en conditions naturelles sur un ancien sol agricole du sud-ouest de la France, que le chêne rouge d'Amérique (Quercus rubra L) est capable d'exprimer au stade juvénile plusieurs cycles de croissance (polycyclisme) dès la première année de plantation. Ce phénomène est apparu en 1992 uniquement si les plants étaient désherbés et n'a concerné qu'environ 1 tiers des plants désherbés. La fertilisation (NPK) ne semble pas avoir d'influence sur le polycyclisme. En revanche, ce sont les plants de plus petit diamètre initial et bénéficiant d'une alimentation en eau sans excès qui ont la plus grande probabilité de développer plus d'un cycle de croissance annuel. Le polycyclisme a eu pour conséquences une augmentation significative de l'accroissement en diamètre (+130%), de la ramification (qui passe de 24% en volume ligneux à 64%), et de la surface foliaire (+120%), et constitue de ce fait un avantage considérable pour la réussite de ce type de plantation. Son expression s'effectuant en partie sous forme de pousses-relais, il ne contribue pas à augmenter significativement la hauteur totale des plants la première année de leur installation.Factors and consequences of rhythmic growth on young American red oak in field conditions. In field conditions (ex-agricultural soils of south-west France), red oak is able to develop several growth flushes (polycyclism) in the 1st growing period of plantation. Polycyclism occurred only in the weeded treatment, and concerned one-third of weeded plants. NPK fertilization showed no influence on polycyclism. On the other hand, a significantly higher probability of polycyclism arose on small diameter plants or on plants without soil water excess. The consequences of polycyclism were an increase of diameter (+130%), leaf area (+120%) and ramification rate (from 24 to 64%). These advantages are very important for the success of this type of plantation. Polycyclic shoots were frequently basal shoots, and did not increase significantly the total tree height

Facteurs et expression du polycyclisme juvénile chez le chêne rouge d'Amérique (Quercus rubra L.) planté en conditions naturelles

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Facteurs et expression du polycyclisme juvénile chez le chêne rouge d'Amérique (Quercus rubra L) planté en conditions naturelles

International audienc

Modélisation de l'architecture du pin maritime Pinus pinaster Ait. (Pinaceae) : premiers résultats

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