Pharmacological interventions that increase myofiber size counter the functional decline of dystrophic muscles 1,2 . We show that deacetylase inhibitors increase the size of myofibers in dystrophin-deficient (MDX) and a-sarcoglycan (a-SG)-deficient mice by inducing the expression of the myostatin antagonist follistatin 3 in satellite cells. Deacetylase inhibitor treatment conferred on dystrophic muscles resistance to contraction-coupled degeneration and alleviated both morphological and functional consequences of the primary genetic defect. These results provide a rationale for using deacetylase inhibitors in the pharmacological therapy of muscular dystrophies.Enlarging fiber size in dystrophic muscles produces beneficial effects in dystrophin-deficient MDX mice, a model of Duchenne muscular dystrophy (DMD) 2,4-6 . Previous studies have shown that three structurally unrelated deacetylase inhibitors-trichostatin A (TSA), valproic acid (VPA) and phenylbutyrate (PhB)-share the ability to promote myoblast fusion into hypernucleated myotubes with an increased size relative to myotubes formed in the absence of drugs 7,8 . To select a compound for long-term treatment of dystrophic mice, we compared the results of pilot experiments in which MDX mice were exposed to TSA (0.6 mg per kg body weight per day), VPA (160 mg/kg per day) or PhB (90 mg/kg per day) by daily intraperitoneal injections. We chose to begin the treatment when the first manifestations of the disease were already evident, as we sought to evaluate the efficacy of deacetylase inhibitors in a situation simulating the clinical stage at which human patients typically receive the diagnosis of muscular dystrophy 9 . Increased histone acetylation, which reflects the bioactivity of deacetylase inhibitors, was detected in muscles and other peripheral organs (for example, brain) a few hours after injection, indicating rapid uptake of the compounds (Supplementary Figure 1 online). We next evaluated the ability of satellite cells from MDX mice exposed to the deacetylase inhibitors for 10 d to differentiate into multinucleated myotubes. After 24 h in differentiation medium, myotubes were present only in cultures of satellite cells isolated from mice exposed to deacetylase inhibitors (Supplementary Figure 2 online). Notably, satellite cells derived from TSA-treated mice formed myotubes with the highest efficiency and showed an increased expression, relative to that in untreated controls, of myosin heavy chain (MyHC)-a marker of terminal differentiation-and of regeneration markers, such as follistatin and embryonic and perinatal MyHC (Supplementary Figure 2). Only satellite cells from TSA-treated mice showed reduced levels of myostatin mRNA relative to those from untreated controls. Treatment of 12-week-old mice with deacetylase inhibitors for an additional three months prevented an increase in serum concentrations of creatine kinase, a biomarker for the severity of the disease (Supplementary Figure 2). The decline of creatine kinase concentrations was more pronounced i...

Friedreich's ataxia (FRDA) is a devastating orphan disease, with no specific treatment. The disease is caused by reduced expression of the protein frataxin, which results in mitochondrial defects and oxidative damage. Levels of residual frataxin critically affect onset and progression of the disease. Understanding the molecular mechanisms that regulate frataxin stability and degradation may, therefore, be exploited for the design of effective therapeutics. Here we show that frataxin is degraded by the ubiquitin-proteasome system and that K(147) is the critical residue responsible for frataxin ubiquitination and degradation. Accordingly, a K(147)R substitution generates a more stable frataxin. We then disclose a set of lead compounds, computationally selected to target the molecular cleft harboring K(147), that can prevent frataxin ubiquitination and degradation, and increase frataxin levels in cells derived from FRDA patients. Moreover, treatment with these compounds induces substantial recovery of aconitase activity and adenosine-5'-triphosphate levels in FRDA cells. Thus, we provide evidence for the therapeutic potential of directly interfering with the frataxin degradation pathway.

Friedreich's ataxia (FRDA) is an untreatable disorder with neuro- and cardio-degenerative progression. This monogenic disease is caused by the hyper-expansion of naturally occurring GAA repeats in the first intron of the FXN gene, encoding for frataxin, a protein implicated in the biogenesis of iron-sulfur clusters. As the genetic defect interferes with FXN transcription, FRDA patients express a normal frataxin protein but at insufficient levels. Thus, current therapeutic strategies are mostly aimed to restore physiological FXN expression. We have previously described SINEUPs, natural and synthetic antisense long non-coding RNAs, which promote translation of partially overlapping mRNAs through the activity of an embedded SINEB2 domain. Here, by in vitro screening, we have identified a number of SINEUPs targeting human FXN mRNA and capable to up-regulate frataxin protein to physiological amounts acting at the post-transcriptional level. Furthermore, FXN-specific SINEUPs promote the recovery of disease-associated mitochondrial aconitase defects in FRDA-derived cells. In summary, we provide evidence that SINEUPs may be the first gene-specific therapeutic approach to activate FXN translation in FRDA and, more broadly, a novel scalable platform to develop new RNA-based therapies for haploinsufficient diseases.

Friedreich's ataxia (FRDA) is the most common hereditary ataxia, affecting ∼3 in 100 000 individuals in Caucasian populations. It is caused by intronic GAA repeat expansions that hinder the expression of the FXN gene, resulting in defective levels of the mitochondrial protein frataxin. Sensory neurons in dorsal root ganglia (DRG) are particularly damaged by frataxin deficiency. There is no specific therapy for FRDA. Here, we show that frataxin levels can be upregulated by interferon gamma (IFNγ) in a variety of cell types, including primary cells derived from FRDA patients. IFNγ appears to act largely through a transcriptional mechanism on the FXN gene. Importantly, in vivo treatment with IFNγ increases frataxin expression in DRG neurons, prevents their pathological changes and ameliorates the sensorimotor performance in FRDA mice. These results disclose new roles for IFNγ in cellular metabolism and have direct implications for the treatment of FRDA.

SummaryFriedreich ataxia (FRDA) is a severe genetic neurodegenerative disease caused by reduced expression of the mitochondrial protein frataxin. To date, there is no therapy to treat this condition. The amount of residual frataxin critically affects the severity of the disease; thus, attempts to restore physiological frataxin levels are considered therapeutically relevant. Frataxin levels are controlled by the ubiquitin-proteasome system; therefore, inhibition of the frataxin E3 ligase may represent a strategy to achieve an increase in frataxin levels. Here, we report the identification of the RING E3 ligase RNF126 as the enzyme that specifically mediates frataxin ubiquitination and targets it for degradation. RNF126 interacts with frataxin and promotes its ubiquitination in a catalytic activity-dependent manner, both in vivo and in vitro. Most importantly, RNF126 depletion results in frataxin accumulation in cells derived from FRDA patients, highlighting the relevance of RNF126 as a new therapeutic target for Friedreich ataxia.