NF-kappaB is a major pleiotropic transcription factor modulating immune, inflammatory, cell survival, and proliferative responses, yet the relevance of NF-kappaB signaling in muscle physiology and disease is less well documented. Here we show that muscle-restricted NF-kappaB inhibition in mice, through targeted deletion of the activating kinase inhibitor of NF-kappaB kinase 2 (IKK2), shifted muscle fiber distribution and improved muscle force. In response to denervation, IKK2 depletion protected against atrophy, maintaining fiber type, size, and strength, increasing protein synthesis, and decreasing protein degradation. IKK2-depleted mice with a muscle-specific transgene expressing a local Igf-1 isoform (mIgf-1) showed enhanced protection against muscle atrophy. In response to muscle damage, IKK2 depletion facilitated skeletal muscle regeneration through enhanced satellite cell activation and reduced fibrosis. Our results establish IKK2/NF-kappaB signaling as an important modulator of muscle homeostasis and suggest a combined role for IKK inhibitors and growth factors in the therapy of muscle diseases.

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...

MicroRNAs are small noncoding RNAs that regulate gene expression post-transcriptionally. Here we applied microRNA profiling to 17 human lymphocyte subsets to identify microRNA signatures that were distinct among various subsets and different from those of mouse lymphocytes. One of the signature microRNAs of naive CD4+ T cells, miR-125b, regulated the expression of genes encoding molecules involved in T cell differentiation, including IFNG, IL2RB, IL10RA and PRDM1. The expression of synthetic miR-125b and lentiviral vectors encoding the precursor to miR-125b in naive lymphocytes inhibited differentiation to effector cells. Our data provide an 'atlas' of microRNA expression in human lymphocytes, define subset-specific signatures and their target genes and indicate that the naive state of T cells is enforced by microRNA.

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Duchenne muscular dystrophy is an X-linked muscle disease characterized by mutations in the dystrophin gene. Many of these can be corrected at the posttranscriptional level by skipping the mutated exon. We have obtained persistent exon skipping in mdx mice by tail vein injection with an adeno-associated viral (AAV) vector expressing antisense sequences as part of the stable cellular U1 small nuclear RNA. Systemic delivery of the AAV construct resulted in effective body-wide colonization, significant recovery of the functional properties in vivo, and lower creatine kinase serum levels, suggesting an overall decrease in muscle wasting. The transduced muscles rescued dystrophin expression and displayed a significant recovery of function toward the normal values at single muscle fiber level. This approach provides solid bases for a systemic use of AAV-mediated antisense-U1 small nuclear RNA expression for the therapeutic treatment of Duchenne muscular dystrophy.exon skipping ͉ adeno-associated virus vectors ͉ antisense ͉ small nuclear RNA ͉ dystrophin D eletions and point mutations in the human 2.5-Mb-long dystrophin gene cause either the severe progressive myopathy Duchenne muscular dystrophy (DMD) or the milder Becker muscular dystrophy (BMD), depending on whether the translational reading frame is lost or maintained (1).The mdx mouse, carrying a stop codon inside exon 23 of the dystrophin gene, provides a useful system to study the effectiveness of different therapeutic strategies for the cure of this disease (2). The two challenging issues in the gene therapy of DMD are related on one side to the type of therapeutic gene to use and on the other to the delivery system suitable for efficient muscular transduction. Due to the large size of the protein, a traditional gene replacement approach is difficult: only adenoviral vectors could allow the expression of a full-length dystrophin cDNA. However, treatments of mdx mice with ''gutted'' vectors carrying the full-length dystrophin cDNA induced a weak immune reaction and transduction was not very effective (3, 4).A different approach took advantage of adeno-associated viral (AAV) vectors for the delivery of microdystrophin gene (5). AAV vectors with an AAV8 capsid (or the very similar but not identical AAV1, or AAV6) have been shown to transduce efficiently and widely murine muscles after administration in the tail vein of WT mice (6). Those with an AAV6 capsid have been shown to correct the phenotype of dystrophic mdx mice when carrying microdystrophin (7).Recently, other alternative ways of correcting the DMD phenotype have been achieved that consist in the delivery of antisense sequences able to induce exon skipping and cure the genetic alteration at the posttranscriptional level. Many of the internal in-frame deletions fall in the region encoding the spectrin-like central rod domain that is largely dispensable and produce only mild myopathic symptoms; therefore, for the out-of-frame mutations, it should be possible, by preventing the inclusion of specific mutated ...