Circulating α-Klotho Counteracts Transforming Growth Factor-ß-Induced Sarcopenia.

α-Klotho is a longevity-related protein. Its deficiency shortens lifespan with prominent senescent phenotypes, including muscle atrophy and weakness in mice. α-Klotho has two forms: membrane α-Klotho and circulating α-Klotho (c-α-Klotho). Loss of membrane α-Klotho impairs a phosphaturic effect, thereby accelerating phosphate-induced aging. However, the mechanisms of senescence on c-α-Klotho loss remain largely unknown. Herein, with the aging of wild-type mice, c-α-Klotho declined, whereas Smad2, an intracellular transforming growth factor (TGF)-ß effector, became activated in skeletal muscle. Moreover, c-α-Klotho suppressed muscle-wasting TGF-ß molecules, including myostatin, growth and differentiation factor 11, activin, and TGF-ß1, through binding to ligands as well as type I and type II serine/threonine kinase receptors. Indeed, c-α-Klotho reversed impaired in vitro myogenesis caused by these TGF-ßs. Oral administration of Ki26894, a small-molecule inhibitor of type I receptors for these TGF-ßs, restored muscle atrophy and weakness in α-Klotho (-/-) mice and in elderly wild-type mice by suppression of activated Smad2 and up-regulated Cdkn1a (p21) transcript, a target of phosphorylated Smad2. Ki26894 also induced the slow to fast myofiber switch. These findings show c-α-Klotho's potential as a circulating inhibitor counteracting TGF-ß-induced sarcopenia. These data highlight the potential of a novel therapy involving TGF-ß blockade to prevent sarcopenia.

Alterations of ATG4A and LC3B in neurons derived from Alzheimer's disease patients.

We investigated the alterations in autophagy-related molecules in neurons differentiated from induced pluripotent stem cells obtained from patients with Alzheimer's disease (AD). Consistent with our previous microarray data, ATG4A protein was upregulated in the neurons derived from a familial AD patient with an APP-E693Δ mutation who showed accumulation of intracellular amyloid ß peptide (Aß). This upregulation was reversed by inhibiting Aß production, suggesting that the intracellular Aß may be responsible for the upregulation of ATG4A. The LC3B-II/LC3B-I ratio, an index of autophagosome formation, was lower in the neurons derived from the AD patient with APP-E693Δ as well as the neurons derived from other familial and sporadic AD patients. These findings indicate that dysregulation of autophagy-related molecules may accelerate the pathogenesis of AD.

Becker Muscular Dystrophy Accompanied by Anti-HMGCR Antibody-positive Immune-mediated Necrotizing Myopathy.

Becker muscular dystrophy (BMD) is an X-linked neuromuscular disease characterized by progressive muscle weakness that currently has no cure. Immune-mediated necrotizing myopathy (IMNM) is a type of autoimmune inflammatory myopathy characterized by proximal muscle weakness that is treated with immunosuppressive therapy. We herein report a patient diagnosed with BMD complicated with IMNM by a pathological analysis. Notably, the patient had an elevated serum anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibody level. Oral glucocorticoid and methotrexate treatment partially improved the muscle weakness with decreased levels of serum creatine kinase. An accurate diagnosis is important for therapeutic decisions in these complicated cases.

Caveolin 3 suppresses phosphorylation-dependent activation of sarcolemmal nNOS.

Mutations of the caveolin 3 gene cause autosomal dominant limb-girdle muscular dystrophy (LGMD)1C. In mice, overexpression of mutant caveolin 3 leads to loss of caveolin 3 and results in myofiber hypotrophy in association with activation of neuronal nitric oxide synthase (nNOS) at the sarcolemma. Here, we show that caveolin 3 directly bound to nNOS and suppressed its phosphorylation-dependent activation at a specific residue, Ser1412 in the nicotinamide adenine dinucleotide phosphate (NADPH)-flavin adenine dinucleotide (FAD) module near the C-terminus of the reduction domain, in vitro. Constitutively active nNOS enhanced myoblast fusion, but not myogenesis, in vitro. Phosphorylation-dependent activation of nNOS occurred in muscles from caveolin 3-mutant mice and LGMD1C patients. Mating with nNOS-mutant mice exacerbated myofiber hypotrophy in the caveolin 3-mutant mice. In nNOS-mutant mice, regenerating myofibers after cardiotoxin injury became hypotrophic with reduced myoblast fusion. Administration of NO donor increased myofiber size and the number of myonuclei in the caveolin 3-mutant mice. Exercise also increased myofiber size accompanied by phosphorylation-dependent activation of nNOS in wild-type and caveolin 3-mutant mice. These data indicate that caveolin 3 inhibits phosphorylation-dependent activation of nNOS, which leads to myofiber hypertrophy via enhancing myoblast fusion. Hypertrophic signaling by nNOS phosphorylation could act in a compensatory manner in caveolin 3-deficient muscles.

Maximal Multistage Shuttle Run Test-induced Myalgia in a Patient with Muscle Phosphorylase B Kinase Deficiency.

Muscle phosphorylase b kinase (PHK) deficiency is a rare mild metabolic disorder caused by mutations of the PHKA1 gene encoding the αM subunit of PHK. A 16-year-old boy experienced myalgia during the maximal multistage 20-m shuttle run test targeting the maximal oxygen consumption. Although an ischemic forearm exercise test was normal, a muscle biopsy revealed subsarcolemmal glycogen accumulation. He harbored a novel insertion mutation in the PHKA1 gene that resulted in premature termination of the αM subunit close to the C-terminus. Compared with previously reported cases, his reduction in PHK activity was relatively mild.

Taurine supplementation for prevention of stroke-like episodes in MELAS: a multicentre, open-label, 52-week phase III trial.

OBJECTIVE: The aim of this study was to evaluate the efficacy and safety of high-dose taurine supplementation for prevention of stroke-like episodes of MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes), a rare genetic disorder caused by point mutations in the mitochondrial DNA that lead to a taurine modification defect at the first anticodon nucleotide of mitochondrial tRNALeu(UUR), resulting in failure to decode codons accurately. METHODS: After the nationwide survey of MELAS, we conducted a multicentre, open-label, phase III trial in which 10 patients with recurrent stroke-like episodes received high-dose taurine (9 g or 12 g per day) for 52 weeks. The primary endpoint was the complete prevention of stroke-like episodes during the evaluation period. The taurine modification rate of mitochondrial tRNALeu(UUR) was measured before and after the trial. RESULTS: The proportion of patients who reached the primary endpoint (100% responder rate) was 60% (95% CI 26.2% to 87.8%). The 50% responder rate, that is, the number of patients achieving a 50% or greater reduction in frequency of stroke-like episodes, was 80% (95% CI 44.4% to 97.5%). Taurine reduced the annual relapse rate of stroke-like episodes from 2.22 to 0.72 (P=0.001). Five patients showed a significant increase in the taurine modification of mitochondrial tRNALeu(UUR) from peripheral blood leukocytes (P<0.05). No severe adverse events were associated with taurine. CONCLUSIONS: The current study demonstrates that oral taurine supplementation can effectively reduce the recurrence of stroke-like episodes and increase taurine modification in mitochondrial tRNALeu(UUR) in MELAS. TRIAL REGISTRATION NUMBER: UMIN000011908.

Functional validation and expression analysis of myotubes converted from skin fibroblasts using a simple direct reprogramming strategy.

Previously, we reported that MyoD, a master gene for myogenic cells, could efficiently convert primary skin fibroblasts into myoblasts and myotubes, thereby effecting direct reprogramming. In this study, we further demonstrated that MyoD-expressing primary fibroblasts displayed rapid movement in culture, with a movement velocity that was significantly faster, almost four times, than mouse primary myoblasts. MyoD-transduced cells obtained the characteristics of Ca2 + release and electrically-stimulated contraction, which was comparable to C2C12 myotubes, suggesting that the essential features of muscle were observed in the transduced cells. Furthermore, the ability to fuse to the host myoblasts means that gene transfer from MyoD-transduced cells to host muscle cells could be obtained by cell fusion. In comparison with the iPS method (indirect reprogramming), our transduction method has a low risk for tumorigenesis and carcinogenesis because the starting cells are fibroblasts and the transduced cells are myoblasts, both normal and mortal cells. Accordingly, MyoD transduction of human skin fibroblasts using the adenoviral vector is a simple, inexpensive and promising candidate as a new cell transplantation therapy for patients with muscular disorders.

Clinical and pathological findings in familial amyloid polyneuropathy caused by a transthyretin E61K mutation.

Familial amyloid polyneuropathy (FAP) is an autosomal dominant hereditary systemic amyloidosis caused by mutation of the transthyretin (TTR) gene, and usually shows sensory-dominant polyneuropathy and autonomic neuropathy at the initial stage. The pathogenesis of this neuropathy remains unknown, although several mechanisms, including mechanical compression, vessel occlusion, TTR toxicity and Schwann cell dysfunction have been proposed. We describe a patient with late-onset FAP caused by a TTR E61K mutation. Amyloid deposits were not detected in the endoneurium or perineurium of the sural nerve 7years after the onset of the disease, but a marked loss of nerve fibers was observed in the sural nerve. TTR-derived amyloid deposits were confirmed in the peroneus brevis muscle, salivary gland and heart tissue. DNA analysis revealed a heterozygous mutation in TTR. These findings suggest that proximal parts of the peripheral nervous system might be strongly affected by TTR aggregates or amyloid fibrils, and that the blood-nerve barrier in distal parts of peripheral nerves are initially preserved in this patient. This case indicates that several biopsy sites other than nerves may be helpful and necessary for the diagnosis of TTR amyloidosis in mild or late-onset FAP.

A simplified and sensitive method to identify Alzheimer's disease biomarker candidates using patient-derived induced pluripotent stem cells (iPSCs).

We developed a simplified and sensitive method to identify Alzheimer's disease (AD) biomarker candidates by a quantitative and targeted proteomic analysis (combination of liquid chromatography tandem mass spectrometry and multiplexed-multiple reaction monitoring/selected reaction monitoring analysis) of culture media from neurons differentiated from induced pluripotent stem cells (iPSCs) established from AD patients. We found that alpha-1-acid glycoprotein (ORM1) was decreased in the culture media of AD-iPSC-derived neurons, consistent with previous observations for AD patient cerebrospinal fluid, thus validating our new strategy. Moreover, our method is applicable for identifying biomarker candidates for other neurodegenerative disorders using patient-derived iPSCs.

Cleavage of ß-dystroglycan occurs in sarcoglycan-deficient skeletal muscle without MMP-2 and MMP-9.

BACKGROUND: The dystroglycan complex consists of two subunits: extracellular α-dystroglycan and membrane-spanning ß-dystroglycan, which provide a tight link between the extracellular matrix and the intracellular cytoskeleton. Previous studies showed that 43 kDa ß-dystroglycan is proteolytically cleaved into the 30 kDa fragment by matrix metalloproteinases (MMPs) in various non-muscle tissues, whereas it is protected from cleavage in muscles by the sarcoglycan complex which resides close to the dystroglycan complex. It is noteworthy that cleaved ß-dystroglycan is detected in muscles from patients with sarcoglycanopathy, sarcoglycan-deficient muscular dystrophy. In vitro assays using protease inhibitors suggest that both MMP-2 and MMP-9 contribute to the cleavage of ß-dystroglycan. However, this has remained uninvestigated in vivo. METHODS: We generated triple-knockout (TKO) mice targeting MMP-2, MMP-9 and γ-sarcoglycan to examine the status of ß-dystroglycan cleavage in the absence of the candidate matrix metalloproteinases in sarcoglycan-deficient muscles. RESULTS: Unexpectedly, ß-dystroglycan was cleaved in muscles from TKO mice. Muscle pathology was not ameliorated but worsened in TKO mice compared with γ-sarcoglycan single-knockout mice. The gene expression of MMP-14 was up-regulated in TKO mice as well as in γ-sarcoglycan knockout mice. In vitro assay showed MMP-14 is capable to cleave ß-dystroglycan. CONCLUSIONS: Double-targeting of MMP-2 and MMP-9 cannot prevent cleavage of ß-dystroglycan in sarcoglycanopathy. Thus, matrix metalloproteinases contributing to ß-dystroglycan cleavage are redundant, and MMP-14 could participate in the pathogenesis of sarcoglycanopathy.

Slow-Myofiber Commitment by Semaphorin 3A Secreted from Myogenic Stem Cells.

Recently, we found that resident myogenic stem satellite cells upregulate a multi-functional secreted protein, semaphorin 3A (Sema3A), exclusively at the early-differentiation phase in response to muscle injury; however, its physiological significance is still unknown. Here we show that Sema3A impacts slow-twitch fiber generation through a signaling pathway, cell-membrane receptor (neuropilin2-plexinA3) → myogenin-myocyte enhancer factor 2D → slow myosin heavy chain. This novel axis was found by small interfering RNA-transfection experiments in myoblast cultures, which also revealed an additional element that Sema3A-neuropilin1/plexinA1, A2 may enhance slow-fiber formation by activating signals that inhibit fast-myosin expression. Importantly, satellite cell-specific Sema3A conditional-knockout adult mice (Pax7CreERT2 -Sema3Afl °x activated by tamoxifen-i.p. injection) provided direct in vivo evidence for the Sema3A-driven program, by showing that slow-fiber generation and muscle endurance were diminished after repair from cardiotoxin-injury of gastrocnemius muscle. Overall, the findings highlight an active role for satellite cell-secreted Sema3A ligand as a key "commitment factor" for the slow-fiber population during muscle regeneration. Results extend our understanding of the myogenic stem-cell strategy that regulates fiber-type differentiation and is responsible for skeletal muscle contractility, energy metabolism, fatigue resistance, and its susceptibility to aging and disease. Stem Cells 2017;35:1815-1834.

Calcium dysregulation contributes to neurodegeneration in FTLD patient iPSC-derived neurons.

Mutations in the gene MAPT encoding tau, a microtubules-associated protein, cause a subtype of familial neurodegenerative disorder, known as frontotemporal lobar degeneration tauopathy (FTLD-Tau), which presents with dementia and is characterized by atrophy in the frontal and temporal lobes of the brain. Although induced pluripotent stem cell (iPSC) technology has facilitated the investigation of phenotypes of FTLD-Tau patient neuronal cells in vitro, it remains unclear how FTLD-Tau patient neurons degenerate. Here, we established neuronal models of FTLD-Tau by Neurogenin2-induced direct neuronal differentiation from FTLD-Tau patient iPSCs. We found that FTLD-Tau neurons, either with an intronic MAPT mutation or with an exonic mutation, developed accumulation and extracellular release of misfolded tau followed by neuronal death, which we confirmed by correction of the intronic mutation with CRISPR/Cas9. FTLD-Tau neurons showed dysregulation of the augmentation of Ca2+ transients evoked by electrical stimulation. Chemogenetic or pharmacological control of neuronal activity-relevant Ca2+ influx by the introduction of designer receptors exclusively activated by designer drugs (DREADDs) or by the treatment with glutamate receptor blockers attenuated misfolded tau accumulation and neuronal death. These data suggest that neuronal activity may regulate neurodegeneration in tauopathy. This FTLD-Tau model provides mechanistic insights into tauopathy pathogenesis and potential avenues for treatments.

The Inhibitory Core of the Myostatin Prodomain: Its Interaction with Both Type I and II Membrane Receptors, and Potential to Treat Muscle Atrophy.

Myostatin, a muscle-specific transforming growth factor-ß (TGF-ß), negatively regulates skeletal muscle mass. The N-terminal prodomain of myostatin noncovalently binds to and suppresses the C-terminal mature domain (ligand) as an inactive circulating complex. However, which region of the myostatin prodomain is required to inhibit the biological activity of myostatin has remained unknown. We identified a 29-amino acid region that inhibited myostatin-induced transcriptional activity by 79% compared with the full-length prodomain. This inhibitory core resides near the N-terminus of the prodomain and includes an α-helix that is evolutionarily conserved among other TGF-ß family members, but suppresses activation of myostatin and growth and differentiation factor 11 (GDF11) that share identical membrane receptors. Interestingly, the inhibitory core co-localized and co-immunoprecipitated with not only the ligand, but also its type I and type II membrane receptors. Deletion of the inhibitory core in the full-length prodomain removed all capacity for suppression of myostatin. A synthetic peptide corresponding to the inhibitory core (p29) ameliorates impaired myoblast differentiation induced by myostatin and GDF11, but not activin or TGF-ß1. Moreover, intramuscular injection of p29 alleviated muscle atrophy and decreased the absolute force in caveolin 3-deficient limb-girdle muscular dystrophy 1C model mice. The injection suppressed activation of myostatin signaling and restored the decreased numbers of muscle precursor cells caused by caveolin 3 deficiency. Our findings indicate a novel concept for this newly identified inhibitory core of the prodomain of myostatin: that it not only suppresses the ligand, but also prevents two distinct membrane receptors from binding to the ligand. This study provides a strong rationale for the use of p29 in the amelioration of skeletal muscle atrophy in various clinical settings.

A second pedigree with amyloid-less familial Alzheimer's disease harboring an identical mutation in the amyloid precursor protein gene (E693delta).

A 59-year-old woman developed early-onset, slowly progressive dementia and spastic paraplegia. positron emission tomography (PET) imaging revealed a large reduction in the level of glucose uptake without amyloid deposition in the cerebral cortex. We identified a homozygous microdeletion within the amyloid ß (Aß) coding sequence in the amyloid precursor protein (APP) gene (c.2080_2082delGAA, p.E693del) in three affected siblings and a heterozygous microdeletion in an unaffected sibling. The identical mutation was previously reported in the first Alzheimer's pedigree without amyloid deposits. Furthermore, an increase in high-molecular-weight Aß-reactive bands was detected in the patient's CSF. Our findings suggest that soluble Aß-oligomers induce neuronal toxicity, independent of insoluble Aß fibrils.

Identification of the minimum peptide from mouse myostatin prodomain for human myostatin inhibition.

Myostatin, an endogenous negative regulator of skeletal muscle mass, is a therapeutic target for muscle atrophic disorders. Here, we identified minimum peptides 2 and 7 to effectively inhibit myostatin activity, which consist of 24 and 23 amino acids, respectively, derived from mouse myostatin prodomain. These peptides, which had the propensity to form α-helix structure, interacted to myostatin with KD values of 30-36 nM. Moreover, peptide 2 significantly increased muscle mass in Duchenne muscular dystrophy model mice.

Local applications of myostatin-siRNA with atelocollagen increase skeletal muscle mass and recovery of muscle function.

BACKGROUND: Growing evidence suggests that small-interfering RNA (siRNA) can promote gene silencing in mammalian cells without induction of interferon synthesis or nonspecific gene suppression. Recently, a number of highly specific siRNAs targeted against disease-causing or disease-promoting genes have been developed. In this study, we evaluate the effectiveness of atelocollagen (ATCOL)-mediated application of siRNA targeting myostatin (Mst), a negative regulator of skeletal muscle growth, into skeletal muscles of muscular dystrophy model mice. METHODS AND FINDINGS: We injected a nanoparticle complex containing myostatin-siRNA and ATCOL (Mst-siRNA/ATCOL) into the masseter muscles of mutant caveolin-3 transgenic (mCAV-3Tg) mice, an animal model for muscular dystrophy. Scrambled (scr) -siRNA/ATCOL complex was injected into the contralateral muscles as a control. Two weeks after injection, the masseter muscles were dissected for histometric analyses. To investigate changes in masseter muscle activity by local administration of Mst-siRNA/ATCOL complex, mouse masseter electromyography (EMG) was measured throughout the experimental period via telemetry. After local application of the Mst-siRNA/ATCOL complex, masseter muscles were enlarged, while no significant change was observed on the contralateral side. Histological analysis showed that myofibrils of masseter muscles treated with the Mst-siRNA/ATCOL complex were significantly larger than those of the control side. Real-time PCR analysis revealed a significant downregulation of Mst expression in the treated masseters of mCAV-3Tg mice. In addition, expression of myogenic transcription factors was upregulated in the Mst-siRNA-treated masseter muscle, while expression of adipogenic transcription factors was significantly downregulated. EMG results indicate that masseter muscle activity in mCAV-3Tg mice was increased by local administration of the Mst-siRNA/ATCOL complex. CONCLUSION: These data suggest local administration of Mst-siRNA/ATCOL complex could lead to skeletal muscle hypertrophy and recovery of motor disability in mCAV-3Tg mice. Therefore, ATCOL-mediated application of siRNA is a potential tool for therapeutic use in muscular atrophy diseases.

Modeling Alzheimer's disease with iPSCs reveals stress phenotypes associated with intracellular Aß and differential drug responsiveness.

Oligomeric forms of amyloid-ß peptide (Aß) are thought to play a pivotal role in the pathogenesis of Alzheimer's disease (AD), but the mechanism involved is still unclear. Here, we generated induced pluripotent stem cells (iPSCs) from familial and sporadic AD patients and differentiated them into neural cells. Aß oligomers accumulated in iPSC-derived neurons and astrocytes in cells from patients with a familial amyloid precursor protein (APP)-E693Δ mutation and sporadic AD, leading to endoplasmic reticulum (ER) and oxidative stress. The accumulated Aß oligomers were not proteolytically resistant, and docosahexaenoic acid (DHA) treatment alleviated the stress responses in the AD neural cells. Differential manifestation of ER stress and DHA responsiveness may help explain variable clinical results obtained with the use of DHA treatment and suggests that DHA may in fact be effective for a subset of patients. It also illustrates how patient-specific iPSCs can be useful for analyzing AD pathogenesis and evaluating drugs.

A novel mutation in the uromodulin gene in a Japanese family with a mild phenotype of familial juvenile hyperuricemic nephropathy.

Familial juvenile hyperuricemic nephropathy (FJHN) is an autosomal-dominant disorder that is characterized by hyperuricemia and chronic renal failure and results in end-stage renal failure. FJHN is caused by mutations in the UMOD gene, which encodes uromodulin. Uromodulin contains three epidermal growth factor (EGF)-like domains, a domain of eight cysteine residues (D8C), and a zona pellucid-like domain. Over 90 % of UMOD mutations are missense mutations, and over 80 % exist in exon 4, which encodes both D8C and the EGF-like domains. A 56-year-old woman was diagnosed with hyperuricemia with a serum uric acid level of 7.5 mg/dL, and stage III chronic kidney disease (CKD) with a serum creatinine level of 1.12 mg/dL and an estimated glomerular filtration rate of 39.9 mL/(min 1.73 m2). The patient had a family history of hyperuricemia and stage IV CKD; both the patient and her affected family members had a novel mutation in the UMOD gene: c.C518G (p.P173R), located between the EGF-like domains and D8C. This mutation, along with previously reported nearby mutations, causes a clinically mild phenotype of FJHN. It is important that physicians consider the diagnosis of FJHN in patients with a family history of hyperuricemia associated with renal dysfunction, even if the patient has only mild renal impairment.

Taurine ameliorates impaired the mitochondrial function and prevents stroke-like episodes in patients with MELAS.

OBJECTIVE: Post-transcriptional taurine modification at the first anticodon ("wobble") nucleotide is deficient in A3243G-mutant mitochondrial (mt) tRNA(Leu(UUR)) of patients with myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Wobble nucleotide modifications in tRNAs have recently been identified to be important in the accurate and efficient deciphering of codons. We herein examined whether taurine can alleviate mitochondrial dysfunction in patient-derived pathogenic cells and prevent clinical symptoms in MELAS patients. METHODS AND RESULTS: The addition of taurine to the culture media ameliorated the reduced oxygen consumption, decreased the mitochondrial membrane potential, and increased the oxidative stress in MELAS patient-derived cells. Moreover, high dose oral administration of taurine (0.25 g/kg/day) completely prevented stroke-like episodes in two MELAS patients for more than nine years. CONCLUSION: Taurine supplementation may be a novel potential treatment option for preventing the stroke-like episodes associated with MELAS.

An inhibitor of transforming growth factor beta type I receptor ameliorates muscle atrophy in a mouse model of caveolin 3-deficient muscular dystrophy.

Skeletal muscle expressing Pro104Leu mutant caveolin 3 (CAV3(P104L)) in mouse becomes atrophied and serves as a model of autosomal dominant limb-girdle muscular dystrophy 1C. We previously found that caveolin 3-deficient muscles showed activated intramuscular transforming growth factor beta (TGF-ß) signals. However, the cellular mechanism by which loss of caveolin 3 leads to muscle atrophy is unknown. Recently, several small-molecule inhibitors of TGF-ß type I receptor (TßRI) kinase have been developed as molecular-targeting drugs for cancer therapy by suppressing intracellular TGF-ß1, -ß2, and -ß3 signaling. Here, we show that a TßRI kinase inhibitor, Ki26894, restores impaired myoblast differentiation in vitro caused by activin, myostatin, and TGF-ß1, as well as CAV3(P104L). Oral administration of Ki26894 increased muscle mass and strength in vivo in wild-type mice, and improved muscle atrophy and weakness in the CAV3(P104L) mice. The inhibitor restored the number of satellite cells, the resident stem cells of adult skeletal muscle, with suppression of the increased phosphorylation of Smad2, an effector, and the upregulation of p21 (also known as Cdkn1a), a target gene of the TGF-ß family members in muscle. These data indicate that both TGF-ß-dependent reduction in satellite cells and impairment of myoblast differentiation contribute to the cellular mechanism underlying caveolin 3-deficient muscle atrophy. TßRI kinase inhibitors could antagonize the activation of intramuscular anti-myogenic TGF-ß signals, thereby providing a novel therapeutic rationale for the alternative use of this type of anticancer drug in reversing muscle atrophy in various clinical settings.