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.

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.

A novel method to measure sensory nerve conduction of the posterior antebrachial cutaneous nerve.

INTRODUCTION/AIMS: Posterior antebrachial cutaneous (PABC) nerve conduction studies could be useful for distinguishing PABC neuropathy from C7 radiculopathy. In the conventional method using an antidromic method, the sensory nerve action potential (SNAP) is sometimes followed by a large volume-conducted motor potential. In this report we describe a reliable nerve conduction study using an orthodromic method for recording SNAPs of the PABC nerve. METHODS: Thirty-six healthy volunteers participated in this study. PABC SNAPs were recorded by placing a surface-active electrode 2 cm anterior to the lateral epicondyle. The PABC nerve was stimulated 10 cm distal to the active recording electrode along a line from the recording point to the mid-dorsum of the wrist, midway between the radial and ulnar styloid processes. We also performed PABC nerve conduction studies using an antidromic method and compared the findings. RESULTS: PABC SNAPs were recorded bilaterally from all subjects. The mean peak-to-peak amplitude for SNAPs was 13.4 ± 4.8 µV. Mean maximum conduction velocity was 62.7 ± 3.9 m/s and mean negative peak conduction velocity was 51.2 ± 2.6 m/s. The mean side-to-side difference in amplitude was 22.1 ± 16.0%. The mean amplitude of SNAPs obtained by our method was 48.9% higher than that of SNAPs obtained by the conventional method (13.4 vs 9.0 µV; P < .001). In contrast to the conventional method, our method enabled SNAPs to be recorded without a volume-conducted motor potential. DISCUSSION: The higher mean amplitude of SNAPs with our method enables them to be obtained easily.

A low amyloidogenic E61K transthyretin mutation may cause familial amyloid polyneuropathy.

Patients with transthyretin (TTR)-type familial amyloid polyneuropathy (FAP) typically exhibit sensory dominant polyneuropathy and autonomic neuropathy. However, the molecular pathogenesis of the neuropathy remains unclear. In this study, we characterize the features of FAP TTR the substitution of lysine for glutamic acid at position 61 (E61K). This FAP was late-onset, with sensory dominant polyneuropathy, autonomic neuropathy, and cardiac amyloidosis. Interestingly, no amyloid deposits were found in the endoneurium of the four nerve specimens examined. Therefore, we examined the amyloidogenic properties of E61K TTR in vitro. Recombinant wild-type TTR, the substitution of methionine for valine at position 30 (V30M) TTR, and E61K TTR proteins were incubated at 37°C for 72 hr, and amyloid fibril formation was assessed using the thioflavin-T binding assay. Amyloid fibril formation by E61K TTR was less than that by V30M TTR, and similar to that by wild-type TTR. E61K TTR did not have an inhibitory effect on neurite outgrowth from adult rat dorsal root ganglion (DRG) neurons, but V30M TTR did. Furthermore, we studied the sural nerve of our patient by terminal deoxynucleotidyl transferase dUTP nick end labeling and electron microscopy. A number of apoptotic cells were observed in the endoneurium of the nerve by transferase dUTP nick end labeling. Chromatin condensation was confirmed in the nucleus of non-myelinating Schwann cells by electron microscopy. These findings suggest that E61K TTR is low amyloidogenic, in vitro and in vivo. However, TTR aggregates and amyloid fibrils in the DRG may cause sensory impairments in FAP because the DRG has no blood-nerve barrier. Moreover, Schwann cell apoptosis may contribute to the neurodegeneration.

Anatomical variations of the superficial branch of the radial nerve and the dorsal branch of the ulnar nerve: A detailed electrophysiological study.

INTRODUCTION: In this study we evaluated anatomic variations of the superficial branch of the radial nerve (SBRN) and the dorsal branch of the ulnar nerve (DBUN) electrophysiologically. METHODS: Antidromic nerve conduction studies (NCS) of the SBRN and DBUN were performed on healthy individuals. To identify individual responses from the distal branches of the SBRN and DBUN, sensory nerve action potentials of each finger (lateral side/medial side) were recorded. RESULTS: NCS were performed in 50 hands of 27 healthy control subjects. The thumb and the index finger were supplied by the SBRN in all cases. The lateral and medial sides of the third finger were supplied by the SBRN in 94.0% and 74.0% of the cases, but the lateral and medial sides of the fourth finger were supplied by the SBRN in only 10.0% and 2.0% of cases. The fifth finger and the medial side of the fourth finger were always supplied by the DBUN. The lateral side of the fourth finger was supplied by the DBUN in 98.0% of cases, but the lateral and medial sides of the third finger were supplied by the DBUN in 40.0% and 70.0% of cases. Dual innervation by the SBRN and DBUN was found in 34.0% and 46.0% of the lateral and medial sides of the third finger, but in only 8.0% and 2.0% of the lateral and medial sides of the fourth finger. DISCUSSION: There are considerable anatomic variations of the SBRN and DBUN in healthy individuals.

Recent Advances in Biomarkers and Regenerative Medicine for Diabetic Neuropathy.

Diabetic neuropathy is one of the most common complications of diabetes. This complication is peripheral neuropathy with predominant sensory impairment, and its symptoms begin with hyperesthesia and pain and gradually become hypoesthesia with the loss of nerve fibers. In some cases, lower limb amputation occurs when hypoalgesia makes it impossible to be aware of trauma or mechanical stimuli. On the other hand, up to 50% of these complications are asymptomatic and tend to delay early detection. Therefore, sensitive and reliable biomarkers for diabetic neuropathy are needed for an early diagnosis of this condition. This review focuses on systemic biomarkers that may be useful at this time. It also describes research on the relationship between target gene polymorphisms and pathological conditions. Finally, we also introduce current information on regenerative therapy, which is expected to be a therapeutic approach when the pathological condition has progressed and nerve degeneration has been completed.

A multicenter retrospective study of charcot-marie-tooth disease type 4B (CMT4B) associated with mutations in myotubularin-related proteins (MTMRs).

OBJECTIVE: Charcot-Marie-Tooth (CMT) disease 4B1 and 4B2 (CMT4B1/B2) are characterized by recessive inheritance, early onset, severe course, slowed nerve conduction, and myelin outfoldings. CMT4B3 shows a more heterogeneous phenotype. All are associated with myotubularin-related protein (MTMR) mutations. We conducted a multicenter, retrospective study to better characterize CMT4B. METHODS: We collected clinical and genetic data from CMT4B subjects in 18 centers using a predefined minimal data set including Medical Research Council (MRC) scores of nine muscle pairs and CMT Neuropathy Score. RESULTS: There were 50 patients, 21 of whom never reported before, carrying 44 mutations, of which 21 were novel and six representing novel disease associations of known rare variants. CMT4B1 patients had significantly more-severe disease than CMT4B2, with earlier onset, more-frequent motor milestones delay, wheelchair use, and respiratory involvement as well as worse MRC scores and motor CMT Examination Score components despite younger age at examination. Vocal cord involvement was common in both subtypes, whereas glaucoma occurred in CMT4B2 only. Nerve conduction velocities were similarly slowed in both subtypes. Regression analyses showed that disease severity is significantly associated with age in CMT4B1. Slopes are steeper for CMT4B1, indicating faster disease progression. Almost none of the mutations in the MTMR2 and MTMR13 genes, responsible for CMT4B1 and B2, respectively, influence the correlation between disease severity and age, in agreement with the hypothesis of a complete loss of function of MTMR2/13 proteins for such mutations. INTERPRETATION: This is the largest CMT4B series ever reported, demonstrating that CMT4B1 is significantly more severe than CMT4B2, and allowing an estimate of prognosis. ANN NEUROL 2019.

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.

Schwann Cell and the Pathogenesis of Charcot-Marie-Tooth Disease.

Charcot-Marie-Tooth (CMT) disease is the most common hereditary neuropathy and genetically heterogeneous. CMT1 and CMTX are autosomal dominant and X-linked demyelinating neuropathies, respectively. CMT1A, CMT1B, and CMTX1 are the common forms of CMT, which are attributed to the genes encoding the myelin or gap junction proteins expressed in the myelinating Schwann cells. CMT4 is a rare autosomal recessive demyelinating neuropathy that usually shows an early-onset severe phenotype. Twelve genes have been described as CMT4, which encodes many kinds of proteins including mitochondrial proteins, phosphatases in the endosomal pathway, endocytic recycling proteins, and trafficking proteins. The genes responsible for CMT4 are expressed in Schwan cells and necessary for the development and maintenance in the peripheral nervous system. However, CMT1, CMT4, and CMTX1 are primarily demyelinating neuropathies, axonal degeneration is necessary for symptoms to develop. Schwann cell-axon interactions are impaired in the pathogenesis of demyelinating CMT.

Transthyretin Amyloid Neuropathy: The Schwann Cell Hypothesis.

Transthyretin (TTR)-familial amyloid polyneuropathy (FAP) is a systemic amyloidosis caused by mutations in the TTR gene. Typically, patients initially present with sensory and autonomic symptoms, which can lead to sensory dominant polyneuropathy and autonomic neuropathy. Mutations in TTR cause the tetrameric protein to dissociate and form amyloid deposits in the peripheral nervous system, most prominently in dorsal root ganglia (DRG), autonomic ganglia, and nerve trunks. Teased fiber studies have shown that segmental demyelination and axonal degeneration preferentially occur in the proximal and distal regions of the peripheral nerves, respectively. Nevertheless, it remains unknown why genetic variants of TTR lead to neurodegeneration in the peripheral nervous system. Recent studies in our laboratory have uncovered an important role for Schwann cells in the disease progression of FAP. In this review, we summarize findings implicating Schwann cells in FAP, and provide evidence that DRG may serve as the initial site of lesion formation in the disease.

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.

Variations in the distal branches of the superficial fibular sensory nerve.

INTRODUCTION: We evaluated anatomic variations of distal branches of the superficial fibular sensory nerve electrophysiologically. METHODS: Orthodromic nerve conduction studies (NCS) of the first and third branches (M-I, M-III) of the medial dorsal cutaneous nerve and the fourth and fifth branches (I-IV, I-V) of the intermediate dorsal cutaneous nerve (IDCN) were performed. To find anomalous innervations from the dorsal sural nerve (DSN) in the IDCN territory, NCS of the fourth and fifth branches (S-IV, S-V) of the DSN were also performed. RESULTS: All sensory nerve action potentials (SNAPs) of M-I and M-III could be obtained bilaterally from 31 healthy Japanese volunteers. SNAPs of I-IV and I-V were recordable in 85.5% and 43.5% of feet, respectively. Anomalous innervations from the DSN were confirmed in 71.0% of S-IV and 93.5% of S-V. CONCLUSION: These results suggest that anatomical variations in the IDCN territory are very frequent in Japanese subjects. Muscle Nerve 55: 74-76, 2017.

Whole plantar nerve conduction study with disposable strip electrodes.

INTRODUCTION: A new method to evaluate whole plantar nerve conduction with disposable strip electrodes (DSEs) is described. METHODS: Whole plantar compound nerve action potentials (CNAPs) were recorded at the ankle. DSEs were attached to the sole for simultaneous stimulation of medial and lateral plantar nerves. We also conducted medial plantar nerve conduction studies using an established method and compared the findings. RESULTS: Whole plantar CNAPs were recorded bilaterally from 32 healthy volunteers. Mean baseline to peak amplitude for CNAPs was 26.9 ± 11.8 µV, and mean maximum conduction velocity was 65.8 ± 8.3 m/s. The mean amplitude of CNAPs obtained by our method was 58.2% higher than that of CNAPs obtained by the Saeed method (26.9 µV vs. 17.0 µV; P < 0.0001). CONCLUSIONS: The higher mean amplitude of whole plantar CNAPs obtained by our method suggests that it enables CNAPs to be obtained easily, even in elderly people.

Schwann cells contribute to neurodegeneration in transthyretin amyloidosis.

Familial amyloidotic polyneuropathy (FAP) is one of the transthyretin (TTR) amyloidoses characterized by extracellular amyloid deposits and peripheral nerve involvement. Recently, we found significant expression of the TTR gene in Schwann cells of the peripheral nervous system. We hypothesized that local expression of variant TTR in Schwann cells may contribute to neurodegeneration in FAP. Schwann cells derived from the dorsal root ganglia (DRG) of transgenic mice expressing variant human TTR in a mouse null background were cultured long term to obtain spontaneously immortalized cell lines. We established an immortalized Schwann cell line, TgS1, derived from the transgenic mice. TgS1 cells synthesized variant TTR and secreted it into the medium. As sensory neuropathy usually arises early in FAP, we examined the effect of the conditioned medium derived from TgS1 cells on neurite outgrowth from DRG sensory neurons. Conditioned medium derived from TgS1 cells inhibited neurite outgrowth from the sensory neurons. TTR deposition in the DRG of aged transgenic mice was investigated by immunohistochemistry. TTR aggregates were observed in the cytoplasm of Schwann cells and satellite cells. Proteasome inhibition induced TTR aggregates as aggresomes in TgS1 cells. In conclusion, local variant TTR gene expression in Schwann cells might trigger neurodegeneration in FAP. We established a spontaneously immortalized Schwann cell line derived from familial amyloidotic polyneuropathy transgenic mice. Conditioned medium from the cells contained variant transthyretin (TTR), and inhibited neurite outgrowth of neurons. TTR aggregates were observed in the Schwann cells and satellite cells of aged mice. Proteasome inhibition induced TTR aggregates as aggresomes in the cultured cells. These results support the hypothesis that Schwann cells contribute to neurodegeneration in familial amyloidotic polyneuropathy (FAP).

A novel method to measure sensory nerve conduction of the supraclavicular nerve.

INTRODUCTION: In this report we describe a reliable method for recording sensory nerve action potentials (SNAPs) of the supraclavicular nerve. METHODS: Supraclavicular SNAPs were recorded by placing a surface active electrode at the posterior border of the sternocleidomastoid muscle at a distance of 6 cm from the sternoclavicular joint. The nerve was stimulated at the lower border of the clavicle 4.5 cm lateral to the sternoclavicular joint. RESULTS: Supraclavicular SNAPs were recorded bilaterally from 20 healthy volunteers. Mean onset latency was 1.0 ± 0.2 ms, and mean peak latency was 1.4 ± 0.3 ms. Mean baseline-to-peak amplitude for the SNAPs was 6.1 ± 2.2 µV, and mean maximum conduction velocity was 59.8 ± 6.2 m/s. The mean percentage of side-to-side difference in amplitude was 12.9 ± 11.0%. CONCLUSIONS: Supraclavicular SNAPs could be obtained in all normal subjects. Assessment of supraclavicular nerve conduction is very useful in the diagnosis of supraclavicular neuropathy.

Molecular analysis of the genes causing recessive demyelinating Charcot-Marie-Tooth disease in Japan.

Charcot-Marie-Tooth disease (CMT), the most common hereditary neuropathy, has been classified into two types, demyelinating and axonal types. We previously analyzed the genes causing dominant demyelinating CMT in 227 Japanese patients to identify the genetic background, but could not find any mutations in 110 patients. To investigate the frequency of patients with autosomal recessive demyelinating CMT (CMT4) mutations, we analyzed the coding sequence of known causative genes of CMT4 in 103 demyelinating CMT patients, excluding seven patients owing to lack of specimens. We found one patient with a GDAP1 mutation, one patient with an MTMR2 mutation, two patients with SH3TC2/KIAA1985 mutations and three patients with FGD4 mutations. Twelve patients, including five previously detected patients with PRX mutations, were diagnosed as CMT4, accounting for 5.5% of demyelinating CMT. In the patient with GDAP1 mutation, only one mutation inherited from his mother was detected by genomic sequencing. Analysis by reverse transcription polymerase chain reaction using messenger RNA (mRNA) from the patient's leukocytes revealed the absence of transcription from the allele inherited from his father, suggesting the existence of one more mutation leading to a lack or destabilization of mRNA. Most patients carrying CMT4 gene mutations present with early-onset and slowly progressive symptoms, which may be associated with the function of mutants. We could not identify the disease-causing gene in 96 patients (about 45%). Further studies including studies with next-generation sequencers will be required to identify the causative gene in Japanese CMT.

Human transthyretin gene expression is markedly increased in repair Schwann cells in an in vitro model of hereditary transthyretin amyloidosis.

Hereditary transthyretin (TTR) amyloidosis (ATTRv) is characterized by TTR amyloid deposition in the peripheral nervous system. It remains unknown why variant TTR preferentially deposits in the peripheral nerves and dorsal root ganglia. We previously detected low levels of TTR expression in Schwann cells and established an immortalized Schwann cell line, TgS1, derived from a mouse model of ATTRv amyloidosis expressing the variant TTR gene. In the present study, the expression of TTR and Schwann cell marker genes was investigated in TgS1 cells by quantitative RT-PCR. TTR gene expression was markedly upregulated in TgS1 cells incubated in non-growth medium-Dulbecco's modified Eagle's medium supplemented with 10% fetal bovine serum. The expression levels of c-Jun, Gdnf and Sox2 were increased, while Mpz was downregulated, suggesting that TgS1 cells exhibit a repair Schwann cell-like phenotype in the non-growth medium. Western blot analysis revealed that TTR protein was produced and secreted by the TgS1 cells. Furthermore, downregulation of Hsf1 with siRNA induced TTR aggregates in the TgS1 cells. These findings indicate that TTR expression is markedly increased in repair Schwann cells, likely to promote axonal regeneration. Therefore, aged dysfunctional repair Schwann cells may cause the deposition of variant TTR aggregates in the nerves of patients with ATTRv.

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.

Magnetic resonance imaging of dorsal root ganglion in a pre-symptomatic subject with familial amyloid polyneuropathy transthyretin E61K.

We recently reported evidence of transthyretin (TTR) familial amyloid polyneuropathy (TTR FAP) associated with TTR E61K, which is characterized by late-onset sensory dominant polyneuropathy, autonomic disturbances, and cardiomyopathy. In those TTR FAP patients, no amyloid deposits were observed in the endoneurium of examined sural nerves. Furthermore, the amyloidogenicity of E61K TTR was similar to that of wild-type TTR in vitro. Thus, we speculated that dorsal root ganglia (DRGs) may be the initial sites for the lesions in amyloid neuropathy because there is no blood-nerve barrier. In the present study, lumbar magnetic resonance imaging was performed to evaluate the DRGs in pre-symptomatic TTR E61K and V30M subjects. Magnetic resonance imaging (3 T) was used for three-dimensional T2-weighted imaging (coronal sections; slice thickness, 2 mm), and the DRG volumes were measured. The mean volumes of the bilateral L3, L4, and S1 DRGs in the pre-symptomatic TTR E61K subject were larger than those for the pre-symptomatic TTR V30M subject and five control patients. The mean volumes of the bilateral L4 to S1 DRGs in the pre-symptomatic TTR V30M subject were similar to those in control patients. A number of lumbar DRGs were enlarged in the pre-asymptomatic TTR E61K subject, suggesting that DRGs may be the sites of the initial lesions in the peripheral nervous system of this FAP.

A Novel PRPS1 Mutation in a Japanese Patient with CMTX5.

The PRPS1 gene encodes phosphoribosyl pyrophosphate synthetase 1 (PRS-1). The phenotypes associated with PRPS1 mutations include DFN2 (mild PRS-1 deficiency), X-linked Charcot-Marie-Tooth disease type 5 (CMTX5) (moderate PRS-1 deficiency), Arts syndrome (severe PRS-1 deficiency), and PRS-1 superactivity1. CMTX5 is a very rare hereditary neuropathy characterized by deafness, optic atrophy, and polyneuropathy. We herein report a Japanese patient with CMTX5 who had a novel hemizygous mutation c.82 G>C in PRPS1. Despite showing a typical clinical picture, the decrease in enzyme activity measured in the patient's erythrocytes was milder than in previously reported cases.