Mitochondrial fission and remodelling contributes to muscle atrophy.

Mitochondria are crucial organelles in the production of energy and in the control of signalling cascades. A machinery of pro-fusion and fission proteins regulates their morphology and subcellular localization. In muscle this results in an orderly pattern of intermyofibrillar and subsarcolemmal mitochondria. Muscular atrophy is a genetically controlled process involving the activation of the autophagy-lysosome and the ubiquitin-proteasome systems. Whether and how the mitochondria are involved in muscular atrophy is unknown. Here, we show that the mitochondria are removed through autophagy system and that changes in mitochondrial network occur in atrophying muscles. Expression of the fission machinery is per se sufficient to cause muscle wasting in adult animals, by triggering organelle dysfunction and AMPK activation. Conversely, inhibition of the mitochondrial fission inhibits muscle loss during fasting and after FoxO3 overexpression. Mitochondrial-dependent muscle atrophy requires AMPK activation as inhibition of AMPK restores muscle size in myofibres with altered mitochondria. Thus, disruption of the mitochondrial network is an essential amplificatory loop of the muscular atrophy programme.

FoxO3 controls autophagy in skeletal muscle in vivo.

Autophagy allows cell survival during starvation through the bulk degradation of proteins and organelles by lysosomal enzymes. However, the mechanisms responsible for the induction and regulation of the autophagy program are poorly understood. Here we show that the FoxO3 transcription factor, which plays a critical role in muscle atrophy, is necessary and sufficient for the induction of autophagy in skeletal muscle in vivo. Akt/PKB activation blocks FoxO3 activation and autophagy, and this effect is not prevented by rapamycin. FoxO3 controls the transcription of autophagy-related genes, including LC3 and Bnip3, and Bnip3 appears to mediate the effect of FoxO3 on autophagy. This effect is not prevented by proteasome inhibitors. Thus, FoxO3 controls the two major systems of protein breakdown in skeletal muscle, the ubiquitin-proteasomal and autophagic/lysosomal pathways, independently. These findings point to FoxO3 and Bnip3 as potential therapeutic targets in muscle wasting disorders and other degenerative and neoplastic diseases in which autophagy is involved.

Human MYO18B, a novel unconventional myosin heavy chain expressed in striated muscles moves into the myonuclei upon differentiation.

We have characterized a novel unconventional myosin heavy chain, named MYO18B, that appears to be expressed mainly in human cardiac and skeletal muscles and, at lower levels, in testis. MYO18B transcript is detected in all types of striated muscles but at much lower levels compared to class II sarcomeric myosins, and it is up regulated after in vitro differentiation of myoblasts into myotubes. Phylogenetic analysis shows that this myosin belongs to the recently identified class XVIII, however, unlike the other member of this class, it seems to be unique to Vertebrate since it contains two large amino acid domains of unknown function at the N and C-termini. Immunolocalization of MYO18B protein in skeletal muscle cells shows that this myosin heavy chain is located in the cytoplasm of undifferentiated myoblasts. After in vitro differentiation into myotubes, a fraction of this protein is accumulated in a subset of myonuclei. This nuclear localization was confirmed by immunofluorescence experiments on primary cardiomyocytes and adult muscle sections. In the cytoplasm MYO18B shows a punctate staining, both in cardiac and skeletal fibers. In some cases, cardiomyocytes show a partial sarcomeric pattern of MYO18B alternating that of alpha-actinin-2. In skeletal muscle the cytoplasmic MYO18B results much more evident in the fast type fibers.

Gene expression of myogenic factors and phenotype-specific markers in electrically stimulated muscle of paraplegics.

The transcription factors myogenin and MyoD have been suggested to be involved in maintaining slow and fast muscle-fiber phenotypes, respectively, in rodents. Whether this is also the case in human muscle is unknown. To test this, 4 wk of chronic, low-frequency electrical stimulation training of the tibialis anterior muscle of paraplegic subjects were used to evoke a fast-to-slow transformation in muscle phenotype. It was hypothesized that this would result from an upregulation of myogenin and a downregulation of MyoD. The training evoked the expected mRNA increase for slow fiber-specific markers myosin heavy chain I and 3-hydroxyacyl-CoA dehydrogenase A, whereas an mRNA decrease was seen for fast fiber-specific markers myosin heavy chain IIx and glycerol phosphate dehydrogenase. Although the slow fiber-specific markers citrate synthase and muscle fatty acid binding protein did not display a significant increase in mRNA, they did tend to increase. As hypothesized, myogenin mRNA was upregulated. However, contrary to the hypothesis, MyoD mRNA also increased, although later than myogenin. The mRNA levels of the other myogenic regulatory factor family members, myogenic factor 5 and myogenic regulatory factor 4, and the myocyte enhancer factor (MEF) family members, MEF-2A and MEF-2C, did not change. The results indicate that myogenin is indeed involved in the regulation of the slow oxidative phenotype in human skeletal muscle fibers, whereas MyoD appears to have a more complex regulatory function.

Topology of Homer 1c and Homer 1a in C2C12 myotubes and transgenic skeletal muscle fibers.

mRNA transcripts for Homer 1a and Homer 1c have been detected in skeletal muscle [Biochem. Biophys. Res. Commun. 279 (2000) 348]. Here, the subcellular distribution of recombinant HA1-tagged Homer 1c and HA1-tagged Homer 1a was investigated in C(2)C(12) myotubes and in transgenic skeletal muscle fibers of the adult rat by epifluorescent and confocal microscopy. In C(2)C(12) myotubes, Homer 1a was homogeneously localized in the cytosol and also labeled some nuclei whereas Homer 1c displayed a diffuse reticular/punctuate pattern in the cytosol with scattered punctuate labeling around nuclei; no co-localization was observed with the ryanodine receptor/Ca(2+) release channel (RYR1). The subcellular localization of the Homer 1 isoforms was markedly different in transgenic muscle fibers: Homer 1c was diffusely distributed at the I band and enlightened the Z line, whereas Homer 1a labeled both the I band and the A band with distinct reinforcement of the H line; neither Homer 1c nor Homer 1a co-localized with either calsequestrin or RYR1, two sarcoplasmic reticulum markers. Our findings are discussed in relation to reported effects of Homer 1 isoforms on RYR1 function.

Training by low-frequency stimulation of tibialis anterior in spinal cord-injured men.

The tibialis anterior muscle of nine paraplegic men was chronically stimulated (2-6 h per day; at 10 Hz, 5 s on, 5 s off) under isometric loading conditions for 5 days per week for 4 weeks. After 4 weeks of training, muscle fatigue resistance in an electrically evoked test had increased by an average of 75% (P <.01, n = 9), but there were no changes in the relative composition of the three myosin heavy chain (MHC) isoforms. Five of the subjects continued training for an additional 5 weeks (2 h per day, 3 days per week). Although there was a tendency for twitch time to peak torque to increase after this additional period, no change occurred in relative MHC isoform content. However, in situ hybridization analysis revealed that even after 2 weeks of stimulation, there was evidence of upregulation of the mRNA for the MHC-I isoform and downregulation of the MHC-IIX isoform, a development that continued in weeks 4 and 9. This study provides evidence, at the level of gene transcription, that a fast-to-slow change in MHC isoform composition may be possible in human muscle when its usage is significantly increased.

Heart morphogenesis is not affected by overexpression of the Sh3bgr gene mapping to the Down syndrome heart critical region.

Congenital heart disease (CHD) is the most common birth defect in humans and is present in 40% of newborns affected by Down syndrome (DS). The SH3BGR gene maps to the DS-CHD region and is a potential candidate for the pathogenesis of CHD, since it is selectively expressed in cardiac and skeletal muscle. To determine whether overexpression of Sh3bgr in the murine heart may cause abnormal cardiac development, we have generated transgenic mice using a cardiac- and skeletal-muscle-specific promoter to drive the expression of a Sh3bgr transgene. We report here that heart morphogenesis is not affected by overexpression of Sh3bgr.

Foxo transcription factors induce the atrophy-related ubiquitin ligase atrogin-1 and cause skeletal muscle atrophy.

Skeletal muscle atrophy is a debilitating response to fasting, disuse, cancer, and other systemic diseases. In atrophying muscles, the ubiquitin ligase, atrogin-1 (MAFbx), is dramatically induced, and this response is necessary for rapid atrophy. Here, we show that in cultured myotubes undergoing atrophy, the activity of the PI3K/AKT pathway decreases, leading to activation of Foxo transcription factors and atrogin-1 induction. IGF-1 treatment or AKT overexpression inhibits Foxo and atrogin-1 expression. Moreover, constitutively active Foxo3 acts on the atrogin-1 promoter to cause atrogin-1 transcription and dramatic atrophy of myotubes and muscle fibers. When Foxo activation is blocked by a dominant-negative construct in myotubes or by RNAi in mouse muscles in vivo, atrogin-1 induction during starvation and atrophy of myotubes induced by glucocorticoids are prevented. Thus, forkhead factor(s) play a critical role in the development of muscle atrophy, and inhibition of Foxo factors is an attractive approach to combat muscle wasting.

Importância do raio X e exame físico no diagnóstico da artrite psoriática e sua prevalência no Hospital Universitário Evangélico de Curitiba (HUEC) / The importance of radiologic evaluation and physical examination in diagnosis of psoriatic arthritis and its prevalance in the Hospital Universitário Evangélico de Curitiba

FUNDAMENTOS: A artrite psoriática (AP) é doença inflamatória associada com a psoríase da pele ou das unhas, com fator reumatóide (FR) negativo e ausência de nódulos reumatóides. Pode ser extremamente agressiva, deixando o paciente incapacitado para realizar funções do dia-a-dia. A prevalência populacional é muito variável; historicamente oscila entre 2,6 por cento e 7 por cento, mas estudos recentes demonstram porcentagem variável de 23 a 69 por cento na população com psoríase. O diagnóstico é de exclusão e, se realizado na fase inicial, oferece possibilidade de tratamento mais adequado, evitando complicações. O que define a presença da artrite é o exame físico adequado das articulações, já que o raio X pode estar normal. OBJETIVO: Este estudo tem a finalidade de avaliar a importância do raio X e do exame físico no diagnóstico da AP e sua prevalência nos pacientes com psoríase cutânea e ungueal do Hospital Universitário Evangélico de Curitiba. MATERIAL E MÉTODOS: Trinta pacientes com psoríase em acompanhamento nesse serviço foram submetidos a anamnese e exame físico minuciosos. Eles foram questionados quanto a alterações articulares, tempo e severidade de doença e comprometimento ungueal. Os que apresentavam queixas articulares foram encaminhados para investigação por exames complementares: hemograma, FR, VHS, e raio X da articulação comprometida. RESULTADOS: A maioria dos pacientes (56,5 por cento) referiu atralgia; contudo apenas três apresentavam artrite. Dos indivíduos com AP, um mostrou raio X normal, mas o exame físico estava alterado. CONCLUSÃO: O exame físico é fundamental para diagnóstico da AP; o raio X não. A prevalência de AP foi de 10 por cento.

BACKGROUND: Psoriatic arthritis (PA) is an inflammatory disorder associated with skin and nail disease, negative rheumatoid factor (RF) and absence of rheumatoid nodules. It can be a devastating and incapacitating condition. Its prevalence is highly variable, ranging from 2,6 to 7 percent; however, recent data shows prevalence as high as 23 to 69 percent. Its diagnosis is one of exclusion, and when detected early in the course of the disease gives chance to adequate treatment, thus avoiding its sequelae. The diagnosis is made by physical examination, laboratory and radiological evaluation. A normal radiological finding does not exclude the disease. OBJECTIVE: This study aims to evaluate the importance of a detailed physical examination associated with radiological findings in the diagnosis of PA and its prevalence in our institution. METHODS: Thirty patients with skin psoriasis were submitted to a thorough physical examination and radiological evaluation. All patients were inquired about articular complaints, time and severity of skin and nail disease. Those that presented any articular symptom were submitted to a laboratory evaluation with: Complete Blood Count (CBC), RF, Erythrocyte Sedimentation Rate (ESR) and radiography of the involved joint. RESULTS: The majority of patients (56,5 percent) presented arthralgia; however, only three patients had arthritis. Of those 3 that had PA, one presented a normal radiography but with an altered physical examination. CONCLUSION: The physical examination is an extremely important tool in the evaluation of patients with psoriasis. The radiological evaluation is not as important as the physical examination. The prevalence of PA was 10 percent.

Reação hansênica: estudo clínico, epidemiológico e terap~eutico de 27 casos / Hansenic reaction: clinical, epidemiological and therapeutic study of 27 cases

Introdução: reações hansênicas são reações do sistema imunológico do portador de hanseníase ao Mycobacterium leprae. Apresentam-se através de episódios inflamatórios agudos e subagudos que podem ocorrer antes, durante ou após tratamento específico tanto em paucibacilares quanto multibacilares. Sendo a principal causa de morbidade, seu diagnóstico e tratamento precoces assumem grande importância. Objetivo: análise clínica, epidemiológica e terapêutica de 27 casos de reação hansênica. Material e métodos: foram avaliados 78 pacientes com hanseníase no período de 1991-2004. Foram classificados quanto à forma clínica e, na presença de reação, em tipos Ie II. Todos os pacientes foram tratados com a poliquimioterapia segundo a Organização Mundial de Saúde. Resultados: cinte e sete pacientes desenvolveram reações na maioria tipo II e nos primeiros seis meses de tratamento. Os multibacilares foram mais acometidos. Conclusão: apesar da poliquimioterapia atual, a prevalência de reações hansênicas mantém-se elevada, levando-nos a questionar a eficácia dessa terapia na prevenção dessas complicações.