Duchenne muscular dystrophy (DMD) is a severe and fatal muscle wasting disease characterized by a high mutation rate in the gene that encodes the membrane-associated protein dystrophin that results in absence of expressed protein. Although the primary genetic defect for DMD is known, the mechanisms that initiate the onset of DMD are not currently understood. This study tested the hypothesis that pathophysiological processes involved in DMD could be identified by the global expression of mRNA in maturing dystrophin- and utrophin-deficient mouse (mdx:utrn-/-) muscles. Two potential dystrophic onset mechanisms targeted for analysis were (1) disrupted expression of calcium handling proteins; and, (2) increased expression of immune response markers. An mRNA expression profile was developed following isolation of total RNA from control and mdx:utrn-/- triceps surae (TS) muscles at ages 9-10 and 20-21 days using Affymetrix® Mu74Av2 GeneChips®. Compared to control, the mRNA expression profile in mdx:utrn-/- muscles revealed there was a 3-fold increase in the number of gene transcripts differentially expressed more than 2-fold (53 transcripts at ages 9-10 days; 153 at ages 20-21 days). However, there were no changes in the mRNA transcripts for calcium handling proteins. In distinct contrast, there was up-regulation of transcripts that corresponded to an immune response (40 transcripts), extracellular matrix activity (14), and proteolysis (8). Up-regulation of several transcripts corresponded to cytokines and their receptors (11), chemokines and their receptors (5), and lymphoid and myeloid markers (16) suggesting that dystrophic muscle is susceptible to invasion by macrophages, leukocytes, B- and T-cells. These results are consistent with several reports (Spencer et al., 1997; Chen et al., 2000; Porter et al., 2002; Porter et al., 2003a; Porter et al., 2003b; Porter et al., 2004) that indicate the immune system may play an important role in the early pathophysiology of DMD. Understanding the functional aspects of an immune response in DMD onset should lead to more effective therapeutics. / Master of Science

A Distrofia Muscular de Duchenne (DMD) é uma importante e severa doença músculo degenerativa causada pela mutação do gene da distrofina. Na ausência da distrofina, o sarcolema das células torna-se vulnerável devido a danos induzidos por ciclos contínuos de degeneração e regeneração. Consequentemente, a força muscular diminui e as miofibras são substituídas por tecido fibrótico. Dentre os músculos esqueléticos afetados, o diafragma, destaca-se por ser o principal músculo respiratório acometido na DMD. Similarmente a DMD humana, o modelo mdx, apesar de exibir um fenótipo suave, este apresenta um severo acometimento no músculo diafragma, assim como observado em nosso estudo prévio, aqui descritos. Entretanto, este é considerado um modelo pobre, porque ele não consegue reproduzir, o fenótipo severo observado nos pacientes. O camundongo mdx/utrn+/- (dystrophin-null heterozygous urtrophin mice) com haploinsuficiência da utrofina, tem sido hipotetizado como um modelo com um fenótipo intermediário, ganhando popularidade nos laboratórios. Porém, infelizmente, até os dias de hoje, não existe evidências fisiológicas e funcionais suficientes que justifiquem a escolha deste modelo para as terapias experimentais. Portanto, neste estudo objetivou-se esclarecer a real contribuição do camundongo mdx/utrn+/- para as terapias experimentais. Para testar esta hipótese, elegeu-se analisar a morfologia e a função muscular do músculo diafragma do mdx e mdx/utrn+/- com 2 e 6 meses de idade. Para elucidar a morfopatologia do diafragma foi utilizado microscopia de luz e análises de imunohistoquímica. A função muscular do diafragma foi analisada através da avaliação das propriedades contráteis e passivas. A forma de como executar a função muscular do diafragma foi atualizada através da criação de dois clips, os quais permitiram avaliar o músculo de forma segura. A adaptação de um novo protocolo de avaliação da função muscular mostrou-se eficaz e capaz de ser utilizada para avaliar as propriedades contráteis e passivas. Aos 2 meses de idade, as colorações de Hematoxilina e eosina, Tricômio de Masson e Alizarina vermelha revelaram que o mdx/utrn+ apresentou maior quantidade de infiltrado inflamatório, tecido conectivo e áreas de calcificação do que o mdx. Já aos 6 meses de idade, não houve diferença morfológica entre o mdx e o mdx/utrn+/-. Na análise de imunohistoquímica para eMyHC (miosina embrionária de cadeia pesada eMyHC), não foi observada diferença entre o mdx e o mdx/utrn+/-aos 2 e 6 meses de idade. Entretanto, os resultados obtidos em ambas as idades, demonstraram a presença de regeneração muscular. Na marcação da proteína distrofina e utrofina, as células inflamatórias e os tipos de fibras musculares também foram detectados por imunohistoquímicas. A marcação da proteína distrofina, mostrou-se ausente no mdx e mdx/utrn+/- com 2 e 6 meses de idade. A marcação da proteína utrofina mostrou-se mais evidente no mdx do que no mdx/utrn+/-, videnciando a haploinsuficiência nos mdx/utrn+/-. Macrófagos foram encontrados em maior quantidade no camundongo mdx/utrn+/- com 2 e 6 meses do que no mdx, mostrando que o processo de inflamação encontrou-se aumentado nos mdx/utrn+/- Neutrófilos encontraram-se aumentados no mdx/utrn+/- com 2 meses, evidenciando a fase aguda da inflamação. Entretanto nos animais de 6 meses, quantidades semelhantes de neutrófilos foram detectadas no mdx/utrn+/- e mdx. Fibras marcadas pelas isoformas MyHC- I, IIa e IIx foram detectadas em maior porcentagem no BL10 do que no mdx e mdx/utrn+/- aos 2 meses de idade, demonstrando que a diminuição destas, no mdx e mdx/utrn+/- pode colaborar para a diminuição da força nestes animais. Aos 6 meses, porcentagem similares de MyHC- I foram detectadas no BL10, mdx e mdx/utrn+/-. MyHC-IIa não foram encontradas nos animais de 6 meses. MyHC-IIx encontraram-se em maior porcentagem no BL10 do que no mdx e mdx/utrn+/- com 6 meses de idade. Baixa porcentagem de isoformas de MyHC- I/IIa foram detectadas no mdx e mdx/utrn+/- aos 2 e 6 meses de idade e encontraram-se ausentes no BL10 de mesma idade. Fibras marcadas pela isoformas MyHC-IIa/IIx apresentaram-se aumentadas no mdx e mdx/utrn+/- aos 2 e 6 meses, podendo este aumento auxiliar na manutenção da força muscular. MyHC-IIx-IIb foram detectadas em maior porcentagem no mdx, reduzidas no BL10 e ausentes no mdx/utrn+/- com 2 meses de idade. Estas não foram identificadas nos animais de 6 meses. As propriedades contráteis do camundongo mdx/utrn+/- aos 2 meses de idade apresentaram-se mais comprometidas do que no mdx. Pt (contração isométrica máxima), sPt (força específica de Pt), Po (Força tetânica máxima) e sPo (força específica de Po) exibiram-se mais afetadas no mdx/utrn+/- do que no mdx. Porém aos 6 meses de idade não houve diferença significativa de força entre o mdx/utrn+/- e o mdx. As propriedades passivas do mdx/utrn+/- com 2 meses apresentou mais acometida do que no mdx. Entretanto, aos 6 meses, esta propriedade não se diferenciou entre o mdx/utrn+/- e o mdx. Em suma, conclui-se que o mdx/utrn+/- representa um modelo superior ao mdx com 2 meses de idade, uma vez que este apresentou morfologia, propriedades contráteis e passiva mais comprometidas do que no mdx. Aos 6 meses as propriedades contráteis e passivas e morfológicas do camundongo mdx/utrn+/- não se diferenciou do mdx. Sugerimos que o uso do mdx/utrn+/- com 2 meses de idade pode potencializar os testes pré-clinicos / Duchenne Muscular Dystrophy (DMD) is an important and severe muscle wasting disease caused by a dystrophin mutation. In the absence of dystrophin, sarcolemma becomes vulnerable to damage due a damage caused by continuous cycles of degeneration regeneration. Consequently, the muscle force reduces and the myofibers are replaced by fibrotic tissue. Between the skeletal muscles, the diaphragm is main affected muscle in DMD. Similarly, to a human DMD, despite the mdx model exhibit a milder phenotype, he presents the diaphragm muscle severely affected, as it was observed in our previous study, here described. However, it is also considered a poor model because it cannot reproduce the severe dystrophic phenotype seen in patients. An utrophin heterozygous utrophin mice (mdx/utrn+/- ), has been hypothesized as an intermediate model and they are gaining popularity in many laboratories. However unfortunately there is currently, no physiological enough evidence to justify the choice of this model for experimental therapies. Therefore, in this study, we aimed to elucidate the real contribution of the mdx/utrn+/- for the experimental therapies. To test this hypothesis, we evaluated the diaphragm muscle morphology and muscle function of the mdx and mdx/utrn+/- with 2 and 6 months. To elucidate the diaphragm morphology, we used light microscopy techniques and immunostaining analysis. Muscle function was evaluated through the active and passive properties. The clamps allowed to safe evaluate the diaphragm function. The update of the new protocol was efficient and able to evaluate the active and passive properties. At 2 months, the Hematoxylin and eosin, Masson Thrichome, Alisarine red, revealed that the mdx/utrn+ showed more inflammatory infiltrate, connective tissue and more areas with calcification than mdx model. At 6 months, there was no significant differences between mdx and mdx/utrn+. In the immunohistochemical analysis for eMyHC (embryonic myosin heavy chain), there was no difference between mdx and mdx/utrn+/- at 2 and 6 months. However, the results obtained in both ages, showed muscle regeneration Marking for dystrophin and utrophin protein, inflammatory cells and fiber type were also detected by immunohistochemistry. Marking for dystrophin was absent in mdx and mdx/utrn+/- with 2 and 6 months. Marking for utrophin protein was more evident in mdx than in mdx/utrn+/- mice, evidencing the utrophin haploinsufficiency in mdx/utr+/-. Macrophages were increased in mdx/utrn+/- than in mdx mice with 2 and 6 months, showing an inflammation. Neutrophils were increased in mdx/utrn+/- at 2 month-old, evidencing the acute phase of inflammation. However, at 6 months similar amounts of neutrophil were detected in mdx and mdx/utrn+/-. Fibers marked by MyHC-I, IIa and IIx were detected in a higher percentage in BL10 than in mdx and mdx/utrn+/- at 2 months, showing that this change could collaborate with force decrease in these animals. At 6 months, similar percentage of MyHC-I was detected in BL10, mdx and mdx/utrn+/-. MyHC-IIa animals were not found at 6 months. Higher percentage of MyHC-IIx was found in BL10 than in mdx and mdx/utrn+/- with 6 months. Low percentage of MyHC- I/IIa was detected in mdx and mdx/utrn+/- at 2 and 6 months and it was absent in BL10 in the same age. Fibers marked by MyHC-IIa/IIx isoforms were increased in mdx and mdx/utrn+/- with 2 and 6 months. These changes could help to maintain the muscle force. MyHC-IIx-IIb was detected in higher percentage in mdx, reduced the BL10 and it was absent in mdx/utrn+/- with 2 months. MyHC-IIx-IIb was not identified in the animals with 6 months. Contractile properties in mdx/utrn+/- at 2 months were more affected than in mdx mice. Pt (maximal twitch force), sPt (specific twitch force), Po (maximal tetanic force) and sPo (specific tetanic force) showed more severely affected in mdx/utrn+/- than in mdx mice. At 6 months there were no significant difference in Pt, sPt, Po and sPo between mdx/utrn+/- and mdx mice. Passive properties of mdx/utrn+/- with 2 months presented more affected than the in mdx mice. However, at 6 months, this property did not differ between mdx/utrn+/- and mdx mice. In summary, we concluded that the mdx/utrn+/- at 2 month represent a superior model than the mdx with matched-age, since they presented morphology and contractile and passive properties more compromised than mdx mice. At 6 months, the mdx/utrn+/-contractile and the passive properties and morphology did not differ from the mdx mice age-matched. We suggest that the use of mdx/utrn+/- with 2 months-old would represent would represent a better model to test the potential of the therapies than mdx mice

The dystrophinopathies are a group of disorders characterised by cellular absence of the membrane stabilising protein, dystrophin. Duchenne muscular dystrophy is the most severe disorder clinically. The deficiency of dystrophin, in the muscular dystrophy X-linked (mdx) mouse causes an elevation in intracellular calcium in cardiac myocytes. Potential mechanisms contributing to increased calcium include enhanced influx, sarcoplasmic reticular calcium release and\or reduced sequestration or sarcolemmal efflux. This dissertation examined the potential mechanisms that may contribute to an intracellular calcium overload in a murine model of muscular dystrophy. The general cardiomyopathy of the mdx myocardium was evident, with the left atria from mdx consistently producing less force than control atria. This was associated with delayed relaxation. The role of the L-type calcium channels mediating influx was initially investigated. Dihydropyridines had a lower potency in contracting left atria corresponding to a redued dihydropyridine receptor affinity in radioligand binding studies of mdx ventricular homogenates (P<0.05). This was associated with increased ventricular dihydropyridine receptor protein and mRNA levels (P<0.05). The function of the sarcoplasmic reticulum in terms of release and also sequestration of calcium via the sarco-endoplasmic reticulum ATPase were investigated. A lower force of contraction was evident in mdx left atria in response to a range of stimulation frequencies (P<0.05) and concentrations of extracellular calcium (P<0.05). However, in the presence of 1 nM Ryanodine to block sarcoplasmic reticular calcium release, increased stimulation frequency caused similar forces to those obtained in control mice suggesting enhanced calcium influx via L-type calcium channels in mdx. Rapid cooling contractures showed a reduced contracture in mdx compared to control in response to cooling. This suggests some dysfunction in SR storage, which may be associated with the delayed relaxation time. Concentration-response curves to inhibitors of the sarco-endoplasmic reticulum showed no difference in function of the enzyme responsible for calcium uptake into the sarcoplasmic reticulum. Although sarco-endoplasmic reticulum ATPase mRNA was upregulated, no functional benefit was evident. This study indicates that a deficiency of dystrophin leads to upregulation of L-type calcium channels that contribute to increased calcium influx, with no functional change in sarcoplasmic reticular sequestration. Upregulation of the influx pathway is a potential mechanism for the calcium overload observed in mdx cardiac muscle.

A Distrofia Muscular de Duchenne (DMD) é uma importante e severa doença músculo degenerativa causada pela mutação do gene da distrofina. Na ausência da distrofina, o sarcolema das células torna-se vulnerável devido a danos induzidos por ciclos contínuos de degeneração e regeneração. Consequentemente, a força muscular diminui e as miofibras são substituídas por tecido fibrótico. Dentre os músculos esqueléticos afetados, o diafragma, destaca-se por ser o principal músculo respiratório acometido na DMD. Similarmente a DMD humana, o modelo mdx, apesar de exibir um fenótipo suave, este apresenta um severo acometimento no músculo diafragma, assim como observado em nosso estudo prévio, aqui descritos. Entretanto, este é considerado um modelo pobre, porque ele não consegue reproduzir, o fenótipo severo observado nos pacientes. O camundongo mdx/utrn+/- (dystrophin-null heterozygous urtrophin mice) com haploinsuficiência da utrofina, tem sido hipotetizado como um modelo com um fenótipo intermediário, ganhando popularidade nos laboratórios. Porém, infelizmente, até os dias de hoje, não existe evidências fisiológicas e funcionais suficientes que justifiquem a escolha deste modelo para as terapias experimentais. Portanto, neste estudo objetivou-se esclarecer a real contribuição do camundongo mdx/utrn+/- para as terapias experimentais. Para testar esta hipótese, elegeu-se analisar a morfologia e a função muscular do músculo diafragma do mdx e mdx/utrn+/- com 2 e 6 meses de idade. Para elucidar a morfopatologia do diafragma foi utilizado microscopia de luz e análises de imunohistoquímica. A função muscular do diafragma foi analisada através da avaliação das propriedades contráteis e passivas. A forma de como executar a função muscular do diafragma foi atualizada através da criação de dois clips, os quais permitiram avaliar o músculo de forma segura. A adaptação de um novo protocolo de avaliação da função muscular mostrou-se eficaz e capaz de ser utilizada para avaliar as propriedades contráteis e passivas. Aos 2 meses de idade, as colorações de Hematoxilina e eosina, Tricômio de Masson e Alizarina vermelha revelaram que o mdx/utrn+ apresentou maior quantidade de infiltrado inflamatório, tecido conectivo e áreas de calcificação do que o mdx. Já aos 6 meses de idade, não houve diferença morfológica entre o mdx e o mdx/utrn+/-. Na análise de imunohistoquímica para eMyHC (miosina embrionária de cadeia pesada eMyHC), não foi observada diferença entre o mdx e o mdx/utrn+/-aos 2 e 6 meses de idade. Entretanto, os resultados obtidos em ambas as idades, demonstraram a presença de regeneração muscular. Na marcação da proteína distrofina e utrofina, as células inflamatórias e os tipos de fibras musculares também foram detectados por imunohistoquímicas. A marcação da proteína distrofina, mostrou-se ausente no mdx e mdx/utrn+/- com 2 e 6 meses de idade. A marcação da proteína utrofina mostrou-se mais evidente no mdx do que no mdx/utrn+/-, videnciando a haploinsuficiência nos mdx/utrn+/-. Macrófagos foram encontrados em maior quantidade no camundongo mdx/utrn+/- com 2 e 6 meses do que no mdx, mostrando que o processo de inflamação encontrou-se aumentado nos mdx/utrn+/- Neutrófilos encontraram-se aumentados no mdx/utrn+/- com 2 meses, evidenciando a fase aguda da inflamação. Entretanto nos animais de 6 meses, quantidades semelhantes de neutrófilos foram detectadas no mdx/utrn+/- e mdx. Fibras marcadas pelas isoformas MyHC- I, IIa e IIx foram detectadas em maior porcentagem no BL10 do que no mdx e mdx/utrn+/- aos 2 meses de idade, demonstrando que a diminuição destas, no mdx e mdx/utrn+/- pode colaborar para a diminuição da força nestes animais. Aos 6 meses, porcentagem similares de MyHC- I foram detectadas no BL10, mdx e mdx/utrn+/-. MyHC-IIa não foram encontradas nos animais de 6 meses. MyHC-IIx encontraram-se em maior porcentagem no BL10 do que no mdx e mdx/utrn+/- com 6 meses de idade. Baixa porcentagem de isoformas de MyHC- I/IIa foram detectadas no mdx e mdx/utrn+/- aos 2 e 6 meses de idade e encontraram-se ausentes no BL10 de mesma idade. Fibras marcadas pela isoformas MyHC-IIa/IIx apresentaram-se aumentadas no mdx e mdx/utrn+/- aos 2 e 6 meses, podendo este aumento auxiliar na manutenção da força muscular. MyHC-IIx-IIb foram detectadas em maior porcentagem no mdx, reduzidas no BL10 e ausentes no mdx/utrn+/- com 2 meses de idade. Estas não foram identificadas nos animais de 6 meses. As propriedades contráteis do camundongo mdx/utrn+/- aos 2 meses de idade apresentaram-se mais comprometidas do que no mdx. Pt (contração isométrica máxima), sPt (força específica de Pt), Po (Força tetânica máxima) e sPo (força específica de Po) exibiram-se mais afetadas no mdx/utrn+/- do que no mdx. Porém aos 6 meses de idade não houve diferença significativa de força entre o mdx/utrn+/- e o mdx. As propriedades passivas do mdx/utrn+/- com 2 meses apresentou mais acometida do que no mdx. Entretanto, aos 6 meses, esta propriedade não se diferenciou entre o mdx/utrn+/- e o mdx. Em suma, conclui-se que o mdx/utrn+/- representa um modelo superior ao mdx com 2 meses de idade, uma vez que este apresentou morfologia, propriedades contráteis e passiva mais comprometidas do que no mdx. Aos 6 meses as propriedades contráteis e passivas e morfológicas do camundongo mdx/utrn+/- não se diferenciou do mdx. Sugerimos que o uso do mdx/utrn+/- com 2 meses de idade pode potencializar os testes pré-clinicos / Duchenne Muscular Dystrophy (DMD) is an important and severe muscle wasting disease caused by a dystrophin mutation. In the absence of dystrophin, sarcolemma becomes vulnerable to damage due a damage caused by continuous cycles of degeneration regeneration. Consequently, the muscle force reduces and the myofibers are replaced by fibrotic tissue. Between the skeletal muscles, the diaphragm is main affected muscle in DMD. Similarly, to a human DMD, despite the mdx model exhibit a milder phenotype, he presents the diaphragm muscle severely affected, as it was observed in our previous study, here described. However, it is also considered a poor model because it cannot reproduce the severe dystrophic phenotype seen in patients. An utrophin heterozygous utrophin mice (mdx/utrn+/- ), has been hypothesized as an intermediate model and they are gaining popularity in many laboratories. However unfortunately there is currently, no physiological enough evidence to justify the choice of this model for experimental therapies. Therefore, in this study, we aimed to elucidate the real contribution of the mdx/utrn+/- for the experimental therapies. To test this hypothesis, we evaluated the diaphragm muscle morphology and muscle function of the mdx and mdx/utrn+/- with 2 and 6 months. To elucidate the diaphragm morphology, we used light microscopy techniques and immunostaining analysis. Muscle function was evaluated through the active and passive properties. The clamps allowed to safe evaluate the diaphragm function. The update of the new protocol was efficient and able to evaluate the active and passive properties. At 2 months, the Hematoxylin and eosin, Masson Thrichome, Alisarine red, revealed that the mdx/utrn+ showed more inflammatory infiltrate, connective tissue and more areas with calcification than mdx model. At 6 months, there was no significant differences between mdx and mdx/utrn+. In the immunohistochemical analysis for eMyHC (embryonic myosin heavy chain), there was no difference between mdx and mdx/utrn+/- at 2 and 6 months. However, the results obtained in both ages, showed muscle regeneration Marking for dystrophin and utrophin protein, inflammatory cells and fiber type were also detected by immunohistochemistry. Marking for dystrophin was absent in mdx and mdx/utrn+/- with 2 and 6 months. Marking for utrophin protein was more evident in mdx than in mdx/utrn+/- mice, evidencing the utrophin haploinsufficiency in mdx/utr+/-. Macrophages were increased in mdx/utrn+/- than in mdx mice with 2 and 6 months, showing an inflammation. Neutrophils were increased in mdx/utrn+/- at 2 month-old, evidencing the acute phase of inflammation. However, at 6 months similar amounts of neutrophil were detected in mdx and mdx/utrn+/-. Fibers marked by MyHC-I, IIa and IIx were detected in a higher percentage in BL10 than in mdx and mdx/utrn+/- at 2 months, showing that this change could collaborate with force decrease in these animals. At 6 months, similar percentage of MyHC-I was detected in BL10, mdx and mdx/utrn+/-. MyHC-IIa animals were not found at 6 months. Higher percentage of MyHC-IIx was found in BL10 than in mdx and mdx/utrn+/- with 6 months. Low percentage of MyHC- I/IIa was detected in mdx and mdx/utrn+/- at 2 and 6 months and it was absent in BL10 in the same age. Fibers marked by MyHC-IIa/IIx isoforms were increased in mdx and mdx/utrn+/- with 2 and 6 months. These changes could help to maintain the muscle force. MyHC-IIx-IIb was detected in higher percentage in mdx, reduced the BL10 and it was absent in mdx/utrn+/- with 2 months. MyHC-IIx-IIb was not identified in the animals with 6 months. Contractile properties in mdx/utrn+/- at 2 months were more affected than in mdx mice. Pt (maximal twitch force), sPt (specific twitch force), Po (maximal tetanic force) and sPo (specific tetanic force) showed more severely affected in mdx/utrn+/- than in mdx mice. At 6 months there were no significant difference in Pt, sPt, Po and sPo between mdx/utrn+/- and mdx mice. Passive properties of mdx/utrn+/- with 2 months presented more affected than the in mdx mice. However, at 6 months, this property did not differ between mdx/utrn+/- and mdx mice. In summary, we concluded that the mdx/utrn+/- at 2 month represent a superior model than the mdx with matched-age, since they presented morphology and contractile and passive properties more compromised than mdx mice. At 6 months, the mdx/utrn+/-contractile and the passive properties and morphology did not differ from the mdx mice age-matched. We suggest that the use of mdx/utrn+/- with 2 months-old would represent would represent a better model to test the potential of the therapies than mdx mice

No description available.

Duchenne Muscular Dystrophy (DMD) is a fatal condition occurring in approximately 1 in 3500 male births and is due to the lack of a protein called dystrophin. Initially DMD was considered a skeletal myopathy, but the pathology and consequences of cardiomyopathy are being increasingly recognised. Fibrosis, resulting from continual cycles of degeneration of the muscle tissues followed by inadequate regeneration of the muscles, is progressive in both cardiac and skeletal dystrophic muscle. In the heart fibrosis interferes with contractility and rhythm whereas it affects contractile function and causes contractures in skeletal muscles. This study utilised the mdx mouse which exhibits a pathological loss of muscle fibres and fibrosis characteristic of DMD, to examine a range of mechanisms that can influence muscle function and fibrosis. Ageing and workload both appear to contribute to the development of dystrophic features in cardiac and skeletal muscle of the mdx mouse. Therefore the effect of eccentric exercise on cardiac and skeletal muscle was examined in older mdx mice. Mice ran in 30 minute sessions for five months, 5 days per week. Downhill treadmill running did not exacerbate the contractile function or fibrosis of the mdx heart or the EDL, SOL or diaphragm muscles suggesting that cytokines influence function and fibrosis to a greater extent than workload alone. The role of the cytokine TGF-beta was examined by treating mdx mice with the TGF-beta antagonist pirfenidone at 0.4, 0.8 or 1.2 per cent in drinking water for six months. Pirfenidone improved cardiac contractility (P<0.01) and coronary flow (P<0.05), to levels comparable to control mice, despite no reduction in cardiac fibrosis. Pirfenidone did not reduce fibrosis or improve function in skeletal muscle. A deficiency of neuronal nitric oxide synthase (nNOS) in DMD and mdx mice causes a lowered production of nitric oxide indicating that the substrate of nNOS, l-arginine, may be beneficial to cardiac and skeletal muscle function in mdx mice. Oral l-arginine (5 mg/g bw) improved cardiac contractility, coronary flow and reduced cardiac fibrosis (P<0.05) without improving skeletal muscle function or fibrosis. In contrast, 10 mg/g bw l-arginine improved cardiac function and coronary flow (P<0.01), despite also elevating cardiac collagen. This increment in collagen was prevented by co-administration of prednisone. The experiments described in this dissertation reveal for the first time that pharmacological treatments in mdx mice can improve cardiac structure and function. Further elucidation of the optimum time and doses of such treatments may result in future pharmacological treatments to improve cardiac function and fibrosis in DMD.

Duchenne Muscular Dystrophy (DMD) is an x-linked neuromuscular disease that is caused by an absence of dystrophin protein, rendering skeletal muscle more susceptible to contraction-induced damage. One therapeutic strategy focuses on increasing the expression of endogenous utrophin A, a dystrophin homologue. Interestingly, slow muscle is more resistant to the dystrophic pathology and has increased utrophin A expression (Webster 1998; Gramolini 2001b). These observations led researchers to explore the therapeutic potential of stimulating the slow, oxidative myogenic program (SOMP) in the mdx context. Beneficial adaptations were seen with pharmacological activation of PPARδ and AMPK. We treated mdx mice with resveratrol (~100mg/kg/day), a putative SIRT1 activator, for 6-7 weeks and evaluated the activity of phenotypic modifiers that are known to influence the SOMP. SIRT1 activity and protein levels increased significantly, as well as downstream PGC-1α activity. There was evidence of a fibre type conversion as the treated mice had a higher proportion of the slow myosin heavy chain isoforms in both the EDL and Soleus skeletal muscles. Utrophin A protein levels showed modest, but consistent increases with resveratrol treatment. Finally, histological analysis revealed improvements in central nucleation and fibre size variability. These findings were promising, but raised the question of whether modifying the treatment regimen may result in greater therapeutic benefits. Surprisingly, we discovered that an elevated dose of 500mg/kg/day was ineffective in its promotion of the SOMP. SIRT1 was not activated and there was no change in utrophin A levels with resveratrol treatment. Taken together, this study demonstrates that resveratrol has the ability to promote the SOMP through SIRT1 and PGC-1α activation. It also highlights the importance of selecting an appropriate dose of resveratrol to maximize its effectiveness.

Orientador: Humberto Santo Neto / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-20T21:05:12Z (GMT). No. of bitstreams: 1 Ferretti_Renato_D.pdf: 15919724 bytes, checksum: 2e3e4ba8b562aaaaf3dde85b2e810561 (MD5) Previous issue date: 2012 / Resumo: Os músculos intrínsecos da laringe (MIL) são protegidos da mionecrose em camundongos mdx, modelo da distrofia muscular de Duchenne (DMD). A DMD caracteriza-se pela mionecrose, causada pela ausência da proteína distrofina (DIS). A DIS se une a um complexo glicoproteínas (CDG), que auxilia na estabilidade da fibra e interage com proteínas reguladoras do Ca2+. O sarcolema instável dado pela ausência da DIS, diminuição de proteínas do CDG, desregulação de canais de Ca2+ e leva ao influxo de Ca2+ exacerbado, associado à diminuição da homeostase do Ca2+ intracelular e capacidade do estresse oxidativa, resulta na mionecrose. A utrofina (Utrn), semelhante à proteína DIS, se conecta às proteínas do CDG, parece ter papel na agregação dos receptores de acetilcolina (AChRs) nas junções neuromusculares (JNM) e auxiliaria na proteção da mionecrose. Neste trabalho examinamos os níveis das proteínas do CDG (beta-distroglicana [b-DG], beta-sarcoglicana [b-SG] e alfa-sintrofina [a-SIN]), da Utrn, de canais de estoque do Ca2+ (SOCE; proteínas Orai e STIM1) e proteína relacionada ao estresse oxidativo na mitocôndria (PGC-1a) em MIL distróficos. Além disso, analisamos o padrão de distribuição da Utrn e AChRs nas JNM de MIL distróficos. A análise da b-DG, b-SG, a- SIN e da Utrn pela técnica de imunohistoquímica e western blotting, mostrou que nos MIL distróficos os níveis da b-DG e da Utrn são normais em MIL adultos comparados com controle. Com envelhecimento, os níveis de proteínas do CDG e Utrn são alterados em MIL distróficos e parece não estar relacionado a proteção da mionecrose. Com emprego de técnicas moleculares e bioquímicas para análise de canais de estoque do Ca2+ (Orai e STIM1) e proteína do estress oxidativo na mitocôndria (PGC-1a), foram observados níveis aumentados de STIM1, com similar aumento da proteína calmodulina (CaM), bem como aumento da expressão do PGC-1a em MIL distróficos. Músculos acometidos distróficos apresentaram diminuição na expressão destas proteínas. Utilizando imunohistoquimica e microscopia confocal, foi observado que o padrão de distribuição da Utrn e dos AChRs não se altera nas JNM de MIL mdx. Em fibras regeneradas tanto o padrão de distribuição da Utrn quanto dos AChRs mostraram-se alterados. Pode-se concluir que os MIL de camundongos mdx apresentam manutenção dos níveis normais de proteínas do CDG e da Utrn, bem como o aumento de STIM1, CaM e PGC-1a, poderiam auxiliar, pelo menos em parte, à proteção da mionecrose / Abstract: The intrinsic laryngeal muscles (ILM) are protected from myonecrosis in the mdx mouse model of Duchenne muscular dystrophy (DMD). The DMD is characterized by myonecrosis, resulting from the absence of dystrophin protein. Dystrophin links the cytoskeleton to a complex of glycoprotein, the dystrophin-glycoprotein complex (DGC), which interacts with Ca2+-dependent channels for signaling and stability of the muscle membrane. In the absence of dystrophin, the sarcolemma becomes instable due to a decrease in the DGC level, deregulation of Ca2+-dependent channels, which increase Ca2+ influx, decreased Ca2+-handling and oxidative stress capacity, that result in muscle fiber necrosis. Utrophin (Utrn), similarly to the dystrophin, conects to DGC proteins, assembles the acethylcoline receptors (AChRs) at the neuromuscular junctions (NMJ) and may play a role in dystrophic muscle sparing. In this study, we examined the levels of DGC proteins (beta-dystroglycan [b-DG], beta-sarcoglycana [b-SG], alpha-syntrophin [a-SIN]), Utrn, store-operated Ca2+ channels (SOCE; STIM1 and Orai1 proteins), and mitochondrial oxidative protein (PGC-1a) in dystrophic ILM. We also examined the distribution of Utrn and AChRs in the dystrophic ILM NMJ. Immunohistochemistry and western blotting analyses of b-DG, b-SG and a-SIN, and the Utrn showed normal levels in adult dystrophic ILM compared with adult control. In aged mice, a dramatic decrease in DGC levels was observed in all dystrophic muscles compared with control. There are age-related alterations in DGC in the ILM of mdx mice, regardless of their protection against the lack of dystrophin. Using biochemical and molecular techniques to analyze SOCE proteins and mitochondrial oxidative protein (PGC-1a), we observed increased levels of STIM1, associated with increased level of calmodulin (CaM), and increased level of PGC-1a in dystrophic ILM. Dystrophic affected muscles have decreased levels of those proteins. Using molecular and biochemical methods we observed that Utrn and AChRs are fragmented only in affected muscle fibers and remaining unchanged in dystrophic MIL. We conclude that in adult dystrophic MIL the rescue of the DGC, increased levels of STIM1, CaM and PGC-1a, may be associated, at least in part, with their protection against myonecrosis / Doutorado / Anatomia / Doutor em Biologia Celular e Estrutural

Duchenne Muscular Dystrophy (DMD) is an x-linked neuromuscular disease that is caused by an absence of dystrophin protein, rendering skeletal muscle more susceptible to contraction-induced damage. One therapeutic strategy focuses on increasing the expression of endogenous utrophin A, a dystrophin homologue. Interestingly, slow muscle is more resistant to the dystrophic pathology and has increased utrophin A expression (Webster 1998; Gramolini 2001b). These observations led researchers to explore the therapeutic potential of stimulating the slow, oxidative myogenic program (SOMP) in the mdx context. Beneficial adaptations were seen with pharmacological activation of PPARδ and AMPK. We treated mdx mice with resveratrol (~100mg/kg/day), a putative SIRT1 activator, for 6-7 weeks and evaluated the activity of phenotypic modifiers that are known to influence the SOMP. SIRT1 activity and protein levels increased significantly, as well as downstream PGC-1α activity. There was evidence of a fibre type conversion as the treated mice had a higher proportion of the slow myosin heavy chain isoforms in both the EDL and Soleus skeletal muscles. Utrophin A protein levels showed modest, but consistent increases with resveratrol treatment. Finally, histological analysis revealed improvements in central nucleation and fibre size variability. These findings were promising, but raised the question of whether modifying the treatment regimen may result in greater therapeutic benefits. Surprisingly, we discovered that an elevated dose of 500mg/kg/day was ineffective in its promotion of the SOMP. SIRT1 was not activated and there was no change in utrophin A levels with resveratrol treatment. Taken together, this study demonstrates that resveratrol has the ability to promote the SOMP through SIRT1 and PGC-1α activation. It also highlights the importance of selecting an appropriate dose of resveratrol to maximize its effectiveness.

The dystrophin-associated protein complex (DAPC) provides a mechanical link between the intracellular cytoskeleton and extracellular matrix, serving as a mechanosensor and signal transducer across the sarcolemma. Pharmacological stimulation of AMP-activated protein kinase (AMPK) induces the expression of DAPC components in skeletal muscle, whereas physiological reductions in AMPK are associated with DAPC dysfunction. We sought to determine whether AMPK was necessary for the maintenance of DAPC expression in skeletal muscle. Fast glycolytic extensor digitorum longus (EDL) and slow oxidative soleus (SOL) muscles from wild-type (WT) mice, as well as from littermates deficient in both isoforms of the AMPK-β subunit in skeletal muscle (MKO) were analyzed. DAPC mRNA levels, as well as protein expression and localization were similar between genotypes, with the exception of nNOS, which displayed a compensatory sarcolemmal enrichment in MKO muscles. The content of transcriptional and post-transcriptional regulators of the DAPC, such as PGC-1α and KSRP, were also not affected by the loss of AMPK. However, MyoD and myogenin expression was significantly diminished in MKO muscles, which is consistent with previous reports of myopathy in these animals. Furthermore, we observed decrements in extrasynaptic utrophin expression selectively in MKO SOL muscles, despite an adaptive accumulation of PGC-1α at the sarcolemmal compartment. Collectively the evidence indicates that AMPK is sufficient, but not essential for the maintenance of DAPC expression in skeletal muscle. However, AMPK is required for preserving extrasynaptic utrophin levels in slow, oxidative muscles, which underscores the role of AMPK in the gene expression of this disease modifying protein. / Thesis / Master of Science (MSc) / The dystrophin-associated protein complex (DAPC) connects the interior and exterior of muscle cells. Activation of AMP-activated protein kinase (AMPK) increases the expression of the DAPC in skeletal muscle. We sought to determine whether AMPK was necessary for DAPC expression in skeletal muscle. Fast and slow muscles from normal mice, as well as from those deficient in skeletal muscle AMPK (MKO) were analyzed. We found DAPC levels and localization were similar between both groups, with the exception of nNOS, which was enriched at the muscle membrane in MKO muscles. Regulators of the DAPC were also not affected by the loss of AMPK. However, genes important for the production of muscle were significantly diminished in MKO muscles. Furthermore, we observed decrements in utrophin at the muscle membrane selectively in slow MKO muscles. Our work indicates that AMPK is not essential for the DAPC expression in skeletal muscle, however it is required for preserving utrophin levels in slow, oxidative muscles.