Muscular dystrophy is a genetic disease which affects the morphology, physiology and biochemical nature of the muscle fiber. This study was designed to examine the progressive effects of muscular dystrophy on the differentiation process of skeletal muscle. Chapter 1 examines the neonatal development of muscle spindles and their intrafusal fibers in the soleus and extensor digitorum longus (EDL) of genetically dystrophic mice according to histochemical, quantitative, and ultrastructural parameters. Despite alterations in the surrounding extrafusal fibers, muscle spindles and their intrafusal fibers appeared enzymatically and histologically unaffected in incipient stages of murine dystrophy. In the second chapter the distribution and concentration of parvalbumin (PV), a calcium-binding protein, in 32 and 2-week-old dystrophic mice was mapped by immunohistochemical and biochemical procedures. The number of parvalbumin-immunoreactive fibers was significantly reduced in the adult dystrophic EDL but slightly increased in the adult dystrophic soleus. No differences between strains were observed in the 2-week samples. These findings were supported by routine myosin ATPase histochemistry. Parvalbumin was isolated on SDS-PAGE gels and the concentration of PV was estimated by a RIA. These results confirmed the immunohistochemical data in that PV content was dramatically reduced in the adult dystrophic EDL and significantly increased in the dystrophic soleus. No changes were detected in the samples of the 2-week-old muscles. The similarity in the distribution and content of PV between the fast and slow dystrophic muscles at 32 weeks of age suggests an alteration in the distribution and phenotypic expression of fiber types in muscular dystrophy and supports the hypothesis that dystrophy alters the normal differentiation process of skeletal muscle. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

As distrofias musculares constituem um grupo heterogêneo de doenças genéticas, caracterizadas por uma degeneração progressiva e irreversível dos músculos. Modelos murinos distróficos, como o mdx, SJL/J, Largemyd e Lama2dy-2J/J, são ferramentas importantes para o estudo destas doenças. O objetivo deste trabalho consistiu em estabelecer parâmetros de avaliação funcional que visem a sua utilização para elucidar os benefícios clínicos de futuras terapias. Para tanto, foram avaliadas as quatro linhagens distróficas, em diferentes idades, e comparadas a controle normal. Os testes padronizados consistiram em nado forçado, avaliação de resistência/equilíbrio pelos membros anteriores e pelos quatro membros, caminhar em plataforma suspensa, suspensão pela cauda, grip strength e rota rod. Comprovou-se a existência de diferentes padrões de força, resistência, coordenação motora e aprendizagem/memória ao longo do tempo de vida de cada linhagem, o que permitiu traçar parâmetros a serem utilizados em futuras pesquisas de terapia celular e farmacológica. / Muscular dystrophies are a heterogeneous group of genetic diseases characterized by a progressive and irreversible degeneration of the muscles. Dystrophic mouse models, like the mdx, SJL/J, Largemyd and Lama2dy-2J/J, are important tools for studying these diseases. The aim of this study was to establish parameters for functional evaluation aiming its use to elucidate the clinical benefits of future therapies. Thus, we evaluated the four strains of dystrophic mice, at different ages, and compared to normal control. Standardized tests consisted of forced swimming, evaluation of resistance/balance by forelimb and four members, walking on suspended platform, suspension by the tail, grip strength and rota rod. We observed the existence of different patterns of strength, endurance, coordination and learning / memory over the lifetime of each strain, which allowed tracing parameters to be used in future studies of cell and pharmacology therapies.

As distrofias musculares constituem um grupo heterogêneo de doenças genéticas, caracterizadas por uma degeneração progressiva e irreversível dos músculos. Modelos murinos distróficos, como o mdx, SJL/J, Largemyd e Lama2dy-2J/J, são ferramentas importantes para o estudo destas doenças. O objetivo deste trabalho consistiu em estabelecer parâmetros de avaliação funcional que visem a sua utilização para elucidar os benefícios clínicos de futuras terapias. Para tanto, foram avaliadas as quatro linhagens distróficas, em diferentes idades, e comparadas a controle normal. Os testes padronizados consistiram em nado forçado, avaliação de resistência/equilíbrio pelos membros anteriores e pelos quatro membros, caminhar em plataforma suspensa, suspensão pela cauda, grip strength e rota rod. Comprovou-se a existência de diferentes padrões de força, resistência, coordenação motora e aprendizagem/memória ao longo do tempo de vida de cada linhagem, o que permitiu traçar parâmetros a serem utilizados em futuras pesquisas de terapia celular e farmacológica. / Muscular dystrophies are a heterogeneous group of genetic diseases characterized by a progressive and irreversible degeneration of the muscles. Dystrophic mouse models, like the mdx, SJL/J, Largemyd and Lama2dy-2J/J, are important tools for studying these diseases. The aim of this study was to establish parameters for functional evaluation aiming its use to elucidate the clinical benefits of future therapies. Thus, we evaluated the four strains of dystrophic mice, at different ages, and compared to normal control. Standardized tests consisted of forced swimming, evaluation of resistance/balance by forelimb and four members, walking on suspended platform, suspension by the tail, grip strength and rota rod. We observed the existence of different patterns of strength, endurance, coordination and learning / memory over the lifetime of each strain, which allowed tracing parameters to be used in future studies of cell and pharmacology therapies.

A proteína miostatina, é um regulador negativo do crescimento muscular e a modulação de sua expressão pode consistir em tratamento para distrofias musculares. Nós estudamos expressão endógena da miostatina no músculos gastrocnêmio e diafragma de 4 modelos murinos de degeneração muscular: os camundongos Dmdmdx, SJL/J, Largemyd e Lama2dy-2J/J. Observamos que a miostatina é menos expressa no músculo gastrocnêmio do que diafragma normal, refletindo um músculo mais sujeito a lesão. Nas quatro linhagens distróficas a miostatina é menos expressa do que em camundongos normais, tanto no músculo gastrocnêmio como diafragma, sem diferença entre os dois. A analise comparativa da degeneração e regeneração muscular mostrou maior correlação da inibição da miostatina com o padrão de degeneração. Nossos resultados sugerem que o processo de degeneração, quando iniciado, e independentemente de seu grau, causa molecular primária, ou músculo afetado, parece atuar de forma similar na inibição da expressão da miostatina, possivelmente como estimulo a regeneração do dano. / Myostatin is a negative regulator of muscle growth, and its inhibition has been considered a therapeutic strategy for muscular dystrophies. We evaluated the endogenous expression of myostatin in the gastrocnemius and diaphragm muscles from 4 mouse dystrophic models including Dmdmdx, SJL/J>, Largemyd and Lama2dy2J/J. In normal mice, we observed that myostatin is less expressed in the gastrocnemius than in the diaphragm, reflecting a muscle most prone to lesions. In the 4 dystrophic models, myostatin expression was reduced, in both gastrocnemius and diaphragm muscles. The comparative analysis of the histopathology of the muscles with the expression of myostatin showed a stronger correlation with the pattern of degeneration then regeneration. Our results suggest that, when started, the process of degeneration of the muscle, independently of the primary molecular defect, or degree, seems to act in a similar pathway leading to the inhibition of the expression of myostatin in the affected muscles, possibly as a stimulus to regeneration of damage.

A proteína miostatina, é um regulador negativo do crescimento muscular e a modulação de sua expressão pode consistir em tratamento para distrofias musculares. Nós estudamos expressão endógena da miostatina no músculos gastrocnêmio e diafragma de 4 modelos murinos de degeneração muscular: os camundongos Dmdmdx, SJL/J, Largemyd e Lama2dy-2J/J. Observamos que a miostatina é menos expressa no músculo gastrocnêmio do que diafragma normal, refletindo um músculo mais sujeito a lesão. Nas quatro linhagens distróficas a miostatina é menos expressa do que em camundongos normais, tanto no músculo gastrocnêmio como diafragma, sem diferença entre os dois. A analise comparativa da degeneração e regeneração muscular mostrou maior correlação da inibição da miostatina com o padrão de degeneração. Nossos resultados sugerem que o processo de degeneração, quando iniciado, e independentemente de seu grau, causa molecular primária, ou músculo afetado, parece atuar de forma similar na inibição da expressão da miostatina, possivelmente como estimulo a regeneração do dano. / Myostatin is a negative regulator of muscle growth, and its inhibition has been considered a therapeutic strategy for muscular dystrophies. We evaluated the endogenous expression of myostatin in the gastrocnemius and diaphragm muscles from 4 mouse dystrophic models including Dmdmdx, SJL/J>, Largemyd and Lama2dy2J/J. In normal mice, we observed that myostatin is less expressed in the gastrocnemius than in the diaphragm, reflecting a muscle most prone to lesions. In the 4 dystrophic models, myostatin expression was reduced, in both gastrocnemius and diaphragm muscles. The comparative analysis of the histopathology of the muscles with the expression of myostatin showed a stronger correlation with the pattern of degeneration then regeneration. Our results suggest that, when started, the process of degeneration of the muscle, independently of the primary molecular defect, or degree, seems to act in a similar pathway leading to the inhibition of the expression of myostatin in the affected muscles, possibly as a stimulus to regeneration of damage.