Twenty-one days of low-intensity eccentric training improve morphological characteristics and function of soleus muscles of mdx mice.

Duchene muscular dystrophy (DMD) is caused by the absence of the protein dystrophin, which leads to muscle weakness, progressive degeneration, and eventually death due to respiratory failure. Low-intensity eccentric training (LIET) has been used as a rehabilitation method in skeletal muscles after disuse. Recently, LIET has also been used for rehabilitating dystrophic muscles, but its effects are still unclear. The purpose of this study was to investigate the effects of 21 days of LIET in dystrophic soleus muscle. Thirty-six male mdx mice were randomized into six groups (n = 6/each): mdx sedentary group; mdx training group-3 days; mdx training group-21 days; wild-type sedentary group; wild-type training group-3 days and wild-type training group-21 days. After the training sessions, animals were euthanized, and fragments of soleus muscles were removed for immunofluorescence and histological analyses, and measurements of active force and Ca2+ sensitivity of the contractile apparatus. Muscles of the mdx training group-21 days showed an improvement in morphological characteristics and an increase of active force when compared to the sedentary mdx group. The results show that LIET can improve the functionality of dystrophic soleus muscle in mice.

Caraterização morfoquantitativa do plexo mioentérico do esôfago no modelo de distrofia muscular camundongo MDX / Morphoquantitative features of myenteric plexus of the oesophagus in MDX mice

A Distrofia Muscular de Duchenne (DMD) [...]. Além dos graves distúrbios cardiorrespiratórios e da motricidade, o paciente apresenta disfunções do sistema digestório, caracterizadas pelas desordens da motilidade. Entretanto, sabe-se que tais disfunções não ocorrem no camundongo MDX. O objetivo deste estudo foi estimar a densidade numérica por área da população total de neurônios (QA[T]) e dos neurônios nitrérgicos (QA[N]); assim como a área de secção transversal média do corpo celular destes neurônios (A[T] e A[N]) do plexo mioentérico esofágico e a largura média das fibras estriadas (L) das camadas musculares. Foram utilizados 40 camundongos machos da linhagem C57BL/10 nas idades de 4 e 10 semanas, distribuídos entre grupos experimentais (MDX4 e MDX10), e controles (C4 e C10). As estimativas foram analisadas em preparados de membrana dos esôfagos, e técnicas histoquímicas de NADH-diaforase (NADH-d) e NADPH-diaforase (NADPH-d) foram utilizadas para evidenciar toda a população de neurônios e os neurônios nitrérgicos, respectivamente. Os resultados mostraram que a QA[T] foi significativamente maior no grupo MDX10 em relação ao C10 (p<0.05); enquanto a QA[N] foi menor no grupo MDX4 em relação ao C4 (p<0.05). A A[T] foi menor no grupo MDX10 em relação ao MDX4 e ao C10 (p<0.05); enquanto que para a A[N] não houve diferença significativa entre os grupos controle e experimental, e tampouco entre os grupos de 4 e de 10 semanas. A variável L foi maior nos grupos MDX4 e MDX10 em relação aos seus respectivos controles de mesma idade (p<0.05). Concluímos que no plexo mioentérico esofágico de camundongos MDX existe uma redução dos neurônios mediadores do relaxamento, especialmente em animais jovens (MDX4), provavelmente porque o organismo tenta manter íntegra a função peristáltica do órgão. Esse fato pode explicar a adaptação e ausência de disfunções esofágicas durante quase toda a vida desses animais

Duchenne Muscular Dystrophy (DMD) [...]. DMD is degenerative, progressive and a genetic X-linked disease. Besides the cardiomyopathy and the movement disorders, the patients have serious disfunctions in the alimentary system, characterized by motility disorders. However, it is known that such changes do not exist in MDX mice. The aim of this study was to estimate the neuronal numerical density/area of total (QA[T]) and nitregic neurons (QA[N]), the average cross-sectional area of total (A[T]) and nitregic (A[N]) neurons in myenteric plexus of the oesophagus and the average width of striped muscle of muscular layer (L). Forty C57BL/10 male mice were studied from four to ten weeks of age, divided into four groups: MDX mice formed the experimental groups (MDX4 and MDX10) and C57BL/10 male mice without the mutation formed the control groups (C4 and MDX10). Whole mounts preparations were obtained from the samples and histochemistry for NADH-diaphorase (NADH-d) and NADPH-diaphorase (NADPH-d) were used for morphometric evaluation. The results showed a significant increase of the QA[T] in the MDX10 than C10 (p<0.05), and a decrease of the QA[N] in MDX4 comparing to C4 (p<0.05). The A[T] decreased significantly in MDX10 comparing to both MDX4 and C10 (p<0.05), while no significant differences were observed among all the groups regarding the A[N]. The groups MDX4 and MDX10 showed a significant increase in L when compared to its controls at the same age (p<0.05). We conclude that in the myenteric plexus of the oesophagus in MDX mice there is a reduction of the inhibitory neurons, manly in the young animals (MDX4), probably to keep normal the peristaltic functions. Thus, it may explain the adaptation and the absence of oesophageal disfunction during almost the whole life in this animal model

Animal models for genetic neuromuscular diseases.

The neuromuscular disorders are a heterogeneous group of genetic diseases, caused by mutations in genes coding sarcolemmal, sarcomeric, and citosolic muscle proteins. Deficiencies or loss of function of these proteins leads to variable degree of progressive loss of motor ability. Several animal models, manifesting phenotypes observed in neuromuscular diseases, have been identified in nature or generated in laboratory. These models generally present physiological alterations observed in human patients and can be used as important tools for genetic, clinic, and histopathological studies. The mdx mouse is the most widely used animal model for Duchenne muscular dystrophy (DMD). Although it is a good genetic and biochemical model, presenting total deficiency of the protein dystrophin in the muscle, this mouse is not useful for clinical trials because of its very mild phenotype. The canine golden retriever MD model represents a more clinically similar model of DMD due to its larger size and significant muscle weakness. Autosomal recessive limb-girdle MD forms models include the SJL/J mice, which develop a spontaneous myopathy resulting from a mutation in the Dysferlin gene, being a model for LGMD2B. For the human sarcoglycanopahties (SG), the BIO14.6 hamster is the spontaneous animal model for delta-SG deficiency, whereas some canine models with deficiency of SG proteins have also been identified. More recently, using the homologous recombination technique in embryonic stem cell, several mouse models have been developed with null mutations in each one of the four SG genes. All sarcoglycan-null animals display a progressive muscular dystrophy of variable severity and share the property of a significant secondary reduction in the expression of the other members of the sarcoglycan subcomplex and other components of the Dystrophin-glycoprotein complex. Mouse models for congenital MD include the dy/dy (dystrophia-muscularis) mouse and the allelic mutant dy(2J)/dy(2J) mouse, both presenting significant reduction of alpha2-laminin in the muscle and a severe phenotype. The myodystrophy mouse (Large(myd)) harbors a mutation in the glycosyltransferase Large, which leads to altered glycosylation of alpha-DG, and also a severe phenotype. Other informative models for muscle proteins include the knockout mouse for myostatin, which demonstrated that this protein is a negative regulator of muscle growth. Additionally, the stress syndrome in pigs, caused by mutations in the porcine RYR1 gene, helped to localize the gene causing malignant hypertermia and Central Core myopathy in humans. The study of animal models for genetic diseases, in spite of the existence of differences in some phenotypes, can provide important clues to the understanding of the pathogenesis of these disorders and are also very valuable for testing strategies for therapeutic approaches.