RESUMO
Duchenne muscular dystrophy (DMD) and other types of muscular dystrophies are caused by the loss or alteration of different members of the dystrophin protein complex. Understanding the molecular mechanisms by which dystrophin-associated protein abnormalities contribute to the onset of muscular dystrophy may identify new therapeutic approaches to these human disorders. By examining gene expression alterations in mouse skeletal muscle lacking alpha-dystrobrevin (Dtna(-/-)), we identified a highly significant reduction of the cholesterol trafficking protein, Niemann-Pick C1 (NPC1). Mutations in NPC1 cause a progressive neurodegenerative, lysosomal storage disorder. Transgenic expression of NPC1 in skeletal muscle ameliorates muscular dystrophy in the Dtna(-/-) mouse (which has a relatively mild dystrophic phenotype) and in the mdx mouse, a model for DMD. These results identify a new compensatory gene for muscular dystrophy and reveal a potential new therapeutic target for DMD.
Assuntos
Distrofia Muscular de Duchenne , Proteínas , Transgenes , Animais , Modelos Animais de Doenças , Distrofina/genética , Distrofina/metabolismo , Proteínas Associadas à Distrofina/genética , Proteínas Associadas à Distrofina/metabolismo , Perfilação da Expressão Gênica , Regulação da Expressão Gênica , Humanos , Peptídeos e Proteínas de Sinalização Intracelular , Lisossomos/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos mdx , Camundongos Transgênicos , Músculo Esquelético/citologia , Músculo Esquelético/patologia , Músculo Esquelético/fisiologia , Distrofia Muscular de Duchenne/genética , Distrofia Muscular de Duchenne/metabolismo , Proteína C1 de Niemann-Pick , Análise de Sequência com Séries de Oligonucleotídeos , Fenótipo , Proteínas/genética , Proteínas/metabolismoRESUMO
alpha-Dystrobrevin associates with and is a homologue of dystrophin, the protein linked to Duchenne and Becker muscular dystrophies. We used a transgenic approach to restore alpha-dystrobrevin to the sarcolemma in mice that lack dystrophin (mdx mice) to study two interrelated functions: (1) the ability of alpha-dystrobrevin to rescue components of the dystrophin complex in the absence of dystrophin and (2) the ability of sarcolemmal alpha-dystrobrevin to ameliorate the dystrophic phenotype. We generated transgenic mice expressing alpha-dystrobrevin-2a linked to a palmitoylation signal sequence and bred them onto the alpha-dystrobrevin-null and mdx backgrounds. Expression of palmitoylated alpha-dystrobrevin prevented the muscular dystrophy observed in the alpha-dystrobrevin-null mice, demonstrating that the altered form of alpha-dystrobrevin was functional. On the mdx background, the palmitoylated form of alpha-dystrobrevin was expressed on the sarcolemma but did not significantly ameliorate the muscular dystrophy phenotype. Palmitoylated dystrobrevin restored alpha-syntrophin and aquaporin-4 (AQP4) to the mdx sarcolemma but was unable to recruit beta-dystroglycan or the sarcoglycans. Despite restoration of sarcolemmal alpha-syntrophin, neuronal nitric oxide synthase (nNOS) was not localized to the sarcolemma, suggesting that nNOS requires both dystrophin and alpha-syntrophin for correct localization. Thus, although nNOS and AQP4 both require interaction with the PDZ domain of alpha-syntrophin for sarcolemmal association, their localization is regulated differentially.
