RESUMEN
Inclusion body myopathy with Paget's disease of bone and frontotemporal dementia (IBMPFD) is caused by mutations in Valosin-containing protein (VCP), a hexameric AAA ATPase that participates in a variety of cellular processes such as protein degradation, organelle biogenesis, and cell-cycle regulation. To understand how VCP mutations cause IBMPFD, we have established a Drosophila model by overexpressing TER94 (the sole Drosophila VCP ortholog) carrying mutations analogous to those implicated in IBMPFD. Expression of these TER94 mutants in muscle and nervous systems causes tissue degeneration, recapitulating the pathogenic phenotypes in IBMPFD patients. TER94-induced neurodegenerative defects are enhanced by elevated expression of wild-type TER94, suggesting that the pathogenic alleles are dominant active mutations. This conclusion is further supported by the observation that TER94-induced neurodegenerative defects require the formation of hexamer complex, a prerequisite for a functional AAA ATPase. Surprisingly, while disruptions of the ubiquitin-proteasome system (UPS) and the ER-associated degradation (ERAD) have been implicated as causes for VCP-induced tissue degeneration, these processes are not significantly affected in our fly model. Instead, the neurodegenerative defect of TER94 mutants seems sensitive to the level of cellular ATP. We show that increasing cellular ATP by independent mechanisms could suppress the phenotypes of TER94 mutants. Conversely, decreasing cellular ATP would enhance the TER94 mutant phenotypes. Taken together, our analyses have defined the nature of IBMPFD-causing VCP mutations and made an unexpected link between cellular ATP level and IBMPFD pathogenesis.
Asunto(s)
Adenosina Trifosfato/metabolismo , Proteínas de Ciclo Celular/genética , Modelos Animales de Enfermedad , Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Demencia Frontotemporal/genética , Miositis por Cuerpos de Inclusión/genética , Osteítis Deformante/genética , Adenosina Trifosfatasas/genética , Adenosina Trifosfato/genética , Alelos , Animales , Proteínas de Ciclo Celular/metabolismo , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Demencia Frontotemporal/metabolismo , Humanos , Mutación , Miositis por Cuerpos de Inclusión/metabolismo , Osteítis Deformante/metabolismo , Ubiquitina/metabolismo , Proteína que Contiene ValosinaRESUMEN
The muscleblind-like (MBNL) proteins are tissue-specific alternative splicing regulators. Dysfunction of MBNL has been implicated in the pathogenesis of expanded CUG repeats-associated myotonic dystrophy (DM). In this study, we describe the identification and functional characterization of a Caenorhabditis elegans muscleblind (CeMbl) gene. CeMbl is a single gene alternatively spliced to generate two isoforms (CeMBL-A and CeMBL-B). It displays a high homology with human MBNL1 in the C3H1 zinc finger domains. CeMbl transcripts are detected in larval and adult stages. However, inactivation of CeMbl by RNA-mediated interference results in muscle phenotype only at adulthood. Immunofluorescence staining using anti-vinculin antibody reveals that the organization of dense body is disrupted in affected worms. Our results demonstrate a growth-dependent requirement of CeMbl on muscle structure and function. They also provide a possible molecular basis for the developmentally regulated toxicity of expanded CUG repeats.