RESUMO
Congenital myasthenia (CM) is a devastating neuromuscular disease, and mutations in DOK7, an adaptor protein that is crucial for forming and maintaining neuromuscular synapses, are a major cause of CM1,2. The most common disease-causing mutation (DOK71124_1127 dup) truncates DOK7 and leads to the loss of two tyrosine residues that are phosphorylated and recruit CRK proteins, which are important for anchoring acetylcholine receptors at synapses. Here we describe a mouse model of this common form of CM (Dok7CM mice) and a mouse with point mutations in the two tyrosine residues (Dok72YF). We show that Dok7CM mice had severe deficits in neuromuscular synapse formation that caused neonatal lethality. Unexpectedly, these deficits were due to a severe deficiency in phosphorylation and activation of muscle-specific kinase (MUSK) rather than a deficiency in DOK7 tyrosine phosphorylation. We developed agonist antibodies against MUSK and show that these antibodies restored neuromuscular synapse formation and prevented neonatal lethality and late-onset disease in Dok7CM mice. These findings identify an unexpected cause for disease and a potential therapy for both DOK7 CM and other forms of CM caused by mutations in AGRIN, LRP4 or MUSK, and illustrate the potential of targeted therapy to rescue congenital lethality.
Assuntos
Proteínas Musculares/genética , Mutação , Síndromes Miastênicas Congênitas/tratamento farmacológico , Síndromes Miastênicas Congênitas/genética , Envelhecimento , Agrina/genética , Agrina/metabolismo , Animais , Animais Recém-Nascidos , Anticorpos/imunologia , Modelos Animais de Doenças , Feminino , Proteínas Relacionadas a Receptor de LDL/genética , Proteínas Relacionadas a Receptor de LDL/metabolismo , Masculino , Camundongos , Terapia de Alvo Molecular , Fibras Musculares Esqueléticas/química , Fibras Musculares Esqueléticas/metabolismo , Proteínas Musculares/química , Proteínas Musculares/metabolismo , Síndromes Miastênicas Congênitas/imunologia , Fosforilação , Fosfotirosina/genética , Fosfotirosina/metabolismo , Proteínas Proto-Oncogênicas c-crk/metabolismo , Receptores Proteína Tirosina Quinases/agonistas , Receptores Proteína Tirosina Quinases/genética , Receptores Proteína Tirosina Quinases/imunologia , Receptores Proteína Tirosina Quinases/metabolismo , Recidiva , Sinapses/metabolismoRESUMO
TGR5 is a G protein-coupled receptor expressed in brown adipose tissue and muscle, where its activation by bile acids triggers an increase in energy expenditure and attenuates diet-induced obesity. Using a combination of pharmacological and genetic gain- and loss-of-function studies in vivo, we show here that TGR5 signaling induces intestinal glucagon-like peptide-1 (GLP-1) release, leading to improved liver and pancreatic function and enhanced glucose tolerance in obese mice. In addition, we show that the induction of GLP-1 release in enteroendocrine cells by 6alpha-ethyl-23(S)-methyl-cholic acid (EMCA, INT-777), a specific TGR5 agonist, is linked to an increase of the intracellular ATP/ADP ratio and a subsequent rise in intracellular calcium mobilization. Altogether, these data show that the TGR5 signaling pathway is critical in regulating intestinal GLP-1 secretion in vivo, and suggest that pharmacological targeting of TGR5 may constitute a promising incretin-based strategy for the treatment of diabesity and associated metabolic disorders.