RESUMEN
Angelman syndrome (AS) is a severe disorder of postnatal brain development caused by neuron-specific loss of the HECT (homologous to E6AP carboxy terminus) domain E3 ubiquitin ligase Ube3a/E6AP. The cellular role of Ube3a remains enigmatic despite recent descriptions of synaptic and behavioral deficits in AS mouse models. Although neuron-specific imprinting is thought to limit the disease to the brain, Ube3a is expressed ubiquitously, suggesting a broader role in cellular function. In the current study, we demonstrate a profound structural disruption and cisternal swelling of the Golgi apparatus (GA) in the cortex of AS (UBE3A(m-/p+)) mice. In Ube3a knockdown cell lines and UBE3A(m-/p+) cortical neurons, the GA is severely under-acidified, leading to osmotic swelling. Both in vitro and in vivo, the loss of Ube3a and corresponding elevated pH of the GA is associated with a marked reduction in protein sialylation, a process highly dependent on intralumenal Golgi pH. Altered ion homeostasis of the GA may provide a common cellular pathophysiology underlying the diverse plasticity and neurodevelopmental deficits associated with AS.
Asunto(s)
Corteza Cerebral/ultraestructura , Aparato de Golgi/genética , Aparato de Golgi/patología , Ácido N-Acetilneuramínico/metabolismo , Ubiquitina-Proteína Ligasas/metabolismo , Análisis de Varianza , Síndrome de Angelman/genética , Síndrome de Angelman/patología , Animales , Animales Recién Nacidos , Proteínas Bacterianas/genética , Células Cultivadas , Corteza Cerebral/citología , Estructuras Citoplasmáticas/genética , Estructuras Citoplasmáticas/metabolismo , Estructuras Citoplasmáticas/ultraestructura , Modelos Animales de Enfermedad , Embrión de Mamíferos , Femenino , Regulación de la Expresión Génica/genética , Regulación de la Expresión Génica/fisiología , Glicina/análogos & derivados , Aparato de Golgi/ultraestructura , Proteínas Fluorescentes Verdes/genética , Células HEK293 , Humanos , Concentración de Iones de Hidrógeno , Lectinas/metabolismo , Proteínas Luminiscentes/genética , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Microscopía Electrónica de Transmisión , Mutagénesis , Neuronas/metabolismo , Neuronas/ultraestructura , Transporte de Proteínas/genética , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/metabolismo , Espermina/análogos & derivados , Transfección , Ubiquitina-Proteína Ligasas/deficiencia , Proteína 2 de Membrana Asociada a Vesículas/genética , Proteína 2 de Membrana Asociada a Vesículas/metabolismo , Proteínas Virales/genética , Proteínas Virales/metabolismoRESUMEN
Experience-dependent maturation of neocortical circuits is required for normal sensory and cognitive abilities, which are distorted in neurodevelopmental disorders. We tested whether experience-dependent neocortical modifications require Ube3a, an E3 ubiquitin ligase whose dysregulation has been implicated in autism and Angelman syndrome. Using visual cortex as a model, we found that experience-dependent maturation of excitatory cortical circuits was severely impaired in Angelman syndrome model mice deficient in Ube3a. This developmental defect was associated with profound impairments in neocortical plasticity. Normal plasticity was preserved under conditions of sensory deprivation, but was rapidly lost by sensory experiences. The loss of neocortical plasticity is reversible, as late-onset visual deprivation restored normal synaptic plasticity. Furthermore, Ube3a-deficient mice lacked ocular dominance plasticity in vivo when challenged with monocular deprivation. We conclude that Ube3a is necessary for maintaining plasticity during experience-dependent neocortical development and suggest that the loss of neocortical plasticity contributes to deficits associated with Angelman syndrome.