N-Acetylcysteine Reduces Skeletal Muscles Oxidative Stress and Improves Grip Strength in Dysferlin-Deficient Bla/J Mice.

Dysferlinopathy is an autosomal recessive muscular dystrophy resulting from mutations in the dysferlin gene. Absence of dysferlin in the sarcolemma and progressive muscle wasting are hallmarks of this disease. Signs of oxidative stress have been observed in skeletal muscles of dysferlinopathy patients, as well as in dysferlin-deficient mice. However, the contribution of the redox imbalance to this pathology and the efficacy of antioxidant therapy remain unclear. Here, we evaluated the effect of 10 weeks diet supplementation with the antioxidant agent N-acetylcysteine (NAC, 1%) on measurements of oxidative damage, antioxidant enzymes, grip strength and body mass in 6 months-old dysferlin-deficient Bla/J mice and wild-type (WT) C57 BL/6 mice. We found that quadriceps and gastrocnemius muscles of Bla/J mice exhibit high levels of lipid peroxidation, protein carbonyls and superoxide dismutase and catalase activities, which were significantly reduced by NAC supplementation. By using the Kondziela's inverted screen test, we further demonstrated that NAC improved grip strength in dysferlin deficient animals, as compared with non-treated Bla/J mice, without affecting body mass. Together, these results indicate that this antioxidant agent improves skeletal muscle oxidative balance, as well as muscle strength and/or resistance to fatigue in dysferlin-deficient animals.

Endosomal abnormalities related to amyloid precursor protein in cholesterol treated cerebral cortex neuronal cells derived from trisomy 16 mice, an animal model of Down syndrome.

The CNh and CTb cell lines are derived from the cerebral cortex of normal and trisomy 16 mice, an animal model of human trisomy 21, Down syndrome (DS), and represent in vitro models to study cellular events associated with the human condition. Amyloid precursor protein (APP) plays an important role in the development of neuropathology associated with DS and cholesterol in the amyloidogenic processing of APP. There is also increasing evidence of alterations in the recycling pathway of the early endosome compartment in nervous tissue from DS. In the present study, we report endosomal abnormalities related to amyloid precursor protein in cholesterol-treated CTb cells. Colocalization studies revealed the presence of APP-derived products in early endosomal compartments in both cell lines. Using internalization and immunoprecipitation techniques, differential effects were observed between the normal and trisomic cell lines when treated with cholesterol. Internalization experiments showed that the CTb cell line accumulates internalized APP in intracellular compartments for longer periods of time when compared to the CNh cell line. Immunoprecipitation revealed a differential interaction between the trafficking-related protein Rab4 and APP in the neuronal cell lines CNh and CTb. The present study suggests a putative mechanism by which overexpressed APP accumulates in intracellular compartments related to the endosomal trafficking pathway in individuals with DS, and highlights the usefulness of the CTb cell line as a model to study altered APP metabolism related to this genetic condition.

Presynaptic DLG regulates synaptic function through the localization of voltage-activated Ca(2+) Channels.

The DLG-MAGUK subfamily of proteins plays a role on the recycling and clustering of glutamate receptors (GLUR) at the postsynaptic density. discs-large1 (dlg) is the only DLG-MAGUK gene in Drosophila and originates two main products, DLGA and DLGS97 which differ by the presence of an L27 domain. Combining electrophysiology, immunostaining and genetic manipulation at the pre and postsynaptic compartments we study the DLG contribution to the basal synaptic-function at the Drosophila larval neuromuscular junction. Our results reveal a specific function of DLGS97 in the regulation of the size of GLUR fields and their subunit composition. Strikingly the absence of any of DLG proteins at the presynaptic terminal disrupts the clustering and localization of the calcium channel DmCa1A subunit (Cacophony), decreases the action potential-evoked release probability and alters short-term plasticity. Our results show for the first time a crucial role of DLG proteins in the presynaptic function in vivo.

Role of the MAGUK protein family in synapse formation and function.

Synaptic function is crucially dependent on the spatial organization of the presynaptic and postsynaptic apparatuses and the juxtaposition of both membrane compartments. This precise arrangement is achieved by a protein network at the submembrane region of each cell that is built around scaffold proteins. The membrane-associated guanylate kinase (MAGUK) family of proteins is a widely expressed and well-conserved group of proteins that plays an essential role in the formation and regulation of this scaffolding. Here, we review general features of this protein family, focusing on the discs large and calcium/calmodulin-dependent serine protein kinase subfamilies of MAGUKs in the formation, function, and plasticity of synapses.