pituitrin and monodansylcadaverine

Mutations in the human gene encoding the antidiuretic hormone vasopressin (VP) cause autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI), a rare inherited disorder that presents as polydipsia and polyuria as a consequence of a loss of secretion of VP from posterior pituitary nerve terminals. Work from our laboratories has shown that adFNDI, like other neurodegenerative diseases such as Alzheimer's, Parkinson's and Huntington's, is associated with autophagy. We have recently shown that the activation of autophagy in mouse neuroblastoma Neuro2a cells after adenoviral vector-mediated delivery of an adFNDI mutant VP transgene (Cys67stop) is a cell survival mechanism; its inhibition induces apoptosis. We now show that expression of Cys67stop sensitizes Neuro2a cells to the lethal effects of dopamine. This mode of cell death exhibits features typically associated with classical apoptosis. Yet inhibition of autophagy reversed these effects and rescued cell viability. We propose that autophagy-mediated cell death is a "two-hit" process: Following the cellular stress of the accumulation of a misfolded mutant protein, autophagy is prosurvival. However, a second insult triggers an autophagy-dependent apoptosis.

Topics: Adenoviridae; Animals; Autophagy; Cadaverine; Caspases; Cell Death; Cell Line, Tumor; Cell Survival; Codon, Terminator; Cysteine; Diabetes Insipidus, Neurogenic; Disease Models, Animal; Dopamine; Fluorescent Dyes; Gene Expression; Genetic Vectors; Mice; Mutation; Neuroblastoma; Phagosomes; Transfection; Transgenes; Vacuoles; Vasopressins

Autosomal dominant familial neurohypophyseal diabetes insipidus (adFNDI) is a progressive, inherited neurodegenerative disorder that presents as polydipsia and polyuria as a consequence of a loss of secretion of the antidiuretic hormone vasopressin (VP) from posterior pituitary nerve terminals. VP gene mutations cause adFNDI. Rats expressing an adFNDI VP transgene (Cys67stop) show a neuronal pathology characterized by autophagic structures in the cell body. adFNDI has thus been added to the list of protein aggregation diseases, along with Alzheimer's, Parkinson's and Huntington's, which are associated with autophagy, a bulk process that delivers regions of cytosol to lysosomes for degradation. However, the role of autophagy in these diseases is unclear. To address the relationships between mutant protein accumulation, autophagy, cell survival, and cell death, we have developed a novel and tractable in vitro system. We have constructed adenoviral vectors (Ads) that express structural genes encoding either the Cys67stop mutant protein (Ad-VCAT-Cys67stop) or an epitope-tagged wild-type VP precursor (Ad-VCAT). After infection of mouse neuroblastoma Neuro2a cells, Ad-VCAT encoded material enters neurite processes and accumulates in terminals, while the Cys67stop protein is confined to enlarged vesicles in the cell body. Similar to the intracellular derangements seen in the Cys67stop rats, these structures are of ER origin, and colocalize with markers of autophagy. Neither Ad-VCAT-Cys67stop nor Ad-VCAT expression affected cell viability. However, inhibition of autophagy or lysosomal protein degradation, while having no effect on Ad-VCAT-expressing cells, significantly increased apoptotic cell death following Ad-VCAT-Cys67stop expression. These data suggest that activation of autophagy by the stress of the expression of an adFNDI mutant protein is a prosurvival mechanism.

Topics: Acridine Orange; Adenoviridae; Animals; Animals, Genetically Modified; Autophagy; Blotting, Western; Cadaverine; Cathepsin D; Cell Line, Tumor; Codon, Terminator; Cysteine; Diabetes Insipidus, Neurogenic; Fluorescent Antibody Technique; Fluorescent Dyes; Gene Expression; Genetic Vectors; Hydrogen-Ion Concentration; Lysosomes; Mutation; Neurites; Neuroblastoma; Neurons; Organelles; Rats; Recombinant Proteins; Transfection; Transgenes; Vacuoles; Vasopressins