ABSTRACT
Alzheimer disease is characterized by accumulation of ß-amyloid (Aß) and cognitive dysfunctions linked to early loss of cholinergic neurons. As estrogen-based hormone replacement therapy has beneficial effects on cognition of demented patients, and it may prevent memory impairments, we investigated the effect of estrogen-pretreatment on Aß-induced cholinergic neurodegeneration in the nucleus basalis magnocellularis (NBM). We tested which Aß species induces the more pronounced cholinotoxic effect in vivo. We injected different Aß assemblies in the NBM of mice, and measured cholinergic cell and cortical fiber loss. Spherical Aß oligomers had the most toxic effect. Pretreatment of ovariectomized mice with estrogen before Aß injection decreased cholinergic neuron loss and partly prevented fiber degeneration. By using proteomics, we searched for proteins involved in estrogen-mediated protection and in Aß toxicity 24 h following injection. The change in expression of, e.g., DJ-1, NADH ubiquinone oxidoreductase, ATP synthase, phosphatidylethanolamine-binding protein 1, protein phosphatase 2A and dimethylarginine dimethylaminohydrolase 1 support our hypothesis that Aß induces mitochondrial dysfunction, decreases MAPK signaling, and increases NOS activation in NBM. On the other hand, altered expression of, e.g., MAP kinase kinase 1 and 2, protein phosphatase 1 and 2A by Aß might increase MAPK suppression and NOS signaling in the cortical target area. Estrogen pretreatment reversed most of the changes in the proteome in both areas. Our experiments suggest that regulation of the MAPK pathway, mitochondrial pH and NO production may all contribute to Aß toxicity, and their regulation can be prevented partly by estrogen pretreatment.
Subject(s)
Amyloid beta-Peptides/toxicity , Basal Nucleus of Meynert/drug effects , Cell Death/drug effects , Cholinergic Fibers/drug effects , Estradiol/pharmacology , Neuroprotective Agents/pharmacology , Amyloid beta-Peptides/administration & dosage , Amyloid beta-Peptides/chemistry , Animals , Basal Nucleus of Meynert/pathology , Cholinergic Fibers/pathology , Female , Mice , Mice, Inbred C57BL , Microinjections , Particle Size , Proteomics/methods , Signal Transduction/drug effectsABSTRACT
Estrogen (E2) influences brain function to induce gender differences in neuronal processes. In contrast to its well-described effects on signaling systems and gene transcription factors, our knowledge of E2-regulated protein networks is rather limited. Thus, we examined changes in protein expression patterns in the whole brains of ovariectomized mice after 24h estrogen exposure using two-dimensional differential gel electrophoresis. Interpretation of our network-based hypothesis suggested that E2 regulates synaptic proteins and processes, increases cytoskeletal flexibility and alters glucose consumption in the brain. We verified the predicted reduced basal synaptic activity using in vivo microdialysis in conscious mice, showing that E2 decreases the extracellular concentrations of certain amino acids in two different brain areas (in the striatum and in the hypothalamus) and that this is independent from the E2 receptor densities. Our data reveal that E2 induces minor, but substantial changes to functionally different protein networks at the whole brain level, and as a cumulative effect, it adjusts the brain steady-state condition to a more flexible state.
