The phosphatase Pten negatively regulates PI3K/Akt/mTOR signaling, a pathway critical for cell growth and protein synthesis. Germline PTEN mutations are implicated in seizure and autism, suggesting that alterations in PTEN affect neuronal function and development. Several brain-specific conditional Pten knockout (KO) mice exhibit enlarged brains, neuronal hypertrophy and increased seizure susceptibility, which may be indicative of altered glutamate receptor function. mTOR inhibition can suppress seizure activity observed in these Pten mutant models, revealing the importance of mTOR signaling in Pten-dependent phenotypes. To better understand how Pten may regulate neuronal excitability, ionotropic glutamate receptor expression was examined in NEX-Pten homozygous KO mice, which lack Pten in nearly all forebrain excitatory neurons. Biochemical analyses revealed alterations in select NMDA and AMPA receptor subunit protein levels in the forebrains of newly born NEX-Pten KO mice, suggesting developmental loss of Pten can affect synaptic proteins important for neurotransmission. Similarly, initial analysis of CaMKIIα-Pten KO mice indicated postnatal loss of Pten in excitatory neurons may also alter NMDA receptor subunits in the cortex, but not the hippocampus, underscoring the importance of Pten for proper synaptic protein expression. To further characterize the effects of Pten deletion on glutamate receptor subunit expression, dissociated cortical neuronal cultures were used to evaluate how chronic Pten deficiency alters glutamate receptors over time. NMDA receptor abnormalities were modest and transient, indicating that alterations in glutamate receptor subunits may normalize due to homeostatic mechanisms. Further, pharmacological inhibition of PI3K reduced select NMDA receptor subunits in dissociated cortical cultures. Together, these data suggest that in vivo activation of PI3K through loss of Pten leads to selective increases in NMDA receptor subunits in cortical neurons, but not hippocampal neurons, since no alterations were detected in this region. Additional studies with rapamycin and second generation mTOR inhibitors are required to determine how mTOR function contributes to the glutamate receptor phenotype. The NEX-Pten model demonstrates that Pten may be crucial in controlling neuronal excitability at the synapse. Dysregulation of these functions may underlie some of the phenotypes associated with PTEN mutations in the human population.Ph. D.Includes bibliographical referencesby Tatiana Maria Kazdoba-Leac
