ABSTRACT
Angelman syndrome (AS) is a disorder of human cognition characterized by severe mental retardation and epilepsy. Recently, a mouse model for AS (Ube3a maternal null mutation) was developed that displays deficits in both context-dependent learning and hippocampal long-term potentiation (LTP). In the present studies, we examined the molecular basis for these LTP and learning deficits. Mutant animals exhibited a significant increase in hippocampal phospho-calcium/calmodulin-dependent protein kinase II (CaMKII), specifically at sites Thr(286) and Thr(305), with no corresponding change in the levels of total CaMKII. In addition, mutants show a reduction in CaMKII activity, autophosphorylation capability, and total CaMKII associated with postsynaptic density. These findings are the first to implicate misregulation of CaMKII as a molecular cause for the neurobehavioral deficits in a human learning disorder.
Subject(s)
Angelman Syndrome/enzymology , Calcium-Calmodulin-Dependent Protein Kinases/metabolism , Hippocampus/enzymology , Intellectual Disability/enzymology , Angelman Syndrome/etiology , Angelman Syndrome/physiopathology , Animals , Calcium-Calmodulin-Dependent Protein Kinase Type 2 , Calcium-Calmodulin-Dependent Protein Kinases/chemistry , Calcium-Calmodulin-Dependent Protein Kinases/immunology , Cells, Cultured , Hippocampus/physiology , Immunohistochemistry , Intellectual Disability/etiology , Intellectual Disability/physiopathology , Ligases/genetics , Long-Term Potentiation , Mice , Mutation , Phosphoprotein Phosphatases/metabolism , Phosphorylation , Protein Kinases/metabolism , Synapses/enzymology , Threonine/metabolism , Ubiquitin-Protein LigasesABSTRACT
Two apolipoprotein E (apoE) receptors, the very low density lipoprotein (VLDL) receptor and apoE receptor 2 (apoER2), are also receptors for Reelin, a signaling protein that regulates neuronal migration during brain development. In the adult brain, Reelin is expressed by GABA-ergic interneurons, suggesting a potential function as a modulator of neurotransmission. ApoE receptors have been indirectly implicated in memory and neurodegenerative disorders because their ligand, apoE, is genetically associated with Alzheimer disease. We have used knockout mice to investigate the role of Reelin and its receptors in cognition and synaptic plasticity. Mice lacking either the VLDL receptor or the apoER2 show contextual fear conditioning deficits. VLDL receptor-deficient mice also have a moderate defect in long term potentiation (LTP), and apoER2 knockouts have a pronounced one. The perfusion of mouse hippocampal slices with Reelin has no effect on baseline synaptic transmission but significantly enhances LTP in area CA1. This Reelin-dependent augmentation of LTP is abolished in VLDL receptor and apoER2 knockout mice. Our results reveal a role for Reelin in controlling synaptic plasticity in the adult brain and suggest that both of its receptors are necessary for Reelin-dependent enhancement of synaptic transmission in the hippocampus. Thus, the impairment of apoE receptor-dependent neuromodulation may contribute to cognitive impairment and synaptic loss in Alzheimer disease.
