ABSTRACT
Recent experimental data in mice have shown that the inwardly rectifying K channel Kir4.1 mediates K spatial buffering in the hippocampus. Here we used immunohistochemistry to examine the distribution of Kir4.1 in hippocampi from patients with medication-refractory temporal lobe epilepsy. The selectivity of the antibody was confirmed in mice with a glial conditional deletion of the gene encoding Kir4.1. These mice showed a complete loss of labeled cells, indicating that Kir4.1 is restricted to glia. In human cases, Kir4.1 immunoreactivity observed in cells morphologically consistent with astrocytes was significantly reduced in 12 patients with hippocampal sclerosis versus 11 patients without sclerosis and 4 normal autopsy controls. Loss of astrocytic Kir4.1 immunoreactivity was most pronounced around vessels and was restricted to gliotic areas. Loss of Kir4.1 expression was associated with loss of dystrophin and α-syntrophin, but not with loss of ß-dystroglycan, suggesting partial disruption of the dystrophin-associated protein complex. The changes identified in patients with hippocampal sclerosis likely interfere with K homeostasis and may contribute to the epileptogenicity of the sclerotic hippocampus.
Subject(s)
Epilepsy, Temporal Lobe/pathology , Gene Expression Regulation/physiology , Hippocampus/metabolism , Potassium Channels, Inwardly Rectifying/metabolism , Sclerosis/etiology , Adolescent , Adult , Age Factors , Animals , Animals, Newborn , Calcium-Binding Proteins/metabolism , Child , Dystroglycans/metabolism , Dystrophin/metabolism , Epilepsy, Temporal Lobe/complications , Female , Hippocampus/pathology , Humans , Male , Membrane Proteins/metabolism , Mice , Mice, Knockout , Middle Aged , Muscle Proteins/metabolism , Neuroglia/metabolism , Sclerosis/pathology , Young AdultABSTRACT
Alterations of learning and memory in mice with deregulated neuron-specific nuclear factor κB (NF-κB) activity support the idea that plastic changes of synaptic contacts may depend at least in part on IκB kinase (IKK)/NF-κB-related synapse-to-nucleus signaling. There is, however, little information on the molecular requirements and mechanisms regulating this IKK/NF-κB-dependent synapse development and remodeling. Here, we report that the NF-κB inducing IKK kinase complex is localized at the postsynaptic density (PSD) and activated under basal conditions in the adult mouse brain. Using different models of conditional genetic inactivation of IKK2 function in mouse principal neurons, we show that IKK/NF-κB signaling is critically involved in synapse formation and spine maturation in the adult brain. IKK/NF-κB blockade in the forebrain of mutant animals is associated with reduced levels of mature spines and postsynaptic proteins PSD95, SAP97, GluA1, AMPAR-mediated basal synaptic transmission and a spatial learning impairment. Synaptic deficits can be restored in adult animals within 1 week by IKK/NF-κB reactivation, indicating a highly dynamic IKK/NF-κB-dependent regulation process. We further identified the insulin-like growth factor 2 gene (Igf2) as a novel IKK/NF-κB target. Exogenous Igf2 was able to restore synapse density and promoted spine maturation in IKK/NF-κB signaling-deficient neurons within 24 h. This process depends on Igf2/Igf2R-mediated MEK/ERK activation. Our findings illustrate a fundamental role of IKK/NF-κB-Igf2-Igf2R signaling in synapse formation and maturation in adult mice, thus providing an intriguing link between the molecular actions of IKK/NF-κB in neurons and the memory enhancement factor Igf2.