Richard O'Brien

Characterization of Multiple Phosphorylation Sites on the AMPA Receptor GluR1 Subunit

We have characterized the phosphorylation of the glutamate receptor subunit GluR1, using biochemical and electrophysiological techniques. GluR1 is phosphorylated on multiple sites that are all located on the C-terminus of the protein. Cyclic AMP-dependent protein kinase specifically phosphorylates SER-845 of GluR1 in transfected HEK cells and in neurons in culture. Phosphorylation of this residue results in a 40% potentiation of the peak current through GluR1 homomeric channels. In addition, protein kinase C specifically phosphorylates Ser-831 of GluR1 in HEK-293 cells and in cultured neurons. These results are consistent with the recently proposed transmembrane topology models of glutamate receptors, in which the C-terminus is intracellular. In addition, the modulation of GluR1 by PKA phosphorylation of Ser-845 suggests that phosphorylation of this residue may underlie the PKA-induced potentiation of AMPA receptors in neurons.

Amyloid Precursor Protein Processing and Alzheimer's Disease

Alzheimers disease (AD), the leading cause of dementia worldwide, is characterized by the accumulation of the β-amyloid peptide (Aβ) within the brain along with hyperphosphorylated and cleaved forms of the microtubule-associated protein tau. Genetic, biochemical, and behavioral research suggest that physiologic generation of the neurotoxic Aβ peptide from sequential amyloid precursor protein (APP) proteolysis is the crucial step in the development of AD. APP is a single-pass transmembrane protein expressed at high levels in the brain and metabolized in a rapid and highly complex fashion by a series of sequential proteases, including the intramembranous γ-secretase complex, which also process other key regulatory molecules. Why Aβ accumulates in the brains of elderly individuals is unclear but could relate to changes in APP metabolism or Aβ elimination. Lessons learned from biochemical and genetic studies of APP processing will be crucial to the development of therapeutic targets to treat AD.

Regulation of morphological postsynaptic silent synapses in developing hippocampal neurons.

Many excitatory synapses are thought to be postsynaptically silent, possessing functional NMDA but lacking functional AMPA glutamate receptors. The acquisition of AMPA receptors at silent synapses may be important in synaptic plasticity and neuronal development. Here we characterize a possible morphological correlate of silent synapses in cultured hippocampal neurons. Initially, most excitatory synapses contained NMDA receptors, but only a few contained detectable AMPA receptors. Synapses progressively acquired AMPA receptors as the cultures matured. AMPA receptor blockade increased the number, size and fluorescent intensity of AMPA receptor clusters and rapidly induced the appearance of AMPA receptors at silent synapses. In contrast, NMDA receptor blockade increased the size, intensity and number of NMDA receptor clusters and decreased the number of AMPA receptor clusters, resulting in an increase in the proportion of silent synapses. These results suggest that the number of silent synapses is regulated during development and by changes in synaptic activity.

Molecular mechanisms of glutamate receptor clustering at excitatory synapses

The targeting of AMPA- and NMDA-type glutamate receptors to synapses in the central nervous system is essential for efficient excitatory synaptic transmission. Recent studies have indicated that protein-protein interactions of these receptors with synaptic proteins that contain PDZ domains are crucial for receptor targeting. NMDA receptors have been found to bind to the PSD-95 family of proteins, whereas AMPA receptors interact with the PDZ-domain-containing protein GRIP (glutamate receptor interacting protein). PSD-95 and GRIP contain multiple PDZ domains as well as other protein-protein interaction motifs that help to form large macromolecular complexes that may be important for the formation and plasticity of synapses.

The Alzheimer's Association external quality control program for cerebrospinal fluid biomarkers.

The cerebrospinal fluid (CSF) biomarkers amyloid β (Aβ)‐42, total‐tau (T‐tau), and phosphorylated‐tau (P‐tau) demonstrate good diagnostic accuracy for Alzheimers disease (AD). However, there are large variations in biomarker measurements between studies, and between and within laboratories. The Alzheimers Association has initiated a global quality control program to estimate and monitor variability of measurements, quantify batch‐to‐batch assay variations, and identify sources of variability. In this article, we present the results from the first two rounds of the program.

Mycophenolate mofetil: A safe and promising immunosuppressant in neuromuscular diseases

The authors report the use mycophenolate mofetil (MM) in the treatment of neuromuscular diseases. Thirty-eight patients (32 with MG, three with inflammatory myopathy, and three with chronic acquired demyelinating neuropathy) were treated with MM for an average duration of 12 months. All patients tolerated MM without major side effects. Twenty-four patients improved either in their functional status or in their ability to reduce corticosteroid dose. Mean time to improvement was 5 months.

Narp and NP1 form heterocomplexes that function in developmental and activity-dependent synaptic plasticity

Narp is a neuronal immediate early gene that plays a role in excitatory synaptogenesis. Here, we report that native Narp in brain is part of a pentraxin complex that includes NP1. These proteins are covalently linked by disulfide bonds into highly organized complexes, and their relative ratio in the complex is dynamically dependent upon the neurons activity history and developmental stage. Complex formation is dependent on their distinct N-terminal coiled-coil domains, while their closely homologous C-terminal pentraxin domains mediate association with AMPA-type glutamate receptors. Narp is substantially more effective in assays of cell surface cluster formation, coclustering of AMPA receptors, and excitatory synaptogenesis, yet their combined expression results in supraadditive effects. These studies support a model in which Narp can regulate the latent synaptogenic activity of NP1 by forming mixed pentraxin assemblies. This mechanism appears to contribute to both activity-independent and activity-dependent excitatory synaptogenesis.

Effect of Infarcts on Dementia in the Baltimore Longitudinal Study of Aging

To define the magnitude and mechanism of the effect of brain infarcts on the odds of dementia in a prospective study.

Atherosclerosis, dementia, and Alzheimer disease in the Baltimore Longitudinal Study of Aging cohort.

Although it is now accepted that asymptomatic cerebral infarcts are an important cause of dementia in the elderly, the relationship between atherosclerosis per se and dementia is controversial. Specifically, it is unclear whether atherosclerosis can cause the neuritic plaques and neurofibrillary tangles that define Alzheimer neuropathology and whether atherosclerosis, a potentially reversible risk factor, can influence cognition independent of brain infarcts.

Impact of Alzheimer's pathology on cognitive trajectories in nondemented elderly

Some individuals who are asymptomatic for dementia while alive have substantial Alzheimers disease (AD) neuropathology at autopsy. We investigated whether cognitive trajectories differ between clinically normal elderly individuals with and without AD neuropathology and how they compare with trajectories of clinically impaired individuals before dementia diagnosis.