Currently, the major drug discovery paradigm for neurodegenerative diseases is based upon high affinity ligands for single disease-specific targets. For Alzheimer's disease (AD), the focus is the amyloid beta peptide (Aß) that mediates familial Alzheimer's disease pathology. However, given that age is the greatest risk factor for AD, we explored an alternative drug discovery scheme that is based upon efficacy in multiple cell culture models of age-associated pathologies rather than exclusively amyloid metabolism. Using this approach, we identified an exceptionally potent, orally active, neurotrophic molecule that facilitates memory in normal rodents, and prevents the loss of synaptic proteins and cognitive decline in a transgenic AD mouse model.

Glial fibrillary acidic protein (GFAP) is the main astroglial marker during astrogliogenesis, but it is also expressed in other cell types, including neural stem cells and old neurons. Activation of the JAK/STAT pathway by the IL-6 family of cytokines is the canonical pathway regulating GFAP expression, whereas retinoic acid is thought to be the only inducer of GFAP to operate independently of this pathway. Here, we show that retinoic acid receptor α not only links retinoic acid signaling to the canonical cytokine-stimulated pathway leading to GFAP expression but that it also plays a key role in the synergistic actions of retinoic acid and cytokines on this pathway. Cytokines both potentiate retinoic acid receptor α expression and enhance its binding to DNA and to the Stat3-p300/CBP-Smad transcriptional complex, the cornerstone of the canonical pathway. PI3K is upstream to all the key events leading to the expression of GFAP. Our results give new insights about the role of retinoic acid signaling in GFAP expression.

Axonal dysfunction is the major phenotypic change in many neurodegenerative diseases, but the processes underlying this impairment are not clear. Modifier of cell adhesion (MOCA) is a presenilin binding protein that functions as a guanine nucleotide exchange factor for Rac1. The loss of MOCA in mice leads to axonal degeneration and causes sensorimotor impairments by decreasing cofilin phosphorylation and altering its upstream signaling partners LIM kinase and p21-activated kinase, an enzyme directly downstream of Rac1. The dystrophic axons found in MOCA-deficient mice are associated with abnormal aggregates of neurofilament protein, the disorganization of the axonal cytoskeleton, and the accumulation of autophagic vacuoles and polyubiquitinated proteins. Furthermore, MOCA deficiency causes an alteration in the actin cytoskeleton and the formation of cofilin-containing rod-like structures. The dystrophic axons show functional abnormalities, including impaired axonal transport. These findings demonstrate that MOCA is required for maintaining the functional integrity of axons and define a model for the steps leading to axonal degeneration.

Since diabetes is a risk factor for Alzheimer's disease (AD), we asked if there is a functional interaction between high glucose and elevated beta amyloid peptide (Abeta) in cultured brain microvascular endothelial cells and presymptomatic AD transgenic mice. When cultured brain microvascular endothelial cells are exposed to both high glucose and low levels of Abeta, there is a synergistic interaction to cause an increased accumulation of advanced glycation products (AGE) and reactive oxygen species (ROS). When presymptomatic mice expressing mutant human amyloid precursor protein and presenilin are made diabetic, they have a decrease in cognitive function relative to control mice. Associated with the cognitive deficit are increases in brain microvascular AGE and iNOS expression, and the loss of the synaptic spine protein drebrin. No amyloid plaques or tangles are observed within the brains of any group. These data show that diabetes causes a synergistic potentiation of some indices of AD in transgenic animals that are presymptomatic for the classical features of the disease.

Modifier of cell adhesion (MOCA) is a member of the dedicator of cytokinesis 180 family of proteins and is highly expressed in CNS neurons. MOCA is associated with Alzheimer's disease tangles and regulates the accumulation of amyloid precursor protein and β-amyloid. Here, we report that MOCA modulates cell-cell adhesion and morphology. MOCA increases the accumulation of adherens junction proteins, including N-cadherin and β-catenin, whereas reducing endogenous MOCA expression lowers cell-cell aggregation and N-cadherin expression. MOCA colocalizes with N-cadherin and actin in areas of cell-cell and cell substratum contact and is expressed in neuronal processes. MOCA accumulates during neuronal differentiation, and its expression enhances NGF-induced neurite outgrowth and morphological complexity. We conclude that MOCA regulates N-cadherin-mediated cell-cell adhesion and neurite outgrowth.

Modifier of cell adhesion protein (MOCA; previously called presenilin [PS] binding protein) is a DOCK180-related molecule, which interacts with PS1 and PS2, is localized to brain areas involved in Alzheimer's disease (AD) pathology, and is lost from the soluble fraction of sporadic Alzheimer's disease (AD) brains. Because PS1 has been associated with γ-secretase activity, MOCA may be involved in the regulation of β-amyloid precursor protein (APP) processing. Here we show that the expression of MOCA decreases both APP and amyloid β-peptide secretion and lowers the rate of cell-substratum adhesion. In contrast, MOCA does not lower the secretion of amyloid precursor-like protein (APLP) or several additional type 1 membrane proteins. The phenotypic changes caused by MOCA are due to an acceleration in the rate of intracellular APP degradation. The effect of MOCA expression on the secretion of APP and cellular adhesion is reversed by proteasome inhibitors, suggesting that MOCA directs nascent APP to proteasomes for destruction. It is concluded that MOCA plays a major role in APP metabolism and that the effect of MOCA on APP secretion and cell adhesion is a downstream consequence of MOCA-directed APP catabolism. This is a new mechanism by which the expression of APP is regulated.

Familial Alzheimer's disease (FAD) accounts for 5–10% of deaths from Alzheimer's disease (AD), and approximately 50% of these cases have been definitely linked to missense mutations in three genes, encoding the amyloid precursor protein (APP), presenilin 1 (PS1) and presenilin 2 (PS2). Of these, the vast majority of FAD-linked mutations are within PS1. There has been an extensive effort to identify proteins that functionally interact with PS1 and PS2 because of their clear roles in FAD. The goal of this review is to describe these proteins and to discuss in more detail the probable biological functions of a subset of the better-studied interacting proteins. In particular, the review examines APP, Notch, nicastrin, modifier of cellular adhesion (MOCA), β-catenin, and the group of proteins involved in cell death, calcium metabolism and cell adhesion. We argue that, although a few of the interacting proteins are unambiguously involved in well-studied cellular pathways, their exact roles within these pathways have not been clearly defined, and indeed might vary between cell types. We also question the physiological relevance of some of the work linking PS to cell death pathways. Finally, we point out the value of using flies and worms to sort out the often contradictory work in the PS field, and we mention how knowledge of PS-interacting pathways will contribute to the development of new therapeutic strategies in AD.

Epidemiological data from retrospective and case-control studies have indicated that estrogen replacement therapy (ERT) can decrease the risk of developing Alzheimer's disease. In addition, ERT has been found to promote cellular correlates of memory and to promote neuronal survival both in vivo and in vitro. Phytoestrogens have been proposed as potential alternatives to ERT. To determine whether phytoestrogens exert estrogen agonist effect in neural tissue, investigations of neuroprotective and neurotrophic efficacy of phytoestrogens were conducted. Six phytoestrogens, genistein, genistin, daldzein, daidzin, formononetin, and equol, were tested for their neuroprotective efficacy against two toxic insults, glutamate excitotoxicity and β-amyloid25–35. Neuronal membrane damage was quantitatively measured by lactate dehydrogenase (LDH) release, and neuronal mitochondrial viability was determined by 3-[4,5-dimethylthiazoi-2-yl]-2,5-diphenyl tetrazolium bromld (MTT) assay. Results of these studies demonstrated that all phytoestrogens induced a modest but significant reduction in LDH release following exposure to glutamate and β-amyloid25–35. In contrast, none of phytoestrogens induced a significant increase in reduced MTT levels, which occurred in the presence of a full estrogen agonist, 17β-estradiol. Analysis of the neurotrophic potential of genistein and daidzein, two phytoestrogens that exerted a significant reduction in LDH release, demonstrated that neither of these molecules promoted hippocampal neuron process outgrowth. Results of these analyses indicate that although phytoestrogens exert a neuroprotective effect at the plasma membrane, they do not sustain neuron mitochondrial viability nor do they induce cellular correlates of memory as neurite outgrowth and synaptogenesis are putative mechanisms of memory. Data derived from these investigations would predict that phytoestrogens could exert some neuroprotective effects analogous to that of antioxidants, but that these molecules are not functional equivalents to endogenously active 17β-estradiol or to estrogen replacement formulations and, therefore, would raise the concern that they may not reduce the risk of Alzheimer's disease or sustain memory function in postmenopausal women.

Approximately 50% of familial Alzheimer's disease (AD) cases are linked to the presenilin (PS) gene. This suggests that an altered function of mutated PSs accounts for a fundamental process leading to AD. Here we identify a new PS binding protein, PBP, which is highly expressed in cerebral cortex and hippocampus. Immunohistochemical studies and cell fractionation analysis show that PBP redistributes from cytoplasm to membranes in the presence of PS. In addition, PBP is deficient in the soluble fraction of sporadic AD brains.