Citations

Abstract With the increasing life expectancy in developed countries, the incidence of Alzheimer's disease (AD) and thus its socioeconomic impact are growing. Increasing knowledge over the last years about the pathomechanisms involved in AD allow for the development of specific treatment strategies aimed at slowing down or even preventing neuronal death in AD. However, this requires also that (1) AD can be diagnosed with high accuracy, because non‐AD dementias would not benefit from an AD‐specific treatment; (2) AD can be diagnosed in very early stages when any intervention would be most effective; and (3) treatment efficacy can be reliably and meaningfully monitored. Although there currently is no ideal biomarker that would fulfill all these requirements, there is increasing evidence that a combination of currently existing neuroimaging and cerebrospinal fluid (CSF) and blood biomarkers can provide important complementary information and thus contribute to a more accurate and earlier diagnosis of AD. The Alzheimer's Disease Neuroimaging Initiative (ADNI) is exploring which combinations of these biomarkers are the most powerful for diagnosis of AD and monitoring of treatment effects.

Currently no definitive biomarker of Alzheimer's disease (AD) is available, and this impedes both clinical diagnosis in humans and drug discovery in transgenic animal models. Proton magnetic resonance spectroscopy ( 1 H MRS) provides a noninvasive way to investigate in vivo neurochemical abnormalities. Each observable metabolite can potentially provide information about unique in vivo pathological processes at the molecular or cellular level. In this study, the age-dependent 1 H MRS profile of transgenic AD mice was compared to that of wild-type mice. Twenty-seven APP-PS1 mice (which coexpress mutated human presenilin 1 and amyloid-β precursor protein) and 30 wild-type mice age 66-904 days were examined, some repeatedly. A reduction in the levels of N -acetylaspartate and glutamate, compared with total creatine levels, was found in APP-PS1 mice with advancing age. The most striking finding was a dramatic increase in the concentration of myo -inositol with age in APP-PS1 mice, which was not observed in wild-type mice. The age-dependent neurochemical changes observed in APP-PS1 mice agree with results obtained from in vivo human MRS studies. Among the different transgenic mouse models of AD that have been studied with 1 H MRS, APP-PS1 mice seem to best match the neurochemical profile exhibited in human AD. 1 H MRS could serve as a sensitive in vivo surrogate indicator of therapeutic efficacy in trials of agents designed to reduce neurotoxicity due to microglial activation. Because of its noninvasive and repeatable nature, MRS in transgenic models of AD could substantially accelerate drug discovery for this disease.

We measured 366 microsatellite markers genome-wide to search for loci contributing to subcortical white matter ischemic damage (leukoariosis) and brain atrophy in 488 non-Hispanic white subjects (193 men, 295 women; mean age±SD=64.1±7.7 years; 79% hypertensive) from 223 sibships recruited through ≥2 members with essential hypertension diagnosed before age 60. Leukoariosis was quantitated by magnetic resonance imaging (MRI), brain atrophy by the difference between intracranial and brain volumes, and calculated mean arterial pressure and pulse pressure provided measures of steady-state level and pulsatile components of blood pressure. After adjustment for sex and age, variance components models estimated significant heritability of leukoariosis (0.72), brain atrophy (0.52), mean arterial pressure (0.084), and pulse pressure (0.294) ( P <0.0001 for each trait). Univariate maximum logarithm of odds scores (MLS) were observed for leukoariosis on chromosome 5 (MLS=1.91; P =0.00150); for brain atrophy on 1q and 17p (MLS=2.76, P =0.00018); for mean arterial pressure on 11p (MLS=1.57; P =0.00354); and for pulse pressure on 11p (MLS=3.02; P =0.00070). Bivariate linkage analyses provided evidence of loci with pleiotropic effects on brain atrophy and pulse pressure on chromosomes 11p (MLS = 5.07 at 16 cM; P =0.00001) and 16q (MLS of 4.56 at 124 cM; P =0.00003). These results demonstrate usefulness of multivariate linkage analyses to detect loci with pleiotropic effects on genetically correlated traits and suggest overlap between the genes influencing blood pressure and those contributing to brain atrophy.

The function of Type 1, classic cadherins depends on their association with the actin cytoskeleton, a connection mediated by α- and β-catenin. The phosphorylation state of β-catenin is crucial for its association with cadherin and thus the association of cadherin with the cytoskeleton. We now show that the phosphorylation of β-catenin is regulated by the combined activities of the tyrosine kinase Fer and the tyrosine phosphatase PTP1B. Fer phosphorylates PTP1B at tyrosine 152, regulating its binding to cadherin and the continuous dephosphorylation of β-catenin at tyrosine 654. Fer interacts with cadherin indirectly, through p120ctn. We have mapped the interaction domains of Fer and p120ctn and peptides corresponding to these sequences release Fer from p120ctn in vitro and in live cells, resulting in loss of cadherin-associated PTP1B, an increase in the pool of tyrosine phosphorylated β-catenin and loss of cadherin adhesion function. The effect of the peptides is lost when a β-catenin mutant with a substitution at tyrosine 654 is introduced into cells. Thus, Fer phosphorylates PTP1B at tyrosine 152 enabling it to bind to the cytoplasmic domain of cadherin, where it maintains β-catenin in a dephosphorylated state. Cultured fibroblasts from mouse embryos targeted with a kinase-inactivating ferD743R mutation have lost cadherin-associated PTP1B and β-catenin, as well as localization of cadherin and β-catenin in areas of cell-cell contacts. Expression of wild-type Fer or culture in epidermal growth factor restores the cadherin complex and localization at cell-cell contacts.

Ischemic damage to the subcortical white matter of the brain, referred to as leukoaraiosis, is a frequent complication of hypertension-related microvascular disease and contributes to the risk of stroke and vascular dementia. A large genetic contribution to this late-life form of target organ damage was suggested by a study of elderly male twins. As part of the Genetic Epidemiology Network of Arteriopathy (GENOA), 483 non-Hispanic white subjects were recruited to undergo MRI for determination of the brain volume of leukoaraiosis (291 women and 192 men from 210 sibships providing 434 sibling pairs; mean age±SD=65.2±7.3 years). The GENOA–Rochester sibships contain 2 or more siblings with essential hypertension diagnosed before age 60. The frequency distribution of the volume of leukoaraiosis was positively skewed, with a median value of 6.61 cm 3 (interquartile range: 4.77 to 9 0.83 cm 3 ). Variance component models were used to estimate the heritability (ie, the proportion of phenotypic variation caused by additive genetic factors). After logarithm transformation of the volume of leukoaraiosis, the estimated heritability (±SE) was 0.802±0.102 ( P <0.0001). Adjustments for sex, age, systolic blood pressure, and brain volume reduced the heritability estimate to 0.671±0.110 ( P <0.0001). This evidence of strong genetic influence on the susceptibility to leukoaraiosis justifies efforts to localize the responsible genes and characterize the predisposing genetic polymorphisms.

Mutations of c-KIT causing spontaneous activation of the KIT receptor kinase are associated with sporadic adult human mastocytosis (SAHM) and with human gastrointestinal stromal tumors. We have classified KIT-activating mutations as either “enzymatic site” type (EST) mutations, affecting the structure of the catalytic portion of the kinase, or as “regulatory” type (RT) mutations, affecting regulation of an otherwise normal catalytic site. Using COS cells expressing wild-type or mutant KIT, 2 compounds, STI571 and SU9529, inhibited wild-type and RT mutant KIT at 0.1 to 1 μM but did not significantly inhibit the Asp816Val EST mutant associated with SAHM, even at 10 μM. Using 2 subclones of the HMC1 mast cell line, which both express KIT with an identical RT mutation but which differ in that one also expresses the Asp816Val EST mutation, both compounds inhibited the RT mutant KIT, thereby suppressing proliferation and producing apoptosis in the RT mutant-only cell line. Neither compound suppressed activation of Asp816Val EST mutant KIT, and neither produced apoptosis or significantly suppressed proliferation of the cell line expressing the Asp816Val mutation. These studies suggest that currently available KIT inhibitors may be useful in treating neoplastic cells expressing KIT activated by its natural ligand or by RT activating mutations such as gastrointestinal stromal tumors but that neither compound is likely to be effective against SAHM. Furthermore, these results help establish a general paradigm whereby classification of mutations affecting oncogenic enzymes as RT or EST may be useful in predicting tumor sensitivity or resistance to inhibitory drugs.

The reduction in levels of the potentially toxic amyloid-β peptide (Aβ) has emerged as one of the most important therapeutic goals in Alzheimer's disease. Key targets for this goal are factors that affect the expression and processing of the Aβ precursor protein (βAPP). Earlier reports from our laboratory have shown that a novel cholinesterase inhibitor, phenserine, reduces βAPP levels in vivo . Herein, we studied the mechanism of phenserine's actions to define the regulatory elements in βAPP processing. Phenserine treatment resulted in decreased secretion of soluble βAPP and Aβ into the conditioned media of human neuroblastoma cells without cellular toxicity. The regulation of βAPP protein expression by phenserine was posttranscriptional as it suppressed βAPP protein expression without altering βAPP mRNA levels. However, phenserine's action was neither mediated through classical receptor signaling pathways, involving extracellular signal-regulated kinase or phosphatidylinositol 3-kinase activation, nor was it associated with the anticholinesterase activity of the drug. Furthermore, phenserine reduced expression of a chloramphenicol acetyltransferase reporter fused to the 5′-mRNA leader sequence of βAPP without altering expression of a control chloramphenicol acetyltransferase reporter. These studies suggest that phenserine reduces Aβ levels by regulating βAPP translation via the recently described iron regulatory element in the 5′-untranslated region of βAPP mRNA, which has been shown previously to be up-regulated in the presence of interleukin-1. This study identifies an approach for the regulation of βAPP expression that can result in a substantial reduction in the level of Aβ.